Argon Oxygen Decarburization (AOD) Treatment is the recognized standard for stainless steel refining worldwide. Whether you are producing castings, wrought . Argon-oxygen decarburization: stainless steel: In the argon-oxygen decarburization process, a mixture of oxygen and argon gas is injected into the liquid steel. Argon Oxygen Decarburization, frequently referred to as “AOD”, is an advanced technology for the refinement of iron, nickel, and cobalt based alloys. By.
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The next step is the reduction step, in which the reduction additions are charged and stirred with an inert gas for a desired time. The molten metal is then decarburized and refined in a special AOD vessel to less than 0.
At this point, the process gases can be decarburizatiob off and a small cooling flow protects the tuyeres.
When the vessel is rotated, the tuyeres are above the bath. Donate Grateful for your donation! Dolomitic refractories are usually less costly than decarburizagion chromite refractories and chromium pickup is not a factor. Designed by Elegant Themes Powered by WordPress. Unsourced material may be challenged and removed.
The burning of carbon increases the bath temperature. Such an approach is usually practiced by steelmakers to reduce argon usage and costs and still achieve a desired nitrogen specification. High wear areas of the converter, usually the tuyere wall, slag line, and transfer pad are zoned thicker and with higher quality refractory than other parts of the converter.
Typical internal volumes of AOD converters are in the range 0. AOD converter decarburization refractories Side blown stainless steel.
Additions of lime are made to dilute the sulphur in the liquid steel bath. Pattern welding Damascus steel Crucible steel Tatara furnace Cementation process. Would like to more details of how to increase vessel life and to reduce refractory wear near tuyers. The stages of blowing remove carbon by the combination of oxygen and carbon forming CO gas. Converters that tap into a ladle car usually have a BOF type concentric cone top section. Bessemer process Open hearth furnace Electric arc furnace Basic oxygen process.
Sulfur removal is a slag — metal reaction that occurs during the reduction phase of the process. Lime and dolomitic lime are sometimes added before the end of the blow to cool the bath and to reduce the volume of reduction additions. AOD provides an economical way to produce stainless steel with a minimal loss of precious elements.
Decarburization occurs when dissolved carbon reduces the chromium and iron oxides that form. Praxair can review your system and design an upgrade using:.
Process gases are injected through submerged tuyeres that are installed in the side wall or bottom of the converter. The amount of stirring energy from the gas blown through the subsurface tuyeres and the formation of the carbon monoxide deep within the metal bath results in the converter processes being among the most intensely stirred metallurgical reactors.
A major modification of the AOD process involves the use of top blowing lance in addition to the side blowing tuyeres. This argon dilution minimizes unwanted oxidation of precious elements contained in specialty steels, such as chromium.
The blow is continued to attain 0. To achieve this, alloy additions are made with elements that have a higher affinity decaarburization oxygen than chromium, using either decatburization silicon alloy or aluminum. The formation of a high basicity slag and the reduction of oxygen potential in the metal bath are good conditions for sulfur removal. Desulphurization to very low levels is generally easier in dolomitic refractories because very basic slags can be used without decarburiization effects on the bricks.
The liquid steel, which contains most of the chromium and nickel needed to meet the final heat composition, is tapped at a temperature of to deg C from the EAF or the IF into a transfer ladle. It is part of a duplex process in which scrap or virgin raw materials are first melted in an electric arc furnace EAF or induction furnace.
Tuyere size and number depend on specific process parameters. The oxyten accurately controls the flow rates and monitors the amount of gas injected into the bath to enable the operator to control the process and measure the total oxygen injected. These are achieved by having a high lime concentration in the slag and a low oxygen activity in the metal bath. During the oxygen blow, silicon is oxidized before carbon. The key feature in decarburiation AOD converter is that oxygen for decarburization is mixed with inert gas such as argon or nitrogen and injected through submerged tuyeres.
Argon-oxygen decarburization | metallurgy |
After sulfur levels have been achieved the slag is removed from the AOD vessel and the metal bath is ready for tapping. Modern instrumentation has been developed which can take melt samples as well as steel decarburizatin using a specially designed sub lance with the converter in the upright position. The process is so popular because it combines higher metallic yields with lower material costs.
Argon oxygen decarburization AOD is a process primarily used in stainless steel making and other high grade alloys with oxidizable elements such as chromium and aluminum. Praxair can quote a server-only option for these systems. The choice of refractory is dependent on the vessel operation pattern, final product specifications, and economics.
If necessary, additional raw materials may be charged for small chemistry adjustments before tapping. The process is very popular because it combines higher metallic yields with lower material costs.
Metal Refining with Argon Oxygen Decarburization (AOD) Refining Systems
The desire to increase the productivity has led to continuous charging of raw materials during the blow period as well as reduction period. There are usually two to four tuyeres in the bottom. This is due to the very low oxygen potential of the gas mixture, which minimizes chromium oxidation. Other trimming alloy additions might be added at the end of the step. For example, with a start sulphur of 0.
The top lance can also be designed for blowing mixed gases such as inert gas — oxygen mixtures. Oxidation of carbon continues, but oxidation of chromium is limited.
November Learn how and when to remove this template message. Since the blowing is done along with argon it is possible to carry out the decarburization at a lower temperature. Haynes International Case Study Video.