AOD procedure
The AOD process (from English argon oxygen decarburization ; German argon-oxygen decarburization ) is a converter fresh process for the production of stainless steel and other high-alloy steels .
The process was developed in 1954 by the US company Praxair . In 2007 around 130 AOD converters with capacities between 1 and 160 tons were in use worldwide.
process
The raw steel to be treated is usually obtained from scrap in an electric arc furnace and then filled into a so-called converter to carry out the AOD process. The process is similar to the Linz-Donawitz process , but differs from it in that no pure oxygen is inflated, but an argon- oxygen mixture is blown into the molten steel through nozzles in the converter wall. The proportion of oxygen in the mixed gas is continuously reduced during the approximately one hour blowing process - usually from approximately 80 percent to 20 percent. The feed takes place via nozzles in the floor and in the side walls of the converter.
The addition of argon as an inert gas reduces the partial pressure of the oxygen. This favors the oxidation of the carbon, while the undesirable slagging of alloy metals such as chromium and manganese is suppressed.
However, this slagging cannot be completely prevented.
In order to recover the oxidized metals, the slag is reduced after refining by adding lime and silicates . The melt is then desulfurized with quick lime .
For better mixing, the melt is blown with pure argon during the reduction and desulfurization.
Consumption values
At the end of the process, the carbon content in the steel is only around 0.015 percent. Around two percent chromium is lost. 25 cubic meters of oxygen and 20 cubic meters of argon are used per ton of steel. To reduce costs, argon is sometimes replaced with nitrogen or compressed air at the beginning of the process. Up to 7 tons of lime are used.
