Inclusion characteristics and control process optimization of 27SiMn steel

doi:10.13228/j.boyuan.issn0449-749x.20220676

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Iron and Steel ›› 2023, Vol. 58 ›› Issue (6) : 61-71. DOI: 10.13228/j.boyuan.issn0449-749x.20220676

Steelmaking

Inclusion characteristics and control process optimization of 27SiMn steel

LÜ Ming¹, LIU Kunlong¹, GAO Zhizhe¹, SONG Baomin², ZHANG Zhaohui¹

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Abstract

High melting point inclusions in 27SiMn steel are the main cause of flaw detection defects. In order to further control the inclusions in 27SiMn steel, a study was conducted on 27SiMn steel produced by the "BOF→LF→CC" process in a domestic steel company. Liquid steel were sampled at the initial stage, before calcium treatment, after soft blowing in LF refining process, in tundish and casting billet. The samples were analyzed to investigate the characteristics of inclusions in 27SiMn steel. The results show that the inclusions are mainly MgO-Al₂O₃, MgO-SiO₂ and Al₂O₃-CaO-MgO inclusions in LF refining process. In the soft-blowing and casting stage, there is existing (CaS)-Al₂O₃-MgO-SiO₂-CaO inclusion, while a large number of CaS particles exist in the molten steel, which indicates that there are still high melting point inclusions in 27SiMn steel after calcium treatment. On this basis, the thermodynamical formation mechanism of CaS and calcium aluminate inclusions within the 27SiMn steel liquid were investigated. It is found that w([Al]) is 0.022% when w([Ca]) is controlled between 0.001 3% and 0.003 5% in liquid steel, which is conducive to the generation of 12CaO·7Al₂O₃. At the same time, in order to prevent the generation of CaS in molten steel and hinder the transformation of Al₂O₃ inclusions into 12CaO·7Al₂O₃, w([S]) should be controlled in the range of 0.001 5%-0.003 9%. Based on the study of inclusion characteristics and thermodynamic calculations, the process optimization scheme was proposed. The basicity of refining slag was adjusted to above 3.2 to increase the sulfur capacity, and w((Al₂O₃)) in slag was increased from 10%-11% to above 13% to promote the fluidity. The addition of aluminum deoxidizer was reduced from 130 kg to 120 kg. silica-calcium wire was decreased from 400 m to 200 m to carry out light calcium treatment. The industrial optimization test was conducted, and it was found that w([Ca]) in molten steel was about 0.002 4% after soft blowing, which was further reduced to about 0.0018% at the continuous casting stage, and w([S]) was controlled at about 0.002%. In the Al₂O₃-SiO₂-CaO-(8%) MgO system, the average composition of inclusions changes from the high melting point region of 1 600-1 800 ℃ to the 1 400-1 500 ℃ in the liquid phase zone. The effect of calcium treatment is significantly improved and the quality of steel is improved.

Key words

27SiMn / calcium treatment / inclusion evolution / LF refining / thermodynamics

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LÜ Ming, LIU Kunlong, GAO Zhizhe, SONG Baomin, ZHANG Zhaohui. Inclusion characteristics and control process optimization of 27SiMn steel[J]. Iron and Steel, 2023, 58(6): 61-71 https://doi.org/10.13228/j.boyuan.issn0449-749x.20220676

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