Calcium Modification of Spinel Inclusions in Aluminum-Killed Steel: Reaction Steps

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

“…12, as for Sample 1, as explained above, it is considered that the reactions between liquid steel and the inclusions do not reach an equilibrium state. It can be realized that Sample 2 is plotted in the (Mn, Mg)O·Al 2 The agreement of the measured inclusion compositions with the stability diagrams proves that the following fact. Inclusion composition can be determined on the basis of thermodynamic equilibrium, and it also implies that the kinetic consideration of the reactions between inclusions and molten steel can be ignored during the period of the sampling interval of this study.…”

“…In the figure, alumina is observed in the Sample 1 though plotted in the In Table 3, a trace of dissolved Ca is formed during the refining process in the present study, and some calcium aluminate inclusions (Type 6 and Type 7) are found after LF refining and VD treatment. Many studies 1,2,4,6,17) pointed out that MgO·Al 2 O 3 spinel inclusions are not stable and would transform into calcium aluminate inclusions, when there is a trace of dissolved Ca in liquid steel. Note that these study results are mainly based on conventional Al-killed steel grades.…”

“…[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.…”

“…In order to control these inclusions, a lot of researchers [1][2][3][4] have studied the formation and evolution mechanism of MgO·Al 2 O 3 spinel inclusions in steel. Some of them [7][8][9][10]12,21,29) thought that the formation of MgO·Al 2 O 3 spinel inclusions depends on the concentration of dissolved Mg, Al and O in liquid 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.…”