This article describes the use of magnesia carbon bricks in converters, electric furnaces and ladles.
Key words: magnesia carbon brick; converter lining; electric furnace; ladle
Magnesia carbon bricks are very suitable for the requirements of iron and steel smelting due to their superior high temperature resistance, slag erosion resistance, and good thermal shock stability. Taking advantage of the properties of carbon materials that are difficult to be wetted by slag and molten steel, and magnesia has high refractory properties, high slag resistance and solvent resistance, and low high temperature creep, magnesia carbon bricks are used in severely corroded slag lines and outlets. Steel mouth and other parts. So far, due to the extensive use of magnesia carbon bricks in the steelmaking process and the improvement of the steel smelting process, huge economic benefits have been created.
The use of magnesia carbon bricks on the converter lining
Since the working conditions of each part of the working lining of the converter are different, the effect of using magnesia carbon bricks is also different. The mouth of the furnace lining is constantly impacted by molten steel in cold and hot states, so the refractory materials used for the furnace mouth must be resistant to high-temperature slag and high-temperature exhaust gas, and it is not easy to hang steel and easy to clean in time. The furnace cap is not only subject to severe slag erosion, but also undergoes rapid cooling and rapid heating temperature changes, as well as the comprehensive action of high-temperature airflow due to carbon oxidation and high-temperature dust exhaust gas. Magnesia carbon brick. The charging side requires magnesia-carbon bricks to have high resistance to slag erosion, high temperature strength and good spalling resistance, so high-strength magnesia-carbon bricks with metal antioxidants are usually used. Studies have shown , the high-temperature strength of magnesia-carbon bricks added with metal aluminum at lower temperatures is lower than that of samples with composite metal aluminum and metal silicon added, but at high temperatures, its high-temperature strength increases instead. The slag line is the three-phase junction of the furnace lining refractory material, high-temperature slag and furnace gas, and is the most severely slag-corroded part. Therefore, it is necessary to build magnesia-carbon bricks with excellent slag erosion resistance, and the slag line needs to have a higher carbon content. magnesia carbon bricks.
The use of magnesia carbon bricks on electric furnaces
At present, almost all the furnace walls of electric furnaces are built with magnesia-carbon bricks, so the service life of magnesia-carbon bricks determines the service life of electric furnaces. The main factors that determine the quality of magnesia-carbon bricks for electric furnaces include the purity of magnesia of MgO source, the type of impurities, and periclase. Grain bonding state and grain size; the purity, degree of crystallization and scale size of flaky graphite used as a source of carbon introduction; thermosetting phenolic resin is usually used as a binder, and the main influencing factors are the amount added and the amount of residual carbon. Now it has been proved that adding antioxidants to magnesia carbon bricks can change and improve its matrix structure, but when used under normal operating conditions of electric furnaces, antioxidants are not a necessary raw material for magnesia carbon bricks, but only for arcs with high FeOn slag Furnace, such as the use of direct reduced iron or irregularly oxidized parts and hot spots of electric furnaces, adding various metal antioxidants can become an important part of magnesia carbon bricks. The corrosion behavior of magnesia-carbon bricks used in the slag line shows the formation of obvious reaction dense layer and decarburized loose layer. The reaction compact zone also becomes the slag erosion zone, which is the erosion area where the high temperature liquid phase slag penetrates into the interior of the brick body after the decarburization of the magnesia carbon brick forms a large number of pores. In this region, FeOn in the slag is reduced to metallic iron, and even the presolvated phase and intergranular Fe2O3 dissolved in MgO are also reduced to metallic iron. The depth of slag penetration into the brick is mainly determined by the thickness of the decarburized loose layer, which usually ends at the place where the graphite remains. Under normal circumstances, the decarburization layer in magnesia carbon bricks is relatively thin due to the presence of graphite. The tapping port of the electric furnace has two methods: the tapping of the tapping chute and the tapping of the bottom of the furnace. When using the tapping groove to tilt the steel, the magnesia carbon brick is basically not used, but the Al2O3 or ZrO2 quality is selected, and non-oxygen substances such as C, SiC and Si3N4 are added. When tapping from the bottom of the furnace is adopted, the tapping hole is composed of outer sleeve bricks and inner pipe bricks. The tapping hole at the bottom of the furnace adopts magnesia-carbon brick pipe bricks, and the aperture size of the pipe bricks is determined according to factors such as furnace capacity and tapping time. Generally, the internal diameter is 140-260mm. The electric furnace of a steel factory used medium and low-grade magnesia-carbon bricks in the steel outlet, and the two sides of the copper outlet replaced the original sintered magnesia bricks and achieved good results. The furnace life was increased from about 60 furnaces to more than doubled. . After use, the magnesia carbon brick at the slag line remains relatively intact and does not stick to slag. There is no need to repair the furnace at the slag line, which not only reduces labor intensity but also improves the purity and productivity of molten steel.
The use of aluminum-magnesia-carbon bricks on ladles
When MgO-C bricks are used in refining ladle furnaces and ladles, they are mainly used in headroom and slag lines. According to the operating conditions, the refractory materials used in these parts must have high temperature resistance, thermal shock resistance, and mechanical corrosion resistance caused by slag erosion. Therefore, in the past, these parts used to use magnesia-chromium refractory materials, but considering the pollution of chromium to the environment, its dosage has been reduced, and now magnesia-carbon bricks are used.
Since the magnesia-carbon bricks in the new ladle will be severely damaged during the preheating process, the loose and decarburized layer can reach a thickness of 3060mm. This layer is washed away during the injection of molten steel and brings the magnesia grains into the slag. Obviously, preventing the carbon in the magnesia carbon brick from being burned during preheating becomes one of the important steps to improve the service life of the magnesia carbon brick at the ladle clearance and slag line. Its technical measures, in addition to adding composite antioxidants to the magnesia-carbon bricks, the key is to cover the surface of the magnesia-carbon bricks with an alkali-containing low-melting glass phase liquid after lining to protect the magnesia-carbon bricks. Carbon is not burned off during the preheating of the ladle.