Evolution of Nonmetallic Inclusions in GCr15 Bearing Steels During Continuous Casting Process
Yanhui Zhang, Gong Cheng, Jujin Wang, Wen Yang
Abstract
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 Al 2 O 3 , 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 Al 2 O 3 content. Based on thermodynamic consideration, in molten steel, the lower content of T.O, the lower Al 2 O 3 content of inclusions. For solid steel, with the increase in content of T.O, mainly the Al 2 O 3 content of inclusions gradually increases and the CaS content gradually decreases when the T.O content is between 4 and 8 ppm. However, the Al 2 O 3 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.