The effect of nitrogen and manganese on the mechanical properties in TWIP steels

Abstract

The present study focused on the design and testing of the new 3rd generation TWIP steels to reduce maganese content of the existing high Mn FeMnC and FeMnAlC alloy systems. Fe-12Mn-0.6C-N steel was examined to investigate the effect of nitrogen addition and Fe-18Mn-0.6C-N steel was used as a reference. Effects of nitrogen and manganese on the microstructure, mechanical properties, and strengthening mechanism such as dynamical strain aging (DSA) were investigated. The deformation microstructures of Fe-12Mn-0.6C-N steel were the mixtures of twinned austenite and 5~10% ε-martensite. Only deformation twinning was observed in Fe-18Mn-0.6C-N during the deformation due to its higher stacking fault energy. Fe-18Mn-0.6C-N steel exhibited higher strength and elongation than Fe-12Mn-0.6C-N steel. The effect of the strain rate on the tensile behavior of both steels was examined. While Fe-18Mn-0.6C-N steel showed clear negative strain rate sensitivity, Fe-12Mn-0.6C-N steel did not show a clear relationship between flow stress and strain rate. Grain orientation relasionship with deformation twinning was investigated.