Effect of Prestrain on Stress Corrosion Cracking of Type 304 Stainless Steel by Means of the Stress Relaxation Method^*

The relationship between the susceptibility of stress corrosion cracking (SCC) and the amount of deformation structures in Type 304 stainless steel in an H₂SO₄/NaCl solution system at room temperature was investigated by means of the stress relaxation method. SCC was observed in the prestrained specimens, whereas no cracking occurred in specimens without prestraining. The number of cracks was affected by the amount of deformation structures, which varied according to the annealing temperature after prestraining or according to the prestraining temperature. The results of magnetic measurements on the prestrained specimens as a function of the annealing temperature showed that the cracking region was in good agreement with the range of existence of strain induced α′-martensites. Transmission electron microscope observation showed that ϵ- and α′-martensites formed by prestraining at temperatures below 413 K (140 C) dissolved in preference to the austenite matrix. A strain induced martensite in Type 304 stainless steel seems to precede cracking in this system.