Permeable bricks are mainly composed of sintered magnesia, magnesia, high alumina and corundum.
1. Sintered magnesia permeable brick
Sintered magnesia material refers to refractory material with MgO content above 80%. It belongs to alkaline refractory material. It has high refractoriness, strong resistance to alkali slag erosion, no corrosion from Ca and CaO, and no pollution to molten steel. However, its thermal expansion coefficient is large and its thermal shock resistance is poor, which makes the material easy to peel off, which greatly reduces the service life of the magnesium refractory.
2, magnesium chrome permeable brick
Magnesia-chromium material is a refractory material with MgO and Cr2O3 as main components, and periclase and tipped stone as main mineral components. The chrome ore is not inert to the steel slag and has compatibility with other refractories. Therefore, the appearance of the magnesia chrome material improves the thermal shock resistance of the magnesium material.
3, high aluminum permeable brick
High-aluminum material refers to refractory material with Al2O3 content greater than 48%. It has the characteristics of high thermal strength, good wear resistance, thermal shock resistance, anti-flaking and good volume stability at high temperature. However, its slag resistance and penetration performance are not good enough to resist the infiltration and penetration of slag into the brick during the entire service.
Which of the four commonly used steel ladle permeable bricks is the most suitable?
4, corundum permeable brick
Corundum material refers to refractory material with Al2O3 content greater than 90%. Corundum is made by sintering or electrofusion of industrial alumina or bauxite. When industrial alumina is used for electrofusion, white corundum is obtained. The content of Al2O3 is more than 98.5%; when using bauxite as raw material, ordinary corundum is obtained; when adding iron filings, brown corundum is formed; when adding bismuth or strontium oxide, corundum is obtained, and when adding Cr2O3, chrome is obtained. Corundum, fused plate corundum is directly made of industrial alumina as the main raw material. The plate-shaped corundum formed in the semi-molten state in the 1900-2000℃ electric arc furnace is beneficial to the ultra-high temperature in the formation area of the electro-melting plate-like corundum. The volatilization of volatile impurities such as Na2O is also a process of purifying and purifying itself. The platy alumina material is characterized by high thermal conductivity, good thermal stability, high temperature strength, strong corrosion resistance, and high cost of production.
Under high temperature and vacuum, the order of wetting angle of molten steel to several refractory oxides is as follows: Cr2O3>Al2O3>MgO, the stability of oxides is as follows: Al2O3>CaO>MgO>Cr2O3, considering the above two points, It is a good choice to use corundum as the main crystalline phase of the permeable brick. At the same time, the melting point of Cr2O3 is 2275℃, which is higher than the melting point of Al2O3 (2050℃). Alumina and chromium oxide can form a continuous solid solution, and the solid solution formed by AI2O3-Cr2O3 can significantly enhance the erosion resistance of iron oxide or slag. The addition of a small amount of Cr2O3 can inhibit the excessive growth of the alumina crystal, thereby reducing the internal stress of the crystal and improving the physical properties of the material. However, if Cr2O3 is added too much, the growth rate of corundum grains is seriously affected, thereby reducing the physical properties of the material. Therefore, the introduction of Cr2O3 in an appropriate amount can improve the thermal shock stability, erosion resistance and erosion resistance of the material. However, from the perspective of environmental protection, the introduction of Cr2O3 will cause environmental pollution, so the introduction of Cr2O3 should be carefully considered.
To realize the argon blowing process at the bottom of the ladle ventilated brick, the ladle permeable brick must have good resistance to high temperature, erosion, thermal shock resistance, high temperature volume stability and high strength, good gas permeability, stable operation, accurate dimensions and less penetration of molten steel specifications.