Large inclusions captured by the solidifying shell deteriorate the surface quality of interstitial free steel. To investigate the capture of large inclusion in slab continuous casting, a three-dimensional model coupling flow field, solidification and inclusion motion has been developed. Additionally, to study the effect of in-mold electromagnetic stirring (M-EMS) on large inclusion capture, the electromagnetic field has been also coupled in the model. The results of electromagnetic field indicates its centrally symmetrical distribution on the cross-section, and the electromagnetic force swirls on the cross-section. The effects of M-EMS on flow pattern, solidification and inclusion capture have been discussed. The M-EMS significantly changes the flow pattern and solidifying shell thickness. The inhomogeneous distribution of large inclusions existing in the slab surface in the slab surface are different between the cases with and without M-EMS. Furthermore, the number of captured inclusions increases at 0-0.02 m beneath the wide surface and decreases at 0.02-0.04 m beneath the wide surface in response to the application of M-EMS. Large inclusions in steel were quantitatively analyzed by the galvanostatic electrolysis method. The experimental results are in agreement with the simulation results, suggesting that the model is valid.
A three-dimensional mathematical model for natural decarburization process of ultra-low carbon Al killed steel during RH refining has been established. The decarburization behavior in RH degasser was discussed on the basis of a comparison between simulation data and the actual plant trials ones. The effects of the different initial carbon content, initial oxygen content, the lift gas rate and inside diameter on decarburization were investigated. The results showed that when the dissolved oxygen concentration was 0.08% in the molten steel, the flow rate of gas injected through the up-leg was 120 Nm 3 /h, the inside diameter of up and down-leg was 650 mm, under these conditions, the initial carbon content was 0.03%, 0.023% and 0.015%, respectively, after about 25 minute, the average carbon content in molten steel was 0.011%, 0.01% and 0.0008%. The final dissolved carbon content is related to the initial dissolved oxygen content in molten steel. The average carbon concentration and the decarburization rate of the molten steel will decrease with the increasing of the initial dissolved oxygen content. The effects of different inside diameter of up and down-leg were also compared, it shows that the increasing of the diameter of up/down-leg will promote decarburization effectively, which can increase the circulation flow rate and promote the reaction rate.
Limited by reduction radio, heavy plates manufactured from slabs are always subjected to deterioration of soundness and mechanical properties. For overcoming these defects, in the current works, a new approach, named heavy reduction process to improve segregation and porosity, was presented. The aim this study was to fix the dividing position of improving centerline segregation or porosity. Based on the world's maximum thickness vertical‐bending type caster, a two‐step strategy was preceded using software THERCAST, which was coupled macroscopic segregation with thermal‐mechanical GNS method firstly. According to the real production condition of superheat, casting speed and spray intensity, the depth of mushy zone and the terminal end of solidification in width direction were modeled. After this, the distribution of pressure and bulging were presented, and four positions were preliminarily determined based on the curves. Finally, the element concentration, cracks and reduction rate at these different reduction positions were discussed further. The results indicate that the division point of improving centerline segregation or porosity is confirmed ultimately.
A three-dimensional numerical simulation of transient fluid flow field during the solidification process of casting mold has been developed to predict the solidification front capturing the inclusions and the distribution of the inclusions at the different location in the inner surface layer has been given out. The motion behavior of non-metallic inclusions which are more than 50 μm has been simulated and visually displayed.The results show the large inclusions and the small inclusions cluster at different location in the inner surface layer through numerical simulation, and the inclusion cluster at the quarter of the broad face through numerical simulation and experiment.
Limited by reduction radio, heavy plates manufactured from slabs are always subjected to deterioration of soundness and mechanical properties. For overcoming these defects, in the current works, a new approach, named Heavy Reduction Process to Improve Segregation and Porosity (HRPISP), was presented. The aim this study was to investigate the process of rear heavy reduction, felling only one segment, at the end of slab solidification (about 0.85 solid fraction in the centerline). According to the real production condition of superheat, casting speed and spray intensity, a two-step strategy was preceded using software THERCAST3D firstly. Then, a special forging simulation product FORGE3D had been used, based on the end results of THERCAST3D, to simulate the rear heavy reduction process. Results showed the distribution of temperature, strain and strain rate under both types of segment. Interestingly, something valuable had been found. After the analysis of dynamic recrystallization (DRX) model, derived from the slabs hot uniaxial compressive tests, it revealed that a certain degree of X DRX was existed. In addition, there were significant differences in distribution of X DRX volume fraction and grain size. The results of such studies provided some valuable information on the parameters of heavy reduction and the design of reduction segment.
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