Preparation And Properties Of Nitrogenous Nickel-free Stainless Steel Metal Powder Feed For Injection Molding

In this paper,a nitrogen-containing nickel-free stainless steel feedstock for injection molding was prepared and its properties were studied,with a focus on the rheological properties of the feedstock.Secondly,the effects of injection moldability,degreasing,sintering and solution treatment on the microstructure,mechanical properties,friction and wear properties of the samples were studied.A large number of research work and theoretical analysis have been carried out by using high pressure capillary rheometer,scanning electron microscope,thermal analyzer and other modern analysis and detection technologies.The main research conclusions are as follows:(1)In this paper,a new type of catalytic degreasing binder system was developed,which was uniformly mixed with metal powder to prepare the feed,and the rheological properties of the feed were studied.When the temperature is 195°C,the metal powder loading is 62%(volume fraction),and the binder formula is 88%POM+5%HDPE+2%EVA+5%SA(mass fraction),feed B has the best performance The comprehensive rheological properties,that is,the non-Newtonian exponent n value is 0.39,the viscous flow activation energy E value is 35.6KJ/mol,and the comprehensive rheological factor?_STVis 2.2.(2)When the injection temperature is 195°C,the holding pressure is 90 MPa,and the injection speed is 55 mm/s,the injection green part has no macroscopic and internal defects,and the average mass is 21.25 g.The best feed B has good injection moldability.(3)When the catalytic degreasing temperature is 130°C and the time is 12 h,the degreasing rate of the green body is 93%,the surface and interior of the degreasing part are free of defects,and the shape retention is good.The best feed B has good degreasing performance.(4)When the sintering temperature is 1310°C and the holding time is 2 h,the microstructure of the sample is austenite,ferrite and Cr₂N,the average density is7.633g/cm³,and the relative density is 98%.sinterability.After the tensile test of the sample,it was found that the average tensile strength?_band yield strength?_0.2of the sample were 574 MPa and 473 MPa respectively,which exceeded the performance standard of the stainless steel MIM material(MIM-316L sintered state)in the American MPIF standard;And the average tensile strength?_bis 10%higher than that of stainless steel MIM-316L(sintered).The average hardness of the sample is 39 HRC,and the average elongation,area shrinkage and impact energy are 21%,73%,and 192 J,respectively.The sample has good plasticity.(5)When the solution temperature is 1150?and the holding time is 1.5 h,the microstructure of the sample is austenite and a very small amount of ferrite,and there is no precipitation phase.The comprehensive mechanical properties test of the samples shows that the average tensile strength?b and yield strength?_0.2of the samples are 622 MPa and502 MPa respectively,and the average tensile strength?_bis 8%higher than that of the sintered sample(574 MPa).The hardness is 39 HRC,which is consistent with the sintered parts.The average elongation and area shrinkage are 18%and 86%,respectively.The plasticity and toughness are slightly higher than that of the sintered parts,and the mechanical properties of the samples are significantly improved.The wear rate of the sample is 4.167×10^-4mm³/Nm,the average friction coefficient is 0.5739,and the wear resistance is good.