Study And Application On Tundish Plasma Heating Technology For Bloom Continuous Casting

Maintaining low superheat and constant temperature during the casting process is an effective method for improving continuous casting efficiency and the quality of continuous casting slab.The temperature drop of molten steel in the tundish is inevitable during the casting process,which cannot maintain low superheat and constant temperature stably.Plasma heating is an effective method for controlling the temperature of the molten steel in the tundish.It fully ionizes the working gas through energizing the electrodes to generate a high-energy arc plasma to heat the molten steel in the tundish.Therefore,if the plasma heating can be used efficiently,it will help to achieve low superheat constant temperature casting.This thesis focuses on the study and application of plasma heating technology for bloom continuous casting process,and the following conclusions are obtained:The simulation study of the plasma heating process of the tundish is achieved.High temperature steam was used to simulate the plasma heating process in hydraulic experiments.The results show that after plasma heating,the uniformity of the molten steel temperature field in the tundish is improved,which compensates for the temperature drop of the molten steel under the condition of no plasma heating,effectively improves the temperature field and flow field of the molten steel in the tundish,and promotes the heat transfer of molten steel.The VOF model was adopted in numerical simulation,and the plasma arc was assumed to be a simple heat source.The temperature field and flow field of molten steel in tundish were compared under the conditions of no plasma heating and heating power of 300 kW,500 kW and 1000 kW.The microstructure growth model of 45 steel bloom was established,and the effect of different superheat on the solidification structure of the bloom under plasma heating conditions was calculated by coupling the macroscopic temperature field model.The shell thickness of the crystallizer,the foot roller,the first segment and the second segment of the secondary cooling zone when the degree of superheat increases from 20? to 60? is analyzed.As the degree of molten steel superheat decreases from 60? to 20?,the number of grains on the cross-section of the bloom increases by about 26.05%,while the average grain radius decreases by about 20.75%,and the equiaxed crystal ratio increases by about 16.52%.Under the condition of ensuring the smooth continuous casting,a uniform solidification structure can be obtained by using a plasma heating process to control the superheat of the molten steel to maintain a temperature range of 20-30?.The plasma heating equipment with three hollow graphite electrodes is applied to the continuous casting process of bloom(370 mm×480 mm).Aiming at the non plasma heating and the typical plasma heating test of 9 furnaces,the effects of plasma heating on the temperature rise of the molten steel,the change of the molten steel composition and the inclusions are analyzed.Under conditions wherein no plasma heating,the rate of molten steel temperature drop can reach 1.06?/min.After plasma heating,the temperature rises and remains stable,and the heating rate can reach up to 0.8?/min.The[O]content decreased significantly after plasma heating.The inclusions characteristics of steel in the tundish before and after plasma heating were analyzed.After plasma heating,the number density of inclusions decreased,which is mainly due to the change of flow field in tundish by plasma heating.And it promotes the collision and floating behavior of small-sized oxide inclusions.It indicates that the plasma heating improves the cleanliness of molten steel.There is no obvious change in[N]content;the slight increase in content of[C]was caused by the loss of graphite electrodes.The influence of plasma heating on the tundish covering flux was studied for the first time.And the changes in the composition,morphology,crystallization characteristics,phase and composition of the liquid phase area of tundish covering flux before and after plasma heating are analyzed.After plasma heating,the macro morphology of the tundish covering flux changes from loose and porous to dense glass state.XRD results show that its crystallization rate becomes lower and the glass performance becomes better.Through the observation of the samples' micro morphology and composition analysis by scanning electron microscope,it shows that there are more irregular mineral phases in the sample before heating,and the precipitated phase of the sample after heating is obviously reduced.The structure is uniform and dense,and only a few mineral phases with irregular shape and some free oxides are embedded on the light gray matrix after plasma heating.It is analyzed by FactSage thermodynamics software that plasma heating has no significant effect on the composition of the liquid phase area of the tundish covering flux.