Regular Article

Effect of Ce-La on inclusion evolution in Al-killed high strength steel

¹ State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing (USTB), 30 Xueyuan Road, Haidian District, Beijing 100083, PR China
² Baotou Iron and Steel Group Corp., Kundulun District, Baotou 014010, Inner Mongol, PR China

^* e-mail: lijing@ustb.edu.cn

Received: 16 September 2020
Accepted: 5 October 2020

Abstract

The mechanism of inclusion evolution after rare earth addition based on oxide metallurgy was investigated experimentally and using thermodynamic calculations, where Ce-La was added to Al-killed high strength steel during Ruhrstahl-Heraeus refining to modify the oxide inclusions within the steel. The typical inclusions observed before Ce-La addition were spherical magnesium aluminate spinel inclusions. And fewer individual Al₂O₃ inclusions and Al₂O₃–TiO_x inclusions were also observed. The addition of Ce-La led to transformation of MgO · Al₂O₃ spinel inclusions to (Ce,La)₂O₃, (Ce,La)₂O₂S and (Ce,La)₂O₂S + MgO · Al₂O₃ inclusions. Thermodynamic calculations indicated that Ce-La combined with dissolved oxygen and sulfur in molten steel to form rare earth inclusions, while the remainder of the Ce and La modified MgO · Al₂O₃ to (Ce,La)₂O₃ and (Ce,La)₂O₂S.