Nkk Corporation

Jfe Steel Corporation

Other

Sadanori Imada

Yoichi Motoyashiki

Tadashi Inoue

Hiroyasu Kikuchi

Akio Fujibayashi

Yoshimichi Hino

Toru Minote

Toru Inazumi

Shozo Ikemune

Yasuhide Ishiguro

Yoshimasa Funakawa

Hiroshi Nakata

Akira Hiura

Takayuki Odake

Takeshi Nakahara

Satoshi Ishijima

A method for cooling a hot rolled steel strip including transferring a hot rolled steel strip while ejecting cooling water from a cooling means at a specified ejecting condition; pinching a top end of the hot rolled steel strip by a pinching roll, at the inlet of the cooling means and/or just behind the cooling means and/or at a position on the way of the cooling means; and releasing the hot rolled steel strip sequentially from a pinch roll arranged at an upstream side, concurrently with the arrival of a top end of the steel strip to a tension adding means arranged at a downstream side.

Method for cooling hot roller steel strip, and method for manufacturing hot rolled steel strip

An apparatus for cooling a hot rolled steel strip including a transfer means comprising transfer rolls to feed a steel strip which has been hot rolled by a finishing mill; a cooling means for cooling the steel strip; and accompanying rolls arranged with a clearance over the thickness of the steel strip at a position where the accompanying rolls face the transfer rolls through the steel strip to be transferred. The accompanying rolls rotate at nearly an equal peripheral speed as the transfer rolls or at a peripheral speed greater than the transfer speed of the steel strip.

Method and apparatus for cooling hot rolled steel strip, and method for manufacturing hot rolled steel strip

An apparatus for cooling a hot rolled steel strip comprising a transfer means arranged behind a final finishing mill, the transfer means comprising a plurality of transfer rolls for transferring the steel strip; at least one upper surface cooling means arranged at an upper surface side of the transfer means for cooling the steel strip by ejecting cooling water to an upper surface of the steel strip, the upper surface cooling means being capable of moving freely up and down and having a water breaking means at least at an outlet side of the cooling apparatus and at a position corresponding to the transfer rolls; and at least one lower surface cooling means arranged at a lower surface side of the transfer means relative to the upper surface cooling means and the steel strip to be transferred, for cooling the hot strip by ejecting cooling water at a lower surface of the steel strip.

A method for manufacturing a steel sheet comprising continuously casting a steel containing 0.04 to 0.2 wt. % C, 0.25 to 2 wt. % Si, 0.5 to 2.5 wt. % Mn, and 0.1 wt. % or less Al to form a slab; hot-rolling by rough-rolling the slab to form a sheet bar and finish-rolling the sheet bar with a reduction in thickness at the final stand of less than 30%, the finish-rolling being completed at a temperature from the Ar transformation point to the Ar transformation point &plus;60&deg; C.; primary-cooling the hot-rolled steel sheet, the primary cooling being started within 1 second after the completion of hot-rolling and conducting the cooling at a cooling speed of higher than 200&deg; C./sec down to a temperature of Ar &minus;30&deg; C. to the Ar transformation point; slow cooling or air-cooling the primary-cooled steel sheet at a temperature of the Ar transformation point to the Ar transformation point at 10&deg; C./sec or less for 2 seconds or more; secondary-cooling the steel sheet after the slow cooling or the air-cooling at 30&deg; C./sec or more; and coiling the secondary-cooled steel sheet at 300&deg; C. or less.

Method for manufacturing a steel sheet

A lower surface cooling box is arranged between transfer rolls on a runout table and an upper cooling box moving freely is arranged at a position corresponding to the cooling box to eject cooling water to the steel strip symmetrically in the vertical direction. The steel strip passes the center of converge of cooling water from upper and lower surfaces of the steel strip. A water breaking roll is provided elevating freely at least at the outlet side rotating at the same peripheral speed as the transfer rolls and is rotated to lower concurrently with passing of the steel strip top at the cooling apparatus. The upper cooling box is also lowered concurrently to cool the steel strip.

The present invention relates to a high strength steel sheet consisting essentially of 0.04 to 0.1% C, 0.5% or less Si, 0.5 to 2% Mn, 0.05% or less P, 0.005% or less 0, 0.005% or less S, by weight, having 10 &mgr;m or less of average ferritic grain size, and 20 mm/mm or less of generation frequency A, which generation frequency A is defined as the total length of a banded secondary phase structure observed per 1 mm of steel sheet cross section along the rolling direction thereof. The steel sheet is manufactured by, for example, a method comprising the steps of: hot-rolling a continuously cast slab having the composition described above at temperatures of Ar transformation point or above directly or after reheating thereof; and cooling the hot-rolled steel sheet within 2 seconds down to the temperatures of from 600 to 750&deg; C. at cooling speeds of from 100 to 2,000&deg; C./sec, followed by coiling the cooled steel sheet at temperatures of from 450 to 650&deg; C. The present invention provides a high strength steel sheet having strengths of 340 MPa or more and having excellent stretch flanging performance, ductility, and shock resistance, providing a sufficient coil shape with good surface properties, even when hot dip zinc-coating is applied.

High strength steel sheet and method for manufacturing the same

The method for manufacturing steel sheet comprises the steps of: rough-rolling to form a sheet bar; finish-rolling the sheet bar to form a steel strip; applying primary cooling and secondary cooling to the finish-rolled steel strip; and coiling the secondary-cooled steel strip. The primary cooling is conducted at cooling speeds of 120&deg; C./sec or more down to the temperatures of from 500 to 800&deg; C. The secondary cooling is conducted at cooling speeds of less than 60&deg; C./sec.

Steel sheet and method for manufacturing the same

High tensile strength hot-rolled steel sheet and method for manufacturing the same

The method for manufacturing steel sheet comprises the steps of: forming a sheet bar; forming a steel strip; primary-cooling; air-cooling; secondary-cooling; and coiling. The sheet bar is finish-rolled at finish temperatures of (Ar transformation point &minus;20&deg; C.) or more. The primary cooling cools the finish-rolled steel strip at cooling speeds of more than 120&deg; C./sec down to the temperatures ranging from 500 to 800&deg; C.

The method for manufacturing cold-rolled steel sheet comprises the steps of: rough-rolling a slab using a rough-rolling unit; finish-rolling the sheet bar using a continuous hot finishing-rolling mill; cooling the hot-rolled steel strip on a runout table; coiling thus cooled hot-rolled steel strip; and applying picking, cold-rolling the hot-rolled steel strip, and final annealing to the cold-rolled steel strip.

Growing community of inventors

Fukuyama, Japan

Sadanori Imada