Influence Of Low Frequency Electroslag Remelting On Inclusions And Solidification Quality In Steel

As a special metallurgical method,electroslag remelting plays an important role in the production of high-quality materials.At present,the vast majority of electroslag furnaces in China are powered by power frequency and single-phase operation,that is,the power supply to electroslag furnace is powered by high-voltage power frequency direct voltage reduction,this power supply method will cause problems such as threephase unbalance,large short-circuit voltage drop,low power factor,and serious waste of electric energy.With the development of electrical and electronics,the advantages of high-power low-frequency power supply,such as high power factor and three-phase balance,have attracted the attention of metallurgical workers,and put forward the viewpoint of low-frequency electroslag remelting.However,the domestic lowfrequency electroslag remelting is still in the exploratory stage,and the technology is not mature,especially the research on inclusions and solidification quality is less.This paper mainly explores the influence of low-frequency electroslag remelting on the quality of electroslag ingots,and provides more comprehensive basic data for the application of low-frequency electroslag remelting.On the basis of the previous research,based on the self-designed electroslag furnace with low-frequency power supply system,taking 304 austenitic stainless steel and GCr15 bearing steel as the research objects,and studies the effect of power frequency change on the inclusions and solidification quality of electroslag ingots.and the following main conclusions are drawn:(1)Compared with the power frequency,the low-frequency electroslag remelting will obviously increase the oxygen content in the two steels;the overall variation of nitrogen content in 304 steel fluctuates less,while the nitrogen content in GCr15 steel first decreases,then increases,and then decreases again.(2)For the two steels,low frequency electroslag remelting will increase the number of inclusions in the electroslag ingot,and the increased inclusions are mostly A-O inclusions,and the size of the inclusions is mostly less than 10 μm;appropriate low frequency can control the inclusions in the electroslag ingot.(3)For 304 stainless steel,when the power frequency is reduced to 0.4Hz,the depth of the molten metal pool is the shallowest at this time,the crystallization process tends to grow axially,the uniformity of the thickness of the slag skin is improved,the solidification quality is improved,and the element segregation is smaller;however,as the frequency further decreases,the depth of the molten metal pool becomes deeper,the degree of element segregation increases,and the solidification quality deteriorates.(4)Low frequency can affect the change of liquefied carbides in GCr15 bearing steel.Compared with power frequency remelting,low frequency can effectively reduce the number of carbides,especially for the edge and 2/3R,the number of carbides decreased greatly,while the number of carbides in the core increased slightly;proper low frequency can reduce the maximum size of liquid carbides,while the average size does not change much.(5)The reason for the increase in the content of oxygen and inclusions in the electroslag ingot during low-frequency remelting is that the low-frequency effect makes the electrolysis process that is not easy to occur at power frequency more likely to occur,the electrolysis time becomes longer,and the metal elements generated by reduction and the atomic oxygen generated by oxidation react again in the molten metal pool to generate oxides,thereby increasing the oxygen content and the number of inclusions in the electroslag ingot.(6)Low frequency can reduce the depth of the molten metal pool,increase the external heat transfer capacity,increase the cooling rate,improve the solidification quality of the electroslag ingot,and reduce the segregation of components;when the cooling rate is increased,the crystallization can be completed in a faster time,the enrichment degree of C and Cr elements in the dendrites decreases,and the size of liquefied carbides in GCr15 becomes smaller.