Marks Standard Handbook for Mechanical Engineers 11th Editio

Section 6

Materials of Engineering

BY

EUGENE A.AVALLONE Consulting Engineer; Professor of Mechanical Engineering, Emeritus,The City College of The City University of New Y ork

HAROLD W.PAXTON United States Steel Professor Emeritus, Carnegie Mellon University JAMES D.REDMOND Principal, T echnical Marketing Resources, Inc.

MALCOLM BLAIR T echnical and Research Director, Steel Founders Society of America ROBERT E.EPPICH Vice President, T echnology, American Foundry Society

L.D.KUNSMAN Late Fellow Engineer, Research Labs, Westinghouse Electric Corp.

C.L.CARLSON Late Fellow Engineer, Research Labs, Westinghouse Electric Corp.J.RANDOLPH KISSEL President, The TGB Partnership

LARRY F.WIESERMAN Senior T echnical Supervisor, ALCOA

RICHARD L.BRAZILL T echnology Specialist, ALCOA

FRANK E.GOODWIN Executive Vice President, ILZRO, Inc.

DON GRAHAM Manager, Turning Products, Carboloy, Inc.

ARTHUR COHEN Formerly Manager, Standards and Safety Engineering, Copper Development Assn.

JOHN H.TUNDERMANN Formerly Vice President, Research and T echnology, INCO International, Inc.

JAMES D.SHEAROUSE,III Late Senior Development Engineer, The Dow Chemical Co.PETER K.JOHNSON Director, Marketing and Public Relations, Metal Powder Industries Federation

JOHN R.SCHLEY Manager, T echnical Marketing, RMI Titanium Co.

ROBERT D.BARTHOLOMEW Associate, Sheppard T. Powell Associates, LLC DAVID A.SHIFLER MERA Metallurgical Services

DAVID W.GREEN Supervisory Research General Engineer, Forest Products Lab, USDA ROLAND HERNANDEZ Research Engineer, Forest Products Lab, USDA

JOSEPH F.MURPHY Research General Engineer, Forest Products Lab, USDA ROBERT J.ROSS Supervisory Research General Engineer, Forest Products Lab, USDA WILLIAM T.SIMPSON Research Forest Products T echnologist, Forest Products Lab, USDA ANTON TENWOLDE Supervisory Research Physicist, Forest Products Lab, USDA ROBERT H.WHITE Supervisory Wood Scientist, Forest Products Lab, USDA STAN LEBOW Research Forest Products T echnologist, Forest Products Lab, USDA ALI M.SADEGH Professor of Mechanical Engineering, The City College of The City University of New York

WILLIAM L.GAMBLE Professor Emeritus of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign

ARNOLD S.VERNICK Formerly Associate, Geraghty & Miller, Inc.

GLENN E.ASAUSKAS Lubrication Engineer, Chevron Corp.

STEPHEN R.SWANSON Professor of Mechanical Engineering, University of Utah

6-16.1GENERAL PROPERTIES OF MATERIALS

Revised by E.A.Avallone

Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

Specific Gravities and Densities and Other Physical Data . . . . . . . . . . . . . . . 6-7

6.2IRON AND STEEL

by Harold W.Paxton

Classification of Iron and Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12

Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13

Effect of Alloying Elements on the Properties of Steel. . . . . . . . . . . . . . . . . 6-18Principles of Heat Treatment of Iron and Steel. . . . . . . . . . . . . . . . . . . . . . . 6-19Composite Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-20Thermomechanical Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21Commercial Steels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21Tool Steels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28Spring Steel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29Special Alloy Steels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29Stainless Steels (BY J AMES D. R EDMOND ). . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29

6.3IRON AND STEEL CASTINGS

by Malcolm Blair and Robert E.Eppich Classification of Castings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-34

Cast Iron. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-35

Steel Castings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-40

6.4NONFERROUS METALS AND ALLOYS;

METALLIC SPECIALITIES

Introduction(BY L. D. K UNSMAN AND C. L. C ARLSON, Amended

by Staff) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-46

Aluminum and Its Alloys(BY J. R ANDOLPH K ISSELL, L ARRY F. W IESERMAN, AND R ICHARD L. B RAZILL). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-49 Bearing Metals(BY F RANK E. G OODWIN). . . . . . . . . . . . . . . . . . . . . . . . . . . 6-58

Cemented Carbides(BY D ON G RAHAM). . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-58

Copper and Copper Alloys(BY A RTHUR C OHEN). . . . . . . . . . . . . . . . . . . . . 6-62

Jewelry Metals(Staff Contribution). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-71

Low-Melting-Point Metals and Alloys(BY F RANK E. G OODWIN). . . . . . . . . 6-72

Metals and Alloys for Use at Elevated Temperatures

(BY J OHN H. T UNDERMANN). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-73

Metals and Alloys for Nuclear Energy Applications(BY L. D. K UNSMAN AND C. L. C ARLSON;Amended by staff). . . . . . . . . . . . . . . . . . . . . . . . . 6-79 Magnesium and Magnesium Alloys(BY J AMES D. S HEAROUSE, III). . . . . . . 6-82 Powdered Metals(BY P ETER K. J OHNSON). . . . . . . . . . . . . . . . . . . . . . . . . . 6-83 Nickel and Nickel Alloys(BY J OHN H. T UNDERMANN). . . . . . . . . . . . . . . . . 6-86 Titanium and Zirconium(BY J OHN R. S CHLEY). . . . . . . . . . . . . . . . . . . . . . . 6-88 Zinc and Zinc Alloys(BY F RANK E. G OODWIN). . . . . . . . . . . . . . . . . . . . . . 6-90

6.5CORROSION

by Robert D.Bartholomew and David A.Shifler Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-92 Thermodynamics of Corrosion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-93 Corrosion Kinetics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-94 Factors Influencing Corrosion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-95 Forms of Corrosion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-97 Corrosion Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-102 Corrosion Protection Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-103 Corrosion in Industrial and Power Plant Steam-Generating Systems. . . . . 6-105 Corrosion in Heating and Cooling Water Systems and Cooling Towers. . . 6-109 Corrosion in the Chemical Process Industry. . . . . . . . . . . . . . . . . . . . . . . . 6-110

6.6PAINTS AND PROTECTIVE COATINGS

Revised by Staff

Paint Ingredients. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-111

Paints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-111

Other Protective and Decorative Coatings. . . . . . . . . . . . . . . . . . . . . . . . . 6-113

Varnish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-114

Lacquer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-115

6.7WOOD

by Staff,Forest Products Laboratory,USDA Forest Service.

Prepared under the direction of David W.Green Composition, Structure, and Nomenclature(BY D A VID W. G REEN). . . . . . . 6-115 Physical and Mechanical Properties of Clear Wood(BY D A VID W. G REEN, R OBERT W HITE, A NTON T EN W OLDE, W ILLIAM S IMPSON, J OSEPH

M URPHY,AND R OBERT R OSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-116

Properties of Lumber Products(BY R OLAND H ERNANDEZ

AND D A VID W. G REEN). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-121 Properties of Structural Panel Products(BY R OLAND H ERNANDEZ). . . . . . . 6-127 Durability of Wood in Construction(BY S TAN L EBOW AND R OBERT W HITE). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-129 Commercial Lumber Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-131

6.8NONMETALLIC MATERIALS

by Ali M.Sadegh

Abrasives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-131

Adhesives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-133Brick, Block, and Tile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-134 Ceramics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-139 Cleansing Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-140 Cordage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-141 Electrical Insulating Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-141 Fibers and Fabrics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-143 Freezing Preventives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-144 Glass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-145 Natural Stones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-146 Paper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-147 Roofing Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-148 Rubber and Rubberlike Materials (Elastomers). . . . . . . . . . . . . . . . . . . . . 6-150 Solvents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-151 Thermal Insulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-153 Silicones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-154 Refractories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-154 Sealants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-158

6.9CEMENT,MORTAR,AND CONCRETE

by William L.Gamble

Cement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-162 Lime. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-163 Aggregates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-163 Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-164 Admixtures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-164 Mortars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-165 Concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-166

6.10WATER

by Arnold S.Vernick and Amended by Staff

Water Resources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-171 Measurements and Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-172 Industrial Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-174 Water Pollution Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-175 Water Desalination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-176

6.11LUBRICANTS AND LUBRICATION

by Glenn E.Asauskas

Lubricants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-180 Liquid Lubricants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-180 Lubrication Regimes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-181 Lubricant Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-181 Viscosity Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-181 Other Physical and Chemical Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-182 Greases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-183 Solid Lubricants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-184 Lubrication Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-185 Lubrication of Specific Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-185

6.12PLASTICS

Staff Contribution

General Overview of Plastics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-189 Raw Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-189 Primary Fabrication Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-205 Additives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-205 Adhesives, Assembly, and Finishes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-205 Recycling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-205

6.13FIBER COMPOSITE MATERIALS

by Stephen R.Swanson

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-206 Typical Advanced Composites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-206 Fibers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-206 Matrices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-206 Material Forms and Manufacturing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-207 Design and Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-207

6-2MATERIALS OF ENGINEERING

R EFERENCES:“International Critical Tables,” McGraw-Hill. “Smithsonian Physical Tables,” Smithsonian Institution. Landolt, “Landolt-B?rnstein, Zahlenwerte und Funktionen aus Physik, Chemie, Astronomie, Geophysik und Technik,” Springer. “Handbook of Chemistry and Physics,” Chemical Rubber Co.“Book of ASTM Standards,” ASTM. “ASHRAE Refrigeration Data Book,”ASHRAE. Brady, “Materials Handbook,” McGraw-Hill. Mantell, “Engineering Materials Handbook,” McGraw-Hill. International Union of Pure and Applied Chemistry, Butterworth Scientific Publications. “U.S. Standard Atmosphere,”Government Printing Office. Tables of Thermodynamic Properties of Gases, NIST Circ. 564, ASME Steam Tables.

Thermodynamic properties of a variety of other specific materials are listed also in Secs. 4.1, 4.2, and 9.8. Sonic properties of several materi-als are listed in Sec. 12.6.

CHEMISTRY

Every elementary substance is made up of exceedingly small particles called atoms which are all alike and which cannot be further subpided or broken up by chemical processes.It will be noted that this statement is virtually a definition of the term elementary substance and a limitation of the term chemical process. There are as many different classes or families of atoms as there are chemical elements.See Table 6.1.1.

Two or more atoms, either of the same kind or of different kinds, are, in the case of most elements, capable of uniting with one another to form a higher order of distinct particles called molecules.If the mole-cules or atoms of which any given material is composed are all exactly alike, the material is a pure substance.If they are not all alike, the mate-rial is a mixture.

If the atoms which compose the molecules of any pure substances are all of the same kind, the substance is, as already stated, an elementary

substance.If the atoms which compose the molecules of a pure chemical substance are not all of the same kind, the substance is a compound

substance.The atoms are to be considered as the smallest particles which occur separately in the structure of molecules of either compound or elementary substances, so far as can be determined by ordinary chemi-cal analysis. The molecule of an element consists of a definite (usually small) number of its atoms. The molecule of a compound consists of one or more atoms of each of its several elements, the numbers of the

6-3

6.1GENERAL PROPERTIES OF MATERIALS

Revised by E.A.Avallone

Table 6.1.1Chemical Elements a

Element Symbol Atomic no.Atomic weight b Valence Actinium Ac89

Aluminum A11326.98153 Americium Am95

Antimony Sb51121.753, 5 Argon c Ar1839.9480 Arsenic d As3374.92163, 5 Astatine At85

Barium Ba56137.342 Berkelium Bk97

Beryllium Be49.01222 Bismuth Bi83208.9803, 5 Boron d B510.811l3 Bromine e Br3579.904m1, 3, 5 Cadmium Cd48112.402 Calcium Ca2040.082 Californium Cf98

Carbon d C612.01115l2, 4 Cerium Ce58140.123, 4 Cesium k Cs55132.9051 Chlorine f Cl1735.453m1, 3, 5, 7 Chromium Cr2451.996m2, 3, 6 Cobalt Co2758.93322, 3 Columbium (see Niobium)

Copper Cu2963.546m1, 2 Curium Cm96

Dysprosium Dy66162.503 Einsteinium Es99

Erbium Er68167.263 Europium Eu63151.962, 3 Fermium Fm100

Fluorine g F918.99841 Francium Fr87

Gadolinium Gd64157.253 Gallium k Ga3169.722, 3 Germanium Ge3272.592, 4 Gold Au79196.9671, 3 Hafnium Hf72178.494 Helium c He2 4.00260 Holmium Ho67164.9303 Hydrogen h H1 1.00797i1 Indium In49114.821, 2, 3 Iodine d I53126.90441, 3, 5, 7

6-4GENERAL PROPERTIES OF MATERIALS

Table 6.1.1Chemical Elements a(Continued)

