Technical Measures in The Production Of Gray Iron Castings (4)

The formation of crystal nuclei

(1) The influence of inoculation Inoculation treatment can sometimes increase casting defects, and the tendency of forming carbides in iron castings that are rapidly nucleated due to strong inoculation is increased. Therefore, it is recommended that the amount of inoculant used in the inoculation treatment can prevent the white mouth. The crystal nucleus in the healthy casting is much less than the casting with shrinkage cavity.

(2) The role of sulfur As most scraps contain low S content, when the electric furnace melts the scrap, only cast iron with low S content (≤0.05%) can be obtained. This kind of cast iron does not work for many inoculants. The reason is that the inoculation decays very quickly. Therefore, when scrap steel is melted in an electric furnace, white holes are often produced in the castings. Therefore, sometimes a carburizer with a relatively high sulfur content is used, which can make the final ws ≥ 0.05% to ensure that the inoculant is fully absorbed.

(3) Heat preservation and overheating temperature of molten iron In recent years, people tend to use electric furnaces to melt and heat molten iron. However, increasing the overheating temperature and increasing the holding time will reduce the formation of crystal nuclei, so there is a danger of white mouth. Considering the reasons of economy and material performance, the temperature should be as low as possible during long-term heat preservation.