Formation and Evolution of Non-metallic Inclusions in Ti-Bearing Al-Killed Steel During Secondary Refining Process
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Industrial and laboratory experiments were carried out to investigate the formation and evolution of the inclusions in Ti-bearing Al-killed steel, and thermodynamic calculations were also conducted to check the stability of inclusions in steel. It is found that the addition of Ti influences the inclusions evidently. Before Ti addition, the inclusions transform along the route of “Al2O3 → MgO·Al2O3 spinel → CaO-Al2O3(-MgO) system” with the generation of dissolved Mg and Ca in liquid steel. When there is no sufficient Ca in liquid steel, the addition of Ti during refining process would lead to the transformation of MgO·Al2O3 spinel inclusions into MgO-Al2O3-TiOx inclusions. When a trace of dissolved Ca is formed, CaO-Al2O3-TiOx system inclusions can be generated from MgO-Al2O3-TiOx inclusions or CaO-Al2O3 inclusions. Higher calcium content originated from calcium treatment would result in the formation of CaO·TiO2 inclusions, and then weaken the castability of Ti-bearing Al-killed steel grades. Calcium treatment could also increase the frequency of macro-inclusions in steel, and evidently decline the quality of the steel. Cancellation of calcium treatment is suggested to improve the cleanliness of Ti-bearing Al-killed steel grades.
The authors are grateful to The National Key R&D Program of China (Grant No. 2017YFB0304100) and the Fundamental Research Funds for the Central Universities (Grant No. N182504016) as well as China Postdoctoral Science Foundation (Grant No. 2019M651131) for the financial support of the present study.
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