Formation of CaS on Al2O3-CaO inclusions during solidification of steels

Abstract

In this article, the effect of CaS formation on the evolution of Al 2 O 3 -CaO inclusions in low-carbon Al-killed and Ca-treated steel during the solidification process is investigated through high-temperature confocal scanning laser microscopy (CSLM). The inclusions started as mostly liquid-globular inclusions that did not agglomerate with each other on the melt surface but during solidification were seen to change shape into an irregular morphology. The shape change was found to be due to the reaction between the Al 2 O 3 -CaO inclusions with the dissolved S and Al in the melt, resulting in the formation of dense CaS shells around the inclusions. The melt composition during solidification, estimated from the observed solid ␦ -front advance rate, was compared to the thermodynamic limit for CaS precipitation. The observed growth rate of the CaS shell was found to initially increase with decreasing temperature because of the higher, solid ␦ -front advance rates at lower temperatures, which results in higher rates of S and Al partitioning. Once CaS had precipitated, the inclusions were found to form agglomerates on the melt surface because of fluid flow, initially, and later, the capillary depression.

Characterisation of solidification using combined confocal scanning laser microscopy with infrared thermography

“…Use of high temperature CSLM, pioneered by Emi and co-workers at Tohoku University [6][7][8], and the mechanism of how it works has been documented and explained in detail in literature [5,[9][10][11][12][13][14][15]. Figure 1 shows a schematic of the set up used in this report.…”

Inclusion Evolution during Modification of Alumina Inclusions by Calcium in Liquid Steel and Deformation during Hot Rolling Process

“…Wang et al 5) studied the effect of CaS formation on the evolution of Al 2 O 3 -CaO inclusions in low-carbon Al-killed steel and found that the formation of dense CaS shells around the inclusions was mainly due to the reaction between the Al 2 O 3 -CaO inclusions with the dissolved S and Al in melt. Yang et al 6) showed that calcium treatment could generate many large inclusions and the modification effect would be dramatically decreased by the formation of large amount of CaS inclusions.…”

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

“…Wang et al 25) investigated effect of CaS formation on the agglomerate ability of Al2O3-CaO inclusions in lowcarbon and Ca-treated steel through high-temperature confocal scanning laser microscopy (CSLM). They found liquid-globular Al2O3-CaO inclusions don't agglomerate with each other, but when CaS forms outside Al2O3-CaO, these inclusions begin to agglomerate with each other, and finally becomes clusters.…”