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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Fachliteratur
- Sprache: Englisch
As critically important as welding is to a wide spectrum of manufacturing, construction, and repair, it is not without its problems. Those dependent on welding know only too well how easy it is to find information on the host of available processes and on the essential metallurgy that can enable success, but how frustratingly difficult it can be to find guidance on solving problems that sooner or later arise with welding, welds, or weldments.
Here for the first time is the book those that practice and/or depend upon welding have needed and awaited. A Practical Guide to Welding Solutions addresses the numerous technical and material-specific issues that can interfere with success. Renowned industrial and academic welding expert and prolific author and speaker Robert W. Messler, Jr. guides readers to the solutions they seek with a well-organized search based on how a problem manifests itself (i.e., as distortion, defect, or appearance), where it appears (i.e., in the fusion zone heat-affected zone, or base metal), or it certain materials or situations.
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Veröffentlichungsjahr: 2019
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Table of Contents
Cover
Preface
1 Introduction
Further Reading
2 Categorization of Welding and Weld Problems
2.1 What Is Welding?
2.2 Microstructural Zones of Welds
2.3 Origin of Problems in Welding and Welds
2.4 How Problems Can Be Logically Categorized?
References
Further Reading
Part IManifestation of Problems with Welds and Weldments
3 Problems with Joint Setup and Weld Joints
3.1 Joint Efficiency
3.2 Weld Joint Types and Weld Configurations
3.3 Joint Setup Problems
3.4 Problems with Weld Profile
3.5 Troubleshooting Guide
References
Further Reading
4 Shape Distortion, Dimensional Shrinkage, and Geometric Instability
4.1 Thermal Versus Mechanical Stresses in a Structure
4.2 Residual Stresses Versus Distortion
4.3 Origin and Effect of Volumetric Shrinkage
4.4 Origin and Effect of Thermal Contraction
4.5 Problems from Nonuniform Thermal Contraction and CTE Mismatches
4.6 Problems from Distortion and from Residual Stresses
4.7 Distortion Control and Residual Stress Reduction
4.8 Troubleshooting Guide
References
Further Reading
5 Porosity
5.1 The Most Common Problem in Welds
5.2 Types of Weld Porosity
5.3 Gases in Molten Weld Metal
5.4 The Many Possible Causes of Porosity in Welds
5.5 Attempting to Minimize Porosity Formation in Fusion Welds
5.6 Troubleshooting Porosity Problems in Welds
References
Further Reading
6 Cracks
6.1 The Most Dreaded Defect in Welds
6.2 Classification of Cracking and Cracks in Welds and Welding
6.3 Hot Cracking and Cracks
6.4 Cold Cracking and Cracks
6.5 Other Weld‐Related Cracking and Cracks
6.6 Crack‐Prone Metals and Alloys
6.7 Troubleshooting Cracking Problems in Welds
References
Further Reading
7 Nonmetallic and Metallic Inclusions
7.1 Solid Versus Gas Inclusions
7.2 Nonmetallic Inclusions in Welds
7.3 Metallic Inclusions in Welds
7.4 Troubleshooting Problems with Inclusions in Welds
References
Further Reading
8 Weld Appearance
8.1 Can You Judge a Book by Its Cover? Is Beauty Only Skin Deep?
8.2 Weld Crown Bead Faults
8.3 Weld Root Bead Faults
8.4 Fillet Weld Faults
8.5 Reading Weld Ripple Marks
8.6 Weld Spatter
8.7 Arc Strikes
8.8 Weld Heat Tint
8.9 Troubleshooting Weld Appearance Problems
References
Further Reading
Part IILocation of Problems in Welds
9 Fusion Zone of Fusion Welds
9.1 A Refresher on Microstructural Zones in and Around Welds
9.2 Gas Porosity in the Fusion Zone of Welds
9.3 Cracking in the Fusion Zone of Welds
9.4 Inclusions in the Fusion Zone of Welds
9.5 Macrosegregation in the Fusion Zone of Welds
9.6 Troubleshooting Problems in the Fusion Zone of Welds
References
Further Reading
10 Partially Melted Zone of Fusion Welds
10.1 Origin and Location of the PMZ in Fusion Welds
10.2 Conventional Hot Cracking in the PMZ
10.3 Constitutional Liquation Cracking in the PMZ
10.4 Cold Cracking in the PMZ
10.5 Overcoming Cracking Problems in the PMZ
10.6 Troubleshooting Problems in the PMZ
References
Further Reading
11 Heat‐Affected Zone of Fusion Welds
11.1 Origin and Location of the HAZ for Fusion Welds
11.2 Manifestation of Problems in the HAZ of Fusion Welds
11.3 Precipitation‐Hardening Alloy HAZ Problems
11.4 Sensitization in the HAZ of Austenitic Stainless Steels
11.5 Transformation‐Hardening Steel HAZ Problems
11.6 Reheat Cracking
11.7 Troubleshooting Problems in the HAZ of Fusion Welds
References
Further Reading
12 Unaffected Base Metal Cracking Associated with Welding
12.1 Weld‐Related Problems in the Unaffected Base Metal
12.2 Lamellar Tearing in Thick Steel Weldments
12.3 Corrosion Cracking Caused by Fusion Welding
12.4 Fatigue Cracking Outside Fusion Welds
12.5 Troubleshooting Weld‐Related Problems in the Unaffected Base Metal
References
Further Reading
13 Discontinuities in Multi‐pass Welds
13.1 Needs for Multi‐pass Welding and Welds
13.2 Various Functions of Multi‐pass Welding and Welds
13.3 Defects Found in Multi‐pass Welds
13.4 Composition Adjustment with Multi‐pass Welding
13.5 Property Alteration with Multi‐pass Welding
13.6 Troubleshooting Problems in Multi‐pass Welding and Welds
References
Further Reading
14 Problems with Non‐fusion Welding and Non‐fusion Welds
14.1 Non‐fusion Welding Processes Versus Fusion Welding Processes
14.2 Overview of Non‐fusion Processes
14.3 Problems with Non‐fusion Welds and Non‐fusion Welding Processes
14.4 Inspection and Repair Challenges with Non‐fusion Welds
14.5 Troubleshooting Problems with Non‐fusion Welds
References
Further Reading
Part IIIMaterial-Specific Weld-Related Problems
15 Embrittlement of Carbon and Low‐ and Medium‐alloy Steels
15.1 The Importance of Steel
15.2 Four Causes of Embrittlement in Carbon and Low‐ and Medium‐alloy Steels
15.3 Hydrogen Embrittlement: A Misnomer in Steels
15.4 Secondary Hardening in Steels
15.5 Ductile‐to‐Brittle Transition in Steels
15.6 Compromise of Fatigue and Impact Behavior by Residual Stresses in Steels
15.7 Troubleshooting Problems from Embrittlement of Steels by Welding
References
Further Reading
16 Sensitization or Weld Decay and Knife‐line Attack in Stainless Steels
