Analysis And Control Of Submerged Nozzle Clogging In Continuous Casting Of 25MnB Steel

In the process of continuous casting,nozzle clogging is closely related to slab quality and production cost.Therefore,it is a key issue to restrain or avoid nozzle clogging.In this paper,aiming at the problem of casting interruption caused by nozzle clogging of 25 MnB produced by EAF-continuous casting in a domestic steel plant,the sources and causes of nodulation are systematically analyzed.By improving the calcium treatment process,the quality of liquid steel is improved,and the generation of nodulation is reduced,so as to provide a certain theoretical and experimental basis for inhibiting nozzle clogging.In this paper,the nodulation on the inner wall of submerged entry nozzle was collected and analyzed when 25 MnB steel was produced in a steel plant.It is found that at the beginning of casting,a thin layer of Fe3O4 is formed on the surface of Al-C refractories for nozzle,and then high melting point nodulation Al2O3 precipitates on the surface of Fe3O4.Finally,composite inclusions such as calcium aluminate and magnesium aluminum spinel in molten steel are deposited on the surface of Al2O3 and grow up continuously,and finally the nozzle is blocked.It is confirmed that the nodulation mainly comes from alumina inclusion in molten steel.Based on this,this paper uses calcium treatment process to change the existing form of inclusions in steel,so as to improve the nozzle clogging problem.The results show that the Ca/Al ratio of molten steel in tundish is 0.38 after LF and VD,The inclusions in billet are mainly spherical Ca S-Ca O-Al2O3 compound inclusions smaller than 3?m,The inclusion content satisfying the requirement of12C·7A is 73.67%.The production test shows that the deoxidation and desulfurization effect of 25 MnB steel is obvious in LF refining and VD vacuum treatment,which meets the requirements of molten steel purity.Adding proper amount of calcium wire after VD is in a proper range can ensure the full denaturation of inclusions,reduce nozzle nodulation and meet the quality requirements of slab.The production process is adjusted and the flocculent flow rate in production practice is controlled at 7.6%.