257 Ironmaking and Steelmaking 2010 VOL 37 NO 4 ' 2010 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute DOI 10.1179/030192310X12628786049396 Improving manufacturing of ULC steel grades by revamping of RH degasser in steelmaking shop No. 2 of ILVA, Taranto Works G. R. Demaglie 1 , P. Tangari 1 , S. Fera 2 and V. Colla* 3 1 ILVA, Riva Group, Taranto Works  Via Appia Km 648, 74100 Taranto, Italy 2 ILVA, Riva Group, Genoa Works  Via Pionieri e Aviatori dItalia 8, 16152 Genoa, Italy 3 Scuola Superiore SantAnna, Polo SantAnna Valdera, Viale R. Piaggio 34, 56025 Pontedera (Pisa), Italy *Corresponding author, email colla@sssup.it In recent years, as the demand for steels of high added value, such as the ultralow carbon (ULC) steels, the demands on the Ruhrstahl–Heraeus- oxygen blowing (RH-OB) process, have increased. In order to meet these strong demands, the RH-OB equipment at Taranto Works has been revamped, particularly by means of the enlarge- ment of the snorkel diameter. This has led not only to increase in the decarburisation rate due to the improvement of the metal recirculation, but also to an increase in productivity, improved process control and savings in electrical power and process gas consumption. Degassing is one of the ladle treat- ments currently used to manufacture special steel grades such as ultralow carbon (ULC). In this case, the degassing treatment is mainly required to decrease carbon content lower than 0·01%, but also to reduce the content of other undesired elements, such as nitrogen, hydrogen and oxygen. At Taranto Works, the degassing treatment is performed by means of the Ruhrstahl–Heraeus-oxygen blowing (RH-OB) process. In October 2004, the RH-OB unit was revamped and, among other improvements, the inner diameter of the snorkels was increased from 60 to 65 cm, with the aim of improving metal recirculation and hence decarburisation rate. 1–5 This paper, after some consider- ations on the basic concepts of vacuum treatment, will outline the benefits resulting from this modification in the manufacture of ULC grades. 6–8 Degassing treatment at Taranto Works The vacuum degassing plant consists of the following equipment (Fig. 1): • two vessels alternatively operated • one top lance with two coaxial ducts for oxygen blowing and powders injection • one off-gas cooler • vacuum system consisting of eight ejectors • condensation system consisting of five water condensers • condensation water and cooling water treatment facility • transportation device of the ladle to the vacuum treatment location • ladle lifting device • ferroalloys additions facility. 1 Cross-section of RH vessel and ladle during treatment The two vessels are operated alternatively by connection to the vacuum system by means of a suction pipe when the vessel is in the treat- ment position. During the process, the two snorkels are immersed to a specified depth and the vacuum system is connected to the operating vessel. Inert argon gas is blown throughout small pipes inserted inside the inlet snorkel which causes a decrease in density due to the mix liquid metal–gas with an increase in the liquid column inside the inlet snorkel of the RH vessel. 7,9 Only the steel which enters the vessel is exposed to the vacuum, which is mixed with the steel left in the ladle when exiting from the vessel; thus, several cycles of treatment are needed for achieving the desired carbon content which is very close to the equilibrium conditions. During treatment ferroalloys additions can be made under low pressure conditions in order to achieve the desired final steel composition. Basic concepts of the degassing process The ferrostatic pressure inside molten metal in static conditions at a given depth and under the effect of the atmospheric pressure can be expressed by the following formula p p gh Fe a Fe = + ◊ ◊ ( ) r (1) where p Fe is the ferrostatic pressure, p a is the atmospheric pressure, r Fe is the molten metal density, g is the gravity constant and h is the depth considered. If the pressure inside the snorkel immersed in the liquid metal p c is lower than atmospheric pressure p a , the liquid inside the snorkel will rise to a height h′ given by the following expression ¢= - ( ) ◊ ( ) h p p g a c Fe r (2) Under the conditions of absolute vacuum, the maximum height rise of the liquid melt would be 1·48 m, but as zero pressure is not practically achievable due to the vapour pressure of the liquid melt and to plant limitations, the maximum actual rise is around 1·42 m, achievable under a pressure of 10 mbar, which is the case of a vacuum system equipped with multistage vapour ejectors.