Element Symbol Atomic no.Atomic weight b Valence

Iridium Ir77192.22, 3, 4, 6

Iron Fe2655.847m2, 3

Krypton c Kr3683.800

Lanthanum La57138.913

Lead Pb82207.192, 4

Lithium i Li3 6.9391

Lutetium Lu71174.973

Magnesium Mg1224.3122

Manganese Mn2554.93802, 3, 4, 6, 7

Mendelevium Md101

Mercury e Hg80200.591, 2

Molybdenum Mo4295.943, 4, 5, 6

Neodymium Nd60144.243

Neon c Ne1020.1830

Neptunium Np93

Nickel Ni2858.712, 3, 4

Niobium Nb4192.9062, 3, 4, 5

Nitrogen f N714.00673, 5

Nobelium No102

Osmium Os76190.22, 3, 4, 6, 8

Oxygen f O815.9994l2

Palladium Pd46106.42, 4

Phosphorus d P1530.97383, 5

Platinum Pt78195.092, 4

Plutonium Pu94

Polonium Po842, 4

Potassium K1939.1021

Praseodymium Pr59140.9073

Promethium Pm615

Protactinium Pa91

Radium Ra882

Radon j Rn860

Rhenium Re75186.21, 4, 7

Rhodium Rh45102.9053, 4

Rubidium Rb3785.471

Ruthenium Ru44101.073, 4, 6, 8

Samarium Sm62150.353

Scandium Sc2144.9563

Selenium d Se3478.962, 4, 6

Silicon d Si1428.086l4

Silver Ag47107.868m1

Sodium Na1122.98981

Strontium Sr3887.622

Sulfur d S1632.064l2, 4, 6

Tantalum Ta73180.9484, 5

Technetium Tc43

Tellurium d Te52127.602, 4, 6

Terbium Tb65158.9243

Thallium T181204.371, 3

Thorium Th90232.0383

Thulium Tm69168.9343

Tin Sn50118.692, 4

Titanium Ti2247.903, 4

Tungsten W74183.853, 4, 5, 6

Uranium U92238.034, 6

Vanadium V2350.9421, 2, 3, 4, 5

Xenon c Xe54131.300

Ytterbium Yb70173.042, 3

Yttrium Y3988.9053

Zinc Zn3065.372

Zirconium Zr4091.224

a All the elements for which atomic weights listed are metals, except as otherwise indicated. No atomic weights are

listed for most radioactive elements, as these elements have no fixed value.

b The atomi

c weights are base

d upon nuclidic mass of C12?12.

c Inert gas.

d Metalloid.

e Liquid.

f Gas.

g Most active gas.

h Lightest gas.

i Lightest metal.

j Not placed.

k Liquid at

258C.

l The atomic weight varies because of natural variations in the isotopic composition of the element. The observed

ranges are boron, ?0.003; carbon, ?0.00005; hydrogen, ?0.00001; oxygen, ?0.0001; silicon, ?0.001; sulfur,

?0.003.

m The atomic weight is believed to have an experimental uncertainty of the following magnitude: bromine, ?0.001;

chlorine,?0.001; chromium, ?0.001; copper, ?0.001; iron, ?0.003; silver, ?0.001. For other elements, the last digit

given is believed to be reliable to ?0.5.

S OURCE: Table courtesy IUPAC and Butterworth Scientific Publications.

CHEMISTRY 6-5

various kinds of atoms and their arrangement being definite and fixed and determining the character of the compound. This notion of mole-cules and their constituent atoms is useful for interpreting the observed fact that chemical reactions—e.g., the analysis of a compound into its elements, the synthesis of a compound from the elements, or the chang-ing of one or more compounds into one or more different compounds—take place so that the masses of the various substances concerned in a given reaction stand in definite and fixed ratios.

It appears from recent researches that some substances which cannot by any available means be decomposed into simpler substances and which must, therefore, be defined as elements, are continually under-going spontaneous changes or radioactive transformation into other substances which can be recognized as physically and chemically dif-ferent from the original substance. Radium is an element by the defini-tion given and may be considered as made up of atoms. But it is assumed that these atoms, so called because they resist all efforts to break them up and are, therefore, apparently inpisible, nevertheless split up spontaneously, at a rate which scientists have not been able to influence in any way, into other atoms, thus forming other elementary substances of totally different properties. See Table 6.1.3.The view generally accepted at present is that the atoms of all the chemical elements, including those not yet known to be radioactive, con-sist of several kinds of still smaller particles, three of which are known as protons, neutrons,and electrons.The protons are bound together in the atomic nucleus with other particles, including neutrons, and are pos-itively charged. The neutrons are particles having approximately the mass of a proton but are uncharged. The electrons are negatively charged particles, all alike, external to the nucleus, and sufficient in number to neutralize the nuclear charge in an atom. The differences between the atoms of different chemical elements are due to the different numbers of these smaller particles composing them. According to the original Bohr theory, an ordinary atom is conceived as a stable system of such elec-trons revolving in closed orbits about the nucleus like the planets of the solar system around the sun. In a hydrogen atom, there is 1 proton and 1electron; in a radium atom, there are 88 electrons surrounding a nucleus 226 times as massive as the hydrogen nucleus. Only a few, in general the outermost or valence electrons of such an atom, are subject to rearrange-ment within, or ejection from, the atom, thereby enabling it, because of its increased energy, to combine with other atoms to form molecules of either elementary substances or compounds. The atomic number of an

Table 6.1.2Solubility of Inorganic Substances in Water

(Number of grams of the anhydrous substance soluble in 1,000 g of water. The common name of the substance is given in parentheses)

Temperature, 8F (8C)

Substance

Composition 32 (0)122 (50)212 (100)Aluminum sulfate

Al 2(S04)3

313521891Aluminum potassium sulfate (potassium alum)Al 2K 2(SO 4)4и24H 2O 301701,540Ammonium bicarbonate

NH 4HCO 3119Ammonium chloride (sal ammoniac)NH 4Cl 297504760Ammonium nitrate NH 4NO 31,1833,4408,710Ammonium sulfate (NH 4)2S04

7068471,033Barium chloride BaCl 2и2H 2O 317436587Barium nitrate

Ba(N03)250

172

345Calcium carbonate (calcite)CaCO 30.018*0.88Calcium chloride

CaCl 25941,576

Calcium hydroxide (hydrated lime)Ca(OH)2

1.770.67Calcium nitrate

Ca(NO 3)2и4H 2O 9313,561

3,626

Calcium sulfate (gypsum)CaSO 4и2H 2O 1.76 2.06 1.69Copper sulfate (blue vitriol)CuSO 4и5H 2O 140334753Ferrous chloride FeCl 2и4H 2O 644§

8201,060Ferrous hydroxide

Fe(OH)2

0.0067?Ferrous sulfate (green vitriol or copperas)FeSO 4и7H 2O 156482Ferric chloride FeCl 37303,1605,369Lead chloride PbCl 2 6.7316.7

33.3Lead nitrate Pb(N03)2403

1,255Lead sulfate

PbSO 40.042?Magnesium carbonate MgCO 3

0.13?Magnesium chloride

MgCl 2и6H 2O 524

723

Magnesium hydroxide (milk of magnesia)Mg(OH)2

0.009?Magnesium nitrate

Mg(NO 3)2и6H 2O 665903Magnesium sulfate (Epsom salts)MgSO 4и7H 2O 269500710Potassium carbonate (potash)K 2CO 38931,2161,562Potassium chloride

KCl 284435566Potassium hydroxide (caustic potash)KOH 9711,4141,773Potassium nitrate (saltpeter or niter)KNO 31318512,477Potassium sulfate

K 2SO 474165241Sodium bicarbonate (baking soda)

NaHCO 3

69145Sodium carbonate (sal soda or soda ash)NaCO 3и10H 2O 204475452Sodium chloride (common salt)NaCl 357366392Sodium hydroxide (caustic soda)NaOH 4201,4483,388Sodium nitrate (Chile saltpeter)NaNO 3

7331,1481,755Sodium sulfate (Glauber salts)Na 2SO 4и10H 2O 49466422Zinc chloride ZnCl 2

2,0444,7026,147Zinc nitrate Zn(NO 3)2и6H 2O 947Zinc sulfate

ZnSO 4и7H 2O

419

768

807

* 598F.? 688F.

? In cold water.§ 508F.

6-6

Table 6.1.3Periodic Table of the Elements

SPECIFIC GRAVITIES AND DENSITIES AND OTHER PHYSICAL DATA6-7 element is the number of excess positive charges on the nucleus of the

atom. The essential feature that distinguishes one element from another

is this charge of the nucleus. It also determines the position of the ele-

ment in the periodic table. Modern researches have shown the existence

of isotopes,that is, two or more species of atoms having the same atom-

ic number and thus occupying the same place in the periodic system, but

differing somewhat in atomic weight. These isotopes are chemically

identical and are merely different species of the same chemical element.

Most of the ordinary inactive elements have been shown to consist of a

mixture of isotopes. This convenient atomic model should be regarded

as only a working hypothesis for coordinating a number of phenomena

about which much yet remains to be known.

Calculation of the Percentage Composition of Substances Add

the atomic weights of the elements in the compound to obtain its molec-

ular weight. Multiply the atomic weight of the element to be calculated

by the number of atoms present (indicated in the formula by a subscript

number) and by 100, and pide by the molecular weight of the com-

pound. For example, hematite iron ore (Fe

2O

3

) contains 69.94 percent

of iron by weight, determined as follows: Molecular weight of Fe

2O

3?

(55.84?2)?(16?3)?159.68. Percentage of iron in compound ?(55.84?2)?100/159.68?69.94.

SPECIFIC GRAVITIES AND DENSITIES

AND OTHER PHYSICAL DATA

Table 6.1.5Approximate Specific Gravities and Densities

(Water at 398F and normal atmospheric pressure taken as unity) For

more detailed data on any material, see the section dealing with the

properties of that material. Data given are for usual room temperatures.

Specific

Avg density Substance gravity lb/ft3kg/m3

Metals, alloys, ores*

Aluminum, cast-hammered 2.55–2.801652,643 Brass, cast-rolled8.4–8.75348,553 Bronze, aluminum7.74817,702 Bronze, 7.9–14% Sn7.4–8.95098,153 Bronze, phosphor8.885548,874 Copper, cast-rolled8.8–8.955568,906 Copper ore, pyrites 4.1–4.32624,197 German silver8.585368,586 Gold, cast-hammered19.25–19.351,20519,300 Gold coin (U.S.)17.18–17.21,07317,190 Iridium21.78–22.421,38322,160 Iron, gray cast7.03–7.134427,079 Iron, cast, pig7.24507,207 Iron, wrought7.6–7.94857,658 Iron, spiegeleisen7.54687,496 Iron, ferrosilicon 6.7–7.34376,984 Iron ore, hematite 5.23255,206 Iron ore, limonite 3.6–4.02373,796 Iron ore, magnetite 4.9–5.23155,046 Iron slag 2.5–3.01722,755 Lead11.3471011,370 Lead ore, galena7.3–7.64657,449 Manganese7.424757,608 Manganese ore, pyrolusite 3.7–4.62594,149 Mercury13.54684713,570Table 6.1.5Approximate Specific Gravities

and Densities(Continued)

Specific

Avg density Substance gravity lb/ft3kg/m3 Monel metal, rolled8.975558,688 Nickel8.95378,602 Platinum, cast-hammered21.51,33021,300 Silver, cast-hammered10.4–10.665610,510 Steel, cold-drawn7.834897,832 Steel, machine7.804877,800 Steel, tool7.70–7.734817,703 Tin, cast-hammered7.2–7.54597,352 Tin ore, cassiterite 6.4–7.04186,695 Tungsten19.221,20018,820 Uranium18.71,17018,740 Zinc, cast-rolled 6.9–7.24407,049 Zinc, ore, blende 3.9–4.22534,052

Various solids

Cereals, oats, bulk0.4126417 Cereals, barley, bulk0.6239625 Cereals, corn, rye, bulk0.7345721 Cereals, wheat, bulk0.7748769 Cordage (natural fiber) 1.2–1.5851,360 Cordage (plastic)0.9–1.3691,104 Cork0.22–0.2615240 Cotton, flax, hemp 1.47–1.50931,491 Fats0.90–0.9758925 Flour, loose0.40–0.5028448 Flour, pressed0.70–0.8047753 Glass, common 2.40–2.801622,595 Glass, plate or crown 2.45–2.721612,580 Glass, crystal 2.90–3.001841,950 Glass, flint 3.2–4.72473,960 Hay and straw, bales0.3220320 Leather0.86–1.0259945 Paper0.70–1.1558929 Plastics (see Sec. 6.12)

Potatoes, piled0.6744705 Rubber, caoutchouc0.92–0.9659946 Rubber goods 1.0–2.0941,506 Salt, granulated, piled0.7748769 Saltpeter 2.111322,115 Starch 1.53961,539 Sulfur 1.93–2.071252,001 Wool 1.32821,315

Timber, air-dry

Apple0.66–0.7444705 Ash, black0.5534545 Ash, white0.64–0.7142973 Birch, sweet, yellow0.71–0.7244705 Cedar, white, red0.3522352 Cherry, wild red0.4327433 Chestnut0.4830481 Cypress0.45–0.4829465 Fir, Douglas0.48–0.5532513 Fir, balsam0.4025401 Elm, white0.5635561

Table 6.1.4Solubility of Gases in Water

(By volume at atmospheric pressure)

t,8F (8C)t,8F (8C)

