Study Of Processing,Microstructure And Properties Of Powder Knife Steel

China is a big country in the production and use of knife in the world,but the high-end knife market of the china is basically monopolized by foreign brands.The reason is that China's knife-related production technology lags behind foreign countries and there was a lack of research on the process system of knife,which leads the ideal microstructure cannot be obtained in different production stages.Therefore,it was very important that the systematic study on the evolution of the knife material structure during the production process for the rational development of the production process.In this thesis,scanning electron microscopy and X-ray diffraction were used to characterize the structure of the three original M390 powders prepared,and the changes of the microstructure and mechanical properties of the original powder during subsequent hot isostatic pressing and hot rolling process were systematically studied.At the same time,in order to clarify the law of the transformation of the M390 tool material at different cooling rates,the phase transition temperature was measured by the Gleeble thermal simulator and the continuous cooling transition curve of M390 was drawn.In order to further discuss the related influences of different machining processes,the effect of different starting rolling temperature,finishing rolling temperature and annealing temperature on the microstructure and properties of the tool materials under study was studied,and then the mechanism of the influence of carbide evolution on the properties was revealed.The research results show that with the increase of the particle size of the three original powders 2M390,3M390 and M390E,the solidification structure of the powder particles gradually changes from dendrite to cell crystal,and the average grain size gradually increases,and the matrix structure was changed from delta ferrite+Austenite gradually transforms to martensite;all three powder particles have Cr-rich M₂₃C₆ and other carbides,while V-rich MC carbides only appear in 3M390 and M390E with relatively high N content.After hot isostatic pressing,the three tool material structures were composed of ferrite matrix and carbide precipitated on the matrix.However,due to the V and N content of 3M390 and M390E were significantly higher than 2M390,solid solution strengthening makes the ferrite matrix The strength was improved and at the same time more MC carbides were precipitated,so the plasticity was relatively low.The three HIP states M390 showed a tendency to increase in strength but significantly decrease in plasticity after hot rolling.This was because the matrix structure was transformed into martensite.On the other hand,the material grows at high temperature for a long time and the grain grows.A large amount of carbides were dissolved,and the V-rich MC carbides in 3M390 and M390E were not easily decomposed at high temperatures,resulting in a low solid solution strengthening increment.At the same time,pinning the original Austrian grain boundaries inhibits the growth of grains,which ultimately increases the strength of the material Has maintained a certain plasticity.After annealing at different temperatures of hot-rolled 2M390,it was found that with the increase of annealing temperature,the matrix structure was transformed into ferrite,and the number of carbides such as M₂₃C₆ distributed on the matrix was significantly reduced,which weakened the precipitation strengthening effect,so it was higher During temperature annealing,the strength was low but the plasticity was better;on the other hand,the group of M390 with a higher initial rolling temperature will reduce the number of carbides after subsequent annealing at different temperatures,so that the solid solution strengthening effect was obvious,so the overall strength of the group M390 was higher.The results of S35VN microstructure and properties after finishing rolling at different temperatures show that with the increase of finishing temperature,the matrix structure changes from ferrite to martensite,and it shows a trend of increasing strength and decreasing plasticity.Compared with 900?and 950?final rolling,850?low temperature final rolling,because the matrix was low strength ferrite,and the distribution of more fine Cr-rich M23C6on the matrix reduces the solid solution strengthening effect,so The tensile strength at room temperature was lower,but the plasticity was significantly better than the two groups of materials after high temperature final rolling.Through the systematic study of powder tool material forming process and organization and performance at different stages of preparation and processing,the key factors and influencing mechanism that affect the performance of tool materials were clarified,which provides strong support for optimizing the production process of powder tool materials and achieving the localization of high-quality tool.