Deep steel desulphurisation technology in ladle furnace at KSC

Abstract

At the Mizushima Works of Kawasaki Steel Corporation, a new deep desulphurisation technology to produce ultralow sulphur steels has been developed to replace the conventional process that comprised ladle furnace treatment followed by flux injection. In the new process, the use of a double plug gas injection system in the ladle furnace to promote desulphurisation, and optimisation of the ladle slag composition by thermodynamic calculations to maximise sulphide capacity, have enabled the flux injection stage to be omitted and shortened the desulphurisation time. As a result of these modifications, 35min after treatment start the sulphur content can be reduced to 5·3 ppm. On average, the time from tapping at converter until teeming start at caster has been reduced by 20·8min enabling production schedules to be synchronised and the maximum number of sequential casting heats to be increased from 3 to 10. There have also been economic benefits: the total steelmaking cost of ultralow sulphur steel has been reduced by 25·5%.