Effect of SiO2 containing slag for electroslag remelting on inclusion modification of 42CrMo steel

Five heats were carried out to study the effects of SiO2 containing slag for electroslag remelting (ESR) on inclusion characteristics of 42CrMo steel. Fluoride vaporization at elevated temperature from slags was also explored by thermogravimetric analysis. The results show that fluoride vaporization is dominated by slag viscosity and component activities in the melt. Slag composition has an important effect on the composition of the oxide inclusion. For 70 wt% CaF2–30 wt% Al2O3 slag, the compositions of oxide inclusions in remelted steel show no obvious differences compared with the virgin steel. Whereas, SiO2 content in oxide inclusions of steel processed by slag bearing SiO2 show an increasing trend with increase of SiO2 content in 50 wt% CaF2–CaO–SiO2 slag, and the MgO · Al2O3 inclusions are modified to (Al,Ca,Mg,Si)O inclusions with low melting temperature. Al2O3 contents in oxide inclusions are also closely related to the Al2O3 concentration in the molten slag, which increase with the addition of Al2O3 in slag bearing SiO2. In testing various slags, the incorporation of slag T2 with 50 wt% CaF2–30 wt% CaO–20 wt% SiO2 shows the highest cleanliness in remelted steel. This implies that slag T2 can be a promising slag for ESR process of alloy steel requiring Al content refinement due to less fluoride vaporization from slag and better inclusions modification.