Sintering optimisation and solution annealing of high nitrogen nickel free austenitic stainless steels prepared by PIM

The effects of various sintering parameters (temperature, time and nitrogen pressure) on the density, nitrogen content and the mechanical properties of high nitrogen nickel free austenitic stainless steel (0Cr-17Mn-11Mo-3N) prepared by powder injection moulding were investigated, and the influence of solution annealing on the microstructure and mechanical properties was also discussed. The results show that the optimal sintering conditions are as follows: sintering temperature 1300 degrees C, sintering time 2 h and nitrogen pressure 0.1 MPa, under which a favourable combination of the relative density of 99.1% and the nitrogen content of 0.78 wt-% can be obtained. After solution annealing at 1150 degrees C for 90 min, the yield strength and ultimate tensile strength can reach 580 and 885 MPa respectively, which are about 2.9 and 1.7 times greater than those of 316L Metal Injection Molding (MIM) stainless steel. Before solution annealing, the sintered specimens mainly consist of gamma-austenite, alpha-ferrite and network of Cr2N phase, while after solution annealing, they reveals a fully austenitic structure without any intergranular nitrides.