Effects of Carbon Content on the Properties of Novel Nitrogen-Free Austenitic Stainless Steel with High Hardness Prepared via Metal Injection Molding

A novel nitrogen-free austenitic stainless steel with a hardness of >200 HV was developed using metal injection molding (MIM), and the effects of graphite addition on the sintering behavior, mechanical properties, and corrosion resistance of heat-treated samples were investigated. The results show that a certain amount of graphite addition increases the relative density to >98%. In samples with the addition of 0–500 ppm graphite, large grain-boundary precipitates reduced corrosion resistance and ductility. In contrast, when graphite addition was increased to 750–1500 ppm, fine precipitates, which exhibited coherent lattice relationships with the matrix, were uniformly distributed within the grain and grain boundaries; this significantly improved the mechanical properties and corrosion resistance. The tensile strength and elongation intervals were 546.94–608.62 MPa and 29.68–24.63%, respectively. To prevent overburning, samples with a graphite content higher than 3000 ppm were sintered at a lower temperature, resulting in a higher porosity and lower performance.