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

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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 mgo-c brick, spalling damage, shortening the service life of the slag line mgo-c brick and affecting the refining production of LF furnace. In order to extend the service life of magnesia carbon bricks, LMM engineers 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.

Keywrods:Slag line, magnesia carbon bricks, prolonged, service life

Experimental materials and process

The experiment uses low-iron slag and high-iron slag for LF furnace, and the magnesia-carbon brick uses the slag line magnesia-carbon brick MT-14 currently used by An Steel.

After the researcher made the slag line magnesia-carbon bricks 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 test of magnesia carbon bricks. 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 of the molten slag and the magnesia carbon brick when the sample reaches the hemispheric temperature to characterize the wettability of the molten slag on the magnesia carbon brick.

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 wetting is more obvious, and the erosion of the bricks is more obvious. Therefore, the slag composition of the LF furnace can be adjusted within a certain range, and the wetting angle of the slag to the product can be increased, thereby improving the corrosion resistance of the magnesia carbon brick.

Anti-slag erosion analysis

The SEM morphology of magnesia carbon bricks after corrosion by LF slag shows a thin slag layer on the surface. Samples with less iron show a more obvious slag layer. Due to the short erosion time, the erosion layer on the surface remains thin. The scaly graphite on the surface oxidizes, making the matrix loose. Low-iron LF slag corrodes magnesia-carbon bricks more strongly than high-iron LF slag. The erosion layer is deeper because low-iron slag has a smaller wetting angle, accelerating corrosion.

Researchers found that LF slag first wets the magnesia carbon brick surface. It then invades the matrix through pores left by graphite oxidation. The slag fills around magnesia particles and chemically attacks them. This generates a low-melting liquid phase containing Ca, Si, and Al, gradually encroaching on magnesia particles. As reaction time increases, a cemented structure forms. Magnesia particles embed in the liquid phase, and their edges become smooth. This makes the corroded brick layer different from the original layer, especially in thermal expansion.

Thermal shock during use will peel and damage the magnesia-carbon brick’s working surface. High refining temperatures in LF furnaces decrease slag viscosity. The internal lining temperature also rises, allowing slag to penetrate deeper into the refractory material. This forms a thicker reaction layer, aggravating the melting loss of the magnesia carbon brick lining. Serious peeling and chip damage occur. Therefore, LF slag impacts magnesia-carbon bricks through chemical attack and poor thermal shock stability, leading to spalling damage.

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

In summary, the wetting angles of the two LF furnace slags to the magnesia-carbon bricks are less than 90°, which is easy to wet the surface of the magnesia-carbon bricks. 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 corrosion resistance life of LF furnace magnesia carbon bricks, we can start by adjusting the composition of the slag and increasing 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 magnesia carbon bricks by slag, or by optimizing the matrix structure of magnesia carbon bricks, the introduction form and amount of graphite in the magnesia carbon bricks can be improved, and the ingredients composition 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.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

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