| 摘要 |
PROBLEM TO BE SOLVED: To provide a method by which a steel sheet capable of suppressing the generation of brittle fracture cracks in a structure even in the low temperature environment and also excellent in low temperature toughness at <=-100 deg.C can be produced with high productivity. SOLUTION: In this producing method, by hot rolling, a steel sheet satisfying 0.03 to 0.2% C, <=0.5% Si, <=1.8% Mn, 0.01 to 0.1% Al and <=$0.01% N, and in which microstructure is also substantially composed of a ferritic structure and a pearlitic structure is obtained, thereafter, the region from both surfaces of the sheet thickness respectively to 5 to 15% of the sheet thickness is subjected to primary cooling to the temperature range of 450 to 650 deg.C at the average cooling rate of 4 to 15 deg.C, is next recuperated to the Ar3 transformation point or below and is then subjected to secondary cooling at the average cooling rate of 1 to 10 deg.C/s.
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