| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a thick steel plate excellent in toughness and strain aging property maintaining the demanded strength as a material of a marine structure or the like. <P>SOLUTION: The thick steel plate includes C, Si, Mn, N, and Ti, and further includes: at least two chosen from the group consisting of Nb, Ni, and Cu; and the remainder consisting of iron and inevitable impurities, wherein the chemical composition satisfies following formula (1)-formula (3), in the metal structure, the average circle equivalent diameter of the mixture of martensite and retained austenite is at most 2.0 μm (0 micron is not included), and the volume fraction of the retained austenite is 0.5-4.0%. In the following formulas, [ ] shows the content (mass%) of each element in the thick steel plate. 2.0≤[Ti]/[N]≤5.0 (1), 5.3≤7×[Si]+2×[Ni]+[Mn]+12×(5×[Nb]+3×[Ti])≤7.1 (2), and 65≤39×[Mn]+17×[Ni]+10×[Cu]≤78 (3). <P>COPYRIGHT: (C)2013,JPO&INPIT |
