Effect of in situ formation of tungsten semicarbide on the microstructure and mechanical properties of medium carbon steel composites

Fabrication with the in-situ formation of W2C reinforced medium carbon steel (MCS) MMC’s was attempted using W or WO3 and graphite addition to steel. The P/M route comprising milling, compaction and sintering at 1050 °C and 1120 °C respectively in 90% N2 + 10% H2 atmosphere was adopted. Both SEM and BET studies revealed the particle size to be around 100, 7 and 40 µm for MCS, W and WO3, respectively. A complete conversion of tungsten into tungsten semicarbide (W2C) was noted in XRD for the tungsten additions of ∼6, 9 and 12 wt.% with stoichiometrically balanced C (graphite) addition of 0, 0.2 and 0.4 wt.%. However, WO3 + C addition (balanced as above) revealed the partial conversion of WO3 to W2C. The peaks of Fe3C were observed only for MCS + W + C samples and not for MCS + WO3 + C samples in XRD. In SEM, the WO3 phase appeared porous and partially converted, whereas, W2C phase was dense. Sintered density improved for the addition of W, whereas it monotonically reduced for WO3 addition to MCS + C samples. Higher hardness, compressive strength, and wear resistance was noted for W addition than WO3 to MCS+C samples.