To provide a method capable of stably manufacturing online a steel plate the bar cutting distortion of which is small even though bar cutting is executed in the state of being cold and moreover which has homogeneous material quality over the whole steel plate.
After a thick steel plate 6 which is rolled with a finishing mill 1 is straightened into flatness with a hot straightening machine 2 so as to be suitable for being inserted into an accelerated cooling device 3, accelerated cooling is executed with the accelerated cooling device 3. The steel plate is cooled so that a temperature drop in the vicinity of the end part of the plate which is generated from a heating furnace to the completion of finish rolling is dissolved while being hot straightened in the forward stage part of the hot straightening machine 2 and moreover so that the temperature of the steel plate is not dropped to an Ar3 transformation point or below. In the backward stage part of the hot straightening machine 2, hot straightening is executed by being cooled in the open air so that the temperature of the both surfaces of the steel plate is recuperated in the position of the last leveling roll of the hot straightening machine 2 almost simultaneously with the completion of straightening. Thereafter, accelerated cooling is executed under a uniform cooling condition in the width direction to manufacture the steel plate.
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