| 摘要 |
PROBLEM TO BE SOLVED: To improve the cold cracking resistance of a 780 MPa class high tensile strength steel plate at the time of small heat input welding to eliminate the necessity of preheating and also to improve its toughness in heat-affected zone at the time of large heat input welding. SOLUTION: This high tensile strength steel plate has a composition which contains, by weight, 0.010-0.060% C, 1.25-2.5% Mn, 0.1-2.0% Cr, 0.1-1.5% Mo, 0.0006-0.0050% B, <0.25% Cu, and <=0.030% Nb and in which the value of KP(%) defined by equation KP=[Mn]+1.5×[Cr]+2×[Mo] satisfies KP>=3.20, where [Mn], [Cr], and [Mo] represent the contents (%) of respective elements.
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