Transformation of Alumina Inclusions by Calcium Treatment

Abstract

The objectives of this study were to investigate reactions of calcium with Al 2 O 3 by different model experiments both on the laboratory and on the industrial scale. Experiments with solid Al 2 O 3 and CaO were performed between 1350°C and 1600°C. Reaction rate constants were determined based on scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) observations of reaction products and weight measurements of the Al 2 O 3 reacted via dissolution of the CaO bearing phases from the specimens after the annealing period. The results showed that the formation of calcium aluminate phases proceeded rapidly at temperatures greater than 1405°C when a liquid calcium aluminate was formed. In the lowest temperature range (1350°C-1405°C), when the formation of liquid phase ceased, the reaction rate was several orders of magnitude lower. Industrial trials including Ca-alloy injection into steel, sampling and SEM/EDS analyses, as well as an inclusion rating in the samples show the concept of rapid transformation of the alumina inclusions with Ca treatment.

Effect of Mg Addition on the Evolution of Inclusions in Al–Ca Deoxidized Melts

“…After the deoxidants added in the melt, CaO·6Al 2 O 3 can be firstly formed by dissolved calcium, aluminium and oxygen react directly, which is shown in Eq. (9). This reaction is determined by linear combination from Eqs.…”

“…Therefore, performing calcium treatment is very common in steelworks in order to have complex liquid inclusions, which can avoid or prevent the inclusions from clogging the nozzle. As result, many researches of nonmetallic inclusions in Al-Ca deoxidized steel, such as thermodynamic calculation, [1][2][3] size distribution, [4][5][6] formation mechanism and kinetics, [7][8][9][10] have been intensively studied in recent years. It has been proven by thermodynamic calculation that very small amount of calcium enables the formation of liquid inclusion.…”

Transient Evolution of Inclusions during Calcium Modification in Linepipe Steels

“…[10][11][12][13][14][15][16] Calcium treatment is employed to modify Al2O3 inclusions. [17][18][19][20][21][22][23][24][25][26][27] The addition of calcium in the molten steel could modify oxide inclusions, desulphurization of steel and control shape of sulfide inclusions. However, insufficient or superfluous addition of calcium leads to incomplete or excessive modification of alumina inclusions and the formation of solid calcium aluminates or CaS, which are detrimental to the castability of linepipe steels.…”

Segregation of Mn, Si, Al, and Oxygen During the Friction Stir Welding of DH36 Steel

“…2 and 3, respectively. The melting point of (CaOAl 2 O 3 ) is in the range of 1450-1850°C depending on the amount of CaO compound with Al 2 O 3 [13]. Pure MnS melts at 1600°C, but it is expected that the melting point is lower when it forms compounds with other elements [14].…”