Analysis and Significance of Non-metallic Inclusions in Non Grain-oriented Electrical Steel

Abstract

NMI in electrical steels are known to have a very complex chemical makeup and history of formation, and exert a large influence on the handling of this steel in secondary metallurgy and casting. We have developed routines to analyse the non-metallic inclusion contents of non grain-oriented electrical steels by automated FEG-SEM analysis. We automatically analyze NMI of sizes down to 0.08 μm 2 in a steel that has significant amount of alloyed Si (2.3 wt%) by employing a matrix spectrum subtraction routine that leaves only the signal of the NMI itself to be quantified. We describe data reduction procedures for the NMI populations that consist out of duplexing oxides, sulfides, and nitrides. The chemical complexity can be represented and understood in terms of using a multicomponent projection technique, and based on the analysis of the particles it is possible to calculate quantitatively the amount of elements contained in the NMI assemblage of a steel sample. We find that this mass balance gives results in good to excellent agreement with bulk steel analyses for elements that are dominantly inclusion bound, such as Ca, if the complete inclusion size range above 0.08 μm 2 is taken into account. Based on these data analysis methods, we compare the NMI development in two heats through the secondary metallurgy process. Although the same steel composition was alloyed, the NMI developed vastly different depending on the details of treatment on the ladle furnace.KEY WORDS: electrical steel; non-metallic inclusions; automated inclusion analysis; ladle metallurgy.

Inclusion Evolution after Calcium Addition in Low Carbon Al-Killed Steel with Ultra Low Sulfur Content

“…In the sample collected 4 min after calcium treatment, the inclusions changed to liquid CaO-Al2O3 with a low CaS content. 15) found inclusion number increased by a large factor after calcium treatment in Al-killed steel.…”

Assessment of Si–O Equilibria and Nonmetallic Inclusion Characteristics in High Silicon Steels

“…[7] Therefore, assessing the Si-O equilibria and nonmetallic inclusions' characteristics in high Si steels is crucial, considering the significant effect of inclusions and O content on the magnetic and mechanical properties. [3,6,8] Although Al deoxidation of liquid steel has been widely studied, [2] the studies on Si-O deoxidation equilibria of liquid steel are somewhat limited. [1,9,10] Over the past several decades, many authors [1,[9][10][11][12][13][14] measured the total oxygen (TO) content in equilibrium with silicon content in liquid steel using high-temperature experiments and thermodynamic analysis.…”

“…[ 7 ] Therefore, assessing the Si–O equilibria and nonmetallic inclusions’ characteristics in high Si steels is crucial, considering the significant effect of inclusions and O content on the magnetic and mechanical properties. [ 3,6,8 ]…”

The Role of Slag Carryover on the Non-metallic Inclusion Evolution and Magnetic Behavior in Electrical Steel

“…It is to be noted that the presence of non-metallic inclusions (NMIs), even in a very small amount within the steel matrix, is sufficient to significantly influence the downstream processing, mechanical, electrical, and magnetic properties of the steel. Several studies [1][2][3][4][5][6] focused on controlling oxide inclusions during the secondary steelmaking process to improve the magnetic property of the electrical steels. Zinngrebe et al [1] studied the evolution of the inclusion population and reported the dependency of complex assemblages of oxides, sulfides, and nitrides in silicon steel during secondary steelmaking.…”

“…Several studies [1][2][3][4][5][6] focused on controlling oxide inclusions during the secondary steelmaking process to improve the magnetic property of the electrical steels. Zinngrebe et al [1] studied the evolution of the inclusion population and reported the dependency of complex assemblages of oxides, sulfides, and nitrides in silicon steel during secondary steelmaking. Kurosaki et al [2] studied the effect of morphology of oxide inclusions on the core loss of semi-finished electrical steel.…”