Welding Metallurgy of Stainless Steels

288 Pages·1988·11.336 MB·English

by  a. o. Univ.-Prof. Dipl.-Ing. Dr. mont. Erich Folkhard (auth.)

Erich Folkhard
Welding Metallurgy
of Stainless Steels
In collaboration with
Gunther Rabensteiner
Ernst Perteneder
Heinz Schabereiter
Josef Tosch
Springer-Verlag Wien New York
a. o. Univ.-Prof. Dipl.-Ing. Dr. mont. Erich Folkhard, Dir. ret.
Dipl.-Ing. Dr. mont. Gunther Rabensteiner,
Head of Research, Development and Technology Department
Dipl.-Ing. Dr. mont. Ernst Perteneder,
Head of Development Department for Filler Metals
Heinz Schabereiter,
Head of Welding Technology Department
Ing. (HTL) Josef Tosch,
Development Engineer for Filler Metals
Bohler Ges. m. b. H.
Welding Division
A-8605 Kapfenberg, Austria
Revised Translation of
Metallurgie der SchweiBung nichtrostender Stahle
Wien New York: Springer-Verlag 1984
© 1984 by Springer-Verlag/Wien
ISBN-13: 978-3-7091-8967-2
This work is subject to copyright.
All rights are reserved, whether the whole or part of the material is concerned, specifically
those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photo
copying machine or similar means, and storage in data banks.
© 1988 by Springer-Verlag/Wien
Softcover reprint of the hardcover 1st edition 1988
With 115 partly coloured Figures
Library of Congress Cataloging-in-Publication Data: Folkhard, Erich. [Metallurgie der
SchweiBung nichtrostender Stahle. English] Welding metallurgy of stainless steels I Erich
Folkhard in collaboration with Gunther Rabensteiner ... let at.]. p. cm. Translation of:
Metatlurgie der SchweiBung nichtrostender Stahle. Bibliography: p. Includes index.
ISBN-13: 978-3-7091-8967-2 1. Steel, Stainless-Welding. 2. Steel, Stainless-Metallurgy.
I. Rabensteiner, Gunther. II. Title. TS227.2.F64 1988. 672.5'2-dc 19.88-16021.
ISBN-13: 978-3-7091.s967-2 e-ISBN-13: 978-3-7091.s965-8
DOl: 1O.1007/978-3-7091.s965-8
Preface to the German Edition
When considering the operational performance of stainless steel weldments the
most important points to consider are corrosion resistance, weld metal mechanical
properties and the integrity ofthe weldedjoint. Mechanical and corrosion resistance
properties are greatly influenced by the metallurgical processes that occur during
welding or during heat treatment of welded components. This book is aimed, there
fore, at providing information on the metallurgical problems that may be
encountered during stainless steel welding. In this way we aim to help overcome a
certain degree of insecurity that is often encountered in welding shops engaged in
the welding of stainless steels and is often the cause of welding problems which may
in some instances lead to the premature failure of the welded component.
The metallurgical processes that occur during the welding of stainless steel are
of a highly intricate nature. The present book focuses in particular on the signif
icance of constitution diagrams, on the processes occurring during the solidification
of weld metal and on the recrystallization and precipitation phenomena which take
place in the area of the welds. There are specific chapters covering the hot cracking
resistance during welding and the practical welding of a number of different
stainless steel grades. In addition, recommendations are given as to the most
suitable procedures to be followed in order to obtain maximum corrosion resistance
and mechanical properties from the weldments.
During the compilation and writing this book, an attempt has been made to
combine a sense of practical usefulness together with a respect for theoretical
soundness, arriving thus at a discussion of the highly complex mechanisms that
occur during the welding of stainless steel which is designed to be both thorough
and easy to understand for those involved in welding engineering at all levels. In
order to accomplish this, complicated metallurgical problems have sometimes been
represented in a somewhat simplified manner. However a certain basic knowledge
of the fundamentals of metallurgy, e.g. the use of constitution diagrams and the
evaluation of time-temperature-transformation and precipitation diagrams is
required in order to understand the metallurgical processes that are discussed. The
survey of basic metallurgical literature that is given at the beginning of the
comprehensive list of supplementary literature may help to complete or renew any
existing gaps.
