While minding the nozzle which is soaked to forecasting manner of the surface defective generation dangerous region in the continuous casting

摘要

PROBLEM TO BE SOLVED: To provide a method for predicting a dangerous portion causing a surface defect in a continuously cast slab, and a method for manufacturing continuously cast slab, which method can efficiently manufacture a continuously cast slab having high quality.;SOLUTION: When continuously cast a slab with a vertical type continuous casting machine, the molten metal level is continuously measured, and a lowering speed Vm of the molten metal level is calculated, and simultaneously a lowering amount of the cast slab is measured synchronously with the measurement of the molten metal level, and the lowering speed Vc of the cast slab is calculated. The portion satisfying the condition (1), Vm-Vc0, is predicted as the dangerous portion causing a surface defect. When d_m is defined as d_m=k_m(t_mc)ⁿ+c, where k_m is a solidification factor (mm×min^-n) of the molten metal in a meniscus portion, t_mc is a duration time (min) satisfying the condition (1), n and c are constants depending upon casting metals and casting conditions, and d_md₀ is satisfied, where d₀ is an amount (mm) to be scaled-off in a heating step of a hot rolling process of the cast slab (a depth in the thickness direction), the surface layer in the dangerous portion causing a surface defect is conditioned in a conditioning depth of (d_m-d₀) or more. By this method, the generation of surface defects due to air bubbles, inclusions, fluxes, etc. can be remarkably suppressed.;COPYRIGHT: (C)2007,JPO&INPIT