Enhanced mechanical properties of injection molded 17-4PH stainless steel through reduction of silica particles by graphite additions

Abstract

Silica particles are often found in sintered 17-4PH stainless steels when water atomized powder is used. To eliminate the SiO2 particles and to improve the mechanical properties and corrosion resistance, graphite powders were mixed in this study with 17-4PH powders and binders during the kneading step of the powder injection molding process. The measurements of carbon and oxygen contents in tensile specimens and microstructure observations confirm the reduction of silica particles by graphite powders during vacuum sintering. The optimum content of the graphite addition is 0.26 mass%, with which most SiO 2 particles are reduced and the final carbon and oxygen contents are 0.03 and 0.01 mass%, respectively. These changes of compositions decrease the amount of δ-ferrite in the as-sintered compact to 4 vol%, lower than the 10 vol% of the compact without any graphite additions. After solutioning and aging treatment, the hardness, tensile strength, and ductility are HRC 41, 1310MPa, and 9.0%, respectively. These properties are better than the typical values of 17-4PH reported in the literature and the corrosion resistance remains similar to that without any graphite additions. The relevant mechanisms on the changes of these properties are discussed with a focus on the effects of graphite addition on the residual carbon content, fractions of δ-ferrite and martensite, silica amount, and density. ©2010 The Japan Institute of Metals.