Steel material cooling device and cooling method

A steel material cooling device which is a device to cool a steel material having undergone hot rolling mills, the device comprising:

• a conveying mechanism which conveys the steel material while accelerating the steel material;
• a water cooling mechanism which cools the steel material while the conveying mechanism conveys the steel material;
• and
• a control unit which controls the conveying mechanism and the water cooling mechanism to cause the cooling of the steel material to satisfy Formula (1) below,
• wherein a water cooling time decrease rate γ in Formula (1) below is decided based on a length of a water cooling zone where the water cooling mechanism is provided and a time Δtc(0) required to cool a leading end portion of the steel material down to a target temperature,
• Δtc(x)=Δtc(0)−γ·x Formula (1),
• where x:
• a conveyance-direction position in the steel material relative to the leading end portion of the steel material serving as a reference point, and Δtc(x):
• a time required to cool a portion at the position x of the steel material down to the target temperature.

A steel material cooling control method which is a control method when a steel material having undergone hot rolling mills is cooled by a water cooling mechanism while the steel material is conveyed in an accelerated manner, the method comprising:

• a step of deciding a water cooling time decrease rate γ based on a length of a water cooling zone where the water cooling mechanism is provided and a time Δtc(0) required to cool a leading end portion of the steel material down to a target temperature;
• and
• a step of controlling the cooling of the steel material so as to satisfy Formula (1) below using the water cooling time decrease rate γ,
• Δtc(x)=Δtc(0)−γ·x Formula (1),
• where x:
• a conveyance-direction position in the steel material relative to the leading end portion of the steel material serving as a reference point, and Δtc(x):
• a time required to cool a portion at the position x of the steel material down to the target temperature.