Argon oxygen decarburization: Difference between revisions

Revision as of 09:39, 6 June 2010

Revision as of 13:59, 3 September 2010

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{{Unreferenced|date=March 2008}}

'''Argon oxygen decarburization''' ('''AOD''') is a process primarily used in [[stainless steel]] [[steel making|making]] and other high grade alloys with oxidizable elements such as [[chromium,]] aluminum,and etc[[aluminum]]. After initial melting the metal is then transferred to an AOD vessel where it will be subjected to three steps of refining; [[decarburization]], [[Reduction (chemistry)|reduction]], and [[desulphurization]]. AOD was invented in 1954 by [[Praxair]].

== Decarburization ==

Prior to the decarburization step Decarburization, one more step should be taken into consideration: i.e De''de-siliconization'', which is very important factor for refractory lining &and further processing.

Prior to the step Decarburization one more step should be taken into consideration i.e De-siliconization which is very important factor for refractory lining & further processing.

The decarburization step is controlled by ratios of oxygen to argon or nitrogen to remove the carbon from the metal bath. The ratios can be done in any number of phases to facilitate the reaction. The gases are usually blown through a top lance (oxygen only) and tuyeres in the sides/bottom (oxygen with an inert gas shroud). The stages of blowing remove carbon by the combination of oxygen and carbon forming CO gas.

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== Reduction ==

After a desired carbon and temperature level have been reached the process moves to reduction. Reduction recovers the oxidized elements such as Crchromium from the slag. To achieve this, alloy additions are made with elements that have a higher affinity for oxygen than Crchromium, using either a Silicon alloy or Aluminum. The reduction mix also includes lime (CaO) and fluorspar (CaF₂). The addition of lime and fluorspar help with driving the reduction of Cr₂O₃ and managing the slag, keeping the slag fluid and volume small.

After a desired carbon and temperature level have been reached the process moves to reduction. Reduction recovers the oxidized elements such as Cr from the slag. To achieve this, alloy additions are made with elements that have a higher affinity for oxygen than Cr, using either a Silicon alloy or Aluminum. The reduction mix also includes lime (CaO) and fluorspar (CaF₂). The addition of lime and fluorspar help with driving the reduction of Cr₂O₃ and managing the slag, keeping the slag fluid and volume small.

== Desulphurization ==

Desulphurization is achieved by having a high lime concentration in the slag and a low oxygen activity in the metal bath.

:<math>\mathrm{S _{(bath)} + CaO _{(slag)} \longrightarrow CaS_{(slag)} + O _{(bath)}}</math>

So, additions of lime are added to dilute sulfur in the metal bath. Also, aluminum or silicon maybemay be added to remove oxygen. Other trimming alloy additions might be added at the end of the step. After sulfur levels have been achieved the slag is removed from the AOD vessel and the metal bath is ready for tapping. The tapped bath is then either sent to a stir station for further chemistry trimming or to a caster for casting.

[[Category:Steelmaking]]