| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for cooling a steel sheet, a method and equipment for manufacturing a steel sheet, for manufacturing a high strength steel sheet which has the low surface hardness of the steel sheet.SOLUTION: In the method for cooling the steel sheet using cooling equipment which includes a plurality of cooling zones which are divided with table rollers and dewatering rollers which are opposed to the table rollers and with which the cooling water is supplied to the upper and back surfaces of the steel sheet at the flow rate of water per unit area of ≥2.0 m/mmin, after applying accelerated cooling to the steel sheet after hot rolling until the outer layer of the steel sheet becomes a temperature of not higher than the starting point of martensitic transformation from a temperature of not lower than the Arpoint in the cooling zone on the most upstream side, the accelerated cooling is once interrupted by making succeeding one or a plurality of cooling zones as an air cooling section and after recuperating until the temperature of the outer layer part of the steel sheet becomes ≥640°C, the accelerated cooling is again performed until the average temperature in the sheet thickness direction of the steel sheet becomes ≤520°C in the cooling zone thereafter. |
