Nozzle clogging behaviour of Ti-bearing Al-killed ultra low carbon steel

In the present work, attempt has been made to investigate the influence of Ti on the castability of Al-killed ultra low carbon (ULC) steel, and to establish the possible reasons for the inferior castability of the Ti-bearing ULC steel vis-a-vis Ti-free grades. The work also attempted to identify suitable counter-measures for prevention of inclusion deposition in the submerged entry nozzles (SEN) during continuous casting of Ti-bearing Al-killed ULC steels. Characteristics of inclusions in the submerged entry nozzle deposit and corresponding liquid steel and slag samples from RH degasser and tundish were investigated. The presence of small quantity of Ti-bearing alumina inclusion was identified to be responsible for the extensive melt freezing inside the SEN deposit and poor castability of Ti-bearing Al-killed ULC steels. The influence of all materials contacting liquid steel subsequent to the RH degassing, on the reoxidation behaviour and castability of liquid steel, was assessed from their chemical composition. The present investigation indicated that while reoxidation is bad for the castability of all Al-killed steels, it becomes worse in the case of Ti-bearing Al-killed steels, primarily due to the formation of Ti-bearing inclusions that promote large-scale melt freezing inside the nozzle deposits.