16.1 A Primer on the Metallurgy of Stainless Steels
16.2 Sensitization of Austenitic Stainless Steels by Welding
16.3 Sensitization of Other Grades of Stainless Steel
16.4 Knife‐line Attack in Stabilized Austenitic Stainless Steels
16.5 Troubleshooting Problems from Sensitization or Knife‐line Attack
References
Further Reading
17 Stress Relief Cracking of Precipitation‐Hardening Alloys
17.1 Different Names, Same Phenomenon
17.2 Stress Relief Cracking in Ferritic Alloy Steels
17.3 Stress Relaxation Cracking in Stainless Steels
17.4 Strain‐age Cracking in Ni‐Based Superalloys
17.5 Troubleshooting Problems from Stress Relief or Strain‐age Cracking
References
Further Reading
18 Loss of Properties in Cold‐Worked Metals and Alloys
18.1 Cold Work, Recovery, Recrystallization, and Grain Growth
18.2 Cold‐Worked Metals and Alloys in Engineering
18.3 Avoiding or Recovering Properties Loss from Fusion Welding
18.4 The Worked Zone in Pressure‐Welded Metals and Alloys
18.5 Troubleshooting Welding Problems in Cold‐Worked Metals and Alloys
References
Further Reading
19 Embrittlement with High‐chromium Contents
19.1 Phase Formation and Structure
19.2 Adverse Effects of σ‐Phase
19.3 Susceptible Alloys
19.4 Guidelines for Avoiding or Resolving Problems from σ‐Phase
19.5 Troubleshooting Problems with σ‐Phase Associated with Welding
References
Further Reading
20 Weld Dilution and Chemical Inhomogeneity
20.1 The Designer's Druthers
20.2 Chemical Inhomogeneity in Welds
20.3 Weld Dilution
20.4 The Unmixed Zone in the Weld Metal
20.5 Impurities in the Weld Metal
20.6 Troubleshooting Problems from Weld Dilution and Chemical Inhomogeneity
References
Further Reading
21 Dissimilar Metal and Alloy Welding
21.1 Joining Dissimilar Materials
21.2 The Need for Welding Dissimilar Metals and Alloys
21.3 Chemical Incompatibility
21.4 Mechanical Incompatibility
21.5 Thermal Incompatibility
21.6 Troubleshooting Problems with Dissimilar Metal and Alloy Welding
References
Further Reading
Closing Thoughts
Index
End User License Agreement
List of Tables
Chapter 3
Table 3.1 Joint setup problems: cause and effect.
Table 3.2 Weld joint discontinuities.
Table 3.3 Troubleshooting joint and weld profile problems.
Chapter 4
Table 4.1 Key properties of commonly welded metals and alloys, as these affect s...
Table 4.2 Troubleshooting weld shrinkage, weldment distortion, and residual stre...
Chapter 5
Table 5.1 Solubility of hydrogen, nitrogen, and oxygen in various liquid metals ...
Table 5.2 Principal gases causing porosity in the most commonly welded engineeri...
Table 5.3 Troubleshooting problems with porosity in welds.
Chapter 6
Table 6.1 Troubleshooting weld cracking problems.
Chapter 7
Table 7.1 Troubleshooting problems with inclusions in welds.
Chapter 8
Table 8.1 Troubleshooting problems with weld appearance.
Chapter 9
Table 9.1 Troubleshooting problems in a weld's fusion zone.
Chapter 10
Table 10.1 Major engineering alloys prone to PMZ constitutional liquation or hyd...
Table 10.2 Troubleshooting problems in a fusion weld's PMZ.
Chapter 11
Table 11.1 Troubleshooting problems with HAZs.
Chapter 12
Table 12.1 Alloy/environment systems that exhibit stress corrosion cracking.
Table 12.2 Troubleshooting problems in the unaffected base metal around fusion w...
Chapter 13
Table 13.1 Troubleshooting problems in multi‐pass welds.
Chapter 14
Table 14.1 List of the eight major non‐fusion welding processes with variations.
Table 14.2 Troubleshooting problems in non‐fusion welds.
Chapter 15
Table 15.1 Global primary metal production in 2017 (in million MT).
Table 15.2 Ranking as a steel producer versus ranking of economy (by GDP in 2017...
Table 15.3 Comparisons among the United States, China, and the world in terms of...
Table 15.4 Troubleshooting problems from embrittlement of carbon and low‐ and me...
Chapter 16
Table 16.1 Troubleshooting problems with sensitization or weld decay and knife‐l...
Chapter 17
Table 17.1 Nominal composition, mechanical properties, and recommended maximum s...
Table 17.2 Recommended preheat and interpass temperatures for common creep‐resis...
Table 17.3 Typical PWHT temperatures and times for common ferritic alloy steels.
Table 17.4 Austenitic and PH stainless steels used for their creep resistance (c...
Table 17.5 Troubleshooting the various manifestations of stress relief cracking ...
Chapter 18
Table 18.1 Recrystallization temperatures for some important metals.
Table 18.2 Examples of pure metals and alloys commonly used in the cold‐worked c...
Table 18.3 Troubleshooting problems in cold‐worked metals and alloys.
Chapter 19
Table 19.1 Troubleshooting problems with embrittling σ‐phase formation in stainl...
Chapter 20
Table 20.1 List of the problems from weld dilution and chemical inhomogeneity in...
Chapter 21
Table 21.1 Metal combinations prone to liquid metal embrittlement (liquid at acr...
Table 21.2 Coefficient of thermal expansion (
α
l
) and modulus of elasticity ...
Table 21.3 List of problems from dissimilar metal and alloy welding.
List of Illustrations
Chapter 1
Figure 1.1 Remains of the #4 light water graphite‐moderated reactor unit at th...
Figure 1.2 After several iterations to safely contain the highly radioactive re...
Figure 1.3 Two examples of superbly made fusion arc welds using manual gas tung...
Chapter 2
Figure 2.1 Photographs showing (a) the welding of a metal (here, using the gas...
Figure 2.2 Schematic illustrations showing the three strong primary types of at...
Figure 2.3 Schematic illustrations showing the three distinct ways in which met...
Figure 2.4 A typical comprehensive scheme for classifying welding processes. Th...
Figure 2.5 Schematic of the cross section of a hypothetical weldment showing th...
Figure 2.6 Schematic illustration showing the inextricable interrelationship am...
Figure 2.7 Schematic illustrations showing various microstructural zones that a...
Chapter 3
Figure 3.1 Schematic illustrations of the five basic designs for weld joints: ...
Figure 3.2 Schematic illustrations of some typical welds for various preparatio...
Figure 3.3 Schematic illustrations showing properly made fusion welds (shaded) ...
Figure 3.4 Schematic illustration showing a single V‐joint weld preparation wit...
Figure 3.5 Schematic illustration showing the two types of misalignments that c...
