Advanced High-Strength Steels

Advanced High-Strength Steels Science, Technology, and Applications Mahmoud Y. Demeri ASM International Materials Park, Ohio 44073-0002

Copyright 2013 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 written permission of the copyright owner. First printing, August 2013 Great care is taken in the compilation and production of this book, but it should be made clear that NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING, WITHOUT LIMITATION, WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE GIVEN IN CONNECTION WITH THIS PUBLICATION. Although this information is believed to be accurate by ASM, ASM cannot guarantee that favorable results will be obtained from the use of this publication alone. This publication is intended for use by persons having technical skill, at their sole discretion and risk. Since the conditions of product or material use are outside of ASM s control, ASM assumes no liability or obligation in connection with any use of this information. No claim of any kind, whether as to products or information in this publication, and whether or not based on negligence, shall be greater in amount than the purchase price of this product or publication in respect of which damages are claimed. THE REMEDY HEREBY PROVIDED SHALL BE THE EXCLUSIVE AND SOLE REMEDY OF BUYER, AND IN NO EVENT SHALL EITHER PARTY BE LIABLE FOR SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES WHETHER OR NOT CAUSED BY OR RESULTING FROM THE NEGLIGENCE OF SUCH PARTY. As with any material, evaluation of the material under end-use conditions prior to specification is essential. Therefore, specific testing under actual conditions is recommended. Nothing contained in this book shall be construed as a grant of any right of manufacture, sale, use, or reproduction, in connection with any method, process, apparatus, product, composition, or system, whether or not covered by letters patent, copyright, or trademark, and nothing contained in this book shall be construed as a defense against any alleged infringement of letters patent, copyright, or trademark, or as a defense against liability for such infringement. Comments, criticisms, and suggestions are invited, and should be forwarded to ASM International. Prepared under the direction of the ASM International Technical Book Committee (2012 2013), Bradley J. Diak, Chair. ASM International staff who worked on this project include Scott Henry, Senior Manager, Content Development and Publishing; Karen Marken, Senior Managing Editor; Sue Sellers, Product and Project Administrator; Madrid Tramble, Manager of Production; and Diane Whitelaw, Production Coordinator. Library of Congress Control Number: 2013931685 ISBN-13: 978-1-62708-005-7 ISBN-10: 1-62708-005-8 SAN: 204-7586 ASM International Materials Park, OH 44073-0002 Printed in the United States of America

Advanced High-Strength Steels Science, Technology, and Application Copyright 2013 ASM International M.Y. Demeri All rights reserved Contents Preface.............................................vii Acknowledgments..................................... ix CHAPTER 1 Introduction... 1 1.1 Drivers and Solutions... 2 1.2 Importance of Steel... 12 1.3 Advanced Steels.... 17 1.4 Significance of High Strength... 20 CHAPTER 2 Steel Fundamentals... 23 2.1 Compositions and Metallurgical Phases... 23 2.2 Microstructure and Heat Treatment... 25 2.3 Structure-Property Relationships.... 38 2.4 Categories of Steels... 41 2.5 Deformation Mechanisms... 50 2.6 Strengthening Mechanisms... 53 2.7 Deformation Processing and Annealing.... 56 CHAPTER 3 Advanced High-Strength Steels... 59 3.1 Nomenclature.... 59 3.2 Generations... 60 3.3 Thermomechanical Processing... 63 3.4 Microstructure Development... 64 3.5 Property Trends... 65 iii

