Abstract: A steel for welding includes steel components in which PCTOD is less than or equal to 0.065%, CeqH is less than or equal to 0.225%, FB is greater than or equal to 0.0003%, and Bp is 0.09% to 0.30%. In the steel for welding, in a thickness center portion of a cross-section in a thickness direction, the number of oxide particles having an equivalent circle diameter of 2 ?m or greater is less than or equal to 20 particles/mm2 and the number of Ti oxides having an equivalent circle diameter of 0.05 ?m to 0.5 ?m is 1.0×103 particles/mm2 to 1.0×105 particles/mm2.

Abstract: A steel for a welded structure includes the following composition: by mass %, C at a C content [C] of 0.010 to 0.065%; Si at a Si content [Si] of 0.05 to 0.20%; Mn at a Mn content [Mn] of 1.52 to 2.70%; Ni at a Ni content [Ni] of 0.10% to 1.50%; Ti at a Ti content [Ti] of 0.005 to 0.015%; O at an O content [O] of 0.0010 to 0.0045%; N at a N content [N] of 0.002 to 0.006%; Mg at a Mg content [Mg] of 0.0003 to 0.003%; Ca at a Ca content [Ca] of 0.0003 to 0.003%; and the balance composed of Fe and unavoidable impurities. A steel component parameter PCTOD is 0.065% or less, and a steel component hardness parameter CeqH is 0.235% or less.

Abstract: A steel for welding includes steel components in which PCTOD is less than or equal to 0.065%, CeqH is less than or equal to 0.225%, FB is greater than or equal to 0.0003%, and Bp is 0.09% to 0.30%. In the steel for welding, in a thickness center portion of a cross-section in a thickness direction, the number of oxide particles having an equivalent circle diameter of 2 ?m or greater is less than or equal to 20 particles/mm2 and the number of Ti oxides having an equivalent circle diameter of 0.05 ?m to 0.5 ?m is 1.0×103 particles/mm2 to 1.0×105 particles/mm2.

Abstract: A steel for a welded structure includes the following composition: by mass %, C at a C content [C] of 0.015 to 0.045%; Si at a Si content [Si] of 0.05 to 0.20%; Mn at a Mn content [Mn] of 1.5 to 2.0%; Ni at a Ni content [Ni] of 0.10 to 1.50%; Ti at a Ti content [Ti] of 0.005 to 0.015%; O at an O content [O] of 0.0015 to 0.0035%; and N at a N content [N] of 0.002 to 0.006%, and a balance composed of Fe and unavoidable impurities. In the steel for a welded structure, the P content [P] is limited to 0.008% or less, the S content [S] is limited to 0.005% or less, the Al content [Al] is limited to 0.004% or less, the Nb content [Nb] is limited to 0.005% or less, the Cu content [Cu] is limited to 0.24% or less, the V content [V] is limited to 0.020% or less, and a steel composition parameter PCTOD is 0.065% or less, and a steel composition hardness parameter CeqH is 0.235% or less.

Abstract: A steel for a welded structure includes the following composition: by mass %, C at a C content [C] of 0.015 to 0.045%; Si at a Si content [Si] of 0.05 to 0.20%; Mn at a Mn content [Mn] of 1.5 to 2.0%; Ni at a Ni content [Ni] of 0.10 to 1.50%; Ti at a Ti content [Ti] of 0.005 to 0.015%; O at an O content [O] of 0.0015 to 0.0035%; and N at a N content [N] of 0.002 to 0.006%, and a balance composed of Fe and unavoidable impurities. In the steel for a welded structure, the P content [P] is limited to 0.008% or less, the S content [S] is limited to 0.005% or less, the Al content [Al] is limited to 0.004% or less, the Nb content [Nb] is limited to 0.005% or less, the Cu content [Cu] is limited to 0.24% or less, the V content [V] is limited to 0.020% or less, and a steel composition parameter PCTOD is 0.065% or less, and a steel composition hardness parameter CeqH is 0.235% or less.

