PRODUCTION OF HOT ROLLED STEEL BAR

摘要

PURPOSE:To obtain a steel bar having high strength, excellent toughness and uniform quality by dividing a cooling zone for the steel bar after hot rolling to a plurality, controlling the cooling in each zone and controlling the pearlite transformation temp. CONSTITUTION:The cooling zones 3 divided to a plurality are provided in the progressing direction of the steel bar 1 after the end of the hot rolling. Sensors 5 are provided just before the respective cooling zones 3 to continuously measure the surface temp. of the steel bar 1. The average temp. at every specified time is inputted to an arithmetic unit 4. The difference between the surface temp. of the steel bar and reference cooling pattern is calculated in the unit 4 and the cooling of each cooling zone 3 is controlled according to such difference. The pearlite transformation can be started within the temp. range of TC-TC +40 deg.C by such uniform speed cooling when the critical temp. tangential to the pearlite transformation initiation point of the CCT curve of the steel bar 1 is designated as Tc. The max. temp. during the transformation is suppressed to <=Tc+80 deg.C.