32 (0)68 (20)212 (100)32 (0)68 (20)212 (100) Air0.0320.0200.012Hydrogen0.0230.0200.018 Acetylene 1.89 1.12Hydrogen sulfide 5.0 2.80.87 Ammonia1,250700Hydrochloric acid560480

Carbon dioxide 1.870.960.26Nitrogen0.0260.0170.0105 Carbon monoxide0.0390.025Oxygen0.0530.0340.185 Chlorine 5.0 2.50.00Sulfuric acid8743

Table 6.1.5Approximate Specific Gravities

and Densities(Continued)

Specific

Avg density Substance gravity lb/ft3kg/m3 Hemlock0.45–0.5029465 Hickory0.74–0.8048769 Locust0.67–0.7745722 Mahogany0.56–0.8544705 Maple, sugar0.6843689 Maple, white0.5333529 Oak, chestnut0.7446737 Oak, live0.8754866 Oak, red, black0.64–0.7142673 Oak, white0.7748770 Pine, Oregon0.5132513 Pine, red0.4830481 Pine, white0.4327433 Pine, Southern0.61–0.6738–42610–673 Pine, Norway0.5534541 Poplar0.4327433 Redwood, California0.4226417 Spruce, white, red0.4528449 Teak, African0.9962994 Teak, Indian0.66–0.8848769 Walnut, black0.5937593 Willow0.42–0.5028449

Various liquids

Alcohol, ethyl (100%)0.78949802 Alcohol, methyl (100%)0.79650809 Acid, muriatic, 40% 1.20751,201 Acid, nitric, 91% 1.50941,506 Acid, sulfuric, 87% 1.801121,795 Chloroform 1.500951,532 Ether0.73646738 Lye, soda, 66% 1.701061,699 Oils, vegetable0.91–0.9458930 Oils, mineral, lubricants0.88–0.9457914 Turpentine0.861–0.86754866

Water

Water, 48C, max density 1.062.426999.97 Water, 1008C0.958459.812958.10 Water, ice0.88–0.9256897 Water, snow, fresh fallen0.1258128 Water, seawater 1.02–1.03641,025

Ashlar masonry

Granite, syenite, gneiss 2.4–2.71592,549 Limestone 2.1–2.81532,450 Marble 2.4–2.81622,597 Sandstone 2.0–2.61432,290 Bluestone 2.3–2.61532,451

Rubble masonry

Granite, syenite, gneiss 2.3–2.61532,451 Limestone 2.0–2.71472,355 Sandstone 1.9–2.51372,194 Bluestone 2.2–2.51472,355 Marble 2.3–2.71562,500

Dry rubble masonry

Granite, syenite, gneiss 1.9–2.31302,082 Limestone, marble 1.9–2.11252,001 Sandstone, bluestone 1.8–1.91101,762

Brick masonry

Hard brick 1.8–2.31282,051 Medium brick 1.6–2.01121,794 Soft brick 1.4–1.91031,650 Sand-lime brick 1.4–2.21121,794

Concrete masonry

Cement, stone, sand 2.2–2.41442,309 Cement, slag, etc. 1.9–2.31302,082 Cement, cinder, etc. 1.5–1.71001,602Table 6.1.5Approximate Specific Gravities

and Densities(Continued)

Specific

Avg density Substance gravity lb/ft3kg/m3

Various building materials

Ashes, cinders0.64–0.7240–45640–721 Cement, portland, loose 1.5941,505 Portland cement 3.1–3.21963,140 Lime, gypsum, loose0.85–1.0053–64849–1,025 Mortar, lime, set 1.4–1.91031,650

941,505 Mortar, portland cement 2.08–2.251352,163 Slags, bank slag 1.1–1.267–721,074–1,153 Slags, bank screenings 1.5–1.998–1171,570–1,874 Slags, machine slag 1.5961,538 Slags, slag sand0.8–0.949–55785–849

Earth, etc., excavated

Clay, dry 1.0631,009 Clay, damp, plastic 1.761101,761 Clay and gravel, dry 1.61001,602 Earth, dry, loose 1.2761,217 Earth, dry, packed 1.5951,521 Earth, moist, loose 1.3781,250 Earth, moist, packed 1.6961,538 Earth, mud, flowing 1.71081,730 Earth, mud, packed 1.81151,841 Riprap, limestone 1.3–1.480–851,282–1,361 Riprap, sandstone 1.4901,441 Riprap, shale 1.71051,681 Sand, gravel, dry, loose 1.4–1.790–1051,441–1,681 Sand, gravel, dry, packed 1.6–1.9100–1201,602–1,922 Sand, gravel, wet 1.89–2.161262,019

Excavations in water

Sand or gravel0.9660951 Sand or gravel and clay 1.00651,041 Clay 1.28801,281 River mud 1.44901,432 Soil 1.12701,122 Stone riprap 1.00651,041

Minerals

Asbestos 2.1–2.81532,451 Barytes 4.502814,504 Basalt 2.7–3.21842,950 Bauxite 2.551592,549 Bluestone 2.5–2.61592,549 Borax 1.7–1.81091,746 Chalk 1.8–2.81432,291 Clay, marl 1.8–2.61372,196 Dolomite 2.91812,901 Feldspar, orthoclase 2.5–2.71622,596 Gneiss 2.7–2.91752,805 Granite 2.6–2.71652,644 Greenstone, trap 2.8–3.21872,998 Gypsum, alabaster 2.3–2.81592,549 Hornblende 3.01872,998 Limestone 2.1–2.861552,484 Marble 2.6–2.861702,725 Magnesite 3.01872,998 Phosphate rock, apatite 3.22003,204 Porphyry 2.6–2.91722,758 Pumice, natural0.37–0.9040641 Quartz, flint 2.5–2.81652,645 Sandstone 2.0–2.61432,291 Serpentine 2.7–2.81712,740 Shale, slate 2.6–2.91722,758 Soapstone, talc 2.6–2.81692,709 Syenite 2.6–2.71652,645

Stone, quarried, piled

Basalt, granite, gneiss 1.5961,579 Limestone, marble, quartz 1.5951,572 Sandstone 1.3821,314

6-8GENERAL PROPERTIES OF MATERIALS

SPECIFIC GRAVITIES AND DENSITIES AND OTHER PHYSICAL DATA6-9

Table 6.1.5Approximate Specific Gravities

and Densities(Continued)

Specific

Avg density Substance gravity lb/ft3kg/m3 Shale 1.5921,474 Greenstone, hornblend 1.71071,715

Bituminous substances

Asphaltum 1.1–1.5811,298 Coal, anthracite 1.4–1.8971,554 Coal, bituminous 1.2–1.5841,346 Coal, lignite 1.1–1.4781,250 Coal, peat, turf, dry0.65–0.8547753 Coal, charcoal, pine0.28–0.4423369 Coal, charcoal, oak0.47–0.5733481 Coal, coke 1.0–1.4751,201 Graphite 1.64–2.71352,163 Paraffin0.87–0.9156898 Petroleum0.8754856 Petroleum, refined0.78–0.8250801 (kerosene)

Petroleum, benzine0.73–0.7546737 Petroleum, gasoline0.70–0.7545721 Pitch 1.07–1.15691,105 Tar, bituminous 1.20751,201

Coal and coke, piled

Coal, anthracite0.75–0.9347–58753–930 Coal, bituminous, lignite0.64–0.8740–54641–866 Coal, peat, turf0.32–0.4220–26320–417 Coal, charcoal0.16–0.2310–14160–224 Coal, coke0.37–0.5123–32369–513

Gases (see Sec. 4)

* See also Sec. 8b225f6825c52cc58bd6be64pressibility of Liquids

If v

1

and v

2

are the volumes of the liquids at pressures of p

1

and p

2

atm, respectively, at any temperature, the coefficient of compressibility b is given by the equation

The value of b?106for oils at low pressures at about 708F varies from about 55 to 80; for mercury at 328F, it is 3.9; for chloroform at 328F, it is 100 and increases with the temperature to 200 at 1408F; for ethyl alcohol, it increases from about 100 at 328F and low pressures to 125 at 1048F; for glycerin, it is about 24 at room temperature and low pressure.

Table 6.1.6Average Composition of Dry Air between Sea Level and 90-km (295,000-ft) Altitude

Molecular Element Formula% by V ol.% by Mass weight

Nitrogen N

2

78.08475.5528.0134

Oxygen0

2

20.94823.1531.9988 Argon Ar0.934 1.32539.948

Carbon Dioxide C0

2

0.03140.047744.00995 Neon Ne0.001820.0012720.183 Helium He0.000520.000072 4.0026 Krypton Kr0.0001140.00040983.80

Methane CH

4

0.00020.00011116.043

From 0.0 to 0.00005 percent by volume of nine other gases.

Average composite molecular weight of air 28.9644.

S OURCE: “U.S. Standard Atmosphere,” Government Printing Office.

b5

1

v

1

v

1

2v2

p

2

2p1

Table 6.1.7Specific Gravity and Density of Water at Atmospheric Pressure* (Weights are in vacuo)

Temp,Specific Density

Temp,Specific

Density

8C gravity lb/ft3kg/m38C gravity lb/ft3kg/m3

00.9998762.4183999.845400.9922461.9428992.228

20.9999762.4246999.946420.9914761.894991.447

4 1.0000062.4266999.955440.9906661.844990.647

60.9999762.4246999.946460.9898261.791989.797

80.9998862.4189999.854480.9889661.737988.931

100.9997362.4096999.706500.9880761.682988.050

120.9995262.3969999.502520.9871561.624987.121

140.9992762.3811999.272540.9862161.566986.192

160.9989762.3623998.948560.9852461.505985.215

180.9986262.3407998.602580.9842561.443984.222

200.9982362.3164998.213600.9832461.380983.213

220.9978062.2894997.780620.9822061.315982.172

240.9973262.2598997.304640.9811361.249981.113

260.9968162.2278996.793660.9800561.181980.025

280.9962662.1934996.242680.9789461.112978.920

300.9956762.1568995.656700.9778161.041977.783

320.9950562.1179995.033720.9766660.970976.645

340.9944062.0770994.378740.9754860.896975.460

360.9937162.0341993.691760.9742860.821974.259

380.9929961.9893992.973780.9730760.745973.041

* See also Secs. 4.2and 6.10.

Table 6.1.8Volume of Water as a Function of Pressure and Temperature

Temp,

Pressure, atm

8F (8C)05001,0002,0003,0004,0005,0006,5008,000 32(0) 1.00000.97690.95660.92230.89540.87390.85650.8361

68 (20) 1.00160.98040.96190.93120.90650.88550.86750.84440.8244 122 (50) 1.01280.99150.97320.94280.91830.89740.87920.85620.8369 176 (80) 1.0287 1.00710.98840.95680.93150.90970.89130.86790.8481 S OURCE:“International Critical Tables.”

6-10

Table 6.1.9Basic Properties of Several Metals

(Staff contribution)*

Coefficient

of linear

thermal Thermal Specific Approx Modulus of Ultimate

Density,?expansion,?conductivity,heat,?melting elasticity,Poisson’s Yield stress,stress,Elongation, Material g/cm3in/(inи8F)?10?6Btu/(hиftи8F)Btu/(lb и8F)temp, 8F lb/in2?106ratio lb/in2?103lb/in2?103% Aluminum 2024-T3 2.7712.61100.2394010.60.33507018 Aluminum 6061-T6 2.7013.5900.231,08010.60.33404517 Aluminum 7079-T6 2.7413.7700.2390010.40.33687814 Beryllium, QMV 1.85 6.4–10.2850.452,34040–440.024–0.03027–3833–511–3.5 Copper, pure8.909.22270.0921,98017.00.32See“Metals Handbook”

Gold, pure19.321720.0311,95010.80.421830 Lead, pure11.3429.321.40.031620 2.00.40–0.45 1.3 2.620–50 Magnesium AZ31B-H24 (sheet) 1.7714.5550.251,100 6.50.35223715 Magnesium HK31A-H24 1.7914.0660.131,100 6.40.3529378 Molybdenum, wrought10.3 3.0830.074,73040.00.3280120–200Small Nickle, pure8.97.2530.112,65032.00.31§See“Metals Handbook”

Platinum21.45 5.0400.0313,21721.30.3920–2435–40 Plutonium, alpha phase19.0–19.730.0 4.80.0341,18414.00.15–0.214060Small Silver, pure10.511.02410.0561,76010–110.371848 Steel, AISI C1020 (hot-worked)7.85 6.3270.102,75029–300.29486536 Steel, AISI 304 (sheet)8.039.99.40.122,600280.29398765 Tantalum16.6 3.6310.035,42527.00.3550–1451–40 Thorium, induction melt11.6 6.9521.70.033,2007–100.27213234 Titanium, B 120VCA (aged) 4.85 5.2 4.30.133,10014.80.31902009 Tungesten19.3 2.5950.0336,200500.2818–6001–3 Uranium D-3818.97 4.0–8.0170.0282,100240.2128564 Room-temperature properties are given. For further information, consult the “Metals Handbook” or a manufacturer’s publication.

* Compiled by Anders Lundberg, University of California, and reproduced by permission.

? To obtain the preferred density units, kg/m3, multiply these values by 1,000.

? See also Tables 6.1.10and 6.1.11.

§ At 258C.

