TWIP-effect and thermo-mechanical treatment of a stable high-manganese austenitic stainless steel

Austenitic carbon steels that exhibit excellent mechanical properties due to the twinning-induced plasticity effect have been studied extensively. On the other hand, austenitic stainless steels usually achieve good strength and ductility via transformation-induced plasticity. However, relying on martensite transformation for strength may cause problems such as delayed cracking. Therefore, the twinning behavior of a stable low-nickel high-manganese austenitic stainless steel (Type 201Cu) was studied. The steel showed extensive twin formation during deformation, which was observed using SEM-EBSD and HR-TEM. Consequently, a high strain hardening rate was seen, which can be attributed to the dynamic Hall-Petch effect. However, the yield strength was low as is typical for austenitic steels in the annealed condition. The yield strength was increased markedly by taking advantage of the twinned microstructure and the stability of the twins during annealing. Cold-rolling to a 33% reduction and annealing at 600°C for an hour led to high yield strength together with good uniform elongation. The thermo-mechanical treatment reduces the effective grain size via mechanical twinning, but leaves some strain hardening capacity via the dislocation slip mechanism.