| Considering the problem of longitudinal surface cracks in the CSP thin slab continuous casting production, the causes of the cracks in the mold were analyzed, which from perspectives of the molten steel transfer behavior. Influences of molten steel level fluctuation, inclusion gathered and uneven surface temperature distribution on longitudinal cracks of thin slab were discussed. Considering the CSP mold characteristics of funnel type surface shape, the extrusion force of slab with different curvature crystal shapes were compared through the optical plasticity method. Based on the formation analysis of thin slab longitudinal surface cracks, influences of Electromagnetic brakes on the slab quality were studied.With the high speed casting of CSP thin slab production, characteristics of molten steel flow and solidification heat transfer in the mold were analyzed by numerical simulation method. When the casting speed is6m/min, the fluctuation of liquid steel is up to±16mm. Larger level fluctuation is the main reason of slag.In the production of thin slab continuous casting, the location of the maximum temperature gradient is usually at the edge of funnel shape area. The horizontal surface temperature difference at mold exit for70mm thick CSP slabs is110K, the non-uniform distribution of surface temperature may be one reason for longitudinal cracks at funnel shape area of the mold.Restricted by the shape of funnel type mold, the CSP slabs withstand extra squeezing force. The squeezed status of CSP slabs under three types of CSP funnel type mold with increased curvature, ordinary curvature and decreased curvature is studied using photo-plastic experiment. Results show that the maximum strain is2.7%,2.1%and1.9%, respectively.The inclusions distribution and accumulation in CSP thin slabs are researched using large sample electrolysis method and metallographic analysis. Results for SPHC steel thin slabs illustrate that large size inclusions would accumulate mostly in the1/4position along width direction of slabs, taking up over40%of the total, which might be one cause for longitudinal surface cracks at funnel shape area of the mold.Based on analysis for cause of longitudinal surface cracks in CSP funnel type mold, the coupling model of flow, heat transfer, solidification and electromagnetic field in the mold was establishedel, and the influence of external field-electromagnetic braking on liquid steel transportation in CSP mold is studied to clarify the conversion characteristics between electric/magnetic field and to analyze the effect of magnetic field distribution on liquid steel flow and heat transfer thus optimizing the production parameters and discussing the prohibiting effect of electromagnetic braking on longitudinal crack sources. Relative results show that electromagnetic braking obviously improves the flow status of liquid steel in CSP mold. When magnetic field intensity increases to0.2T, the liquid steel surface fluctuation level decreases within±5mm. With application of electromagnetic braking, surface temperature tends to be evener at CSP mold exit, which contributes to improving of such slab quality problems as longitudinal surface cracks. |
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