SPECIFIC GRAVITIES AND DENSITIES AND OTHER PHYSICAL DATA

6-11

Table 6.1.10Coefficient of Linear Thermal Expansion for Various Materials [Mean values between 32 and 2128F except as noted; in/(in и8F)?10?4]Metals

Other Materials

Paraffin:

Aluminum bronze 0.094Bakelite, bleached 0.12232–618F 0.592Brass, cast 0.104Brick 0.05361–1008F 0.724Brass, wire 0.107Carbon—coke 0.030100–1208F 2.612Bronze

0.100Cement, neat 0.060Porcelain 0.02Constantan (60 Cu, 40 Ni)0.095Concrete 0.060Quartz:

German silver 0.102Ebonite 0.468Parallel to axis 0.044Iron:Glass:

Perpend. to axis 0.074Cast

0.059Thermometer 0.045Quarts, fused 0.0028Soft forged 0.063Hard 0.033Rubber 0.428Wire

0.080Plate and crown 0.050Vulcanite

0.400Magnalium (85 Al, 15 Mg)0.133Flint 0.044Wood (II to fiber):Phosphor bronze 0.094Pyrex 0.018Ash

0.053Solder

0.134Granite 0.04–0.05Chestnut and maple 0.036Speculum metal 0.107Graphite 0.044Oak 0.027Steel:

Gutta percha 0.875Pine

0.030Bessemer, rolled hard 0.056Ice 0.283Across the fiber:Bessemer, rolled soft 0.063Limestone 0.023–0.05Chestnut and pine 0.019Nickel (10% Ni)0.073Marble 0.02–0.09Maple 0.027Type metal

0.108

Masonry 0.025–050

Oak

0.030

Table 6.1.11Specific Heat of Various Materials [Mean values between 32 and 2128F; Btu/(lb и8F)]Solids

Granite 0.195Wood:Alloys:

Graphite 0.201Fir 0.65Bismuth-tin 0.040–0.045Gypsum 0.259Oak 0.57Bell metal 0.086Hornblende 0.195Pine

0.67Brass, yellow 0.0883Humus (soil)0.44Liquids

Brass, red 0.090Ice:Acetic acid 0.51Bronze 0.104?48F 0.465Acetone

0.544Constantan 0.098328F

0.487Alcohol (absolute)0.58German silver 0.095India rubber (Para)0.27–0.48Aniline 0.49Lipowits’s metal 0.040Kaolin 0.224Bensol 0.40Nickel steel 0.109Limestone 0.217Chloroform 0.23Rose’s metal

0.050Marble 0.210Ether

0.54Solders (Pb and Sn)0.040–0.045Oxides:

Ethyl acetate 0.478Type metal 0.0388Alumina (Al 3O 2)0.183Ethylene glycol 0.602Wood’s metal 0.040Cu 2O

0.111Fusel oil 0.5640 Pb ?60 Bi 0.0317Lead oxide (PbO)0.055Gasoline 0.5025 Pb ?75 Bi 0.030Lodestone 0.156Glycerin

0.58Asbestos 0.20Magnesia

0.222Hydrochloric acid 0.60Ashes 0.20Magnetite (Fe 3O 4)0.168Kerosene 0.50Bakelite 0.3–0.4Silica 0.191Naphthalene 0.31Basalt (lava)0.20Soda

0.231Machine oil 0.40Borax 0.229Zinc oxide (ZnO)0.125Mercury 0.033Brick

0.22Paraffin wax 0.69Olive oil 0.40Carbon-coke 0.203Porcelain 0.22Paraffin oil 0.52Chalk 0.215Quarts 0.17–0.28Petroleum 0.50Charcoal 0.20Quicklime 0.21Sulfuric acid 0.336Cinders 0.18Salt, rock 0.21Sea water 0.94Coal 0.3Sand

0.195Toluene 0.40Concrete 0.156Sandstone 0.22Turpentine 0.42Cork

0.485Serpentine 0.25Molten metals:

Corundum 0.198Sulfur 0.180Bismuth (535–7258F)0.036Dolomite 0.222Talc 0.209Lead (590–6808F)0.041Ebonite 0.33Tufa 0.33Sulfur (246–2978F)0.235Glass:Vulcanite

0.331

Tin (460–6608F)

0.058

Normal 0.199Crown 0.16Flint

0.12

R EFERENCES :“Metals Handbook,” ASM International, latest ed., ASTM Standards, pt. 1. SAE Handbook. “Steel Products Manual,” AISI. “Making,Shaping and Treating of Steel,” AISE, latest ed.CLASSIFICATION OF IRON AND STEEL

Iron (Fe) is not a high-purity metal commercially but contains other chemical elements which have a large effect on its physical and mechanical properties. The amount and distribution of these elements are dependent upon the method of manufacture. The most important commercial forms of iron are listed below.

Pig iron is the product of the blast furnace and is made by the reduc-tion of iron ore.

Cast iron is an alloy of iron containing enough carbon to have a low melting temperature and which can be cast to close to final shape. It is not generally capable of being deformed before entering service.

Gray cast iron is an iron which, as cast, has combined carbon (in the form of cementite, Fe 3C) not in excess of a eutectoid percentage—the balance of the carbon occurring as graphite flakes. The term “gray iron”is derived from the characteristic gray fracture of this metal.

White cast iron contains carbon in the combined form. The presence of cementite or iron carbide (Fe 3C) makes this metal hard and brittle,and the absence of graphite gives the fracture a white color.

Malleable cast iron is an alloy in which all the combined carbon in a special white cast iron has been changed to free or temper carbon by suitable heat treatment.

Nodular (ductile) cast iron is produced by adding alloys of magnesium or cerium to molten iron. These additions cause the graphite to form into small nodules, resulting in a higher-strength, ductile iron.

Ingot iron, electrolytic iron (an iron-hydrogen alloy),and wrought iron are terms for low-carbon materials which are no longer serious items of commerce but do have considerable historical interest.

Steel is an alloy predominantly of iron and carbon, usually containing measurable amounts of manganese, and often readily formable.

Carbon steel is steel that owes its distinctive properties chiefly to the carbon it contains.

Alloy steel is steel that owes its distinctive properties chiefly to some element or elements other than carbon, or jointly to such other elements and carbon. Some alloy steels necessarily contain an important per-centage of carbon, even as much as 1.25 percent. There is no complete agreement about where to draw the line between the alloy steels and the carbon steels.

Basic oxygen steel and electric-furnace steel are steels made by the basic oxygen furnace and electric furnace processes, irrespective of carbon content; the effective inpidual alloy content in engineering steels can range from 0.05 percent up to 3 percent, with a total usually less than 5 percent. Open-hearth and Bessemer steelmaking are no longer prac-ticed in the United States.

Iron ore is reduced in a blast furnace to form pig iron,which is the raw material for practically all iron and steel products. Formerly, nearly 90 percent of the iron ore used in the United States came from the Lake Superior district; the ore had the advantages of high quality and the cheapness with which it could be mined and transported by way of the Great Lakes. With the rise of global steelmaking and the availability of high-grade ores and pellets (made on a large scale from low-grade ores)from many sources, the choice of feedstock becomes an economic decision.

The modern blast furnace consists of a vertical shaft up to 10 m or 40 ft in diameter and over 30 m (100 ft) high containing a descending column of iron ore, coke, and limestone and a large volume of ascending

hot gas. The gas is produced by the burning of coke in the hearth of the furnace and contains about 34 percent carbon monoxide. This gas reduces the iron ore to metallic iron, which melts and picks up consid-erable quantities of carbon, manganese, phosphorus, sulfur, and sili-con. The gangue (mostly silica) of the iron ore and the ash in the coke combine with the limestone to form the blast-furnace slag. The pig iron and slag are drawn off at intervals from the hearth through the iron notch and cinder notch, respectively. Some of the larger blast furnaces produce around 10,000 tons of pig iron per day. The blast furnace pro-duces a liquid product for one of three applications: (1) the huge majority passes to the steelmaking process for refining; (2) pig iron is used in foundries for making castings; and (3) ferroalloys, which con-tain a considerable percentage of another metallic element, are used as addition agents in steelmaking. Compositions of commercial pig irons and two ferroalloys (ferromanganese and ferrosilicon) are listed in Table 6.2.1.

Physical Constants of Unalloyed Iron Some physical properties of iron and even its dilute alloys are sensitive to small changes in compo-sition, grain size, or degree of cold work. The following are reasonably accurate for “pure” iron at or near room temperature; those with an asterisk are sensitive to these variables perhaps by 10 percent or more.Those with a dagger (?) depend measurably on temperature; more extended tables should be consulted.

Specific gravity, 7.866; melting point, 1,5368C (2,7978F); heat of fusion 277 kJ/kg (119 Btu/lbm); thermal conductivity 80.2 W/(m иC)[557 Btu/(h иft 2иin и8F)*?; thermal coefficient of expansion 12 ?10?6/8C (6.7 ?10?6/8F)?; electrical resistivity 9.7 m ?иcm*?; and temperature coefficient of electrical resistance 0.0065/8C (0.0036/8F).?Mechanical Properties Representative mechanical properties of annealed low-carbon steel (often similar to the former ingot iron) are as follows: yield strength 130 to 150 MPa (20 to 25 ksi); tensile strength 260 to 300 MPa (40 to 50 ksi); elongation 20 to 45 percent in 2 in;reduction in area of 60 to 75 percent; Brinell hardness 65 to 100. These figures are at best approximate and depend on composition (especially trace additives) and processing variables. For more precise data, suppli-ers or broader databases should be consulted.

Young’s modulus for ingot iron is 202,000 MPa (29,300,000 lb/in 2)in both tension and compression, and the shear modulus is 81,400 MPa (11,800,000 lb/in 2). Poisson’s ratio is 0.28. The effect of cold rolling on the tensile strength, yield strength, elongation, and shape of the stressstrain curve is shown in Fig. 6.2.1, which is for Armco ingot iron but would not be substantially different for other low-carbon 8b225f6825c52cc58bd6be64es Low-carbon materials weld evenly and easily in all processes,can be tailored to be readily paintable and to be enameled, and with other treatments make an excellent low-cost soft magnetic material with high permeability and low coercive force for mass-produced motors and transformers. Other uses, usually after galvanizing, include cul-verts, flumes, roofing, siding, and housing frames; thin plates can be used in oil and water tanks, boilers, gas holders, and various nonde-manding pipes; enameled sheet retains a strong market in ranges, refrig-erators, and other household goods, in spite of challenges from plastics.World Production From about 1970 to 1995, the annual world pro-duction of steel was remarkably steady at some 800,000,000 tons.Reductions in some major producers (United States, Japan, some European countries, and the collapsing U.S.S.R.) were balanced by the many smaller countries which began production. The struggle for markets led to pricing that did not cover production costs and led to international political strains. A major impact began in the 1990s as China pushed its own production from a few tens of million tons toward 300,000,000tons in 2004, pushing world production to over 1 billion tons.

6-12

6.2IRON AND STEEL

by Harold W.Paxton

STEEL

6-13

Fig.6.2.1Effect of cold rolling on the stress-strain relationship of Armco ingot iron.(Kenyon and Burns.)

The world raw material infrastructure (iron ore, coke, and scrap) was not able to react quickly to support this increase, and prices soared;steel prices followed. Recently (2006) long-term ore contracts reflected large price increases, so it appears that for some time steel prices will remain high by historical comparisons. The effects of material substitu-tion are not yet clear, but as end users examine their options more closely,the marketplace will most likely settle the matter.

STEEL

Steel Manufacturing

Steel is produced by the removal of impurities from pig iron in a basic oxygen furnace or an electric furnace.

Basic Oxygen Steel This steel is produced by blowing pure (99percent) oxygen either vertically under high pressure (1.2 MPa or 175 lb/in 2) onto the surface of molten pig iron (BOP) or through tuyeres in the base of the vessel (the Q-BOP process). Some facilities use a com-bination depending on local circumstances and product mix. This is an autogenous process that requires no external heat to be supplied. The furnaces are similar in shape to the former Bessemer converters but range in capacity to 275 metric tons (t) (300 net tons) or more. The barrel-shaped furnace or vessel may or may not be closed on the bottom, is open at the top, and can rotate in a vertical plane about a horizontal axis for charging and for pouring the finished steel. Selected scrap is charged into the vessel first, up to 30 percent by weight of the total charge. Molten pig iron (often purified from the raw blast-furnace hot metal to give lower sulfur, phosphorus, and sometimes silicon) is poured into the vessel. In the Q-BOP, oxygen must be flowing through the bottom tuyeres at this time to prevent clogging; further flow serves to refine the charge and carries in fluxes as powders. In the BOP process, oxygen is introduced through a water-cooled lance introduced through the top of the vessel. Within seconds after the oxygen is turned on, some iron in the charge is converted to ferrous oxide, which reacts rapidly with the impurities of the charge to remove them from the metal. As soon as reaction starts, limestone is added as a flux. Blowing is continued until the desired degree of purification is attained. The reactions take place very rapidly, and blowing of a heat is completed in

about 20 min in a 200-net-ton furnace. Because of the speed of the process, a computer is used to calculate the charge required for making a given heat of steel, the rate and duration of oxygen blowing, and to regulate the quantity and timing of additions during the blow and for finishing the steel. Production rates of well over 270 t per furnace hour (300 net tons) can be attained. The comparatively low investment cost and low cost of operation have already made the basic oxygen process the largest producer of steel in the world, and along with electric fur-naces, it almost completely replaces the basic open hearth as the major steelmaking process. No open hearths operate in the United States today.

