Views: 20 Author: Site Editor Publish Time: 2022-08-24 Origin: Site
The AOD furnace method is the more advanced method in refining stainless steel. Because of its simple equipment, low investment, convenient operation, strong adaptability and low production cost, it will be widely used.
The AOD furnace reduces the partial pressure of carbon monoxide in the basic method of lean gas level. As the high pressure oxygen and hydrogen gas mixture is blown into the furnace, the air bubbles will come into contact with the molten steel and slag more frequently, which will allow the sulfur, carbon and non-metallic inclusions to be quickly removed.
During the blowing smelting process, the properties and composition of the slag will change during the smelting process. The basicity changes from about 0.6 to about 4.2 from the early stage to the later stage, and the refractory material will also be eroded from strong acid to strong alkalinity. erosion. Therefore, the AOD furnace uses refractory materials with high high temperature strength, good shock resistance, wear resistance and erosion resistance.
Commonly used refractory materials for AOD furnaces are: ordinary magnesia-chrome bricks, high-alumina plastics, magnesia castables, directly combined magnesia-chrome bricks, recombined magnesia-chrome bricks, semi-recombined magnesia-chrome bricks, high-purity directly combined magnesia-chrome bricks and Combined with magnesia chrome brick, asphalt combined with dolomite brick, dolomite brick, magnesia dolomite brick, ultra-high temperature fired dolomite brick, fused dolomite brick.
1. Magnesium-chromium series refractories
AOD furnaces use linings that directly combine MaO and Cr203, or use recombined or semi-combined MaO and Cr203 linings.
The magnesia-chrome brick is a direct-bonded magnesia-chrome brick made of high-quality high-purity magnesia and concentrate chrome ore calcined at high temperature. It has the advantage of good slag resistance, and it is much better to use than the magnesia-chrome brick produced by direct combination.
The semi-bonded magnesia-chrome brick has the comprehensive properties of direct bonding and re-bonding of the magnesia-chrome brick, and the infiltration of slag is the main reason for the deterioration and shedding of the brick structure. Therefore, in order to improve the quality of magnesia-chrome bricks, the following aspects should be considered during production:
(1) When making bricks, the particle gradation should be as reasonable as possible, and high-pressure forming technology and ultra-high temperature should be used to fire them.
(2) Strictly control the chemical composition ratio of magnesia-chrome bricks. It is reasonable to control the content of Cr203 with 18%-20% (mass fraction), because SiO2 can greatly affect the corrosion resistance of the material, its content should preferably be controlled below 1%, and the CaO content is also should be strictly controlled.
2. Magnesium calcium series refractories
Due to the diversification of raw materials and low price of magnesium-calcium series refractories, people have paid much attention. But the easy hydration of this material makes its application limited.
AOD furnace mainly uses fused unburned magnesia dolomite bricks and sintered magnesia dolomite bricks as furnace lining materials. Fused unburned magnesia dolomite is made by pressing fused magnesia dolomite sand under high pressure, and then placing it in a low temperature drying process. Pressed under high pressure, and then placed in an environment above 1600 ° C for firing. Because the fused magnesia dolomite sand has been fully smelted, it is very stable and the crystal lattice is very complete, which makes it have strong hydration resistance and corrosion resistance.
Magnesium-chromium-based refractories and magnesium-calcium-based refractories are the main refractories used in AOD furnaces. From the perspective of the service life of AOD furnaces using refractory linings of different materials, refractory materials of different materials have their own advantages and disadvantages. Comprehensive consideration, magnesium-calcium-based refractories have more advantages, and the application of magnesium-calcium-based refractories in AOD refining furnaces has become a development trend.
Compared with magnesium-chromium-based refractory materials, magnesium-calcium-based refractories have the following advantages:
1. The raw material resources are abundant, the price is low, and it does not contain chromium, so it will not increase the chromium inclusions in the molten steel. It is very important to control not only the chromium-free molten steel, but also the chromium content of the chromium-containing molten steel.
2. The main components MgO and CaO have high melting points (2800°C and 2570°C respectively), low vapor pressure and stable thermodynamic properties.
3. The combination of MgO-CaO has a larger dihedral angle than the combination of MgO-MgO, which is beneficial to improve the resistance to slag penetration and slag erosion. The thermal shock resistance of magnesium-calcium-based materials is better than that of magnesium-chromium-based materials.
4. Magnesium-calcium-based materials are highly resistant to redox reactivity, even in AOD furnaces and at high temperatures.
5. Magnesium-calcium-based materials exhibit obvious creep properties at temperatures as low as 1260°C. It shows that this kind of material is very resistant to spalling on the hot surface, so it can become a dense material with maximum corrosion resistance when used.
6. Magnesium-calcium refractories contain highly reactive f-CaO (free calcium oxide can repair the cracks of such materials and form a very dense and impermeable working surface, so it has high resistance to Corrosion ability.
7. The existence of f-CaO can purify molten steel, especially suitable for smelting pure steel.