STEEL PLATE EXCELLENT IN TOUGHNESS AT PLATE THICKNESS CENTER PART AND ITS MANUFACTURING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a steel plate having improved Charpy impact property and strength at a plate thickness center part of a 50 kilo class thick material alloy steel plate and its manufacturing method.SOLUTION: There is provided a steel excellent in Charpy impact property having a yield strength of 340 to 500 MPa, a plate thickness of 60 to 100 mm, and a composite containing, by mass%, C:0.01 to 0.07%, Si:0.05 to 0.30%, Mn:0.80 to 1.40%, P:0.01% or less, S:0.005% or less, Al:0.004% or less, Ti:0.005 to 0.020%, N:0.0020 to 0.0060%, O:0.0025 to 0.0045%, B:0.0005 to 0.0030% and the balance iron with inevitable impurities.