The steelmaking electric furnace is usually in an alkaline corrosive atmosphere during the working process, so the refractory materials used in the electric furnace are mostly alkaline refractory materials. Such as MgO-C bricks, asphalt-impregnated MgO bricks, MgO-Cr₂O₃ bricks, MgO-CaO ramming materials, etc., and a small number of neutral refractories, such as Al₂O₃-C materials, high alumina materials, etc.
In general, the main damage factors of electric furnace refractories are: erosion, oxidation, scouring, melting, spalling and hydration, among which oxidation, chemical erosion and scouring are the dominant ones.
(1) Chemical attack
A chemical reaction occurs between iron oxide (FeO) or acidic components in the slag, such as SiO₂, with CaO and MgO, as follows:
All of the above reactions can turn the furnace lining into slag, resulting in damage to the refractory material.
Oxidation is one of the main causes of erosion of refractory materials in the lining of electric furnaces. During this process, the carbon component in the refractory material is oxidized by oxygen-containing components (such as iron oxide, oxygen, and magnesium oxide), resulting in decarburization and damage to the material.
The iron oxide in the slag reacts with the graphite or tar/resin in the hot side of the brick lining, or oxygen erodes the graphite or binder in the cold side of the brick lining. In both cases the strength of the brick is reduced and may be eroded by slag or molten steel.
Under the atmospheric conditions of the actual electric furnace, starting from above 1700 ° C, the reaction (6) is particularly easy to occur, and the generated Mg vapor is easily diffused, resulting in structural deterioration, which is one of the main factors that cause high temperature damage to magnesia-carbon bricks.
(3) scouring or mechanical shock
Physical damage occurs as molten steel or slag flows over the refractory surface and physically wears or scours the furnace lining. Erosion damage is most common at the tapping port, slag line, electrode port or exhaust platform of the electric furnace.
Spalling is an intricate damage mechanism of refractory materials. This is due to the stress in the refractory material caused by the rapid heating and cooling of the lining refractory material. This stress often exceeds the strength of the refractory material, resulting in the intersection of cracks and fragments of the lining will peel off or fall off completely, which commonly occurs on the roof of electric furnaces.
Hydration is also a factor in refractory damage in electric furnaces. During use, water easily penetrates into the furnace cover or furnace wall, and water or water vapor can erode the refractory lining, wherein magnesium oxide (or other basic oxides) react with water (or water vapor) as follows to be hydrated.
Reaction (7) will result in a substantial weakening of the refractory properties and poor slag and molten steel permeability.
part of the steelmaking electric furnace have the following performance requirements:
①Good chemical stability and volume stability:
②The material composition is not easy to react with molten steel and SiO₂, and it is not easy to produce nodules;
③It is not easy to be wetted and penetrated by molten steel;
④It has good resistance to rapid cooling and rapid heating, and is not easy to be damaged and peeled off;
⑤High density, low porosity, uniform distribution of pores, and impermeable molten steel;
⑥High strength, can resist the impact and erosion of mechanical external force.