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摘要
In order to control the [O] content and inclusions in 20SiMn structural steel for forgings, firstly, the iso-oxygen line of CaO-SiO2-Al2O3-5%MgO refining slag in equilibrium with 20SiMn liquid steel at 1 600 ℃ were calculated by using thermodynamic software FactSage 8.1, and the composition of refining slag was optimized. At the same time, the dominant area diagram of Fe-Mg-Al-O system in steel with different oxygen content was calculated. Secondly, four groups of refining slag components were designed in the laboratory, and the slag-steel equilibrium experiments were carried out in a high-temperature resistance furnace at 1 600 ℃. After the test, the slag components were determined by X-ray fluorescence spectrometry, and the composition of the steel samples were analyzed by inductively coupled plasma optical emission spectrometer, infrared carbon sulfur analyzer and oxygen nitrogen combined analyzer. The composition and morphology of inclusions in the sample were analyzed by field emission scanning electron microscope, and the number and composition of inclusions in steel were counted. The effects of different refining slags on the oxygen content, composition, number and size of inclusions in steel were experimentally studied. Finally, a dynamic model was established to describe the inclusion removal behavior on the steel-slag interface. The experimental and thermodynamic model results reveal the relationship between typical Al2O3 and MgO·Al2O3 inclusions in steel and the contents of oxygen, magnesium and aluminum in steel. The kinetic model describes the corresponding relationship between inclusion separation rate, total oxygen content and overall wettability. When the contents of CaO, SiO2, Al2O3 and MgO in the optimized slag system are 0-24.7%, 44.3%-55.1%, 20.5%-48.2% and 5%-8% respectively, the dissolved oxygen in steel can be controlled within 0.000 5%. The slag system with typical composition of 50.4%CaO-40.3%Al2O3-4.3%SiO2-5%MgO can control the amount of T[O] and impurities in steel at 0.001 42% and 9.9 pieces/mm2 respectively. The experimental results are basically consistent with the model prediction. ? 2023 Chinese Society for Metals.
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