iv / Advanced High-Strength Steels Science, Technology, and Application CHAPTER 4 Attributes of Advanced High-Strength Steels.... 71 4.1 Stiffness... 71 4.2 Strength... 72 4.3 Strain Hardening... 72 4.4 Fatigue... 75 4.5 Crashworthiness.... 77 4.6 Formability.... 81 4.7 Toughness.... 89 4.8 Bake Hardening... 91 CHAPTER 5 Dual-Phase Steels... 95 5.1 Composition and Microstructure of Dual-Phase Steels.... 95 5.2 Processing of Dual-Phase Steels... 98 5.3 Deformation Mechanism of Dual-Phase Steels... 102 5.4 Mechanical Properties of Dual-Phase Steels... 102 5.5 Formability of Dual-Phase Steels... 105 5.6 Special Attributes of Dual-Phase Steels.... 105 CHAPTER 6 Complex-Phase Steels... 107 6.1 Compositions and Microstructures of Complex-Phase Steels.. 107 6.2 Processing of Complex-Phase Steels.... 107 6.3 Deformation Mechanism of Complex-Phase Steels... 108 6.4 Mechanical Properties of Complex-Phase Steels... 109 6.5 Formability of Complex-Phase Steels...111 6.6 Special Attributes of Complex-Phase Steels...112 CHAPTER 7 Transformation-Induced Plasticity Steels.... 115 7.1 Composition and Microstructure of Transformation-Induced Plasticity Steels...115 7.2 Processing of Transformation-Induced Plasticity Steels...117 7.3 Deformation Mechanism of Transformation-Induced Plasticity Steels...119 7.4 Mechanical Properties of Transformation-Induced Plasticity Steels... 120 7.5 Formability of Transformation-Induced Plasticity Steels... 123 7.6 Special Attributes of Transformation-Induced Plasticity Steels... 123 CHAPTER 8 Martensitic Steels... 127 8.1 Compositions and Microstructures of Martensitic Steels... 127

Contents / v 8.2 Processing of Martensitic Steels... 128 8.3 Deformation Mechanism of Martensitic Steels... 128 8.4 Mechanical Properties of Martensitic Steels.... 129 8.5 Hot Forming of Martensitic Steels.... 130 8.6 Tempering Martensite... 132 8.7 Special Attributes of Martensitic Steels.... 133 CHAPTER 9 Twinning-Induced Plasticity Steels... 135 9.1 Twins and Stacking Faults... 135 9.2 Compositions and Microstructures of Twinning-Induced Plasticity Steels... 137 9.3 Thermodynamics of Twinning-Induced Plasticity Steels... 138 9.4 Processing of Twinning-Induced Plasticity Steels... 139 9.5 Deformation Mechanism of Twinning-Induced Plasticity Steels.... 140 9.6 Mechanical Properties of Twinning-Induced Plasticity Steels.... 142 9.7 Formability of Twinning-Induced Plasticity Steels... 148 9.8 Special Attributes of Twinning-Induced Plasticity Steels... 148 CHAPTER 10 Austenitic Stainless Steels... 151 10.1 Compositions and Microstructures of Austenitic Stainless Steels.... 152 10.2 Processing of Austenitic Stainless Steels.... 153 10.3 Deformation Mechanism of Austenitic Stainless Steels... 153 10.4 Mechanical Properties of Austenitic Stainless Steels... 153 10.5 Formability of Austenitic Stainless Steels... 155 10.6 Special Attributes of Austenitic Stainless Steels... 157 CHAPTER 11 Applications of Advanced High-Strength Steels.... 159 11.1 Automotive Applications... 159 11.2 Nonautomotive Applications... 169 11.3 Utilization and Trend... 171 CHAPTER 12 Consequences of Using Advanced High-Strength Steels... 177 12.1 Press Requirements... 177 12.2 Springback and Residual Stress.... 180 12.3 Binders and Draw Beads... 187 12.4 Tool Material and Die Wear.... 189 12.5 Hot Forming.... 192

vi / Advanced High-Strength Steels Science, Technology, and Application 12.6 Downgaging Limits... 193 12.7 Welding... 194 CHAPTER 13 Global Projects on Advanced High-Strength Steels... 199 13.1 Steel Industry Projects... 199 13.2 Government/Industry/Academia Collaboration.... 203 13.3 Academic Research and Development.... 205 CHAPTER 14 Design Guidelines for Advanced High-Strength Steels... 215 14.1 Forming Guidelines... 216 14.2 Welding Guidelines... 217 14.3 Performance Evaluation.... 221 CHAPTER 15 Innovative Forming Technologies... 225 15.1 Real-Time Process Control... 228 15.2 Active Drawbeads... 230 15.3 Active Binders.... 232 15.4 Flexible Binders.... 236 15.5 Flexible Rolling... 243 CHAPTER 16 Sustainability and Economics of Advanced High-Strength Steels... 249 16.1 Advanced High-Strength Steels and the Environment.... 250 16.2 Life Cycle Assessment.... 257 16.3 Recycling... 259 16.4 Economics of Advanced High-Strength Steels... 261 CHAPTER 17 Evolving Advanced High-Strength Steel Grades... 263 17.1 Third-Generation Advanced High-Strength Steels... 263 17.2 Microstructure Design... 266 17.3 Novel Processing Methods... 268 17.4 Nanosteels... 271 17.5 Integrated Computational Materials Engineering Approach... 273 Index............................................. 275

