Role of Calcium Magnesium Aluminate in Carbon-containing Bricks for Steel Ladle

doi:10.19691/j.cnki.1004-4493.2021.01.004

China's Refractories ›› 2021, Vol. 30 ›› Issue (1): 23-30.DOI: 10.19691/j.cnki.1004-4493.2021.01.004

• Original article • Previous Articles Next Articles

Role of Calcium Magnesium Aluminate in Carbon-containing Bricks for Steel Ladle

GAO Jianying¹^,^*(), WOHRMEYER Christoph², DETEUF Cyrille²

1 Imerys Aluminates (China) Co., Ltd., Tianjin 300457, China
2 Imerys Aluminates, Puteaux 92800, France

Online:2021-03-15 Published:2021-05-01
Contact: GAO Jianying
About author:Dr. Gao Jianying was born in 1977 in Inner Mongolia. He studied in Xi’an University of Architecture and Technology and obtained his bachelor’s degree in 1999 and master’s degree in 2002. He received his PhD from Shanghai Institute of Ceramics, Chinese Academy of Science, in 2005. He joined RHI R&D team in 2006 and gained plenty of experiences on microstructural research of basic shaped refractories. Since 2011, he has been working in Imerys Aluminates (ex-Kerneos) and taking critical positions of R&D Manager, Senior Technical Manager and Refractory Technical Director. His responsibilities cover technical support for refractory businesses, advanced ceramics and investment casting. He is engaged in not only application development but also knowhow generation of various refractory raw materials. In addition, he works as a visiting professor and a supervisor for master students in the school of Materials Engineering, Xi’an University of Architecture and Technology.

Abstract

Abstract:

Calcium magnesium aluminate, with the commercial name of MagArmour, is a synthetic material consisting of 70 mass% Al₂O₃, 20 mass% MgO and 10 mass% CaO, approximately. It is characterized by porous microstructure, intergranular aluminates phases and micro-crystalline spinel. Since globally launched in 2017, MagArmour has been successfully applied to various carbon-containing refractories serving for steel refining process. Lots of cases have demonstrated the role of MagArmour in enhancing the service life of carbon containing bricks for ladle lining. The benefits embody in formation of protective coating on hot surface, relief of drilling corrosion in joint positions, and elimination of grooves or cracks caused by mechanical stress concentration. In addition, MagArmour is effective in protecting graphite from deep oxidization so as to be capable of replacing the metallic or carbide anti-oxidants in carbon-containing bricks entirely. By means of chemical analysis and microstructural dissection, postmortem investigations on the used MgO-C bricks from both metal and slag zones of 120t steel refining ladle were conducted to clarify the working mechanism of MagArmour. The formation of protective coating on hot face is attributed to the dissolution of micro-crystalline spinel into contacting slag, which changes the slag chemistry so as to enhance viscosity. The improvement in corrosion/erosion resistance is highly related to the porous microstructure and dispersive aluminates. As well known, evaporation of Mg, Al and SiO, and/or internal migration, occurs in MgO-C bricks at elevated temperatures. The gaseous phases are absorbed by MagArmour particles due to the high surface area of porous microstructure and condense as corresponding oxides. These oxides react with the intergranular calcium aluminates forming liquid phase. With increasing temperature, the liquid phase seeps into the matrix under capillary force. The increased liquid amount improves the flexibility of the matrix and thus releases the internal stresses concentration resulting from mechanical stress and temperature gradient. Meanwhile, densification of the matrix microstructure occurs under the static pressure generated by liquid steel and molten slag, which blocks the channels of oxygen infiltration.

Key words: calcium magnesium aluminate, MagArmour, protective coating, flexibility, oxidation resistance

GAO Jianying, WOHRMEYER Christoph, DETEUF Cyrille. Role of Calcium Magnesium Aluminate in Carbon-containing Bricks for Steel Ladle[J]. China's Refractories, 2021, 30(1): 23-30.

Figures/Tables 21

Table 1 Chemical composition, phase constituent and physical properties of MagArmour

Item	Specification
Chemical composition	Al₂O₃	69%-72%
	MgO	19%-22%
	CaO	7.5%-10.5%
Phase constituent	CaO·Al₂O₃	18%-22%
	CaO·2Al₂O₃	8%-12%
	MgAl₂O₄	68%-72%
Physical property	Bulk density	2.2-2.4 g/cm³
	Apparent porosity	24%-32%
	Refractoriness	1 755 ℃

Fig. 1 Appearance of MagArmour aggregates

Fig. 2 MagArmour aggregate and its microstructural characteristics: porous texture (a), dispersive aluminate phases (b),and micro-crystalline spinel cluster (c)

Table 2 Chemical composition of metal zone bricks for comparison /mass%

Brick	MgO	Al₂O₃	CaO	SiO₂	Fe₂O₃	C
MgO-C	79.14	2.23	1.14	3.06	0.91	13.52
MgO-MagA.-C	76.69	5.66	1.71	1.92	0.74	13.28

Table 3 Chemical composition of slag zone bricks for comparison /mass%

Brick	MgO	Al₂O₃	CaO	SiO₂	Fe₂O₃	C
MgO-C	79.48	2.17	1.29	2.73	0.67	13.66
MgO-MagA.-C	79.52	3.88	1.85	0.62	0.71	13.42

Table 4 Working conditions of 120t refining ladle

Items	Value
Tapping temperature /℃	1 620-1 650
Mean holding duration /min	100
Mean tapping cycle /min	45
LF treatment /%	95
LF treating duration /min	35-40
RH treatment /%	5
RH treating duration /min	40

Table 5 Chemical composition of slag /mass%

Al₂O₃	CaO	SiO₂	MgO	Fe₂O₃	MnO	P₂O₅	S	Others
17.5	52.2	14.0	9.3	3.49	0.32	0.03	0.72	4.55

Fig. 3 Lining surface of MgO-C (a) and MgO-MagA.-C bricks (b) in metal zone of ladle

Fig. 4 Used MgO-MagA.-C brick (a) and its cutting section (b)

Fig. 5 Chemical composition change of matrix from hot face to cold end

Fig. 6 Micrograph of protective coating

Table 6 Chemical composition of various phases in protective coating /mass%

	MgO	Al₂O₃	SiO₂	CaO	Fe₂O₃	TiO₂
Dark grey phase	85.54	-	-	-	15.46	-
Light grey phase	-	3.34	33.19	61.89	1.58	-
White matrix phase	0.77	6.45	3.30	41.49	43.11	4.89

Fig. 7 Micrographs of matrix corresponding to 3 mm (a), 9 mm (b), 23 mm (c), 33 mm (d), and 42 mm (e) away from hot face

Fig. 8 Chemical composition change of MagArmour from hot face to cold end

Fig. 9 Micrographs of residual MagArmour particle in zones of 5 mm (a), 9 mm (b), 33 mm (c), and 42 mm (d)

Fig. 10 Detailed microstructure of MagArmour particles in zones of 5 mm (a) and 42 mm (b) from hot face

Fig. 11 Used MgO-C brick (a) and MgO-MagA.-C brick (b) from slag zone

Fig. 12 Chemical composition change of matrix from hot face to cold end

Fig. 13 Hot face micrographs of used MgO-C (a) and MgO-MagA.-C bricks (b)

Fig. 14 Decarburized zone micrographs of used MgO-C (a) and MgO-MagA.-C bricks (b)

Fig. 15 Micrographs of MagArmour particles in decarburized zone (a) and cold end in used MgO-MagA.-C brick (b)

References 12

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