COOLING METHOD OF STEEL STRIP IN CONTINUOUS ANNEALING FURNACE

PURPOSE:To suppress the nonuniform cooling of a steel strip in a continuous annealing furnace, by controlling the temp. distribution in the transverse direction of the steel strip prior to quick cooling with spray cooling of gas and bringing the steel strip into contact with multiple-stages cooling rolls while controlling the tension of the steel strip only in the quick cooling zone in a prescribed tension range before and after the quick cooling at the same instant. CONSTITUTION:A steel strip X is heated to the recrystallization temp. or above in a heating zone 2 after cold rolling is held in a holding zone 3 and is then cooled. The steel strip is subjected to spray cooling with gas using gas sprayers 10 provided on the outlet side of the zone 3 and roll cooling with multiple-stages cooling rolls 11 provided on the down stream side thereof. More specifically, the steel strip is cooled while the temp. distribution in the transverse direction thereof is controlled by the abovementioned spray cooling with gas, whereafter the strip is brought into contact with the rolls 11 and is cooled in a 2-5kg/mm. unit tension range. As a result, the nonuniform cooling of the strip X is suppressed; therefore, the steel strip having a good shape and quality before the overaging treatment and on the outlet side of a continuous annealing furnace 1 is obtd.