Dynamic Injection Molding Of High Nitrogen Nickel Free Austenitic Stainless Steel

Due to their superior corrosion resistance,biocompatibility and non-magnetic features,austenitic stainless steels play an important role in the fields of biological medicine,chemical metallurgy.However,most of those materials are Ni-Cr stainless steels,in which nickel ion is considered asa typical sensitive element.In addition,the content of nickel element is not abundant on the Earth.In order to solve nickel allergy and reduce cost,high nitrogen nickel free austenitic stainless steel is produced.Its mechanical properties,corrosion resistance and biological compatibility are better than traditional austenitic stainless steel thus it is very suitable for biomedical fieldsIn this project,a dynamic powder injection molding technique for high nitrogen nickel free austenitic stainless steel was developed.In the process of metal powder injection molding(MIM),the injection green billet was prepared by introducing electromagnetic vibration force field,and then the stainless steel parts were obtained by sintering in nitrogen atmosphere.Firstly,the effects of different vibration parameters(frequency and amplitude)on the injection green billet during powder injection were studied,and the optimized vibration parameters were obtained as follows: frequency of 3 Hz and amplitude of 30 ?m.Secondly,the influence of sintering process parameters on the density,shrinkage,nitrogen content and microstructure of the samples in nitrogen atmosphere was systematically evaluated by orthogonal experiment method.The optimized sintering parameters were obtained as follows: sintering temperature 1200 ?,sintering time 6 h,nitriding pressure 110 Kpa,resulting a high density(7.52 g/cm3)and nitrogen content(0.76%)for the sample.Finally,the sintered samples were treated with solid solution,and the effects of solid solution time on the microstructure and mechanical properties of the materials were studied.The optimized solution parameters were as follows: 1150 ? for 10 min followed by rapid water cooling.The mechanism of eliminating the precipitation of nitrogen compounds was analyzed.In addition,the mechanical properties and corrosion resistance of the stainless steel were evaluated.It was found that introducing vibration force field in the process of MIM injection could increase the density of injection green billet and final sintered product.After solid solution treatment,the elongation and corrosion resistance of the sintered workpiece will be significantly improved.The performance of MIM stainless steel products was improved using our optimized fabrication conditions.It provides a feasible solution for breaking through the technical bottleneck of preparing large parts by MIM process.