Electric Steel The biggest change in steelmaking over the last 20 years is the fraction of steel made by remelting scrap in an electric furnace (EF), originally to serve a relatively nondemanding local market, but increasingly moving up in quality and products to compete with mills using the blast-furnace/oxygen steelmaking route. The economic compe-tition is fierce and has served to improve choices for customers. In the last decade the fraction of steel made in the EF in the United States has gone above 50 percent by a combination of contraction in blast-furnace (BF)production (no new ones built, retirement of some, and a shortage of suit-able coke) and an increase of total production, which has been met with EFs. At one time, there was concern that some undesirable elements in scrap that are not eliminated in steelmaking, notably copper and zinc,would increase with remelting cycles. However, the development of alter-native iron units (direct reduced iron, iron carbide, and even pig iron) to dilute scrap additions has at least postponed this as an issue.

Early processes used three-phase alternating current, but increasingly the movement is to a single dc electrode with a conducting hearth. The high-power densities necessitate water cooling and improved basic refractory linings. Scrap is charged into the furnace, which usually con-tains some of the last heat to improve efficiency. Older practices often had a second slag made after the first meltdown and refining by oxygen blowing, but today, final refining takes place outside the melting unit in a ladle furnace, which allows refining, temperature control, and alloy-ing additions to be made without interfering with the next heat. The materials are continuously cast including slabs only 50 mm (2 in) thick and casting directly to sheet in the 1- to 2-mm (0.04- to 0.08-in) thick-ness range is passing through the pilot stage.

The degree to which electric melting can replace more conventional methods is of great interest and depends in large part on the availability of sufficiently pure scrap at an attractive price and some improvements in surface quality to be able to make the highest-value products.Advances in EF technology are countered aggressively by new devel-opments and cost control in traditional steelmaking; it may well be a decade or more before the pattern clarifies.

The induction furnace is simply a fairly small melting furnace to which the various metals are added to make the desired alloy, usually quite specialized. When steel scrap is used as a charge, it will be a high-grade scrap the composition of which is well known (see also Sec. 7).Ladle Metallurgy One of the biggest contributors to quality in steel products is the concept of refining liquid steel outside the first melting unit—BOP, Q-BOP, or EF, none of which is well designed to perform

Table 6.2.1Types of Pig Iron for Steelmaking and Foundry Use

Chemical composition, %*

Designation

Si P Mn C?Principal use

Basic pig, northern 1.50 max 0.400 max 1.01–2.00 3.5–4.4Basic oxygen steel In steps of

0.250.50Foundry, northern 3.50 max 0.301–0.7000.50–1.25 3.0–4.5 A wide variety of castings In steps of

0.250.25Foundry, southern 3.50 max 0.700–0.9000.40–0.75 3.0–4.5Cast-iron pipe

In steps of

0.250.25Ferromanganese (3 grades) 1.2 max 0.35 max 74–827.4 max Addition of manganese to steel or cast iron Ferrosilicon (silvery pig)

5.00–17.00

0.300 max

1.00–

2.00

1.5 max

Addition of silicon to steel or cast iron

* Excerpted from “The Making, Shaping and Treating of Steel,” AISE, 1984; further information in “Steel Products Manual,” AISI, and ASTM Standards, Pt. 1.

? Carbon content not specified—for information only. Usually S is 0.05 max (0.06 for ferrosilicon) but S and P for basic oxygen steel are typically much lower today.

the final refining function. In this separate unit, gases in solution (oxy-gen, hydrogen, and, to a lesser extent, nitrogen) can be reduced by vac-uum treatment, carbon can be adjusted to desirable very low levels by reaction with oxygen in solution, alloy elements can be added, the tem-perature can be adjusted, and the liquid steel can be stirred by inert gases to float out inclusions and provide a homogeneous charge to the continuous casters which are now virtually ubiquitous. Reducing oxy-gen in solution means a “cleaner” steel (fewer nonmetallic inclusions) and a more efficient recovery of active alloying elements added with a purpose and which otherwise might end up as oxides.

Steel Ingots With the advent of continuous casters, ingot casting is now generally reserved for the production of relatively small volumes of material such as heavy plates and forgings which are too big for cur-rent casters. Ingot casting, apart from being inefficient in that the large volume change from liquid to solid must be handled by discarding the large void space usually at the top of the ingot (the pipe), also has sev-eral other undesirable features caused by the solidification pattern in a large volume, most notably significant differences in composition throughout the piece (segregation) leading to different properties, inclusions formed during solidification, and surface flaws from poor mold surfaces, splashing and other practices, which if not properly removed lead to defects in finished products (seams, scabs, scale,etc.). Some defects can be removed or attenuated, but others cannot; in gen-eral, with the exception of some very specialized tool and bearing steels, products from ingots are no longer state-of-the-art unless they are needed for size.

Continuous Casting This concept, which began with Bessemer in the 1850s, began to be a reliable production tool around 1970 and since then has replaced basically all ingot casting. Industrialized countries all continuously cast close to 100 percent of their production. Sizes cast range from 2-m (80-in)—or more—by 0.3-m (12-in) slabs down to 0.1-m (4-in) square or round billets.Multiple strands are common where pro-duction volume is important. Many heats of steel can be cast in a con-tinuous string with changes of width possible during operation. Changes of composition are possible in succeeding ladles with a dis-card of the short length of mixed composition.

By intensive process control, it is often possible to avoid cooling the cast slabs to room temperature for inspection, enabling energy savings since the slabs require less reheating before hot rolling. If for some rea-son the slabs are cooled to room temperature, any surface defects which might lead to quality problems can be removed—usually by scarfing with an oxyacetylene torch or by grinding. Since this represents a yield loss, there is a real economic incentive to avoid the formation of such defects by paying attention to casting practices.

Mechanical Treatment of Steel

Cast steel, in the form of slabs, billets, or bars (these latter two differ somewhat arbitrarily in size) is treated further by various combinations of hot and cold deformation to produce a finished product for sale from the mill. Further treatments by fabricators usually occur before delivery to the final customer. These treatments have three purposes: (1) to change the shape by deformation or metal removal to desired toler-ances; (2) to break up—at least partially—the segregation and large grain sizes inevitably formed during the solidification process and to redistribute the nonmetallic inclusions which are present; and (3) to change the properties. For example, these may be functional—strength or toughness—or largely aesthetic, such as reflectivity.

These purposes may be separable or in many cases may be acting simultaneously. An example is hot-rolled sheet or plate in which often the rolling schedule (reductions and temperature of each pass, and the cooling rate after the last reduction) is a critical path to obtain the prop-erties and sizes desired and is often known as “heat treatment on the mill.”The development of controls to do this has allowed much higher tonnages at attractive prices, and increasing robustness of rolls has allowed steel to be hot-rolled down to the 1 mm (0.04-in) range, where it can compete with the more expensive “cold-rolled” material.

Most steels are reduced after appropriate heating (to above 1,0008C) in various multistand hot rolling mills to produce sheet, strip, plate, tubes,shaped sections,or bars.More specialized deformation, e.g., by hammer forging,can result in working in more than one direction, with a distri-bution of inclusions which is not extended in one direction. Rolling,

e.g., more readily imparts anisotropic properties. Press forging at slow

strain rates changes the worked structure to greater depths and is pre-

ferred for high-quality products. The degree of reduction required to

eliminate the cast structure varies from 4:1 to 10:1; clearly smaller

reductions would be desirable but are currently not usual.

The slabs, blooms, and billets from the caster must be reheated in an

atmosphere-controlled furnace to the working temperature, often from

room temperature, but if practices permit, they may be charged hot to

save energy. Coupling the hot deformation process directly to slabs at

the continuous caster exit is potentially more efficient, but practical dif-

ficulties currently limit this to a small fraction of total production.

The steel is oxidized during heating to some degree, and this oxida-

tion is removed by a combination of light deformation and high-pressure

water sprays before the principal deformation is applied. There are

differences in detail between processes, but as a representative example,

the conventional production of wide “hot-rolled sheet” [?1.5 m (60 in)]

will be discussed.

The slab, about 0.3 m (12 in) thick at about 12008C is passed through

a scale breaker and high-pressure water sprays to remove the oxide

film. It then passes through a set of roughing passes(possibly with

some modest width reduction) to reduce the thickness to just over 25 mm

(1 in), the ends are sheared perpendicular to the length to remove irreg-

ularities, and finally they are fed into a series of up to seven roll stands

each of which creates a reduction of 50 to 10 percent passing along the

train. Process controls allow each mill stand to run sufficiently faster

than the previous one to maintain tension and avoid pileups between

stands. The temperature of the sheet is a balance between heat added by

deformation and that lost by heat transfer, sometimes with interstand

water sprays. Ideally the temperature should not vary between head and

tail of the sheet, but this is hard to accomplish.

The deformation encourages recrystallization and even some grain

growth between stands; even though the time is short, temperatures are

high. Emerging from the last stand between 815 and 9508C, the austenite*

may or may not recrystallize, depending on the temperature. At higher

temperatures, when austenite does recrystallize, the grain size is usual-

ly small (often in the 10- to 20-m m range). At lower exit temperatures

austenite grains are rolled into “pancakes” with the short dimension

often less than 10 m m. Since several ferrite* grains nucleate from each

austenite grain during subsequent cooling, the ferrite grain size can be

as low as 3 to 6 m m(ASTM 14 to 12). We shall see later that small fer-

rite grain sizes are a major contributor to the superior properties of

today’s carbon steels, which provide good strength and superior tough-

ness simultaneously and economically.

Some of these steels also incorporate strong carbide* and nitride*

formers in small amounts to provide extra strength from precipitation

hardening; the degree to which these are undissolved in austenite dur-

ing hot rolling affects recrystallization significantly. The subject is too

complex to treat briefly here; the interested reader is referred to the

ASM“Metals Handbook.”

After the last pass, the strip may be cooled by programmed water sprays

to between 510 and 7308C so that during coiling, any desired precipitation

processes may take place in the coiler. The finished coil, usually 2 to 3 mm

(0.080 to 0.120 in) thick and sometimes 1.3 to 1.5 mm (0.052 to 0.060 in)

thick, which by now has a light oxide coating, is taken off line and either

shippped directly or retained for further processing to make higher value-

added products. Depending on composition, typical values of yield

strength are from 210 up to 380 MPa (30 to 55 ksi), UTS in the range of

400 to 550 MPa (58 to 80 ksi), with an elongation in 200 mm (8 in) of

about 20 percent. The higher strengths correspond to low-alloy steels.

About half the sheet produced is sold directly as hot-rolled sheet.

The remainder is further cold-worked after scale removal by pickling

and either is sold as cold-worked to various tempers or is recrystal-

lized to form a very formable product known as cold-rolled and annealed,

6-14IRON AND STEEL

* See Fig. 6.2.4and the discussion thereof.

STEEL 6-15

To make the highest class of formable sheet is a very sophisticated operation. After pickling, the sheet is again reduced in a multistand (three, four, or five) mill with great attention paid to tolerances and sur-face finish. Reductions per pass range from 25 to 45 percent in early passes to 10 to 30 percent in the last pass. The considerable heat gener-ated necessitates an oil-water mixture to cool and to provide the neces-sary lubrication. The finished coil is degreased prior to annealing.

The purpose of annealing is to provide, for the most demanding applications, pancake-shaped grains after recrystallization of the cold-worked ferrite, in a matrix with a very sharp crystal texture containing little or no carbon or nitrogen in solution. The exact metallurgy is com-plex but well understood. Two types of annealing are possible: slow heating, holding, and cooling of coils in a hydrogen atmosphere (box annealing) lasting several days, or continuous feeding through a furnace with a computer-controlled time-temperature cycle. The latter is much quicker but very capital-intensive and requires careful and complex process control.

As requirements for formability are reduced, production controls can be relaxed. In order of increasing cost, the series is commercial quality (CQ), drawing quality (DQ), deep drawing quality (DDQ), and extra deep drawing quality (EDDQ). Even more formable steels are possible,but often are not commercially necessary.

Some other deformation processes are occasionally of interest, such as wire drawing, usually done cold, and extrusion, either hot or cold.Hot extrusion for materials that are difficult to work became practical through the employment of a glass lubricant. This method allows the hot extrusion of highly alloyed steels and other exotic alloys subjected to service at high loads and/or high temperatures.

Constitution and Structure of Steel

As a result of the methods of production, the following elements are always present in steel: carbon, manganese, phosphorus, sulfur, silicon,and traces of oxygen, nitrogen, and aluminum. Various alloying ele-ments are frequently deliberately added, such as nickel, chromium, cop-per, molybdenum, niobium (columbium), and vanadium. The most important of the above elements in steel is carbon, and it is necessary to understand the effect of carbon on the internal structure of steel to understand the heat treatment of carbon and low-alloy steels.

