AOD refining method is the abbreviation of Argon Oxygen Decarburization (Argon Oxygen Decarburization), in refining stainless steel, by reducing the partial pressure of CO, to achieve the effect of false vacuum, so as to make the carbon content down to a very low level, and inhibit the oxidation of chromium in the steel.
The principle of AOD oxygen blowing decarburization is that the oxygen blown into the furnace enters the molten steel and reacts with the carbon and chromium in the molten steel, the chromium in the molten steel reacts with the oxygen to generate chromium oxide into 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 then returns to the molten steel, in which the carbon-chromium equilibrium is a function of the temperature and the CO partial pressure. According to the relative position of the carbon-chromium oxidation reaction Gibbs energy curve on the iron-carbon phase diagram to achieve the reduction of carbon and chromium protection, it is necessary to make the carbon superior to constitute a selective oxidation relationship. By continuously blowing nitrogen and argon into the molten steel to reduce the CO partial pressure, so that the above reaction to the direction of the generation of CO, will be reduced to chromium in the slag dissolved in the molten steel, so as to achieve the purpose of carbon reduction and chromium protection.
VOD refining method is Vacuum Oxygen Decarburization (Vacuum Oxygen Decarburization) for short. It is a kind of off-furnace refining technology to produce high-chromium stainless steel by blowing oxygen decarburization and argon stirring under vacuum conditions, top blowing oxygen decarburization under vacuum conditions and argon blowing at the bottom of the ladle to promote the circulation of the liquid steel, which can easily reduce the carbon in the steel to the range of 0.02% to 0.08% without oxidizing the chromium when smelting the stainless steel. And the liquid steel vacuum treatment, coupled with the stirring effect of argon, the reaction of the kinetic conditions are very favorable, can obtain a good removal of harmful gases, there is the effect of removing inclusions.
VOD type ladle refining furnace is under vacuum blowing oxygen, decarburization, vacuum degassing, vacuum alloy composition fine-tuning, mainly used for refining ultra-low-carbon stainless steel and electrical pure iron and so on. The main form: VOD type ladle refining furnace can be used in a separate station, can also be used in a double station, the vacuum tank for the elevated or pit type, can also be used in car-carrying type, the vacuum tank cover of the move usually take the car-carrying move open type.
AOD refining process is AOD receives stainless steel pre-melt from the electric furnace, decarbonization and then enter the reduction stage, using ferrosilicon to reduce chromium, manganese and iron in the slag; add lime, calcium fluoride (CaF2) slag desulfurization. In the reduction process to adjust the composition and temperature of the steel. After reduction can be directly out of steel. For some special steel grades, samples can be taken after reduction. If necessary, the final composition and temperature can be adjusted in LF/LATS, and then the qualified steel can be sent to the rotary table of continuous casting machine. For ultra-low carbon and nitrogen steel grades, AOD is used as an intermediate treatment link to remove carbon to a certain extent and then sent to VOD for final treatment.
VOD refining process is traveling ladle containing liquid steel lifted into the VOD furnace vacuum tank, manually connected to the argon blowing pipe, while the temperature measurement and sampling. After that, the vacuum tank cover truck drives from the parking station to the VOD station and lowers the tank cover. Next, vacuum treatment, oxygen blowing decarburization, alloy fine-tuning, blowing argon mixing, to be processed after the end of the main valve to close the vacuum → broken empty → lifting the tank cover → vacuum tank cover car to the parking station → temperature measurement and sampling → to stop blowing argon → add insulation → ladle lifting to the casting station.
VOD type vacuum refining process has many advantages such as simple equipment, less investment, low cost, and it can be applied to various steel types.
AOD refining method and VOD refining method have their own advantages in the field of application.
