High-tensile steel plate having excellent low-temperature toughness

Abstract

The high-tensile steel plate contains, in terms of mass%, 0.08%-0.15% C, 0.80%-1.60% Mn, 3.00%-4.50% Ni, 0.50%-1.00% Cr, 0.50%-1.00% Mo, 0.020%-0.085% Al, 0.0020%-0.0070% N, and 0.0005%-0.0020% B, theplate thickness tmm being more than 200 mm and no more than 300 mm, the plate having a chemical composition in which Ts is 380-430, Ceq is 0.80-1.05, Ac1 is 580-647, and x is 46-90, the combined total amount of martensite and bainite in terms of vol% being 99%-100%, the plate having a tensile strength of 780 MPa-930 MPa, and the absorbed energy in a Charpy impact test at -60 degree centigrade ofa center part of the plate thickness being at least 69 J.

Description

technical field [0001] The present invention relates to a high-strength steel sheet that is excellent in low-temperature toughness and has a large plate thickness. More specifically, it relates to a steel plate having a thickness of more than 200 mm, a tensile strength of 780 MPa or more, and an absorbed energy at -60° C. of the central part of the plate thickness of 69 J or more. The steel plate is suitable for structures such as marine structures, pressure vessels, penstocks, and large cranes for ships. Background technique [0002] Among the above-mentioned structures, in general, in order to ensure the safety of the structure, low-temperature toughness is required for the steel plate used as the base material. In recent years, the scale of structures has increased remarkably, and in such structures, steel plates with a large plate thickness and high strength tend to be used. [0003] The above-mentioned structures generally use high-strength steel plates of 780MPa clas...

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Problems solved by technology

[0010] As mentioned above, in the conventional method, if the thickness of the steel plate exceeds 200 mm, it is impossibl

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