| 摘要 |
PURPOSE:To manufacture a high strength shape steel having uniform hardness in the plate thickness direction without damaging the weldability by executing a specific forced cooling to a cooling surface in the shape steel before final finish-rolling and rolling the steel to a specific accumulated strain after reheating to a specific temp. CONSTITUTION:The shape steel after executing the final finish-rolling is forcedly cooled to obtain the high strength steel. In the manufacturing method of the high strength shape steel, in the rolling process before the final finish-rolling, to the cooling surface in the shape steel, the forced cooling is applied at 5 deg.C/sec or higher cooling velocity in the temp. range of Ms temp. - Mr3 transformation temp. Thus, austenite on the surface layer part in the cooling surface is once transformed into ferrite or bainite. Thereafter, after the temp. of the cooling surface is recovered to Ac1 transformation temp. - unrecrystallizing temp., the shape steel is immediately rolled. The rolling process is executed in plural times to 10% or more accumulated strain. Thus, alloy component contents and the carbon equivalent can be reduced and the shape steel is made to be high strength without damaging the weldability, and the hardness in the plate thickness direction can be uniformized. |
