Development of Air-Cooled Carbide-Free Bainite/Martensite Multiphase Steel: Transformation Kinetics, Microstructure, and Mechanical Properties

An air-cooled low-carbon Mn-Si-Cr alloyed steel with multiphase microstructure of carbide-free bainite/martensite (CFB/M) is developed. The kinetics of bainitic transformation during air-cooling process is discussed via considering the transformation latent heat with help of the measured temperature-cooling curves. Results show that the CFB formed during air cooling can effectively refine the multiphase microstructure and stabilize the film-like retained austenite that contributes to transformation-induced plasticity effect upon deformation. An optimum combination of strength, ductility, and toughness of the air-cooled bainitic steel is achieved (tensile strength: 1418 MPa, total elongation: 15.8%, and Charpy V-notch impact energy: approximate to 71 J). The newly developed Mn-Si-Cr alloyed air-cooled bainitic steel exhibits superior mechanical properties to the commercial 23CrNi3Mo steel but has a much lower alloy cost. An air-cooled low-carbon Mn-Si-Cr alloyed steel with carbide-free bainite/martensite (CFB/M) multiphase exhibits an optimum combination of strength, ductility, and toughness. The refined CFB/M multiphase and film-like retained austenite can hinder crack propagation and improve the impact toughness of the air-cooled CFB/M multiphase steel.image (c) 2023 WILEY-VCH GmbH