Investigation on the nucleation mechanism of deformation-induced martensite in an austenitic stainless steel under severe plastic deformation

The nucleation mechanism of deformation-induced martensite was investigated by x-ray diffraction and transmission electron microscope in an ultra-low carbon austenitic stainless steel deformed by equal channel angular pressing at room temperature. It was found that two types of martensite transformation mechanism, stress-assisted and strain-induced, occurred via the sequences of γ (fcc) → ɛ (hcp) → α′ (bcc) and/or γ → α′. In both cases, the crystallographic relationships among γ, ɛ, and α′ followed the Kurdjumov-Sachs orientation relationships: {111}_γ //{0001}_ɛ //{011}_α′ and 〈110〉_γ//〈1120〉_ɛ//〈111〉_α′.