Evolution Mechanism of Oxide Inclusions in Titanium-Stabilized AISI 443 Stainless Steel
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The evolution mechanism of oxide inclusions in Ti-bearing AISI 443 stainless steel was investigated by industrial experiment and thermodynamic calculation. The chemical compositions of steel and the characteristics of inclusions in steel were analyzed. After the addition of Al, the main type of inclusions in molten steel was irregular MgO·Al2O3 spinel. The MgO·Al2O3 inclusions were modified to be spherical CaO-Al2O3-MgO inclusions after calcium treatment. Thermodynamic calculation results indicated that several ppm Ca could significantly expand the liquid oxide phase field and decrease the stability of spinel. After titanium addition, two types of inclusions were formed: spherical Al2O3-TiOx inclusions and complex CaO-TiOx-Al2O3-MgO inclusions. The compositions of steel after Ti addition were mostly located in Al2O3-TiOx stability phase field. Based on the characteristics of inclusions in steel and thermodynamic calculation, inclusions consisting of liquid and CaTiO3 were formed in molten steel with more than 10 ppm Ca during the Ti addition process. The evolution mechanism of oxide inclusions was discussed with the consideration of the initial calcium content before Ti addition.
The authors gratefully express their appreciation to the National Nature Science Foundation of China (Grant No. 51674024), the State Key Laboratory of Advanced Metallurgy at University of Science and Technology Beijing (USTB), and Jiuquan Iron and Steel Co. for supporting this work.
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