Effect of PMO on dendritic structure and carbide of high-speed steel
In order to solve the problems of developed dendrite structure,uneven distribution of carbide network and eutectic carbides in high-speed tool steel on natural cooling conditions.The Center for Advanced Solidification Tech-nology of Shanghai University used a unique dual-power vacuum induction melting device,applying Pulse Magneto-oscillation(PMO)for external field intervention during the natural solidification of high-speed steel.The results show that with PMO treatment,the developed dendrites in the as-cast microstructure of high-speed steel are trans-formed into equiaxed grains.PMO technology can effectively optimize the as-cast microstructure and morphology of high-speed steel,refine the size of carbide network and eutectic carbide,and improve the uniformity of carbide distri-bution.PMO has a significant refinement effect on the size of the eutectic carbide network intersection of high-speed steel.Taking the refinement of the eutectic carbide network intersection size of M2 high-speed steel as an example,the average size of the carbide intersection at 1/8D,1/4D,and 1/2D(where D is the radial diameter of the casting bille)is reduced by 48.5％,47.1％,and 43.4％,respectively,compared to the ingots without PMO treatment.Mean-while,PMO can further refine the size of eutectic carbide particles.Taking M2Al high-speed steel as an example,the average size of eutectic carbide particles at 1/8D,1/4D,and 1/2D decreases by 49.1％,54.5％,and 40.2％,respec-tively.It provides a new idea and method to solve the cracking phenomenon in the process of high-speed steel pres-sure machining with large deformation and improve its yield.It also provides a new direction for improving the prob-lems encountered during high-speed steel continuous casting,such as the aggregation of carbides in the center and coarse carbides.
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