Evolution of the Non-metallic Inclusions Influenced by Slag-Metal Reactions in Ti-Containing Ferritic Stainless Steel

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Process metallurgy and materials processing science, 2021-12, Vol.52 (6), p.3986-4001
• Main Authors: Wang, Yong, Cho, Jin-Hyung, Jeong, Tae-Su, Karasev, Andrey, Mu, Wangzhong, Park, Joo Hyun, Jönsson, Pär G.
• Format: Article
• Language: English
• Subjects: Alumina; Aluminum oxide; Characterization and Evaluation of Materials; Chemistry and Materials Science; Chromium oxides; Evolution; Extraction; Ferrite; Ferritic stainless steel; Ferritic stainless steels; Linear functions; Liquid metals; Magnesia; Mass transfer; Materials Science; Melting points; Metallic Materials; Morphology; Nanotechnology; Nonmetallic inclusions; Original Research Article; Oxidation; Silica; Silicon dioxide; Slag; Stainless steel; Steel foundry practice; Structural Materials; Surfaces and Interfaces; Thin Films; Three dimensional analysis; Titanium dioxide; Titanium oxides; Two dimensional analysis
• ISSN: 1073-5615; 1543-1916; 1543-1916
• DOI: 10.1007/s11663-021-02314-3

Laboratory experiment and thermodynamic calculation for the Ti-containing 24 mass pct Cr ferritic stainless steel with a CaO-SiO 2 -Al 2 O 3 -MgO system slag were performed to investigate the effect of slag addition on the inclusion characteristics in molten steel. The morphology, composition, and size evolution of inclusions in steel samples were analyzed in three-dimensional by the electrolytic extraction method and in two-dimensional by the automatic analysis method. The results showed that the Ti content significantly decreased after the slag addition. However, the change of the Si content showed an opposite tendency. The decrease of the Ti content in steel was due to the reduction of SiO 2 and Al 2 O 3 in the slag by dissolved Ti in steel. An increase of the TiO 2 content in the slag can decrease the Ti loss in steel based on the slag-steel kinetic analysis. The total O content in the steel melt decreased from 62 to 26 ppm, and the steel cleanliness was improved, since the number density of inclusions decreased after the slag refining. The results of a kinetic analysis showed that the rate-determining step of the oxidation of Ti in the steel and the reduction of SiO 2 in the slag were the mass transfer on the slag side. In addition, high Ti 2 O 3 -containing inclusions were found to be transformed to Cr 2 O 3 -Ti 2 O 3 -Al 2 O 3 and Cr 2 O 3 -Ti 2 O 3 -SiO 2 system inclusions after the slag addition. The Al 2 O 3 contents in inclusions increased while the Ti 2 O 3 contents decreased with time. However, there were some amount of high melting point inclusions with high Al 2 O 3 content, which were not what we expected. When plotted on logarcxithmic scales, the mole ratio X Al 2 O 3 / ( X Ti 2 O 3 · X Cr 2 O 3 ) values of the inclusions were expressed as a linear function of the a Al 2 / ( a Ti 2 · a Cr 2 · a O 3 ) values of the steel melts with a slope of unity, which was theoretically expected.