Microstructure and corrosion properties of nitrogen stainless steel 316L produced by hipping

Potentiodynamic polarisation and intergranular immersion tests were conducted to study the corrosion behaviour of steel 316L with 0.1 and 0.23%N, prepared by hot isostatic pressing. For comparison the corrosion resistance of conventional, nitrogen free rotted 316L steel was also examined. Specimens were subjected to solution treatment at 1050 and 1200degreesC for 2 h followed by water quenching. The effect of aging temperature and time, in the sensitisation rage 500-900degreesC, on the microstructure and corrosion behaviour was also investigated. The alloy with 0.23%N showed the highest corrosion resistance in the as hipped, as well as solution treated conditions. Addition of nitrogen causes retardation of intergranular corrosion upon aging at 500 and 900degreesC. When aging was performed at 700 C for 2 h or more, the alloy with 0.23%N suffered severe intergranular corrosion attack. The changes in corrosion behaviour of nitrogen containing alloys with different heat treatment conditions were attributed to the presence of Cr,Ti(C-x,N-y) precipitates with variable chromium and titanium contents depending on the aging conditions.