The kinetics of nitrogen and carbon removal from a liquid iron surface in low content regions by blowing Ar gas mixture under reduced pressures have been studied using the samevacuum induction furnace at 1 6000c, respectively. The results obtained are as follows:(1)The nitrogen removal reaction is described as a second order reaction with respect to nitrogen content. The overall reaction rate constant, k~v' decreases with the increase of total pressure. and oxygen and sulfur content.Assumingthat the nitrogen removal reaction progresses by a mixed control and that the chemical reaction for nitrogen gas formation is caused by adsorbed nitrogen atoms, the chemical reaction rate constant, kã nd the adsorption coefficient of oxygen. The relation between kN.. of Fe-20mass"/oCr-0.2 mass"/*C-S system and as is shown in Fig. 3as Kishimoto et al.11) reported that the overall reaction rate constant for carbon removal, kc.., decreased with the decrease of carbon content at less than 0.005 masso/o.

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The formation of the micropores in mould flux is further investigated employing solid-state 1 H NMR with CRAMPS technique that has successfully enabled the quantitative analysis of hydroxyl ions in mould flux. The spectra have revealed that hydroxyl ions exist in mould flux and they increase in molten flux pool especially during the casting of Si-K steel. The result provides the new mechanism for the formation of the micropores: in a continuous casting mould, water vapour in the atmospheric air is absorbed into molten flux pool as hydroxyl ions, and they are usually reduced by soluble Al in molten steel pool. However, during the casting of Si-K steel where Si is a weaker deoxidizing element, the hydroxyl ions are not easily reduced, and they form the micropores of the gas including H 2 O during the crystallization of mould flux in the flux channel. According to the proposed mechanism, mould flux with a lower activity of SiO 2 has been developed for Si-K steel, and it successfully prevents the sticker breakouts.

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