Silicon carbide is available in abrasive and metallurgical grades, with the former being purer but more expensive. Adding silicon carbide to the furnace transforms it into carbon and silicon, increasing carbon equivalence and enhancing the reducibility of molten iron, thus mitigating the adverse effects of refractory corrosion. Silicon carbide addition prevents carbide precipitation, increases the ferrite content, densifies the cast iron structure, significantly improves machinability, and ensures smooth cutting surfaces. Moreover, it increases the number of graphite nodules per unit area, improving nodularity. It also plays a vital role in reducing non-metallic inclusions and slag, eliminating shrinkage, and reducing subcutaneous porosity.
1. Role of pre-treatment:
During the eutectic solidification stage of cast iron, graphite acts as a pioneer, forming biphasic eutectic grains of graphite + austenite. Through pre-treatment, we can promote the massive precipitation of carbon during eutectic solidification to form graphite, reduce the supercooling of molten iron, and increase the number of eutectic nodules in gray cast iron or the number of graphite balls in nodular cast iron.
2. Pre-nucleation of non-equilibrium graphite:
Silicon carbide decomposes in molten iron to form non-equilibrium graphite, which promotes graphite formation and improves the distribution of carbon in the molten iron. The appearance of non-equilibrium graphite makes it easier for graphite to form in the molten iron, as this type of graphite combines more easily with the carbon in the molten iron, resulting in exceptionally superior nucleation effects.
3. Elimination of E-type graphite:
E-type graphite exhibits a distinct directional distribution between dendrites in cast iron, reducing the strength of castings. By using silicon carbide for pre-treatment, the structural foundation for the formation of E-type graphite can be eliminated, thereby enhancing the strength and toughness of cast iron.
4. Improvement of cast iron quality:
Pre-treatment with silicon carbide can increase the yield of magnesium in nodular cast iron and reduce the amount of nodularizer used, thereby improving the quality of cast iron. Its deoxidizing action can effectively purify the molten iron, mitigate the effects of oxide impurities in the furnace lining, and further enhance the quality of cast iron.
