During the working process of steelmaking electric furnaces, they are usually in an alkaline corrosive atmosphere. Therefore, the refractory materials used in electric furnaces are mainly alkaline materials, such as MgO-C bricks, asphalt impregnated MgO bricks, MgO-Cr2O3 bricks, MgO-CaO ramming materials, etc., and a small part is neutral refractories materials, such as Al2O3-C materials, high-alumina materials, etc.
Overall, the main damage factors of electric furnace refractory are: erosion, oxidation, scouring, melting, spalling and hydration, among which oxidation, chemical erosion and scouring are dominant.
01 Chemical erosion
Iron oxide (FeO) or acidic components in slag, such as SiO2, react chemically with CaO and MgO. The reaction can turn the furnace lining into slag, thereby causing damage to the refractory materials.
02 Oxidation
Oxidation is one of the main causes of erosion of refractories materials in electric furnace linings. During this process, the carbon component in the refractory is oxidized by oxygen-containing components (such as iron oxide, oxygen, and magnesium oxide), resulting in decarburization and damage of the material.
The iron oxide in the slag reacts with the graphite or tar/resin in the hot surface of the brick lining, or the oxygen corrodes the graphite or binder on the cold surface of the brick lining. In both cases, the strength of the brick is reduced and it may be eroded by slag or molten steel.
Under the atmosphere conditions of an actual electric furnace, starting from above 1700°C, reaction (6) is particularly prone to occur, and the generated Mg vapor is easy to diffuse, resulting in structural degradation, which is one of the main factors causing high-temperature damage to magnesia carbon bricks.
03 Scouring or mechanical impact
Physical damage is caused by molten steel or slag flowing over the surface of the refractory and physically wearing or scouring the furnace lining. Scouring erosion is most common at the steel outlet, slag line, electrode port or exhaust platform of the electric furnace.
Spalling is a complex refractory damage mechanism. This is caused by the stress generated in the refractory lining due to rapid heating and cooling. This stress often exceeds the strength of the refractory material, resulting in the intersection and penetration of cracks, and the fragments of the lining will peel off or fall off completely. This situation commonly occurs on the top of the electric furnace.
04 Hydration
Hydration is also a factor in the damage of electric furnace refractories materials. During use, water easily penetrates into the furnace cover or furnace wall, and water or water vapor can corrode the refractory lining. Magnesium oxide (or other alkaline oxides) react with water (or water vapor) as follows and are hydrated.
The reaction will cause the performance of the refractories material to be greatly weakened, and the permeability of the slag and molten steel will deteriorate.
From the above analysis of the causes of damage, it can be seen that the refractory materials selected for various parts of the steel-making electric furnace have the following performance requirements: ① good chemical stability and volume stability; ② the material composition is not easy to react with molten steel and SiO2, and it is not easy to produce nodules; ③ it is not easy to be wetted and penetrated by molten steel; ④ it has good resistance to rapid cooling and rapid heating, and it is not easy to break and peel off; ⑤ high density, low porosity, uniform pore distribution, and molten steel is not easy to penetrate; ⑥ high strength, can resist mechanical external force impact and erosion.
