Abstract
In the current study, the reduction of CaO-Al2O3 inclusions in steel by the subsequent addition of aluminum is revealed through industrial trials, laboratory experiments, and thermodynamic calculations. During the industrial production of the Al-killed Ca-treated steel, the Al2O3 content in CaO-Al2O3 inclusions increased from 72.05% to 79.83%, after the aluminum addition. In laboratory experiments, the addition of aluminum increased the Al2O3 content, and meanwhile lowered the contents of CaS and CaO in the inclusions. The average diameter of the inclusions decreased and the number density increased after the Al addition in steel, due to the formation of tiny inclusions. Based on the thermodynamic consideration, the transformation of the inclusions was attributed to the re-equilibrium of the reaction between steel and the inclusions after aluminizing. The Al2O3-riched calcium aluminate with a high melting point increased the possibility of the nozzle clogging during the continuous casting process, reducing the effect of the calcium treatment. Therefore, the addition of aluminum after calcium treatment should be avoided as far as possible.
Highlights
Non-metallic inclusions in steel, such as oxides, sulfides, and nitrides [1,2,3], are harmful to the continuity of the steel matrix
Aluminum was added into the molten steel as a deoxidizer, leading to the formation of a large number of Al2 O3 inclusions [8,10], which were seriously harmful to the steel performance [1,11,12,13,14,15,16,17,18]
Zhang et al [31] reported that a weak calcium treatment can modify solid inclusions to full liquid ones in high-titanium steels with a low Al content, while it was hardly suitable for the high Al steel
Summary
Non-metallic inclusions in steel, such as oxides, sulfides, and nitrides [1,2,3], are harmful to the continuity of the steel matrix. Calcium (Ca) treatment was widely used to modify solid Al2 O3 to liquid calcium aluminates in the molten steel. Discussed the precipitation and modification of CaS in the calcium treatment process. Zhang et al [31] reported that a weak calcium treatment can modify solid inclusions to full liquid ones in high-titanium steels with a low Al content, while it was hardly suitable for the high Al steel. Guo et al [32] found that for 20Mn steel, the precipitation temperature of solid calcium aluminate inclusions decreased with the increase in the ratio of calcium to aluminum. The effect of aluminum on the calcium aluminate inclusions during the production process of steel has been little-reported. Industrial trials, laboratory experiments, and thermodynamic calculations were performed to reveal the evolution mechanism of calcium aluminate inclusions after the aluminum addition
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