Temperature Dependence of Mechanical Properties and Deformation Behavior of Austenite-Base High Mn steels

Abstract

High Mn steels have received great attention in recent years since they have excellent combination of high tensile strength and elongation. It is expected that these steels would exhibit good toughness at low temperatures due to their austenitic structures. However, most of high Mn steels have microstructure consisting of austenite with various volume fraction of other constituent phase such as ε-martensite and α’-martensite. Although the transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) are generally known as the dominant deformation mechanisms in high Mn steels, actual deformation behavior might be quite complex depending on the volume fraction of ε-martensite and α’-martensite. The objective of this research is to investigate the effect of constituent phases on the temperature dependence mechanical properties of high Mn steels. 17 wt% Mn steels with 0.1%C and 0.2%C have been chosen to have various volume fractions of austenite and ε–martensite. They have been subjected to internal friction, tensile and Chary impact tests at various temperatures. The steels show the deformation-induced phase transformation such as γ -> ε, γ -> α’ and γ -> ε -> α’ during tensile deformation. Such deformation mechanisms are dependent on the stacking fault energy, which is a function of chemical composition of the material, temperature and magnetic property. It shows that the Neel temperature (TN), where a paramagnetic to antiferromagnetic transformation occurs in γ and ε, plays an important role in controlling the deformation behavior of 17 Mn steels at low temperatures. Detailed deformation behavior of the steels has been investigated by EBSD and correlated with tensile and impact properties.