Influence of manganese content on ε-/α′-martensitic transformation and tensile properties of low-C high-Mn TRIP steels

Publication date: 15 March 2018
Source:Materials & Design, Volume 142
Author(s): Xing Li, Liqing Chen, Yang Zhao, Raja Devesh Kumar Misra
Low carbon steels containing 15–19 wt% Mn were processed to study the influence of Mn content on the thermally induced and deformation-induced ε-/α′-martensitic transformation and tensile properties of high-Mn TRIP steels. The stability of austenite and ε-martensite was studied in terms of thermodynamics, and the work hardening behavior during tensile deformation was divided into two stages using Hollomon analysis. The results indicated that Mn increased the stability of austenite and ε-martensite and austenite grain refinement had a larger effect on γ → ε than γ → α′ transformation. During early stages of tensile deformation, the steel having ~15 wt% Mn continued the γ → ε, ε → α′ and γ → α′ transformation because deformation energy compensated the Gibbs free energy required for phase transformation. But α′-martensitic transformation was difficult in steel having ~19 wt% Mn even after fracture because of the high stability of ε-martensite. On account of high density of dislocations in α′-martensite, the dynamic strain aging process was obvious when deformation-induced α′-martensitic transformation occurred in steel. The significant α′-martensitic transformation and intense dynamic strain aging improved work hardening exponent and ultimate tensile strength of steel, while the coordinated transformation of γ → ε and ε → α′ during tensile deformation was beneficial to improve ultimate elongation.

Graphical abstract

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