Fatigue Properties at Elevated Temperatures of Secondary Tempered Nanostructured Bainite: A Study of Deformation Mechanisms

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. Herein, 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 degrees C is presented. Based on the present deformation, mechanism results are discussed supported by microstructure evolution results obtained through dilatometry, X-ray diffraction, and microscopy. Depending on secondary tempering temperature, main influencing mechanisms are martensite formation after secondary tempering during cooling, transformation-induced plasticity effect, and precipitation hardening obtained by secondary tempering. Nanostructured bainitic steel consists of bainitic ferrite and retained austenite. Secondary tempering of those microstructures tailors their mechanical properties. Herein, fatigue and tensile properties in different secondary tempering conditions are presented and discussed based on the deformation mechanisms. Depending on secondary tempering temperature, main influencing mechanisms are martensite formation, transformation-induced plasticity effect, and precipitation hardening influenced by secondary tempering.image (c) 2024 WILEY-VCH GmbH