| 摘要 |
PROBLEM TO BE SOLVED: To obtain bar steel billet having no surface defects and internal check or center porosity therein is ensurely crimped, by specifying the size and form of the cross-section of the continuous casting piece and after the completion of solidification, by cutting the casting piece in a given length, and heating to a given temperature, and by rolling it so that the form ratio and the drawing ratio stand for given values. SOLUTION: The continuous casting is conducted so that the cross-section of the casting piece is formed in a perfect square of which a side length is to be 140 to 300 mm, or is to be formed in a rectangular which has the equivalent section area of the square and the ratio of the major side to the minor side is less than 1.6. The billets are cut off in a given length after the completion of the solidification, and are heated to a given temperature. The billets are rolled 1 pass each of the perpendicular and cross direction so that the form ratio meets (the arc of contact/the average casting thickness) >=1.0. Two to four pass rolling is carried out so that the drawing ratio of the casting thickness to the billet is 1.5 to 2.8. It is desirable that the rolling works are conducted by flat rolls without pores having a diameter above 950 mmϕ. It is also desirable that the temperature upon completion of the rolling is higher than 940 deg.C.
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