Relation Of Heat Extraction In Mold And Simulated Heat Flux Through Slag Film In Laboratory

Heat transfer property of mold slags has direct effect on slab surface qualitybecause of its prominent contributions to horizontal heat transfer in continuous castingmold. Currently, a method to test heat transfer property of mold slags has beenestablished by our research group. But the obtained heat flux in laboratory couldn’tpresent actual heat transfer in mold due to negligence of casting speed and steel grade,which are the main factors that influence the horizontal heat transfer in mold.Consequently, relationship of polynomial functions have been set up between heatextraction in mold and simulated heat flux in lab when the casting speed is variableaccording to heat flux data both in mold and laboratory, including slab （peritecticmiddle carbon steel and low carbon steel） and billet （bloom and small billet） continuouscasting. And the functions were confirmed with high accuracy.In addition, a series of mold slags with different composition were designed toanalysis the relation of physical properties （including basicity, melting point andviscosity） and heat transfer property. The results showed that:①Heat flux decreasedwith increasing melting point and viscosity. It is considered that viscosity is the keyfactor affecting the heat flux, and significant linear relationship between heatflux and the reciprocal of viscosity was found.②Melting points of mold slags withidentical basicity rapidly increased with viscosity increasing when η<0.12Pas, and thenremained stable. That’s because the type and content of fluxing agent changed.③Properties of mold slags could be altered according to the different effect of fluxingagent on melting point and viscosity. For instance, alkali oxides such as Li₂O and Na₂Ocan be used to adjust melting point and viscosity dramatically. Other components suchas MgO, MnO, Al₂O₃and F-are favorable to adjust viscosity while maintain presentmelting point.Mold slags with identical composition that designed by various raw materials havethe same viscosity, melting point and crystalline phase, but different heat transferperformance and microstructure of slag film. It is suggested that selection of basematerials should on the basis of steel grade. As for the crack sensitive steel, lower heatflux can be achieved by reducing the mixture ratio of prefused material with Na₂Owithout changing the composition of mold flux; On the contrary, heat flux can beincreased by increasing the amount of prefused material with Na₂O for the steel which is sensitive to sticking breakout.Mold slag of stainless steel continuous casting was optimized on heat transfercapability on the basis of relationship between simulated heat flux in lab and heatextraction in mold. Expected results as following were confirmed through plant trial:①more reasonable heat extraction ratio of wide side and narrow side in mold,②morestable horizontal heat transfer in mold,③slab surface depression （longitudinal andhorizontal） was well controlled.