The Effect of the Pre-strain Process on the Mechanical Properties, Microstructure, Fatigue Life, and Fracture Mode of 304 Austenitic Stainless Steel

In the present study, the effect of pre-strain process on the mechanical properties, microstructure, fatigue life, and fracture mode of 304 austenitic stainless steel was discussed. Six different pre-strain states ranging from the original state to the 35% pre-strain state were investigated. The mechanical properties of different pre-strain state samples were tested first. A bilinear relationship between mechanical properties and pre-strain was established. Both yield strength and tensile strength of 304 stainless steel increase with increasing pre-strain, but the yield strength obviously increases more than the tensile strength. Combined with the observation of the microstructure, a critical pre-strain point was proposed. When the pre-strain is lower than the critical value, only work hardening occurs. When it is greater than the critical value, the mechanical properties are affected by the combined effects of work hardening and martensitic transformation. There is also a critical pre-strain point in the fatigue life of 304 stainless steel, as shown in the fatigue life test results of different pre-strain specimens. The inherent essence of fatigue life improvement of pre-strained material is the comprehensive effect of material phase transformation and plastic deformation strengthening.