Comparison of tensile properties and work hardening rate of fine and coarse-grained 304 austenitic stainless steel

In this study, the effects of grain size on the tensile properties and the work-hardening behavior of 304 austenitic stainless steel was investigated. For this purpose, the thermomechanical processing was carried out by applying a 75% thickness reduction to the as-received 304 stainless steel sheet followed by annealing at two different temperatures of 750 and 1000 °C to produce sheets with two different fine- and coarse-grained microstructures. The average grain size decreased from 25 μm in the as-received matrix to 1.93 μm in the sample, which was annealed at 750 °C for 90 min (fine-grained sample). Also, the mean grain size of 35.52 μm (coarse-grained sample) was obtained after annealing at 1000 °C for 90 min. XRD and optical microscopy were used for characterizing the microstructure. The tensile tests were performed in the directions of 0°, 45°, and 90° to the rolling direction of the samples. The yield strength of as-received, fine-grained, and coarse-grained samples were obtained 405, 733, and 305 MPa, respectively. However, the total elongation decreased from 73% in the as-received sample to about 52% in the fine-grained sample. The work hardening behavior of both fine- and coarse-grained samples was observed in three stages: an initial sharp drop until a minimum value was reached, then an increase until a maximum value was reached, and finally a reduction in the work hardening rate until the beginning of necking. The work-hardening rate (dσ/dε) of the coarse-grained sample was higher than that of the fine-grained sample. This was due to the higher martensitic transformation rate in the coarse-grained sample.