Abstract: The present invention provides a high strength steel having unprecedentedly superior CTOD (fracture toughness) properties satisfying not only the CTOD properties of the FL zone at ?60° C., but also the CTOD properties of the ICHAZ zone in small and medium heat input multilayer welding, etc.; and a method of production of the same. The steel of the present invention is steel superior in CTOD properties of the heat-affected zone containing, by mass %, C: 0.015 to 0.045%, Si: 0.05 to 0.2%, Mn: 1.5 to 2.0%, Cu: 0.25 to 0.5%, Ni: 0.7 to 1.5%, P: 0.008% or less, S: 0.005% or less, Al: 0.004% or less, Ti: 0.005 to 0.015%, Nb: 0.005% or less, O: 0.0015 to 0.0035%, and N: 0.002 to 0.006%, PCTOD: 0.065 or less, CeqH: 0.235 or less and the balance consisting of Fe and unavoidable impurities.

Abstract: A steel for a welded structure includes the following composition: by mass %, C at a C content [C] of 0.010 to 0.065%; Si at a Si content [Si] of 0.05 to 0.20%; Mn at a Mn content [Mn] of 1.52 to 2.70%; Ni at a Ni content [Ni] of 0.10% to 1.50%; Ti at a Ti content [Ti] of 0.005 to 0.015%; 0 at an O content [O] of 0.0010 to 0.0045%; N at a N content [N] of 0.002 to 0.006%; Mg at a Mg content [Mg] of 0.0003 to 0.003%; Ca at a Ca content [Ca] of 0.0003 to 0.003%; and the balance composed of Fe and unavoidable impurities. A steel component parameter PCTOD is 0.065% or less, and a steel component hardness parameter CeqH is 0.235% or less.

Abstract: A method of production of 780 MPa class high strength steel plate excellent low temperature toughness comprising heating a steel slab of containing, by mass %, C: 0.06 to 0.15%, Si: 0.05 to 0.35%, Mn: 0.60 to 2.00%, P: 0.015% or less, S: 0.015% or less, Cu: 0.1 to 0.5%, Ni: 0.1 to 1.5%, Cr: 0.05 to 0.8%, Mo: 0.05 to 0.6%, Nb: less than 0.005%, V: 0.005 to 0.060%, Ti: less than 0.003%, Al: 0.02 to 0.10%, B: 0.0005 to 0.003%, and N: 0.002 to 0.006% to 1050° C. to 1200° C. in temperature, hot rolling ending at 870° C. or more, waiting for 10 seconds to 90 seconds, then cooling from 840° C. or more in temperature by a 5° C./s or more cooling rate to 200° C., then tempering at 450° C. to 650° C. in temperature for 20 minutes to 60 minutes.

Abstract: The present invention provides a high strength thick steel plate for marine structures superior in weldability and low temperature toughness of the HAZ, which is able to be produced at a low cost without use of a complicated method of production, and a method of production of the same, that is, steel for welded structures excellent in low temperature toughness of the weld heat affected zone and a method of production of the same characterized by casting molten steel containing, by mass %, C: 0.03 to 0.12%, Si: 0.05 to 0.30%, Mn: 1.2 to 3.0%, P: 0.015% or less, S: 0.001 to 0.015%, Cu+Ni: 0.10% or less, Al: 0.001 to 0.050%, Ti: 0.005 to 0.030%, Nb: 0.005 to 0.10%, and N: 0.0025 to 0.0060% by the continuous casting method, making the cooling rate from near the solidification point to 800° C. in the secondary cooling at that time 0.06 to 0.6° C./s, hot rolling the obtained slab, and cooling it from a temperature of 800° C. or more.

