| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-tension steel plate which can obtain a satisfactory HAZ (heat affected zone) toughness even when performing a large heat-input welding of 30-100 kJ/mm heat input quantity, and can secure a satisfactory fatigue service life by suppressing the progressing speed of cracking. SOLUTION: As for the high-tension steel plate, values specified by predetermined relational expressions (1)-(3) are appropriately controlled; Ti-contained nitrides having ≤0.05 μm circle-based diameter corresponded to the circle, exist ≥5.0×10<SP>6</SP>pieces per 1 mm<SP>2</SP>; the pieces of the Ti-contained nitrides of 0.01-0.03 μm circle-based diameter therein occupies ≥75% to the whole pieces of the Ti-contained nitride; and Cr-contained carbide of 0.05-0.3 μm circle-based diameter exist ≥5.0×10<SP>3</SP>pieces per 1 mm<SP>2</SP>. Here, the BP value specified by the following equation (1) is present within the range of 90 to 190 (mass%). BP value (mass%)=414[C]+78[Si]+31[Mn]+79[Cr]-14[Cu]-26[Ni]+218[Mo] (1). the DI<SB>1</SB>value or DI<SB>2</SB>value specified by the following equations (2) or (3) is at least 50. DI<SB>1</SB>=1.16×([C]/10)<SP>1/2</SP>×(0.75[Si]+1)×ä5.1([Mn]-1.2)+5.0}×(0.35[Cu]+1)×(0.36[Ni]+1)×(2.16[Cr]+1)×(3[Mo]+1)×(1.75[V]+1)×(200[B]+1) (1), when [Mn>1.2%], DI<SB>2</SB>=1.16×([C]/10)<SP>1/2</SP>×(0.75[Si]+1)×3.33([Mn]+1)×(0.35[Cu]+1)×(0.36[Ni]+1)×(2.16[Cr]+1)×(3[Mo]+1)×(1.75[V]+1)×(200[B]+1) (3), when [Mn≤1.2%]. COPYRIGHT: (C)2010,JPO&INPIT
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