Strain hardening mechanisms during cold rolling of a high-Mn steel: Interplay between submicron defects and microtexture

Abstract

The formation of submicron structural defects within austenite (γ), ε- and α′-martensite during cold rolling was followed in a 17.6 wt.% Mn steel. Several probes, including XRD, EBSD, and ECCI-imaging, were used to reveal the complex superposition of the strain hardening mechanisms of these phases. The maximum amount of ε-martensite is observed at a strain of ε = 0.11. At larger strains, the amount of ε decreases suggesting that it precedes the α′-formation (γ → ε → α′). Stacking faults and twins are the main planar defects noticed in ε-martensite. The remaining γ is finely subdivided by stacking faults and twins up to ε = 0.22. From ε = 0.51 on, twinning and multiplication of dislocations are the principal strain hardening mechanisms in austenite. Deformation is accommodated in α′ by the rearrangement of dislocation tangles into dislocation cells plus shear banding at ε = 1.56. During cold rolling, austenite develops a Brass-type texture component, which can be associated to mechanical twinning. ε-martensite presents its basal planes tilted ∼24° from the normal direction towards the rolling direction. The α′-martensite develops and strengthens both, the bcc α- and γ-texture fibers during cold rolling.