FINISH ROLLING METHOD OF STEEL BAR AND WIRE ROD

摘要

PROBLEM TO BE SOLVED: To provide a finish rolling method of a steel bar and a wire rod capable of maintaining the dimensional tolerance of±0.20 mm without causing biting flaws and also capable of preventing crystal grain from coarsening regionally. SOLUTION: In the finish rolling method which uses n units of a three roll rolling mill in the finish rolling mill group, the roll hole die shape of the three roll rolling mill in the (n-1)th and nth unit from the upstream side is arranged with a circular arc diameter 1.0 to 1.20 times against each product nominal diameter and with relief of angle 5 to 40 deg. and at the same time, drafting of the three roll rolling mill in the nth unit is selected independently and rolling is executed when the gross reduction rate is 30% or more in the finish rolling mill group and when the passing time of the material to be rolled among each three roll rolling mill is one second or less. Here, n is an integer 4 or bigger. M is an integer 3 or bigger and m units of the three roll rolling mill in the finish rolling mill group, and either one or both of one unit or more of the two roll rolling mill and/or one unit or more of the four roll rolling mill situated in the upstream side of m units of the three roll rolling mill can be used.