Effects of aging treatment on the precipitation behavior of ε-Cu phase and mechanical properties of metal injection molding 17-4PH stainless steel

This study mainly investigates the influence of artificial aging at 480 °C, 520 °C and 620 °C on the microstructure and mechanical properties of metal injection molding (MIM) 17-4PH. The results show the microstructure of the as-sintered MIM 17-4PH to be mainly composed of lath martensite, δ-ferrite, and nodular SiO₂ inclusions. The effect of precipitation hardening is to strengthen the MIM 17-4PH by the precipitation of a large number of fine spherical ε-Cu phases on the lath martensite matrix, which effectively block the movement of dislocations. The highest hardness is obtained by artificial aging at 480 °C for 4 h. As the aging temperature increases, the ε-Cu phase grows coarser, which results in over aging of the MIM 17-4PH and decreases the hardness.