There is a wealth of comprehensive literature covering the fields of stainless
steel and stainless steel welding. The shop ope rater often has restricted access to
this literature due to the fact that it is spread over a great number of technical or
VI Preface
scientific journals dealing with metallurgy, material technology and welding
technology problems as well as the question of corrosion behaviour and chemical
plant engineering. In the list of supplementary literature, which includes 442
entries, the author has attempted to compile the most important publications from
the vast field of pertinent literature which were known to the author and to arrange
them for the reader in a way that is easy to survey.
Obviously, the first edition of this book leaves room for further improvement.
For this reason, the author appeals to all readers and colleagues to kindly let him
share their knowledge in the field of stainless steel welding metallurgy and supply
him with suggestions as to expansion, changes or wise restrictions.
I wish to sincerely thank G. Rabensteiner, E. Perteneder, H. Schabereiter and
J. Tosch for their valuable assistance given during the compilation and editing of
the individual chapters of this book. They have helped the author with unfailing
enthusiasm during the completion and editing of the manuscript and have contributed
important improvements to the final draft. My thanks also go to H. Kohl, E. Krainer
and A. Kulmburg for reading the manuscript or parts of it, to Vereinigte Edelstahl
werke Aktiengesellschaft (YEW) for supporting the publication of this book and for
the courtesy of supplying technical and metallurgical data, and to Springer, Verlag,
Vienna, for their kind cooperation and the excellent way in which they have printed
and illustrated this book.
Kapfenberg, June 1984 Erich Folkhard
Preface to the English Edition
The widespread interest shown in the first edition of this book encouraged us to
publish an English translation. In principle, the text corresponds to the German
edition but individual chapters have been reviewed and updated. Whenever
possible, the designation of individual steel and weld metal grades are derived from
the internationally well known US Standards. In addition, all abbreviations used in
this book are listed in alphabetic order and explained in the appendix at the end of
the book. The list of supplementary literature has been updated and expanded to a
total of 487 entries. I would like to thank H. Daurer, Vienna, for translating the book
into English and G. T. Finnerty, Birmingham, England, for reviewing the transla
tion. My thanks also go to the co-authors for their indispensable assistance in
editing the English edition of this book, to the Bohler Welding Division in
Kapfenberg and to Springer-Verlag, Vienna, for their active support of the English
edition.
Kapfenberg, November 1987 Erich Folkhard
Contents
1 Significance of Constitution Diagrams for the Understanding of Welding
Phenomena ............................................. .
1.1 Iron-Chromium, Iron-Nickel and Chromium-Nickel Constitution Diagrams 2
1.2 The Ternary Iron-Chromium-Nickel Constitution Diagram ......... . 5
1.2.1 Solidification and Crystallization Phenomena of Iron-Chromium-
Nickel Steel Alloys ............................... . 5
1.2.2 Phenomena During Cooling from the End of Solidification to Ambient
Temperature .................................... . 9
1.3 Influence of Other Elements on the Iron-Chromium-Nickel Constitution
Diagram ........................................... . 14
1.3.1 Influence of Carbon ............................... . 15
1.3.2 Influence of Nitrogen .............................. . 19
1.3.3 Influence of Molybdenum ........................... . 24
1.3.4 Influence of Manganese ............................ . 29
1.3.5 Influence of Niobium .............................. . 31
1.3.6 Influence of Titanium 34
1.3.7 Influence of Silicon ............................... . 35
1.3.8 Influence of Sulphur .............................. . 38
1.3.9 Influence of Phosphorus ........................... . 41
