Characteristics of alumina magnesia carbon brick and problems in ladle application

1. Characteristics of alumina magnesia carbon brick

Alumina magnesia carbon brick is used as refractory for lining of refining furnace. It gives full play to magnesia's strong slag corrosion resistance, low expansion and high thermal conductivity of carbon, and makes up for the defect of poor spalling resistance of magnesia. The excellent properties of alumina magnesia carbon brick are as follows

(1) MgO and C have no eutectic relationship at high temperature. The melting point of carbon is 3000 ℃ and that of MgO is 2800 ℃.

Magnesia carbon brick factory

(2) MgO has a strong resistance to alkaline slag and high iron slag, and graphite has a large wetting angle to slag, which makes slag not permeable and has thin metamorphic layer.

(3) Al 2O 3 reacts with MgO in the matrix at high temperature to form Al Mg spinel. Ma spinel has small elastic modulus and small thermal expansion coefficient. It can transfer the secondary MF spinel in periclase, accompanied by volume expansion, which can block the pores and inhibit the further penetration of slag.

A large amount of slag reacts with Al2O3 to form high melting point columnar CA6 and a small amount of Ca2. With the formation of Ca and other minerals, a large amount of slag is consumed, which makes the slag viscosity increase and the slag permeability decreases. At the same time, spinel in the matrix can capture FeO and MnO in the slag and form spinel solid solution, which can further improve the slag resistance of alumina magnesia carbon brick. Because of the expansion performance, AMC brick has tight joint and good integrity after use.

2. Problems in application of alumina magnesia carbon brick in ladle

Alumina magnesia carbon bricks are mostly used as working linings for large and medium-sized refining ladles in China. Due to the high carbon content of alumina magnesia carbon brick, it may have carburizing effect on molten steel, and affect the smelting of low carbon steel, carbon steel and other varieties of steel. At the same time, its thermal conductivity is very large, which will increase the temperature drop of molten steel, which is not conducive to the temperature control of casting technology.

Because of the chemical reaction between Al2O3 and MgO in the matrix of Al Mg carbon steel clad brick, alumina magnesia spinel is formed, which causes the volume expansion of products, causes the stress of ladle working lining in use, causes the brick structure to peel off, and affects the use safety.

In order to improve the market competitiveness, a LF refining system is added in No.3 Steel Plant of Maanshan Iron and Steel Co., Ltd. to realize the secondary refining of arc heating, gas mixing and composition adjustment. By strengthening the reaction conditions of kinetics and thermodynamics, the molten steel can be purified and homogenized in a short period of time, and the refining effect can be achieved. Due to high temperature stirring and scouring, strong alkaline slag erosion and long time immersion of molten steel, the working environment of ladle lining becomes very harsh. In order to meet the normal operation of LF refining system and the working conditions of ladle in No.3 Steel Plant of Maanshan Iron and Steel Group Co., Ltd., the long life Al Mg C lining brick for ladle has been specially developed. Al2o3-mgo-c ladle lining brick has good high temperature performance, slag resistance and thermal shock stability.