THICK, HIGH TENSILE-STRENGTH HOT-ROLLED STEEL SHEETS WITH EXCELLENT LOW TEMPERATURE TOUGHNESS AND MANUFACTURING METHOD THEREFOR

Title:

THICK, HIGH TENSILE-STRENGTH HOT-ROLLED STEEL SHEETS WITH EXCELLENT LOW TEMPERATURE TOUGHNESS AND MANUFACTURING METHOD THEREFOR

Document Type and Number:

WIPO Patent Application WO/2010/013848

Kind Code:

A1

Abstract:

Provided are thick, high tensile-strength hot-rolled steel sheets that have high strengths of TS: 521 MPa or higher and excellent low temperature toughness. Specifically, steel raw material of a composition that comprises C: 0.02-0.08%, Nb: 0.01-0.10% and Ti: 0.001-0.05%, and such that C, Ti and Nb satisfy (Ti + (Nb/2))/C < 4, is heated, and after hot-rolling that comprises roughing-down and finish rolling, cooling of 10°C/s by mean cooling rate at the center of the sheet thickness is performed to below a specified end cooling temperature that is dependent on the amounts of alloy elements and the cooling rate. Then the steel is taken up at below a specified take-up temperature that is dependent on the amounts of alloy elements. It thereby becomes a thick hot-rolled steel sheet of excellent structural uniformity in the thickness direction that has a structure wherein the difference DD in mean crystal particle diameters of the main ferrite phases between a position that is 1 mm in the thickness direction from the surface of the steel sheet and at the center of the steel sheet thickness is less than 2 µm, and the difference DV in proportion (volume%) of secondary phase structures is less than 2%. Thereby, low temperature toughness, particularly DWTT characteristics and CTOD characteristics, that are toughness tests over the entire thickness, are markedly improved.

Inventors:

KAMI CHIKARA (JP)
NAKATA HIROSHI (JP)
NAKAGAWA KINYA (JP)

Application Number:

PCT/JP2009/063981

Publication Date:

February 04, 2010

Filing Date:

July 31, 2009

Export Citation:

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Assignee:

JFE STEEL CORP (JP)
KAMI CHIKARA (JP)
NAKATA HIROSHI (JP)
NAKAGAWA KINYA (JP)

International Classes:

C22C38/00; B21B3/00; C21D8/02; C21D9/46; C22C38/14; C22C38/58

Foreign References:

JP2006299415A	2006-11-02
JPS6425916A	1989-01-27
JP2005240051A	2005-09-08
JPH0421719A	1992-01-24
JP2001286927A	2001-10-16
JPH08319538A	1996-12-03
JPH09296216A	1997-11-18
JP2008056962A	2008-03-13
JP2001240936A	2001-09-04
JP2001207220A	2001-07-31
JP2004315957A	2004-11-11

Other References: