Abstract: A part of a plate member is machined to remove material therefrom so as to obtain an intermediate product having a thickness difference. Then, the intermediate product is bent and both edges thereof are joined to obtain a cylindrical body. Further, a first heat treatment of heating the cylindrical body is performed. Then, through holes penetrating from the outside to the inside of the peripheral wall of the cylindrical body are formed. Pipe parts are joined to the tubular body thus obtained to form a tubular member. This tubular member is subjected to a second heat treatment.

Abstract: Continuous casting mold is provided having a mold copper plate having plural separate portions filled with foreign metal formed by filling concave grooves formed on the inner wall surface of the mold copper plate and having a diameter of 2 mm to 20 mm in the inner wall surface at least in the region from a meniscus to a position located 20 mm or more lower than the meniscus with the foreign metal whose thermal conductivity is 80% or less or 125% or more of the mold copper plate, the ratio of the Vickers hardness HVc of the mold copper plate to the Vickers hardness HVm of the filling metal satisfies expression (1), and the ratio of the thermal expansion coefficient ?c of the mold copper plate and the thermal expansion coefficient ?m of the filling metal satisfies expression (2). 0.3?HVc/HVm?2.3??(1), 0.7??c/?m?3.

Abstract: In a method for oxygen-blowing refining of molten iron, an oxygen-containing gas as a main supply gas is supplied from an inlet side of a blowing nozzle for the oxygen-containing gas passing through an outer shell of the top-blowing lance and blown from the blowing nozzle while a control gas is jetted toward inside of the blowing nozzle for at least part of a period of the oxygen-blowing refining from a spout arranged in a side face of the nozzle at a site where the cross-sectional area of the nozzle minimum takes the minimum in the axial direction of the nozzle or a neighborhood thereof so that at least part of the spout exists in each space formed by dividing into two portions by an arbitrary plane passing through a central axis of the nozzle.

Abstract: A part of a plate member is machined to remove material therefrom so as to obtain an intermediate product having a thickness difference. Then, the intermediate product is bent and both edges thereof are joined to obtain a cylindrical body. Further, a first heat treatment of heating the cylindrical body is performed. Then, through holes penetrating from the outside to the inside of the peripheral wall of the cylindrical body are formed. Pipe parts are joined to the tubular body thus obtained to form a tubular member. This tubular member is subjected to a second heat treatment.

Abstract: When the decarburization refining of molten iron is performed by top-blowing oxygen gas from the top blowing lance, the oscillation of molten iron, a bubble burst, and spitting due to the bubble burst are suppressed. A refining method for a converter includes decarburizing molten iron in the converter with a top blowing lance having Laval nozzles disposed at the lower end thereof by blowing oxygen gas on the surface of the molten iron in the converter through the Laval nozzles, in which one or both of an oxygen feeding rate from the top blowing lance and lance height LH are adjusted in such a manner that an oxygen accumulation index S(F) is 40 or less.

Abstract: A continuous casting mold including a water-cooled copper mold having a mold copper plate including an inner wall surface, recessed portions disposed partially or entirely in a region of the inner wall surface of the water-cooled copper mold from at least a position located at a meniscus to a position located 20 mm lower than the meniscus, and material-filled layers disposed in the recessed portions with a metal or nonmetal having a thermal conductivity different from that of the mold copper plate of the water-cooled copper mold. A shape of each of the recessed portions at a surface of the mold copper plate includes a curved surface.

Abstract: A continuous steel casting method includes producing a strand. The producing of the strand includes pouring molten steel into a mold of a continuous casting machine and withdrawing a solidified shell from the mold, the solidified shell being a solidified portion of the molten steel. The method includes applying a static magnetic field to at least a portion of a region of the strand, the strand being in the continuous casting machine, the region being a region where a solid fraction fs at a thickness-wise middle position of the strand is in a given range, the static magnetic field having a magnetic field strength of greater than or equal to 0.15 T and being in a direction orthogonal to a direction in which the strand is withdrawn, the static magnetic field being applied at an application time ratio of greater than or equal to 10%.

