Relation between Intergranular Stress Corrosion Cracking and Intergranular Corrosion of Sensitized 304 Stainless Steel in Acid Solutions

Intergranular attack behaviour of sensitized 304 stainless steel, e.g., the effects of potential and stress on intergranular attack, was studied in both polythionic acid and 15%H2SO4 solutions, and the difference between intergranular stress corrosion cracking (IGSCC) and intergranular corrosion behaviours was discussed. The results obtained are as follows:(1) Susceptibility to IGSCC in the polythionic acid solution was greatest in the potential range of −0.1 to 0 V (vs SCE), and intergranular corrosion occurred between −0.4 and −0.1 V. No intergranular corrosion was observed at the corrosion potential.(2) The formation of a sulfide film plays an important role in the mechanism of IGSCC in the polythionic acid solution, and it is considered that the destruction of the film by stress is essential to the occurrence of intergranular attack at the corrosion potential.(3) In 15%H2SO4 solution at 373 K, intergranular corrosion occurred in the potential range of −0.2 to +0.1 V. Stress is not necessary for the intergranular attack, although it accelerates intergranular corrosion.(4) The mechanism was proposed on the intergranular attack of sensitized stainless steel in the polythionic acid solution.