Research On Interfacial Properties Of The Mold Flux For Casting Interstitial Free Steel

Interstitial free steel（IF steel）which has very few interstitial atoms are widely used in automotive industry because of its excellent performance such as superior ductility,plasticity,aging resistance,deep drawing properties and so on.For the production of IF steel,the steel melt is generally created through the Basic Oxygen Furnace-RH refining-Continuous Casting process,and the continuous casting is the core steps which transition molten steel into slabs.In the continuous casting process of IF steel,the interfacial behavior between the mold flux and the liquid steel would affect many metallurgical processes,such as inclusion absorption,entrapment and nozzle corrosion.The interfacial behavior is directly related to continuous casting production efficiency and slab quality.In this paper,therefore,the research is focused on the interfacial properties between mold flux and IF steel in continuous casting process.The effect of roughness of IF steel on slag-steel interfacial contact angle was studied by sessile drop apparatus in this paper.When the roughness of IF steel substrate increases from 3.555μm to 10.270μm,the contact angle of the mold flux on the steel substrate decreases from 64.1°to 59.6°at 1500℃.This result suggests that the wettability between mold flux and IF steel is improved with the increase of substrate roughness.The surface tension of mold flux with different contents of Na₂O and B₂O₃ was calculated to be 339.1～414.5 mN/m by Tanaka model.The influence of Na₂O and B₂O₃ in mold flux on the properties of slag-steel interface was further studied.With the content of Na₂O increases from 0to 9 wt.%,the contact angle of mold flux decreases from 71.2°to 58.4°,and the interfacial tension decreases from 1752.96 mN/m to 1683.50mN/m.The result of XPS analysis show that Na₂O destroys part of Si-O-Si structure,leading to a decrease of bridge oxygen in the melt and a depolymerization of melt structure.The interfacial layer between mold flux and steel substrate was studied by SEM&EDS.Its thickness was in the range of 3.88～6.04μm,and it would be thicker when the Na₂O content increases.With the content of B₂O₃ increases from 0 to 9 wt.%,the contact angle of mold flux decreases from 68.0°to 56.8°,and the interfacial tension decreases from 1734.55 mN/m to 1700.50 mN/m.The result of XPS analysis show that with the addition of B₂O₃,part of the three-dimensional[BO₄]^5-tetrahedral structural units in the melt is transformed into a two-dimensional[BO₃]^3-trihedral structural units,and the bridging oxygen transformed into non-bridging oxygen,which would simplify the melt structure.In addition,the thickness of slag-steel interfacial layer was in the range of 5.25～6.89μm,and it would be thicker when the B₂O₃ content increases.