Study on the deformation mechanism of the inflection point in tensile curve of nano/ultrafine-grained austenite stainless steel rolled at different temperature

Nano/ultrafine-grained (NG/UFG) 304 austenite stainless steel can be fabricated through a phase reversion transformation after severe deformation at cryogenic and room temperatures. Here, to understand the deformation mechanisms, a function of rolling temperature was established to determine the typical inflection point of transformation-induced plasticity. The typical inflection point in the tensile curve of annealed NG/UFG 304 austenite stainless steel was found after rolling at room-temperature (RTA) rather than at cryogenic temperatures (LTA). Our results show that tensile deformation of LTA was governed by twin boundaries and a phase reversion transformation compared to RTA. As a result, the increased ultimate strength of LTA can be attributed to the effect of twin boundaries, twin size, and twin quantity on dislocation motion. The presence of twin boundaries suppresses the softening effect induced by martensite transformation. •An inflection point was found during tensile tests of room temperature-rolled steel.•The reason typical inflection points are not seen in LTA samples is explained.•The LTA sample the strength increased without losing plasticity.