In-situ Characterization of Microstructural Damage in QP980 Steel

During deformation of a steel, retained austenite can transform to martensite through transformation induced plasticity, thereby enhancing elongation to failure. However, obtaining high amounts of retained austenite in the final microstructure is challenging. The quench and partitioning (Q&P) heat treatment has been proposed as a cost-effective solution for stabilization of austenite at ambient temperatures. In this paper, a commercial QP980 steel was investigated by SEM-based in-situ tensile testing to determine micromechanisms of damage during plastic deformation. Results show that ferrite and martensite deform simultaneously and cracks are initiated at both phases. The martensite phase in QP980 steel shows a considerable amount of deformation. However, cracking of the blocky retained austenite happens from a very early stage of necking. X-ray computed tomography shows that most of the damage is found very close to the fracture surface.