1.3.10 Influence of Copper ............................... . 42
1.3.11 Influence of Boron ................................ . 43
1.3.12 Influence of Oxygen ............................... . 45
1.3.13 Influence of Hydrogen ..................... . ...... . 48
2 Metallurgical Processes Occurring During Solidification and Cooling in Stainless
Steel Weld Metal ......................................... . 52
2.1 Primary Crystallization of Weld Pools ....................... . 54
2.2 Primary Crystallization of Binary and Ternary Systems ............ . 55
2.3 Phenomena at the Liquid-Solid Interface (Solidification Front) ....... . 58
2.4 Crystal Growth During Solidification and Crystal Configurations ..... . 61
2.5 Primary Crystallization of Stainless Steel Weld Metals ............ . 63
2.6 Cooling Rate and Thermal Supercooling During Solidification of Stainless
Steel Weld Metal ..................................... . 70
2.7 Segregations in Stainless Steel Weld Metal During Solidification ..... . 72
3 Metallurgical Phenomena in Secondary Crystallization of Stainless Steels and Weld
Metals .............. _ ................................. . 78
3.1 Recrystallization of Weld Metal ............................ . 78
VIII Contents
3.2 o-y Transformation of Stainless Steel Weld Metal . . . . . . . . . . . . . . . . . 80
3.3 Schaeffier Diagram, Ferrite Measurement, DeLong Diagram ......... 88
3.4 y-a Transformation of Stainless Steel Alloys .................... 94
3.4.1 Transformation in the Pearlite Range .................... 96
3.4.2 Transformation in the Martensite Range .................. 97
3.4.3 Formation of Stable Austenite During Tempering . . . . . . . . . . .. 100
4 Precipitation Phenomena in Stainless Steels and Weld Metals . . . . . . . . . . . .. 103
4.1 Carbide Precipitations in Stainless Steels with Special Consideration to
Intergranular Corrosion .................................. 104
4.1.1 Influence of the Type of Structure on the Tendency Towards Carbide
Precipitation in Stainless Steels ........................ 106
4.1.2 Influence of Alloying Elements on. Carbide Precipitation and Inter
granular Corrosion (IC) in Austenitic Stainless Chromium-Nickel
Steels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 107
. 4.1.2.1 Influence of Carbon and Nickel. . . . . . . . . . . . . . . . . .. 107
4.1.2.2 Influence of Silicon . . . . . . . . . . . . . . . . . . . . . . . . . .. 107
4.1.2.3 Influence of Chromium ........................ 109
4.1.2.4 Influence of Nitrogen. . . . . . . . . . . . . . . . . . . . . . . . .. 109
4.1.2.5 Influence of Molybdenum. . . . . . . . . . . . . . . . . . . . . .. 110
4.1.2.6 Influence of Titanium and Niobium. . . . . . . . . . . . . . .. 112
4.1.2.7 Influence of Manganese ........................ 114
4.1.3 Carbide Precipitation in Ferritic, Low Carbon Martensitic
and Austenitic-Ferritic (Duplex) Steels ................... 114
4.1.3.1 Ferritic Stainless Chromium Steels. . . . . . . . . . . . . . . .. 114
4.1.3.2 Low Carbon Cr-Ni Martensitic Stainless Steels (Soft
Martensitic Steels) . . . . . . . . . . . . . . . . . . . . . . . . . . .. 116
4.1.3.3 Austenitic-Ferritic (Duplex) Steels with Low Carbon Contents 118
4.1.4 Carbide Precipitations in Stainless Steel Weld Metal and in the Heat
Affected Zone (HAZ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 120
4.1.4.1 Knife Line Corrosion in Weldments Made from Stabilized
Austenitic Stainless Steels after Heat Treatment in the
Temperature Range of 500-7000 C . . . . . . . . . . . . . . . .. 121
4.1.4.2 Increased Intergranular Corrosion in Weld Metal Due to
Segregations and Phase Separations ................ 124
4.1.4.3 Ferrite Track Corrosion in Austenitic Weld Metal ...... 124
4.2 The Precipitation oflntermetallic Phases in Stainless Steels and Weld Metals 125
4.2.1 The Precipitation of Sigma Phase in Austenitic Stainless Steels and
Weld Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 125
4.2.2 The Precipitation of Sigma Phase in Ferritic and Austenitic-Ferritic
Stainless Steels ................................... 130
4.2.3 The Precipitation of Sigma Phase in Austenitic, Austenitic-Ferritic
