How to prolong the service life of magnesia carbon brick for slag line?

When the magnesia carbon brick is in contact with liquid steel and slag, the slag erodes the magnesia carbon brick, resulting in poor thermal shock stability, peeling and damage of the magnesia carbon brick, shortening the service life of the magnesia carbon brick in the slag line and affecting the refining production of LF furnace. In order to prolong the service life of magnesia carbon bricks, the researchers studied the effect of LF furnace slag on the corrosion resistance of magnesia carbon bricks, and discussed the ways to prolong the service life of magnesia carbon bricks for LF slag line. Magnesia brick

Experimental raw materials and process

Low iron slag and high iron slag used in LF furnace are selected in the experiment, and their components are shown in the attached table. The magnesia carbon brick is the slag line magnesia carbon brick mt-14 currently used in Angang.

The researchers made magnesia carbon bricks with an inner diameter of ф 60mm × 50mm, outer diameter ф 120mm × After 100 mm crucible sample, lf low iron slag and high iron slag are respectively loaded into the prepared crucible and kept at 1600 ℃ for 3 hours. The slag corrosion resistance test of magnesia carbon brick is carried out by static crucible method. They ground two kinds of LF furnace slag into 200 mesh fine powder and pressed it with thermoplastic phenolic resin as binder ф 6mm × Place a 5mm cylindrical sample on the gasket made of magnesia carbon brick in the slag line, place it in the fire resistance detector drh-iii, and observe the wetting angle between the slag and magnesia carbon brick when the sample reaches the hemispherical temperature, so as to characterize the wettability of the slag to magnesia carbon brick.

Experimental results and analysis

Wetting angle detection. According to the schematic diagram of wetting angle of two kinds of LF slag on MgO-C brick, the researchers calculated that the wetting angle of LF slag with less iron on MgO-C brick is 45 °, and that of LF slag with more iron on MgO-C brick is 58 °. It can be seen that both slag of LF furnace can wet magnesia carbon brick, and the wetting phenomenon of slag with less iron is more obvious, and the erosion of brick is more obvious. Therefore, the composition of LF furnace slag can be adjusted within the range, and the wetting angle of slag to products can be increased, so as to improve the corrosion resistance of magnesia carbon brick.

Unburned magnesia brick

Slag erosion resistance analysis. The SEM morphology of the crucible of MgO-C brick eroded by LF slag with less and more iron shows that a thin slag layer is formed on the surface of MgO-C brick after being eroded by LF slag, and the slag layer of the sample with less iron is relatively obvious. Due to the short erosion time, after being eroded by two kinds of slag, the erosion layer on the surface of MgO-C brick is relatively thin. At the same time, the flake graphite on the surface of MgO-C brick in contact with slag is oxidized and the matrix is relatively loose. Moreover, the erosion of low iron LF slag on magnesia carbon brick is significantly stronger than that of high iron LF slag, and the erosion layer is relatively deep. This is because the wetting angle of low iron slag on MgO-C brick is relatively small, and the wetting rate of MgO-C brick is fast under the same conditions, which accelerates the melting corrosion of MgO-C brick.

The researchers further found that the LF slag first wetted the surface of the magnesia carbon brick, then invaded the matrix of the magnesia carbon brick along the pores left after graphite oxidation, filled around the magnesia particles, chemically eroded and melted with the magnesia particles, and formed a low melting point liquid phase containing Ca, Si and Al, thus eroding the magnesia particles step by step. It can be inferred that with the extension of reaction time, the cemented structure will be formed in the magnesia carbon brick, the magnesia particles will be embedded in the liquid phase, and the edges and corners of the magnesia particles will be melted by the slag and become smooth, so that the composition and performance of the erosion layer of the magnesia carbon brick and the original brick layer are very different, especially the coefficient of thermal expansion. When it is subjected to thermal shock and thermal shock during use, the working face of magnesia carbon brick will be peeled off and damaged. Under the condition of LF refining outside the furnace, due to the high refining temperature, the viscosity of slag decreases, and the internal temperature of furnace lining is also high, the slag can penetrate deeper into the interior of refractory materials to form a thicker reaction layer, which will aggravate the melting loss of magnesia carbon brick lining and cause serious peeling off and damage. Therefore, the effect of LF slag on MgO-C brick is mainly manifested in chemical corrosion and poor thermal shock stability, spalling and damage.

Ways to prolong the service life of magnesia carbon brick for slag line

To sum up, the wetting angle of the two LF furnace slags to the MgO-C brick is less than 90 °, which is easy to wet the surface of MgO-C brick. When contacting with MgO-C brick, it will accelerate the damage rate of MgO-C brick, and the wetting phenomenon of low iron LF slag is more obvious. In the erosion experiment, this phenomenon reduces the corrosion resistance of magnesia carbon brick in contact with low iron slag.

In order to prolong the anti slag corrosion life of magnesia carbon brick of LF furnace, we can start with adjusting the composition of slag and increasing the wetting angle of slag to magnesia carbon brick, form a stable slag hanging layer on the surface of magnesia carbon brick, prevent the oxidation of surface graphite and inhibit the wetting of slag to the surface of magnesia carbon brick, or optimize the matrix structure of magnesia carbon brick, improve the introduction form and amount of graphite in magnesia carbon brick and adjust the ingredient composition of matrix, Thus, the number, size, shape and distribution of pores formed by carbon oxidation in the service process of magnesia carbon brick are affected, so as to prolong the service life of magnesia carbon brick in LF slag line.