| 摘要 |
Provided are a steel plate for a thick-walled steel pipe with excellent CTOD performance in a heat affected zone formed as a result of performing girth welding, a method for manufacturing the steel plate, and a thick-walled steel pipe. The steel plate has a chemical composition containing, by mass%, C: 0.03% or more and 0.10% or less, Si: 0.05% or more and 0. 50% or less, Mn: 1.00% or more and 2. 00% or less, P: 0.015% or less, S: 0.005% or less, Mo: 0.20% or less (including 0%), Nb: 0.01% or more and 0.05% or less, and the balance being Fe and inevitable impurities, and, if desired, containing one or more of Al: 0.005% or more and 0.1% or less, Cu: 1.00% or less, Ni: 1.00% or less, Cr: 0.50% or less, and V: 0.05% or less, in which Pcm* (%) (= C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/2 + V/10) is 0.20 or less. The steel plate has a volume fraction of bainite in a base material of 50% or more, and has a volume fraction of island martensite (MA) in a coarse-grain region reheated in a dual-phase temperature range of 5.0% or less. A slab having the chemical composition described above that is cast using a continuous casting method is reheated at a specified temperature, hot-rolled, and then subjected to accelerated cooling to a temperature of 550°C or lower and 250°C or higher. |
