Crack Analysis of T91/TP347HFG Dissimilar Steel Welding Joint

T91/TP347HFG dissimilar steel welding joints of superheater in a heat-engine plant cracked during service. The samples obtained from the normal and cracked welding joints were examined by the metallographic microscopy, scanning electron microscopy, and micro hardness testing to make comparison and analyze the cracking reason. The results showed that the improper process of welding and postweld heat treatment led to the formation of quenched structure and made the heat-affected zone at the T91 side have greater brittleness. At the same time, a larger range of welding parameter made the heat-affected-zone wider, from which the cracks initiated and propagated under certain stress. Eventually, the dissimilar steel welded joints cracked and failed.