| 摘要 |
<p>Provide is a method for manufacturing a tapered plate having a tensile strength of 570 MPa or more capable of being subjected to high-heat input welding with a heat input of more than 300 kJ/cm. Specifically, the method includes heating to a temperature of 1000°C or higher and 1200°C or lower, a steel slab having a chemical composition containing, by mass%, C: 0.03% or more and 0.12% or less, Si: 0.03% or more and 0.5% or less, Mn: 0.8% or more and 2.2% or less, P: 0.015% or less, S: 0.0005% or more and 0.0050% or less, Al: 0.005% or more and 0.1% or less, Nb: 0.003% or more and 0.014% or less, Ti: 0.003% or more and 0.02% or less, B: 0.0003% or more and 0.0025% or less, N: 0.0030% or more and 0.0070% or less, Ca: 0.0005% or more and 0.0050% or less and the balance being Fe and inevitable impurities, in which expression (1) is satisfied, performing hot rolling on the heated slab in which plate thickness changes in the longitudinal direction so as to form a tapered shape at a finishing rolling temperature of 900°C or lower and equal to or higher than the Ar 3 point and then performing accelerated cooling on the hot-rolled steel plate down to a temperature of 500°C or lower:
where N and Ti respectively represent the contents (mass%) of N and Ti.</p> |
