© 2002 ASM International. All Rights Reserved. www.asminternational.org Surface Hardening of Steels: Understanding the Basics (#06952G) Surface Hardening of Steels Understanding the Basics Edited by J.R. Davis Davis & Associates ASM International Materials Park, OH 44073-0002 www.asminternational.org © 2002 ASM International. All Rights Reserved. www.asminternational.org Surface Hardening of Steels: Understanding the Basics (#06952G) Copyright © 2002 by ASM International® All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the writ- ten permission of the copyright owner. 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ASM International staff who worked on this project included; Bonnie Sanders, Manager of Pro- duction; Nancy Hrivnak and Jill Kinson, Production Editors; and Scott Henry, Assistant Direc- tor of Reference Publications. Library of Congress Cataloging-in-Publication Data Surface hardening of steels : understanding the basics / edited by J.R. Davis p. c.m. Includes bibliographical references and index. 1. Steel—Metallurgy. I. Title: Surface treatment of steels. II. Davis, J.R. (Joseph R.) TN731.S85 2002 672.3′6—dc21 2002034248 ISBN: 0-87170-764-0 SAN: 204-7586 ASM International® Materials Park, OH 44073-0002 www.asminternational.org Printed in the United States of America © 2002 ASM International. All Rights Reserved. www.asminternational.org Surface Hardening of Steels: Understanding the Basics (#06952G) Contents Introduction Chapter 1 Process Selection Guide . 1 Diffusion Methods of Surface Hardening . 1 Surface Hardening by Applied Energy . 5 Surface Hardening by Coating or Surface Modification . 7 Important Considerations for Process Selection . 11 Process Comparisons . 12 Surface Hardening by Thermochemical Diffusion Treatments Chapter 2 Gas Carburizing . 17 Gas Curburizing Practices . 17 Characteristic Features of Carburized Cases . 17 Carbon Sources . 18 Carburizing Equipment . 19 Preparation of Parts for Carburizing . 21 Carburizing Process Variables . 21 Gas Carburizing Atmospheres . 25 Carbon Concentration Gradients and Surface Carbon Content . 29 Process Planning . 39 Selective Carburizing . 42 Dimensional Control . 43 Case Depth Measurement . 44 Microstructures of Carburized Steels . 46 Martensite . 46 Austenite . 49 Carbides . 53 Alloying Effects . 55 Intergranular Fracture at Austenite Grain Boundaries . 57 Microcracking in Carburized Steels . 60 Excessive Retained Austenite and Massive Carbides . 60 Residual Stresses . 62 Surface and Internal Oxidation . 64 Properties of Carburized Steels . 65 Bending Fatigue Strength . 66 Other Properties of Interest . 79 iii © 2002 ASM International. All Rights Reserved. www.asminternational.org Surface Hardening of Steels: Understanding the Basics (#06952G) Chapter 3 Vacuum and Plasma Carburizing . 91 Vacuum Carburizing . 91 Plasma Carburizing . 105 Chapter 4 Pack and Liquid Carburizing . 115 Pack Carburizing . 115 Liquid Carburizing and Cyaniding . 118 Chapter 5 Carbonitriding . 127 Applicable Steels and Applications . 127 Composition of Case . 128 Depth of Case . 128 Hardenability of Case . 131 Hardness Gradients . 132 Void Formation . 133 Furnaces and Furnace Atmospheres . 133 Control of Retained Austenite . 134 Quenching Media and Practices . 135 Tempering . 136 Carbonitriding of Powder Metallurgy Parts . 137 Combined Carburizing/Carbonitriding Treatments . 138 Chapter 6 Nitriding . 141 Gas Nitriding . 141 Modified Gas Nitriding Processes . 165 Pack Nitriding . 167 Liquid Nitriding . 167 Plasma (or Ion) Nitriding . 177 Wear Resistance of Nitrided Steels . 187 Chapter 7 Nitrocarburizing . 195 The Compound Layer and Diffusion Zone . 195 Liquid Nitrocarburizing . 195 Gas Ferritic Nitrocarburizing . 204 Plasma Nitrocarburizing . 208 Chapter 8 Boriding . 213 Advantages and Disadvantages of Boriding . 213 Boride Layer Characteristics . 214 Steel Selection . 215 Effects of Alloying Elements . 215 Boriding Processes . 217 Properties of Borided Steels . 221 Applications for Pack Boriding . 223 Chapter 9 Thermal Diffusion Process . 227 Process Characteristics . 227 Characteristics of TD-Processed Materials . 232 Applications . 233 iv © 2002 ASM International. All Rights Reserved. www.asminternational.org Surface Hardening of Steels: Understanding the Basics (#06952G) Surface Hardening by Non-Diffusion Methods Chapter 10 Surface Hardening by Applied Energy . 237 Flame Hardening . 237 Induction Surface Hardening . 242 Laser Surface Hardening . 264 Electron-Beam Surface Hardening . 267 Chapter 11 Surface Hardening by Coating or Surface Modification . 275 Hard Chromium Plating . 275 Electroless Nickel Plating . 282 Hardfacing . 286 Thermal Spraying . 293 Chemical and Physical Vapor Deposition Processing . 297 Ion Implantation . 301 Laser Surface Processing . 302 Appendix Appendix 1 Iron-Carbon Phase Diagram . 311 Appendix 2 Austenitizing Temperatures for Steels . 315 Appendix 3 Hardness Conversion Tables . 317 Subject Index . ..