| 摘要 |
PROBLEM TO BE SOLVED: To reduce C segregation in a cast billet and pro-eutectoid cementite in a wire rod by forming the solidified thickness on the upper surface and the lower surface in the cross section of the cast billet to a specific dimension before straightening the bent cast billet and natural-cooling for at least specific time during the interval from the start of straightening to the completion of solidifying. SOLUTION: In the casting of the billet having <=160 mm square, the solidified thicknesses on the upper surface and the lower surface in the cross section of the cast billet are secured to be >=30 mm, and the cast billet is naturally cooled for >=100 sec. Desirably, when the last solidified position satisfies the formula II: L-Lb>100×Vc/60 and the formula III: L=(d/2)2×Vc/K2, the natural cooling zone having the length or longer shown with the formula I:L=100×Vc/60, is arranged on and after the start of straightening. In these formulas, Lc is the min. length (m) of the natural cooling zone, Vc is casting velocity (m/min), L is the solidification completing length (m) decided with the formula III, Lb is the distance (m) from the start of casting to the straightening point, (d) is the thickness (mm) of the cast billet and K is the solidifying factor, which is different according to the casting machine and ordinarily 30 (mm/min0.5). Further, light rolling reduction is executed at the portion which is >=0.2 solid phase ratio at the center of the cast slab.
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