Mechanism of Underclad Cracking—Combined Effects of Residual Strain and Heat-Affected Zone Ductility

The mechanism of heat-affected zone cracking under weld overlay cladding has been investigated for four kinds of ferritic steel overlay-welded with austenitic stainless steel. Cracking occurs during postweld heat treatment because the ductility of the heat affected zone is insufficient to relieve internal stress. This low ductility is caused by the combined effects of fine carbide precipitate and coarse-grained structure. High internal stresses at postweld heat treating are due to the combined effects of residual stress as well as thermal stress resulting from the difference in thermal expansion coefficients of base metal and cladding material. Means for preventing cracking during fabrication are described, based on this cracking mechanism.