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1 WELDING METALLURGY SECOND EDITION Sindo Kou Professor and Chair Department of Materials Science and Engineering University of Wisconsin A JOHN WILEY & SONS, INC., PUBLICATION

3 WELDING METALLURGY SECOND EDITION

5 WELDING METALLURGY SECOND EDITION Sindo Kou Professor and Chair Department of Materials Science and Engineering University of Wisconsin A JOHN WILEY & SONS, INC., PUBLICATION

6 Copyright 2003 by John Wiley & Sons, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. No part of this publication may be reproduced,stored in a retrieval system,or transmitted in any form or by any means,electronic,mechanical,photocopying,recording,scanning,or otherwise,except as permitted under Section 107 or 108 of the 1976 United States Copyright Act,without either the prior written permission of the Publisher,or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center,Inc.,222 Rosewood Drive,Danvers,MA 01923, ,fax ,or on the web at to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) , fax (201) , permreq@wiley.com. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services please contact our Customer Care Department within the U.S. at , outside the U.S. at or fax Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic format. Library of Congress Cataloging-in-Publication Data Kou, Sindo. Welding metallurgy / Sindo Kou. 2nd ed. p. cm. A Wiley-Interscience publication. Includes bibliographical references and index. ISBN Welding. 2. Metallurgy. 3. Alloys. I. Title. TS227.K dc Printed in the United States of America

7 To Warren F. Savage for his outstanding contributions to welding metallurgy

9 CONTENTS Preface xiii I INTRODUCTION 1 1 Fusion Welding Processes Overview Oxyacetylene Welding Shielded Metal Arc Welding Gas Tungsten Arc Welding Plasma Arc Welding Gas Metal Arc Welding Flux-Core Arc Welding Submerged Arc Welding Electroslag Welding Electron Beam Welding Laser Beam Welding 29 References 33 Further Reading 34 Problems 34 2 Heat Flow in Welding Heat Source Analysis of Heat Flow in Welding Effect of Welding Parameters Weld Thermal Simulator 58 References 60 Further Reading 62 Problems 62 3 Chemical Reactions in Welding Overview Gas Metal Reactions Slag Metal Reactions 82 References 92 vii

10 viii CONTENTS Further Reading 95 Problems 95 4 Fluid Flow and Metal Evaporation in Welding Fluid Flow in Arcs Fluid Flow in Weld Pools Metal Evaporation Active Flux GTAW 116 References 117 Further Reading 119 Problems Residual Stresses, Distortion, and Fatigue Residual Stresses Distortion Fatigue Case Studies 137 References 140 Further Reading 141 Problems 141 II THE FUSION ZONE Basic Solidification Concepts Solute Redistribution during Solidification Solidification Modes and Constitutional Supercooling Microsegregation and Banding Effect of Cooling Rate Solidification Path 166 References 167 Further Reading 168 Problems Weld Metal Solidification I: Grain Structure Epitaxial Growth at Fusion Boundary Nonepitaxial Growth at Fusion Boundary Competitive Growth in Bulk Fusion Zone Effect of Welding Parameters on Grain Structure Weld Metal Nucleation Mechanisms Grain Structure Control 187

11 CONTENTS ix References 195 Further Reading 197 Problems Weld Metal Solidification II: Microstructure within Grains Solidification Modes Dendrite and Cell Spacing Effect of Welding Parameters Refining Microstructure within Grains 209 References 213 Further Reading 213 Problems Post-Solidification Phase Transformations Ferrite-to-Austenite Transformation in Austenitic Stainless Steel Welds Austenite-to-Ferrite Transformation in Low-Carbon, Low-Alloy Steel Welds 232 References 239 Further Reading 241 Problems Weld Metal Chemical Inhomogeneities Microsegregation Banding Inclusions and Gas Porosity Inhomogeneities Near Fusion Boundary Macrosegregation in Bulk Weld Metal 255 References 260 Further Reading 261 Problems Weld Metal Solidification Cracking Characteristics, Cause, and Testing Metallurgical Factors Mechanical Factors Reducing Solidification Cracking Case Study: Failure of a Large Exhaust Fan 295 References 296 Further Reading 299 Problems 299

