Ladle glaze: major source of oxide inclusions during ladle treatment of steel

Abstract

It was found in the samples taken at and below the slag line that a slag infiltrated layer was covered by an outer layer containing many MgO 'islands' of various sizes. The microstructure of the infiltrating slag was the same as the matrix of the outer layer. The slag was found to decompose into the compound 3CaO.Al 2 O 3 and a liquid phase during the cooling process. The former phase along with tiny MgO particles from the ladle glaze was found to be one of the major sources of inclusions during the degassing and flotation periods of ladle treatment. Thermodynamic analysis indicated that the reaction between the ladle glaze and the slag from the electric arc furnace resulted in the formation of MgO-Al 2 O 3 spinel and an oxide solution, which were also the main inclusions found at the initial stages of ladle treatment. Evidence of this reaction was found in the lining samples taken above the slag line.

Chemical Reaction of Glazed Refractory with Al-deoxidized Molten Steel

“…The feasibility of the physical detachment can be supported by the microstructure of the glaze layer showing the existence of spinel particles on the interface of glaze and molten steel. Several previous studies [7][8][9][10][11] for the ladle glaze of a magnesite lining also suggested that the particles like MgO originally formed in the glaze layer can be retained in the liquid steel as inclusions. For example, Beskow and Du Sichen 10) reported that the complex inclusion of liquid CaO-Al 2 O 3 (-MgO-SiO 2 ) bearing MgO particles, one of the typical inclusions in a practical ladle treatment, was most probably originated from the ladle glaze itself.…”

“…Recently, Beskow and Du Sichen 10) studied the formation of ladle glaze and its influence on the generation of nonmetallic inclusions in a practical ladle treatment. The ladle lining (refractory) in their study was magnesite refractory (carbon-bearing MgO lining).…”

“…In particular, refractory materials have been indicated as one of the major sources of non-metallic inclusions in the molten steel during ladle metallurgy. [1][2][3][4][5][6][7][8][9][10][11] Upon the discharge of molten steel into a tundish, the top slag moves down together with the molten steel, causing the molten slag to adhere onto the ladle wall, and freeze when cooled down. This slag film adhered to the ladle refractory is called "ladle glaze".…”

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

“…13,14) Spinel inclusions have been thought to be hard, irregular and nondeformable, and it is commonly very harmful to the final products.…”

Evolution Mechanism of Non-metallic Inclusions in Al-Killed Alloyed Steel during Secondary Refining Process

“…Calcium aluminate inclusions are usually globular with low melting points, so performing calcium treatment is very common in steelworks in order to have such inclusions, but there is still lack of agreement about the harmness of these inclusions. Spinel and calcium aluminate inclusions are mainly found in Al-killed steel, [4][5][6] and many scholars have contributed to research the formation and evolution mechanism of these inclusions, such as Itoh el al., 7,8) Park et al, [9][10][11] Kang et al, 12) Seo et al 13) and Wang et al 5,6,[14][15][16] The proposed mechanism was commonly mentioned that the dissolved Mg and Ca were supplied from the slag and refractory, and the MgO-Al2O3 system inclusions formed by the reaction between alumina inclusions and dissolved Mg. Besides, Kang et al 12) and Wang et al 6,[14][15][16] indicated that MgO-Al2O3 system was not stable when there was a trace of dissolved Ca, would transfer into CaO-MgO-Al2O3 system.…”