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

The formation of submicron structural defects within austenite (gamma), epsilon- and alpha'-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 epsilon-martensite is observed at a strain of epsilon = 0.11. At larger strains, the amount of epsilon decreases suggesting that it precedes the alpha'-formation (gamma -> epsilon -> alpha'). Stacking faults and twins are the main planar defects noticed in epsilon- martensite. The remaining gamma is finely subdivided by stacking faults and twins up to epsilon = 0.22. From epsilon= 0.51 on, twinning and multiplication of dislocations are the principal strain hardening mechanisms in austenite. Deformation is accommodated in alpha' by the rearrangement of dislocation tangles into dislocation cells plus shear banding at epsilon = 1.56. During cold rolling, austenite develops a Brass-type texture component, which can be associated to mechanical twinning. epsilon-martensite presents its basal planes tilted similar to 24 degrees from the normal direction towards the rolling direction. The alpha'-martensite develops and strengthens both, the bcc alpha- and gamma-texture fibers during cold rolling. (AU)