123 results about "Brittle crack" patented technology

This present invention relates to 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 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.

Provided are a high strength steel plate having excellent brittle crack arrestability and a method for manufacturing the same. A steel plate, which contains C, Si, Mn, Al, P, S and N each in a definite amount, satisfies the requirement Ceq (=C+Mn/6+(Cu+Ni)/15+(V+Mo+Cr)/5) being 0.34-0.49% inclusive, and may further contain, if required, one or more members selected from among Nb, Ti, Cu, Ni, Cr, Mo, V, Ca, B and REM, wherein a region with an aggregate tissue, said region having an X-ray diffraction intensity ratio according to plane (211) in a plane parallel to the surface of the steel plate of 1.0 or greater, is disposed within at least 1/3 of the sheet thickness including the central part of the sheet thickness, the bainite fraction at the central part of the sheet thickness is 80% or greater, and the Charpy fracture transition temperature at a position of 1/4 of the sheet thickness is -40 DEG C or lower. The method according to the present invention comprises hot rolling a steel material in such a manner that the cumulative rolling reduction ratio is at least 50% within a temperature range at the central part of the sheet thickness from (Ar3+60) DEG C to Ar3 inclusive, and then cooling to 450 DEG C or lower at a cooling speed of 4.0 DEG C/s or higher.

The invention provides a steel sheet which has the characteristics of low manufacturing cost, high production efficiency, base metal brittle crack propagation stop performance and excellent tenacity of a welding heat affected zone in high heat input welding. The steel sheet has prescribed chemical components: 0.30-0.40 mass% of a carbon equivalent, and -0.0015-+0.0015 mass% of SOLB. At 1/2 part of a sheet thickness, the weighted average DAVE of a grain size of a grain is 3.0-17.0 [mu] m; at 1/2 part of a sheet thickness, the weighted average DAVE of a grain size of a grain is 3.0-17.0 [mu] m; the area percentage of a surface (100) forming a angle within 15 DEG relative to a surface in a rolling direction is 2.0-20.0%; at 1/4 part of a sheet thickness, the total number density of circle diameter TiN particles, MnS particles and composite particles with 0.5-2.0 [mu] m equivalents is 20-200/mm2; at 1/4 part of a sheet thickness, the number density of circle diameter oxide particle with 1-10 [mu] m equivalents is 20-200/mm2, the sheet thickness being 10-35mm, and the yield stress being 300-500 MPa.

The invention discloses a production method of microalloyed tin bronze alloy. The production method of the microalloyed tin bronze alloy includes the steps of firstly, subjecting alloy to smelting, thermal insulation, degassing, deslagging and refining in a smelting furnace; secondly, adding refiner to refined melt for microalloying; thirdly, performing alloy casting, namely subjecting the microalloyed melt to ingot casting; and fourthly, performing cold rolling and cogging, namely subjecting the alloy subjected to alloy casting to cold rolling so as to obtain deformed tin bronze alloy. Casting grain of the microalloyed tin bronze alloy produced by the production method is small in size, segregation degree of Sn in the alloy can be lowered, brittle cracking in rolling can be eliminated, and the alloy is highly plastic. Especially, the microalloyed castings can be directly subjected to cold rolling, and accordingly a homogenizing step in the existing production method is omitted, energy resources are economized, process flow is shortened, production efficiency is improved, and production cost is reduced.

Provided is a welded structure suitable for a hull structure and excellent in brittle-cracking propagation stopping characteristics. The welded structure is provided with a fillet welded joint having an unwelded portion (4) left on the abutting face of a web (1) against a flange (2). A percentage (X) (= 100/L) (%) to the sum (L) of the width (n) of the unwelded portion (4) and the leg length (3 (3a and 3b)) of the left and right fillet welded joints in the joint section of the fillet welded joint, and the brittle-cracking propagation stopping toughness (Kca (N/mm3/2)) at the using temperature of the flange satisfy X (%) >= {5900 - Kca(N/mm3/2/85. The unwelded portion (4) in the fillet-welded joints is given a width of 15 to 90 % of the sum of the thickness (t) of the web (1) and the leg length (3 (3a and 3b)) of the left and right fillet welded joints. In case the web has the butt-welded joint portion of the thickness (t), the percentage (X) (%) and the brittle-cracking propagation stopping toughness (Kca)(N/mm3/2) satisfy the aforementioned formula.

