Microstructure and deformation behaviour of submicrocrystalline 304 stainless steel produced by severe plastic deformation

The deformation behaviour and structural changes in a 304-type stainless steel were studied in uniaxial compression at temperatures of 873–1073 K (0.5–0.6 Tm) and under strain rates from 10−4 to 10−2 s−1. The starting material, with an initial grain size of ≈0.3 μm, was produced by multiple warm deformation passes, changing of the loading direction from pass to pass. At high temperature, the resulting fine-grained steel has a low dislocation density and steady-state flow stresses lower than that of an annealed coarse-grained steel. Moreover, the strain rate sensitivity of the fine-grained material reaches high values, up to 0.3, which clearly differs from that of ≈0.1–0.2 for the coarse-grained steel. At room temperature, the initially fine-grained steel has higher hardness after warm deformation than the conventional steel.