Figure 3.6 Schematic illustration showing weld joint mismatch (or linear misali...
Figure 3.7 (a) Schematic illustration showing offset or mismatch of a single V‐...
Figure 3.8 Photograph showing properly made tack welds to maintain tight fit‐up...
Figure 3.9 Schematic illustrations showing various possible backup bars, strips...
Figure 3.10 Schematic illustrations showing examples of incomplete weld or join...
Figure 3.11 (A) Schematic illustration showing the various ways lack of fusion ...
Figure 3.12 Schematic illustrations showing underfill in fusion welds made in a...
Figure 3.13 Schematic illustrations showing the proper profile for (a) a fillet...
Figure 3.14 Schematic illustrations showing excessive concavity and excessive c...
Figure 3.15 Schematic illustrations of the various problems that can appear in ...
Figure 3.16 Schematic illustrations showing both overlap and undercut discontin...
Chapter 4
Figure 4.1 (a) Illustration showing the 104.45° conformation angle between the...
Figure 4.2 Photograph showing buckling of the steel rails of a railroad track b...
Figure 4.3 Schematic illustration showing the fundamental dimensional changes t...
Figure 4.4 Schematic illustrations showing typical distribution of temperature ...
Figure 4.5 Schematic illustrations showing the typical distribution of residual...
Figure 4.6 Schematic illustrations showing typical residual stress patterns for...
Figure 4.7 A plot showing the effect of temperature on the CTE (as in./in./°F) ...
Figure 4.8 Illustration of a modern IGBT module showing the complex thermal–mec...
Figure 4.9 Schematic illustrations showing several techniques for preventing or...
Figure 4.10 Plots showing the effect of (a) time at temperature and (b) tempera...
Chapter 5
Figure 5.1 Photomacrographs showing (a) very severe internal porosity in a wel...
Figure 5.2 Close‐up photograph showing a crater pipe at the termination of a fu...
Figure 5.3 Schematic illustration showing various types of porosity found in fu...
Figure 5.4 (a) Schematic and (b) radiograph showing scattered porosity in a wel...
Figure 5.5 (a) Schematic and (b) radiograph showing cluster porosity in a weld.
Figure 5.6 Photograph showing severe wormhole porosity because of excessive shi...
Figure 5.7 Plot showing the solubility of nitrogen in molten iron (at 1600 °C) ...
Figure 5.8 Plots showing the equilibrium solubility of nitrogen and oxygen in p...
Figure 5.9 Plots showing the equilibrium solubility of hydrogen in pure aluminu...
Figure 5.10 Plots showing the effect of various solutes on the solubility of ni...
Figure 5.11 Plots showing the influence of alloying elements on the oxygen cont...
Figure 5.12 Bar graphs of oxygen and nitrogen levels expected in steel after fu...
Figure 5.13 Bar graphs of the amount of hydrogen found in welds in steel as a f...
Figure 5.14 Schematic illustration of the two possible effects of different con...
Chapter 6
Figure 6.1 Schematic illustrations showing various forms of hot cracks and col...
Figure 6.2 Photographs showing (a) a longitudinal crack commonly referred to as...
Figure 6.3 Photomacrographs showing centerline cracking (a) open to the surface...
Figure 6.4 A photograph showing a crater crack caused by insufficient filling a...
Figure 6.5 Photomacrograph showing transverse cracks in a circumferential weld ...
Figure 6.6 Photomacrographs showing (a) toe cracking form of hydrogen‐induced c...
Figure 6.7 Photomacrograph showing characteristic “fisheyes” in the surface of ...
Figure 6.8 Schematic illustrations of fatigue and corrosion cracking related to...
Chapter 7
Figure 7.1 Schematic illustrations (a) showing various locations and forms of ...
Figure 7.2 Photographs showing the weld crown surfaces of (a) a poorly made wel...
Figure 7.3 Schematic illustrations (a) showing the possible locations of oxide ...
Figure 7.4 Schematic illustrations (a) showing the possible locations of tungst...
Chapter 8
Figure 8.1 Schematic illustrations showing the appearance of the crown bead su...
Figure 8.2 Photographs showing arc welds made under various conditions are as f...
Figure 8.3 Photographs showing good‐looking manual welds made by GMAW/
metal ine
...
Figure 8.4 Photographs showing a GTAW/TIG weld being made (a) and in a close‐up...
Figure 8.5 Photograph showing lack of root fusion defect (near the left end of ...
Figure 8.6 Photograph showing excessive root penetration in a fusion weld to cr...
(a) A photograph showing “sugaring” on the root side of a full‐penetration fus...
Figure 8.8 Schematic illustrations showing (a) desirable fillet weld profiles, ...
Figure 8.9 Schematic illustrations made from stills from a movie of weld pool s...
Figure 8.10 Photograph showing a topside view of fusion arc welds made at 7 ipm...
Figure 8.11 Photograph showing sparks from globules of molten metal known as “s...
Figure 8.12 Photographs showing spatter produced by shielded metal‐arc welding ...
Figure 8.13 Photographs showing an arc strike, which may occur intentionally wh...
Figure 8.14 Photograph showing heat tinting on and adjacent to a fusion weld ma...
Figure 8.15 Reference photograph published in AWS D18.2, 1999, that shows the r...
Figure 8.16 Photograph showing the heat tint color or titanium and titanium all...
Chapter 9
Figure 9.1 Schematic illustration showing the correlation between the various ...
Figure 9.2 The metastable phase diagram for Fe–Fe
3
C commonly used instead of th...
Figure 9.3 A schematic of the “heat solid” suggested by Portevin and Seferian (...
Figure 9.4 Photomacrographs showing centerline hot cracking in steel: (a) an in...
Figure 9.5 Photomacrograph showing a centerline hot crack all the way through a...
Figure 9.6 A series of progressively higher magnification photomacrographs and ...
Figure 9.7 Plots showing the susceptibility of some aluminum alloys to solidifi...
Figure 9.8 Schematic illustration showing the relationship between the surface ...
Figure 9.9 Schematic growth rate (
R
) versus temperature gradient (
G
) map showin...
Figure 9.10 Photomacrograph showing cold cracks in a multi‐pass weld joint made...
Figure 9.11 Transverse macrograph of a Cu‐to‐steel arc weld showing various fea...
Chapter 10
Figure 10.1 Schematic illustration of characteristic solidification or cooling...
Figure 10.2 Schematic illustration showing the relationship between (a) a porti...
Figure 10.3 Schematic illustration showing the location of the partially melted...
Figure 10.4 Schematic illustration showing the effect of base alloy thermal con...
Figure 10.5 Schematic illustration showing a portion of a phase diagram for a h...
Figure 10.6 Schematic illustrations showing extension of the partially melted z...
Figure 10.7 Schematic representation of the formation of a ghost boundary netwo...
Figure 10.8 Schematic illustration showing the suggested sequence for the devel...
