High tensile strength steel and marine structure having excellent weld toughness

Abstract

In order to provide a high tensile strength steel having excellent low temperature toughness and which can withstand large heat input welding, a steel comprises, in mass percent, C: 0.01-0.10%, Si: at most 0.5%, Mn: 0.8-1.8%, P: at most 0.020%, S: at most 0.01%, Cu: 0.8-1.5%, Ni: 0.2-1.5%, Al: 0.001-0.05%, N: 0.0030-0.0080%, O: 0.0005-0.0035%, if necessary at least one of Ti: 0.005-0.03%, Nb: 0.003-0.03%, and Mo: 0.1-0.8%, and a remainder of Fe and impurities, and the N / Al ratio is 0.3-3.0.

Description

TECHNICAL FIELD [0001] The present invention relates to a high tensile strength steel and a marine structure, and particularly to a high tensile strength steel for welding and a marine structure having excellent weld toughness. [0002] More specifically, the present invention relates to a high tensile strength steel for welding for use in welded structures such as buildings, civil engineering projects, construction equipment, ships, pipes, tanks, and marine structures, and particularly to a high tensile strength steel for welding to construct marine structures as well as to a marine structure thus constructed. For example, it relates to a thick, high strength steel plate with a thickness of at least 50 mm and a yield strength of at least 420 N / mm2 and to a marine structure using such a plate. BACKGROUND ART [0003] In recent years, as energy demands show a tendency to increase more and more, the search for undersea oil resources is being actively carried out. Marine structures used fo...

AI Technical Summary

Benefits of technology

[0016] Accordingly, the object of the present invention is to provide a high tensile strength steel for welding which is improved generally in low temperature toughness of welds and particularly in low temperature toughness in HAZ.

Problems solved by technology

This is thought to be because when the N / Al ratio is too small, coarse AlN precipitates, and not only does this itself have an adverse effect on toughness, but also it impedes fine dispersion of TiN in large amounts.

On the other hand, if the N / Al ratio is too large, the amount of solid solution N increases, and the density of AlN and TiN dispersed in the steel becomes very small.