This article describes the use of magnesia carbon bricks in converters, electric furnaces and ladles.
Magnesia-carbon bricks are very suitable for the requirements of iron and steel smelting due to their excellent high temperature resistance, slag corrosion 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, high refractory properties of magnesia, high slag resistance and solubility resistance, and small creep at high temperature, magnesia-carbon bricks are used in slag lines and outflows with severe corrosion damage. Steel mouth and other parts. So far, huge economic benefits have been created due to the extensive use of magnesia-carbon bricks in the steelmaking process and the improvement of the iron and steel smelting process.
Application of magnesia-carbon bricks on converter lining
Since the use conditions of each part of the converter working lining are different, the use effect of magnesia-carbon bricks is also different.
The furnace lining furnace mouth is continuously impacted by cold and hot molten steel, so the refractory material used for the furnace mouth must be resistant to the erosion of high-temperature slag and high-temperature exhaust gas, and is not easy to hang steel and easy to clean in time. The furnace cap is not only subject to severe slag corrosion, but also to the rapid cooling and rapid heating temperature changes, as well as the combined effect of the high-temperature airflow due to carbon oxidation and the scouring of dust and high-temperature exhaust gas. Magnesia carbon brick.
The charging side requires magnesia-carbon bricks not only to have high slag corrosion resistance, but also to have high high temperature strength and very good anti-stripping performance. Therefore, high-strength magnesia-carbon bricks with metal antioxidants are usually used. Research shows that , the high temperature strength of magnesia-carbon bricks added with metal aluminum at lower temperature is lower than that of the samples with composite addition of metal aluminum and metal silicon, but at high temperature, the high temperature strength increases instead. The slag line is the three-phase junction of the furnace lining refractory material, the high-temperature molten slag and the furnace gas, and it is the most serious part of the slag corrosion. Therefore, it is necessary to build magnesia-carbon bricks with excellent slag corrosion resistance, and the slag line needs to have a higher carbon content. magnesia carbon bricks.
Magnesia-carbon bricks uses in electric furnaces
At present, the furnace walls of electric furnaces are almost all built with magnesia-carbon bricks, so the 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 magnesia purity of MgO source, types of impurities, periclase Grain bonding state and grain size; purity, degree of crystallization and flake size of flake graphite as a source of carbon introduction; thermosetting phenolic resin is usually used as a binder, and the main influencing factors are the amount of addition and residual carbon. It has now 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. Furnaces, such as the use of direct reduced iron or parts with irregular oxidation and hot spots of electric furnaces, can become an important part of magnesia-carbon bricks by adding various metal antioxidants.
The corrosion behavior of magnesia-carbon bricks used in the slag line is characterized by the formation of an obvious reactive dense layer and a decarburized loose layer. The reaction dense zone also becomes the slag intrusion zone, which is the erosion area where the high temperature liquid slag infiltrates the inside of the brick body after the magnesia-carbon brick is decarburized to form a large number of pores. In this region, FeOn in the slag is reduced to metallic iron, and even the desolubilized 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 residual graphite is present. Under normal circumstances, the decarburized layer of magnesia-carbon bricks is relatively thin due to the presence of graphite.
There are two ways of tapping in the electric furnace: tilting tapping and bottom tapping. When the tapping groove is used for tilting, the magnesia-carbon brick is basically not used, but Al2O3 or ZrO2 is selected, and non-oxygen substances such as C, SiC and Si3N4 are added. When bottom tapping is used, the tapping hole is composed of outer sleeve bricks and inner tube bricks. The tapping port at the bottom of the furnace adopts magnesia carbon brick tube bricks, and the diameter of the tube bricks is determined according to factors such as furnace capacity and tapping time. Generally, the inner diameter is 140~260mm.
The electric furnace of a steel plant uses medium- and low-block magnesia-carbon bricks in the tap hole, and the two sides of the copper tap instead of the original sintered magnesia bricks have initially achieved good results, and the furnace age has been 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. The slag line part does not need to make up the furnace, which not only reduces the labor intensity but also improves the purity and productivity of the molten steel.
Aluminum magnesia carbon bricks uses on ladle
When MgO-C bricks are used for refining ladle furnaces and ladles, they are mainly used in clearance 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. Therefore, magnesia-chromium refractories were used in these parts in the past, but considering the pollution of chromium to the environment, the amount of chromium has been reduced, and now magnesia-carbon bricks are used.
Since the magnesia-carbon bricks in the new ladle will be seriously damaged during the preheating process, the loose decarburized layer can reach a thickness of 30~60mm. This layer of belt is washed away during the injection of molten steel, bringing the magnesia grains into the slag. Obviously, preventing the carbon in the magnesia-carbon brick from being burned during preheating has become 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 magnesia-carbon bricks, the key is that the surface of magnesia-carbon bricks should be covered with alkali-containing low-melting glass phase liquid after lining to protect magnesia-carbon bricks. Carbon is not burned during the preheating of the ladle.