MICROSTURE AND PITTING CORROSION RESISTANCE OF UNS S32304 DUPLEX STAINLESS STEELS WELDED JOINT WITH PLASMA-ARC WELDING

Microstructure and pitting corrosion resistance of UNS S32304 duplex stainless steels welded joint with plasma-arc welding (PAW) were studied by means of OM, SEM, energy dispersive X-ray spectroscopy (EDX) and potentiostatic electrochemical technique. The results show that the microstructures of the heat affected zone (HAZ) and fusion zone differ from the base metal greatly, with ferrite fraction greater than 70%. Furthermore, a lot of nitrides are precipitated at the interface between ferrite and austenite phases and inside the ferrite grains. Consequently, pitting corrosion resistance of the welded joint declines obviously and pitting preferentially occurs at ferrite phase in the high temperature HAZ near the fusion line.