Microstructure Evolution and Mechanical Properties of Heterogeneous Nano/Ultrafine‐Grained Austenitic Stainless Steel Prepared by Low‐Temperature Rolling and Annealing

Abstract

An 18Cr–8Ni austenitic stainless steel is subjected to cold rolling at room temperature and low temperature (−50 °C) under different amounts of deformation. The samples cold rolled to 70% deformation are then annealed to obtain nano/ultrafine‐grained steels with a good strength–ductility combination. The effects of cold rolling temperature and deformation amount on the microstructure evolution of austenitic stainless steel during rolling are investigated. The results reveal that low‐temperature rolling reduces the stacking fault energy of austenitic stainless steel and promotes the formation of shear bands, ε‐martensite, and α′‐martensite. For both low‐temperature and room‐temperature rolling, the austenite and α′‐martensite, austenite and ε‐martensite, α′‐martensite and ε‐martensite pairs follow the Kurdjumov–Sachs (K–S), Shoji–Nishiyama (S–N), and Burgers orientation relationships, respectively. The deformation‐induced martensite transformation sequence of austenitic stainless steel follows the processes γ → α' and γ → ε → α'. A heterogeneous nano/ultrafine‐grained structure with a grain size of 560 nm is obtained by low‐temperature rolling and annealing; room‐temperature rolling achieves a grain size of 690 nm. The heterogeneous nano/ultrafine‐grained steel exhibits a high yield strength of 908 MPa and maintains a satisfactory total elongation of 43%.