Effect of sintering temperature on microstructural evolution of M48 high speed tool steel bonded NbC matrix cemented carbides sintered in inert atmosphere

This work presents the results on microstructure and hardness evaluation of NbC-12 wt% M48 high speed steel (HSS) cemented carbides, pressureless sintered at different temperatures in argon atmosphere. To evaluate the effect of sintering process on the microstructure, sintering was performed in the range of 1260 °C to 1420 °C according to dilatometer analysis. The sintered samples were characterized using several techniques, including determination of density by Archimedes, measurement of hardness and fracture resistance, microstructural analysis by scanning electron microscope (SEM), phase analysis using X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). As expected, microstructural results indicated higher NbC grain growth at elevated sintering temperatures. The high speed steel wetted the NbC particles at high temperature (>1340 °C). As a result, the metallic binder spread and a homogenous distribution between the NbC grains could be achieved. Mechanical analysis showed a dependence of mechanical properties on NbC grain size and the state of the microstructure. A maximum hardness of 14.91 ± 0.14 GPa was measured for cemented carbide samples sintered at 1300 °C, while the highest fracture resistance (1.56 ± 0.3 MPa·m1/2) was associated with the sample sintered at 1380 °C.