The use of magnesia carbon bricks on EAF



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, EAF magnesia carbon brick 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 EAF 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.