Research On High Speed Steel Heat Treatment Process Boron

With the development of modern industry, developing of low alloy steel has become an inevitable trend to reduce the production cost. In this context, using of boron element instead of alloy elements in high-boron high speed steel is the ideal choice of the researchers. This paper analyzes the quenching and tempering temperature on the microstructure and mechanical properties of the high-boron high speed steel by adopting the method of heat treatment of quenching and tempering. The purpose is to solve the problem of high-boron high speed steel mechanics performance is low because of the borocarbide distribute in network and herringbone along the grain boundaries and lead to dissever to the matrix of high-boron high speed steel, laying the foundation for the high-boron high speed steel of applying to practical production.Using the JB30A impact toughness test machine to test the impact toughness value of the high-boron high speed steel, adopting Lecia Metallographic microscope to observe and analyze the microstructure of the as-cast and after heat-treated sample and determining the volume fraction of the borocarbides, using HR-150rockwell hardness tester and HV-1000digital vickers hardness tester to measure the macrohardness and microhardness of sample, analysing of as-cast and after heat treatment phase by Bruker D8Advance x-ray diffractometer.The analysis of microstructure and phase show that the as-cast microstructure of high-boron high speed steel is mainly composed of martensite, pearlite and borocarbide. The borocarbide composed of M23(B,C)6, M(B,C), M2(B,C) and M3(B,C), and the volume fraction of borocarbide is30.2%. After quenching, the matrix microstructure changed into martensite, and containing a small amount of residual austenite, the content of borocarbide have certain reduction. After quenching, the volume fraction of borocarbide is29.5%,28.8%,27.1%and25.9%, the amount of residual austenite is3.3%、3.9%、4.3%and4.9%.The coronal scan of sample show that the elements distribution of C and B were not uniform, the carbon are mainly distribute in the matrix and the boron element mainly formed borocarbide, little diffused into matrix, which helps improve the hardenability and hardenability of matrix. After heat-treatment, the distribution of C have no basic change, which become more uniform, but the content of matrix is increased, the boron element still enrich at grain boundary.The mechanics performance testing indicate that th macrohardness is55.6HRC, the microhardness is595HV, the impact toughness is4.5J/cm2. After quenching, the hardness and impact toughness have been improved, the microhardness of matrix is unchanged basically, the microhardness of matrix reach peak at1050℃, when the quenching temperature exceeds1050℃, the matrix microhardness declined. After tempering, the hardness increased gradually with the increase of tempering temperature, after the tempering temperature of more than525℃, the hardness decrease gradually with increasing tempering temperature. And with the increase of tempering temperature, the impact toughness also improve gradually.