Metal injection moulding of 17-4PH stainless steel: Effects of porosity on the mechanical properties of the sintered products

17-4PH stainless steel (SS) is a martensitic precipitation hardenable alloy which normally contains approximately 15.5-18.5 wt.% Cr and 2.5-4.5 wt.% Ni and Cu. It is well known for its high impact strength and fracture toughness, and excellent corrosion resistance at service temperatures below 300 degrees C promoted by its Cu-rich precipitates. 17-4PH SS is widely used as a structural material in various sectors such as aerospace, medical, petrochemical, etc. The high strength of the alloy makes it difficult to machine, especially when making complex shaped products. Metal injection moulding (MIM) uses the shaping advantage to produce small-to-medium intricate products in high volumes at a relatively low cost. However, due to the nature of MIM process, the mechanical properties of the sintered products depend strongly on various metallurgical MIM variables with porosity included. Porosity is largely dependent on the starting powder characteristics, powder loading, and sintering conditions. In this study, the mechanical properties of the sintered 17-4PH SS MIM samples fabricated at different powder loadings, viz. 55, 60 and 65 vol.%, will be evaluated. The starting powder particle size distribution is -5, -15 and -45 mu m. The sintered density, microstructure and hardness response of the samples are presented. These properties are influenced by the nature of the pores, i.e. size, density and distribution.