Characterisation of 9% Cr-1% Mo Ferritic Steel Weldments for Susceptibility to Corrosion During Hydrogen Charging and Repair-Welding

Weldments of 9%Cr-1%Mo steel may become prone to accelerated localized corrosion attack if inadequately post-weld heat treated. The phenomenon is mechanistically identical to that observed in austenitic stainless steels where Cr-depleted regions along the grain boundaries are attacked in preference to the grain interiors. This paper describes a systematic study carried out to investigate the influence of initial microstructure, heat input, PWHT, accelerated ageing and repair-welding on the sensitization behaviour of 9%Cr-1%Mo steel weldments. It was found that repair-welding without PWHT resulted in the sensitization of the weld metal and base metal heat affected zones. Ageing of such repaired weldments led to the sensitization of both weld metal and HAZ. This study has also established the increased susceptibility of the sensitized regions to hydrogen induced cracking thus indicating that the region is microstruci.’rally weaker, where cracking due to environment may initiate preferentially.