| 摘要 |
PROBLEM TO BE SOLVED: To provide steel which has excellent toughness in a base metal and large-small heat input weld heat-affected zones. SOLUTION: The steel having excellent toughness in a base metal and large -small heat input weld heat-affected zones has a composition comprising by mass, 0.03 to 0.2% C,≤0.5% Si, 0.5 to 2.0% Mn,≤0.02% P,≤0.006% S,≤0.01% Al, 0.005 to 0.02% Ti, 0.005 to 0.02% Zr, 0.003 to 0.012% O and 0.003 to 0.012% N, and the balance iron with inevitable impurities. Zr oxides having means particle diameters of 0.002 to 3.0μm are dispersed into the central part of the cross-section of the steel by 10<SP>2</SP>to 5×10<SP>6</SP>pieces/mm<SP>2</SP>, and Ti nitrides and Zr nitrides having means particle diameters of 0.002 to 0.5μm are jointly dispersed into the central part of the cross-section of the steel by 10<SP>3</SP>to 5×10<SP>6</SP>pieces/mm<SP>2</SP>. COPYRIGHT: (C)2003,JPO
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