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The refining agent is also known as refining slag or slag modifier. Its functions are as follows: 1. Deoxidation: It deoxidizes and modifies the steel slag, reducing the contents of FeO and MnO in the slag and thereby decreasing its oxidizing capacity. Depending on the requirements of the steel grade and the amount of refining slag added, the oxygen content in the steel should be reduced by 20–30 ppm or more. 2. Desulfurization: It basically involves a calcium aluminate slag system; this refining slag possesses strong desulfurization capabilities. CaO reacts with sulfur to form calcium sulfate or calcium sulfite, which end up in the slag, thereby reducing the sulfur content in the steel. Under normal conditions, the desulfurization rate can reach 30–60% or more. 3. Foaming: The refined slag solidifies rapidly and exhibits good foaming properties in submerged arc welding. The mechanism of foaming involves redox reactions at high temperatures between the carbon in the electrodes or a small amount of carbon present in the slag, and elements such as FeO, MnO, and SiO2 in the slag, resulting in the formation of bubbles like CO. 4. Removal of inclusions in steel: A refining slag system that is reducing in nature and based primarily on calcium aluminate allows, due to stirring at high temperatures during refining, the inclusions in the steel to rise to the surface and be absorbed by the refining slag. 5. Aluminum: Aluminum is primarily used for the final deoxidation of steel; the refining slag contains aluminum with high activity and chemical reactivity, which helps to reduce the oxygen content in steel. 6. Others: For steel grades that are sensitive to nitrogen content or those requiring very low nitrogen levels, special refining agents must be used. So, refining agents and slag removers are essentially the same type of product, but their composition can be customized according to different customer requirements.