Study of the nature of non-metallic inclusions in samples of aluminum and silicon killed low carbon steels, collected in the refining treatment and continuous casting stages

Abstract

The amount, distribution, size and chemical composition of non-metallic inclusions have a direct influence on steel properties. By controlling size and chemical composition of these inclusions, it is possible to get a product with good quality. The identification of the nature and the control of inclusion formation are very important for steel cleanness. The behavior of these inclusions is predictable, in some extent, by the determination of the chemical composition of nonmetallic phases that form such inclusions. With the objective of studying the chemical composition, the size and the distribution of such inclusions, samples of aluminum and silicon killed low carbon steels were collected in a national steel industry in the secondary refining and continuous casting stages. These samples were analyzed in the scanning electron microscope (SEM) coupled to an energy dispersive analysis system (EDS). From the results, it was possible to evaluate the nature of inclusions and to analyze the effectiveness of the refining process in the reduction of the number and area fraction of the inclusions. It was also possible to verify that the inclusions that remained after treatment, are less damage both to the steel properties as to the continuous casting process (clogging of the submerged valve).

Formation and Evolution of Non-metallic Inclusions in Medium Mn Steel during Secondary Refining Process

“…In conventional Al-killed steel grades, no (Mn, Mg)O·Al 2 O 3 spinel inclusions can be found. 1,2,[4][5][6][7] Due to the similar spinel structure, the effect of (Mn, Mg)O·Al 2 O 3 spinel inclusions on the properties of medium Mn steel is probably close to that of MgO·Al 2 O 3 spinel inclusions. However, there is lack of studies in this field, so it is hard to draw an exact conclusion, and will be a new study topic in the near future.…”

“…[1][2][3][4][5][6][7] Due to their high hardness and irregular shape, this kind of inclusions tend to induce microcosmic cracks and lead to fatigue failure of final product, and they are usually considered as harmful inclusions for steel.…”

“…Additionally, Todoroki et al 16) and Wang et al 20) also proposed SiO 2 in slag would hinder the formation of MgO·Al 2 O 3 inclusions. Moreover, many researchers [2][3][4][5][6][7] believed that when a trace of dissolved Ca is formed in liquid steel, the MgO·Al 2 O 3 inclusions in steel are not stable, and could be easily modified into CaO-MgO-Al 2 O 3 inclusions and even CaO-Al 2 O 3 with a low melting temperature.…”

Levantamento das inclusões nos principais grupos de aços produzidos em aciaria do tipo LD.

“…Contudo, defeitos estruturais, alguns como inclusões não metálicas, são também responsáveis pela performance deste material quando submetido a esforço mecânico. (1) O conceito de aço limpo leva em conta a composição química, tamanho, morfologia, tipo e distribuição das inclusões, além de considerar também a baixa quantidade de impurezas nocivas ao aço, tais como oxigênio, enxofre, fósforo, hidrogênio e nitrogênio. (1) Neste trabalho, buscou-se conhecer as inclusões produzidas em uma aciaria do tipo São apresentados também os ensaios utilizados atualmente para detectar inclusões, e seu emprego na indústria e centros de pesquisa.…”