Evaluation of the strengthening mechanism and mechanical properties of high alloyed PM 23-NbC?TaC composite materials through vacuum sintering, sub-zero and heat treatments

This study added different ratios of niobium carbide (NbC) and tantalum carbide (TaC) powders to PM 23 high speed steel (PM 23) powders. The composite powders (PM 23-NbC?TaC) utilized vacuum sintering at 1250, 1270, 1290, and 1310 ?C for 1 h, respectively, and the experimental results show that good mechanical properties were obtained by the addition of 6.3 mass% NbC-2.7 mass% TaC (N6.3T2.7) sintered at 1290 ?C for 1 h. Meanwhile, the apparent porosity was decreased to 0.23%, and the transverse rupture strength (TRS) and hardness reached 1648.1 MPa and 79.4 HRA, respectively. When optimally sintered PM 23 composites (N6.3T2.7) underwent a series of heat treatments, the TRS and hardness values were obviously enhanced to 1703.3 MPa and 83.5 HRA after quenching, sub-zero, and tempering treatments. Notably, the sub-zero and heat treatments obviously reduced the retained austenite content (0.6 vol%), which effectively enhanced hardness and strength. Consequently, sub-zero plus heat treatment are effective in improving the microstructure and strengthening the sintered PM 23 composites.