Welding Metallurgy

Sindo Kou

• Editore: Wiley
• Anno: 2020
• ISBN:
  9781119524915
• Edizione: 3
• Argomento: Tecnologia e ingegneria
• Categoria: Scienza dei materiali

Discover the extraordinary progress that welding metallurgy has experienced over the last two decades

Welding Metallurgy, 3 rd Edition is the only complete compendium of recent, and not-so-recent, developments in the science and practice of welding metallurgy. Written by Dr. Sindo Kou, this edition covers solid-state welding as well as fusion welding, which now also includes resistance spot welding. It restructures and expands sections on Fusion Zones and Heat-Affected Zones. The former now includes entirely new chapters on microsegregation, macrosegregation, ductility-dip cracking, and alloys resistant to creep, wear and corrosion, as well as a new section on ternary-alloy solidification. The latter now includes metallurgy of solid-state welding. Partially Melted Zones are expanded to include liquation and cracking in friction stir welding and resistance spot welding. New chapters on topics of high current interest are added, including additive manufacturing, dissimilar-metal joining, magnesium alloys, and high-entropy alloys and metal-matrix nanocomposites.

Dr. Kou provides the reader with hundreds of citations to papers and articles that will further enhance the reader's knowledge of this voluminous topic. Undergraduate students, graduate students, researchers and mechanical engineers will all benefit spectacularly from this comprehensive resource.

The new edition includes new theories/methods of Kou and coworkers regarding:

· Predicting the effect of filler metals on liquation cracking

· An index and analytical equations for predicting susceptibility to solidification cracking

· A test for susceptibility to solidification cracking and filler-metal effect

· Liquid-metal quenching during welding

· Mechanisms of resistance of stainless steels to solidification cracking and ductility-dip cracking

· Mechanisms of macrosegregation

· Mechanisms of spatter of aluminum and magnesium filler metals,

· Liquation and cracking in dissimilar-metal friction stir welding,

· Flow-induced deformation and oscillation of weld-pool surface and ripple formation

· Multicomponent/multiphase diffusion bonding

Dr. Kou's Welding Metallurgy has been used the world over as an indispensable resource for students, researchers, and engineers alike. This new Third Edition is no exception.

Part I
Introduction

1
Welding Processes

This chapter is intended to be a brief introduction to most fusion welding processes and some solid‐state welding processes. The former includes gas welding, arc welding, laser‐beam welding, electron‐beam welding, and resistance spot welding (RSW). The latter includes friction stir welding (FSW), friction welding, explosion welding (EXW), magnetic pulse welding (MPW), and diffusion welding. The advantages and disadvantages of these processes are discussed.

1.1 Overview

1.1.1 Fusion Welding Processes

Fusion welding is a joining process that uses fusion of the base metal to make the weld. It is the most widely used joining process. Four major types of fusion welding processes will be discussed: gas welding, arc welding, high‐energy beam welding, and resistance spot welding. These processes are listed as follows:

1. (a) Gas welding:
   Oxyacetylene welding (OAW)
2. (b) Arc welding:
   Shielded metal arc welding (SMAW)
   Gas−tungsten arc welding (GTAW)
   Plasma arc welding (PAW)
   Gas−metal arc welding (GMAW)
   Flux‐cored arc welding (FCAW)
   Submerged arc welding (SAW)
   Electroslag welding (ESW)
3. (c) High‐energy beam welding:
   Electron beam welding (EBW)
   Laser beam welding (LBW)
4. (d) Resistance spot welding:
   Resistance spot welding (RSW)

There is no arc in ESW except during initiation of the process. For convenience of discussion, however, it is grouped with arc welding processes.

1.1.1.1 Power Density of Heat Source

In fusion welding except for RSW, the power density is the power of the heat source divided by its cross‐sectional area at the workpiece surface. Consider directing a 1.5‐kW hair drier very closely to a 304 stainless steel sheet 0.25 mm thick. Obviously, the power spreads out over an area of roughly 50 mm diameter or greater, and the sheet just heats up gradually but will not melt. With GTAW at 1.5 kW, however, the arc can concentrate on a small area of about 5 mm diameter and can produce a weld pool. This example illustrates the importance of the power density of the heat source in welding.

As shown schematically in Figure 1.1, the size of the heat source increases from high‐energy beam welding to arc welding and to gas welding. The power density of the heat source and hence its ability to melt and weld deep decrease in the same order. As shown in Figure 1.2, as the power density of the heat source increases, the amount of heat absorbed by the workpiece before welding is completed decreases. A gas flame tends to heat up the workpiece so slowly that, before any melting occurs, a large amount of heat is already conducted away into the bulk workpiece. Excessive heating can damage the workpiece, weakening and distorting it. Contrarily, the same material heated by a sharply focused electron or laser beam can melt or even vaporize to form a deep keyhole instantaneously. This allows welding to be completed before much heat is conducted away into the bulk workpiece to cause any damage [1].

Figure 1.1 The size of the heat source and its effect on welding.

Figure 1.2 Heating of and hence damage to workpiece vs. power density of heat source.

Therefore, the advantages of increasing the power density of the heat source include deeper weld penetration, higher welding speed, and better weld quality with less damage to ...