The experience of using magnesia carbon bricks in converters, electric furnaces, and ladles shows that: due to its superior high temperature resistance, slag erosion resistance, and good thermal shock stability, it is very suitable for the requirements of steel smelting. Taking advantage of the fact that carbon materials are difficult to be wetted by slag and molten steel and the high refractory properties of magnesia sand, high slag resistance and solubility resistance, and low high-temperature creep, magnesia carbon bricks are used in slag lines and steel outlets with severe corrosion.
So far, due to the large-scale use of magnesia carbon bricks in the steelmaking process and the improvement of steel smelting technology, huge economic benefits have been created. At present, magnesia carbon bricks have the disadvantages of high-priced graphite consumption, increased heat consumption, and continuous carbonization of molten steel, thereby polluting molten steel. In order to reduce the cost of raw materials and purify molten steel, the low carbonization of low-carbon magnesia carbon bricks can solve these problems well.
The characteristics of magnesia carbon bricks are mainly reflected in the following aspects:
The density of magnesia carbon bricks
The density of magnesia carbon bricks depends on the type and amount of binders and antioxidants, the type of magnesia sand, the particle size and amount of graphite, etc. In addition, the molding equipment, brick pressing technology and heat treatment conditions have a certain influence. In order to achieve an apparent porosity below 3.0%, ensure that the molding pressure is 2t/cm2, and strengthen the volume density of the matrix part to improve its anti-corrosion performance, magnesia carbon bricks with a particle size of less than 1mm are used in the wind eye bricks and the steel outlet bricks. Different binders also have a certain influence on the density of magnesia carbon bricks. The binder with a high residual carbon rate has a higher volume density.
The addition of different antioxidants has significantly different effects on the density of magnesia carbon bricks. Below 800 degrees, the apparent porosity increases with the oxidation of the antioxidant. After exceeding 800 degrees, the apparent porosity of magnesia carbon bricks without metal does not change, while the apparent porosity of those containing metal decreases significantly. At 1450 degrees, it is only half of that at 800 degrees. Among them, the apparent porosity of magnesia carbon bricks with added metal aluminum is the lowest.
The heating speed of magnesia carbon bricks during use will also affect the change of its apparent porosity. Therefore, when using magnesia carbon bricks for the first time, try to increase the temperature at a low speed so that the binder can be completely decomposed at a lower temperature. During the use of magnesia carbon bricks, the effect of temperature difference on porosity is also obvious. The greater the temperature difference, the faster the porosity increases.
The compactness of the organization of magnesium carbon bricks
High-temperature mechanical propertiesDifferent additives have different effects on improving the high-temperature strength of magnesium carbon bricks. Studies have shown that for high-temperature flexural strength above 1200℃, no additives < calcium boride < aluminum < aluminum magnesium < aluminum + calcium boride < aluminum magnesium + calcium boride, among which aluminum magnesium + boron carbide is between aluminum magnesium and aluminum magnesium + calcium boride.
Thermal expansion performanceThe participating expansion value of magnesium carbon bricks without metal addition is much lower than the expansion value of metal addition, and the participating expansion value increases with the increase of metal addition.
The thermal expansion and high-temperature flexural strength of magnesium carbon bricks in different directions of various anisotropies are different, mainly due to the orientation of flake graphite, which determines the principles and methods of working lining brick masonry. Magnesium carbon bricks in the vertical direction have higher high-temperature strength and lower thermal expansion.
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