With the increase of steel production, the method of increasing ring flow and blowing a large amount of gas is being vigorously promoted for the stable production and high-speed treatment of ultra-low carbon steel. Increasing the ring flow will increase the wear of refractory lining, increase the amount of cold air blowing, resulting in high-temperature spalling, increase the amount of ladle slag suction, and increase the structural spalling and erosion. All these factors will accelerate the damage of lining refractory. Therefore, the current Rh / RH-OB lining is dominated by directly bonded magnesia chrome bricks, while semi recombined or recombined MgO-Cr þ o ₃ bricks are used around the OB port (oxygen blowing port) of RH-OB, and some MgO C bricks are used.
How to choose refractory for RH vacuum degassing device?
The refractory used for the top and upper tank lining of RH device is generally less damaged than the lower part because it does not directly contact with molten steel and slag.
The refractory lining of the middle groove is damaged due to contact with molten steel and slag, or peeling off at high temperature.
The refractory lining of the lower tank including the impregnation pipe is the high corrosion area of the device, which often determines its service life. In the lower groove lining, due to the infiltration of molten slag, a metamorphic layer is formed in the brick, which leads to the cracking parallel to the working face between the metamorphic layer and the non metamorphic layer, resulting in peeling and leading damage. At the same time, because of the infiltrated slag, the particle combination of the lining material is cut off, so the particles become easy to lose. Therefore, refractory materials with less tissue deterioration and difficult penetration of slag should be selected for this part, which can maintain the combination between particles and high spalling resistance even if infiltrated.
The reasons for the damage of the immersion tube due to the molten steel erosion and temperature change caused by gas injection are as follows:
- Damage around the air nozzle caused by gas injection;
- Layered debris from the end of the impregnation tube;
- Cracking of cast refractory.
Because the air nozzle is greatly affected by the erosion of molten steel, the directly bonded Mg0 Cr þ o ₃ brick with high high temperature strength fired at ultra-high temperature has the best use effect when used in this part.
In RH furnace, molten steel treatment generally goes through the process of degassing and gas injection, and the refractory is greatly worn in the injection state.
The most serious part of the lower part of the furnace body is the circulating pipe. The reason is that the lining structure limits its thickness, and the refractory products with complex shapes have to be heated twice, so no refractory material has a long enough service life.
In addition, in RH-OB furnace, OB also has an important impact on the use of refractories. When the upper spray gun method is adopted, the refractories are damaged by oxygen blown in, oxides generated by iron and other elements in molten steel (which will quickly erode the working face of refractories) and high-temperature reaction gas. Therefore, MgO-Cr2O3 brick with high Cr2O3 content will have a high service life. MgO-Cr2O3 bricks with low Cr2O3 content will have better comprehensive service performance in the parts exposed to high-temperature gas.