The Use of Gilsonite in Steel Making Additives Gilsonite is an ingredient in several additives used in the production of steel. It is used in Limestone, Lime, Magnesium, and Calcium Carbide additive systems. The function of these additives is to remove impurities such as sulfur, silica, and phosphorus from the molten steel and move them to the molten slag layer. Gilsonite fulfills several roles as a component in Steel Making Additives. First, Gilsonite is approximately 75% volatile at 1900°F, and when added to the molten steel it promotes the mixing of the additives so the chemical reactions that will move the impurities to the molten slag layer can take place. Next, the volitiles that are given off are high in lustrous carbon, which will further reduce the Iron Oxide to steel. Although CO reduces most of the Fe3+ by indirect reduction, a portion must be reduced directly by elemental carbon. Finally, the portion of Gilsonite that is not volatilized is a very highly structured asphaltene structure that is nearly pure carbon. This will add carbon content to the steel.