Regular Article

Evolution of inclusions in Mg-RE-Ti treated steels with different Al contents and their influence on acicular ferrite

¹ School of Metallurgical and Ecological Engineer, University of Science and Technology Beijing, Beijing 100083, PR China
² Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, PR China

^* e-mail: songbo@metall.ustb.edu.cn

Received: 30 November 2020
Accepted: 19 February 2021

Abstract

The size distribution and composition of inclusions in Mg-RE-Ti treated steels with different Al contents were investigated systematically, while the microstructure and the nucleation potency of inclusions for AF were analyzed. The results show that the inclusions were refined with Mg treatment, and then coarsen following La addition in the samples. The particles in high Al sample were more likely to collide, aggregate and form clusters due to the relatively high amount of inclusions in melt steel. The dominate inclusions were composed of two layer structures with Mg-bearing inclusions cores and La-bearing inclusions shells. With the increase of Al content, the cores evolved from MgO to MgO•Al₂O₃ and the shells evolved from La₂O₂S and La₂O₃ to LaAlO₃. The nucleation potency of inclusions for AF decreased due to relatively high lattice misfit between inclusions and α-Fe in high Al sample. The AF fraction decreased with the increase of Al content because of the decrease of the amount of effective inclusions.