Influences Of EMBr On Metallurgical Behavior And Slab Quality In CSP Processes

In this study, the effect of EMBr on steel flow behavior and interaction with mold slag were investigated for the worldwide advanced second generation CSP caster at Lianyuan Steel. The steel flow pattern without EMBr was analyzed by means of water model simulation. Numerical simulation was conducted to understand and optimize the metallurgical factors of EMBr on slab quality and productivity.The results of water model simulation on submerged entry nozzle (SEN) and mold indicated that the steel flow pattern was quite different for wide and narrow mold sizes with the same SEN. The penetration depth reached up to 800-1000 mm. Flow turbulence and back-flow at large area were formed so that the inclusions in liquid steel is difficult to float up, and that obvious level fluctuation resulted in slag entrapment. Therefore, with regard to different slab sizes, the design of submerged entry nozzle should be optimized to reduce steel flow turbulence and slag entrapment etc. In addition, EMBr is a necessary measure to improve slab quality.With regard to numerical simulation, both semi-quantitativemethods ( F_x/S = ρV_x~2 -σV_xB_y~2·Δx and τ=μ(ΔV_z)/(Δx) ) were presented toanalyze the impact of steel flow on the inner wall and initial solidified shell and to describe the effect of EMBr with the subtraction of casting speed and turbulent kinetic energy. The results of numerical simulation indicated that over-high speed of horizontal steel flow and bias-flow resulted in turbulence flow around SEN and consequently entrapmentof slag occurred. EMBr can effectively prevent from random turbulence flow on the surface.Numerical simulation was performed for the slab size 1500x70 mm at the casting speed of 4.5 m/min to analyze the steel flow behavior with EMBr. The results showed that the penetration of steel flow into the mold was reduced by 45% compared with that without EMBr and that the steel flow was developed into a one-dimensional stable laminar flow below 500-700 mm, which is facilitated to increase casting speed and prevent from breakout and longitudinal cracking. Steel flow velocity on horizontal direction was remarkably reduced on the steel surface and no abnormal steel flow was formed so that no slag entrapment occurred around SEN. Additionally, the flowrate of back-flow increased at the narrow face, by 4.4% compared with that no EMBr, to promote inclusions to float up and mold fluxes to melt. The numerical simulation of steel flow in the mold with EMBr demonstrated that impact point goes up by 40% at narrow face and that impact intensity of up-flow and down-flow decreased by 86% and 10%, respectively, which is beneficial to avoid the re-melting of the solidified shell so that solidification defect such as transverse crack can be reduced.In order to check the effect of EMBr on the metallurgical process and slab quality, industrial test was conducted at Lianyuan Steel under the constant condition, that is, the test was performed for the same steel grade at 4.5 m/min casting speed in one casting sequence. The results pointed out that (1) total number of inclusions in slab was decreased by 6.9%, among which the amount of inclusions at the slab center was...