Patent ID: 10023946

Abstract:
Provided are a thick steel plate with which a welded joint having good CTOD property is formed by low-to-medium heat input multipass welding and a method for producing the thick steel plate.The steel plate has a composition containing, by mass, C: 0.03% to 0.10%, Si: 0.5% or less, Mn: 1.0% to 2.0%, P: 0.015% or less, S: 0.0005% to 0.0050%, Al: 0.005% to 0.060%, Ni: 0.5% to 2.0%, Ti: 0.005% to 0.030%, N: 0.0015% to 0.0065%, O: 0.0010% to 0.0050%, Ca: 0.0005% to 0.0060%, and, as needed, one or more elements such as Cu. Ti/N, Ceq, Pcm, and ACR each fall within the specific range. The effective crystal grain size of the base metal at the center of the plate in the thickness direction is 20 μm or less. A specific amount of a composite inclusion including a sulfide containing Ca and Mn and an oxide containing Al having an equivalent circular diameter of 0.1 μm or more is present at the ¼-thickness position and the ½-thickness position of the plate. The steel having the above-described composition is heated to a specific temperature, hot rolled, and cooled.