Abstract
The mechanism of localized corrosion and phase transformation of tube-to-tube sheet welds of hyper duplex stainless steel (HDSS) were investigated in acidified chloride environments. The HDSS tube-to-tube sheet welded with an Ar shielding gas without a filler metal, which increases the ferrite content, Cr2N and pitting resistance equivalent number (PREN) difference between the two phases, demonstrated the lower corrosion resistance than that with Ar shielding gas with a filler metal. The pitting corrosion of the weld metal (WM) in the HDSS tube-to-tube sheet welded using a pure Ar shielding gas with a filler metal occurred at the dendrite core (DC) that Cr and Mo were depleted and at the region adjacent to Mu phase that Mo and W were depleted. The localized corrosion was selectively initiated at the α-phase because the PREN value of the α-phase was much smaller than that of the γ-phase, irrespective of the chemical compositions of the shielding, and the areas of the WM, heat affected zone (HAZ) and base metal (BM) (except for the WM in the HDSS tube-to-tube sheet welded using Ar with a filler metal).