Abstract: In a method for oxygen-blowing refining of molten iron, an oxygen-containing gas as a main supply gas is supplied from an inlet side of a blowing nozzle for the oxygen-containing gas passing through an outer shell of the top-blowing lance and blown from the blowing nozzle while a control gas is jetted toward inside of the blowing nozzle for at least part of a period of the oxygen-blowing refining from a spout arranged in a side face of the nozzle at a site where the cross-sectional area of the nozzle minimum takes the minimum in the axial direction of the nozzle or a neighborhood thereof so that at least part of the spout exists in each space formed by dividing into two portions by an arbitrary plane passing through a central axis of the nozzle.

Abstract: A high strength steel sheet having excellent surface quality and formability with a tensile strength of 980 MPa or more and a TS-El balance of 30000 MPa % or more is provided. A high strength steel sheet comprises: a chemical composition containing C: 0.08% to 0.30%, Si: 2.0% or less, Mn: more than 3.0% and 10.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 1.5% or less, Ti: 0.010% to 0.300%, and N: 0.0020% to 0.0100% in a range satisfying 1.1?(Ti+Mn1/2/400)/(0.01+5N)?6.0; and a microstructure including a retained austenite phase and a ferrite phase, wherein a ratio ?Mn/?Mn of an average Mn concentration (?Mn) of the retained austenite phase to an average Mn concentration (?Mn) of the ferrite phase is 1.5 or more.

Abstract: A continuous casting mold according to the present invention has plural separate portions filled with a metal of low thermal conductivity formed by filling a metal having a thermal conductivity of 30% or less of that of copper into circular concave grooves having a diameter of 2 to 20 mm which are formed in the region of the inner wall surface of the copper mold from an arbitrary position higher than a meniscus to a position 20 mm or more lower than the meniscus, in which the filling thickness of the metal in the portions filled with the metal of low thermal conductivity is equal to or less than the depth of the circular concave grooves and satisfies the relationship with the diameter of the portions filled with the metal of low thermal conductivity expressed by expression (1) below: 0.5?H?d??(1).

Abstract: A molten steel refining method includes throwing a powder to molten steel while heating the powder with a flame formed by combustion of a hydrocarbon gas at the leading end of a top blowing lance. The lance height of the top blowing lance (the distance between the static bath surface of the molten steel and the leading end of the lance) is controlled to 1.0 to 7.0 m, and the dynamic pressure P of a jet flow ejected from the top blowing lance calculated from equation (1) below is controlled to 20.0 kPa or more and 100.0 kPa or less. P=?g× U2/2 . . . (1) wherein P is the dynamic pressure (kPa) of the jet flow at an exit of the top blowing lance, ?g the density (kg/Nm3) of the jet flow, and U the velocity (m/sec) of the jet flow at the exit of the top blowing lance.

Abstract: When the decarburization refining of molten iron is performed by top-blowing oxygen gas from the top blowing lance, the oscillation of molten iron, a bubble burst, and spitting due to the bubble burst are suppressed. A refining method for a converter includes decarburizing molten iron in the converter with a top blowing lance having Laval nozzles disposed at the lower end thereof by blowing oxygen gas on the surface of the molten iron in the converter through the Laval nozzles, in which one or both of an oxygen feeding rate from the top blowing lance and lance height LH are adjusted in such a manner that an oxygen accumulation index S(F) is 40 or less.

Abstract: A continuous casting mold including a water-cooled copper mold having a mold copper plate including an inner wall surface, recessed portions disposed partially or entirely in a region of the inner wall surface of the water-cooled copper mold from at least a position located at a meniscus to a position located 20 mm lower than the meniscus, and material-filled layers disposed in the recessed portions with a metal or nonmetal having a thermal conductivity different from that of the mold copper plate of the water-cooled copper mold. A shape of each of the recessed portions at a surface of the mold copper plate includes a curved surface.

Abstract: Conditions for soft reduction are determined in a method of continuous casting in accordance with a method utilizing the thickness of a slab strand to prevent center segregation from occurring in the strand due to an insufficient pressing rate or internal cracks from occurring in the strand due to an excessively high pressing rate.

