Research On Dimensional Accuracy Of 17-4PH Stainless Steel Produced By Metal Injection Molding

17-4PH stainless steel has high strength and strong corrosion resistance,and is widely used in machinery manufacturing,aerospace and medical fields.But it is difficult to process,so it is mostly prepared by MIM technology.However,MIM is a technology that includes multiple process links.If a certain link is not properly controlled,it is easy to cause defects such as deformation and cracking of the product,which seriously affects the performance and accuracy of the product.Therefore,this study systematically explored the influence of relevant factors in each process link of MIM on the dimensional accuracy of 17-4PH stainless steel.In the feedstock preparation phase,this study firstly discusses the influence of the melt flow index(MFI)of POM on the feedstock performance,and further explores the relationship between the feedstock performance and the dimensional accuracy of MIM17-4PH on this basis.The results show that with the increase of the MFI value of POM,the fluidity of the feedstock is continuously improved,and the uniformity is obviously deteriorated when the MFI value of POM reaches 230 g/10min;Combined with the result of the fluidity and uniformity of different feedstock and dimensional accuracy results of samples prepared with different feedstock,it can be seen that with the increase of feedstock fluidity,the dimensional accuracy of samples will first increase and then decrease,while the better the uniformity of feedstock,the higher the dimensional accuracy of samples;Secondly,the single variable method was used in this study to explore the effect of powder loading on the dimensional accuracy of 17-4PH stainless steel.The results show that with the increase of powder loading,the dimensional accuracy of the samples will first increase and then decrease;When the powder loading is 62%,the dimensional accuracy of the samples in the height direction is ±0.13%,which is relatively good.In the injection phase,the single-variable method was used to study the effects of injection parameters and injection cycle times on the dimensional accuracy of 17-4PH stainless steel.The results show that the injection temperature,injection pressure,injection speed,pressure holding time,cooling time and the number of injection cycles all have important effects on the dimensional accuracy of 17-4PH stainless steel;When the injection temperature is 195 ℃,the injection pressure is 120 MPa,the injection speed is 60 mm/s,the pressure holding time is 2.5 s,and the cooling time is 10 s,the dimensional accuracy of the samples in the height direction is ±0.17%,which is relatively good;The number of injection cycles should not exceed 10,otherwise the POM and SA in the feedstock will be seriously lost,resulting in a significant drop in the dimensional accuracy of the samples.In the debinding phase,the effects of thermal debinding temperature and heating rate on the dimensional accuracy of 17-4PH stainless steel were studied by single-variable method.The results show that the change of thermal debinding temperature has no obvious effect on the dimensional accuracy of the samples in the range of 600 ℃-900 ℃;With the acceleration of the heating rate,the residual binder content in the debinding part increases,resulting in the gradual decline of the dimensional accuracy of the samples;When the heating rate of thermal degreasing is 2 ℃/min,the dimensional accuracy in the height direction of the sample is ±0.13%,which is relatively good.In the sintering phase,the single-variable method was used to study the effects of sintering temperature,holding time and heating rate on the dimensional accuracy of 17-4PH stainless steel.The results show that when the sintering temperature is 1340 ℃,the holding time is 1 h,and the heating rate is 5 ℃/min,the internal pores of the samples are less and the microstructure of the samples is more uniform,so its dimensional accuracy and mechanical properties are comprehensively better;Under this sintering condition,the density of the samples is 98%,the hardness is 322.64 HV,and the tensile strength is 924.85 MPa,which reaches the usual performance levels of MIM17-4PH stainless steel;At this time,the dimensional accuracy of the samples in the height direction is ±0.15%.Through all single-factor variable control experiments,it can be seen that the highest level of dimensional accuracy in the height direction of the samples is ±0.13%.It can be speculated that under the optimal process conditions,the dimensional accuracy of 17-4PH stainless steel can be controlled within ±0.13%.