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Effect of Trace of Oxygen in Ar Gas on Initial Growth of Nozzle Clogging Deposits on SEN for Ti Added Ultra‐Low C Steel Casting

The possibility of reoxidation of Ti‐ultra‐low C (Ti‐ULC) steel by a trace of oxygen in Ar gas, which is injected in a submerged entry nozzle (SEN), is investigated. A commercial‐grade unpurified Ar gas with PO2 = ≈10−4 bar and a purified Ar gas with PO2 = ≈10−18 bar by a set of cleaning kits are employed. Preliminary thermodynamic calculations revealed that the unpurified Ar gas could cause significant oxidation of the Ti‐ULC steel, irrespective of the steel composition, while the purified Ar gas did not oxidize the steel. A series of laboratory‐scale oxidation experiments are carried out using various Ti‐ULC steel samples and the two Ar gases. The oxidation under unpurified Ar gas causes the oxidation of all the samples but only on the surface, in partial agreement with the thermodynamic calculation. The partial agreement between the calculation and the experiment is explained by the availability of oxygen and other metallic elements. It is found that the trace of oxygen in a commercial grade of Ar gas could cause reoxidation of Ti‐ULC steel in an SEN, which may be no better than the reoxidation by CO gas generated by the carbothermic reaction in the SEN refractory. A purity control of Ar gas is recommended.