Temperature effect on deformation mechanisms and mechanical properties of a high manganese C+N alloyed austenitic stainless steel

Recently developed high-manganese stainless Fe-Cr-Mn-CN steels exhibit an exceptional combination of strength and ductility and show great promise for structural applications. Understanding the relationships between temperature, stacking fault energy (SFE) and strain-hardening behavior is critical for alloying, design, and further optimization of these steels. The present study investigates the influence of temperature and SFE on the microstructural evolution to explain the deformation behavior and mechanical properties of an austenitic Fe-14Cr-16Mn-0.3C-0.3N alloy. The flow behavior is homogenous and no serrations in the flow stress occur during tensile deformation in the temperature range from −150 to 250 °C. Mechanical twinning and the formation of (planar) dislocation substructures strongly influence the mechanical properties and work-hardening behavior in the intermediate temperature range from −40 to 45 °C (SFE range from 17 to 24 mJ m−2). In the high temperature interval from 100 to 250 °C the SFE ranges from 29 to 44 mJ m−2 and the initiation of mechanical twinning is delayed leading to reduced work-hardening in the intermediate and final stages of strain-hardening. In the low temperature regime from −150 to 100 °C (SFE approximately 15 mJ m−2), εh.c.p.-martensite is the dominant secondary deformation mechanism, contributing to the enhanced work-hardening in the early and intermediate stages of deformation and slightly lower total elongations. The yield strength of the studied alloy is significantly larger and exhibits greater sensitivity to temperature within the thermal and athermal ranges for dislocation motion compared to conventional Fe-Mn-(Al)-C TWIP or austenitic stainless steels, which may be attributed to phenomena such as short range ordering.