| 摘要 |
PURPOSE:To satisfactorily heat treat a hot steel sheet by gradually increasing the speed of conveyance of the steel sheet during passing through a cooling zone so as to uniformly cool the steel sheet over the whole region from the top to the bottom. CONSTITUTION:When a hot steel sheet 1 leaving a rolling mill 2 is heat treated by passing through a cooling zone 3 at a constant speed of conveyance, the cooling start temp. and the cooling stop temp. of the steel sheet 1 are higher at the top 1a of the steel sheet 1 and lower at the bottom 1b, respectively. In order to prevent the ununiform cooling, the speed of conveyance of the steel sheet 1 is gradually increased at the time when the top 1a leaves the cooling zone 3. By this cooling method, the cooling start temp. and the cooling stop temp. of the steel sheet 1 can be uniformized over the whole region from the top 1a to the bottom 1b. |
