Precipitation Mechanism and Reduction of Amount of Primary Carbides During Electroslag Remelting of 8Cr13MoV Stainless Steel

The precipitation and growth of primary carbides in 8Cr13MoV steel during electroslag remelting (ESR) were studied. The effects of melting rate and fill ratio of ESR on the reduction of primary carbides were clarified. Primary carbides M₇C₃ precipitated from liquid steel at the final stage of solidification, which is attributed to an enrichment of carbon and chromium in liquid steel. The carbon content in the residual liquid steel was the determining factor for the formation of primary carbides. The growth of primary carbides was affected mainly by the chromium-concentration and temperature-field gradients. An appropriate melting rate facilitated the nucleation and growth of dendrites, which caused dendrite closure and prevented the further enrichment of carbon atoms. Primary carbides were refined and their amount was reduced when using a lower ESR melting rate. The fill ratio can affect the uniformity of the temperature field in the liquid metal pool and heat transfer from the slag pool to the liquid metal pool, and an optimal fill ratio resulted in a minimum mushy zone and less primary carbides. The volume fraction of primary carbides was reduced by 23 pct when the melting rate decreased from 150 to 133 kg/h and the fill ratio increased from 0.23 to 0.33.