Optimization and research on refining slag of large tube billet

    The refining slag series of large tube blank is studied by methods of chemical analysis, lithofacies analysis, SEM and 

simulative calculation. The results show that the percentage of original slag higher than 1 440 ~C is 60 % of the total 

melting temperature. The high proportion of 2CaO·SiO2 and 3CaO·SiO2 in the slag leads to the viscosity of refine slag 

above 2 Pa·s. After the optimization and application of new slag series, the mass fraction of average total oxygen is 

reduced by 5×10^-6 ,the mass fraction of average nitrogen reduced by 15 × 10^-6 ,and the mass fraction of average

 sulfur reduced by 60%after VD refining in the steel. The mass fraction of lowest sulphur is controlled to 0. 003 %.