Study On Flow Phenomena Of Molten Steel And Behavior Of Non-metallic Inclusions During Electroslag Remelting

The evolution of the total oxygen,sulfur content and non-metallic inclusions in steel during Electroslag Remelting process was studied by an industrial trial,and the dynamic model for the composition evolution of inclusions was established.Then,the multiphase flow,heat transfer and solidification model of ESR was established to study and quantitatively analyze the formation,dripping and interior fluid flow of droplets.Finally,the movement of non-metallic inclusions in molten steel,the removal of non-metallic inslusions at steel-slag interface and the entrapment of non-metallic inclusions at the solidification front of steel were numerically simulated by the Decrete Phase Model.Firstly,the composition evolution of non-metallic inclusions in Q235B steels before and after the Electroslag Remelting process was analyzed.After the Electroslag Remelting process,the oxide composition of inclusions in Q235B steel varied from SiO2 and SiO2-MnO to Al2O2 and Al2O3-MnO during ESR.The transformation was due to that the aluminum in the molten slag continuously transferred to the molten steel,which resulted in the increase of the aluminum content in the steel and promoted the reduction of MnO and SiO2 to Al2O3 and Al2O3-MnO in inclusions by aluminum.The reduction reaction mainly occurred at the liquid film-slag interface and the droplet-slag interface.The liquid film-slag interface was the dominated one,accounting for 70.18%.The kinetic model for the composition evolution of non-metallic inclusions in steel showed that the transformation rate of inclusion composition varied at different stages of the Electroslag Remelting process.In the liquid film stage,although the temperature was the lowest than other two stages,the specific surface area was larger,leading to the high transformation rate of inclusion composition.In the slag pool stage,due to the high temperature and the largest specific surface area,the transformation rate of inclusion composition was the largest.In the melt pool stage,the fluid flow was relatively slow compared to the slag pool,and the mass transfer coefficient was low,resulting in the lowest transformation rate of inclusion composition.Secondly,the dripping process of droplets was studied using the multiphase flow,heat transfer and solidification model of Electroslag Remelting.The results showed that the movement of metal droplet from electrode to final entering the melt pool experienced three stages:i)the stage of that from liquid film formation to droplet detaching,ii)the stage of droplet dripping in slag pool,iii)the stage of droplets entering the metal pool.In the process of droplet dripping,the non-uniform distribution of flow field inside the droplet made the droplet deform,and the fluid flow in droplets coexisted a circlulating flow inside the droplet and a downward flow due to the gravity.In addition,the droplet might break up into a main droplet and several satellite droplets.The dripping speed of the main droplet in the slag pool increased all the time,and reached approximately 0.4 m/s when the droplets were close to the interface between the slag pool and the melt pool.The dripping speed of satellite droplets firstly increased and then decreased during the dripping process,and reached the maximum of 0.15-0.2 m/s at about 35 mm below the electrode.Finnally,the removal of non-metallic inclusions in steel during Electroslag Remelting process was numerical simulated.a model assuming that the random walk model was not used in the liquid film and droplet but in the melt pool was established.When ignoring the rebound force,the entrappment of 1 ?m,10 ?m,50?m and 100 ?m inclusions were 1.40%,1.28%,0.31%and 0.00%,respectively.When considering the rebound force,the entrappment of 1 ?m,10 ?m and 100?m inclusions were 4.24%,3.49%and 0.01%,respectively.The results showed that when considering the rebound force,the entrap fraction of 1?m inclusions was more consistant with the industrial test results.For 10 ?m inclusions,due to the ignoring of the precipitation of inclusions in the simulation model,the entrap fraction was different from the industrial test results.