| 摘要 |
<p>A high-strength steel plate includes the following composition: 0.18 to 0.23 mass% of C; 0.1 to 0.5 mass% of Si; 1.0 to 2.0 mass% of Mn; 0.020 mass% or less of P; 0.010 mass% or less of S; 0.5 to 3.0 mass% ofNi; 0.003 to 0.10 mass% ofNb; 0.05 to 0.15 mass% of Al; 0.0003 to 0.0030 mass% of B; 0.006 mass% or less ofN; and a balance composed of Fe and inevitable impurities. A weld crack sensitivity index Pcm of the high-strength steel plate is 0.36 mass% or less. The A c3 transformation point is equal to or less than 830°C, the percentage value of a martensite structure is equal to or greater than 90%, the yield strength is equal to or greater than 1300 MPa, and the tensile strength is equal to or greater than 1400 MPa and equal to or less than 1650 MPa. A prior austenite grain size number N³ is calculated by N³=-3+log 2 m using an average number m of crystal grains per 1 mm 2 in a cross section of a sample piece of the high-strength steel plate. If the tensile strength is less than 1550 MPa, the prior austenite grain size number N³ satisfies the formulae N³‰¥([TS]-1400)×0.004+8.0 and N³‰¤11.0, and if the tensile strength is equal to or greater than 1550 MPa, the prior austenite grain size number N³ satisfies the formulae N³‰¥([TS]-1550)×0.008+8.6 and Na³‰¤11.0, where [TS] (MPa) is the tensile strength.</p> |
