Study On Solidification Behavior And Microstructure Control Of High Alloy Steel Electroslag Remelting Process

With the continuous advancement of industrialization,the performance of cutting materials has been constantly demanded by the mechanical processing industry and the high-speed steel is widely used for its features such as high hardness,high wear resistance,good thermal stability and toughness.However,the decline of high-speed steel performance caused by the uneven distribution of carbides in high-speed steel is a major problem encountered in the current high-speed steel production.Although the electroslag remelting process effectively improves the uneven distribution of carbides,the phenomenon of core inhomogeneity is still serious when producing the large-size high-speed steel products.The electroslag remelting involves many parameters and the research efficiency is low through tests.In the paper,the process of electroslag remelting high-speed steel is optimizes based on numerical simulation technology and the influence mechanism of different electroslag process on the core is discussed as well as the influence of the addition of microalloying elements in the electroslag remelting on the microstructure.The electromagnetic field,temperature field and microstructure during the process of the electroslag remelting are simulated by simulation software and the simulation results are verified by text.According to the results,the molten pool area around the edge of the electrode has the highest current density and slag and the upper part of the slag pool is the high temperature area.There are two large eddy currents in the lower part of the slag pool which have the maximum velocity near the side wall.The upper part of the ingot is equiaxed crystal and the other part is the columnar crystal which presents a certain angle with the axis.The flow field and temperature field of the two-electrode remelting system are simulated based on the above model.For the two-electrode remelting process,two vortices are generated in the upper part of the slag pool and the maximum flow rate is almost four times that of the single electrode.The maximum temperature of the slag pool of the two-electrode remelting process is lower than that of the single electrode remelting process.By studying the effect of the single and two-electrode process on the microstructure,it is found that at the center,coarse equiaxed dendrites are formed in the single-electrode remelted ingot,while more uniform columnar dendrites appear in the two-electrode remelted ingot.The width of the M2 C carbide of the single electrode remelting ingot is also smaller than that of the single electrode.At the position near the edge,there is almost no difference in the columnar dendrites of the two ingots and the amount of carbides formed in the single-electrode remelted ingot is also higher than that of the two electrodes.The two-electrode process not only makes the carbide distribution in the ingot more uniform but also more energy efficient.After the high and low melting rate tests,it was found that the change of the melting rate does not have much influence on the morphology and size of the M2 C carbide in the steel.However,when the melting rate is high,the amount of MC type carbide in the high speed steel is significantly higher than that in the low melting speed ingot and the MC carbide size is generally smaller than that in the low-melting speed ingot.In addition,the V content in the MC carbide in the high and low melting speed ingot is also different.Compared with the normal melting speed,the melting speed too high or low is not conducive to improving the quality of high-speed steel ingots.The microalloying of high speed steel can be well realized by the in-situ microalloying based on electroslag remelting.The addition of rare earth elements makes the form of carbide in high speed steel become regular fiber shape which plays the same role as improving the cooling rate,but the resulting promotion of the formation of M6 C carbide is disadvantageous in post processing.The addition of Ti effectively reduces the grain size,but the carbide is coarser and its size is increased compared with the size of the carbide in the rare earth microalloying.The composite microalloying of rare earth and Ti has achieved good results.Although the grain size is not further refined,the carbide layer is thinner and tends to be split at different grain edges,which facilitates the subsequent heat treatment of the carbide transformation.