Figure 10.9 Plot showing the favorable effect of reducing grain size on the ten...
Chapter 11
Figure 11.1 Schematic illustration showing a hypothetical binary phase diagram...
Figure 11.2 Schematic illustration showing the generic correlation between the ...
Figure 11.3 Schematic illustrations showing the effect of the heat of welding o...
Figure 11.4 Schematic illustration showing a plot of the strength or hardness f...
Schematic illustration showing the effect of several approaches to attempt to ...
Figure 11.6 Schematic representation of the precipitation of chromium carbide (...
Figure 11.7 Photomicrographs showing (a) the appearance of the normal grain str...
Figure 11.8 Photograph showing a severe stress corrosion crack running along th...
Figure 11.9 Schematic illustration showing the various microstructural regions ...
Figure 11.10 Photomicrograph showing a hydrogen‐induced cold crack through the ...
Figure 11.11 Schematic plots of hardness profile across the HAZ of an AISI 1040...
Figure 11.12 Photomicrographs showing reheat cracking associated with the coars...
Chapter 12
Figure 12.1 (a) An optical micrograph of wrought iron showing typical numerous...
Figure 12.2 Photomacrograph showing lamellar tearing beneath a fusion weld, nea...
Figure 12.3 Photograph showing a portion of the steel support structure of an o...
Figure 12.4 Schematic illustrations showing several weld joint details suscepti...
Figure 12.5 Photomicrograph showing banding of soft, low‐carbon (<0.02 wt%), an...
Figure 12.6 (a) SEM micrograph showing the unique river branching that allows i...
Figure 12.7 Schematic illustration showing typical locations vulnerable to stre...
Figure 12.8 Schematic illustration showing the path of a fatigue crack during S...
(a) Schematic illustration showing the characteristic topographical features o...
Figure 12.10 SEM micrograph showing typical fatigue striations demarcating indi...
Figure 12.11 (a) Photograph showing devastation after The Great Hanshin Earthqu...
Chapter 13
Figure 13.1 Schematic illustrations showing the fundamental types of welds, in...
Figure 13.2 Photographs of (a) multi‐pass butt weld (using
gas tungsten‐arc wel
...
Figure 13.3 Schematic illustration showing the use of root pass, hot pass, fill...
Figure 13.4 Schematic illustrations showing (a) the use of rebuild layer(s) and...
Figure 13.5 Macrograph of a single‐sided multi‐pass V‐groove weld in thick‐sect...
Figure 13.6 Photographs showing multi‐pass weld application of (a) hard‐facing ...
Figure 13.7 Photograph showing an example of the use of shape welding for rapid...
Figure 13.8 Schematic illustration of cracks in multi‐pass welds in Alloy 617, ...
Figure 13.9 Macrograph showing hydrogen‐induced cold cracking in a multi‐pass w...
Figure 13.10 Schematic illustration showing a single U‐groove and root pass bei...
Figure 13.11 Photomacrograph showing use of multi‐pass butter weld, multi‐pass ...
Figure 13.12 Schematic illustration showing the favorable effect of multi‐pass ...
Chapter 14
Figure 14.1 Schematic illustration showing details of the friction stir welding...
Figure 14.2 Photograph showing a friction stir weld being made in difficult‐to‐...
Figure 14.3 Schematic plot showing the combination of rotational speed (rpm) an...
Figure 14.4 Macrograph showing a large mass of flash and of ribbon flash on the...
Figure 14.5Figure 14.5 Macrograph showing tunneling defect, cavity, and void in ...
Figure 14.6Figure 14.6 Macrographs and micrograph showing a kissing bond and a l...
Figure 14.7Figure 14.7 Micrographs showing various examples of oxide‐induced def...
Figure 14.8Figure 14.8 Micrographs showing various oxide‐induced defects on the ...
Chapter 15
Figure 15.1 Plots showing the phenomenon of secondary hardening during either t...
Figure 15.2 Schematic plots showing the three general types of behavior for Cha...
Figure 15.3 Plots showing the effect of carbon content on the Charpy V‐notch en...
Figure 15.4 Bar graphs showing the effect of post‐weld stress relief heat treat...
Figure 15.5 Illustrative plots showing the general increased effect of higher t...
Chapter 16
Figure 16.1 Schematic illustration of the Cr–Fe equilibrium phase diagram.
Figure 16.2 Schematic representation of the depletion of Cr in the region of gr...
Figure 16.3 Photomicrograph showing intergranular corrosive attack from sensiti...
Figure 16.4 Schematic plots showing weld thermal cycles at various locations in...
Figure 16.5 Schematic plots showing weld thermal cycle (a) responsible for the ...
Chapter 17
Figure 17.1 Schematic plot of typical creep behavior in metals or alloys, with...
Figure 17.2 Light optical micrographs showing failed samples of HCM2S creep‐res...
Figure 17.3 An example of crack formation (a) and void formation (b) at prior a...
Figure 17.4 Schematic illustration depicting how post‐weld heat treatment rehea...
Figure 17.5 Plot of Al versus Ti content indicating susceptibility to strain‐ag...
Chapter 18
Figure 18.1 Schematic plots of engineering stress (
σ
) versus engineering ...
Figure 18.2 Schematic illustration showing plots of various properties as a fun...
Figure 18.3 Schematic plot showing the softening at three locations in the HAZ ...
Figure 18.4 Schematic plots showing the effect of net linear heat input (in J/i...
Figure 18.5 Schematic illustration showing the occurrence and effect of dynamic...
Chapter 19
Figure 19.1 The Fe–Cr equilibrium phase diagram (shown earlier in Figure 16.1 ...
Figure 19.2 Schematic illustration of the complex unit cell for Cr–Fe (
σ
) ...
Figure 19.3 Schematic diagrams depicting three different morphologies for
σ
...
Figure 19.4 Micrographs showing σ‐phase in representative susceptible alloys, i...
Figure 19.5 Schematic plot of C‐curves showing the kinetics of the formation of...
Figure 19.6 The Schaeffler diagram of microconstituents found in stainless stee...
Chapter 20
Figure 20.1 Image of the effect of the weakest link in a chain; literally or f...
Figure 20.2 Schematic representation of the circulation patterns induced by eac...
Figure 20.3 At the top, a schematic illustration showing the region of a root p...
Figure 20.4 Schematic illustration showing the different discrete zones present...
Figure 20.5 Image showing an elemental‐analysis trace across the unmixed zone i...
Chapter 21
Figure 21.1 A general schematic showing the three fundamental classes or types...
Figure 21.2 An illustration showing how various parts of a typical modern autom...
Figure 21.3 A transverse macrograph showing a Cu‐to‐steel arc weld showing thre...
Figure 21.4 Schematic for a dissimilar metal joint made between chemically and ...
Guide
Cover
Table of Contents
Begin Reading
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E1
A Practical Guide to Welding Solutions
Overcoming Technical and Material-Specific Issues
Robert W. Messler, Jr.
