Effects of multiaxial non-proportional cyclic pre-hardening on monotonic tensile and fatigue properties of 316L stainless steel

Effects of multiaxial non-proportional cyclic pre-hardening (CPH) treatment by performing tension-torsion cyclic test in a circular path on the monotonic tensile and fatigue properties of 316L austenitic stainless steel are studied. Results show that the circular path pre-hardening treatment significantly improves the yield strength but reduces the elongation of materials in comparison with the as-received (AR) material. Moreover, the fatigue resistance of 316L stainless steel after CPH treatment gets markedly degraded at the strain amplitude of 0.4 % with a 26 % decrease of fatigue life, however, the 62 % life increase is obtained at the lower strain amplitude of 0.2 %. Therefore, it is reasonable to believe that the CPH treatment can be regarded as an effective method to increase the fatigue resistance within a certain range of strain amplitude if the proper loading path and cycles of the multiaxial pre-hardening process are used. The different life variations at the high and low strain amplitudes are explained from the perspectives of macroscopic deformation energy and microscopic deformation modes based on EBSD and TEM characterizations.