Study On The Microstructures And Properties Of High Speed Steel Roll By Electromagnetic Centrifugal Casting

In the dissertation, a new wear resistant layer of high speed steel roll was prepared by self-made electromagnetic centrifugal casting machine. Through hardness test, impact test and wear test and by means of Optical microscope (OM), scanning electron microscopy (SEM), energy spectrum analysis (EDS), X-ray diffraction (XRD), the microstructure, properties and wear resistance of the wear resistant layer for high speed steel roll made of sand casting, centrifugal casting and electromagnetic centrifugal casting in as-cast and heat-treated were studied. The effects of magnetic induction intensity on the microstructures and properties of the wear resistant layer were especially researched.The experiment results indicated that:the solidification microstructures of high speed steel were mainly composed of eutectic carbides (MC+M2C+M7C3+M23C6), martensite and residual austenite. When adding to electromagnetic fields, carbides in grain boundary reduced, intragranular carbide increased, carbides can be changed from grain boundary network, daisy-like to the granular and small block. It could improve the shape and distribution of carbides effectively in material, and also fine grain. Electromagnetic fields can make C, Cr, W, Mo, V distributed more evenly, reducing the segregation of alloying elements and the MC-type carbide. With the magnetic induction B increased, the amount of eutectic ledeburite constant increased, carbide lath for eutectic ledeburite became thinner and spacing larger. As the quenching temperature increased from 1050℃to 1200℃, the secondary precipitation of small MC type carbide constant increased, and they could be dispersive, homogeneous distribution. The mechanical properties of high speed steel such as hardness, impact toughness continuously improved, wear resistance is also gradually increased. With the magnetic induction B from 0T increased to 0.15T, hardness, impact toughness and wear resistance of high speed steel are presented first increased and then decreased phenomenon: when the magnetic induction B= 0.10T, the mechanical properties of high speed steel and wear resistance than sand casting and centrifugal cast high speed steel has significantly improved. But the magnetic induction B=0.15T, the mechanical properties and wear resistance was instead of decreased, which were closed to sand cast. When the magnetic induction density B=0.10T, heat treatment process for quenching temperature 1200℃+ twice 560℃tempered, the mechanical properties and wear resistance of high speed steel were best.The wear-resistant layer of high speed steel rolls made by electromagnetic centrifugal casting can effectively improve the carbide morphology and distribution of high speed steel, refine grain, reduce segregation of alloying elements and enhance the wear-resistant layer of high speed steel roll hardness, toughness and wear resistance.