Bhadeshia H.K.D.H., Honeycombe R. Steels: Microstructure and Properties
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Steels
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Steels
Microstructure and Properties
Third edition
H. K. D. H. Bhadeshia
Professor of Physical Metallurgy
University of Cambridge
and
Adjunct Professor of Computational Metallurgy
Graduate lnstitute of Ferrous Technology, POSTECH
and
Sir Robert Honeycombe
Emeritus Goldsmiths’ Professor of Metallurgy
University of Cambridge
AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD
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First edition 1981
Second edition 1995
Reprinted 1976, 2000
Transferred to digital printing 2003
Third edition 2006
Copyright © 2006, R. W. K. Honeycombe and H. K. D. H. Bhadeshia. Published by Elsevier Ltd.
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ISBN-13: 978-0-750-68084-4
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Cover Images, used with permission
Inset: δ-TRIP steel, S. Chatterjee
Background: magnetic field due to a small particle of iron, enclosed in a carbon tube,
T. Kasama, R. Dunin–Borkowski, K. Koziol and A. H. Windle.
Typeset by Charon Tec Ltd, Chennai, India
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Printed and bound in Great Britain
0607080910 10987654321
CONTENTS
Preface to the first edition ix
Preface to the second edition x
Preface to the third edition xi
1 Iron and its interstitial solid solutions 1
1.1 Introduction 1
1.2 The allotropes of pure iron 2
1.3 The phase transformation: α- and γ-iron 4
1.4 Carbon and nitrogen in solution in α- and γ-iron 8
1.5 Some practical aspects 15
Further reading 16
2 The strengthening of iron and its alloys 17
2.1 Introduction 17
2.2 Work hardening 18
2.3 Solid solution strengthening by interstitials 20
2.4 Substitutional solid solution strengthening of iron 27
2.5 Grain size 27
2.6 Dispersion strengthening 32
2.7 An overall view 33
2.8 Some practical aspects 34
2.9 Limits to strength 35
Further reading 38
3 The iron–carbon equilibrium diagram and plain carbon steels 39
3.1 The iron–carbon equilibrium diagram 39
3.2 The austenite–ferrite transformation 42
3.3 The austenite–cementite transformation 44
3.4 The kinetics of the γ → α transformation 45
3.5 The austenite–pearlite reaction 53
3.6 Ferrite–pearlite steels 67
Further reading 69
4 The effects of alloying elements on iron–carbon alloys 71
4.1 The γ- and α-phase fields 71
4.2 The distribution of alloying elements in steels 74
v
vi CONTENTS
4.3 The effect of alloying elements on the kinetics of the
γ/α transformation 77
4.4 Structural changes resulting from alloying additions 84
4.5 Transformation diagrams for alloy steels 91
Further reading 92
5 Formation of martensite 95
5.1 Introduction 95
5.2 General characteristics 95
5.3 The crystal structure of martensite 100
5.4 The crystallography of martensitic transformations 103
5.5 The morphology of ferrous martensites 106
5.6 Kinetics of transformation to martensite 112
5.7 The strength of martensite 120
5.8 Shape memory effect 126
Further reading 127
6 The bainite reaction 129
6.1 Introduction 129
6.2 Upper bainite (temperature range 550–400
◦
C) 129
6.3 Lower bainite (temperature range 400–250
◦
C) 132
6.4 The shape change 135
6.5 Carbon in bainite 135
6.6 Kinetics 139
6.7 The transition from upper to lower bainite 143
6.8 Granular bainite 144
6.9 Tempering of bainite 145
6.10 Role of alloying elements 146
6.11 Use of bainitic steels 147
6.12 Nanostructured bainite 152
Further reading 154
7 Acicular ferrite 155
7.1 Introduction 155
7.2 Microstructure 155
7.3 Mechanism of transformation 157
7.4 The inclusions as heterogeneous nucleation sites 161
7.5 Nucleation of acicular ferrite 162
7.6 Summary 164
Further reading 164
8 The heat treatment of steels: hardenability 167
8.1 Introduction 167
8.2 Use of TTT and continuous cooling diagrams 168
CONTENTS vii
8.3 Hardenability testing 170