The iron–iron carbide equilibrium diagram in Fig. 6.2.4shows the phases that are present in steels of various carbon contents over a range of temperatures under equilibrium conditions. Pure iron when heated to 9108C (1,6708F) changes its internal crystalline structure from a body-centered cubic arrangement of atoms, alpha iron,to a face-centered

or more usually as cold-rolled,sheet. Strengthening by cold work is common in sheet, strip, wire, or bars. It provides an inexpensive addi-tion to strength but at the cost of a serious loss of ductility, often a bet-ter surface finish, and a finished product held to tighter tolerances. It improves springiness by increasing the yield strength, but does not change the elastic moduli. Examples of the effect of cold working on carbon-steel drawn wires are shown in Figs. 6.2.2and 6.2.3.

Fig.6.2.2Increase of tensile strength of plain carbon steel with increasing amounts of cold working by drawing through a wire-drawing die.

Fig.6.2.3Reduction in ductility of plain carbon steel with increasing amounts of cold working by drawing through a wire-drawing die.

Fig.6.2.4Iron–iron carbide equilibrium diagram, for carbon content up to 5 percent. (Dashed lines represent equilibrium with cementite, or iron carbide;adjacent solid lines indicate equilibrium with graphite.)

cubic structure, gamma iron.At 1,3908C (2,5358F), it changes back to the body-centered cubic structure, delta iron,and at 1,5398C (2,8028F)the iron melts. When carbon is added to iron, it is found that it has only slight solid solubility in alpha iron (much less than 0.001 percent at room temperature at equilibrium). These small amounts of carbon,however, are critically important in many high-tonnage applications where formability is required. On the other hand, gamma iron will hold up to 2.0 percent carbon in solution at 1,1308C (2,0668F). The alpha iron containing carbon or any other element in solid solution is called ferrite,and the gamma iron containing elements in solid solution is called 8b225f6825c52cc58bd6be64ually when not in solution in the iron, the carbon forms a compound Fe 3C (iron carbide) which is extremely hard and brittle and is known as cementite.Other carbides of iron exist but are only of interest in rather specialized instances.

The temperatures at which the phase changes occur are called critical points (or temperatures) and, in the diagram, represent equilibri-um conditions. In practice there is a lag in the attainment of equilibrium,and the critical points are found at lower temperatures on cooling and at higher temperatures on heating than those given, the difference increasing with the rate of cooling or heating.

The various critical points have been designated by the letter A ; when obtained on cooling, they are referred to as Ar,on the heating as Ac.The subscripts r and c refer to refroidissement and chauffage,respectively,and reflect the early French contributions to heat treatment. The various critical points are distinguished from each other by numbers after the letters, being numbered in the order in which they occur as the temper-ature increases. Ac 1represents the beginning of transformation of fer-rite to austenite on heating; Ac 3the end of transformation of ferrite to austenite on heating, and Ac 4the change from austenite to delta iron on heating. On cooling, the critical points would be referred to as Ar 4,Ar 3,and Ar 1, respectively. The subscript 2, not mentioned here, refers to a magnetic transformation. The error came about through a misunder-standing of what rules of thermodynamics apply in phase diagrams. It must be remembered that the diagram represents the pure iron-iron car-bide system at equilibrium. The varying amounts of impurities in com-mercial steels affect to a considerable extent the position of the curves and especially the lateral position of the eutectoid point.

Carbon steel in equilibrium at room temperature will have present both ferrite and cementite. The physical properties of ferrite are approx-imately those of pure iron and are characteristic of the metal. Cementite is itself hard and brittle; its shape, amount, and distribution control many of the mechanical properties of steel, as discussed later. The fact that the carbides can be dissolved in austenite is the basis of the heat treatment of steel, since the steel can be heated above the A 1critical temperature to dissolve all the carbides, and then suitable cooling through the appropriate range will produce a wide and predictable range of the desired size and distribution of carbides in the ferrite.

If austenite with the eutectoid composition at 0.76 percent carbon (Fig. 6.2.4) is cooled slowly through the critical temperature, ferrite and cementite are rejected simultaneously, forming alternate plates or lamel-lae. This microstructure is called pearlite,since when polished and etched it has a pearly luster. When examined under a high-power optical microscope, however, the inpidual plates of cementite often can be dis-tinguished easily. If the austenite contains less carbon than the eutectoid composition (i.e., hypoeutectoid compositions), free ferrite will first be rejected on slow cooling through the critical temperature until the remain-ing austenite reaches eutectoid composition, when the simultaneous rejection of both ferrite and carbide will again occur, producing pearlite.A hypoeutectoid steel at room temperature will be composed of areas of free ferrite and areas of pearlite; the higher the carbon percentage, the greater the amount of pearlite present in the steel. If the austenite contains more carbon than the eutectoid composition (i.e., hypereutectoid com-position) and is cooled slowly through the critical temperature, then cementite is rejected and appears at the austenitic grain boundaries, form-ing a continuous cementite network until the remaining austenite reaches eutectoid composition, at which time pearlite is formed. A hypereutectoid steel, when slowly cooled, will exhibit areas of pearlite surrounded by a thin network of cementite, or iron carbide.

As the cooling rate is increased, the spacing between the pearlite lamellae becomes smaller; with the resulting greater dispersion of car-bide preventing slip in the iron crystals, the steel becomes harder. Also,with an increase in the rate of cooling, there is less time for the separa-tion of excess ferrite or cementite, and the equilibrium amount of these constituents will not be precipitated before the austenite transforms to pearlite. Thus with a fast rate of cooling, pearlite may contain less or more carbon than given by the eutectoid composition. When the cool-ing rate becomes very rapid (as obtained by quenching), the carbon does not have sufficient time to separate out in the form of carbide, and the austenite transforms to a highly elastically stressed structure super-saturated with carbon called martensite.This structure is exceedingly hard but brittle and requires tempering to increase the ductility.Tempering consists of heating martensite to some temperature below the critical temperature, causing the carbide to precipitate in the form of small spheroids, or especially in alloy steels, as needles or platelets. The higher the tempering temperature, the larger the carbide particle size,the greater the ductility of the steel, and the lower the hardness.

In a carbon steel, it is possible to have a structure consisting either of parallel plates of carbide in a ferrite matrix, the distance between the plates depending upon the rate of cooling, or of carbide spheroids in a ferrite matrix, the size of the spheroids depending upon the temperature to which the hardened steel was heated. (Some spheroidization occurs when pearlite is heated, but only at high temperatures close to the crit-ical temperature range.)

Heat-Treating Operations

The following definitions of terms have been adopted by the ASTM,SAE, and ASM in substantially identical form.

Heat Treatment An operation, or combination of operations, involv-ing the heating and cooling of a metal or an alloy in the solid state, for the purpose of obtaining certain desirable conditions or properties.Quenching Rapid cooling by immersion in liquids or gases or by contact with metal.

Hardening Heating and quenching certain iron-base alloys from a temperature either within or above the critical range for the purpose of producing a hardness superior to that obtained when the alloy is not quenched. Usually restricted to the formation of martensite.

Annealing A heating and cooling operation implying usually a rela-tively slow cooling. The purpose of such a heat treatment may be (1) to remove stresses; (2) to induce softness; (3) to alter ductility, toughness,electrical, magnetic, or other physical properties; (4) to refine the crys-talline structure; (5) to remove gases; or (6) to produce a definite micro-structure. The temperature of the operation and the rate of cooling depend upon the material being heat-treated and the purpose of the treatment. Certain specific heat treatments coming under the compre-hensive term annealing are as follows:

Full Annealing Heating iron base alloys above the critical temper-ature range, holding above that range for a proper period of time, fol-lowed by slow cooling to below that range. The annealing temperature is usually about 508C (<1008F) above the upper limit of the critical temperature range, and the time of holding is usually not less than 1 h for each 1-in section of the heaviest objects being treated. The objects being treated are ordinarily allowed to cool slowly in the furnace. They may, however, be removed from the furnace and cooled in some medi-um that will prolong the time of cooling as compared with unrestricted cooling in the air.

Process Annealing Heating iron-base alloys to a temperature below or close to the lower limit of the critical temperature range fol-lowed by cooling as desired. This heat treatment is commonly applied in the sheet and wire industries, and the temperatures generally used are from 540 to 7058C (about 1,000 to 1,3008F).

Normalizing Heating iron base alloys to approximately 408C (about 1008F) above the critical temperature range followed by cooling to below that range in still air at ordinary temperature.

Patenting Heating iron base alloys above the critical temperature range followed by cooling below that range in air or a molten mixture of nitrates or nitrites maintained at a temperature usually between 425 and

6-16IRON AND STEEL

STEEL 6-17

5658C (about 800 to 1,0508F), depending on the carbon content of the steel and the properties required of the finished product. This treatment is applied in the wire industry to medium- or high-carbon steel as a treatment to precede further wire drawing.

Spheroidizing Any process of heating and cooling steel that pro-duces a rounded or globular form of carbide. The following spheroidiz-ing methods are used: (1) Prolonged heating at a temperature just below the lower critical temperature, usually followed by relatively slow cool-ing. (2) In the case of small objects of high-carbon steels, the spher-oidizing result is achieved more rapidly by prolonged heating to temperatures alternately within and slightly below the critical tempera-ture range. (3) Tool steel is generally spheroidized by heating to a tem-perature of 750 to 8058C (about 1,380 to 1,4808F) for carbon steels and higher for many alloy tool steels, holding at heat from 1 to 4 h, and cooling slowly in the furnace.

Tempering (also termed Drawing)Reheating hardened steel to some temperature below the lower critical temperature, followed by any desired rate of cooling. Although the terms tempering and drawing are practically synonymous as used in commercial practice, the term tempering is preferred.

Transformation Reactions in Carbon Steels Much of, but not all, the heat treatment of steel involves heating into the region above Ac 3to form austenite, followed by cooling at a preselected rate. If the parts are large,heat flow may limit the available cooling rates. As an example selected for simplicity rather than volume of products, we may follow the possible transformations in a eutectoid steel over a range of temperature. (The reac-tions to produce ferrite in hypoeutectoid steels, which are by far the most common, do not differ in principle; the products are, of course, softer.) The curve is a derivative of the TTT (time-temperature-transformation) curves produced by a systematic study of austenite transformation rates isother-mally on specimens thin enough to avoid heat flow complications. The data collected for many steels are found in the literature.

Figure 6.2.5summarizes the rates of decomposition of a eutectoid carbon steel over a range of temperatures. Various cooling rates are shown diagrammatically, and it will be seen that the faster the rate of cooling, the lower the temperature of transformation, and the harder the product formed. At around 5408C (1,0008F), the austenite transforms rapidly to fine pearlite; to form martensite it is necessary to cool very rapidly through this temperature range to avoid the formation of pearlite before the specimen reaches the temperature at which the formation of martensite begins (M s ). The minimum rate of cooling that is required to form a fully martensite structure is called the critical cooling rate.No matter at what rate the steel is cooled, the only products of transforma-tion of this steel will be pearlite or martensite. However, if the steel can be given an interrupted quench in a molten bath at some temperature between 205 and 5408C (about 400 and 1,0008F), an acicular structure,called bainite,of considerable toughness, combining high strength with

Fig.6.2.5Influence of cooling rate on the product of transformation in a eutec-toid carbon steel.

high ductility, is obtained, and this heat treatment is known as austem-pering. A somewhat similar heat treatment called martempering can be utilized to produce a fully martensitic structure of high hardness, but free of the cracking, distortion, and residual stresses often associated with such a structure. Instead of quenching to room temperature, the steel is quenched to just above the martensitic transformation tempera-ture and held for a short time to permit equalization of the temperature gradient throughout the piece. Then the steel may be cooled relatively slowly through the martensitic transformation range without superim-posing thermal stresses on those introduced during transformation. The limitation of austempering and martempering for carbon steels is that these two heat treatments can be applied only to articles of small cross section, since the rate of cooling in salt baths is not sufficient to prevent the formation of pearlite in samples with diameter of more than in.The maximum hardness obtainable in a high-carbon steel with a fine pearlite structure is approximately 400 Brinell, although a martensitic structure would have a hardness of approximately 700 Brinell. Besides being able to obtain structures of greater hardness by forming marten-site, a spheroidal structure will have considerably higher proof stress (i.e., stress to cause a permanent deformation of 0.01 percent) and duc-tility than a lamellar structure of the same tensile strength and hardness.It is essential, therefore, to form martensite when optimum properties are desired in the steel. This can be done with a piece of steel having a small cross section by heating the steel above the critical and quenching in water; but when the cross section is large, the cooling rate at the center of the section will not be sufficiently rapid to prevent the forma-tion of pearlite. The characteristic of steel that determines its capacity to harden throughout the section when quenched is called hardenability.In the discussion that follows, it is pointed out that hardenability is signif-icantly affected by most alloying elements. This term should not be confused with the ability of a steel to attain a certain hardness. The intensity of hardening, i.e., the maximum hardness of the martensite formed, is very largely dependent upon the carbon content of the steel. Determination of Hardenability A long-established test for harden-ability is the Jominy test which performs controlled water cooling on one end of a standard bar. Since the thermal conductivity of steel does not vary significantly, each distance from the quenched end (DQE) cor-responds to a substantially unique cooling rate, and the structure obtained is a surrogate for the TTT curve on cooling. For a detailed account of the procedure, see the SAE Handbook. The figures extract-ed from the Jominy test can be extended to many shapes and quenching media. In today’s practices, the factors discussed below can often be used to calculate hardenability from chemical composition with con-siderable confidence, leaving the actual test as a referee or for circum-stances where a practice is being developed.

