Research On The Injection Molding Process And Properties Of High Nitrogen Austenitic Stainless Steel

Preparing high nitrogen nickel-free austenitic stainless steel by metal injection molding?MIM?can shorten the diffusion distance of nitrogen,make the distribution of nitrogen more uniform and greatly shorten the nitriding time.Based on the research of preparing high nitrogen nickel-free austenitic stainless steel by powder metallurgy at home and abroad,the feedstock preparation,injection molding process,debinding process and sintering process of preparing Cr17Mn11Mo3N high nitrogen nickel-free austenitic stainless steel by MIM were studied in this paper.The main work and conclusions are as follows:?1?Study on the rheological properties of feedstocks.Feedstocks were prepared by mixing Cr17Mn11Mo3N powder and microcrystalline wax-based binder.The optimum powder loading range was calculated to be 62 vol.%⁷0 vol.%.Effects of binder composition and powder loading on the rheological properties of the feedstock were investigated using high pressure capillary rheometer.The rheological index_???of the feedstock were calculated by regression analysis using Second Order mold flow model.Results show that all the prepared feedstocks are pseudoplastic fluid.The feedstock with 68 vol.%powder loading and a binder composed of 65 wt.%MW+20 wt.%HDPE+5 wt.%EVA+5 wt.%SA has good comprehensive rheological properties.?2?Study on the injection molding process.The DSC-TG analysis of the feedstock was carried out to obtain the melting point parameters of each binder component and the feedstock.The injection molding process plan was made based on the melting point parameters.Results show that the process with 160?as injection temperature,45?as mold temperature,30 cm³/s as injection speed,100 MPa as injection pressure,80 MPa as holding pressure,and 3 s as injection time achieves even distribution of powder particles and binder.Phase separation of the feedstock is difficult during the injection,and the injected green parts are free from macro internal and external defects.?3?Study on the solvent debinding and thermal debinding process.According to the solubility parameter calculation of the binder component,petroleum ether,n-heptane and trichloroethylene were selected as solvent.Effects of solvent types,debinding temperature and thickness of green parts on the solvent debinding rate were studied.It was found that n-heptane was the best solvent for this binder;the higher the debinding temperature,the higher the debinding rate,but excessive temperature would cause defects such as blistering and cracking,and the best solvent debinding temperature for this binder system is 58?;the thicker the green part thickness,the lower the solvent debinding rate.The thermal debinding process plan was made based on the decomposition temperature range of each component in the binder.Results show that when the heating rate is 3?/min between 410?and 500?,and keep 1 h at 700?,the brown parts are free from defects and get a certain strength.?4?Research on the sintering nitriding process and effects of solution treatment.Effects of sintering temperature and sintering time on the density,nitrogen content and mechanical properties of the sintered parts under nitrogen atmosphere were studied.It was found that with the increase of sintering temperature,density of the sintered parts increases and the nitrogen content decreases.The density of sintered parts increases with prolonged sintering time,but keeping 3 h at 1380?brings about deterioration of mechanical properties.The microstructure and mechanical properties of the sintered parts before and after solution treatment were compared.Results show that parts sintered at 1380?for 2 h obtain high density of 98.18%and0.62%nitrogen content.The microstructure of the sintered parts after solution treatment at 1150?for 1.5 h is austenite and a small amount of ferrite.The compressive yield strength increases from 526.2 MPa to 603.1 MPa after solution treatment.