The valuation of microstructural evolution in a thermo-mechanically processed transformation-twinning induced plasticity steel during strain hardening

Abstract

The successive evolution of martensitic transformation, twining and dislocation substructure formation in a transformation-twinning induced plasticity steel during room temperature straining was studied in the present work. This was materialized through microstructural observations and micro-texture examinations utilizing the electron backscattered diffraction method. To evaluate the strain hardening behaviour of the thermomechanically processed steel, tensile testing procedure to different strains at ambient temperature was practiced. The results indicated that the dislocation slip, mechanical twinning, and deformation induced ɛ/α′-martensite formation were involved as the deformation mechanisms. At the early stages of deformation, the dynamic formation of dislocation substructure, strain induced ɛ-martensite and twins from austenite played the main role in the observed work hardening behaviour. Furthermore, the results demonstrated that the formation of α′-martensite was the dominant deformation mechanism at higher deformation levels. The corresponding texture analysis indicated to a double fibre texture formation, with a relatively stronger <111> at lower strains and a stronger <100> partial fibre parallel to tensile axis at higher strains. However, in the latter, the Cube, A and Goss Twin (GT)-type textures were dominated. Decreasing of the Goss and S components were attributed to the preferential transformation of austenite to α′- and ɛ-martensites, respectively. The presence of GT component even at higher strains approved the participation of deformation induced twinning as a dominant deformation mechanism up to failure.