8.4 Effect of grain size and chemical composition
on hardenability 176
8.5 Hardenability and heat treatment 177
8.6 Quenching stresses and quench cracking 179
Further reading 181
9 The tempering of martensite 183
9.1 Introduction 183
9.2 Tempering of plain carbon steels 184
9.3 Mechanical properties of tempered plain carbon steels 190
9.4 Tempering of alloy steels 191
9.5 Maraging steels 207
Further reading 207
10 Thermomechanical treatment of steels 209
10.1 Introduction 209
10.2 Controlled rolling of low-alloy steels 210
10.3 Dual-phase steels 220
10.4 TRIP-assisted steels 223
10.5 TWIP steels 229
10.6 Industrial steels subjected to thermomechanical treatments 231
Further reading 233
11 The embrittlement and fracture of steels 235
11.1 Introduction 235
11.2 Cleavage fracture in iron and steel 235
11.3 Factors influencing the onset of cleavage fracture 237
11.4 Criterion for the ductile/brittle transition 240
11.5 Practical aspects of brittle fracture 243
11.6 Ductile or fibrous fracture 245
11.7 Intergranular embrittlement 252
Further reading 258
12 Stainless steel 259
12.1 Introduction 259
12.2 The iron–chromium–nickel system 259
12.3 Chromium carbide in Cr–Ni austenitic steels 264
12.4 Precipitation of niobium and titanium carbides 267
12.5 Nitrides in austenitic steels 270
12.6 Intermetallic precipitation in austenite 270
12.7 Austenitic steels in practical applications 273
viii CONTENTS
12.8 Duplex and ferritic stainless steels 274
12.9 Mechanically alloyed stainless steels 278
12.10 The transformation of metastable austenite 281
Further reading 286
13 Weld microstructures 287
13.1 Introduction 287
13.2 The fusion zone 287
13.3 The HAZ 298
Further reading 306
14 Modelling of microstructure and properties 307
14.1 Introduction 307
14.2 Example 1: alloy design – high-strength bainitic steel 309
14.3 Example 2: mechanical properties of mixed microstructures 315
14.4 Methods 321
14.5 Kinetics 326
14.6 Finite element method 329
14.7 Neural networks 330
14.8 Defining characteristics of models 333
Further reading 334
Index 335
PREFACE TO THE FIRST EDITION
In this book, I have attempted to outline the principles which determine the
microstructures of steels and through these the mechanical properties. At a
time when our metallographic techniques are reaching almost to atomic resolu-
tion, it is essential to emphasize structure on the finest scale, especially because
mechanical properties are sensitive to changes at this level. While this is not a
book on the selection of steels for different uses, I have tried to include sufficient
information to describe how broad categories of steels fulfil practical require-
ments. However, the main thrust of the book is to examine analytically how
the γ/α phase transformation is utilized, and to explain the many effects that
non-metallic and metallic alloying elements have, both on this transformation
and on other phenomena.
This book is written with the needs of metallurgists, materials scientists and
engineers in mind, and should be useful not only in the later years of the first
degree and diploma courses but also in postgraduate courses. An elementary
knowledge of materials science, metallography, crystallography and physics is
assumed.
I am indebted to several colleagues for their interest in this book, particularly
Dr D. V. Edmonds, who kindly read the manuscript, Dr P. R. Howell, Dr B.
Muddle and Dr H. K. D. H. Bhadeshia, who made helpful comments on various
sections,and numerous other numbers of my research group who have provided
illustrations. I wish also to thank my colleagues in different countries for their
kind permission to use diagrams from their work. I am also very grateful to
Mr S. D. Charter for his careful preparation of the line diagrams. Finally, my
warmest thanks go to Mrs Diana Walker and Miss Rosemary Leach for their
careful and dedicated typing of the manuscript.
RWKH
Cambridge
1980
ix