Page 29-1

The Metallurgy of Welding; Welding Design and Process

Selection

CHAPTER 7-3

Page 29-2

Fusion Weld Zone

Figure 29.1 Characteristics of a typical fusion weld zone in oxyfuel gas and arc welding. See also Figs. 27.16 and 28.14.

Page 29-3

Grain Structure in Shallow and Deep Welds

(a) (b)

Figure 29.2 Grain structure in (a) a deep weld (b) a shallow weld. Note that the grains in the solidified weld metal are perpendicular to the surface of the base metal. In a good weld, the solidification line at the center in the deep weld shown in (a) has grain migration, which develops uniform strength in the weld bead.

Page 29-4

Incomplete Fusion

Figure 29.6 Low-quality weld beads, the result of incomplete fusion. Source: American Welding Society.

Page 29-5

Discontinuities in Fusion Welds

Figure 29.7 Schematic illustration of various discontinuities in fusion welds. Source: American Welding Society.

Page 29-6

Cracks in Welded Joints

Figure 29.8 Types of cracks (in welded joints) caused by thermal stresses that develop during solidification and contraction of the weld bead and the surrounding structure. (a) Crater cracks. (b) Various types of cracks in butt and T joints.

Page 29-7

Distortion After Welding

Figure 29.10 Distortion of parts after welding: (a) butt joints; (b) fillet welds. Distortion is caused by differential thermal expansion and contraction of different parts of the welded assembly.

Page 29-8

Residual Stresses Developed During Welding

Figure 29.11 Residual stresses developed during welding of a butt joint. Source: American Welding Society.

Page 29-9

Overview of Commercial Joining Processes

TABLE 29.1 Overview of Commercial Joining Processes*Joining Process

Brazing

MaterialThick-

ness

SMAW

SAW

GMAW

FCAW

GTAW

PAW

ESW

EGW

RW

FW

OFW

DFW

FRW

EBW

LBW

TB

FB

IB

RB

DB

IRB

DFB

Carbon steel SI

MT

xxxx

xxxx

xxxx

xxx

xx

x x

xxx

xxxx

xxxx

xxx

xxxx

xxx

xxx

xxxx

xxx

xx

xx

x xxxx

Low-alloysteel

SI

MT

xxxx

xxxx

xxxx

xxx

xx

x

xx

x

xxxx

x xxxx

xxx

xxxx

xxx

xxxx

xxx

xxx

x x x xxx

Stainlesssteel

SI

MT

xxxx

xxxx

xxxx

xxx

xx

x

xxx x

xx

xxxx

x xxxx

xxx

xxxx

xxx

xxx

xxxx

xxx

x x x xxxx

Cast iron IMT

xxx

xx

xx

xx

xxx

xx

xxx

xx

xxx

Nickel andalloys

SI

MT

xxxx

xx

xxxx

xx

xxx

x

xx

xxxx

xxxx

xxxx

xxx

xxx

xxxx

xx

x x x xxxx

Page 29-10

Overview of Commercial Joining Processes (cont.)

TABLE 29.1 (continued)Joining Process

Brazing

MaterialThick-

ness

SMAW

SAW

GMAW

FCAW

GTAW

PAW

ESW

EGW

RW

FW

OFW

DFW

FRW

EBW

LBW

TB

FB

IB

RB

DB

IRB

DFB S

Aliminumand alloys

SI

MT

xxxx

xxxx

xxx

x

x x

xx

xxxx

x xx

xxx

xxxx

xx

xxx

xxxx

x x xxx

x xxxx

xx

Titaniumand alloys

SI

MT

xxxx

xxx

xxx

x xxxx

xxxx

xx

xxxx

xxx

x

xxxx

x x xxxx

Copper andalloys

SI

MT

xxxx

x xx

xxxx

xx

xxxx

xxx

xxxx

x xx

xxxx

xx

Magnesiumand alloys

SI

MT

xxxx

xx

xx x

xx

xx

xxxx

xxx

xx

xxx

xx

xxx

Refractoryalloys

SI

MT

xx

x xx

x

x

xxx

xx

xx

xx

x x x xx

*This table is presented as a general survey only. In selecting processes to be used with specific alloys, the readershould refer to otherappropriate sources of information.Source: Courtesy of the American Welding Society.

Page 29-11

Overview of Commercial Joining Processes (cont.)

TABLE 29.1 (continued)

LegendProcess code Thickness

SMAW—Shielded Metal-Arc WeldingSAW—Submerged Arc WeldingGMAW—Gas Metal-Arc WeldingFCAW—Flux-Cored Arc WeldingGTAW—Gas Tungsten-Arc WeldingPAW—Plasma Arc WeldingESW—Electroslag WeldingEGW—Electrogas WeldingRW—Resistance WeldingFW—Flash WeldingOFW—Oxyfuel Gas WeldingDFW—Diffusion Welding

FRW—Friction WeldingEBW—Electron Beam WeldingLBW—Laser Beam WeldingTB—Torch BrazingFB—Furnace BrazingIB—Induction BrazingRB—Resistance Brazing DB—Dip BrazingIRB—Infrared BrazingDFB—Diffusion BrazingS—Soldering

S—Sheet: up to 3 mm in.BI—Intermediate: 3 to 6 mm A in.BM—Medium: 6 to 19 mm A in.BT—Thick: 19 mm A in. B and up

Page 29-12

Destructive Techniques

Figure 29.12 Two types of specimens for tension-shear testing of welded joints.

Figure 29.13 (a) Wrap-around bend test method. (b) Three-point bending of welded specimens--see also Fig. 2.11.

Page 29-13

Testing of Spot Welds

Figure 29.14 (a) Tension-shear test for spot welds. (b) Cross-tension test. (c) Twist test. (d) Peel test; see also Fig. 30.8.

Page 29-14

Welding Design Guidelines

Figure 29.15 Design guidelines for welding. Source: J. G. Bralla (ed.), Handbook of Product Design for Manufacturing. Copyright ©1986, McGraw-Hill Publishing Company. Used with permission.

Page 29-15

Standard Identification and Symbols for Welds

Figure 29.16

Page 29-16

Weld Design Selection

Figure 29.17