Deformation behavior of ε martensite in high Mn steels at low strain

Abstract

High Mn steels have been assessed in exceptional ability of high tensile stress with good ductility for automotive and high energy absorption industry. Their properties were attributed to deformation mechanisms called twinning induced plasticity (TWIP), formation of deformation twinning during plastic deformation, and transformation induced plasticity (TRIP), phase transformation during plastic deformation. In TRIP steels, martensitic transformation and reverse transformation were well known behavior. Although models for TRIP phenomena was proposed at 1950s, the real time observation was limited in heating test and only a little research have been conducted with mechanical test. Relatively formation of deformation twinning and martensitic transformation were observed in detail, but reverse transformation was secondary induced plasticity at high strain. In this thesis, we observed the deformation mechanisms in ε phase at low strain with in-situ transmission electron microscopy (TEM) straining test. Before state the in-situ TEM result, sample designs and analysis of microstructure are explained, discussion about reverse transformation will be followed.