Effect of heterogeneous microstructure on martensitic transformation behavior and mechanical properties of a cold rolling medium Mn steel

Abstract

A heterostructured medium Mn steel with duplex phases (ferrite and austenite) and multiple degrees of grain sizes is fabricated by a cold rolling process combined with repeated annealing. The obtained sample exhibits excellent mechanical properties with the ultimate tensile strength above 1110 MPa and the total elongation of 34.4%, the mechanical properties being higher than those of the sample produced by conventional cold rolling. The microstructural evolution and the strain partitioning behavior of the material during deformation are investigated. It is indicated that the great strain hardening ability rely on the combination of the transformation induced plasticity (TRIP) effect and the hetero-deformation induced (HDI) hardening. The sample with heterostructure induces more sufficient martensitic transformation. Meanwhile, the generation of large grains intensifies the mechanical incompatibility and makes it possible to accommodate larger amount of geometrically necessary dislocations (GNDs), thus inducing more effective HDI strengthening and HDI hardening, so that the comprehensive mechanical properties have been improved.