The steelmaking electric furnace is usually in an alkaline corrosive atmosphere during operation. Therefore, the refractory materials used in the electric furnace are mainly alkaline refractory materials, such as MgO-C bricks, asphalt impregnated MgO bricks, MgO-Cr2O3 bricks, MgO-CaO ramming materials, etc. A small part is neutral refractory materials, such as Al2O3-C materials, high alumina materials, etc.
In general, the main damage factors of electric furnace refractory materials are: erosion, oxidation, scouring, melting, spalling and hydration, among which oxidation, chemical erosion and scouring are dominant.
Chemical attack
Iron oxide (FeO) or acidic components in slag, such as SiO2, react chemically with CaO and MgO
All of the above reactions can turn the furnace lining into slag, thus causing damage to the refractory material.
Oxidation
Oxidation is one of the main causes of refractory erosion in the lining of an electric furnace. In 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 to the material.
The iron oxide in the slag reacts with graphite or tar/resin in the hot side of the brick lining, or the oxygen attacks the graphite or binder on the cold side of the brick lining, in both cases the brick is weakened and may be eroded by the molten slag or molten steel.
Under the actual atmosphere conditions of an electric furnace, reaction (6) is particularly likely to occur starting from above 1700°C. The generated Mg vapor is easy to diffuse, resulting in structural degradation, which is one of the main factors causing high-temperature damage to MgC bricks.
Washing or mechanical shock
Physical damage is caused by molten steel or slag flowing over the refractory surface and physically wearing or scouring the lining. Erosion erosion is most common at the tap hole, slag line, electrode port or exhaust platform of the electric furnace.
Spalling is a complex refractory failure mechanism. It is caused by the rapid heating and cooling of the refractory lining, which causes stress in the refractory. This stress often exceeds the strength of the refractory, resulting in intersecting cracks, and fragments of the lining will peel off or fall off completely. This situation commonly occurs on the roof of electric furnaces.
Hydration
Hydration is also a factor in the damage of electric furnace refractory materials. During use, water can easily penetrate into the furnace cover or furnace wall, and water or water vapor can corrode the refractory lining. Magnesium oxide (or other alkaline oxides) reacts with water (or water vapor) as follows and becomes hydrated.
Reaction (7) will lead to a significant weakening of the refractory performance and poor resistance to penetration by slag and molten steel.
From the above analysis of the damage causes, it can be seen that the refractory materials selected for various parts of the steelmaking 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 Good resistance to rapid cooling and rapid heating, not easy to break and peel off;
⑤ High density, low porosity, uniform pore distribution, molten steel is not easy to penetrate;
⑥ High strength, can resist mechanical external force impact and erosion.
