A high-current arc discharge - basic slag refining furnace that can deoxidize and desulfurize cast iron melt prepared by conventional melting methods (e. g. induction or cupola furnace) was fabricated. To optimize the arc slag treatment of cast iron melt, the variation of basic and microelement compositions during the arc-slag treatment process was investigated.

  Strong deoxidization and desulfurization occurred and the silicon content of the heated cast iron melt decreased during the treatment. The nitrogen content increased with decreasing oxygen. Rapid decarburizing occurred at very high temperatures due to the reaction between carbon in the melt and slag, which absorbs microelements.

  The properties of the slag varied during the arc-slag treatment due to reactions with calcined lime used as a refining agent and with magnesia used as refractory. This indicates that the composition of slag needs to be controlled properly to refine the melt effectively in the treatment.

  In recent years, there has been an increase in the amount of manganese (Mn) contained in heavy section cast iron due to changes in raw materials. It is thought that the increase of Mn content has various influences on the mechanical properties of cast iron. It should be considered together with the optimum amount of RE (Rare earth elements) to be added to high-Mn heavy section spheroidal graphite cast iron. However, no such studies have been reported. Therefore, this study aims to investigate the effects of Mn and RE contents for mechanical properties and structural changes of FCD450-10 with different thicknesses. Spheroidal graphite cast iron was used as specimens with a Mn concentration of 0.3, 0.9% and RE concentration of 20ppm, 200ppm. The cooling rate to the eutectic temperature of the specimens with changed thickness was 0.22K/s, 0.12K/s and 0.08K/s respectively, for different specimen thickness.

  When the cooling rate was reduced and concentration of Mn increased, graphite grain size increased and formed a coarse cementite phase. When the specimen with RE concentration decreased from 200ppm to 20ppm, the pearlite area showed decreased nodule count and increased nodularity. For specimens with reduced RE, tensile strength and elongation increased with structural changes.