With the maturation of magnesia carbon brick production technology, the application range of magnesia carbon bricks is getting wider and wider. In 1994, Hu Chaoqun and others used magnesia carbon bricks as linings of electric arc furnaces. The wholesale of magnesia carbon bricks and greatly improved the service of the linings. life. Shihezi Today, magnesium carbon brick has become the main refractory material for most domestic steel companies. Although magnesia-carbon bricks have been widely used in metallurgical processes, due to their harsh working conditions, the service life of magnesia-carbon bricks is still very problematic, especially for the ladle slag line. The damage of magnesia-carbon bricks is particularly serious.

       In the ladle, the chemical composition of the slag is complicated and changeable, and the temperature changes violently and frequently, especially in the slag line part, so the magnesium carbon brick with excellent performance is often applied in the slag line part. At home and abroad, the corrosion mechanism of magnesia-carbon bricks in ladle in slag has been deeply studied, and the detailed summary is summarized as follows.

       (1) Erosion of slag to magnesia-carbon brick:

       In the ladle, due to the complicated physical and chemical environment of the slag line part, the furnace lining at this part is most vulnerable to damage. The chemical attack of slag on magnesia-carbon bricks is mainly caused by the dissolution of magnesia and the oxidation of carbon in the matrix of magnesia-carbon bricks. The combination of the following factors leads to the damage of magnesia-carbon bricks:

       1. The influence of alkalinity: the lower the alkalinity of the slag, the more favorable the erosion of the magnesium carbon brick. If the alkalinity of the slag increases, the activity of SiO2 in the slag will be reduced, and the oxidation of carbon will be reduced. The increase of the degree reduces the activity of FeO in the slag, which relatively slows down the erosion behavior of the slag on the magnesium carbon brick;

       2. The effect of MgO: Osbom and others found that the content of MgO in the slag layer was as high as 30% when analyzing the LF slag line, and believed that the higher the content of MgO in the slag, the slower the erosion of magnesium-carbon bricks and the alkalinity The higher, the slower the erosion of magnesium carbon brick by slag.

       3. The influence of Al2O3: Al2O3 in the slag will reduce the melting point and viscosity of the slag, increase the wettability of the slag and the refractory material, make the slag easier to penetrate from the magnesite grain boundary, and make the periclase out of the magnesium carbon brick matrix. .

       4. The effect of FeO: First, FeO in the slag easily undergoes oxidation reaction with graphite in magnesium carbon brick at high temperature, and produces bright white iron beads, forming a decarburized layer, as shown in Figure 1, and secondly, magnesium in magnesium carbon brick. Stone also reacts with FeO in the slag to form low melting products.

       In the process of repeated heating and cooling of the ladle, due to the inconsistent thermal expansion rate between the formed magnesium-iron composite low melting point product and the magnesite, the magnesium oxide on the surface of the refractory material was broken, and the brick body was dissolved. Foreign scholars also believe that the increased iron content in steel slag is not conducive to the life of magnesium carbon bricks. First, iron FeO accelerates the oxidation of carbon on the surface of magnesium carbon bricks. Second, FeO will react with MgO to make the working surface structure of magnesium carbon bricks loose. The joint effect of the point makes the magnesium-carbon brick accelerate erosion.

       (2) Oxidation of carbon in magnesium carbon brick:

       When the Mg-C brick contacts the slag, carbon will react with FeO and other oxides in the slag, and a de-carbonization layer will be formed under certain conditions, which will cause the structure of the working surface of the Mg-C brick to be loose. This is the damage of the Mg-C brick main reason. Carbon reacts with oxides such as CO2, O2, and SiO2 and is continuously oxidized by iron oxides in the slag; secondly, the loose structure formed by the decarburized layer generates larger cracks and pores under the action of thermal expansion and scouring of the slag, allowing the slag to penetrate easily, It forms a low melting point phase with MgO. At the same time, the structure of the surface layer of magnesium carbon brick changes under the action of severe mechanical agitation in the molten pool and violent scouring of the steel slag. Eventually, the surface structure of the magnesium carbon brick is gradually damaged from the outside to the inside, causing serious damage to the magnesium carbon brick. After the temperature exceeds a certain value, the brick structure will be damaged and sharply damaged, which is due to the self-consumption reaction between MgO and graphite at high temperatures.

       (3) Stomatal effects:

       Because of the existence of micro-pores on the interior and surface of Mg-C bricks, the erosion of Mg-C bricks is more likely to occur. During the use of magnesia-carbon bricks, pores played an accelerated role in the formation of the decarburized layer, which further made the slag corrosive to the magnesia-carbon brick refractories. The outside air enters the pores in the Mg-C bricks for cooling, while the oxygen in the air reacts with the surrounding carbon to generate CO gas and is discharged through the micro pores. The continuous occurrence of the two processes makes the porosity and pore size gradually increase. The most important factor for the generation of pores is the choice of binder in magnesium carbon bricks. Binders are generally selected from phenolic resins. If a small amount of phenolic resin is added to the magnesium carbon brick, the porosity will not be too high in the cold state, about 3%, but after heating, the phenolic resin will decompose to produce water, hydrogen, methane, carbon monoxide, etc. Gas, and the formation of pores under the flow of these gases increases the porosity. Therefore, the magnesia-carbon brick is eroded by the slag passing through the pores, which makes the oxidation of carbon and the dissolution of MgO more severe, thereby causing damage to the magnesia-carbon brick. Due to the repetitive nature of the gas generation process, the damage of magnesia-carbon bricks continues to increase.

       to sum up:

       The damage of magnesia-carbon bricks is mainly considered from the aspects of chemical erosion and physical penetration of slag. In different metallurgical reactors, due to different operating processes and slag composition, the erosion mechanism of magnesia-carbon bricks is also different. At present, steel converters basically adopt the slag splashing furnace protection technology, so most converter furnaces are older than 10,000 furnaces, and the lining of steelmaking electric furnaces and refining ladle is severely corroded. For the corrosion behavior of magnesium carbon bricks in slag, the oxidation of carbon and the dissolution of magnesium oxide are the main factors.

       The damage process of magnesia-carbon brick can be summarized as: oxidation, decarburization, loosening, erosion, scouring, shedding, and damage. First, the graphite on the working surface of the magnesia-carbon brick is oxidized to form a decarburized layer. The magnesia of the decarburized layer is under thermal stress (the thermal expansion rates of graphite and magnesia are 1000% and 1.4% and 0.2%, respectively), chemical erosion, and mechanical erosion Under the conditions, it was gradually eroded and shed, and after the detachment, graphite was leaked out. It continued to be oxidized to form a decarburized layer, and then to the dissolution process of magnesia. Under repeated action, it caused the damage of magnesia-carbon bricks.

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