Formation and Modification of MgO·Al2O3-Based Inclusions in Alloy Steels

Factors to Determine Inclusion Compositions in Molten Steel during the Secondary Refining Process of Case-Hardening Steel

“…It was reported that both MgO·Al 2 O 3 and the CaO-Al 2 O 3 system inclusions were detected in the refining stages of Al-killed steels. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] According to the report, MgO·Al 2 O 3 inclusions have the potential to cause nozzle clogging due to its high sinterability because they are stable with a solid state at the steelmaking temperatures.…”

“…3,9) In addition to the above studies, a number of researchers have conducted work on the inclusion evolutions in detail including the variations from Al 2 O 3 to the CaO-Al 2 O 3 system, 6) from Al 2 O 3 to MgO·Al 2 O 3 or partially to MgO, [7][8][9][10] and from MgO·Al 2 O 3 to the CaO-Al 2 O 3 system or to the CaO-MgO-Al 2 O 3 system. [11][12][13][14][15][16][17][18] It should be pointed out that most of researches stated above were done in laboratory scales. Thus, information about inclusion formation in practice is still lacking to understand inclusion evolution occurring in the practical refining stages.…”

“…[6][7][8][9][10][11][12][13][14][15][16][17][18] Discussion in the following sections focuses on how each phenomenon is related to the variation at each process based on the thermodynamic calculation results. 39) Another cause could be the slag entrapment caused by the gas stirring.…”

“…2(c). Many reports [11][12][13][14][15][16][17][18] have indicated that it takes a long time for the composition evolution of MgO·Al 2 O 3 →CaO-Al 2 O 3 system. Our result was quite similar to these reports in that the unreacted MgO·Al 2 O 3 core surrounded by the CaO-Al 2 O 3 system was observed as seen in Fig.…”

“…Thus, the composition evolution mechanism of MgO·Al 2 O 3 →CaO-Al 2 O 3 system was the same as previously reported. [12][13][14][15][16][17][18] According to the stability of the oxide species, Mg atoms diffuse toward outside while Ca atoms diffuse toward inside. Then, inclusion compositions would converge into the CaO-Al 2 O 3 system in the LF refining step when the reaction time is longer enough.…”