Study of Microbands in a Fe-30mn-6.5al-0.3c Low-Density Steel Deformed at Cryogenic Temperature

Abstract

The microband (MB) formation mechanisms in an austenitic Fe-30Mn-6.5Al-0.3C (wt.%) low-density steel tensile deformed at -196°C were investigated by combined electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). The grain orientation dependences of the MB structure, MB morphology, and MB alignment were quantitatively evaluated in grains oriented with the two main texture components, namely, <111>//tensile axis (TA) and <001>//TA. The interplay between the deformation structure and MB formation was analyzed. Our analysis indicates that the underlying deformation structure controls the MB formation mechanism and, at the current deformation conditions, also determines the crystallographic character of MBs. Most of the evaluated MBs have a crystallographic character (deviation angle <5° from {111} slip plane traces). Specifically, 77% of the MBs in the grains oriented close to <111>//TA directions and all the MBs evaluated in grains oriented close to <001>//TA directions have a crystallographic character. They are associated with a planar strain localization phenomenon occurring along highly-stressed crystallographic slip planes. Non-crystallographic MBs (deviation angle >5° from {111} slip plane traces) only occur in the grains oriented close to <111>//TA directions. They are associated with the splitting of pre-existing dense-dislocation walls (DDWs). At high strain levels, we foresee the activation of a GB-assisted MB formation mechanism associated with twin-GB interactions.