Synergistic effects of impurities and sensitisation on inter granular corrosion and stress corrosion cracking in type 316H austenitic stainless steel

Abstract

AbstractGrain boundary impurity segregation and sensitisation by chromium depletion have been identified as the major metallurgical processes which impair the resistance of austenitic alloys to intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC). The present paper reports an investigation into the conjoint effect of these processes on the corrosion and IGSCC properties of two alloy steels of type 316H, one a conventional heat and the other a high purity heat containing very low levels of phosphorus and sulphur. The susceptibility to IGC and IGSCC was measured using a Huey test in 65 vol.-% boiling HNO3 and a stress corrosion cracking test in an aerated aqueous solution containing NaCI at 90°C. The results obtained show that the high purity steel exhibits weight losses about 40 times smaller and elongation values about 8 times greater than the conventional steel. The reasons for this spectacular improvement are discussed and rationalised on the basis of differences in the grai...