Evolution of Nonmetallic Inclusions in GCr15 Bearing Steels During Continuous Casting Process

• Published in: Steel research international 2022-02, Vol.93 (2), p.n/a
• Main Authors: Zhang, Yanhui, Cheng, Gong, Wang, Jujin, Yang, Wen
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Bearing steels; Calcium oxide; Continuous casting; continuous castings; Iron and steel making; Liquid metals; Magnesium oxide; Nonmetallic inclusions; phase transformation; reoxidation; Steel
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.202100445

Industrial trials and thermodynamic calculation are carried out to systematically investigate the variation of steel cleanliness and inclusions during the reoxidation of molten steel, steady and unsteady continuous casting process of GCr15 bearing steels. Comparing with inclusions in molten steel, the content of Al2O3, CaO, CaS, and MgO of inclusions in the steady bloom is increased by 2.17%, −18.47%, 14.01%, and 2.27%, respectively, due to the reoxidation of molten steel will inhibit the transformation of inclusions. As the casting length in the first bloom increases from 2 to 9 m, the total oxygen (T.O) content reduced from 12.9 to 7.2 ppm and the number density of inclusions decreases from 15.65 to 10.97 # mm−2 with a gradual decrease in Al2O3 content. Based on thermodynamic consideration, in molten steel, the lower content of T.O, the lower Al2O3 content of inclusions. For solid steel, with the increase in content of T.O, mainly the Al2O3 content of inclusions gradually increases and the CaS content gradually decreases when the T.O content is between 4 and 8 ppm. However, the Al2O3 and CaO content of inclusions gradually increases, then the MgO and CaS contents gradually decreases when the T.O content is between 8 and 25 ppm. A serious variation contents of total oxygen (T.O) and total aluminum (T.Al) in the steel between the unsteady and steady states. Meanwhile the reoxidation of the molten steel will inhibit the transformation of inclusions. The effect of reoxidation and solidification transformation on the evolution of inclusions in bearing steels is quantitatively analyzed as well.