AOD refining is the abbreviation of argon oxygen decarburization. When refining stainless steel, the CO partial pressure is reduced to achieve a false vacuum effect, thereby reducing the carbon content to a very low level and inhibiting the oxidation of chromium in the steel.
Working principle of AOD refining method:
The principle of AOD oxygen decarburization is that after the oxygen blown into the furnace enters the molten steel, it reacts with the carbon and chromium in the molten steel. The chromium in the molten steel reacts with oxygen to generate chromium oxide and enters the slag layer. In addition, the carbon in the molten steel reacts with the chromium oxide in the slag to reduce the Cr2O3 in the slag to chromium and return to the molten steel. Among them, the carbon-chromium balance is a function of temperature and CO partial pressure. According to the relative position relationship of the Gibbs energy curve of the carbon-chromium oxidation reaction on the iron-carbon phase diagram, to reduce carbon and preserve chromium, the carbon must form a selective oxidation relationship. By continuously blowing nitrogen and argon into the molten steel to reduce the CO partial pressure, the above reaction is carried out in the direction of generating CO, and the chromium in the slag is reduced to dissolve into the molten steel, thereby achieving the purpose of reducing carbon and preserving chromium.
AOD equipment is mainly composed of a furnace body, support ring, tilting mechanism, gas mixing and blowing system, and temperature measurement and sampling system. The furnace body includes the furnace body and furnace cap. The lower side of the furnace body is inclined at an angle of about 20° to the center line of the furnace body, which helps the blown gas to rise to the furnace mouth along the side wall and reduces the serious erosion of the gas on the upper area of the air gun. To improve the operator’s observation of the furnace and simplify the furnace roof masonry process, the furnace cap is generally symmetrical.
AOD
There are two main types of refractory materials used in AOD furnaces, one is magnesia-chrome refractory material and the other is dolomite refractory material. At present, there is a trend towards dolomite refractory materials.
1. Dolomite bricks or magnesia-alumina-carbon bricks are mostly used for the steel outlet.
2. The furnace body and furnace bottom are made of fired dolomite bricks or resin-bonded dolomite bricks.
3. The upper part is made of fired dolomite bricks or resin-bonded dolomite bricks.
4. The slag line is mainly made of fired magnesia dolomite bricks.
5. The tuyere is made of zirconium-containing fired magnesia dolomite bricks.
6. The bulk material is mainly dolomite ramming material or cement-combined magnesia ramming material.