Three main factors affect the hardenability of steel: (1) austenite composition; (2) austenite grain size; and (3) amount, nature, and distri-bution of undissolved or insoluble particles in the austenite. All three determine the rate of decomposition, in the range of 5408C (about 1,0008F). The slower the rate of decomposition, the larger the section that can be hardened throughout, and therefore the greater the hardena-bility of the steel. Everything else being equal, the higher the carbon content, the greater the hardenability; this approach, however, is often counterproductive in that other strength properties may be affected in undesirable ways. The question of austenitic grain size is of considerable importance in any steel that is to be heat-treated, since it affects the properties of the steel to a considerable extent. When a steel is heated to just above the critical temperature, small polyhedral grains of austenite are formed. With increase in temperature, there is an increase in the size of grains, until at temperatures close to the melting point the grains are very large. Since the transformation of austenite to ferrite and pearlite usually starts at grain boundaries, a fine-grained steel will trans-form more rapidly than a coarse-grained steel because the latter has much less surface area bounding the grains than a steel with a fine grain size.The grain size of austenite at a particular temperature depends primarily on the “pinning” of the boundaries by undissolved particles. These parti-cles, which can be aluminum nitride from the deoxidation or various car-bides and/or nitrides (added for their effect on final properties),

1?2

dissolve as temperature increases, allowing grain growth. While hard-

enability is increased by large austenite grain size, this is not usually

favored since some properties of the finished product can be seriously

downgraded. Small particles in the austenite will act as nuclei for the

beginning of transformation in a manner similar to grain boundaries,

and therefore the presence of a large number of small particles (some-

times submicroscopic in size) will also result in low hardenability. Determination of Austenitic Grain Size The subject of austenite grain size is of considerable interest because of the fact noted above that

the grain size developed during heat treatment has a large effect on the

physical properties of the steel. In steels of similar chemical analysis,

the steel developing the finer austenitic grain size will have a lower

hardenability but will, in general, have greater toughness, show less ten-

dency to crack or warp on quenching, be less susceptible to grinding

cracks, have lower internal stresses, and retain less austenite than

coarse-grained steel. There are several methods of determining the

grain-size characteristics of a steel.

The McQuaid-Ehn test(ASTM E112), which involves the outlining of

austenite grains by cementite after a specific carburizing treatment, is

still valid. It has been largely replaced, however, by quenching from the

austenitizing treatment under investigation and observing the grain size

of the resulting martensite after light tempering and etching with Vilella’s

reagent. There are several ways to report the grain size observed under

the microscope, the one used most extensively being the ASTM index

numbers. In fps or English units, the numbers are based on the formu-

la: number of grains per square inch at 100x?2N?1, in which N is the

grain-size index. The usual range in steels will be from 1 to 128

grains/in2at 100x, and the corresponding ASTM numbers will be 1 to 8,

although today grain sizes up to 12 to 14 are common. Whereas at one

time“coarse” grain sizes were 1 to 4, and “fine” grain sizes 5 to 8, these

would not serve modern requirements. Most materials in service would

be no coarser than 7 or 8, and the ferritic low-alloy high-strength steels

routinely approach 12 or higher. Grain-size relationships in SI units are

covered in detail in Designation E112 of ASTM Standards. For further

information on grain size, refer to the ASM “Metals Handbook.”

EFFECT OF ALLOYING ELEMENTS

ON THE PROPERTIES OF STEEL

When relatively large amounts of alloying elements are added to steel, the characteristic behavior of carbon steels is not lost. Most alloy steel is medium- or high-carbon steel to which various elements have been added to modify its properties to an appreciable extent; the alloys as a minimum allow the properties characteristic of the carbon content to be fully realized even in larger sections, and in some cases may provide additional benefits. The percentage of alloy element required for a given purpose ranges from a few hundredths of 1 percent to possibly as high as 5 percent.

When ready for service, these steels will usually contain only two constituents, ferrite and carbide. The only way that an alloying element can affect the properties of the steel is to change the dispersion of car-bide in the ferrite, change the properties of the ferrite, or change the characteristics of the carbide. The effect on the distribution of carbide is the most important factor, since in sections amenable to close control of structure, carbon steel is only moderately inferior to alloy steel. However, in large sections where carbon steels will fail to harden throughout the section even on a water quench, the hardenability of the steel can be increased at a cost by the addition of any alloying element (except possibly cobalt). The increase in hardenability permits the hard-ening of a larger section of alloy steel than of plain carbon steel. The quenching operation does not have to be so drastic. Consequently, there is a smaller difference in temperature between the surface and center during quenching, and cracking and warping resulting from sharp tem-perature gradients in a steel during hardening can be avoided. The ele-ments most effective in increasing the hardenability of steel are manganese, silicon, and chromium, or combinations of small amounts of several elements such as chromium, nickel, and molybdenum in SAE 4340, where the joint effects are greater than alloys acting singly.

Elements such as molybdenum, tungsten, and vanadium are effective in increasing the hardenability when dissolved in the austenite, but not when present in the austenite in the form of carbides. When dissolved in austenite, and thus contained in solution in the resulting martensite, they can modify considerably the rate of coarsening of carbides in tem-pered martensite. Tempering relieves the internal stresses in the hard-ened steel in part by precipitating various carbides of iron at fairly low temperature, which coarsen as the tempering temperature is increased. The increasing particle separation results in a loss of hardness and strength accompanied by increased ductility. See Fig. 6.2.6. Alloying elements can cause slower coarsening rates or, in some cases at tem-peratures from 500 to 6008C, can cause dissolution of cementite and the precipitation of a new set of small, and thus closely spaced, alloy car-bides which in some cases can cause the hardness to actually rise again with no loss in toughness or ductility. This is especially important in tool steels. The presence of these stable carbide-forming elements enables higher tempering temperatures to be used without sacrificing strength. This permits these alloy steels to have a greater ductility for a given strength, or, conversely, greater strength for a given ductility, than plain carbon steels.

The third factor which contributes to the strength of alloy steel is the presence of the alloying element in the ferrite. Any element in solid solution in a metal will increase the strength of the metal, so that these elements will materially contribute to the strength of hardened and tem-pered steels. The elements most effective in strengthening the ferrite are phosphorus, silicon, manganese, and, to a lesser extent, nickel, molyb-denum, and chromium. Carbon and nitrogen are very strong ferrite strengtheners but generally are not present in interstitial solution in sig-nificant amounts, and there are other processing reasons to actively keep the amount in solution small by adding strong carbide and/or nitride formers to give interstitial-free (IF) steels.

6-18IRON AND STEEL

Fig.6.2.6Range of tensile properties in several quenched and tempered steels

at the same hardness values. (Janitzky and Baeyertz. Source: ASM; reproduced by

permission.)

PRINCIPLES OF HEAT TREATMENT OF IRON AND STEEL6-19 A final important effect of alloying elements discussed above is their

influence on the austenitic grain size. Martensite formed from a fine-

grained austenite has considerably greater resistance to shock than

when formed from a coarse-grained austenite.

In Table 6.2.2, a summary of the effects of various alloying elements

is given. Remember that this table indicates only the trends of the vari-

ous elements, and the fact that one element has an important influence

on one factor does not prevent it from having a completely different

influence on another one.

PRINCIPLES OF HEAT TREATMENT

OF IRON AND STEEL

When heat-treating a steel for a given part, certain precautions have to

be taken to develop optimum mechanical properties in the steel. Some

of the major factors that have to be taken into consideration are outlined

below.

Heating The first step in the heat treatment of steel is the heating of

the material to above the critical temperature to make it fully austenitic.

The heating rate should be sufficiently slow to avoid injury to the mate-

rial through excessive thermal and transformational stresses. In general,

hardened steel should be heated more slowly and uniformly than is nec-

essary for soft stress-free materials. Large sections should not be placed

in a hot furnace, the allowable size depending upon the carbon and alloy

content. For high-carbon steels, care should be taken in heating sections

as small as 50-mm (2-in) diameter, and in medium-carbon steels pre-

cautions are required for sizes over 150-mm (6-in) diameter. The

maximum temperature selected will be determined by the chemical

composition of the steel and its grain-size characteristics. In hypoeu-

tectoid steel, a temperature about 25 to 508C above the upper critical

range is used, and in hypereutectoid steels, a temperature between the

lower and the upper critical temperature is generally used to retain

enough carbides to keep the austenite grain size small and preserve

what is often limited toughness. Quenching temperatures are usually a

little closer to the critical temperature for hypoeutectoid steels than to

those for normalizing; annealing for softening is carried out just below

Ac

1for steels up to 0.3 percent C and just above for higher-carbon

steels. Tables of suggested temperatures can be found in the ASM “Metals Handbook,” or a professional heat treater may be consulted. The time at maximum temperature should be such that a uniform temperature is obtained throughout the cross section of the steel. Care should be taken to avoid undue length of time at temperature, since this will result in undesirable grain growth, scaling, or decarburization of the surface. A practical figure often given for the total time in the hot furnace is 12 min/cm (about h/in) of cross-sectional thickness. When

1?2the steel has attained a uniform temperature, the cooling rate must be

such as to develop the desired structure; slow cooling rates (furnace or

air cooling) to develop the softer pearlitic structures and high cooling

rates (quenching) to form the hard martensitic structures. In selecting a quenching medium(see ASM “Metals Handbook”), it is important to select the quenching medium for a particular job on the basis of size,

shape, and allowable distortion before choosing the steel composition.

It is convenient to classify steels in two groups on the basis of depth of

hardening: shallow hardening and deep hardening. Shallow-hardening steels may be defined as those which, in the form of 25-mm- (1-in-) diameter rounds, have, after brine quenching, a completely martensitic shell not deeper than 6.4 mm (in). The shallow-hardening steels are those of low or no alloy content, whereas the deep-hardening steels have a substantial content of those alloying elements that increase pen-etration of hardening, notably chromium, manganese, and nickel. The high cooling rates required to harden shallow-hardening steel produce severe distortion and sometimes quench cracking in all but simple, sym-metric shapes having a low ratio of length to diameter or thickness. Plain carbon steels cannot be used for complicated shapes where dis-tortion must be avoided. In this case, water quenching must be aban-doned and a less active quench used which materially reduces the temperature gradient during quenching. Certain oils are satisfactory but are incapable of hardening shallow-hardening steels of substantial size.

A change in steel composition is required with a change from water to

an oil quench. Quenching in oil does not entirely prevent distortion.

When the degree of distortion produced by oil quenching is objection-

able, recourse is taken to air hardening. The cooling rate in air is very

much slower than in oil or water; so an exceptionally high alloy content

is required. This means that a high price is paid for the advantage

gained, in terms of both metal cost and loss in machinability, though it

may be well justified when applied to expensive tools or dies. In this

case, danger of cracking is negligible.

Liquids for Quenching Shallow-H ardening Steels Shallow-hardening steels require extremely rapid surface cooling in the quench, particularly in the temperature range around 5508C (1,0208F). A sub-merged water spray will give the fastest and most reproducible quench practicable. Such a quench is limited in application to simple short objects which are not likely to warp. Because of difficulty in obtaining symmetric flow of the water relative to the work, the spray quench is conducive to warping. The ideal practical quench is one that will give the required surface cooling without agitation of the bath. The addition of ordinary salt, sodium chloride, greatly improves the performance of water in this respect, the best concentration being around 10 percent. Most inorganic salts are effective in suppressing the formation of vapor at the surface of the steel and thus aid in cooling steel uniformly and

1?4

Table 6.2.2Trends of Influence of Some Alloying Elements

Effect on grain

Strengthening as Hardenability effects coarsening in austenite Effects on tempered

dissolved in if dissolved if undissolved hardness, strength, Element ferrite in austenite as compound and toughness Al**?None

Cr*??*

Co?Negative None None

Cu?*None None

Mn?***

Mo*??None

Nb (Cb)None????

Ni**None None

P?*None None

Si**None None

Ta?????

Ti????

W*???

V*???

* Effects are moderate at best.

? Effects are strong to very strong.

? Effects not clear, or not used significantly.

eliminating the formation of soft spots. To minimize the formation of vapor, water-base quenching liquids must be kept cool, preferably under 208C (about 708F). The addition of some other soluble materials to water such as soap is extremely detrimental because of increased for-mation of vapor.

Liquids for Quenching Deeper-H ardening Steels When oil quenching is necessary, use a steel of sufficient alloy content to produce a completely martensitic structure at the surface over the heaviest sec-tion of the work. To minimize the possibility of cracking, especially when hardening tool steels, keep the quenching oil warm, preferably between 40 and 658C (about 100 and 1508F). If this expedient is insuf-ficient to prevent cracking, the work may be removed just before the start of the hardening transformation and cooled in air. Whether or not transformation has started can be determined with a permanent magnet, the work being completely nonmagnetic before transformation.

