Role of ordered carbon vacancies on stability and mechanical properties of VC1−X in bainite steel by first-principles calculations and experimental characterization

Abstract

There has been little systematic research into vanadium carbides (VC1−X) configuration in bainite steel. Structural stability, mechanical properties, and thermal properties among vast VC1−X configurations for 20MnSiCrV bainite steel were studied here using first-principles calculations and experiments. The calculated results predicted stable and metastable VC1−X structures, and their intrinsic elasticity and hardness were related to carbon vacancy concentration varies, following parabolic law. A decrease in average bond strength and the number of V-C covalent bonds caused by fewer carbon atoms will lead to VC1−X softening. The calculated values for mechanical properties are in excellent agreement with existed available experimental data. Moreover, lattice thermal conductivity of VC1−X is not only dependent on carbon vacancy contents but also related to compound configuration. Furthermore, the calculated stable structures of VC (Fm3¯m), V8C7 (P4332), and V2C (Pbcn) are verified by TEM (Transmission Electron Microscope) observation. These results of VC1−X structural stability and properties provide a guideline to study vanadium second phases in bainite steel and ensure the subsequent extended research of vanadium microalloying in steel.