Study of the isothermal bainitic transformation and austenite stability in an advanced Al-rich medium-Mn steel

Abstract Isothermal bainitic transformation of a lean medium-Mn steel containing (in mass%) 0.18C–3.6Mn–1.7Al–0.23Si–0.2Mo–0.04–Nb after full austenitization at 1100 ºC was studied by means high resolution dilatometry. The effects isothermal holding temperatures ranging from 450 to 350 °C on the kinetics experimentally characterizing microstructure present time 15 min 2 h. obtained results showed that is uncompleted above 425 °C. carbon enrichment austenite during treatment and not enough avoid martensitic cooling room temperature. Thus, it mixed structure including ferrite martensite. Decreasing austempering temperature resulted in more pronounced bainite formation. 350ºC quite similar observed 400 °C, so 60 are needed both cases complete reaction. However, local variations chemical composition associated segregation Mn Al casting solidification differences rate reaction between different areas material. A balance difference dendritic interdendritic responsible for among test samples final microstructure.