Modification Mechanism of Lanthanum on Alumina Inclusions in a Nonoriented Electrical Steel
Qiang Ren, Zhiyuan Hu, Lin Cheng, Xiao‐Min Kang, Yujie Cheng, Lifeng Zhang
Abstract
The modification mechanism of lanthanum on alumina inclusions in a nonoriented electrical steel at 1600 °C is investigated using laboratory experiments. Inclusions are analyzed using an automatic scanning electron microscope equipped with energy‐dispersive spectrum at 1, 5, 10, and 30 min after lanthanum treatment. The contents of total oxygen (TO), total sulfur (TS), and total lanthanum (TLa) in steel are analyzed. Results show that Al 2 O 3 inclusions are modified by lanthanum in two ways. One is that the dissolved lanthanum directly reduces the aluminum in Al 2 O 3 inclusions and forms LaAl 11 O 18 or LaAlO 3 ones. The other is that a new La 2 O 2 S or LaS x shell is preferentially generated at the outside of Al 2 O 3 and forms multiphase inclusions. With time increasing, the La 2 O 2 S or LaS x shell gradually reacts with the Al 2 O 3 core and generates stable lanthanum‐containing inclusions. At the initial stage of lanthanum treatment, many transient inclusions including LaS x , La 2 O 2 S, and La–P(–As) are formed due to the high concentration of lanthanum, while gradually redissolving with time increasing. With the increase in TLa content in steel, the formation sequence of stable inclusions is Al 2 O 3 → LaAl 11 O 18 → LaAlO 3 → La 2 O 2 S → LaS x , which is consistent with thermodynamic analysis.