Abstract: A method of production of 780 MPa class high strength steel plate excellent low temperature toughness comprising heating a steel slab of containing, by mass %, C: 0.06 to 0.15%, Si: 0.05 to 0.35%, Mn: 0.60 to 2.00%, P: 0.015% or less, S: 0.015% or less, Cu: 0.1 to 0.5%, Ni: 0.1 to 1.5%, Cr: 0.05 to 0.8%, Mo: 0.05 to 0.6%, Nb: less than 0.005%, V: 0.005 to 0.060%, Ti: less than 0.003%, Al: 0.02 to 0.10%, B: 0.0005 to 0.003%, and N: 0.002 to 0.006% to 1050° C. to 1200° C. in temperature, hot rolling ending at 870° C. or more, waiting for 10 seconds to 90 seconds, then cooling from 840° C. or more in temperature by a 5° C./s or more cooling rate to 200° C., then tempering at 450° C. to 650° C. in temperature for 20 minutes to 60 minutes.

Abstract: The present invention provides high strength steel having unprecedentedly superior CTOD (fracture toughness) properties satisfying not only the CTOD properties of the FL zone at ?60° C., but also the CTOD properties of the ICHAZ zone in small and medium heat input multilayer welding etc. and a method of production of the same. The steel of the present invention is steel superior in CTOD properties of the heat-affected zone containing, by mass %, C: 0.015 to 0.045%, Si: 0.05 to 0.2%, Mn: 1.5 to 2.0%, Cu: 0.25 to 0.5%, Ni: 0.7 to 1.5%, P: 0.008% or less, S: 0.005% or less, Al: 0.004% or less, Ti: 0.005 to 0.015%, Nb: 0.005% or less, 0: 0.0015 to 0.0035%, and N: 0.002 to 0.006%, PCTOD: 0.065 or less, CeqH: 0.235 or less and the balance consisting of Fe and unavoidable impurities.

Abstract: The present invention provides a high strength thick steel plate for marine structures superior in weldability and low temperature toughness of the HAZ, which is able to be produced at a low cost without use of a complicated method of production, and a method of production of the same, that is, steel for welded structures excellent in low temperature toughness of the weld heat affected zone and a method of production of the same characterized by casting molten steel containing, by mass%, C: 0.03 to 0.12%, Si: 0.05 to 0.30%, Mn: 1.2 to 3.0%, P: 0.015% or less, S: 0.001 to 0.015%, Cu+Ni: 0.10% or less, Al: 0.001 to 0.050%, Ti: 0.005 to 0.030%, Nb: 0.005 to 0.10%, and N: 0.0025 to 0.0060% by the continuous casting method, making the cooling rate from near the solidification point to 800° C. in the secondary cooling at that time 0.06 to 0.6° C./s, hot rolling the obtained slab, and cooling it from a temperature of 800° C. or more.

Abstract: A wire for gas metal arc welding containing 0.01 to 0.06 wt % of C, 0.10 to 0.60 wt % of Si, 0.9 to 3.1 wt % of Mn, 0.7 to 2.0 wt % of Cr, 0.005 to 0.06% of Ti, not greater than 0.08 wt % of Al and if necessary, 0.05 to 0.30 wt % of Cu, and the balance of Fe and unavoidable impurities. This wire improves the selective corrosion resistance and the low temperature toughness of the resulting weld metal, and is particularly suitable for circumferential welding of line pipes for transporting CO.sub.2 -containing petroleum, natural gases or CO.sub.2.

Abstract: A method for manufacturing high tensile-high toughness steel plate, which the first step 15 preparing a steel slab or ingot consisting essentially, by weight, of0.03 to 0.20% C0.01 to 0.70% Si0.50 to 1.80% Mnlesser concentrations of titanium, zirconium, and mobium, and balac iron.The second step is rolling the slab or ingot with an accumulated rolling reduction of at least 30% in a temperature range between (Ar.sub.3 +150.degree. C.) and Ar.sub.3 in a cooling after casting, or in another cooling after reheating a cold steel slab in a temperature range between 1000.degree. C. and 1300.degree. C.The third step is quenching the rolled steel from a temperature not less than (Ar.sub.3 -30.degree. C.) within a period of time in which neither recovering nor recrystallization substantially occur.The fourth step is tempering at a temperature of not higher than Ac.sub.1.