Development of high ductile ultra high strength structural steel through stabilization of retained austenite and stacking fault

Abstract

In the current study, a bainitic grade steel of 1.5 GPa and ~35% elongation and a martensitic grade steel with 2 GPa and ~20% elongation have been developed. The uniqueness of the work lies in achieving high strength with extended ductility in the bainitic and martensitic grade steels through solid solution strengthening and a possible twin plasticity mechanism. Both the microstructures consist of mechanically stable retained austenite with different morphology and characteristics. The synergic effect of carbon in lowering stacking fault energy and the stability of RA is proposed based on microstructural and mechanical characterisation of the developed steels. TEM investigations reveal the presence of stacking fault in the microstructure. This is one of the major indications of lowering of SFE in the retained austenite and subsequently augment the twin formation during tensile straining and thus contribute towards ductility.