Influence of Nitrogen Addition to Duplex Stainless Steels

Abstract

The influence of nitrogen on structure, notched toughness and pitting corrosion resistance of duplex stainless steels was investigated, and a discussion was focussed on the role of N and Mo to pitting corrosion resistance.
Pitting corrosion test by immersion method showed that the corrosion rate of duplex stainless steels decreased with increasing N content under the presence of Mo. If Mo is absent in the N-bearing steels, beneficial effect of N, which can improve the pitting corrosion resistance of austenite, was not observed.
Corrosion pits tended to initiate at α/γ interface in the specimens water-quenched, and it was considered that the α/γ interfacial strain was responsible to enhanced corrosion rate of N-free steels.
The presence of Mo in N-bearing steel was thought not only to suppress the intergranular precipitation of nitride during cooling, but also to retard the pitting growth by lowering the active dissolution rate of anodic ferrite phase.