Sulfur can cause “hot brittleness” of cast iron during smelting of gray cast iron and reduce the corrosion resistance, welding performance and mechanical properties of cast iron. However, when rare earth inoculates gray cast iron, the sulfur content must not be lower than a specific value, which is determined by the process of inoculating gray cast iron, In the process of rare earth inoculating gray cast iron, rare earth can react with sulfur in gray cast iron to form rare earth sulfide. The rare earth sulfide with high melting point acts as an external core to promote graphite nucleation, so as to promote the graphitization of gray cast iron and protect the inoculation process, Therefore, in the process of rare earth inoculation of gray cast iron, the sulfur content of gray cast iron must be ensured to ensure the inoculation effect.
The research shows that the existence of sulfur in molten iron will reduce the spheroidizing ability of rare earth and aggravate the formation of vermicular graphite layer on the surface of gray cast iron. When gray cast iron is cast, the sulfur content in molten iron is too high or too low, which will lead to the deterioration of cast iron graphite. Even if rare earth inoculation is used, it is difficult to produce inoculation effect. When the sulfur content of original molten iron is less than, The inoculation effect of rare earth is not ideal, and the inoculation amount is not easy to control, which is easy to produce a large number of carbides; When the sulfur content of molten iron is greater than, the number of eutectic clusters inoculated by rare earth increases sharply, and the tendency of shrinkage porosity and intercalation increases; Only when the sulfur content of molten iron is, it is most suitable for rare earth inoculation.