Metal Injection Molding Method of Ni-Free Austenitic Stainless Steel II - Microstructure and Mechanical Properties

Microstructure and mechanical properties of high nitrogen steels whose chemical composition were Fe-17Cr-12Mn-3Mo and that was produced by using metal injection molding method and nitrogen absorption methods were examined. A compact which is furnace cooled from 1573 K has a brittle surface layer with high chromium and nitrogen contents but the surface layer disappears when the compact is held at 1473 K. The compact which is furnace cooled at 1473 K is observed precipitates in the grains and the grain boundary, while the compact which is quenched at 1473 K shows homogeneous microstructure. In the heat treatments at 1473 K for 2, 5, and 10 h, the nitrogen content becomes higher with increasing of holding time. In the holding times of 5 and 10 h, the microstructure is austenite. In the tensile tests, tensile strength becomes larger with increasing of nitrogen content. In the specimen which is conducted the heat treatment at 1473 K for 10 h, tensile strength is about 1,000 MPa and elongation is 80 %, which shows better balance of strength and elongation than SUS304 and SUS316 steels.