Abstract
The effect of fcc (γ)→hcp (ε) martensitic transformation on the tensile deformation behavior of Fe-Mn, Fe-Mn-Si and Fe-Mn-Co alloys was investigated. The amount of ε martensite formed during deformation was drastically increased by the addition of Si or Co which lowers the Neel temperature. On the other hand, the Si addition was revealed to suppress the γ→ε transformation by cooling.
A positive temperature dependence of 0.2% proof stress resulting form the γ→ε a transformation was found above Ms temperature commonly in these three alloy systems. This phenomenon became more pronounced according to an increase in γ strength by Si solid solution and/or dislocation (ausforming) hardening. A pre-existing ε plate was found to be a strong barrier for further plastic flow, so that a high work hardening was produced. Therefore, the tensile property vs. temperature relation for the alloys examined were well understood by considering the linked influences of softening and hardening due to the deformation induced γ→ε transformation. Although the shape of the true stress vs. true strain curve accompanying the γ→ε transformation became unusual one particular to the so-called TRIP (transformation induced plasticity), ductility was not enhanced so much.
