| 摘要 |
Provided are a thick steel sheet having excellent CTOD properties in low-medium heat input multilayer welded joints, and a manufacturing method for the thick steel sheet. The component composition of the steel sheet includes, in mass%, 0.03-0.12% of C, at most 0.5% of Si, 1.0-2.0% of Mn, at most 0.015% of P, 0.0005-0.0050% of S, 0.005-0.060% of Al, 0.5-2.0% of Ni, 0.005-0.030% of Ti, 0.0015-0.0065% of N, 0.0010-0.0050% of O, 0.0005-0.0060% of Ca and contains at least one type of Cu when necessary. The Ti/N, Ceq, Pcm, and ACR values are within a defined range, the effective crystal grain size of the base material in the center of the sheet in the sheet thickness direction is at most 20μm, and a defined amount of composite inclusions having a circle equivalent diameter of at least 0.1 μm are present at 1/4 and 1/2 the sheet thickness, the composite inclusions comprising a sulfide containing Ca and Mn, and an oxide containing Al. After heating steel having the above composition to a defined temperature, the steel is hot rolled and cooled. |