Copyright
Author
Robert W. Messler, Jr.
Emeritus Professor
Materials Science & Engineering
Rensselaer Polytechnic Institute
Ballston Lake, NY
United States
Cover
© Marine Construction
Photos/Alamy Stock Photo
All books published by Wiley‐VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
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Preface
A convincing argument can be made that joining by mechanical fastening or design feature interlocking, adhesive bonding, or welding, including brazing and soldering, is the most important process in manufacturing and most construction because it usually occurs after a considerable value has already been added to produce the near‐net‐shaped detail parts for assembly. As welding is typically the most technically elaborate, requiring the most skilled practitioners, and accounts for about half of all joining, it almost certainly accounts for much more than half of all joining by value.1 Hence, any problem associated with welding that cannot be avoided or resolved is serious.
Major industrial sectors dependent on welding worldwide, as of 2017, included, in a descending order, the following: energy (∼23%), construction (∼20.5%), transportation (∼19.5%), process and others (∼15%), heavy machinery (∼11%), ship building (∼8%), and aerospace and defense (∼3%). Major applications include, in alphabetical order, the following: agricultural equipment; aircraft; airport support equipment; automobiles; bridges; buildings; chemical‐processing equipment; earthmoving equipment; food‐ and beverage‐processing equipment; gas, oil, and water pipelines; heavy machines; locomotives and railcars; marine power plants; mining equipment; oil and gas drilling and recovery equipment; petroleum‐processing equipment; pharmaceutical‐processing equipment; power generation equipment; railroad cars and track equipment; ships; and trucks, buses, and RVs. Although digital electronics has transformed how we live, welding has enabled us to live in our modern world.
Understanding how welding works in terms of various processes and the metallurgy is well treated in books, colleges, and continuing education. Far less well treated is why welding sometimes does not work as expected or needed, what problems can occur, and, most importantly, how to solve problems that do appear. What every practitioner of welding needs to know – and often most aggressively seeks – is how to avoid problems if possible and how to resolve problems once they have occurred.
A Practical Guide to Welding Solutions: Overcoming Technical and Material‐Specific Issues is a first! It focuses precisely on what everyone involved with welding wants to know, i.e. how to identify the root cause of a weld‐induced or welding‐related problem. To be most practical, problems are treated in three ways one may encounter them: (i) by how they manifest themselves (e.g. as distortion or defects); (ii) by where they are located (e.g. in the weld metal or in the surrounding heat‐affected zone); and (iii) by the specific material in which certain problems are most apt to occur or exclusively occur (e.g. brittle martensite formation in hardenable steels or sensitization of stainless steels).
A Practical Guide to Welding Solutions is the latest, if not the last, of the eight technical books I have written over the past 25 years. It has taken me that long to fully appreciate that engineers solve problems, so they need a book that cuts‐to‐the‐chase by focusing on solving problems with welding, welds, and weldments.
My deepest thanks to my assistant editor, Lesley Jebaraj, for all the hard work and patience with a finicky author, and to my production editor, Vishnu Priya, for her talents. Thanks too to my editor, Martin Preuss, for his enthusiasm for my idea for this book.
Sorry so late. However, as they say: Better late than never!
Robert W. Messler, Jr., Ph.D.
July 2018
FASM, FAWS
Emeritus Professor
Materials Science & Engineering
Rensselaer Polytechnic Institute
Note
1
The total global market for welding consumables alone (e.g. stick electrodes and solid and flux‐cored wires) exceeded $15B in 2017 and has been forecast to grow by 1.7× over the next decade. As the cost of labor far exceeds the cost of consumables in welding, with consumables typically accounting for only around 5% of the total cost, the total annual value of welding is staggering.
1Introduction
Welding as a process for joining materials, in general, and metals and alloys, in particular, is a double‐edged sword.1 On the one hand, welding offers one of the best methods for obtaining joints with strength comparable to (or even superior to) the physical elements being joined, with a lesser weight penalty than mechanical fastening (e.g. bolting or riveting) and a greater environmental durability than adhesive bonding (whether using organic adhesives, such as epoxies, or inorganic adhesives, such as cement). It also offers one of the assured ways of achieving leak tightness against fluids (i.e. gases and liquids), can be performed indoors or outdoors, manually or automatically (using mechanization or robots) using a wide variety of process embodiments, and, for better or worse, produces joints that are permanent.2 On the other hand, the use of welding always demands thoughtful structures and joint designs, proper equipment and consumables (e.g. shielding gases or fluxes and fillers), skilled operators, appropriate quality assurance for joint performance demands, and, most importantly, an understanding of what it takes to produce a sound weld. The latter requirement typically leads to most problems encountered with welding.
Problems with welding normally relate to unacceptable welds, i.e. welds that fail to pass nondestructive evaluation immediately following their production or welds that fail to provide intended functions in service. Some examples of the former include welded assemblies that fail to meet the geometric and dimensional criteria (i.e. do not provide needed fit and/or function), welds that contain surface or internal flaws or defects that fail to meet the required quality specifications (e.g. freedom from cracks and freedom from porosity), or welds that degraded the base material components (e.g. because of cracking, severe oxidation, hardness loss, or, contrarily, embrittlement). Also not to be ignored are welds that do not look good, as, in welding, internal “beauty” (i.e. quality) is often related to external “beauty” (i.e. appearance) the reason being a lack of care in welding, in particular, suggest a lack of care in manufacturing, in general, and, ultimately, a lack of care in design, marketing, senior management, etc. Very typically, the quality of an organization, starts at the top, with leadership by example meaning more than rules and regulations.
Figure 1.3a,b shows a couple of examples of extremely well‐executed welds made in stainless steel and an Al alloy using the gas tungsten arc process with a filler wire, whereas Figure 1.3c shows a very badly executed repair weld on a steel automobile part, and Figure 1.3d shows a badly factory‐made gas–metal arc repair weld on an Al alloy boat.
Figure 1.1 Remains of the #4 light water graphite‐moderated reactor unit at the Chernobyl Nuclear Power Plant near Pripyat in Ukraine shortly after it catastrophically failed on 26 April 1986, because of a series of errors by Soviet operators during safety check tests.
Source: Photograph by an unknown source posted by Garvey STS on en.wikibooks.org. Freely used under Creative Commons ShareAlike CC BY‐SA 4.0.
Figure 1.2 After several iterations to safely contain the highly radioactive remnants of the #4 reactor unit at the Chernobyl Nuclear Power Plant, the current New Safe Confinement or NSC was in position as of October 2017. Entombment was necessary because much of the steel structure used in the reactor containment vessel could not be disassembled as it was welded to be permanent and because it is highly radioactive. Besides safe containment of radiation, the €1.5B structure prevents damage by weather and runoff of lingering radioactive contamination.
