Effect of ECAP processing temperature on an austenitic TWIP steel's microstructure, texture and mechanical properties

Abstract

The development of microstructure and texture of twinning-induced plasticity (TWIP) steel sheet during ECAP at two temperatures (250° and 350°) up to four passes were investigated. The high chromium content is the differential of this TWIP steel, a chemical element that reduces the stacking-fault energy and increases corrosion resistance. By imposing ECAP, the volume fraction of twins, dislocation density, and yield strength significantly increase while ductility decreases. This study compared the effect of temperature during applied severe plastic deformation (SPD). Thin parallel slip bands’ high density was observed, and in addition to an intense micro shear, banding took place when pressing was continued by increasing the number of passes. The martensitic transformation was not detected in the deformation-twinning microstructure after more passes. The relationship between the microstructure, strain-hardening behavior, and mechanical properties was investigated after two different deformation schedules of ECAP. The best balance between high strength and good ductility (1915 MPa and 7%) was obtained after four passes at 250 °C and 350 °C. It was found that the quantity of ECAP pass affects the displacement substructure with the formation of shear bands, subgrains, and various variants of twins. These also influenced strain-hardening behavior, microhardness, texture, and ultimate strength.