Grain-orientation-dependent of γ-ε-α′ transformation and twinning in a super-high-strength, high ductility austenitic Mn-steel

A newly developed, austenitic lightweight steel, containing a low-density element, Al, exhibits tensile elongation up to 50% as well as high ultimate-tensile stress (tensile fracture at 1800 MPa) without necking behavior. Electron backscatter diffraction analysis is carried out to investigate the orientation dependence of the martensitic transformation in tensile testing to 30% strain at 323 K (25 degrees C). A pronounced gamma ->epsilon ->alpha' transformation is observed in <111 > and < 110 > parallel to TD (TD: tensile direction) gamma-grains. The alpha'-transformation textures is analyzed. Large misorientation spreads is seen in the < 100 > parallel to TD gamma-grains. Interestingly, twin-assisted martensitic transformation is detected in the < 111 > parallel to TD followed by the twin boundary directly moving to a gamma/alpha' phase boundary. These phenomena are related to a change of Schmid factor for different orientations of grains. (C) 2016 Elsevier B.V. All rights reserved.