and Ferritic Stainless Steel Weld Metals .................. 131
4.2.4 The Precipitation of Intermetallic Phases in Chromium-Nickel-
Molybdenum Stainless Steels and Weld Metals ............. 135
4.3 4750 C Embrittlement in Stainless Steels and Stainless Steel Weld Metals 140
5 Hot Cracking Resistance During the Welding of Austenitic Stainless Steels .... 144
5.1 Formation of Hot Cracks ................................. 145
5.1.1 Formation Mechanics of Solidification Cracks .............. 145
5.1.2 Formation Me-chanics of Liquation Cracks. . . . . . . . . . . . . . . .. 147
Contents IX
5.2 Hot Cracking Tests ..................................... 149
5.2.1 Hot Cracking Tests for the Determination of the Critical Deformation
Rate in the Welding Zone . . . . . . . . . . . . . . . . . . . . . . . . . . .. 150
5.2.2 The Program Controlled Deformation Cracking Test (PVR Test) .. 153
5.3 Criteria which Influence the Hot Cracking Susceptibility of Austenitic Stain-
less Steel Weldments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 157
5.3.1 Influence of Primary Solidification on the Hot Cracking Behaviour of
Austenitic Stainless Steel Weld Metal . . . . . . . . . . . . . . . . . . .. 158
5.3.2 Influence of the Residual Delta Ferrite Content on the Hot Cracking
Behaviour. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 160
5.3.3 Influence of Alloying Elements and Impurities which Promote Hot
Cracking ....................................... 162
5.3.4 Hot Cracking Sensitivity of Fully Austenitic Weld Metal . . . . . .. 166
5.3.5 Influence of Welding Parameters and Material Thickness on the Hot
Cracking Sensitivity of Austenitic Stainless Steel Weldments .... 169
6 Welding Metallurgy of Ferritic Stainless Chromium Steels with Carbon Contents
Below 0.15% ............................................. 172
6.1 Practical Welding of Stainless Chromium Steels . . . . . . . . . . . . . . . . .. 174
6.2 Mechanical Properties of Stainless Steel Weld Metals with 12 and 17%
Chromium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 176
6.3 Precipitation Phenomena in Ferritic Stainless Chromium Steels and Weld
Metals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 178
7 Welding Metallurgy of Low Carbon Chromium-Nickel Martensitic Stainless Steels
(Soft Martensitic Steels) ..................................... 179
7.1 Practical Welding of Low Carbon Martensitic Stainless Steels ........ 181
7.2 Mechanical Properties of Low Carbon Martensitic Stainless Steel Weld Metal 182
7.3 Precipitation Phenomena in Low Carbon Soft Martensitic Stainless Steels and
Weld Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 185
8 Welding Metallurgy of Duplex Austenitic-Ferritic Stainless Steels .......... 186
8.1 Practical Welding of Duplex Austenitic-Ferritic Stainless Steels ....... 192
8.2 Mechanical Properties of Duplex Austenitic-Ferritic Stainless Steel Weld
Metal .............................................. 194
8.3 Precipitation Phenomena in Duplex Austenitic-Ferritic Stainless Steels and
Weld Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 196
9 Welding Metallurgy of Austenitic Stainless Steels ..................... 197
9.1 Welding Metallurgy of Unstabilized Austenitic Stainless Steels ....... 199
9.1.1 Practical Welding of Unstabilized Austenitic Stainless Steels .... 203
9.1.2 Mechanical Properties of Uns tabilized Austenitic Stainless Steel Weld
Metal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 204
9.1.3 Precipitation Phenomena in Unstabilized Austenitic Stainless Steels
and Weld Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 207
9.2 Welding Metallurgy of Stabilized Austenitic Stainless Steels ......... 209
9.2.1 Practical Welding of Stabilized Austenitic Stainless Steels ...... 210
9.2.2 Mechanical Properties of Stabilized Austenitic Stainless Steel Weld
Metal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 211
9.2.3 Precipitation Phenomena in Stabilized Austenitic Stainless Steels and
Weld Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 213
X Contents
9.3 Welding Metallurgy of Fully Austenitic Stainless Steels ............ 214
