Intergranular Corrosion of Nonsensitized Austenitic Stainless Steels — 1. Environmental Variables

Abstract

Abstract Intergranular corrosion of nonsensitized stainless steels is reviewed, with emphasis on corrosion experienced in nitric-dichrornate solutions. Electrical resistance changes occurring during corrosion of Type 304 stainless ' steel in nitric-dichromate solutions are used to measure the rate of intergranular attack. Effects of HN03 concentration, Cr+6 concentration, temperature and stress on the intergranular corrosion reaction have been studied. The over-all corrosion reaction is found to consist of an incubation period, followed by a penetration period in which the rate of intergranular dissolution is linear. Measured activation energies for incubation and penetration periods are identical. The effect of applied stress is to increase both incubation and penetration rates. Low stress levels have greatest effect on the incubation rate, while high stress levels have greatest effect on the penetration rate. Appreciable grain boundary hardening is observed in nonsensitized Type 304 stainless steel. The grain boundary hardening is attributed to adsorbed impurities at grain boundaries. This segregation presents another variable which may be important in this type of intergranular attack.