Influence of austempering temperature on microstructure and mechanical properties of high-carbon nanostructured bainitic steels

We investigated the influence of austempering temperature on microstructure and mechanical properties of high-carbon nanostructured bainitic steels. The austempering temperature changed the volume fraction of bainitic ferrite, martensite, block- and lath-type retained austenite. The mechanical stability of retained austenite is affected by its chemical composition and morphology. For the high-carbon nanostructured bainitic steels, the micro-hardness and strengths are increased with increasing the volume fraction of martensite and decreasing the lath thickness of bainitic ferrite, while the ductility is increased as retained austenite with sufficient mechanical stability increases. In particular, the volume fraction and mechanical stability of retained austenite act as a critical factor for improving the toughness of high-carbon nanostructured bainitic steels. As a result, it has been seen that controlling the mechanical stability of retained austenite with different morphology and fraction is essential to develop advanced high-carbon nanostructured bainitic steels with an excellent combination of hardness, strength, ductility, and toughness for a given chemical composition.