Research On The Key Technology And Theory Of High Cleanliness Stainless Steel On GOR-LF-CC Process

Stainless steels have a very wide range of applications in the civil and industrial fields,most of which were required stringently on surface quality.To obtain the desired production in the course of steelmaking,the stainless steels not only have high requirements on the cleanliness of molten steel,but also on the surface quality of slabs.AOD and VOD process has been generally used for the production of stainless steel.GOR converter is blowing at the bottom and the way of tapping is that the steel is frist out and then the slag,the studies of desulfurization and cleanliness control based on GOR process are little few.Thus,the cleanliness control,desulfurization mechanism,the submerged nozzle of casting and the internal flow field of mold were investigated based on EAF-GOR-LF-CC process.The characterstic of inclusion formed in the process of GOR converter was studied.The results showed that inclusions are mainly CaO-SiO2-MgO-Al2O3-MnO-CrOx liquid spherical inclusions with diferent size,sizes of that in range of 1?m?22?m.The inclusions mainly divided into three categories:the first kind of inclusions is mainly from the GOR slag particles,the sizes of these inclusions are more than 5 ?m.The third kind of clusions generate in the deoxidization process of FeSi alloy,the sizes of these inclusions are less than 2.5?m.The second kind of inclusion from the collision between deoxidizing inclusions and tiny GOR slag particles,the composition is in between the first and the third kind of inclusions and the sizes is in the range of 2.5?m to 5?m.The desulfurization processes of GOR and LF were studied.The results showed the desulfurization efficiency was improved significantly by reducing Cr2O3 content in slag as far as possible.The increase of basicity of slag can lead to the improvement of Ls in GOR process and the increase of desulfurization rate during LF refining.When the Cr2O3 content of GOR reduction slag is lower than 0.3%,Ls increase significantly and final sulfur content of steel is stability under 50ppm.When the Cr2O3 content of GOR reduction slag is lower than 0.2%,Ls increase to above 250 with the increase of basicity to 1.85.The optimal desulfurization rate is obtained when the basicity increase to about 1.9 under the condition that the Cr2O3 content of LF refining slag is lower than 0.2%.Through the numerical simulation of the tundish,physical simulation and factory test,it can be found that the optimization of structural and positional parameters of tundish can significantly improve the fluidity of the molten steel and reduce the excessive disturbance of the steel slag interface.After the optimization of two sides of the tundish,the average dwell time was increased by 33.5%,the dead zone volume was reduced by 56.3%,and the volume increased by 0.73m3.At the same time,reducing the dip angle of the tundish is beneficial to improve the uniformity of the temperature of the molten steel,which is beneficial to the subsequent continuous casting operation.After the overall optimization,the amount of large-sized inclusions in molten steel of the tundish is significantly reduced.The results of numerical simulation are shown that severe rotatable asymmetry of molten steel occurred during the emission at the exit of the submerged nozzle characterized by the shape of an ellipse and the angle of the upward 15°,thereby resulting in asymmetric flow field in the mold,and the optimal submerged nozzle was calculated with the shape of a rectangle and angle of the upward 5°.The results of physical simulation for the original submerged nozzle are the same with the numerical simulation.Besides,the ink movement which was used for exhibiting flow field was shown that a wide fluctuation appeared.In addition,slag entrapment was found on the meniscus and the half of the broadside.The results of physical simulation for the optimized submerged nozzle were shown that non-occurrence of the rotation of water at the exit of submerged nozzle,relatively perfect symmetry of the flow field in the mold,stable wave on the free surface and the improvement of slag entrapment.Combining laboratory numerical simulation and physical simulation results,the factory test was conducted by testify the effectiveness of the optimized submerged nozzle.Light and unclear oscillation marks,the severely slant columnar dendrites and serious porosity were found in the continuous castings with the original submerged nozzle.On the contrary,these problems dramatically improved with the optimized submerged nozzle.