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How to extend the life of magnesia carbon bricks for slag line?

2020-12-02 15:49:39
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When the magnesia carbon brick is in contact with molten steel and slag, the slag corrodes the magnesia carbon brick, which results in poor thermal shock stability of the magnesia carbon brick, spalling damage, shortening the service life of the slag line magnesia carbon brick and affecting the refining production of the LF furnace. In order to extend the service life of magnesia carbon bricks, the researchers studied the influence of LF furnace slag on the corrosion resistance of magnesia carbon bricks, and explored ways to extend the life of magnesia carbon bricks for LF slag line.


Experimental materials and process


Low-iron slag and high-iron slag used in LF furnace were selected for the experiment, and the composition is shown in the attached table. The magnesia carbon brick is selected from the slag line magnesia carbon brick MT-14 currently used by Angang.


After the researcher made the slag line magnesia-carbon brick into a crucible sample with an inner diameter of ф60mm×50mm and an outer diameter of ф120mm×100mm, the LF low-iron slag and high-iron slag were respectively loaded into the prepared crucible, and kept at 1600℃ for 3h , The static crucible method is used to carry out the slag erosion resistance experiment of magnesia carbon brick. They grind two kinds of LF furnace slag into 200 mesh fine powder, use thermoplastic phenolic resin as a binder, press it into a cylindrical sample of ф6mm×5mm, and place it on a gasket made of magnesia carbon brick on the slag line. Place it in the refractoriness tester DRH-III to observe the wetting angle between the slag and the magnesia carbon brick when the sample reaches the hemispheric temperature to characterize the wettability of the slag on the magnesia carbon brick.

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Experimental results and analysis


Wetting angle detection. According to the schematic diagram of the wetting angle of the two slags of the LF furnace on the magnesia carbon bricks, the researchers calculated that the LF slag with less iron has a wetting angle of 45° for the magnesia carbon bricks, and the LF slag with more iron can wet the magnesia carbon bricks. The wet angle is 58°. It can be seen that both slags of the LF furnace can wet the magnesia carbon bricks, and the slag with less iron wets more obviously, and the erosion of the bricks is more obvious. Therefore, the slag composition of the LF furnace can be adjusted within a certain range to increase the wetting angle of the slag to the product, thereby improving the corrosion resistance of the magnesia carbon brick.


Anti-slag erosion analysis. The SEM morphology of the magnesia carbon brick crucible after the LF slag with less iron and more iron is corroded by the LF slag shows that a thin slag layer is formed on the surface of the magnesia carbon brick after being corroded by the LF slag, and the samples with less iron hang The slag layer is relatively obvious. Due to the short erosion time, after being eroded by the two types of slag, the erosion layer on the surface of the magnesia carbon brick is thin. At the same time, the scaly graphite on the surface of the magnesia carbon brick in contact with the slag is oxidized and the matrix is relatively loose. Moreover, the corrosion of low-iron LF slag on magnesia-carbon bricks is significantly stronger than that of high-speed LF slag, and the erosion layer is relatively deep. This is because the low-iron slag has a relatively small wetting angle for the magnesia carbon bricks, and the wetting rate of the magnesia carbon bricks is fast under the same conditions, which accelerates the corrosion of the magnesia carbon bricks.


The researchers further studied and found that the LF slag first wetted the surface of the magnesia carbon brick, and then invaded the matrix of the magnesia carbon brick along the pores left by the graphite oxidation, filled around the magnesia particles, and chemically attacked the magnesia particles. , To generate a low-melting liquid phase containing Ca, Si, Al, thereby gradually encroaching on magnesia particles. It can be inferred from this that as the reaction time increases, a cemented structure will form 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 eroded by the slag and become smooth, thus making the magnesia carbon The composition and performance of the corroded brick layer and the original brick layer, especially the thermal expansion coefficient, are quite different. When subjected to thermal shock and thermal shock during use, the working surface of the magnesia-carbon brick will be peeled off and damaged. Under the condition of refining outside the LF furnace, due to the high refining temperature, the viscosity of the slag decreases, plus the internal lining The temperature is also higher, and the slag can penetrate deeper into the refractory material to form a thicker reaction layer, which will aggravate the melting loss of the magnesia carbon brick lining and cause serious peeling and chipping damage. Therefore, the impact of LF slag on magnesia carbon bricks is mainly manifested in chemical attack and the resulting poor thermal shock stability, spalling damage.


Ways to extend the life of magnesia carbon bricks for slag line


In summary, the wetting angle of the two LF furnace slags to the magnesia carbon brick is less than 90°, which is easy to wet the surface of the magnesia carbon brick. When it comes into contact with the magnesia carbon brick, the damage rate of the magnesia carbon brick will be accelerated, and the iron is low. The wetting phenomenon of LF slag is more obvious. In corrosion experiments, this phenomenon reduces the corrosion resistance of magnesia carbon bricks in contact with low-iron slag.


In order to prolong the slag erosion resistance life of LF furnace magnesia carbon bricks, we can adjust the composition of the slag and increase the wetting angle of the slag to the magnesia carbon bricks to form a stable slag layer on the surface of the magnesia carbon bricks to prevent surface graphite. The oxidation of magnesia carbon bricks can inhibit the wetting of the surface of the magnesia-carbon bricks by the slag, or by optimizing the matrix structure of the magnesia-carbon bricks, the introduction form and amount of graphite in the magnesia-carbon bricks can be improved, and the ingredients of the matrix can be adjusted to affect the During use, the number, size, shape and distribution of pores formed by carbon oxidation will extend the service life of LF slag line magnesia carbon bricks.

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