PROPERTY VARIATION AND MICRO-STRUCTURE EVOLUTION OF 304L STAINLESS STEEL SUBJECTED TO SURFACE MECHANICAL ROLLING TREATMENT

The mechanical property variation and micro-structure evolution of 304L stainless steel subjected to treatment of a new method, the surface mechanical rolling treatment (SMRT), were investigated in both liquid nitrogen and atmosphere at room temperature. The grain refinement, phase transition and hardness of 304L stainless steel treated by SMRT were examined using OM, SEM, XRD, TEM and Vickers hardess tester. The results show that nano-grains are created on the surface of SMRT 304L stainless steel, their sizes vary with treating conditions. Large numbers of intersections and mechanical twins are observed in the steel samples. Due to prominent martensitic transformation during SMRT, the hardness of samples is enhanced greatly and varies with increasing depth from surface. The SMRT method has its advantages compared with the traditional methods to generate thicker hardening layers than other traditional methods. It can be easily industrialized.