Thickness steel plate with excellent ctod - properties of the regions which is influenced by welding and with a yield strength of 460 mpa or more

摘要

A thick steel plate, characterized in that it has a chemical composition in mass %: C: 0.04 to 0.14 %, Si: 0.4 % or less, Mn: 1.0 to 2.0 %, P: : 0.02 % or less, S: 0.001 to 0.005 %, Al: 0.001 to 0.01 %, Ti: 0.005 to 0.03 %, Nb: 0.005 to 0.05 %, Mg: 0.0003 to 0.005 %, O: 0.001 to 0.005 %, N: 0.001 to 0.01 % and balance: Fe and inevitable impurities, TiN which includes a oxide comprising Mg and Al and has a size of 0.01 to 0.5 νm is present in an amount of 10,000 pieces/mm2 or more, and particles of a composite of an oxide and a sulfide containing 0.3 mass % or more of Mn and having a size of 0.5 to 10 νm are present in an amount of 10 pieces/mm2 or more. The steel plate has a yield strength of 460 Mpa or more and a CTOD in HAZ at -10°C of 0.2 mm or more.