Homogenous strength-toughness match for 20Mn2SiCrMoV bainitic large-size parts via processing of VC particles and quenching control

The problem of insufficient hardenability in general large-size parts always occurs in product manufacturing because of their large size, etc. It is restricted mainly by its own alloy composition with micro-alloy and key quenching and partitioning (Q&P) process. The relationship between the cooling rate and properties of small samples was analyzed as the basis of the initial cooling rate at different positions corresponding to large-size parts combined with controlled austenization temperature in this work. Typical as-treated microstructure after a fast cooling rate is mainly composed of lath bainite, martensite, and retained austenite (RA), while bainite and RA after a slow cooling rate. Simulations showed that cooling control via decreasing spray intensity, meeting higher strength at the surface, and good strength and toughness match can be obtained both at the surface and in the center. As-treated large ring part has ~ 1330 MPa tensile strength and ~ 95 J impact energy at the surface, and meantime, ~ 1191 MPa tensile strength and ~ 70 J impact energy in the center, which narrows the property difference.