Improved Hardness of Gas-Carburized 4Cr5Mo2V Tooling Steels by Modification of Vanadium Content

4Cr5Mo2V tooling steels are widely used in shaping of ferrous metals and non-ferrous metals. Present work aims to improve the hardness of gas carburization 4Cr5Mo2V die steels through modification of vanadium (V) content. 4Cr5M2V steels with mass fractions of 0.15% (V15), 0.55% (V55) and 1.25 wt.% (V125) of V were prepared and gas carburized. It was found that carburized 4Cr5Mo2V steels were covered by diffusion layers with thickness ranged from 500 to 900 μm. As content of V in 4Cr5Mo2V tooling steels increased, the diffusion layers (harder than matrix) also increased. Solid solution of V atoms in ferritic matrix played a positive role in decreasing the diffusion activation energy as well as in increasing the diffusion coefficient of carbon atoms. Model of gas carburization was constructed to predict the carbon concentration as a function of depth for Fe-C-V system. The predicted curves of carbon concentration were close to the measured values.