Yoshikazu Kuroda

Metal Injection Molding of Nickel-Free Austenitic Stainless-Steels I-Manufacturing Process

Ni-free austenitic steels containing high nitrogen have been developed to protect against earth resource. High nitrogen steels (HNS) have a lot of advantages, e.g., HNS have high strength, corrosion resistance, toughness, work hardening rate and large rocking parameter in the Hall-Petch equation. On the other hand, it is difficult to fabricate HNS by IM method under 0.1 MPa and to work at room temperature. We have tried to make HNS by combined use of metal injection molding method (MIM) and nitrogen absorption method. Powder compositions used was Fe-17Cr-12Mn-3Mo.The benefit of this method is to make metal parts in near net shape. In order to use this method, we should know the sintering heat schedule, timing for introducing nitrogen gas, gas pressure and setter material etc. Therefore, the shrinkage rate, density and the solution-treated microstructure of MIM compacts were examined to find out the optimum conditions.

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.