Effect of Modified Postweld Heat Treatment on Disbonding of 2.25 Cr-1 Mo Steel Overlay Welded with Austenitic Stainless Steel

The susceptibility to disbonding which occurs at the interface of 2.25 Cr-1 Mo steel overlay welded with austenitic stainless steel can be drastically improved by modified postweld heat treatments (Mod PWHT, heat treatment at 963 K for 25.2 ks followed by annealing at 8l3 K for 54 ks and subsequent air cooling (after overlay welding). Severe disbonding tests under hydrogen atmosphere have revealed that the Mod PWHT steel produced hardly cracks at the interface; whereas, the conventional PWHT steel developed large cracks. This was due to the fact that the Mod PWHT suppresses the appearance of high carbon fresh martensite, which increases the susceptibility to disbonding significantly.