Magnesia-carbon bricks are widely used due to their superior high temperature resistance, slag erosion resistance, and good thermal shock stability. The use of carbon materials is difficult to slag, the molten steel can be combined with the high refractory properties of magnesia, high slag resistance and solubility, and low temperature creep. Magnesia carbon bricks are used in severely corroded slag lines and tapping Mouth and other parts. Then, a large number of magnesia-carbon bricks were used in the steelmaking process and the steel smelting process was improved, which has created huge economic benefits.
1. Converter Lining
As the working conditions of each part of the converter lining are different, the use effect of magnesia carbon bricks is also different.
The furnace mouth part of the furnace lining is constantly impacted by cold and hot molten steel, so the refractory materials used in the furnace mouth must be resistant to the erosion of high temperature slag and high temperature exhaust gas, and it is not easy to hang steel and is easy to clean in time.
The furnace cap is not only subject to severe slag corrosion, but also subject to rapid cold and hot temperature changes, as well as the combined effects of high-temperature airflow due to carbon oxidation and dust and high-temperature exhaust gas. Therefore, the use of slag-resistant and peel-resistant Magnesia carbon brick. The loading side requires magnesia-carbon bricks to have high resistance to slag erosion, but also to have high high temperature strength and good peeling resistance.
Therefore, high-strength magnesia-carbon bricks with metal antioxidants are usually used. Research shows , The high temperature strength of the magnesia-carbon bricks with metal aluminum at lower temperature is lower than that of the samples with metal aluminum and metal silicon, but at high temperatures, its high temperature strength increases instead.
The slag line is the junction of the three phases of lining refractories, high-temperature slag and furnace gas. It is the most severely corroded part. Therefore, it is necessary to build magnesia carbon bricks with excellent slag corrosion resistance. The slag line needs to have a higher carbon content.
At present, the EAF walls are almost entirely built with magnesia carbon bricks. Therefore, the service life of magnesia carbon bricks determines the service life of EAF. The main factors that determine the quality of magnesia carbon bricks for EAF include the purity of MgO source magnesia, impurity types, and periclase grain bonding state and grain size; the purity, crystallinity and scale size of flake graphite as the source of carbon introduction; phenolic resin is usually used as the binder, and the main influencing factors are the addition amount and the amount of residual carbon. It has now been proved that the addition of antioxidants to magnesia carbon bricks can change and improve its matrix structure, but when used under normal operating conditions of EAF, antioxidants are not an essential raw material for magnesia carbon bricks, but only arcs used for high FeOn slag Furnace, such as using direct reduced iron or irregularly oxidized parts and hot spots of EAF, adding various metal antioxidants can become an important part of magnesia carbon bricks.
The corrosion behavior of the magnesia-carbon bricks used at the slag line is manifested by the formation of an obvious reaction dense layer and a decarburized loose layer. The intensive reaction zone also becomes the slag intrusion zone, which is the erosion zone where the high temperature liquid phase molten slag penetrates into the brick body after the decarburization of the magnesia carbon brick forms a large number of pores. In this area, FeOn in the slag is reduced to metallic iron, and even the desolvent phase and inter-granular Fe2O3 solid dissolved in MgO are 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 where graphite remains. Normally, due to the presence of graphite, the decarburized layer of magnesia carbon bricks is relatively thin.
There are two methods for the tapping of the electric furnace: tapping trough tilting tapping and bottom tapping. When the tapping trough is used for tilting steel, magnesia-carbon bricks are basically not used, but Al2O3 or ZrO2 are selected, and non-oxygens such as C, SiC and Si3N4 are added.
When the bottom of the furnace is used for tapping, the tapping port is composed of outer sleeve bricks and inner tube bricks. The tapping port of the furnace bottom adopts magnesia carbon brick pipe bricks, and the hole size of the pipe bricks is determined by factors such as furnace capacity, tapping time, etc. The general inner diameter is 140~260mm.
A steel mill’s electric furnace used medium- and low-speed magnesia-carbon bricks at the tapping port. The two sides of the copper tapping port replaced the original sintered magnesia bricks and achieved good results. The furnace age was increased from about 60 furnaces to more than doubled .
After used, the magnesia-carbon bricks at the slag line remain relatively complete and do not stick to slag. The slag line does not need to be repaired, which reduces labor intensity and improves the purity and productivity of molten steel.
3. Ladle Furnace
When MgO-C bricks are used for 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 resistance to mechanical corrosion caused by slag erosion.
So in the past, these parts used magnesia-chromium refractory materials, but considering that chromium pollutes the environment, its consumption 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 decarburized layer can reach 30-60mm thick. This layer is washed away during the injection of molten steel, bringing the magnesia grains into the slag.
Obviously, preventing the carbon in the magnesia carbon bricks from being burned out during preheating is one of the important steps to improve the service life of the magnesia carbon bricks at the ladle clearance and slag line.
Its technical measures, in addition to compounding the composite antioxidant into the magnesia carbon brick, the key is to cover the surface of the magnesia carbon brick with an alkali-containing low-melting glass phase liquid after lining, so as to protect the magnesia carbon brick. Carbon is not burned off during the preheating process of the ladle.