Advanced High-Strength Steels Science, Technology, and Application Copyright 2013 ASM International M.Y. Demeri All rights reserved Preface Steel is used in many industries because of its favorable attributes and low cost relative to other materials. It is a globally dominant material and is a key driver of the world s economy. The auto industry is one of the biggest markets for steel products. In an era of weight reduction, steel was not perceived as a lightweight or a high-tech material because of its high density. This perception has changed with the introduction of new grades of high-specific-strength steels. The steel industry continues to develop new steel grades and innovative design concepts to meet challenges related to vehicle performance, affordability, safety, fuel efficiency, and the environment. One key driver for steel development is the continuing increase in Corporate Average Fuel Economy (CAFE) standards from the current 27.5 mpg to 34.1 mpg by 2016 and to 54.5 mpg by 2025. A number of advanced high-strength steels (AHSS) that are highly formable and possess an excellent combination of strength, ductility, and strain hardening have been produced or are under development. Advanced high-strength steels are not lighter than traditional steels, but their high strength permits the use of thinner gages to reduce vehicle weight. The new steels extend the tensile strength limit of 800 MPa (116 ksi) provided by traditional high-strength steels (HSS) to over 1600 MPa (232 ksi). The superior properties of AHSS result from microstructural design that utilizes complex deformation and/or phase transformation processes. The auto industry has adopted lightweighting as a greenhouse gas reduction strategy and automakers are now employing more AHSS in their vehicles to maintain affordability, reduce weight, lower emissions, and improve crash safety. Currently, AHSS account for 80 kg (175 lb) per vehicle and this is projected to double by 2020. Advanced high-strength steel panels and structures are becoming thinner, lighter, tougher, and stronger than those made from mild steel and traditional HSS. Studies have indicated that the economic and performance targets of automakers cannot be met without the significant use of steel. Advanced high-strength steels are vii

viii / Advanced High-Strength Steels Science, Technology, and Application currently the fastest growing class of materials offering solutions for current and future vehicles. It is believed that steel will continue to be the dominant material for the automotive market. This book is a comprehensive guide to the grades, types, microstructures, thermal processing, deformation mechanisms, properties, performance, and applications of AHSS. The first objective of the book is to understand the drivers and solutions for building lighter, safer, efficient, and affordable cars. The second objective is to develop a rationale for using AHSS to accomplish weight reduction, fuel economy, crash safety, cost savings, and decrease in greenhouse gases. The third objective is to examine the complex interrelationship between composition, processing, microstructure, and mechanical properties. The fourth objective is to review the design guidelines, manufacturing hurdles, advanced forming, sustainability, and evolving grades of AHSS. The book is an essential reference/text for those who teach, study, develop, produce, use, design, or specify AHSS. A compelling and unique feature of the book is the extensive use of charts, figures, tables, and micrographs to provide a good perspective of the structure-property relationships and performance attributes of AHSS.

Advanced High-Strength Steels Science, Technology, and Application Copyright 2013 ASM International M.Y. Demeri All rights reserved Acknowledgments A number of figures and charts from sources whose permissions are acknowledged and appreciated are used at no cost. Special thanks are extended to WorldAutoSteel and Steel Market Development Institute for allowing the use of information and charts from their websites and photo galleries in the preparation of this book. Thanks are also due to William D. Callister, Jr. and David G. Rethwisch, authors of the 8th edition of the textbook Materials Science and Engineering: An Introduction, published in 2010 by Wiley & Sons. Their photos and figures are an essential part of Chapter 2, Steel Fundamentals. I would also like to acknowledge the efforts of the following ASM International staff in the preparation of this book: Karen Marken, Senior Managing Editor; Sue Sellers, Product and Project Administrator; and Diane Whitelaw, Production Coordinator. ix