| 摘要 |
PROBLEM TO BE SOLVED: To provide a 60 Kg/mm<SP>2</SP>class steel which has a high strength realized by an inexpensive alloy composition and is excellent in weldability and toughness at a weld heat-affected zone formed by medium to high heat input welding; and to provide a method for producing the same. SOLUTION: The steel comprises, by mass%, 0.04 to 0.07% C, 0.1 to 0.3% Si, 1.9 to 2.3% Mn, not more than 0.008% P, not more than 0.005% S, not more than 0.004% Al, 0.03 to 0.06% Nb, 0.005 to 0.015% Ti, not more than 0.0030% O; and not more than 0.0060% N with the balance comprising iron and unavoidable impurities; wherein a weld crack susceptibility composition P<SB>CM</SB>is represented by the equation; (P<SB>CM</SB>=C+1/30 Si+1/20 Mn), and has a P<SB>CM</SB>value of not larger than 0.20 the C and Nb contents satisfy the formula (C+1/3 Nb≤0.09(%)). COPYRIGHT: (C)2007,JPO&INPIT
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