In 1994, Hu Chaoqun and others used brick as lining of electric arc furnace, which greatly increased the service life of lining. Today, the magnesia carbon brick of electric furnace has become the main refractory of most iron and steel enterprises in China. Although it is widely used in metallurgical process, its service life still has a big problem due to its harsh working conditions. The damage of MgO-C brick in ladle slag line is serious.
In ladle, the chemical composition of slag is complex and changeable, and the temperature changes violently and frequently. Therefore, magnesia carbon brick with excellent performance is often used in the slag line of ladle. At home and abroad, the corrosion mechanism of ladle slag has been deeply studied, and the detailed summary is as follows.
(1) The erosion of slag on magnesia carbon brick is as follows
In ladle, the lining of slag line is easy to be damaged due to the complex physical and chemical environment. The chemical attack of slag on MgO-C brick is mainly through the dissolution of MgO and the oxidation of carbon in MgO-C brick matrix
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1. The influence of basicity: the lower the basicity of slag is, the more favorable the erosion of MgO-C brick is. If the basicity of slag increases, the activity of SiO2 in slag will decrease, which can reduce the oxidation of carbon. Meanwhile, with the increase of basicity, the activity of FeO in slag will decrease, which will slow down the erosion behavior of slag on MgO-C brick
2. Influence of MgO: osbom et al. Found that the MgO content in slag layer was 30% when analyzing the composition of LF slag line. It was considered that the higher the MgO content in the slag, the slower the erosion of MgO-C brick, the higher the alkalinity, which also slowed down the corrosion of magnesia carbon brick.
Electric furnace magnesia carbon brick factory
3. The influence of Al2O3: Al2O3 in slag will reduce the melting point and viscosity of slag, increase the wettability between slag and refractory, make slag more easily penetrate from magnesia grain boundary, and make periclase separate from magnesia carbon brick matrix.
4. Effect of FeO: FeO in the first slag is easy to oxidize with graphite in MgO-C brick at high temperature, and bright white iron beads are produced to form decarburization layer, as shown in Figure 1. Secondly, periclase in magnesia carbon brick reacts with FeO in slag to form low melting point products.
In the process of repeated heating and cooling of the ladle, the MgO on the refractory surface is broken and the brick body is dissolved due to the inconsistency of the thermal expansion rate between the magnesium iron compound low melting point product and the magnesite. Foreign scholars also believe that the increase of iron content in steel slag is unfavorable to the service life of MgO-C brick. Firstly, FeO accelerates the oxidation of carbon on the surface of MgO-C brick, and secondly, FeO reacts with MgO to loosen the structure of working face of MgO-C brick.
(2) The oxidation of carbon in magnesia carbon brick is as follows
When MgO-C brick contacts with slag, carbon will react with FeO and other oxides in slag to form decarburization layer under the condition, resulting in loose structure of MgO-C brick working face, which is the main reason for the damage of MgO-C brick. Carbon reacts with oxides such as CO2, O2 and SiO2 and is continuously oxidized by iron oxides in slag; Secondly, the loose structure formed by decarburization layer produces larger cracks and pores under the action of thermal expansion and slag erosion, which makes the slag easy to penetrate and form a low melting point phase with MgO. At the same time, under the action of violent mechanical agitation in the molten pool and the strong scouring of steel slag, the surface layer structure of magnesia carbon brick changes, and finally gradually damages from the outside to the inside, resulting in serious damage to the magnesia carbon brick. When the temperature exceeds the value, the brick structure will be destroyed, which is due to the self consumption reaction between MgO and graphite at high temperature. Magnesia carbon brick for electric furnace
(3) The influence of stomata is as follows
Due to the existence of micro pores in the inner and surface of MgO-C brick, the erosion of MgO-C brick is more likely to occur. In the process of using MgO-C brick, the porosity accelerates the formation of decarburization layer, which makes the erosion of slag on magnesia carbon brick refractory more serious. At the same time, the oxygen in the air reacts with the surrounding carbon to form CO gas, which is discharged through micro pores. The continuous occurrence of the two processes makes the porosity and pore size gradually increase. The important factor of producing porosity is the selection of binder in magnesia carbon brick. Generally, phenolic resin is selected as binder. If a small amount of phenolic resin is added into the magnesia carbon brick, the porosity will not be too high, which is about 3% in cold state. However, after heating, the phenolic resin will decompose to produce gases such as water, hydrogen, methane, and carbon monoxide (II), which will form pores under the flow of these gases, thus increasing the porosity. Therefore, the magnesia carbon brick is eroded by the slag passing through the air hole, which makes the oxidation of carbon and the dissolution of MgO more severe, thus causing damage to the magnesia carbon brick. The damage of MgO-C brick is becoming more and more serious due to the repetitive process of producing gas.