About 70% of refractory products are used in the steel industry. When they are used up, they can become a valuable source of raw materials, so it is necessary to sort and recycle waste. Steel mills are always looking for and continue to find simple ways to rework and use used materials. The steelmaking process involves high-temperature operations. Refractory materials that operate at high temperatures are used in these devices. Tar-bonded dolomite bricks and magnesia carbon bricks are the most commonly used refractory materials. Asphalt and dolomite bricks are mainly used as facing materials in the steel industry. This is because compared with other basic refractory materials, it has unique characteristics, such as cheaper availability, thermodynamic stability, and stronger resistance to slag erosion. However, the use of these bricks in the steel industry has certain limitations. These bricks were eliminated and replaced by magnesia bricks and carbon bricks in seawater.
The following are some commonly used refractories in the steel industry.
Refractory materials for converters Magnesia-carbon bricks are used for furnace cover, converter mouth, front and rear surfaces, molten pool,, and bottom; high-strength magnesia-carbon bricks are used for trunnion and slag line. Generally, the content of MgO in magnesia-carbon bricks is 70 to 75%, graphite is 16 to 20%, the bulk density is 2.8 to 2.9 g/cm3, and the compressive strength is 25 to 30 MPa. The elements of high-strength magnesia-carbon bricks are the same as those of magnesia-carbon bricks, but their compressive strength should be 30-42 MPa.
Refractory furnace, furnace slope, and molten pool used in electric furnaces are all inlaid with magnesia or magnesia bricks made of magnesia briquettes and tar pitch; hot slag line area is made of high-quality magnesia carbon bricks; threaded holes and both sides of the furnace door are made of magnesium Brick and magnet chrome brick; furnace cover adopts high alumina brick or high alumina uncalcined brick.
The refractory material used for the lining of ultra-high power electric arc furnace or permanent ultra-high power electric arc furnace is made of magnesia; the oven door frame is made of magnesia chrome brick; the slag line, the bottom, and the molten pool are made of magnesia brick,using magnesia carbon brick for furnace cover, using high alumina brick; used to fill threaded holes, using filling material with high content of iron olivine.
Depending on the working conditions of various steel furnaces, the working conditions of refractory materials were found to be very difficult. Therefore, the refractory materials used must have the following characteristics:
High-temperature resistance and high fire resistance.
Wear resistance and wear resistance of heat-resistant steel and slag.
For the intermittent operation of the steelmaking furnace, the refractory material must have excellent thermal shock and fracture resistance.
It has high mechanical strength, can tilt the blows of the furnace, and withstand the load of the furnace without damage.
There are many operations and processes for secondary steelmaking, such as vacuum degassing and ladle refinancing. Refractory materials use a unique combination of various bricks to meet diverse requirements. The following can be observed:
The high temperature and long retention time of molten steel in the ladle.
Wide variation of slag composition iii) Various types of vacuum treatment. Thermal changes.
The stirring of molten steel causes erosion of molten steel movement.
In all ladle refining processes such as ladle furnaces, ASE-SKF and VAD processes, MgO-C bricks are used in areas where slag and steel are in contact. For general walls, high alumina bricks are widely used. The bottom zircon bricks are used to prevent molten steel from penetrating into the joints of the bricks. In some cases, MgO-C, Al2O3-C bricks and molds are used in the impact area. MgO-C bricks with added metal pairs have high thermal strength and excellent oxidation resistance.