Study On Heat Treatment Process And Performance Of Centrifugal Cast High Speed ​​Steel

In order to meet the machinery, petroleum, chemical, and mining engineering equipment parts and components of high wear resistance working conditions, a new alloy composition HSS (high-speed steel) is designed and studied by us from the actual conditions of using, metallurgy and heat treatment process in this article. The different heat treatment process is adopted to study of the changes of microstructure and properties of HSS. Analysis of the structure, performance test of the HSS is evaluated. The OM, SEM, EDS and XRD are used to observe and analyze the internal organization of homogenization structural change of the HSS sample in the preliminary heat treatment and the post heat treatment to improve overall strong hardness. The typical mechanical properties and wear resistance in different heat treatment process is tested by the hardness tester, universal bending testing machine and the wear testing machine. In the paper, the correlation of the preliminary heat treatment and post treatment are discussed from the theory, and the HSS dissolution of grain boundary and diffusion of carbide in the matrix is studied through thermodynamic calculation when the sample is put in the high austenite temperature, and give a further summary relationship between preliminary heat treatment process and post heat treatment.On the basis of the above research, the paper gets the following main conclusions:(1) It has a high hardness of52HRC because the centrifugal casting HSS has a complex microstructure, which the microstructure are retained austenite, martensite, and eutectic carbides. And the eutectic carbides morphology showed serious segregation along the grain boundary, which are mainly M7C3, M2C and W6C.(2) By adjusting the internal carbide morphology, improving the degree of tissue homogenization, the quenching and tempering heat treatment, isothermal annealing can reduce the hardness to adapt to the post processing. There is little hardness change by quenching and tempering, which between42and43HRC. When the tempering at620℃, the carbide content is the lowest(is12%) in the grain boundary; The grain boundary carbide maintain a high level of more than20%by isothermal annealing,when at820℃isothermal treatment,the sample is the lowest hardness, which is43HRC.(3) The quenching temperature range is narrow, when implementing quenching strengthening process of HSS,1000℃-1020℃is the suitable heat treatment interval. The temperature is too high, the HSS is overheating. When at1000℃, the two kinds of heat treatment sample both have maximum quenching hardness.(4) In the process of aging strengthened after quenching, the sample will be hardening by twice different temperature tempering. The sample though quenching and tempering& strengthening treatment, the lamellar carbide will broken network and fragmentation. It has a lowest average surface friction coefficient of0.3123, a highest hardness of68HRC, the sample which one after1000℃quenching,380℃and540℃tempering heat treatment. Through the grinding experiment, it has excellent wear resistance, which is17.2times that of wear resistance for KmTBCr26wear-resisting performance.(5) Through thermodynamic calculation, the carbide content in the grain boundary, carbon atoms in the grain has a great influent on the carbides-dissolution and the carbon-diffusion when in high quenching temperature. The carbide solubility and temperature increased nearly linear relationship. The diffusion of carbon atoms is influenced by the activity of carbon atoms, diffusion coefficient and the original state.