12 x CONTENTS III THE PARTIALLY MELTED ZONE Formation of the Partially Melted Zone Evidence of Liquation Liquation Mechanisms Directional Solidification of Liquated Material Grain Boundary Segregation Grain Boundary Solidification Modes Partially Melted Zone in Cast Irons 318 References 318 Problems Difficulties Associated with the Partially Melted Zone Liquation Cracking Loss of Strength and Ductility Hydrogen Cracking Remedies 330 References 336 Problems 338 IV THE HEAT-AFFECTED ZONE Work-Hardened Materials Background Recrystallization and Grain Growth in Welding Effect of Welding Parameters and Process 349 References 351 Further Reading 352 Problems Precipitation-Hardening Materials I: Aluminum Alloys Background Al Cu Mg and Al Mg Si Alloys Al Zn Mg Alloys Friction Stir Welding of Aluminum Alloys 370 References 371 Further Reading 372 Problems Precipitation-Hardening Materials II: Nickel-Base Alloys Background 375

13 CONTENTS xi 16.2 Reversion of Precipitate and Loss of Strength Postweld Heat Treatment Cracking 384 References 390 Further Reading 392 Problems Transformation-Hardening Materials: Carbon and Alloy Steels Phase Diagram and CCT Diagrams Carbon Steels Low-Alloy Steels Hydrogen Cracking Reheat Cracking Lamellar Tearing Case Studies 425 References 427 Further Reading 429 Problems Corrosion-Resistant Materials: Stainless Steels Classification of Stainless Steels Austenitic Stainless Steels Ferritic Stainless Steels Martensitic Stainless Steels Case Study: Failure of a Pipe 451 References 452 Further Reading 453 Problems 454 Index 455

15 PREFACE Since the publication of the first edition of this book in 1987, there has been much new progress made in welding metallurgy. The purpose for the second edition is to update and improve the first edition. Examples of improvements include (1) much sharper photomicrographs and line drawings; (2) integration of the phase diagram, thermal cycles, and kinetics with the microstructure to explain microstructural development and defect formation in welds; and (3) additional exercise problems. Specific revisions are as follows. In Chapter 1 the illustrations for all welding processes have been redrawn to show both the overall process and the welding area. In Chapter 2 the heat source efficiency has been updated and the melting efficiency added. Chapter 3 has been revised extensively, with the dissolution of atomic nitrogen, oxygen, and hydrogen in the molten metal considered and electrochemical reactions added. Chapter 4 has also been revised extensively, with the arc added, and with flow visualization, arc plasma dragging, and turbulence included in weld pool convection. Shot peening is added to Chapter 5. Chapter 6 has been revised extensively, with solute redistribution and microsegregation expanded and the solidification path added. Chapter 7 now includes nonepitaxial growth at the fusion boundary and formation of nondendritic equiaxed grains. In Chapter 8 solidification modes are explained with more illustrations. Chapter 9 has been expanded significantly to add ferrite formation mechanisms, new ferrite prediction methods, the effect of cooling rate, and factors affecting the austenite ferrite transformation. Chapter 10 now includes the effect of both solid-state diffusion and dendrite tip undercooling on microsegregation. Chapter 11 has been revised extensively to include the effect of eutectic reactions, liquid distribution, and ductility of the solidifying metal on solidification cracking and the calculation of fraction of liquid in multicomponent alloys. Chapter 12 has been rewritten completely to include six different liquation mechanisms in the partially melted zone (PMZ), the direction and modes of grain boundary (GB) solidification, and the resultant GB segregation. Chapter 13 has been revised extensively to include the mechanism of PMZ cracking and the effect of the weld-metal composition on cracking. Chapter 15 now includes the heat-affected zone (HAZ) in aluminum lithium copper welds and friction stir welds and Chapter 16 the HAZ of Inconel 718. Chapter 17 now includes the effect of multiple-pass welding on xiii

WELDING METALLURGY. Sindo Kou Professor and Chair Department of Materials Science and Engineering University of Wisconsin SECOND EDITION

WELDING METALLURGY. Sindo Kou Professor and Chair Department of Materials Science and Engineering University of Wisconsin SECOND EDITION WELDING METALLURGY SECOND EDITION Sindo Kou Professor and Chair Department of Materials Science and Engineering University of Wisconsin A JOHN WILEY & SONS, INC., PUBLICATION WELDING METALLURGY SECOND