Argon Oxygen Decarburization Process Apr28

Argon Oxygen Decarburization Process...

Argon Oxygen Decarburization Process Argon oxygen decarburization (AOD) is a process primarily used in production of stainless steel and other high grade alloys such as silicon steels, tool steels, nickel-base alloys and cobalt-base alloys with oxidizable elements such as chromium and aluminum. AOD was invented in 1954 by the Lindé division of The Union Carbide Corporation, which became Praxair in 1992. An AOD converter is shown in Fig 1. Fig 1 AOD converter Today, over 75 % of the world’s stainless steel is made using the AOD process. The process is very popular because it combines higher metallic yields with lower material costs. It provides an economical way to produce stainless steel with a minimum loss of precious elements. 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 (IF). The molten metal is then decarburized and refined in an AOD converter to less than 0.05 % carbon. The key feature in the AOD converter is that oxygen for decarburization is mixed with inert gas such as argon or nitrogen and injected through submerged tuyeres. This argon dilution of oxygen minimizes unwanted oxidation of precious elements contained in specialty steels, such as chromium. Other benefits of AOD process include pinpoint accuracy in chemistry control down to 0.01 % carbon and lower, rapid desulfurization to less than 0.001 %, and lead removal to less than 0.001 %. The end result is a cleaner metal coupled with increased productivity. AOD process uses dilution technique for the decarburization of steel bath. The injection of inert gas (argon or nitrogen) lowers the partial pressure of CO in the bath, thus allowing  higher chromium content to be in equilibrium with lower carbon contents. The amount...

Stainless steels

                         Stainless steels  Stainless steel is a family of alloys of iron that contains at least 10.5% Chromium and a maximum of 1.2 % carbon which is essential of ensuring formation of a self healing surface passive layer. This passive layer provides the corrosion resistance. These characteristics make stainless steels totally different from mild steels. The stainless steel was discovered between 1900 and 1915. In 1904, Leon Guillet discovered alloys with composition similar to steel grades 410, 420, 442, 446 and 440-C. In 1906 he also discovered an iron-nickel-chromium alloy which was similar to the 300 series of stainless steel. In 1909 Giesen researched on the chromium-nickel (austenitic 300 series) stainless steels. In Germany, in 1908, Monnartz & Borchers found that a relationship exists between a minimum level of chromium (10.5%) on corrosion resistance as well as the importance of low carbon content and the role of molybdenum in increasing corrosion resistance to chlorides.  Stainless steel production process Stainless steel is produced in an electric arc furnace where carbon electrodes contact recycled stainless scrap and various alloys of chromium, nickel and molybdenum etc. depending on the type of stainless steel. A current is passed through the electrode and the temperature increases to a point where the scrap and alloys melt. The liquid steel can also be produced in LD converter using hot metal as a major input material. The liquid steel from the electric arc furnace or LD converter is then transferred into an AOD (Argon Oxygen Decarbonization) converter, where the carbon levels are reduced and the final alloy additions are carried out to achieve the desired chemistry.  The liquid steel is either cast into ingots or continually cast into slabs or billets. The slabs or billets are either hot rolled or forged into...