Abstract: The control of non-metallic inclusions in GCr15 bearing steels has been investigated by industrial experiments. It was found that ultrasonic testing defects in the rods of bearing steel were caused by large size clusters of CaO-Al2O3-MgO inclusions, which were originated from the clogs on the submerged entry nozzle (SEN). The SEN clogging was not caused by large size inclusions but by small CaO-Al2O3-MgO inclusions with the size of 2-6 μm. The CaO in inclusions increased significantly after the vacuum degassing treatment, and the type of inclusions shifted from spinel to CaO-Al2O3-MgO. The increment of the CaO in inclusions could be decreased relatively by lowering the vacuum degree during the vacuum degassing treatment, which helped to restrain the transformation of spinel inclusions into calcium aluminate in bearing steels, and was beneficial for the improvement of the fatigue property of bearing steels.
Authors: Gong Cheng, Jiaheng Duan, Wenbo Wang, and Lifeng Zhang
Keywords: Nozzle clogging, Vacuum degree, Inclusions