Arc Welding of Specific Steels and Cast Irons

Arc Welding of Heat-Resistant Low-Alloy Steel
2.2 Cold cracking
Cold cracking may occur in welds of heat-resistant low-alloy steel, caused by the combined
effects of low ductility of the weld, residual stresses and diffusible hydrogen in the weld. Cold
cracking is also known as hydrogen-assisted cracking and hydrogen-induced cracking. It
generally occurs at temperatures below 200℃ immediately upon cooling, or after a period of
several hours or days (Delayed cracking). The time taken before a cold crack occurs depends
on the type of weld, the magnitude of welding stress (or plate thickness), and the hydrogen
content of the weld and heat-affected zone. Fig. 2.4 shows the critical diffusible hydrogen
concentration in relation to the cold crack occurrence in submerged arc welded 2.25Cr-1Mo
steel multiple-pass welds. It reveals that the highest hydrogen concentration, which causes
cold cracking, is seen in the area around 20 to 30mm below the surface of the weld.
Diffusible hydrogen concentration (ml/100g)
Distance from the top surface (mm)
Fig. 2.4 — The effect of concentrated diffusible hydrogen on cold
cracking for 2.25Cr-1Mo submerged arc weld metal
Cold cracking can be prevented by using low-hydrogen welding consumables to minimize
diffusible hydrogen in the weld, preheating and postheating to release diffusible hydrogen
from the weld, and proper welding procedures to minimize stress concentration in the weld.
Fig. 2.5 shows the y-groove restraint cracking test results of various steel welds including
heat-resistant low-alloy steel welds. It clearly shows that preheating can prevent cold cracking
and the minimum preheating temperature to prevent cold cracking depends on the type of
steel. The heat-resistant low-alloy steel welds require higher preheating temperatures when
compared with other types of steels. Table 2.1 shows the chemical compositions and
mechanical properties of the steels used in this test. Fig. 2.6 shows that a thicker plate (up to
150mm) requires higher preheating temperatures to prevent cold cracking.
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