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Improvement of steel quality by using hydrocarbon gas in a converter Lee, Dong-Ryeol

Abstract

Minimizing alumina (Al₂O₃) or other nonmetallic oxide inclusions formed during deoxidation is an important factor in producing 'quality' steel. Although a variety of practices are employed to encourage floatation of such deoxidation products prior to solidification, complete removal is never achieved. The amount of Al₂O₃ formed during deoxidation is determined by the residual dissolved oxygen present in the steel after decarburization. In a combined practice converter with Ar and/or N₂ gas bottomblowing, thermodynamics suggests [%C] x [%0] ≈ 0.0021 at the end of the blow. In practice, the dissolved oxygen content is ~ 525 ppm at 0.04% C which is consistent with thermodynamic predictions and indicates that, for a given %C, the combined blowing practice has achieved its lowest possible (equilibrium) oxygen level. Thermodynamic calculations indicate that injection of gaseous hydrocarbons such as methane (CH₄), partly replacing Ar and/or N₂, might allow significantly lower residual oxygen levels to be achieved; i.e. based on thermodynamics, [%C]x[%0] ≈ 0.000009 which translates into ~ 2 ppm dissolved oxygen at 0.04%C. In addition, the products of the deoxidation reaction are gaseous CO, CO₂ and H₂O rather solid or liquid Al₂O₃ or SiO₂ that can be difficult to completely remove prior to solidification. Substituting relatively cheap CH₄ for traditional deoxidizing additions such as aluminum or ferro-silicon might also lower overall costs. This research involved experimental investigation of methane deoxidation backedup by thermodynamic modeling to assess the theoretical limits for the process. The work also examined deoxidation rate and the impact of H and C solution into the steel. During the trials ~ 20 ppm residual oxygen was achieved. Although greater than thermodynamic predictions, this suggests the process might be of commercial interest.

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