Abstract:
Nanostructured bainitic steel obtained through austempering or bainitic transformation of high Si steels consists of bainitic ferrite and carbon-enriched retained austenite. Secondary tempering of those microstructures’ tailors their mechanical properties through its unique nanostructure and austenite stability. In this work fatigue and tensile properties of a nanobainitic steel in different secondary tempering conditions are presented and the results are discussed based on the deformation mechanisms taking place due to the microstructure evolution during secondary tempering. Influence of secondary tempering and elevated testing temperature on tensile and fatigue properties at room temperature and 250 °C. Based on the present deformation mechanism results were discussed supported by microstructure evolution results obtained through dilatometry, XRD and microscopy. Depending on secondary tempering temperature main influencing mechanisms are martensite formation after secondary tempering during cooling, TRIP-effect and precipitation hardening obtained by secondary tempering.

Keywords: bainite; nanobainite; nanostructured bainite; thermal stability, mechanical properties, fatigue, tempering, deformation mechanism; martensite formation, TRIP-effect; precipitation hardening