Effect of Strain-Induced α'-Martensite on Stress Corrosion Cracking Susceptibility of SUS 301 Stainless Steel

Abstract

The present investigation has been carried out to make clear the effect of strain-induced α'-martensite on stress corrosion cracking (SCC) susceptibility of austenitic stainless steel.
The specimens were prepared from SUS 301 stainless steel sheets with metastable austenite, and were given the prestrain of 10, 20 and 40% at the temperature -80 to 80°C. Then the SCC susceptibility of these specimens was evaluated in boiling 35% MgCl₂ solution under the applied stress of 35kg/mm².
The change of α'-martensite content depending on prestrain and prestraining temperature gave a remarkable effect not only on the mechanical properties but also on the SCC susceptibility. It was found that the SCC susceptibility of prestrained specimens extremely decreased when α'-martensite content was within a specific range: e.g., about 10∼90% on 20% prestrained specimens. On the other hand, the fracture surface morphology was considerably influenced by the change of α'-martensite content. In the case of small α'-martensite content, the fracture mode changed from transgranular cracking with typical fan-shaped pattern to mixed intergranular-transgranular cracking. In the case of large α'-martensite content, however, transgranular cracking was observed, which seemed to be caused by the dissolution of martensite-lath. Based on these results, the possibility of hydrogen cracking was discussed in the SCC behavior of 20% prestrained specimens under anodic and catholic polalization.