Evaluation of a Processing Route and Microstructural Characteristics for the Development of Ultrafine Bainite in Low-Temperature Ausformed Medium-Carbon Steels

Abstract A combination of physical simulation and laboratory rolling experiments, including thermomechanical low-temperature ausforming, was conducted for designing a suitable processing route to enable phase transformation from austenite ultrafine bainite in medium-carbon steel. Following ausforming at 500-550 °C, two different cooling holding paths were tried the study: (1) water close martensite start temperature (300 °C), followed by isothermal (route A), (2) air 350 °C B). For reference, third sample directly water-cooled 300 after hot without treatment, C). Field emission scanning electron microscopy backscatter diffraction, as well x-ray employed microstructural analysis correlations with mechanical properties evaluated respect hardness tensile properties. The subsequent schedules resulted decomposition into some martensite, while stabilizing fraction finely divided, carbon-enriched interlath austenite. Results suggested development novel, multiphase bainite-martensite-austenite microstructure, achieved via air-cooling B), beneficial Most bainitic plates range 50-200 nm occasional presence coalesced wide 2000 nm. Despite differences behavior non-ausformed samples not significantly different. technique paves way developing nanostructured/ultrafine steels high innovative modification routes ausforming. Graphical