Steel for welding structure having welded joint with superior ctod properties in weld heat affected zone

Abstract

There is provided welding structural steel including, by weight, 0.01 to 0.2% C, 0.1 to 0.5% Si, 1.0 to 3.0% Mn, 0.01 to 0.1% Ti, 0.5 to 3.0% Ni, 0.0010 to 0.01% B, 0.003 to 0.006% N, 0.030% or less P, 0.005 to 0.05% Al, 0.030% or less S, 0.05% or less O, unavoidable impurities, and the balance of Fe. The Ti, O, N and B satisfy relations of 0.2=Ti / O=0.5, 2<=Ti / N<=5, 5<=O / B<=10 and 0.7<=(Ti+4B) / O<=1.5. A fine structure of a welded joint of the welding structural steel includes acicular ferrite with a structure fraction of 85% or more. In the welded joint, TiO oxides are distributed uniformly in a structure at a spacing of 0.5mu m or less, and have a grain size ranging from 0.01 to 0.1mu m. The number of TiO oxides is 1.0x10<7> / mm<3> or more. The welding structural steel has high strength characteristics in high heat input welding and employs TiO oxides and soluble B, so that the transformation into acicular ferrite is accelerated in a welded metal zone, thereby ensuring superior CTOD properties at the welded joint.

Description

technical field [0001] The present invention relates to welded joints with excellent Crack Tip Opening Displacement (CTOD) performance for welded structures, and more particularly, to welded structural steels, which can be used in ships, buildings, bridges, marine structures, steel pipes and pipelines. Improving CTOD performance of high heat input welded joints during arc welding (SAW) processes. Background technique [0002] Due to the continued rise in global oil prices and the diversification of construction techniques, offshore structures are being constructed in more extreme environments. In particular, marine structures constructed in cold regions must be manufactured using materials with high strength and excellent crack tip opening displacement (CTOD) at low temperatures. However, high-efficiency welding is necessary to weld such high-strength thick materials and build the desired building in a given time. In this regard, the large heat input welding technology for...

AI Technical Summary

Problems solved by technology

However, those techniques neither control the fine structure and grain size of the weld metal nor the oxygen or nitrogen content of the weld metal

Therefore, it is difficult to ensure the impact toughness of welded joints in large energy input welding processes such as SAW

Images