During the steelmaking process, due to improper batching or charging and excessive decarburization, the carbon content in steel or iron may fail to meet the required standards. In such cases, carbon must be added to the molten steel or iron, typically using petroleum coke as a carbon additive. Tar-based carbon additives are commonly employed for this purpose. These additives are introduced into the metal smelting furnace, where carbon dissolves and diffuses into the molten iron to increase its carbon content. The absorption rate depends on the dissolution and diffusion speed of the carbon additive and the rate of oxidation loss. This process not only enhances the carbon content in the molten iron but also reduces its oxygen content, with the more critical benefit being the improvement of the mechanical properties of the smelted metal or castings. In other words, by utilizing carbon additives, inferior scrap steel can be transformed into high-quality castings.

The new process of adding carbonaceous materials for smelting, compared to the traditional method, involves many coarse hypereutectic graphite in pig iron. This coarse graphite exhibits heredity, resulting in lower smelting temperatures where the coarse graphite is less likely to be broken down. The coarse graphite is inherited from the liquid phase to the solidified cast iron structure, which not only reduces the achievable strength of cast iron and degrades material performance but also weakens the expansion effect that should occur during graphite precipitation in the solidification process, thereby increasing the shrinkage tendency during molten iron solidification.  During cupola smelting, efforts should be made to minimize the use of pig iron charge while employing carbonaceous materials to maintain high carbon equivalent and relatively increasing scrap steel usage. Under high-temperature smelting conditions, carbon can be effectively introduced to yield highly reactive and more graphitizing carbon. This results in better graphite morphology in castings, thereby enhancing mechanical properties, reducing shrinkage tendency, and improving machinability.  Similarly, in electric furnace smelting, high-quality molten iron is achieved by minimizing or even eliminating pig iron usage through carbonaceous material infiltration. From a material performance perspective, the traditional approach of using large proportions of pig iron yields mechanical properties that are half a grade lower than those achieved with equivalent composition but higher scrap steel usage. Thus, the new process of adding carbonaceous materials for smelting is superior to the traditional method of high pig iron usage in terms of both cost and final product performance.