Effect of Local Segregation of Phosphorous on Intergranular Corrosion of Type 310 Stainless Steel in Boiling Nitric Acid

The effect of phosphorous on intergranular corrosion of type 310 stainless steel at transpassive potential was investigated using phosphorous added ultra high purity type 310 stainless steel. Intergranular corrosion depth was measured by scanning electron microscopic observation. Grain boundaries were observed using three dimensional atom probe. Intergranular corrosion was observed on phosphorous added stainless steel. The sample heat treated at 600℃ showed severe integranular corrosion morphology. Observation by three dimensional atom probe revealed that grain boundary with high dissolution rate had segregated zone of chromium and phosphorous about 5nm in width, on the other hand, grain boundary with low dissolution rate had no segregated zone. From these results, it is suggested that intergranular corrosion of phosphorous added type 310 stainless steel at transpassive potential is affected by segregation of phosphorous and chromium along grain boundaries.