9.3.1 Practical Welding of Fully Austenitic Stainless Steels with Fully
Austenitic Stainless Steel Filler Metals . . . . . . . . . . . . . . . . . .. 218
9.3.2 Mechanical Properties of Fully Austenitic Stainless Steel Weld Metal 219
9.3.3 Precipitation Phenomena in Fully Austenitic Stainless Steels and Weld
Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 222
10 General Instructions for the Welding and Post-Weld Surface Treatments of Fabrica-
tions and Welded Components Made from Austenitic Stainless Steel ........ 223
10.1 Welding Procedure ..................................... 223
10.2 Welding of Austenitic Stainless Steel Castings . . . . . . . . . . . . . . . . . .. 224
10.3 Post Weld Surface Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 224
11 Welding Metallurgy of Heat Resisting Steels ........................ 226
12 Welding Metallurgy of Austenitic-Ferritic Dissimilar Joints . . . . . . . . . . . . . .. 229
12.1 Selection of Filler Metals and Importance of Dilution ............. 231
12.2 Practical Welding of Austenitic-Ferritic Dissimilar Joints. . . . . . . . . . .. 233
12.3 Criteria for the Heat Treatment of Austenitic-Ferritic Dissimilar Joints .. 235
12.4 Mechanical Properties of Austenitic-Ferritic Dissimilar Joints ........ 228
Appendix (Abbreviations and Short Designations) ...................... 241
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 243
Author Index 267
Subject Index 274
1 Significance of Constitution Diagrams for the
Understanding of Welding Phenomenal
In order to understand the properties of iron based stainless steel weld metals and
the associated phenomena that take place in the heat affected zone a knowledge of
the constitution diagrams that relate to the alloying elements used in these alloys is
required. Many welding phenomena can be explained and in many cases even
predicted with the aid of constitution diagrams.
There is one restriction, however. Speaking in metallurgical terms, constitution
diagrams are equilibrium diagrams, i.e. they represent the situation at very slow
heating and cooling rates. In welding operations, however, cooling rates are
normally rather high and a certain degree of deviation from constitution diagrams
must be expected. Such deviations may appear, for example, in the form of super
cooling of transformation phenomena or even complete suppression of the latter.
Approximate equilibrium is achieved only during subsequent heat treatment.
Nevertheless, many metallurgical reactions take place during welding and
phenomena such as type of crystallization, segregations, phase transformations,
precipitations and embrittlement can be directly related to the constitution
diagrams.
The knowledge of constitution diagrams of stainless steels and stainless steel
weld metals is also of importance for an additional reason. A major proportion ofthe
stainless steels are made up from the austenitic iron-chromium-nickel alloys, with
their best known representative being the so called 18/8 steel with about 18%
chromium and 8% nickel (AISI 302), developed according to StrauB and Maurer [1]
in 1912 and marketed in the twenties ofthis century. Austenitic materials maintain
their structure even at ambient temperature, i.e. y-a (gamma-alpha) transformation
does not take place. For welding operations, this means that the metallurgical
changes occurring during solidification or crystallization often have a much stronger
impact on the properties of the stainless steel weld metal than in the case of
unalloyed or low alloyed steels and weld metals. In case ofthe latter, changes during
solidification are often superseded by the subsequent y-a transformation and the
influence on weld metal properties is not as strong. A good example in this respect,
regarding austenitic materials, is the direct influence that the type of solidification
or crystallization structure has on the cracking resistance of the weld metal. But
To facilitate practical application, the alloying contents of all constitution diagrams are
1
stated in weight (mass) percent. For information we also call constitution diagrams phase
diagrams or equilibrium diagrams.