| 摘要 |
PROBLEM TO BE SOLVED: To provide steel having excellent toughness in the welding heat affected zone even in the case of welding in which heat input lies in the range of 10 to 50 kJ/mm, and its production method. SOLUTION: In the steel having excellent toughness in the welding heat affected zone, Ceq expressed by Ceq=C+Mn/6+Si/24+Mo/4+Cr/5+Ni/40+V/14 (each element is the content thereof by mass%) lies in the range of 0.28 to 0.45%, and the local maximum value of the area ratio of insular martensite in the vicinity of a bond in the case of welding in which heat input lies in the range of 10 to 50 kJ/mm is <4%. Further, in the method, a slab is heated to a temperature of the Ac3 transformation point to 1,300 deg.C, is rolled at <=950 deg.C at a cumulative draft of >=40%, and is thereafter air-cooled or water-cooled to produce the steel.
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