O were respectively used as modifying agent adding to ladle slag to decrease slag adhesion of LATS-OB refining immersion cover and increase service life of cover. Test results of melting point of slag measured by hemisphere method showed that using
CaO:CaF
2
=1~2
CaO:B
2
O
3
=1~2 or Li
2
O as modifying agent could remarkably decrease melting point of ladle slag. And metal-slag equilibrium test indicated that the sulphur content in steel further decreased by ladle slag added modifying agent.