Source: Wikipedia.com “Chernobyl new safe confinement”. Freely used under CC BY‐SA 4.0; posted by Tim Porter on 13 October 2017.
Figure 1.3 Two examples of superbly made fusion arc welds using manual gas tungsten arc (TIG) welding in (a) steel fittings and (b) Al alloy bicycle frames. In addition, two badly made welds: using a gas–metal arc to repair (c) a steel automobile part and (d) an Al alloy boat structure at a factory repair shop, with neither source being identified – fortunately for them – as images are in the public domain!
Source: The former by Scott Raabe at his Clean Cut Metal Works, Houston, TX, USA and used with his kind permission; and the latter on the website www.cycling.zanconato.com by Mike Zanconato at Zanconato Custom Cycles, Sutton, MA, USA and used with his kind permission.
To date, books that deal with the welding of metals and alloys, at least, have been found to deal with one or the other of (i) the processes employed to make welds or (ii) the metallurgy that underlies welding (i.e. welding metallurgy).3 The former seldom, if ever, mention problems with welding or welds, as welding, not welds, is their purpose. The latter typically spend the first 80–90% of the book presenting the underlying physical metallurgy that allow welds to be made in metals and alloys in the first place and that can produce sound structure in the weld (i.e. fusion zone and surrounding heat‐affected zone using fusion‐welding processes), if everything is done properly. The remaining 10–20% on what can go wrong, how to detect such short‐comings, and, finally, how to resolve any short‐coming(s). It is almost as if the author is telling a story and carefully avoiding the outcome, as in a mystery. Not surprisingly, producing high‐quality welds through welding is a mystery for many users.
This book will approach the problems with welding and the welds produced in a reverse order: starting with the problem(s) and working backward to the
cause(s) and resolution(s).4 As such, not to underestimate the ultimate importance of understanding the process (i.e. physics and chemistry) that is used to make a weld and, even more importantly, the physical metallurgy that underlies and enables the production of welds of sound quality and properties, but to simply deal with the nature of real‐world engineering in which pragmatism often prevails over detailed understanding of principles, the reason for the rising of various problems encountered will be covered briefly. Details will be left to the reader to seek information on welding metallurgy from other references. The rationale behind the approach of this book is as follows: engineers seek answers to problems and often achieve their goal(s) without having to delve into every detail. Every young engineer soon learns upon entering practice from college: the solution to a problem often only needs to be good enough, not perfect. A minimalist approach to engineering is often just as good as the minimalist approach used by a jockey to get a thoroughbred to win a race. Encourage the horse by clicks and chortles, tugs on the mane, and the light snap of a riding crop to increase the length of its stride at full gallop, without needing to know and understand all the details of equine physiology, like a veterinarian. After all, few veterinarians could ever ride a horse to victory in any race, no less in the Kentucky Derby!
This approach will work because those electing to use welding to create a structural assembly employ a backward problem‐solving technique anyway. Knowing the end goal of a challenge (e.g. to get a man onto the Moon and back to the Earth safely), they work backward from the desired goal to identify the steps, methods, and procedures needed at each step to incrementally reach that goal from some given starting point. Regrettably, this enlightenment only dawns on young engineers once they leave engineering school, where most of what they are taught is the step‐by‐step process for reaching a goal by starting from first principles and seeing where the steps lead.
The reason a backward problem‐solving approach often works, and often suffices, is that the first step will be to recognize the shortcoming (e.g. a severely distorted structure following cooling after welding; cracks in the fusion zone of a weld made in an austenitic stainless steel, such as type 304, using a recommended filler metal; cracks in the heat‐affected zone of an arc weld made in a low‐alloy steel that has been successfully welded before using the same process, same operators, and same parameters and procedures; and cracking in the base metal in some component after service). With this as a start, one could – and often does – begin to “troubleshoot” by checking each and every step for some potential cause–effect relationship. However, in this book, an organized collection of problems, categorized by the way in which they manifest themselves (i.e. distortion, cracking, porosity, and inclusions) and/or, in addition or alternatively, by where they are located (e.g. in the fusion zone with or without the use of a filler metal, in the high‐temperature portion of the heat‐affected zone or in the low‐temperature portion of the heat‐affected zone, and in the unaffected base metal), and/or a few problems predominantly, if not uniquely, associated with certain types of alloys (e.g. as‐quenched martensite in hardenable steels; reheat cracking in some age‐hardenable alloys) or, occasionally, pure metals (e.g. abnormal grain‐growth or germination in cold‐worked pure copper, as well as in some brasses), will guide the user toward the means of either avoiding such a problem in the future or, in some cases, attempting to resolve the already‐present problem. Some of these latter‐type problems may, in fact, be covered by manifestation or location but are covered here as well for easier searching by readers.
To facilitate problem solving, each chapter ends with a “Troubleshooting Guide.” Each guide tabulates the problems covered therein, the most likely cause, and a suggested approach to correct the problem. As described in Chapter 2, the chapters are divided into groups (i.e. parts) in the following manner: (i) how the most commonly encountered problems manifest themselves (Part I), (ii) where the problems with welds arise in or around a weld by location (Part II), and (iii) what problems tend to arise only in (or most often in) specific materials (Part III). This arrangement is also intended to guide users during troubleshooting.
Once again, so as not to underestimate the importance of – and, hopefully, natural technical curiosity of – an engineer from seeking to understand why something happens, each problem addressed will include a brief explanation of the cause, with readers desiring more details being encouraged to refer to other references (such as those listed at the end of this chapter).
The goal of this book is simple: help practicing engineers practice their profession and achieve their desired and needed outcomes.
In conclusion, it should not go unnoticed that all professionals – medical doctors, surgeons, attorneys at law, dentists, veterinarians, etc. – refer to what they do as a “practice.” Rather than any intent to downplay the rigor with which each obtains their formal education or to suggest any sense that what one does is take a stab in the dark to achieve the goal, what is meant is simply that only gets better and better at what they do as they do it – repeating and building upon successes and learning from and voiding any repeat of failures.
Further Reading
Althouse, A.D., Turnquist, C.H., Bowditch, W.A. et al. (2004).
Modern Welding
, 10e. London: Goodheart‐Willcox.
American Welding Society (AWS) (2001–2015).
Welding Handbook
, 9, in five volumes. Miami, FL: AWS Volume 1 – Welding Science and Technology, 2001; Volume 2 – Welding Processes, Part 1, 2001; Volume 3 – Welding Processes, Part 2, 2007; Volume 4 – Materials and Applications, Part 1, 2011; Volume 5 – Materials and Applications, Part 2, 2015.
Cary, H.B. and Helzer, S. (2004).
Modern Welding Technology
, 6e. Hoboken, NJ: Pearson Education.
Easterling, K. (1992).
Introduction to the Physical Metallurgy of Welding
, 2e. Oxford: Butterworth‐Heinemann.
Geary, D. and Miller, R. (2011).
Welding
, 2e. New York, NY: McGraw‐Hill Education.
