124 results about "Brittle crack" patented technology

There is provided a high strength and low yield ratio steel for structure that is used as steel for structures of buildings and has excellent characteristics such as low temperature toughness, a tensile strength of approximately 600 MPa or more and a low yield ratio of 80% or less. The high strength and low yield ratio steel includes, by weight percent: C: 0.02 to 0.12%, Si: 0.01 to 0.8%, Mn: 0.3 to 2.5%, P: 0.02% or less, S: 0.01% or less, Al: 0.005 to 0.5%, Nb: 0.005 to 0.10%, B: 3 to 50 ppm, Ti: 0.005 to 0.1%, N: 15 to 150 ppm, Ca: 60 ppm or less, and the balance of Fe and inevitable impurities, and further includes at least one component selected from the group consisting of, by weight percent: Cr: 0.05 to 1.0%, Mo: 0.01 to 1.0%, Ni: 0.01 to 2.0%, Cu: 0.01 to 1.0% and V: 0.005 to 0.3%, wherein a finish cooling temperature is limited to 500 to 600 DEG C after the finish-rolling process. The high strength and low yield ratio steel satisfying characteristics such as low temperature toughness, brittle crack arrestabi lity and low yield ratio, and the manufacturing method thereof may be provided.

[Problem] To provide an arc-welded structural member which includes a Zn-Al-Mg-coated steel plate member and has excellent molten-metal brittle crack resistance, without involving a restriction on the kind of the steel of the plated base or a considerable increase in cost. [Solution] When a welded structural member is produced by bonding steel materials to each other by gas-shielded arc welding, a hot-dip Zn-Al-Mg-coated steel plate member is used as at least one of the members to be bonded and use is made of a shielding gas which comprises, as the base, Ar gas, He gas, or a gas mixture of Ar and He and which has been regulated so as to have a CO2 concentration CCO2 (vol%) that satisfies relationship (2) in accordance with the welding heat input Q (J / cm). 0<=CCO2<=2900Q-0.68 (2)

The purpose of another aspect of the present invention is to provide a high-strength steel having excellent brittle crack arrestability and welding part brittle crack initiation resistance, and a production method therefor. According to one aspect of the present invention, provided are a high-strength steel having excellent brittle crack arrestability and welding part brittle crack initiation resistance, and a production method therefor, the high-strength steel: comprising, in wt%, C: 0.05-0.09%, Mn: 1.5-2.2%, Ni: 0.3-1.2%, Nb: 0.005-0.04%, Ti: 0.005-0.04%, Cu: 0.1-0.8%, Si: 0.05-0.3%, Al: 0.005-0.05%, P: 100ppm or less, S: 40ppm or less, and a remainder made up by Fe and other inevitable impurities; having a center part microstructure comprising an acicular ferrite and granular bainite mixed-phase, upper bainite, and a remainder made up by one type or more selected from the group consisting of ferrite, pearlite, and a martensite-austenite (MA) constituent; having, in a 2mm or less subsurface region, a surface part microstructure comprising ferrite and a remainder made up by one type or more among bainite and martensite; and having a welding heat affected zone, which is formed during welding, that comprises, in area%, 5% or less of a martensite-austenite constituent. According to the present invention, high-strength steel having high yield strength, excellent brittle crack arrestability, and excellent welding part brittle crack initiation resistance may be obtained.

A welding method for manufacturing welded structures having excellent properties to prevent the propagation of brittle fracture occurring in welded joints, characterized by the step of forming a repair weld having a greater toughness than that of a butt weld and an outer edge whose angle φ with respect to the longitudinal direction of the butt weld is not less than 10 degrees and not more than 60 degrees, by applying repair welding to a region to arrest a brittle crack in a butt-welded joint where a brittle crack is likely to propagate after removing part of the butt-welded joint, in said region, by gouging or machining.