For the steel industry, the application of refractory materials covers almost all steel production processes including coking, sintering, blast furnace ironmaking, converter steelmaking and continuous casting and rolling.
Refractory materials are widely used in steel smelting production
- Coke oven refractory materials used
Refractory material is the main component material of the coke oven body. The coke oven's carbonization chamber, combustion chamber, hot air furnace roof, ramp, heat storage chamber and small flue all need to use refractory materials as lining. The refractory materials used in coke ovens are mainly silica refractory bricks, which account for more than 60% of the total amount of refractory bricks. Currently, the age of a generation of coke ovens is generally about 25 years, and can be more than 30 years in the case of good operation and maintenance. This means that coke ovens are less likely to be shut down for medium and major repairs.
- Sintering system refractory use
The roof and sides of the sintering system generally use high alumina shaped refractory bricks, and individual parts use sprayed, moldable and cast refractory materials, while most of the rest are ordinary clay bricks. The refractories of the sintering system are generally used until they are scrapped, so steel mills generally do not overhaul the refractories of the sintering system.
- Refractory use in the blast furnace iron-making process
The blast furnace is divided into furnace throat, furnace body, furnace waist, furnace belly, furnace cylinder and furnace bottom from top to bottom (Figure 6).
The working temperature of the furnace throat is from 400℃ to 500℃, and it is subject to the impact and friction of the furnace charge. The furnace throat generally uses clay bricks with excellent performance or high density high alumina bricks as refractory materials.
The working temperature of the middle and upper part of the furnace body is between 400℃ and 800℃, which needs to bear the impact of the charge, the abrasion and thermal impact of the rising furnace dust and the intrusion of alkali, zinc and other substances; the lower part of the furnace body has a higher temperature and needs to bear the frictional effect of the falling scorched charge, the impact of the dust brought by the rising gas and the erosion effect of the alkali metal steam. The middle and upper part of the furnace body mainly uses low porosity clay bricks and high alumina bricks; the lower part of the furnace body generally uses slag-resistant, alkali-resistant, wear-resistant clay bricks, high alumina bricks, corundum bricks and silicon carbide bricks.
The working temperature of furnace waist is from 1400℃ to 1600℃, high temperature radiation erosion is serious, alkali erosion is serious, material and furnace dust scouring is serious, slag erosion is serious. This part mainly uses silicon nitride bricks and silicon carbide bricks as refractory materials.
Furnace belly working temperature of 1600 ℃ to 1650 ℃, by the heat radiation, slag erosion serious, alkali metal intrusion, melt flushing effect is serious. This part mostly uses silicon carbide bricks as refractory materials.
The bottom of the furnace cylinder is the highest temperature area in the blast furnace, working temperature in 1700 ℃ to 2000 ℃. Mainly by the slag iron water scouring, iron water intrusion and chemical erosion. The cylinder is mostly made of silica bricks, corundum castables and graphite fillers, silicon carbide refractory bricks; while the furnace bottom is mostly made of corundum bricks, corundum mullite bricks and synthetic mullite bricks as refractory lining.
The blast furnace generally only replaces the refractory lining in a large area when it is under repair or overhaul. The current blast furnace medium repair cycle is about 2 years, and the overhaul cycle is 6 to 10 years.
- The use of refractory materials in the steelmaking of the converter
The furnace lining of the converter consists of an insulation layer, a permanent layer and a working layer. Insulation layer is generally used asbestos board or refractory fiber masonry, permanent layer using tar dolomite bricks or low-grade magnesium brick masonry, work layer is currently using different levels of magnesium carbon brick integrated masonry. The so-called integrated masonry means that different refractory bricks are used for masonry in different working parts of the furnace body, which is to ensure that the entire furnace lining maintains a more uniform degree of erosion.
The ladle is used in conjunction with the converter, connecting the converter to the continuous casting process. The refractory lining of the ladle consists of an insulation layer, a permanent layer and a working layer (Figure 9). The insulation layer of the ladle is close to the ladle shell, playing the role of insulation and preventing the deformation of the ladle, and its material is generally refractory fiber board. The role of the permanent layer is to prevent the steel from seeping out when the refractory of the working layer is partially eroded. The permanent layer is made of clay bricks or high alumina bricks masonry and poured with aluminum casting material. The working layer refractory is in direct contact with the steel and is subjected to steel scouring and high temperature chemical erosion. The material and masonry level of the working layer refractory determine the service life of the ladle. The working layer is usually built with high alumina bricks or magnesium bricks, but can also be built with magnesium-aluminum castables as a whole.
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The medium maintenance cycle of converter equipment is 2 to 3 years and the major maintenance cycle is 5 to 8 years. Depending on the condition of the equipment, the plant will make the decision whether to replace the refractory material.
- Refractory use in continuous casting and rolling
In the continuous casting and rolling process, the amount of refractory used in the continuous casting process is much higher than that in the continuous rolling process. Continuous casting refractory materials are mainly used in the intermediate ladle and the various pipes connecting the ladle, intermediate ladle and crystallizer (these pipes are commonly known as the "three major pieces of continuous casting").
The structure of the refractory lining of the intermediate ladle is similar to that of the steel ladle, consisting mainly of a thermal insulation layer, a permanent layer and a working layer (Figure 10). The insulation layer is generally composed of insulating fibers or insulating bricks. The permanent layer is made of mullite or high alumina castings. The working layer is made of magnesia and magnesia-calcium dry vibrating material.
The "three main components of continuous casting" are the ladle long spout (connecting the ladle to the intermediate ladle), the intermediate ladle plug bar (controlling the flow rate of iron from the intermediate ladle to the crystallizer) and the intermediate ladle intrusion spout (connecting the intermediate ladle to the crystallizer) (Figure 11). The main material of the long water spout is aluminum carbon, and the slag line part is made of zirconium oxide. The material of the intermediate ladle rod plug is mainly corundum, aluminous carbon and silicon carbide. The main material of the intrusive spout of the interlayer is aluminum carbon, and in recent years the aluminum carbon - zirconium carbon composite spout and magnesium carbon - aluminum carbon - zirconium carbon composite spout have been developed on this basis.
Based on the above detailed analysis of the use of refractory materials in each process link, it is not difficult to find: coke ovens, blast furnaces and converters because of their own larger volume, the use of refractory materials is relatively high.