Granjon, H. (1991).
Fundamentals of Welding Metallurgy
. Cambridge: Abington Publishing/Woodhead Publishing.
Jeffus, L. (2016).
Welding Principles and Applications
, 8e. Boston, MA: Cengage Learning.
Kou, S. (2003).
Welding Metallurgy
, 2e. Hoboken, NJ: Wiley Interscience, Wiley.
Lancaster, J.F. (1993).
Metallurgy of Welding
, 6e. Cambridge: Woodhead Publishing.
Lippold, J.C. (2014).
Welding Metallurgy and Weldability
, 1e. Hoboken, NJ: Wiley.
Messler, R.W. Jr. (2004/1999).
Principles of Welding: Processes, Physics, Chemistry, and Metallurgy
. Weinheim/New York, NY: Wiley‐VCH Verlag/Wiley.
Messler, R.W. Jr. (2004).
Joining of Materials and Structures: From Pragmatic Process to Enabling Technology
. Oxford: Elsevier Butterworth‐Heinemann.
Notes
1
From the notion that if two sides of the same blade are sharp, it cuts both ways. The metaphor may have originated in Arabic, in the expression (sayf zou hadayn, “
double
‐
edged sword
”), but it is first attested in English in the fifteenth century.
2
The permanency of a joint is desirable only if a structure is never intended to be disassembled, particularly without destroying the components of the assembly or having the process employed be simple. The inability to disassemble the welded components of the #4 light water graphite‐moderated nuclear reactor at the Chernobyl Nuclear Power Plant near Pripyat in Ukraine, which suffered catastrophic failure on 26 April 1986 (
Figure 1.1
), is a prime example, as highly radioactive remains had to be entombed in a massive concrete “Object Shelter” (
Figure 1.2
), or sarcophagus, for the next 1000 years, as the massive welded containment vessel could not be disassembled!
3
A notable exception is
Principles of Welding: Processes, Physics, Chemistry and Metallurgy
by R.W. Messler, Jr., 1st ed., 24 March 1999, Wiley VCH, ISBN‐13: 978‐0471253761 or ISBN‐10: 0471253766.
4
See Part IV, chapter 34, pp. 237–244 of
Engineering Problem‐Solving 101: Time‐Tested and Timeless Techniques
by R.W. Messler, Jr., 1st ed., 5 October 2012, McGraw‐Hill Education, ISBN‐13: 007199966 or ISBN‐10: 007199966.
2Categorization of Welding and Weld Problems
2.1 What Is Welding?
Common published and online dictionaries tend to define welding in a utilitarian sense, appropriately intended for the general public rather than for engineers, in general, and materials and welding engineers, in particular. A good and typical example found in The Merriam‐Webster Dictionary New Edition,1 advertised as “America's Best Selling Dictionary,” defines welding as: “1.a. To unite (metallic parts) by heating and allowing the metals to flow together or by hammering or compressing with or without previous heat. b. To unite (plastics) in a similar manner by heating.” Not bad, overall! In all cases, welding is a joining process intended to unite parts in order to create an assembly, usually (but not only) for structural applications. Beyond this, a specialist – like the author – could quibble over details. So, let us quibble for a moment.
Metals can, indeed, be welded – to one another! In fact, virtually, every solid metallic element, which only excludes mercury at room temperature,2 can be welded to itself and to most other metals by one means or another, with widely varying degrees of difficulty. One means for forming a joint is to heat to melt all the metals to be joined, allowing the melts to intermix and, then, solidify to form the joint. The only pressure needed is that to hold the parts to be joined in contact throughout welding. Performing welding this way is known as fusion welding. Alternatively, a joint can be created by forcing metals together using enough pressure to cause plastic deformation in one or all joint elements, either at the macroscopic (i.e. gross) level or at the microscopic level. Performing welding this way is known as non‐fusion welding.
As stated by the second part of the above definition (i.e. 1.b), plastics (more correctly, polymers and, most precisely, thermoplastic polymers) can also be joined by welding, quite correctly using some heat to cause softening, as opposed to melting. Once softened, the thermoplastics being joined move by a viscous flow under some applied pressure (at either a macroscopic or microscopic level) to unite by intimate contact and some slight intermixing in their plastic state. Welding of thermoplastic polymers is commonly referred to as plastic welding or, by specialists in polymers, thermal bonding.
Like thermoplastic polymers that progressively soften with increasing temperature, rather than melt to form a liquid from a solid at some point, glass materials (i.e. glasses) can also be welded, by what is commonly referred to as fusing. Many people have seen it performed by glassblowers attaching a handle or handles to a blown pitcher or vase or sticking a rod of glass to a figurine being made at a kiosk in a mall.
Finally, it is also possible to weld some, albeit not all, ceramic materials (i.e. ceramics). For those ceramics that melt (as opposed to sublime, directly transforming from a solid to a vapor, or that decompose upon heating at some point), certain fusion welding processes such as laser‐beam welding and electron‐beam welding can be employed. For others too high‐melting (i.e. refractory) to melt or that sublime or decompose rather than melt, welding can sometimes be accomplished in the solid state using friction, which involves microscopic viscous flow in areas heated by friction. It would suffice to say that welding of crystalline ceramics is never easy and is sometimes impossible!
Figure 2.1 shows the (a) welding of metals (here, using the gas tungsten arc process), (b) welding or thermal bonding of a thermoplastic polymer (here, using a resistance‐heated, metal‐tipped tool, commonly referred to as “an iron”), and (c) welding or fusing of glass (here, two tubes made from lead (Pb) glass using a high‐temperature oxy‐fuel torch).
Figure 2.1 Photographs showing (a) the welding of a metal (here, using the gas tungsten arc process). (b) The welding or thermal bonding of plastic (here, a thermoplastic polymer using a resistance‐heated metal‐tipped tool). (c) The welding or fusion of glass (here, using a high‐temperature oxy‐fuel torch to join two tubes made from leaded glass).
Source: Photograph in “c” is from section on “Glass and plastic welding” under Wikipedia article on “Welding,” attributed to Zaereth and used under Creative Commons CC BY‐SA 4.0.
Source: Photograph in “b” is used with permission of ECA Enterprises, Inc.
Source: Photograph in “a” is from the Wikipedia article on “Welding,” attributed to Prowelder87 and used under Creative Commons CC BY‐SA 4.0.
Figure 2.2 Schematic illustrations showing the three strong primary types of atomic bonding, i.e. ionic (a), covalent (b), and metallic (c). Ionic and covalent bonding (or a mix of the two) hold solid ceramics together. Metallic bonding (sometimes with a degree of covalent bonding) holds solid metallic materials (i.e. metals and alloys) together. Although strong covalent bonding holds the atoms in the long‐chain C‐based and Si‐based polymers together, the chains are held together in the solid material by weaker secondary van der Waals bonds that involve either permanent, induced, or fluctuating dipoles.
