Mechanical Properties and Microstructures of Mo<sub>2</sub>C Strengthened Vanadis 4 Extra Alloy Steel by Powder Metallurgy and Heat Treatments

Abstract

In this work, different ratios of molybdenum carbide (1, 3 and 5 mass% Mo2C) powders were added to Vanadis 4 extra alloy steel powders and then mixed by ball milling for 6 h. The composite powders underwent vacuum sintering at 1200, 1220, 1240, 1260 and 1280°C for 1 h, respectively. The results showed that the optimal sintering temperature for the addition of 5 mass% Mo2C powders was 1220°C. It also represented that the apparent porosity was 0.18%, and that a transverse rupture strength (TRS) value of 2281.3 MPa and a hardness value of 79.2 HRA were obtained, respectively. Additionally, the TRS value was obviously enhanced to 2437.6 and 2491.4 MPa by the addition of 5 mass% Mo2C powders after heat treatment and sub-zero plus heat treatments, respectively. Meanwhile, the hardness value also increased to 80.6 and 81.3 HRA, respectively, whereas the Mo-rich M6C carbides distributed in the grain boundaries, and V-rich MC carbides appeared in the grain and grain boundaries after sub-zero plus heat treatments. Significantly, a series of heat treatment processes is effective in improving the microstructure and strengthening the mechanical properties of the sintered Vanadis 4 extra composites.