The significance of the circulation rate on the vacuum treatment of liquid steel with the RH process

Abstract

The RH Vacuum Process is in operation in more than 30 steel plants all over the world, especially for the vacuum treatment of liquid steel, ie vacuum metallurgy, steel refining as well as steel degassing. In the RH process the circulation rate is of great importance, since it exerts a controlling influence on degassing velocity, time of exposure of the liquid steel to vacuum (residence time), alloy addition rate as well as mixing of the steel in the ladle The dependence of circulation rate on the suction tube diameter and lift-gas rate was determined. The influence of the circulation rate on process variation, residence time and mixing in the ladle were also investigated. It can be concluded that suction velocities of 125 cm/sec are attained by lift-gas injection. Based on this lifting mechanism, a circulation rate of 45 t/min can be achieved with suction tube diameters of 330 mm. If ladle size and treatment time require it then the circulation rate can be increased without difficulty by enlarging the suction tube diameter. Such process conditions create residence times which will meet the requirements of the reaction variation and the dissolution of added alloys. In order to obtain short mixing times in the ladle, run-off velocities of more than 150 cm/sec were chosen, so that in a 100 ton ladle a homogeneous distribution of degassed steel or added alloys may be achieved in less than 2 minutes.