Disclosed is a method for determining the brittle crack propagation stopping performance of a high-intensity thick steel plate, comprising: a step of performing a large test and a compound small test using standard steel; a step of calculating a correlation model between the results of the large test and the results of the compound small test using the standard steel; a step of performing the compound small test using sample steel; and a step of estimating the brittle crack propagation stopping performance of the sample steel by substituting the results of the compound small test using the sample steel into the correlation model, wherein the compound small test includes (a) a step of obtaining a surface layer small test piece which includes a portion of the steel plate surface layer; (b) a step of obtaining an inner small test piece respectively from one or no less than two inner regions which do not include the portion of the steel surface layer; (c) a step of performing a drop weight test using the surface layer small test piece; and (d) a step of performing a small test for measuring the percent brittle fracture or the absorption energy using the inner small test piece; and thecompound small test is performed in different fashions for the surface layer small test piece and the inner small test piece respectively.

The invention provides a T shape welded joint structure which is formed by jointing a vertical component and a horizontal component, the vertical component is formed by butt welding with high strength steel plate and the horizontal component is formed by butt welding with high strength steel plate. The structure is charactered in that position of a welding line of the vertical component on the T shape welded joint structure extended direction is inconsistent with position of a welding line of the horizontal component on the T shape welded joint structure extended direction, and the high strength steel plate constituting the horizontal component satisfies (1) Kca value for representing fracture-arrest characteristic that is more than 7000N/mm<3/2> at -10 DEG C., (2) average pendulum absorbing energy value is more than 70J at -100 DEG C. in plate thickness direction 1/2. Brittle crack transmission can be prevented efficiently by using the structure, even if brittle failure generates on large heat quality importing welding part.

The present invention pertains to a welding structure provided with a fillet welded joint obtained by bringing the weld end surface of a joining member into contact with the weld surface of a butt weld joint of a joined member, both members having a plate thickness of at least 50 mm, and joining the joining member and the joined member by fillet welding. The weld leg length and/or the welding width of the fillet welded joint are 16 mm or less. The welding metal in the butt weld joint of the joining member and/or the joined member is set at -65 °C at vTrs-W (°C), and/or a toughness of at least 140 J is set at vE-20-W (J). A non-welded section exists on the surface where the joining member and joined member are brought into contact, where the cross section of the butt weld joint of the fillet welded joint is no less than 95% of the plate thickness (tw) of the joining member. By satisfying a predetermined relationship between vTrs (°C) and/or vE-20 (J) of the fillet welded metal, and the plate thickness (tf) of the joined member, the propagation of brittle cracks is prevented before said cracks lead to large-scale destruction.

Provided are: a high-strength thick steel plate for construction having excellent characteristics for preventing the diffusion of brittle cracks, said plate being used for ships and having a preferred plate thickness of at least 50 mm; and a method for producing the thick steel plate. The thick steel plate has excellent characteristics for preventing the diffusion of brittle cracks, characterized in that: the thick steel sheet has a specific component composition; the main constituent of the metal structure is a ferrite phase; the thick metal sheet has an aggregate structure in which the density (I) in the RD//(110) plane at the plate thickness surface is at least 1.3, and the density (I) in the RD//(110) plane at the plate thickness center is at least 1.8; the Charpy fracture appearance transition temperature (vTrs) at the surface is not more than -60 DEG C, and the Charpy fracture appearance transition temperature (vTrs) at the plate thickness center is not more than -50 DEG C.

Disclosed is a multipass butt-welded joint of a steel sheet, which has excellent brittle crack propagation resistance. In the joint, one or more weld layers or welding passes are arranged between a front welding layer and a rear welding layer in a separately spaced state from each other, wherein each of the weld layers or the welding passes has different properties from those of the surrounding materials and can inhibit and terminate the propagation of a brittle crack.

Provided is a steel plate having excellent resistance to brittle crack initiation in a parent material zone and a weld heat affected zone. More particularly, the present invention relates to a high-strength steel sheet having excellent resistance to brittle crack initiation which includes 0.02 wt% to 0.06 wt% of carbon (C), 0.1 wt% or less of silicon (Si), 1.5 wt% to 2.0 wt% of manganese (Mn), 0.012 wt% or less of phosphorous (P), 0.003 wt% or less of sulfur (S), 0.5 wt% to 1.5 wt% of nickel (Ni), 0.003 wt% to 0.015 wt% of aluminum (Al), 0.005 wt% to 0.02 wt% of titanium (Ti), 0.005 wt% to 0.015 wt% of niobium (Nb), 0.002 wt% to 0.006 wt% of nitrogen (N), and iron (Fe) as well as unavoidable impurities as a remainder, and has a value of C+0.5Si-0.1Ni+6Al+3Nb of 0.1% or less, and a method of manufacturing the high-strength steel sheet.

The invention provides a thick steel board excellent in brittle crack propagation-arresting property without causing increase in production cost. Even if the thickness of the steel board exceeds 50mm,the board still meets the requirement of high strength (tensile strength is over 490MPa), and Kca value under the temperature of -10 DEG C. is over 3500N/mm[3/2]. By appropriately modulating composition of chemical components, the thick steel board has an average area ratio of the quasi-polygonal ferrite of 30-85% in the microscopic constitution at the position t/4-t/2 deep from the surface, wherein t represents the thickness of the board.

