Effects of cold deformation on microstructure and mechanical behavior of a high nitrogen austenitic stainless steel

The influences of cold deformation on the microstructure and mechanical behavior for a high nitrogen austenitic stainless steel (1.2%N) were investigated through cold-rolling to different thickness reductions. No deformation-induced alpha' martensite was found in the steel even deformed up to 56%. It was found that the mechanical twins and dislocations slipping were the main deformation mechanism at the initial deformation stage, and the slipping was strongly obstructed by the twins. With increase of the deformation, the twins were split by slipping lines, and the twin boundaries were blurred. The strain-hardening exponent decreased with increase of the deformation. When the deformation reached to 56%, the yield strength and ultimate tensile strength were increased by about two times and one time, reached to 1654 MPa and 1870 MPa, respectively. By comparing the roles of nitrogen in several austenitic stainless steels, it was suggested that nitrogen obstructs the dislocations slipping and enhances the strain-hardening ability through the short range ordering.