Argon oxygen decarburization: Difference between revisions

Revision as of 19:06, 9 March 2022

Revision as of 10:51, 16 April 2023

Line 1:

{{Refimprove|date=November 2010}}

[[File:AOD (Argon, oxygen decarburisation) vessel.jpg|thumb|Refining of a 9.5%CrMoWVNbN steel in an argon, oxygen decarburisation (AOD) vessel]]

'''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]] and [[aluminumaluminium]]. 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 [[desulfurization]].

The AOD process was invented in 1954 by the Lindé Division of The [[Union Carbide Corporation]]<ref name=krivsky73>{{cite journal | doi = 10.1007/BF02667991| bibcode = 1973MT......4.1439K| title = The linde argon-oxygen process for stainless steel; A case study of major innovation in a basic industry| journal = Metallurgical Transactions| volume = 4| issue = 6| pages = 1439–1447| last1 = Krivsky| first1 = W. A.| year = 1973| s2cid = 135951136|url=https://link.springer.com/article/10.1007/BF02667991}}</ref><ref name=jalkanen14>{{cite journal |last1=Jalkanen |first1=Heikki |last2=Holappa |first2=Lauri |editor1-last=Seetharaman |editor1-first=Seshadri |title=Converter Steelmaking |journal=Treatise on Process Metallurgy: Industrial Processes |date=2014 |doi=10.1016/C2010-0-67121-5 |publisher=Elsevier|isbn=9780080969886 }}</ref> (which became known as [[Praxair]] in 1992).<ref name=uchist>[http://www.unioncarbide.com/History History]. Unioncarbide.com (1917-11-01). Retrieved on 2013-12-28.</ref>

Line 20:

=== Reduction ===

After a desired carbon and temperature level have been reached the process moves to reduction. Reduction recovers the oxidized elements such as chromium from the slag. To achieve this, alloy additions are made with elements that have a higher affinity for oxygen than chromium, using either a silicon alloy or aluminumaluminium. 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.

=== Desulfurization ===

Line 27:

:S_(bath) + CaO_(slag) → CaS_(slag) + O_(bath)

So, additions of lime are added to dilute sulfur in the metal bath. Also, aluminumaluminium or silicon may 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.

== References ==