Mechanical Properties and Deformation Behavior of Nano/ultrafine Fe-18Cr-8Ni Austenitic Steel Processed by Low Temperature Rolling and Annealing Treatment

In the present study, the method of phase reversion process is adopted to obtain nanograined/ultrafine-grained (NG/UFG) structure in 18Cr-8Ni austenitic stainless steel. Severe cold deformation (86% reduction) at room temperature and (64%, 86% reduction) at -50 degrees C is carried out, followed by annealing in the conditions of 650 degrees C-50 min and 700 degrees C-15 min. The influence of different cold rolling and annealing conditions on the microstructure and mechanical properties of stainless steel is studied. The decrease of rolling temperature and the increase of reduction lead to the volume fraction of strain-induced martensite increase. Lath-type martensite, dislocation cell-type martensite, and untransformed austenite in 64% reduction (at -50 degrees C) and mainly dislocation cell-type structure in 86% reduction (at room temperature and -50 degrees C) are observed. Increasing reduction or rolling temperature promotes the cold-rolled alpha texture of strain-induced martensite to the stable orientations. The grain size obtained is in the range of 0.4-0.89 mu m, with yield strength in the range of 684-1017 MPa and high ductility of 23-54%. Deformation behavior shows that the amount of twins and stacking faults at 5 mm distance from the fracture is higher than the fracture.