Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Hitoshi Nikaido

Koji Noguchi

Koichi Sato

Kengo Takeda

Hiroyuki Kawata

Takeshi Toyoda

Takafumi Yokoyama

Yoshihiro Serizawa

Toru Yonebayashi

Tooru Akashi

Noriyuki Hishinuma

Kazuki Matsuda

Takeo Itoh

Shingo Kuriyama

Teruo Ito

Daiki Kamada

Fuminori Tasaki

Kohei Nakada

Yui Yamashita

Hot-rolled steel sheet having a chemical composition including, in mass %, C: 0.02 to 0.20%, Si: 0.01 to 1.50%, Mn: 0.10 to 3.00%, P: 0.10% or less, S: 0.010% or less, Al: 0.005 to 0.100%, Ti: 0.02 to 0.20%, N: 0.001 to 0.010%, Cu: 0 to 0.50%, Ni: 0 to 0.50%, Cr: 0 to 1.00%, Mo: 0 to 0.40%, Nb: 0 to 0.060%, V: 0 to 1.00%, B: 0 to 0.0100%, Ca: 0 to 0.0050%, O: 0.0100% or less, and the balance: Fe and impurities; in which: a steel micro-structure includes, in area %, ferrite: 60 to 80%, and a total of ferrite and bainite: 90% or more; an average of the crystal grain size of ferrite and bainite is 7.0 μm or less, a standard deviation of the crystal grain size is 2.0 μm or less; and a standard deviation of a diameter of Ti carbo-nitrides is 10 nm or less.

Hot-rolled steel sheet and weld joint, and methods for producing same

Provided are: a steel sheet having a high strength and excellent stretch formability; and a method of producing the same. The steel sheet has prescribed chemical composition and structure, in which the integration degree of the (111)&#x3c;112&#x3e; orientation of ferrite is 3.0 or higher, and the integration degree of the (252)&#x3c;2-11&#x3e; orientation of martensite and tempered martensite is 5.0 or lower. The method of producing the steel sheet includes: the step of continuously casting a molten steel having the prescribed chemical composition, and performing 5 to 40% rolling reduction at a temperature of 800&#xb0; C. to lower than 1,200&#xb0; C. in a period after the continuous casting until cooling to room temperature; the hot rolling step of performing hot rolling with a finishing temperature of 650 to 950&#xb0; C.; the step of coiling the resulting hot-rolled steel sheet at a coiling temperature of 400 to 700&#xb0; C.; the step of retaining the hot-rolled steel sheet at (coiling start temperature+20&#xb0; C. to 100&#xb0; C.) for 5 to 300 minutes; the step of cold rolling the hot-rolled steel sheet at a rolling reduction ratio of 10.0 to 90.0%; and the step of annealing the resulting cold-rolled steel sheet at 700 to 900&#xb0; C.

Steel sheet and method of producing same

A method for producing a metal sheet with raised lines uses a rolling mill including roll stands. In a preparing step, a grooved roll is prepared, the grooved roll including grooves. In a choosing step, a stand at least one stage before the last stand is chosen. In an incorporating step, the grooved roll is incorporated in as an upper roll of the chosen, specified stand. In a forming step, a workpiece is formed into a metal sheet with raised lines formed corresponding to the respective grooves. In the forming step, a maximum rolling reduction achieved by rolls of the specified stand is set to a provisional value that is lower than a required value. After the leading edge of the workpiece reaches the stand next to the specified stand, the maximum rolling reduction of the specified stand is changed to the required value.

Method for producing metal sheet with raised lines, metal sheet with raised lines, and structural component

A water-blocking apparatus for cooling water for a hot-rolled steel sheet according to the present invention, which blocks cooling water sprayed onto a hot-rolled steel sheet at a sprayed water density of higher than 4 m/m/min and equal to or less than 10 m/m/min when the hot-rolled steel sheet is cooled after finish rolling of a hot-rolling process, includes: a plurality of water-blocking nozzles which spray water-blocking water onto the hot-rolled steel sheet. Impact areas of the water-blocking water respectively sprayed from the water-blocking nozzles are continuously lined up in a straight line in a width direction of the hot-rolled steel sheet on a surface of the hot-rolled steel sheet and the adjacent impact areas partially overlap.

Water-blocking apparatus and water-blocking method for cooling water for hot-rolled steel sheet

The method for cooling a hot-rolled steel sheet of the invention includes a target ratio-setting process in which a top and bottom heat transfer coefficient ratio X1, at which a temperature standard deviation Y becomes a minimum value Ymin, is set as a target ratio Xt based on correlation data between a top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet and the temperature standard deviation Y of the hot-rolled steel sheet; and a cooling control process in which at least one of an amount of heat dissipated from a top surface by cooling and an amount of heat dissipated from a bottom surface by cooling of the hot-rolled steel sheet in the cooling section is controlled so that the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet in the cooling section matches the target ratio Xt.

Method for cooling hot-rolled steel sheet

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Tokyo, Japan

Hitoshi Nikaido