Preparation,Properties And Microstructure Of PM60 High Speed Steel

High speed steel,the full name of high speed tool steel,is characterized by a large variety and content of alloy elements,so it can still maintain hardness above 60 HRC,good wear resistance and heat resistance at 550℃to 600℃.Therefore,it is widely used in tools,molds,and some special components.However,traditional high speed steels often have problems such as severe carbide segregation.High speed steel produced by powder metallurgy（PM）process can fundamentally solve this problem.PM60 high speed steel is a kind of high speed steel with high C,high V and high Co prepared by powder metallurgy technology,which has better high-temperature properties compared to ordinary powder high speed steel.However,due to technical limitations,the preparation process of this material has not been fully mastered in China.Therefore,exploring the preparation process of PM60 high speed steel is of great significance.In this paper,using Mo₂C,Co,and M2 high speed steel powders as raw materials,PM60 high speed steel was prepared by powder metallurgy sintering in a vacuum environment.The optimal sintering temperature of 1250℃was obtained.Then,at this sintering temperature,the effect of the addition of C and Co elements on the sinterability of PM60 high speed steel was investigated.The mechanism of carbide precipitation during heat treatment was studied by quenching and tempering the finished PM60highspeed steel at different temperatures.The main research results are as follows:After 8 hours of ball milling,the uniformly mixed PM60 high speed steel powder is finely distributed and still retains its original spherical shape.The high speed steel prepared at 1250℃sintering temperature has uniform microstructure,fine carbide size,uniform distribution,and no segregation.At this sintering temperature,increasing the C content can increase the density of PM60 high speed steel and reduce macro porosity;With the increase of C content,the amount of carbide precipitated in high speed steel increases;When the amount of C added reaches 0.6 wt%,the size of carbide in the microstructure increases significantly and a network structure is formed and distributed at the grain boundaries.Co has little effect on the sintering density of high speed steel,and adding Co can slightly increase the hardness of PM60 high speed steel.PM60 high speed steel is quenched and tempered at different temperatures.The annealed,quenched,and tempered carbide phases in PM60 high speed steel are mainly MC and M₆C.After three times of high-temperature tempering treatment at 1180℃and quenching treatment at 540℃,the hardness of PM60 high speed steel can reach 62.3 HRC.The hardness of PM60 high speed steel after quenching and tempering is linearly proportional to the percentage of carbide with size less than 1μm.The larger the amount of carbide with size less than 1μm,the higher the hardness of the material after quenching and tempering.