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 d rastically improved by modified postweld heat treatments (Mod PWHT, he at treatment at 963 K for 25.2 ks followed by annealing at 813 K for 5 4 ks and subsequent air cooling (after overlay welding). Severe disbon ding tests under hydrogen atmosphere have revealed that the Mod PWHT s teel produced hardly cracks at the interface; whereas, the conventiona l PWHT steel developed large cracks. This was due to the fact that the Mod PWHT suppresses the appearance of high carbon fresh martensite, w hich increases the susceptibility to disbonding significantly.