Modification Mechanism of Lanthanum on Alumina Inclusions in a Nonoriented Electrical Steel

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 Al2O3 inclusions are modified by lanthanum in two ways. One is that the dissolved lanthanum directly reduces the aluminum in Al2O3 inclusions and forms LaAl11O18 or LaAlO3 ones. The other is that a new La2O2S or LaS x shell is preferentially generated at the outside of Al2O3 and forms multiphase inclusions. With time increasing, the La2O2S or LaS x shell gradually reacts with the Al2O3 core and generates stable lanthanum‐containing inclusions. At the initial stage of lanthanum treatment, many transient inclusions including LaS x , La2O2S, 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 Al2O3 → LaAl11O18 → LaAlO3 → La2O2S → LaS x , which is consistent with thermodynamic analysis.

Effect of La Content on Inclusion Morphology in Automobile Sulfur‐Containing Gear Steel SCr420H

“…An interesting approach to control the inclusion shape by rare earth (RE) elements was described by Luyckx et al, [17] and results show that RE elements positively affect the globular sulfide formation and mechanical properties of sulfur-containing steel. Much work so far has focused on the metallurgy role of RE elements in steel, and RE elements can contribute to inclusion modification [9,[18][19][20][21][22][23][24][25][26][27][28] and microstructure refinement [22,[29][30][31][32] in steel. Wang et al [23] reported that the inclusion shape changed from cluster to spherical and spindle shapes with a round surface when Ce was added to Al-killed IF steel.…”