Aluminum magnesia carbon bricks are unburned products made of special high-alumina bauxite clinker, fused magnesia or sintered magnesia and graphite as raw materials, and liquid phenolic resin as a binder. Physical and chemical indicators of aluminum-magnesium carbon bricks Based on the development of aluminum-magnesium carbon bricks, aluminum-magnesium spinel carbon bricks for ladle were developed. Aluminum-magnesium spinel carbon bricks are bricks with a certain proportion of pre-synthesized magnesium-aluminum spinel added to the brick material, and their performance is better than that of aluminum-magnesium carbon bricks of the same grade.
1. Characteristics of aluminum-magnesium carbon bricks
As a refractory material for the lining of a refining furnace, aluminum magnesia carbon bricks give full play to the strong slag erosion resistance of magnesia and the low expansion and high thermal conductivity of carbon, making up for the defect of poor spalling resistance of magnesia. The excellent performance of aluminum-magnesium-carbon bricks is as follows:
(1) MgO and C have no eutectic relationship at high temperature. The melting point of carbon is above 3000℃, and the melting point of MgO reaches 2800℃. Both are refractory raw materials with excellent high temperature resistance.
(2) Excellent resistance to alkaline slag corrosion. MgO has strong resistance to alkaline slag and high iron slag. At the same time, the wetting angle of graphite to slag is large, the slag is not easy to penetrate, and the metamorphic layer is thin.
(3) Al2O3 reacts with MgO in the matrix at high temperature to form aluminum-magnesium spinel. MA spinel has a small elastic modulus and a small thermal expansion coefficient. It can transfer the secondary MF spinel in periclase and is accompanied by volume expansion. It can block pores and inhibit further penetration of slag.
A large amount of CaO in the slag reacts with Al2O3 to form high-melting-point columnar CA6 and a small amount of CA2. With the formation of minerals such as CA, a large amount of CaO in the slag is consumed, which increases the viscosity of the slag and reduces the permeability of the slag. At the same time, the spinel in the matrix at high temperature can capture FeO and MnO in the slag to form a spinel solid solution, which can further improve the slag resistance of aluminum-magnesium carbon bricks. AMC bricks have certain expansion properties, so the brick joints are tight and the integrity is good after use.
2. Problems of aluminum magnesia carbon bricks in the application of ladle
Most of the working linings of large and medium-sized refined ladle in China use aluminum-magnesium carbon bricks. Due to the high carbon content of aluminum-magnesium carbon bricks, it may have a carbon-enhancing effect on molten steel, affecting the smelting of low-carbon steel, ultra-low-carbon steel and other varieties of steel. At the same time, its thermal conductivity is very large, which will also increase the temperature drop of molten steel, which is not conducive to the temperature control of casting technology. Aluminum-magnesium carbon ladle bricks react chemically with Al2O3 and MgO in the matrix to generate aluminum-magnesium spinel, causing the volume of the product to expand, resulting in stress in the ladle working lining during use, causing the brick structure to peel off, affecting the safety of use.
In order to improve market competitiveness, Ma Steel No. 3 Steel Plant added a set of LF refining system to realize arc heating, gas stirring and furnace refining for adjusting composition. By strengthening the kinetic and thermodynamic reaction conditions, the molten steel can be purified and uniformed in a short time, achieving the effect of refining. Due to the high-temperature stirring and scouring, strong alkaline slag erosion and long-term immersion of molten steel during refining, the working environment of the ladle lining becomes very harsh. In order to meet the normal use of the LF refining system of Ma Steel No. 3 Steel Plant and the working conditions of the ladle, a long-life aluminum-magnesium-carbon lining brick for the ladle was specially developed. Al2O3-MgO-C series ladle bricks for ladle lining have the characteristics of good high temperature performance, good slag resistance and thermal shock stability.
