Deoxidation Control in Continuously Cast Steel Slabs for ERW Pipe Use

Abstract

Deoxidation control to minimize the amount of large inclusions in continuously cast steel slabs for ERW pipe use has been investigated in commercial heats.
The results obtained are summarized as follows:
1) Care must be taken to deoxidize molten steel with Al at tapping, followed by stirring of molten steel by RH degasser within 20 min, and to control Al content in molten steel in tundish less than 0.005%.
2) The box type alumina graphite immersion nozzle is observed to be superior in refractory erosion with molten steel and in penetration depth of inclusion into crater to the inverse Y type fused silica nozzle.
3) Investigations on the formation of large inclusions which cause the defect of ERW pipe, reveal that entrapment of slag and/or flux into steel and enlargement in size by the reaction between FeO, MnO, SiO₂ in trapped particles and Al, increase progressively with Al content in molten steel.