A hot-rolled steel sheet has a specified chemical composition and has such a steel structure that the area ratio of a ferrite is 5 to 50%, the area ratio of a bainite that is composed of an aggregate of a bainitic ferrite having an average crystal orientation difference of 0.4 to 3° is 50 to 95%, and the total area ratio of a martensite, a pearlite and a retained austenite is 5% or less.

Hot-rolled steel sheet

PROBLEM TO BE SOLVED: To provide a gas shielded arc welding method by which weld metal having a superior strength and toughness is obtained, even in multi-layer welding with high heat input and high interpass temperature, and by which improved weldability is demonstrated by reducing the mount of the occurrence of spatter and of formation of slag at welding SOLUTION: Welding is performed by using: a welding steel wire composed of a steel wire stock containing by mass 001-010% C, 02-12% Si, 10-25% Mn, 005-020% Ti, 0003-0020% S, ≤0020% P, 005-05% Mo, 005-03% Cr, ≤05% Cu, 0005-002% Al, and 00005-00050% B; and gaseous mixture containing 10-50 volume % Co 2 and 50-90 volume% Ar as a shielding gas, thereafter time required until the bead of the final pass is cooled from 800°C to 500°C is adjusted to 15-450 seconds COPYRIGHT: (C)2005,JPO&NCIPI

Gas-shielded arc welding method

Through the disclosed method, it is possible to obtain a highly ductile and high tensile strength high-strength steel sheet having a tensile strength of at least 1470 MPa and a tensile strength × total elongation of at least 29000 MPa · % by means of: a steel composition containing at least 0.30% and no more than 0.73% C, no more than 3.0% Si, no more than 3.0% Al, at least 0.7% Si+Al, at least 0.2% and no more than 8.0% Cr, no more than 10.0% Mn, at least 1.0% Cr+Mn, no more than 0.1% P, no more than 0.07% S, and no more than 0.010% N, the remainder being Fe and unavoidable impurities; and a steel structure of which the area ratio of martensite to the total steel sheet structure is 15-90% inclusive, the amount of residual austenite is 10-50% inclusive, at least 50% of said martensite is tempered martensite, the area ratio of said tempered martensite to the total steel sheet structure is at least 10%, and the area ratio of polygonal ferrite to the total steel sheet structure is 10% or less (including 0%).

High-strength steel sheet and method for producing same

In this study, a novel inter-pass cooling technology was applied during rough rolling (R-IPC) to process a 60 mm ultra-heavy EH47 steel plate with excellent toughness and ductility. The plate was compared to a plate processed through conventional thermo-mechanical controlled processing (TMCP). The microstructure evolution at 1/4-thickness and 1/2-thickness of the plates was studied, while the relationship between microstructure and mechanical properties, through tensile and Charpy V-notch impact toughness, was established. In this study, it was reported that the R-IPC steel deformation penetration was higher compared to the TMCP steel. The ferrite fractions of the R-IPC and TMCP steels were 47% and 10% at 1/4-thickness, as well as 35% and 0.5% at 1/2-thickness, while the acicular ferrite fractions at 1/2-thickness of the R-IPC and TMCP steels were 50% and 9.5%, respectively. The granular bainite width at 1/2-thickness of the R-IPC steel (14 ± 4 µm) was significantly lower than the TMCP steel (27 ± 10 µm). The M/A island volume fraction in R-IPC steel was higher than the TMCP steel at 1/4-thickness, whereas it was reduced dramatically at 1/2-thickness. The high intensity of the desired texture {112} was obtained at 1/2-thickness of the R-IPC steel, while the undesired {411} was obtained at 1/2-thickness of the TMCP steel, which was responsible for the R-IPC steel superior toughness compared to the TMCP steel. The tensile and yield strengths of the two rolled plates were similar, while the elongation at 1/4-thickness of the R-IPC steel was higher compared to the TMCP steel. The low temperature impact energy of the R-IPC steel was significantly higher compared to the TMCP steel, resulting from finer grain size, higher ferrite fraction and higher area of the {110} texture parallel to the impact direction.

Toughness and ductility improvement of heavy EH47 plate with grain refinement through inter-pass cooling

A seamless steel pipe comprises a specific carbide that has an equivalent carbon content (Ceq) of 0.50 to 0.58%, contains Mo in an amount of 50 mass% or more, contains V, additionally contains one or two components selected from the group consisting of Ti and Nb, and has a size of 20 nm or more.

Seamless steel pipe and method for producing same

PROBLEM TO BE SOLVED: To provide a thick steel plate for ultra-low temperature having brittle fracture occurrence suppression properties after strain aging at a low cost.SOLUTION: There are provided the thick steel plate for ultra-low temperature and a method for producing the thick steel plate which has excellent brittle fracture occurrence suppression properties after strain aging, and has a composition comprising, by mass%, 0.01 to 0.12% C, 0.01 to 0.3% Si, 0.4 to 2.0% Mn, ≤0.05 P, ≤0.008% S, >5.0 to <10.0% Ni, 0.002 to 0.05% Al and ≤0.005% N, and the balance Fe with impurities, wherein the amount of residual γ at the position of (1/4)t of the plate thickness is ≥3.0 vol.%, also, the average value of the diameters of the equivalent circle in a structural unit surrounded by high angle grain boundaries of ≥15° observed by an EBSP method at the magnification of 2,000 times is ≤5.5 μm at the position of (1/4)t of the plate thickness, and further, the average value GAM of misorientations between the adjoining measurement points in one crystal grain observed by an EBSP method at the magnification of 10,000 times is ≥0.85°.

