Evolution of inclusion in refining process of IF steel produced by LF-RH duplex process

WANG Haidong, ZHANG Leru, QIAO Degao, YU Yanchong, XU Zhiming, TIAN Shukun, WANG Guang

Continuous Casting ›› 2024, Vol. 43 ›› Issue (4) : 30-37.

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Continuous Casting ›› 2024, Vol. 43 ›› Issue (4) : 30-37. DOI: 10.13228/j.boyuan.issn1005-4006.20240101
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Evolution of inclusion in refining process of IF steel produced by LF-RH duplex process

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Abstract

IF steel is produced by the LF-RH-CSP process in a domestic steel mill, the process has high requirements for the C and N content and the cleanliness of the molten steel. Samples were taken and analyzed at different process nodes to investigate the main source of increasing C and N and the variation of composition, size, and quantity of inclusions in the LF-RH refining process. The results show that the heating slag-making and the slag modification are accompanied by bottom argon blowing and strong stirring phenomenon, which exposes the molten steel and thus lead to a severe C and N increase. The inclusions are mainly irregular Al2O3 after Al deoxidization in the LF station, and the inclusions are transformed into MgO·Al2O3 spinel during LF slagging and leaving the LF station. The inclusions are MgO·Al2O3 and a few single Al2O3 after secondary Al deoxidization at the RH station, and all of the inclusions are modified into spherical CaS-12CaO·7Al2O3-MgO·Al2O3 composite inclusions when leaving the RH station. The inclusion number density shows an overall downward trend, the average diameter gradually decreases from 6.0 μm to 2.3 μm, and the cleanliness of molten steel is significantly improved. Thermodynamic calculations show a strong tendency for the generation of MgO·Al2O3 inclusions, which are the nucleation core of CaS-12CaO·7Al2O3-MgO·Al2O3 composite inclusions. A kinetic model of inclusion evolution was established. The research results provide theoretical support for optimizing the IF steel production process and improving the castability of the steel.

Key words

LF-RH duplex process / IF steel / inclusion / refining / evolution

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WANG Haidong, ZHANG Leru, QIAO Degao, et al. Evolution of inclusion in refining process of IF steel produced by LF-RH duplex process[J]. Continuous Casting, 2024, 43(4): 30-37 https://doi.org/10.13228/j.boyuan.issn1005-4006.20240101

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