Metallography: Principles and Practices - ASM International

Metallography: Principles and Practice (#06785G)
Author(s): George F. Vander Voort
34 METALLOGRAPHY
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Figure 1-23 Macroetching used to reveal the influence of weld parameters on penetration depth and
shape. Top example shows GMA (gas-metal arc) welds at a heat input of 45 kJ/in using atmospheres of
100% C02, argon plus 25% C02, and argon plus 2% 02 (left to right). Bottom example shows
submerged arc welds using heat inputs of 90, 60, and 30 kJ/in (left to right). (The etchant was 10%
aqueous HNOv)
by the type of process employed, the operating parameters, and the materials
used. Thus, metallography is a key tool in weld quality studies. Key terms in
describing the macrostructure of fusion welds are the basic three components—
the weld metal ("nugget"), the heat-affected zone (HAZ), and the base metal.
Within the weld metal and the heat-affected zone, there are changes in composition,
grain size and orientation, microstructure, and hardness. Thus one observes
significant variations in microstructure as the weldment is scanned.
Macroetching is frequently employed to determine the influence of various
changes in weld parameters on the size and shape of the weld metal, on depth of
penetration, on weld structure, and on hardness. Figure 1-23 (top) shows the
influence of the protective atmosphere on the shape and penetration of the weld
metal. A carbon-manganese plate steel was welded using the gas-metal arc
(GMA) procedure with a heat input of 45 kJ/in and 0.045-in diameter A675 filler
metal wire. Three atmospheres were used: 100% C02 (left), argon plus 25% C02
(center), and argon plus 2% 02 (right). Also shown in Fig. 1-23 (bottom) are three
submerged arc weldments that were made using heat inputs of 90 (left), 60
(center), and 30 kJ/in (right). These examples clearly show how welding parameters
can alter the size, shape, and penetration of the weldment.
Figure 1-24 illustrates the macrostructure of a weld in beryllium. This sample
was polished and the macrostructure was revealed using crossed polarized light.
Figure 1-25 shows the macrostructure of flash-welded titanium after etching.