Control of MgO·Al2O3 Spinel Inclusions in Stainless Steels

Abstract

The latest publications regarding the development of technology to control inclusion compositions focusing on MgO · Al 2 O 3 spinel inclusions were summarized in this review article. The problems caused by spinel inclusions, which affect practice as well as products were shown. The formation mechanism of MgO · Al 2 O 3 spinel inclusions is secondly explained thermodynamically from the view points of chemistries of molten steels and slag compositions. Furthermore, crystallization behaviour of spinel was introduced. Countermeasures conducted in practices and laboratories were shown along with some problems still left that should be solved in the future.

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

“…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.…”

“…This consumption might be attributed to the reaction between metal and slag, oxygen supply from the atmosphere and desulfurization. 2,19,27) According to the previous studies, 7,9,19) Ca and Mg were supplied through reduction of CaO and MgO contained in the slag by the Al addition. The concentrations of Ca and Mg were 5.9 and 2.5 ppm, respectively, at the LF initial.…”

“…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.…”

Effect of Ti Content on the Characteristics of Inclusions in Al–Ti–Ca Complex Deoxidized Steel

“…[22][23][24] During past decades, a number of researches on the reaction mechanism, modification behavior and size distribution of nonmetallic inclusions in Al-killed steel during calcium treatment process have been widely conducted. [25][26][27][28][29][30][31][32] However, few systematic reports have been published on the deoxidization, especially inclusion evolution by calcium and titanium complex treatment yet.…”

Thermodynamic Model for Prediction of Slag-Steel-Inclusion Reactions of 304 Stainless Steels

“…1,2) Non-metallic inclusions in steel have a detrimental effect on the performance of steels, such as their strength, toughness, fatigability, cleanliness, surface finishing, etc. 3) A wide range of operating approaches including deoxidation, 4,5) calcium treatment, [6][7][8][9][10][11] slag refining, [12][13][14][15][16][17] and prevention against reoxidation [18][19][20][21] are applied throughout the steelmaking processes of stainless steels. Inclusion composition is greatly influenced by the composition of the top slag and the refractory material.…”