METALLURGY OF WELDING

Transcription

1 METALLURGY OF WELDING

2 Metallurgy of Welding 1. F. LANCASTER London GEORGE ALLEN & UNWIN Boston Sydney

3 First published as Metallurgy of welding, brazing and soldering in 1965 Third edition 1980 This book is copyright under the Berne Convention. All rights are reserved. Apart from any fair dealing for the purpose of private study, research, criticism or review, as permitted under the Copyright Act, 1956, no part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, electrical, chemical, mechanical, optical, photocopying, recording or otherwise, without the prior permission of the copyright owner. Enquiries shouldbe sent tothe publishers at the undermentioned address: GEORGE ALLEN & UNWIN LTD 40 Museum Street, London WCIA llu J. F. Lancaster, 1980 Softcover reprint of the hardcover 1st edition 1980 British Libory Cataloguing in Publication Data Lancaster, John Frederick Metallurgy of welding. - 2nd ed. 1. Welding 2. Solder and soldering 3. Brazing I. Title II. Metallurgy of welding, brazing and soldering TS227 ISBN ISBN (ebook) DOl / Typeset in 10 on 12 point Times by Alden Press Ltd.

4 Preface This book is intended, like its predecessor (The metallurgy of welding, brazing and soldering), to provide a textbook for undergraduate and postgraduate students concerned with welding, and for candidates taking the Welding Institute examinations. At the same time, it may prove useful to practising engineers, metallurgists and welding engineers in that it offers a resume of information on welding metallurgy together with some material on the engineering problems associated with welding such as reliability and risk analysis. In certain areas there have been developments that necessitated complete re-writing of the previous text. Thanks to the author's colleagues in Study Group 212 of the International Institute of Welding, understanding of mass flow in fusion welding has been radically transformed. Knowledge of the metallurgy of carbon and ferritic alloy steel, as applied to welding, has continued to advance at a rapid pace, while the literature on fracture mechanics accumulates at an even greater rate. In other areas, the welding of non-ferrous metals for example, there is little change to report over the last decade, and the original text of the book is only slightly modified. In those fields where there has been significant advance, the subject has become more quantitative and the standard of mathematics required for a proper understanding has been raised. Mass flow in welding, for example, is not comprehensible without some knowledge of fluid dynamics, and fluid dynamics in turn is not comprehensible without a knowledge of vector analysis. In this and in other ways, welding technology will in the future, as it advances from a workshop subject to a full-fledged branch of engineering, demand higher standards of academic achievement from its students. SI units are used throughout the book and a list of conversion factors is to be found in Appendix 2. Symbols are standardised so far as practicable and are listed in Appendix 1. The American Welding Society designations for welding processes have been used, although it is realised that in Europe (including the United Kingdom) there is a general preference for the older terms, TIG as opposed to GTA, for example. The AWS terms have been employed because they are more precise, have been standardised for a wider range of processes, and because A WS practice fmds increasing acceptance internationally, particularly in the oil, gas, petroleum and petrochemical industries, where welding is a key process in the manufacture of plant and equipment. The author is glad to have the opportunity to thank Professor R. L. Apps, Professor C. E. Jackson and Dr. M. F. Jordan, for undertaking the onerous task

5 viii Preface of reading and commenting on the first draft of this book. The majority of the comments thus received were incorporated into the fmal text, thereby much improving its quality. J. F. Lancaster

6 Contents PREFACE CHAPTER 1 INTRODUcrORY 1.1 Welding in ancient and medieval times 1.2 The advent of fusion welding 1.3 The theory of metal joining techniques 1.4 Welding engineering CHAPTER 2 PROCESSES AND TYPES OF JOINT 2.1 The general character of welding, brazing, soldering and adhesive jointing 2.2 The nature of welding processes The classification of fusion welding processes Heat source intensity Heat input rate Shielding methods 2.3 Types of fusion welded joint Page vii CHAPTER 3 MASS AND HEAT FLOW IN WELDING 3.1 General 3.2 Mass flow: general 3.3 Mass flow from the electrode to the workpiece The pinch instability Other modes of instability 3.4 Mass flow in the weld pool 3.5 Heat flow: general Heat sources The welding arc Electrode interactions The arc column Heat flow in the electrode Time-dependent heat flow Heat flow in the weld pool Heat flow in the solid workpiece: theory Heat flow in the solid workpiece: experimental CHAPTER 4 METALLURGICAL EFFECTS OF THE WELD THERMAL CYCLE Metallurgical effects in the weld metal Gas-metal reactions Absorption Reaction Evolution

7 x Contents Dilution and uniformity of the weld deposit Weld pool solidification Weld cracking Supersolidus cracking Sub solidus cracking Metallurgical effects in the parent metal and solidified weld metal Microstructural changes in the heat-affected zone Precipitation and embrittlement in the heat-affected zone Contraction and residual stress 70 CHAPTER 5 SOLID-PHASE WELDING Fundamentals The cohesion and strength of metals Surface deformation Surface films Recrystallisation Diffusion Processes Pressure welding at elevated temperature Diffusion bonding Cold pressure welding Friction welding Explosive welding 84 CHAPTER 6 BRAZING, SOLDERING AND ADHESIVE BONDING Physical aspects Bonding Surface energy and contact angle Capillary action Soldering and brazing Wetting and spreading Filling the joint Solidification range Soldering Joint design Solders Fluxes Soldering methods Application to various metals Brazing Joint design Brazing solders Fluxes and protective atmospheres Brazing methods Bronze welding Application to various metals Adhesive bonding Mechanical strength Contact angle Residual,stress and stress concentration factors Bonding methods Preparing the surface Types of adhesive and the mode of application Curing the joint 107