The cooling characteristics of quenching oils are difficult to evaluate and have not been satisfactorily correlated with the physical properties of the oils as determined by the usual tests. The standard tests are important with regard to secondary requirements of quenching oils. Low viscosity assures free draining of oil from the work and therefore low oil loss. A high flash and fire point assures a high boiling point and reduces the fire hazard which is increased by keeping the oil warm. A low carbon residue indicates stability of properties with continued use and little sludging. The steam-emulsion number should be low to ensure low water content, water being objectionable because of its vapor-film-forming tendency and high cooling power. A low saponification num-ber assures that the oil is of mineral base and not subject to organic deterioration of fatty oils which give rise to offensive odors. Viscosity index is a valuable property for maintenance of composition.

In recent years, polymer-water mixtures have found application because of their combination of range of heat abstraction rates and rel-ative freedom from fire hazards and environmental pollution. In all cases, the balance among productivity, danger of distortion and crack-ing, and minimum cost to give adequate hardenability is not simple; even though some general guides are available (e.g., “Metals Handbook,” vol. 1, 10th ed.), consultation with experienced profession-als is recommended.

Effect of the Condition of Surface The factors that affect the depth of hardening are the hardenability of the steel, the size of specimen, the quenching medium, and finally the condition of the surface of the steel before quenching. Steel that carries a heavy coating of scale will not cool so rapidly as a steel that is comparatively scale-free, and soft spots may be produced; or, in extreme cases, complete lack of hardening may result. It is therefore essential to minimize scaling as much as possible. Decarburization can also produce undesirable results such as nonuni-form hardening and thus lowers the resistance of the material to alter-nating stresses (i.e., fatigue).

Tempering,as noted above, relieves quenching stresses and offers the ability to obtain useful combinations of properties through selection of tempering temperature. The ability of alloying elements to slow tem-pering compared to carbon steel allows higher temperatures to be used to reach a particular strength. This is accompanied by some usually modest increases in ductility and toughness. Certain high-hardenability steels are subject to delayed cracking after quenching and should be tempered without delay. Data on tempering behavior are available from many sources, such as ASM “Metals Handbook” or Bain and Paxton,“Functions of the Alloying Elements in Steel,” 3d ed., ASM International.

Relation of Design to Heat Treatment

Care must be taken in the design of a machine part to prevent cracking or distortion during heat treatment. With proper design the entire piece may be heated and cooled at approximately the same rate during the heat-treating operation. A light section should never be joined to a heavy section. Sharp reentrant angles should be avoided. Sharp corners and inadequate fillets produce serious stress concentration, causing the actual service stresses to build up to a point where they amount to two to five times the normal working stress calculated by the engineer in the original layout. The use of generous fillets is especially desirable with

all high-strength alloy steels.

The modulus of elasticity of all commercial steels, either carbon or

alloy, is the same so far as practical designing is concerned. The deflec-

tion under load of a given part is, therefore, entirely a function of the

section of the part and is not affected by the composition or heat treat-

ment of the steel. Consequently if a part deflects excessively, a change

in design is necessary; either a heavier section must be used or the

points of support must be increased.

COMPOSITE MATERIALS

For some applications, it is not necessary or even desirable that the part

have the same composition throughout. The oldest method of utilizing

this concept is to produce a high-carbon surface on low-carbon steel

by carburizing,a high-temperature diffusion treatment, which after

quenching gives a wear-resistant case 1 or 2 mm (0.04 or 0.08 in) thick

on a fairly shock-resistant core. Clearly, this is an attractive process for

gears and other complex machined parts. Other processes which pro-

duce a similar product are nitriding(which can be carried out at lower

temperatures) and carbonitriding(a hybrid), or where corrosion resis-

tance is important, by chromizing.Hard surfaces can also be obtained

on a softer core by using selective heating to produce surface austenite

(induction, flames, etc.) before quenching, or by depositing various

hard materials on the surface by welding.

Many other types of surface treatment which provide corrosion pro-

tection and sometimes aesthetic values are common, beginning with

paint or other polymeric films and ranging through enamels (a glass

film); films such as zinc and its alloys which can be applied by dipping

in molten baths or can be deposited electrolytically on one or both sides

(galvanizing); tinplate for cans and other containers; chromium plating;

or a light coherent scale of iron oxide. These processes are continually

being improved, and they may be used in combinations, e.g., paint on a

galvanized surface for exposed areas of automobiles. (See Sec. 6.6.) Carburizing Various methods are available depending on the pro-duction volume. Pack carburizing can handle perse feedstock by

enclosing the parts in a sealed heat-resistant alloy box with carbonates

and carbonaceous material, and by heating for several hours at about

9258C. The carbon dioxide evolved reacts with carbon to form carbon

monoxide as the carrier gas, which does the actual carburizing. While

the process can be continuous, much of it is done as a batch process,

with consequent high labor costs and uncertain quality to be balanced

against the flexibility of custom carburizing.

For higher production rates, furnaces with controlled atmospheres

involving hydrocarbons and carbon monoxide provide better controls,

low labor costs, shorter times to produce a given case depth [4 h versus

9 h for a 1-mm (0.04-in) case], and automatic quenching. Liquid car-

burizing using cyanide mixtures is even quicker for thin cases, but often

it is not as economical for thicker ones; its great advantage is flexibility

and control in small lots.

To provide the inherent value in this material of variable composi-

tion, it must be treated to optimize the properties of case and core by a

double heat treatment. In many cases, to avoid distortion of precision

parts, the material is first annealed at a temperature above the carburiz-

ing temperature and is cooled at a rate to provide good machinability.

The part is machined and then carburized; through careful steel selec-

tion, the austenite grain size is not large at this point, and the material

can be quenched directly without danger of cracking or distortion. Next

the part is tempered; any retained austenite from the low M

s

of the high-

carbon case has a chance to precipitate carbides, raise its M

s

, and trans-

form during cooling after tempering. Care is necessary to avoid internal

stresses if the part is to be ground afterward. An alternative approach is

to cool the part reasonably slowly after carburizing and then to heat-

treat the case primarily by suitable quenching from a temperature typi-

cal for hypereutectoid steels between A

1

and A

cm

. This avoids some

retained austenite and is helpful in high-production operations. The

core is often carbon steel, but if alloys are needed for hardenability, this

must be recognized in the heat treatment.

6-20IRON AND STEEL

COMMERCIAL STEELS6-21

Nitriding A very hard, thin case can be produced by exposing an already quenched and tempered steel to an ammonia atmosphere at about 510 to 5408C, but unfortunately for periods of 50 to 90 h. The nitrogen diffuses into the steel and combines with strong nitride form-ers such as aluminum and chromium, which are characteristically pre-sent in steels where this process is to be used. The nitrides are small and finely dispersed; since quenching is not necessary after nitriding, dimensional control is excellent and cracking is not an issue. The core properties do not change since tempering at 5508C or higher tempera-ture has already taken place. A typical steel composition is as follows: C, 0.2 to 0.3 percent; Mn, 0.04 to 0.6 percent; Al, 0.9 to 1.4 percent; Cr, 0.9 to 1.4 percent; and Mo, 0.15 to 0.25 percent.

Carbonitriding (Cyaniding)An interesting intermediate which rapidly adds both carbon and nitrogen to steels can be obtained by immersing parts in a cyanide bath just above the critical temperature of the core followed by direct quenching. A layer of about 0.25 mm (0.010 in) can be obtained in 1 h. The nitrides add to the wear resistance.

Local Surface Hardening For some parts which do not readily fit in a furnace, the surface can be hardened preferentially by local heating using flames, induction coils, electron beams, or lasers. The operation requires skill and experience, but in proper hands it can result in very good local control of structure, including the development of favorable surface compressive stresses to improve fatigue resistance.

Clad steels can be produced by one of several methods, including simple cladding by rolling a sandwich out of contact with air at a tem-perature high enough to bond (1,2008C); by explosive cladding where the geometry is such that the energy of the explosive causes a narrow molten zone to traverse along the interface and provide a good fusion bond; and by various casting and welding processes which can deposit a wide variety of materials (ranging from economical, tough, corrosion-resistant, or high-thermal-conductivity materials to hard and stable carbides in a suitable matrix). Many different product shapes lend themselves to these practices.

Chromizing Chromizing of low-carbon steel is effective in improving corrosion resistance by developing a surface containing up to 40 percent chromium. Some forming operations can be carried out on chromized material. Most chromizing is accomplished by packing the steel to be treated in a powdered mixture of chromium and alumina and then heat-ing to above 1,2608C (2,3008F) for 3 or 4 h in a reducing atmosphere. Another method is to expose the parts to be treated to gaseous chromi-um compounds at temperatures above 8458C (about 1,5508F). Flat rolled sheets for corrosive applications such as auto mufflers can thus be chromized in open-coil annealing facilities.

THERMOMECHANICAL TREATMENT

The effects of mechanical treatment and heat treatment on the mechan-ical properties of steel have been discussed earlier in this section. Thermomechanical treatment consists of combining controlled (some-times large) amounts of plastic deformation with the heat-treatment cycle to achieve improvements in yield strength beyond those attainable by the usual rolling practices alone or rolling following by a separate heat treatment. The tensile strength, of course, is increased at the same time as the yield strength (not necessarily to the same degree), and other properties such as ductility, toughness, creep resistance, and fatigue life can be improved. However, the high strength and hardness of thermo-mechanically treated steels limit their usefulness to the fabrication of components that require very little cold forming or machining, or very simple shapes such as strip and wire that can be used as part of a com-posite structure. Although the same yield strength may be achieved in a given steel by different thermomechanical treatments, the other mechanical properties (particularly the toughness) are not necessarily the same.

There are many possible combinations of deformation schedules and time-temperature relationships in heat treatment that can be used for thermomechanical treatment, and inpidual treatments will not be dis-cussed here. Table 6.2.3classifies broadly thermomechanical treat-ments into three principal groups related to the time-temperature dependence of the transformation of austenite discussed earlier under heat treatment. The names in parentheses following the subclasses in the table are those of some types of thermomechanical treatments that have been used commercially or have been discussed in the literature. At one time it was thought that these procedures would grow in impor-tance, but in fact they are still used in a very minor way with the impor-tant exception of class 1a and class 1c, which are critically important in large tonnages.

Table 6.2.3Classification of Thermomechanical Treatments

Class I. Deformation before austenite transformation

a.Normal hot-working processes

(hot/cold working)

b.Deformation before transformation to martensite

(ausforming, austforming, austenrolling, hot-cold working, marworking,

warm working)

c.Deformation before transformation to ferrite-carbide aggregates (austen-

tempering)

Class II. Deformation during austenite transformation

a.Deformation during transformation to martensite (Zerolling and Ardeform

processes)

b.Deformation during transformation to ferrite-carbide aggregates (flow

tempering of bainite and isoforming)

Class III. Deformation after austenite transformation

a.Deformation of martensite followed by tempering

b.Deformation of tempered martensite followed by aging (flow tempering,

marstraining, strain tempering, tempforming, warm working)

c.Deformation of isothermal transformation products (patenting, flow tem-

pering, warm working)

S OURCE: Radcliffe Kula, Syracuse University Press, 1964.

COMMERCIAL STEELS

The wide variety of applications of steel for engineering purposes is due to the range of mechanical properties obtainable by changes in carbon content and heat treatment. Some typical applications of carbon steels are given in Table 6.2.4. Carbon steels can be subpided roughly into three groups: (1) low-carbon steel, 0.01 to 0.25 percent carbon, for use where only moderate strength is required together with considerable plasticity; (2) machinery steels, 0.30 to 0.55 percent carbon, which can be heat-treated to develop high strength; and (3) tool steels, containing from 0.60 to 1.30 percent carbon (this range also includes rail and spring steels).

Table 6.2.4Some Typical Applications of Carbon Steels

Percent C Uses

0.01–0.10Sheet, strip, tubing, wire nails

0.10–0.20Rivets, screws, parts to be case-hardened

0.20–0.35Structural steel, plate, forgings such as camshafts

0.35–0.45Machinery steel—shafts, axles, connecting rods, etc.

0.45–0.55Large forgings—crankshafts, heavy-duty gears, etc.

0.60–0.70Bolt-heading and drop-forging dies, rails, setscrews

0.70–0.80Shear blades, cold chisels, hammers, pickaxes, band saws

0.80–0.90Cutting and blanking punches and dies, rock drills, hand chisels

0.90–1.00Springs, reamers, broaches, small punches, dies

1.00–1.10Small springs and lathe, planer, shaper, and slotter tools

1.10–1.20Twist drills, small taps, threading dies, cutlery, small lathe tools 1.20–1.30Files, ball races, mandrels, drawing dies, razors

The product mix has changed noticeably over the last 20 years as consumption rose from about 100 million to 120 to 130 million tpy, some of which were imports, both semifinished (slabs, billets, etc.) and finished. Rails, in Carnegie’s time, “ the” product, dropped enormously as track maintenance slipped; tool steels fell, reflecting competition from carbides and oxide tools. Sheet was the main gainer with a large contribution from coated sheet (largely galvanized, reflecting cosmetic influences in the auto industry). Hot-rolled sheet displaced some cold-rolled applications as noted above. As an indication of current (2006)

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