Thick steel plate for ultra-low temperature and method for producing the same

PROBLEM TO BE SOLVED: To inexpensively provide a Ni reduced type thick steel plate for low temperature excelling in breakage resistant safety like 9% Ni steel even in a low-temperature environment.SOLUTION: This thick steel plate for low temperature excelling in breakage resistant safety contains, by mass%, 0.01-0.12% of C, 0.01-0.3% of Si, 0.4-2.0% of Mn, ≤0.05% of P, ≤0.008% of S, >5.0% and <8.0% of Ni, 0.002-0.08% of Al and ≤0.0050% of N, wherein the residual part comprises Fe and impurities; yield strength at ordinary temperature is ≥590 MPa; a residual γ quantity at a position of plate thickness of (1/4)t is ≥3.0 vol.%; an average effective crystal grain size is ≤5.5 μm; and a value represented by the following formula (1) is ≥1.3. This method of manufacturing the same is also provided. σ/σ(1), wherein σand σare yield strength [MPa] at -165°C and yield strength at ordinary temperature, respectively.

Thick steel plate for low temperature, and method of manufacturing the same

PROBLEM TO BE SOLVED: To provide a whose production on an industrial scale is facilitated, and having excellent ductile crack initiation resistance from the surface part, and suitably used for a ground structure field such as bridges and buildings applied with an earthquake load. SOLUTION: The high-tensile steel having excellent ductile crack initiation resistance has a composition containing 0.01 to 0.12% C, 0.05 to 0.5% Si, 0.4 to 2% Mn, ≤0.05% P, ≤0.003% S, 0.002 to 0.05% Al and 0.0015 to 0.01% N, and the balance Fe with impurities, and satisfying (Si/30)+(Mn/20)+(Cu/20)+(Ni/60)+(Cr/20)+(Mo/15)+(V/10)+5B≥0.08%, and, in the microstructure of the surface part in the steel, the fraction of ferrite is 10 to 40%, the fraction of bainite is ≥50%, and the average grain diameter is ≤5 μm. COPYRIGHT: (C)2008,JPO&INPIT

High-tensile steel having excellent ductile crack initiation resistance

PROBLEM TO BE SOLVED: To provide a thick steel plate having satisfactory HIC resistance and DWTT properties, and inexpensively producible by suppressing elevated energy cost.SOLUTION: The thick steel plate has a chemical composition containing, by mass, 0.01 to 0.17% C, 0.01 to 0.60% Si, 0.4 to 1.8% Mn, ≤0.02% P, ≤0.01% S, 0.001 to <0.01% Nb, 0.001 to 0.06% Al, ≤0.01% N, ≤0.005% O, and the balance Fe with impurities, wherein a value expressed by expression of [C+(Mn/5)+5P-(Ni/10)-(Mo/10)+(Cu/10)] is 0.25 to 0.65, and has a microstructure in which the ratio of bainite is ≥90%. The thick plate may further contains predetermined amounts of one or more selected from Cu, Cr, Mo, V, Ti, Ni, B, Ca, Mg and REM.

Thick steel plate having excellent hydrogen-induced cracking resistance and brittle crack arrest property

PROBLEM TO BE SOLVED: To provide a high strength steel having a tensile strength of ≥780 MPa and a yield ratio of ≤90%, and to provide a method for producing the same SOLUTION: The high tensile strength steel comprising, by mass, 002 to 02% C, 001 to 05% Si, 04 to 25% Mn, 01 to 1% Cr, 01 to 1% Mo, 001 to 0035% Ti, 00003 to 0005% B and 0001 to 01% Al, and the balance Fe with impurities in which the content of P is ≤005%, the content of S is ≤0008% and the content of N is ≤001%, also, the value expressed by the following formula (a) is ≤85, and the ratio of martensite is ≥80%: the formula (a) is 446+1086×Nb(%)+773×Ti(%)+244×(R Fe /C(%)); wherein the atomic symbol in the formula is the content (mass%) of the element; and R Fe is the content (mass%) of Fe present as precipitates measured by an extraction residue method The steel may contain one or more kinds selected from Nb, Cu, Ni, V, Ca, Mg, rare earth metals and Zr as well In the production method, specified slab heating temperature, quenching conditions and heat recuperating conditions are used COPYRIGHT: (C)2007,JPO&INPIT

友弥川畑

Papers

Thick steel plate for ultra-low temperature and method for producing the same

Thick steel plate for low temperature, and method of manufacturing the same

High-tensile steel having excellent ductile crack initiation resistance

Thick steel plate having excellent hydrogen-induced cracking resistance and brittle crack arrest property

High tensile strength steel having excellent plastic deformability after cold working, and method for producing the same

友弥 川畑

Papers

Thick steel plate for ultra-low temperature and method for producing the same

Thick steel plate for low temperature, and method of manufacturing the same

High-tensile steel having excellent ductile crack initiation resistance

Thick steel plate having excellent hydrogen-induced cracking resistance and brittle crack arrest property

High tensile strength steel having excellent plastic deformability after cold working, and method for producing the same

友弥川畑