During steelmaking, the carbon content of the molten steel must be adjusted to ensure product quality meets standards. Recarburizers are added to the molten steel to increase carbon content, primarily in electric furnace steelmaking. Decarburization occurs during the steelmaking process, as slag formation removes sulfur (S), phosphorus (P), silicon (Si), and other impurities. Therefore, recarburization is performed during the final composition adjustment phase, following the solution refining stage.
Carbon materials used for recarburization, particularly recarburizers, can be shaped like coal balls, but graphite powder or artificial graphite electrode processing chips are more commonly used. Spherical recarburizers offer advantages such as low dust emission when added to the molten steel, high yield, and ease of use. Furthermore, to facilitate absorption into the molten steel by the slag layer, recarburizer balls are often mixed with 20% to 50% iron in addition to the carbon.
Electrode cuttings have a high carbon content and are easily absorbed by the molten steel, making them excellent recarburizers. Graphite powder or coke dust is also widely used as a recarburizer. Depending on their intended use, their particle size and purity vary. However, recarburizers used in the later stages of refining require high purity, and sulfur and phosphorus impurities are particularly important, with sulfur content ideally below 0.2%.
The phosphorus content in general carbon materials is very low, usually below 0.02%. As a recarburizer, graphite is better than carbon. The dissolution rate of graphite in molten steel is several times that of carbon. Especially when the carbon content is high (more than 90%), graphite recarburizer can give the best effect.