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.

Provided are: a high-strength thick steel plate for construction having excellent characteristics for preventing the diffusion of brittle cracks, said plate being used for ships and having a preferred plate thickness of at least 50 mm; and a method for producing the thick steel plate. The thick steel plate has excellent characteristics for preventing the diffusion of brittle cracks, characterized in that: the main constituent of the metal structure is bainite; the steel plate has an aggregate structure in which the density (I) in the RD//(110) plane at the plate thickness center is at least 1.5; and the Charpy fracture appearance transition temperature (vTrs) at the surface and plate thickness center is not more than -40 DEG C. More preferably, the Charpy fracture appearance transition temperature (vTrs) at the plate thickness center, and the density (I) in the RD//(110) plane satisfy formula (1). vTrs(1/2t) - 12 IRD//(110)[1/2t] <= -70 ...(1), wherein, vTrs(1/2t) is the fracture appearance transition temperature at the plate thickness center ( DEG C), and IRD//(110)[1/2t] is the density in the RD//(110) plane at the plate thickness center.

Disclosed is a weld structure in which a steel plate weld joint is formed by butt-welding steel plates together, wherein: an anti-crack control section in which the propagation of brittle cracks generated in the steel plate weld joint are stopped is disposed on at least one section of the steel plate weld joint; and the outer peripheral section of an arrestor member configuring the anti-crack control section is formed on the front and rear of the steel plate weld joint in the lengthwise direction so as to intersect with the steel plate weld joint at an angle between 60 DEG to 120 DEG relative to the lengthwise direction. As a consequence, it is possible to prevent brittle cracks from propagating the weld joint or the base material even when brittle cracks form on the weld joint.

The present invention relates to a welded structure wherein steel plates having at least parts of the base metal with a brittle crack arrest toughness Kca of 4000 N/mm<1.5> or more are butt welded together so as to form a welded joint, wherein at least one location of the welded joint is provided with a crack control part comprising an arrester member comprising a steel material with a brittle crack arrest toughness Kca of 6000N/mm<1.5> or more and arrester welded joints (6) formed by the arrest member being butt welded to steel plates (1) and wherein outer edges of the arrester member are formed so as to slant from the weld line of the steel plate welded joint (2) by 15 DEG to 50 DEG with respect to the longitudinal direction of the welded joint.

Provided are high-strength steel having superior brittle crack arrestability and a production method therefor. The high-strength steel comprises 0.05-0.1 wt % of C, 0.9-1.5 wt % of Mn, 0.8-1.5 wt % of Ni, 0.005-0.1 wt % of Nb, 0.005-0.1 wt % of Ti, 0.1-0.6 wt % of Cu, 0.1-0.4 wt % of Si, at most 100 ppm of P, and at most 40 ppm of S with the remainder being Fe and other inevitable impurities, and has microstructures including one structure selected from the group consisting of a single-phase structure of ferrite, a single-phase structure of bainite, a complex-phase structure of ferrite and bainite, a complex-phase structure of ferrite and pearlite, and a complex-phase structure of ferrite, bainite, and pearlite. The high-strength steel has high yield strength and superior brittle crack arrestability.

Provided is a testing device and a method for evaluating long brittle crack arresting ability that is appropriate for an actual ship of thick steel plate (mainly thick steel plate having a thickness of at least 50 mm), the thick steel plate having excellent brittle crack arresting ability and being suitable for use in large container ships, bulk carriers, etc. When a tensile load is applied by a tensile tester in the direction perpendicular to the width of a large test sample having a width of at least 1.5 m, and long brittle crack arresting ability is evaluated for a long brittle crack of length 1 m or greater, a transmitting part for transmitting the tensile load from the tensile tester to the large test sample has thickened parts having a thickness at least 2.5 times that of the large test sample on either side of the center in the width of the large test sample spaced apart at least 2.8 times, preferably at least 4.1 times, the width of the large test sample, and the tensile load from the tensile tester is applied in positions on either side of the center of the large test sample in the direction perpendicular to the width by the thickened parts. A testing device having the transmitting part.

Provided are a high strength thick steel plate, which has superior brittle crack arrestability for high heat input welding that has a plate thickness of 50 mm or greater and is suitably used in marine vessels, and a manufacturing method for the same. The present invention is a thick steel plate and a manufacturing method for the same, wherein the thick steel plate has: a specific component composition, a metal structure composed mainly of ferrite, and an aggregate structure in which the density at the RD//(110) plane at the surface layer of the plate thickness is 1.3 or greater and the density at the RD//(110) plane in the center part of the plate thickness is 1.8 or greater. Charpy fracture appearance transition temperature (vTrs) is −50°C or less at the surface layer and in the center part of the plate thickness.