Source: All images are from Wikipedia, and are freely used under Creative Commons ShareAlike, CC BY SA 4.0, as follows: Ionic bonding by EliseEtc on 5 February 2012; covalent bonding by DynaBlast on 28 January 2006; and metallic bonding by Muskid on 2 May 2012.
However, it is not possible to weld a material from one fundamental class (e.g. metal, ceramic, or polymer) to a material from another fundamental class. Let us find out why.
In a most general and unambiguous sense, welding is a process in which materials of the same fundamental class or type are brought together and caused to coalesce through the formation of primary (and, occasionally, secondary) chemical bonds under the combined action of heat and pressure, without or with any filler (Messler, 1993). Most important in this definition, and in the process, is the need for the materials being joined to coalesce, by which the materials are meant to “come together to form one continuous body,” i.e. to obtain material continuity. This is made clear in the definition of welding found in the International Organization of Standardization (ISO) Standard R 857 (1958), which states that “Welding is an operation in which [material] continuity is obtained between parts for assembly, by various means,” although, by this definition, the related processes of brazing and soldering would be considered to be accomplishing welding. Some would find this perfectly acceptable, whereas others would not. For the former, all three processes – welding, brazing, and soldering – accomplish joining metals through the formation of primary metallic bonds.3 For the latter, bond formation (whether primary in nature, as is the case in metals, glasses, and ceramics, or secondary,4 as is the case in thermoplastic polymers) is considered critical for obtaining material continuity. The major difference is that the subprocesses of brazing and soldering are restricted in their use only to metals, whereas welding, as stated before, can be applied to glass, thermoplastic, and some ceramic materials as well.
The reason welding is restricted to joining materials from the same fundamental class is that the type of bonding inherent to each class is different: metallic bonding in metals, ionic or mixed ionic–covalent bonding in ceramics and glasses, and secondary molecular bonding in polymers.
In this book, the process of welding will be considered only when it is applied to metals and alloys. For this reason, before moving on, it is worth considering the achievement of material continuity in metals, i.e. metallic continuity, for the purpose of understanding some of the problems that can arise during welding and/or in welds.
It is fundamental to producing a weld between two or more pieces of material is to obtain material continuity. It suits the intent of this book to focus on obtaining continuity between crystalline (versus amorphous or semicrystalline) materials, in general, and between crystalline metals or alloys, in particular.5
As shown schematically in Figure 2.3, there are three distinct mechanisms for obtaining metallic continuity, as articulated by Granjon (1991), that are employed in welding by one process embodiment or another: (i) solid‐phase plastic deformation, without or with dynamic recrystallization (as with cold welding and ultrasonic welding and with various forms of hot pressure or forge welding, respectively), (ii) diffusion (as with diffusion welding, sometimes called diffusion bonding), and (iii) melting and solidification (as with all forms of fusion welding using exothermic chemical or electric arc, plasma, beam, or resistance heat sources).
Figure 2.3 Schematic illustrations showing the three distinct ways in which metallic continuity can be achieved during welding by bringing atoms together using, first, (a) cold plastic deformation and lattice strain or (b) hot deformation and dynamic recrystallization; second, (c) solid‐phase diffusion across the original interface(shown by a dashed line); and, third, (d) liquid provided by melting the parent materials (or substrates), without or with an added filler, and (e) establishing bond upon epitaxial solidification of this liquid.
Source: Messler (1999), figure 2.1, p. 19. Used with permission of John Wiley & Sons.
Each of these three mechanisms involves bringing the atoms of one substrate into intimate contact with the atoms of another substrate in order to allow the formation of metallic bonds in sufficiently large numbers to produce a strong joint in the final solid state. Atoms from one component can be forced to come into contact with the atoms of another component using pressure, with the pressure required being made lower by heating, as is the case of the so‐called pressure welding in the broader class of non‐fusion welding. Atom movement, and attendant bond formation, can be facilitated by diffusion during the process of dynamic recrystallization in hot pressure processes, including friction welding. An intermediary filler metal is seldom required in non‐fusion welding, but may be useful when the substrate metals are difficult to plastically deform.
As an alternative to relying on plastic deformation to move atoms of mating substrates into intimate contact, atoms can be moved from one substrate to mix with atoms from another substrate by melting a portion (i.e. some small volume) of each substrate or, if necessary, a supplemental metal can be added in the molten form to fill any gap and help melt some portion of each substrate via contained superheat. In either case, the process is known as fusion welding; the former, without a filler, is said to be autogenous.
Figure 2.4 shows one classification or taxonomy of the major welding processes, including the related processes of brazing and soldering, although there are other essential similar schemes.
Figure 2.4 A typical comprehensive scheme for classifying welding processes. This scheme shows how the related processes of brazing and soldering fit into the taxonomy.
Source: Messler (1999), figure 2.3, p. 28. Used with permission of John Wiley & Sons.
With welding defined, let us look at a weld, which is, after all, the intent of welding.
2.2 Microstructural Zones of Welds
Welding is used to fabricate new equipment or structures by building up detail parts (e.g. mill products, such as U‐channels or I‐beams, near‐net‐shaped forgings of net‐shaped castings, or machined components) into a unitized assembly or weldment or to repair equipment or structures that have suffered loss of metal by mechanical wear or chemical corrosion or have cracked or fractured in service, regardless of whether the original was assembled by welding or not. The former is known as OEMwelding (original equipment manufacturer), and the latter is known as repair welding. Although OEM welding might be accomplished using either a fusion or a non‐fusion welding process, repair welding is almost always performed using a fusion welding process.
The fundamental types of welds used in both OEM and repair welding to accomplish joining include those that are used to make butt joints, corner joints, tee or T‐joints, lap joints, and edge joints. These are shown schematically in Figure 2.5. In repair welding, fusion welding may additionally be used to fill a machined out or gouged out volume formerly containing a defect (e.g. crack). The other major application of welding than for joining components is for either restoring metal lost by wear or corrosion or, alternatively, for providing protection against wear or corrosion. Both are known as surface welding. For corrosion protection, the process is typically called weld cladding, while for wear protection, the process is typically called hard‐facing.
Figure 2.5 Schematic of the cross section of a hypothetical weldment showing the five fundamental types of joints found in welding: butt joint, corner joint, tee joint, lap joint, and edge joint. Although fusion welds are shown, similar joints can be made using non‐fusion welding, albeit not by every non‐fusion welding method and often with minor adjustments.
An underlying relationship in materials engineering is known as the structure–property–processing relationship or, more correctly, interrelationship, as each of the three affects the other in all directions. Whenever welding is used to make a joint, one needs to consider how the joint may differ in structure at the microscopic level (i.e. microstructure) and, thus, exhibit different properties as structure determines properties in materials.
The third key factor in this interrelationship is processing, which, in the broadest sense, could involve net‐shape creation by casting from a melt to form a cast product; deformation processing
