Carbon and oxygen behavior in the RH degasser with carbon powder addition

for ultra-low-carbon (ULC) steel production, the higher oxygen content before Ruhrstahl-Heraeus (RH) decarburization (de-C) treatment could shorten the de-C time in the RH degasser. However, this would lead to oxidation rates being exceeded by molten steel production, affecting ULC steel surface quality. In this work, a carbon powder addition (CPA) process was proposed to reduce the dissolved oxygen content at the end of RH de-C through addition of carbon powder to molten steel in the vacuum vessel. Carbon and oxygen behavior during the CPA and conventional process was then studied. The results demonstrated that the de-C rate with CPA was lower compared to the conventional process, but the carbon content at the end of de-C presented no difference. The de-C reaction for CPA process took place in the four reaction sites: (1) within the bulk steel where the spontaneous CO bubbles form; (2) splashing area on the liquid steel surface; (3) Ar bubble surface; (4) molten steel surface. The CPA process could significantly reduce the dissolved oxygen content at the end of de-C, the sum content of FeO and MnO in the slag, the aluminum consumption, and the defect rate of rolled products. This was beneficial in improving ULC steel cleanliness.