Microstructures, mechanical properties and corrosion behaviors of NbC added to Vanadis 4 tool steel via vacuum sintering and heat treatments

In this study, different ratios (1, 3 and 5 mass%) of niobium carbide (NbC) powders were added to Vanadis 4 alloy steel powders. The composite powders utilized vacuum sintering at 1250, 1275 and 1300 °C for 1 h, respectively. The experimental results show that good mechanical properties were obtained by the addition of 5 mass% NbC sintered at 1275 °C for 1 h. Meanwhile, the apparent porosity was decreased to 0.13%, and the transverse rupture strength (TRS) and hardness reached 1822.6 MPa and 81.9 HRA, respectively. When optimally sintered Vanadis 4 composites then underwent a heat treatment, the TRS showed a significant increase to 2093.3 MPa, but the hardness declined slightly to 81.5 HRA. Notably, the heat treatment improved the distribution and size of the VC carbides, which effectively enhanced the strength. The decrease in hardness could be ascribed to the release of internal stress after the tempering process. Consequently, the heat treatment process is effective in improving the microstructure and strengthens the sintered Vanadis 4 composites.