Investigation On Slag Entrapment In Slab Continuous Casting Mold

With the development of the special and high-quality steel,the requirement for the cleanliness of steel is getting higher.The slag entrapment of mold is the main source for the large particle inclusions in continuous casting slab.Large particle inclusions seriously affect the yield strength and tensile strength of steel,reducing the plasticity,toughness and fatigue life.It has significant effect on the strength,extensibility,cutting and welding performance for continuous casting slab.Therefore,it is of theoretical and practical significance to study the slag entrapment behavior and reduce the large particle inclusions.Based on the production practice of 1#continuous caster in Guofeng No.1 steelmaking plant,the slag entrapment in continuous casting mold is systematically studied.Firstly,the crack defects of rolled products are analyzed by Scanning electron microscope and energy spectrum,and the inclusions caused by slag entrapment are found.Then,the influences of the pulling velocity and the depth of the submerged entry nozzle on the flow field and temperature field in the mold are investigated by numerical simulation,and the optimum process parameters are worked out and applied in the field.Meanwhile,the significant conclusions are as follows:(1)The K and Na elements are found in the inclusions of rolled products analyzed by Scanning electron microscope and energy spectrum,which indicate that the presence of slag entrapment in mold.Therefore,in order to prevent the behavior of slag entrapment,it is necessary to optimize the flow field and control the level fluctuation in mold.(2)With the increase of pulling velocity,the average temperature of the free surface increases.Although it is beneficial to the melting of slag,and the surface of the molten pool becomes unstable,which causes the slag entrapment and molten steel to be exposed,resulting in the increase of inclusions in the steel and the reduction of the billet quality.In addition,the increase of pulling velocity will make the high temperature zone move down and increases the probability of accidents such as breakout and bulging.(3)As the depth of the submerged entry nozzle increases,the impact depth of the flow field increases,which is not conducive to the flotation of inclusions and bubbles.The depth of the submerged entry nozzle is too deep,which will make the turbulent kinetic energy of the molten steel in the meniscus are too small,and the free surface is not active,and it is not conducive to the slag melting.The depth of the submerged entry nozzle is too shallow,the turbulent kinetic energy of the molten steel is too large,and it is easily cause the slag entrapment and the molten steel exposure.(4)The numerical simulation results show that the optimum pulling velocity is 1.3?1.4 m·min-1 when the cross section of slab is 1280 mm× 180mm,and optimum depth of the submerged entry nozzle is 155?165 mm.When the cross section of slab is 1030 mm×180 mm,the optimum pulling speed and the depth of the submerged entry nozzle are 1.3?1.4 m·min-1 and 140?160 mm respectively.The above optimized process parameters can control the thickness of liquid slag layer and level fluctuation,and have good effect on inhibiting slag entrapment.