Argon oxygen decarburization: Difference between revisions

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[[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 [[aluminium]]. 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]].

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So, additions of lime are added to dilute sulfur in the metal bath. Also, aluminium 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.

== History ==

The AOD process has a significant place in the history of steelmaking, introducing a transformative method for refining stainless steel and shaping the industry's landscape.

=== 1960s ===

The development of AOD technology began in the 1960s as an alternative to traditional steelmaking methods. The process was initially introduced by European steelmakers who aimed to refine stainless steel more efficiently and economically.

=== Late 1960s ===

In the late 1960s, the AOD process gained recognition for its ability to remove carbon efficiently, achieving lower carbon levels than other refining methods. It also offered the advantage of being able to produce stainless steel with low carbon content, making it suitable for various applications.

=== 1970s ===

During the 1970s, the AOD process underwent further refinements and improvements. Steel companies in Europe and the United States increasingly adopted the AOD method in their operations, attracted by its flexibility and ability to produce high-quality stainless steel.

=== 1980s ===

In the 1980s, the AOD process became widely accepted as a standard refining method for stainless steel worldwide. Its advantages, such as high metallic yields, precise control over chemical composition, carbon control, desulfurization capabilities, and cleaner metal production, contributed to its popularity.

=== Present Day ===

Today, the AOD process remains a prominent method in the stainless steel industry. It offers steelmakers greater flexibility in raw material selection, enabling the use of cost-effective inputs and ensuring accurate and consistent results.The process has also contributed to increased production capacity with relatively small capital investments compared to conventional electric furnace methods.

== Additional Uses ==

In additional to its primary application in the production of stainless steel, many various additional uses have been found for AOD across different industries and materials.

=== Carbon Capture and Utilization ===

AOD slag has shown promising potential for usage as a carbon-capture construction material due to its high capacity for CO2 and its low cost. Carbonation curing, a process utilizing CO2 as a curing agent in concrete manufacturing, enhances the chemical properties of stainless steel slag by stabilizing it. During carbonation, g-C2S in the slag reacts with CO2 to produce compounds like calcite and silica gel, resulting in increased compressive strength and improved durability of cementitious materials. The incorporation of AOD slag as a replacement material in ordinary Portland cement (OPC) during carbonation curing has been studied, demonstrating positive effects on strength and reduced porosity.

=== Cementitious Activity and Modifiers ===

AOD slag exhibits cementitious activity, but its properties can be changed by modifiers. Studies have focused on the impact of modifiers, such as B2O3 and P2O5 on preventing the crystal transition of β-C2S and improving the cementitious activity of the slag. Addition of B2O3 and P2O5 has shown curing effects and increased compressive strength. These findings suggest that proper selection of modifiers can enhance the performance of stainless steel slag in cementitious applications.

=== Chromium Leachability and Carbonation ===

Another aspect of AOD slag research is its carbonation potential and its impact on chromium leachability. Carbonation of the dicalcium silicate in AOD slag leads to the formation of various compounds, including amorphous calcium carbonate, crystalline calcite, and silica gel. The carbonation ratio of the slag affects the mineral phases, which subsequently influence chromium leachability. Optimal carbonation ratios have been identified to minimize chromium leaching risks during carbonation-related production activities.

== References ==