Abstract: A continuous steel casting method includes producing a strand. The producing of the strand includes pouring molten steel into a mold of a continuous casting machine and withdrawing a solidified shell from the mold, the solidified shell being a solidified portion of the molten steel. The method includes applying a static magnetic field to at least a portion of a region of the strand, the strand being in the continuous casting machine, the region being a region where a solid fraction fs at a thickness-wise middle position of the strand is in a given range, the static magnetic field having a magnetic field strength of greater than or equal to 0.15 T and being in a direction orthogonal to a direction in which the strand is withdrawn, the static magnetic field being applied at an application time ratio of greater than or equal to 10%.

Abstract: Provided is a continuous casting method of steel that prevents a solidification completion position from being changed even when a drawing speed V of a cast slab is changed. The method includes drawing a cast slab by setting a drawing speed V0 while spraying cooling water to the cast slab at a cooling water spray amount W0 [kg/ton-cast slab]. Then, changing the drawing speed to the speed V1 while spraying cooling water to the cast slab at a cooling water spray amount W1 [kg/ton-cast slab]. The method further includes spraying cooling water to the cast slab at a cooling water spray amount Wt [kg/ton-cast slab] during a period of time t that is obtained by dividing a target length Lt by the drawing speed V0. The water spray amount Wt satisfying either formula (1): Wt<W1 under a condition of V1<V0, or formula (2): Wt>W1 under a condition of V1>V0.

Abstract: A molten steel refining method includes throwing a powder to molten steel while heating the powder with a flame formed by combustion of a hydrocarbon gas at the leading end of a top blowing lance. The lance height of the top blowing lance (the distance between the static bath surface of the molten steel and the leading end of the lance) is controlled to 1.0 to 7.0 m, and the dynamic pressure P of a jet flow ejected from the top blowing lance calculated from equation (1) below is controlled to 20.0 kPa or more and 100.0 kPa or less. P=?g× U2/2 . . . (1) wherein P is the dynamic pressure (kPa) of the jet flow at an exit of the top blowing lance, ?g the density (kg/Nm3) of the jet flow, and U the velocity (m/sec) of the jet flow at the exit of the top blowing lance.

Abstract: A high strength steel sheet having excellent surface quality and formability with a tensile strength of 980 MPa or more and a TS-El balance of 30000 MPa % or more is provided. A high strength steel sheet comprises: a chemical composition containing C: 0.08% to 0.30%, Si: 2.0% or less, Mn: more than 3.0% and 10.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 1.5% or less, Ti: 0.010% to 0.300%, and N: 0.0020% to 0.0100% in a range satisfying 1.1?(Ti+Mn1/2/400)/(0.01+5N)?6.0; and a microstructure including a retained austenite phase and a ferrite phase, wherein a ratio ?Mn/?Mn of an average Mn concentration (?Mn) of the retained austenite phase to an average Mn concentration (?Mn) of the ferrite phase is 1.5 or more.

Abstract: A method of producing a steel material includes a step of adding Ca to molten steel with an amount of Ca adjusted within a range satisfying the formula (1) below: 0.5 ? { Ca · y ? / ? 100 - ( [ S · W ? / ? 100 ) · 40.08 ? / ? 32.07 } ? 56.08 40.08 ( [ Al 2 ? O 3 ] · W ? / ? 100 ) ? 1.5 ( 1 ) where Ca is the amount [kg] of Ca added, y is an yield [%] of Ca, [S] is a concentration [% by mass] of S in the steel before addition of Ca, [Al2O3] is an amount [% by mass] of Al2O3 in the steel before addition of Ca, and W is a weight [kg] of the molten steel.

Abstract: A method for refining hot metal in a converter using a top-blowing lance having a refining powder supply channel, a combustion oxidizing gas supply channel, and a refining oxidizing gas supply channel that are separate from each other includes supplying at least one of a lime-based flux, iron oxide, and a combustible material as a refining powder from the refining powder supply channel to a surface of the hot metal using a fuel gas or a mixture of the fuel gas and an inert gas as a carrier gas while supplying a combustion oxidizing gas from the combustion oxidizing gas supply channel to form a flame below a leading end of the top-blowing lance, and supplying a refining oxidizing gas from the refining oxidizing gas supply channel to the surface of the hot metal.