HIGH-STRENGTH HOT-ROLLED STEEL PLATE EXHIBITING EXCELLENT STRETCH FLANGEABILITY AND FATIGUE RESISTANCE PROPERTIES, AND PRODUCTION METHOD THEREFOR

Title:

HIGH-STRENGTH HOT-ROLLED STEEL PLATE EXHIBITING EXCELLENT STRETCH FLANGEABILITY AND FATIGUE RESISTANCE PROPERTIES, AND PRODUCTION METHOD THEREFOR

Document Type and Number:

WIPO Patent Application WO/2011/152541

Kind Code:

A1

Abstract:

Provided is a high-strength hot-rolled steel plate which has a tensile strength of 780 MPa or more and which exhibits excellent stretch flangeability and fatigue resistance properties. A steel material which has a composition containing 0.05 to 0.15% of C, 0.2 to 1.2% of Si, 1.0 to 2.0% of Mn, 0.04% or less of P, 0.005% or less of S, 0.05 to 0.15% of Ti, 0.005 to 0.10% of Al, and 0.007% or less of N is heated to 1150 to 1350°C or less, and is hot-rolled such that the finishing temperature is between 850 and 950°C. After the hot-roll process is complete, the steel material is cooled to 530°C at an average cooling rate of 30°C/sec or more, and is further cooled to and wound at a winding temperature of 300 to 500°C at an average cooling rate of 100°C/sec or more. As a consequence, it is possible to obtain a high-strength hot-rolled steel plate which combines stretch flangeability and fatigue resistance properties and which has a tensile strength of 780 MPa or more. Moreover, the high-strength hot-rolled steel plate contains 0.02% or more of solute Ti, and has the structure of a bainite single phase in which the average particle size is 5µm or less, preferably, over 3.0µm, or a structure comprising 90% or more, in area ratio, of the aforementioned bainite phase and a second phase other than said bainite phase in which the average particle diameter is 3µm or less.

Inventors:

NAKAMURA NOBUYUKI (JP)
SAITO HAYATO (JP)
NAKAJIMA KATSUMI (JP)
FUNAKAWA YOSHIMASA (JP)
MORIYASU NORIAKI (JP)
MURATA TAKAYUKI (JP)

Application Number:

PCT/JP2011/062857

Publication Date:

December 08, 2011

Filing Date:

May 30, 2011

Export Citation:

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Assignee:

JFE STEEL CORP (JP)
NAKAMURA NOBUYUKI (JP)
SAITO HAYATO (JP)
NAKAJIMA KATSUMI (JP)
FUNAKAWA YOSHIMASA (JP)
MORIYASU NORIAKI (JP)
MURATA TAKAYUKI (JP)

International Classes:

C22C38/00; C21D8/02; C21D9/46; C22C38/14; C22C38/60

Foreign References:

JP2000109951A	2000-04-18
JP2003129175A	2003-05-08
JP2005206943A	2005-08-04
JP2006161139A	2006-06-22
JP2007111708A	2007-05-10
JP2008069425A	2008-03-27
JP2006274318A	2006-10-12
JPH04329848A	1992-11-18
JP2009280900A	2009-12-03
JP2000109951A	2000-04-18
JP2000282175A	2000-10-10

Other References: