Microstructure of Steels and Cast Irons

406 Pages·2004·19.69 MB·English

by  Prof. Dr ès Sciences Madeleine Durand-Charre (auth.)

Engineering Materials and Processes
Springer-Verlag Berlin Heidelberg GmbH
ONUNE UBRARY
Engineering
springeronline.com
Series Editor
Professor Brian Derby, Professor of Materials Science
Manchester Science Centre,Grosvenor Street, Manchester, MI 7HS, UK
Madeleine Durand-Charre
Microstructure of
Steels and Cast Irons
Translated by
James H. Davidson B.Met. Ph.D. C.Eng. M.I.M.
With 289 illustrations
, Springer
Prof. Dr es Sciences Madeleine Durand-Charre
Institut National Polytechnique de Grenoble
e-mail: [email protected]
Originally published in French as La microstructure des aciers et des fontes.
Genese et interpretation, Ed. SIRPE, Paris 2003
ISBN 978-3-642-05897-4 ISBN 978-3-662-08729-9 (eBook)
DOI 10.1007/978-3-662-08729-9
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Preface
How many times ha ve 1 heard the question MIs there stIll anything to discover in steels ?~
often with the conclusive comment '~know everything about steels - they've been studied
lor years !" On the contrary, in recent decades, the development 01 new grades, extended
lunctions and novel applications has continued at an accelerating pace. More than hali the
steels used today did not even exist live years ago.
This simply demonstrates the vast potential 01 these materials. Starting Irom an iron base,
numerous alloying elements can be added to modi/y the microstructure, the mechanical and
physicalp roperties and the surlace characteristics 01 steels. A wide variety 01 metallurgical
mechanisms, includi ng solidilication, solid state phase translormations, recrystallisation
and precipitation can be used in steels to obtain a whole range 01 uselul properties, by
appropriate thermomechanical and heat treatments. More reliable and simpler manulactu
ring processes, together with modern on line non destructive inspection systems, enable
increasingly closer control 01 microstructures, and consequently the attainment 01 higher
and more reproducible perlormance levels. The melting and processing 01 steels and cast
irons therelore continue to challenge metallurgists and remain an essential driving lorce
lor research and development. This can be illustrated by two noteworthy examples, which
are mentioned in the present book.
The lirst concerns packaging steels, particular/y tllOse used lor beverage cans. The increased
strength 01 today's steels has enabled the strip thickness employed to be reduced to less than
150 pm. This has placed extreme demands on cleanness requirements, with the need to
guarantee no more than one inclusion larger than a micron in size per kllometre 01 strip.
The second example is related to solid state phase translormations. Depending on the steel
composition and the thermomechanicalp rocessing cycles employed, the equilibrium condi
tions at the interlace can vary tremendously, leading to translormation rates that diller by
severalorders 01 magnitude. This can generate high/y localised concentration peaks at the
interlace. The mechanisms involved can be understood and verilied only by the use 01
highly sophisticated modern experimental techniques, such as high resolution transmission
electron microscopy and the tomographic atom probe.
The large number 01 dillerent microstructures observed in steels and cast irons intrigued
ear/y metallurgists. The properties 01 metals in general are close/y related to their micros
tructures. For example, the attractive appearance 01 many old Damascus steel swords was
also a sign 01 their quality. The scientilic study 01 the nature, composition and geometry 01
the blade patterns provided modern metallurgists with valuable clues to the processes
employedb Y ancient smiths to manulacture these swords. TZis historical example, discussed
in detail by way 01 introduction, illustrates the underlying theme 01 the book, name/y, the
central role 01 microstructures in steels and cast irons.
The numerous structural translormations that can occur in steels during solidilication and
cooling complicate the identilication and interpretation 01 the linal microstructures obtai-
LA MICROSTRUCTURE DES ACIERS ET DES FONTES
ned However, their analysis has been signi/icantly clarified by extensive research studies
and modelling work, providing a scienti/ic understanding of the mechanisms involved
Variations in microstructure then become local markersH of the composition and thermo
mechanical history, conserving the memory ofs uccessive metallurgical changes and ena
bling evaluation of transformation rates.
Equilibrium phase diagrams form an essential basis for the interpretation ofm icrostructu
res. Their experimental determination is refined by the precise analysis of equilibrium
constituents. Recent progress in modelling now enables experimental ch:agrams to be com
pleted and enriched by calculating phase equilibria. The great originality of the present
book is a constant and rewarding confrontation between equilibrium aspects, microstructu
ralobservations and modelling predictions. This approach also enables the vast variety of
steels to be treated by considering a series oft ypical examples, illustrating the major catego
ries ofm etallurgical phenomena. A new angle is thus provided for interpreting certain
phase diagrams that appear difficult to understand for the non specialist. Moreover, empha
sis is placed in this way on the limitations associated with the experimental interpretation
ofm icrostructures, on the possibility ofm isleading artelacts, and on the risk ofd rawing too
hasty conclusions without giving due consideration to kinetic factors.
The exhaustive treatment ofm etallurgical changes in steels and cast irons prepares the rea
der for the last part of tbe book, which describes the major lamilies ofs teels in a deductive
manner. Emphasis is placed on the scienti/ic procedure underlying the design ofn ew steel
grades, enabling more rapid development, together with breakthrough innovations that
would be impossible by a purely empirical approach.
The book shouJdp rove useful for a wide range ofr eaders and should -bnd a prominent place
on of/ice bookshelves and those ofm any microscope rooms. It will remind investigation
and quality control specialists of the imperative need to base the interpretation ofm icros
tructures on a rigorous scienti/ic understanding. It will help R iii D englneers to design new
steels to meet increasingly challenging user requirements. For metallurgy teachers, it will
provide a large collection ofp ractical examples to illustrate their lectures, based on the
authors wide experience accumulated during numerous case studies. Finally, it will reveal to
students the lascinating worJd ofs teels and cast irons, at the same time didactically guiding
them through a vast -b'eJd ofm etallurgical knowledge.
While satis/ying the curiosity and thirst for knowledge ofa wide range ofr eaders, the book
also provides food for thought andp roves that, despite the excellent level ofc urrent unders
tanding concerning steels and cast irons, much still remalns to be achieved, by pushing
metallurgical science to its furthermost limits.
Jean-Hubert SCHMITT
Director, Isbergues Research Centre
Ugine iii ALZ -ARCELOR Group
VI
Acknowledgements
Research metallurgists 01 my generation have witnessed prolound changes due ta the pro
gress achieved in the last lew decades in the b:eld 01 metallography. Thanks ta the immense
contribution 01 electron microscopy, microstructures can now be explored in their lin est
details. HoweveI, the task 01 the metallurgist is stIll that 01 analysing and interpreting the
observations in order ta understand the origins 01 the microstructure. The interpretation 01
a micrograph requires an extensive metallurgical culture, since numerous translormations
have olten leit traces an dillerent scales olobservation. The present book aims ta provide
the lundamental concepts necessary lor this purpose. Emphasis is placed throughout an
micrographic leatures, which are discussed and interpreted in detaij The microstructural
characteristics are also used as a guideline lor classilying the major lamilies ollerrous
alloys, enabling beginners ta steer their way through the labyrinth 01 commercial grades.
The objective 01 the book is ta comprise a uselul tool that is sul/iciently compact ta bndi ts
place neri ta a microscope.
An important aspect throughout the book is the role 01 phase eqUllibria. The latter part 01
the 20th century saw the development 01 the theoretical calculation 01 phase diagrams
based an thermodynamic data lor the constituent phases, backed by direct experimental
determinations 01 phase boundaries and characteristic temperatures. The models now
available are extremely powerlu!, quite representative, and lncreaslngly easy ta use. Howe
veI, the excessive simplib·cation 01 these tools and their use as simple "black boxes" can lead
ta a loss 01 scienti/ic inlormation, a sort 01 "data laundering'; that must be avoided by a
thorough understanding 01 the underlying principles. It is lor this reason that Irequent
relerence is made ta ternary diagrams, using examples chosen among the iron base systems,
which undoubtedly represent an excellent basis lor reasoning.
The project 01 the present book was ambitious and 1 am extremely gratelul lor the support
and encouragement received Iram numerous sources. First 01 al!, Bernard Baroux is ta be
thanked lor welcoming the idea and obtaining the backing 01 the Arcelor company. He pro
vided the con/idence necessary at a stage when the outlines 01 the book were stIll hazy, and
proved a staunch ally in promoting the project. 1 am also indebted ta my colleagues in Gre
noble lor the laith accorded ta the success 01 this work, particularly Colette Allibert at the
Institut National Polytechnique de Grenoble (INPG) and Claude Bernard at the Labora
toire de Thermodynamique et Physico-Chimie Metallurgique (LTPCM).
From a scienti/ic standpoint, it appeared a daring and somewhat loolhardy idea ta adven
ture into /ields outside my own research areas. 1 was able ta take up the challenge thanks ta
the kindness and availabiJity 01 numerous lndustrial and university scientists, and the help
01 coJJeagues ln my own lahoratory. For exampJe, incursions have been made lnto territories
as dangerous as the bainite translormation, thanks ta salety nets provided by Yves Brechet
andh is team. In the lield 01p hase equiJibria, my environment in the LTPCM was extremely
heJplu!, and my thanks are due particuJarJy ta Annie Antoni-Zdziobek who satislied my
unquenchabJe thirst lor calculated phase diagram sections. My teaching and research coJ-
LA MlCROSTRUCTURE DES ACIERS ET DES FONTES
leagues, Claude Bernard, Yves Brechet, Catherine Colinet, Patricia Donnadieu, Franfois
Louchet, Catherine Tassin-Arques, Muriel Veron {and Francis Durand, my husband} ior
med an exceptionally constructive reading committee. In industrial circles, 1 am particu
larly grateiul to Laurent Antoni, Pierre Chemelle, James Davidson, Andre Grellier,
Philippe Maugis, Daniel Nesa, Andre Pineau, David Quidort, Pierre-Emmanuel Richy,
Sophie Roure, and Zinedine Zermout, ior much precious iniormation and advice. Special
thanks are also due to the technical team at my laboratory, particularly Alain Domeyne,
who helped to prepare the expenments used as a source oie xamples.
1 am especially grateiul to my translator, Dr. James Davidson, ior his rigorous translation,
combining his linguistic sk11ls with his competence as an industrial research metallurgist.
Indeed, his contribution went beyond a simple translation, since the detailed critical analy
sis necessary to reiormulate the text in English proved an extremely eilicient means oic la
ri!ying the original French version whenever it appeared inexact or not suiiicient1y explicit.
Finally, James Davidson frequently provided precious complementary indications based on
his experience oii ndustrialp roblems.
Over the years, 1 have built up a library oih igh quality electron micrographs, thanks to the
help and competence oit he members oit he Consortium des Moyens Technologiques Com
muns (CMTC) within the INP in Grenoble. lam particularly grateiul to Jacques Garden,
Laurent Maniguet, Rene Molins, Florence Robaut and Nicole Valignat.
In addition, numerous photographs have been kindly supplied by outside laboratories and
museums. 1 always iound a warm welcome and a positive response to my severe demands
concerning the quality oip hotographs. These people and organisations are mentioned in
the ligure captions and 1 am extremely grateful to all those concerned ior their invaluable
contribution.
Madeleine Durand-Charre
viii
Table of contents
First Part
The history of iron and steel of swords and
~
ploughshares
1 From lron to steel
1-1 The long history of iron .............................................. 3
1-2 The three sources ofiron .............................................. 4
1-3 Early ironmaking technology .......................................... 6
1-4 The spread of ironmaking technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8
2 Of swords and swordmaklng
2-1 Swordmaking, the cuning edge of metallurgical history ..................... 13
2-2 The Celtic swordmaking tradition ..................................... 14
2-3 Merovingian and Carolingian swords ................................... 16
2-4 True or oriental Damascus steel swords produced using wootz steel ............ 20
2-5 Mechanical or pattern welded damascene swords .......................... 20
2-6 In search of a lost art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 21
2-7 Asiatic swords ..................................................... 27
2-8 Contemporary damascene structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31
PartZ
The Genesis of Microstructures
3 The principal phases in steels
3-1 The phases of pure iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 37
3-2 Solid solutions .................................................... 39
3-3 Order-disorder transformations ........................................ 40
3-4 Intermediate phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 42
4 The basie phase dlagrams
4-1 Equilibria between condensed phases ................................... 47
4-2 Theoretically calculated phase diagrams ................................. 53
4-3 Experimentally determined phase diagram ............................... 56
4-4 The Fe-Cr-C system : liquidus surfa ce .................................. 56
4-5 The Fe-Cr-C system : isothermal sections and isopleths ..................... 60
4-6 The Fe-Cr-C system : solidification paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 62
4-7 The Fe-Cr-C system : the austenite field ................................. 65
4-8 The Fe-Cr-Ni system ............................................... 69
4-9 The Fe-Mn-S system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 71
4-10 The Fe-Cu-Co system .............................................. 75
4-11 The Fe-Mo-Cr system ............................................. 78
LA MICROSTRUCTURE DES ACIERS ET DES FONTES
4-12 The Fe-C-V system ................................................ 84
4-13 Mixed carbides ................................................... 86
5 The formation of solidlficatlon strudures
5-1 Solute partitioning phenomena during solidification ....................... 91
5-2 Local solute partitioning ............................................. 94
5-3 The growing solid interface ........................................... 95
5-4 The evolution of dendritic microstructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 101
5-5 Secondary dendrite arm spacings ..................................... 106
5-6 Eutectic microstructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 108
5-7 Peritectic microstructures ........................................... 116
6 Liquld/solld strudural transformatlons
6-1 Experimental techniques : controlled solidification . . . . . . . . . . . . . . . . . . . . . . .. 121
6-2 Experimental techniques: thermal analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 124
6-3 Solidification paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 127
6-4 Metastable solidification paths ....................................... 138
6-5 Peritectic transformations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 141
7 Gralns, graln boundarles and interfaces
7-1 General aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 151
7-2 Characteristics associated with grain boundaries .......................... 157
8 Dlffusion
8-1 Chemical diffusion .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 163
8-2 Zones affected by diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 165
8-3 Case hardening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 168
8-4 DifIUsion couples ................................................. 172
8-5 Galvanising ..................................................... 173
9 The decomposltlon of austenite
9-1 The different types of solid state transformatione ......................... 179
9-2 The representation of solid state phase transformations ................... 180
9-3 Growth mechanisms ............................................... 184
9-4 DifIUsive exchanges at interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 187
9-5 The formation of pro-eutectoid ferrite and cementite ..................... 191
10 The pearllte transformation
10-1 The eutectoid transformation in the Fe-C system . . . . . . . . . . . . . . . . . . . . . . .. 195
10-2 The kinetics of pearlite transformation .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 199
10-3 The influence of alloying elements ................................... 200
10-4 The re-dissolution of pearlite ....................................... 206
11 The martenslte transformatlon
11-1 Displacive transformations in the Fe-C system .......................... 209
11-2 Characteristics of the martensite transformation . . . . . . . . . . . . . . . . . . . . . . . .. 211
11-3 The morphology of martensite ...................................... 215
11-4 Softening and tempering of martensite ................................ 219
12 The bainlte transformation
12-1 Bainite structures ................................................ 223
12-2 Upper bainite ................................................... 225
12-3 Lower bainite ................................................... 232
13 Preclpltatlon
13-1 Continuous precipitation .......................................... 239
13-2 Discontinuous precipitation ........................................ 245
x