Research On Powder Injection Molding Of17-4PH Stainless Steel

17-4PH stainless steel is widely used in medical, chemical, automotive, military, aerospace and nuclear industries for various applications that require high strength and good corrosion resistance. The high hardness of the alloy resulting from precipitation hardening, however, makes machining the alloy a challenging task. To overcome the manufacturing difficulties, metal injection molding (MIM) has been considered an alternative for the fabrication of17-4PH stainless steel parts. As a near-net shape process, MIM combines the shaping advantages of plastic injection molding with the capability of powder metallurgy for processing metal powders. Previous work has shown that MIM can be advantageously applied to the fabrication of17-4PH stainless steel parts. In the factual MIM process of17-4PH stainless steel, However, there are such problems as injection defect, low strength of solvent degreasing part, deformation of thermal debinding part and bad dimensional accuracy of sintering part due to improper process parameters of MIM. In this thesis, effect of the content of microcrystalline wax on rheological properties and optimization of process parameters of17-4PH stainless steel was instituded. The results show that:In the process of MIM17-4PH17-4PH stainless steel, injection process parameters have an effect on injection effect, bending strength and shape retention of green parts. In the condition of147centigrade,8.5MPa pressure,70%velocity,1.5second hold time and20second cool time, the green part was with no defect, high bending strength and good shape retention. In solvent degreasing process, degreasing rate increases as temperature rises, thickness reduces and specific surface area increases. in addition, kinetic parameters of solvent degreasing was instituded, which helps to forecast degreasing time and optimize the process of solvent degreasing.The process of thermal debinding was formulated via TGA of binder and feedstock with no defect thermal debinding part. Mechanical properties of thermal debinding part rises with the highest temperature of thermal debinding increased and in the condition of950centigrad, the figures for tensile strength and bending strength of thermal debinding part were117.71MPa and104.81MPa. the highest temperature of thermal debinding was match to sintering temperature and in the condition of900centigrade of thermal debinding and1350centigrade sintering temperature, the figures for tensile strength and bending strength of1350were1538.57MPa and1164.12MPa.inthe process of sintering, bending strength of sintering part rises as hold time and the highest temperature of sintering increases, and in the condition of1350centigrade and60min hold time, the sintering part has the highest tensile strength and the figure for which is1481.35MPa.Certain content of MW into the binder of feedstock can reduce sensibilities of feedstock to the parameters and the feedstock can be injected in wider parameters range with no defect, which helps to overcome volatile of injection machine and environmental factors. Dichloromethane as solvents, at35centigrade, binder of four feedstocks can be degreased rapidly with no defect and the degreasing process of the feedstock with20%MPW is at the soonest, the rate is1.444mm/h. the bending strength of solvent degreasing part rises as content of MW increases. And the part of feedstock with20%MPW has best shape retention. Bending strength of thermal debinding part of four feedstocks rises with more content of MW in, because the MW improve uniformity of dispersion of powders and then the pore thermal debinding part disperses well-distributedly and powders can be linked uniformly. Four feedstocks all have good shape retention, and standard deviations of shrinkage is less than0.25%, and the feedstock with20%MPW have the best shape retention.