Transformation characteristics of <i>γ</i>→<i>ε</i>-M and <i>ε</i>-M→<i>α</i>'-M in high manganese steel under high speed compression

Abstract

The volume fractions of γ (austenite), ε-M (hcp martensite) and α'-M (bcc martensite) in static and high speed compressed high manganese transformation induced plasticity (TRIP) steel were calculated by the XRD technique to investigate the effect of strain rate on the kinetic characteristics of γ→ε-M and ε-M→α'-M transformation. Orientation dependence of γ→ε-M and ε-M→α'-M transformation in high speed compressed specimen was analyzed by the EBSD technique and the calculation of martensitic transformation crystallography. The results show that the effects of strain rate on γ→ε-M and ε-M→α'-M transformation are different. Compared to static compression, the γ→ε-M transformation is inhibited due to the higher stacking fault energy, and ε-M→α'-M transformation is promoted because higher stress during high speed compression. Compared to static compressed specimen, martensitic transformation is accelerated at the early stage of high speed compression. High speed compressed specimen shows orientation dependence of martensitic transformation, which is related to the mechanical work of martensitic transformation in differently orientated γ grains. γ→ε-M phase transformation is only related to the mechanical work of ε-M;ε-M→α'-M phase transformation depends on the mechanical work of both ε-M and α'-M.

Keywords

• high manganese trip steel
• strain rate
• martensite
• orientation dependence
• ebsd