Arc Welding of Specific Steels and Cast Irons

Arc Welding of Heat-Resistant Low-Alloy Steel
Fig. 2.7 shows the effects of immediate postheating (IPH) applied on the weld right after
welding finished and postweld heat treatment (PWHT) on the diffusible hydrogen distribution
in a thick-section 2.25Cr-1Mo steel weld. It obviously shows that IPH and, to a greater extent,
PWHT reduce the concentration of diffusible hydrogen in the weld. Consequently, the cracking
susceptibility of the weld can be reduced.
min
(IPH)
(PWHT)
Fig.2.7 — The effects of postweld
heat treatment (PWHT) and
immediate postheating (IPH) on the
diffusible hydrogen distribution in a
thick-section 2.25Cr-1Mo steel weld
(Preheating and interpass
temperature: 200℃)
Distance from the weld bottom (mm)
Hydrogen content (ml/100g)
2.3 Hot cracking
The occurrence of cracks at high temperatures during solidification of heat-resistant
low-alloy steel welds is affected by the weld chemical composition, the weld configuration, and
the weld stresses. This type of cracking is known as hot cracking. It is referred to as a crack
that develops in the high temperature range between liquidus and solidus or at temperatures
little lower than the solidus of the weld. Hot cracks often occur at the grain boundaries of the
weld. Hot cracking can be prevented by controlling the following:
The amounts of impurity elements such as sulfur and phosphorus
The weld configuration
The amount of heat input
Fig. 2.8 shows the effect of weld configuration on the hot crack susceptibility of the weld. It
suggests that the W/H ratio should be more than 1.0 in order to prevent hot cracking. Fig. 2.9
shows the effect of heat input on the hot crack susceptibility of the weld. It suggests that heat
input should be low in order to prevent hot cracking. Photo 2.1 shows a macroscopic structure
of the weld which contains hot cracks.
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