8 Contents xi Testing Applications 108 CHAPTER 7 CARBON AND FERRITIC-ALLOY STEELS Scope Metallurgy of the liquid weld metal Gas-metal reactions Reactions in the transferring drop Reactions in the weld pool Slag-metal reactions The mechanics of slag-metal interaction The chemistry of slag-metal interaction Solidification and solidification cracking Transformation and microstructure of steel Transformation and microstructure of weld metal Transformation and microstructure in the heataffected zone The mechanical properties of the welded joint The mechanical properties of weld metals The mechanical properties of the heat-affected zone The hardness of the HAZ The fracture toughness of the HAZ Stress intensification, embrittlement, and cracking of fusion welds below the solidus Stress concentration Embrittlement of fusion welds The hydrogen embrittlement and cracking of welds in steel Hydrogen attack Hydrogen embrittlement The solution of hydrogen Cracking due to dissolved hydrogen Hydrogen-induced cold cracking in welds Testing for hydrogen-induced cold cracking Measures to avoid hydrogen-induced cold cracking Chevron cracking Lamellar tearing Reheat cracking Welding problems with iron and steel products Cast iron Steels used primarily for their mechanical properties Carbon and carbon-manganese steels Microalloyed steels Low-alloy normalised and tempered (NT) steels Low-alloy quenched and tempered (QT) steels Steels for subzero temperature use Low-alloy corrosion- and heat-resisting steels Ferritic and austenitic/ferritic chromium stainless steels 173 CHAPTER 8 AUSTENITIC AND HIGH-ALLOY STEELS Scope Metallurgy of the weld metal and heat-affected zone Alloy constitution Carbide precipitation Solidification cracking in the weld deposit 182

9 xii Contents Hot cracking in the heat-affected zone during welding Reheat cracking Corrosion Intergranuiar corrosion Stress corrosion cracking Preferential corrosion of welds Corrosion-resistant steels: alloys and welding procedures Weld overlay cladding and dissimilar metal joints Heat-resisting steels: alloys and welding procedures Hardenable high-alloy steels 195 CHAPTER 9 NON-FERROUSMETALS Aluminium and its alloys Processes and materials Porosity Cracking Mechanical properties Alloys and welding procedures Magnesium and its alloys Alloys and welding procedures Oxide film removal Cracking Mechanical properties Corrosion resistance and fire risk Copper and its alloys Processes and materials Heat input Porosity Cracking Mechanical properties Alloys and welding procedures Nickel and its alloys Cracking Porosity Mechanical properties Corrosion resistance Oxidation and creep resistance Alloys and welding procedures The reactive and refractory metals - beryllium, titanium, zirconium, niobium, molybdenum, tantalum and tungsten Embrittlement due to gas absorption Embrittlement due to recrystallisation Porosity Cracking Tensile properties Alloys and welding procedures The low-melting metals: lead and zinc Lead Zinc The precious metals: silver, gold, platinum Silver Gold Platinum Other platinum-group metals 222

10 C?ontents xiil CHAPTER 10 THE BEHA VIOUR OF WELDS IN SER VIC?E Reliability Service problems associated with welding Fast crack growth General Linear elastic-fracture mechanics (LEFM) Alternative means of estimating or measuring fracture toughness Slow crack propagation Corrosion of welds Risk analysis 242 APPENDIX 1 SYMBOLS 244 APPENDIX 2 CONVERSION FACTORS 247 INDEX 249

11 List of tables 2.1 Fusion welding and cutting processes 2.2 Heat source intensities and type of penetration 3.1 IIW classification of metal transfer 3.2 Dominant forces in metal transfer 3.3 Electron work function and ionisation potential of pure metals 3.4 Temperature of the arc column in various gases 3.5 Dissociation of gases in the arc 5.1 Solid-phase welding processes 6.1 Surface free energy and surface tension of metals and adhesives 6.2 Furnace atmospheres for brazing 6.3 Shear strength of 12'5 mm redux bonded lap joints at room temperature. Mechanical properties of redux (20 DC) page Fracture toughness (MN/m 3/2 ) of weld HAZ in ASTM A533 (Mn-Mo) steel at DC AWS requirements for moisture content of hydrogen-controlled electrode coatings High-strength line pipe steel Typical compositions of pearlite-reduced X 70 line pipe steel Low-alloy high-tensile NT steels for welded fabrication Low-alloy high-strength QT steels for welded fabrication illtra high-strength maraging and QT steels for welded fabrication Heat-resistant and corrosion-resistant chromium-molybdenum steels Chemical composition of ferritic and ferritic/austenitic stainless ~eels Standard intergranular corrosion tests for stainless steels Corrosion-resistant austenitic Cr-Ni steels Heat-resistant austenitic Cr-Ni alloys Nickel and nickel alloys Alloy systems subject to stress corrosion cracking 240

12 METALLURGY OF WELDING