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

Abstract

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: ≈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.