THE CAS-OB PROCESS IN THE STEELSHOP AT SSAB-TUNNPLAT-AB, LULEA-WORKS

Background: In 1992, the decision was taken to build a new secondary l adle station at the SSAB Tunnplat AB, Lulea Works. The CAS-OB process (Composition Adjustment by Sealed argon bubbling-Oxygen Blowing) was c hosen and the start-up was in August 1993. The CAS-OB plant consists o f 2 stations with alloying system, bulk and wire feeding, heating faci lity with oxygen and aluminium, bottom and lance stirring and a contro l room located between the 2 stations. Since the start-up, about 24,00 0 heats have been processed at the CAS-OB plant and the OB facility ha s been used for about 25% of these. The main groups of steel grades pr oduced at the plant are low carbon Al-killed steels, mild Al-killed st eels, HSLA steels and EHS steel. Results and conclusions: The benefits with the process are; high and predictable recoveries of the added al loying materials; low aluminium consumption; low content of total oxyg en after treatment; decrease in tapping temperature at the BOF; decrea se in number of aborted heats; reduced reblowings at the BOF; more sta ble casting speed caused by better accuracy to hit the arrival time an d temperature at the casters; one of the major costs for the CAS-OB pr ocess is the refractory for the bell; increase in life from 20 heats u p to more than 80 heats has been achieved during 1994. This has been a chieved due to: decrease of the time the bell is immersed in the steel ; new refractory material, spineli type; new design of the bell; new s ealing between upper and immersed part of the bell. By using the CAS-O B process, the total production cost has been reduced and the quality of our final products has been improved. With the CAS-OB plant, logist ics in the BOF-shop has been improved and also made production increas e possible. (C) Munksgaard, 1996