Effects of Particle Size of Pre-Alloy Powders and Vacuum Sintering Temperatures on the Microstructure and Mechanical Properties of 440C Stainless Steel

This study utilized two different sizes of 440C pre-alloy powders for vacuum sintering under different sintering temperatures (1523, 1533, 1543 and 1553 K) to explore the microstructure and mechanical properties of 440C stainless steel. The experimental results indicated that the sintered specimens of the refined alloy powders had good hardness and transverse rupture strength (TRS), due to the smaller grain size of the sintered body and the uniform distribution of the carbides. In addition, two types of carbide precipitates appeared in the microstructure. Fine carbides (M23C6) within the grains and rod-shaped types of carbide (M7C3) on the grain boundaries were observed after sintering at 1543 K for 1 h. The research also showed that a suitable amount of carbides is helpful in improving the TRS. However, the fine carbides (M23C6) within the grains almost disappeared and the rod-shaped types of carbide (M7C3) on the grain boundaries coarsen after sintering at higher temperatures (1553 K), and so detrimental to the TRS.