During the steelmaking process, factors such as extended smelting, heat preservation, and excessive heating can result in significant carbon loss from the molten iron, leading to a lower carbon content than the desired level.
To compensate for this carbon loss, carburizers are added. These carbon-rich materials are made from various sources like wood, coal, coke, and graphite, and they are often graphitized to enhance their properties. Graphitization reduces impurities, increases carbon content, and decreases sulfur content.
In the casting process, carburizers allow for increased use of scrap steel and reduced or eliminated use of pig iron. When added to an electric furnace, carburizers should be charged along with other materials, with smaller quantities added to the molten iron’s surface. Large additions directly to the molten iron can lead to excessive oxidation, reducing the carburizing effect and causing insufficient carbon in the final castings.
The specific carburizer used depends on the desired properties of the cast iron. By selecting pure, graphitized carbon-containing materials, it is possible to reduce impurities and lower production costs.