Title:
THICK HOT-ROLLED STEEL SHEET HAVING EXCELLENT PROCESSABILITY AND EXCELLENT STRENGTH/TOUGHNESS AFTER THERMAL TREATMENT, AND METHOD FOR PRODUCTION OF THE STEEL SHEET
Document Type and Number:
WIPO Patent Application WO/2009/004909
Kind Code:
A1
Abstract:
Disclosed is a thick hot-rolled steel sheet which has a tensile strength of 440
to 640 MPa, preferably 490 to 590 MPa, an elongation of 20% or more, excellent uniformity
in the thickness-wise direction, high strength, excellent processability,
and excellent strength/toughness after a thermal treatment, and is therefore
suitable for use as a structural member for an automobile, a construction machine
or the like. Also disclosed is a method for producing the steel sheet. A steel
material is provided, which contains 0.10 to 0.20% of C, in which the contents
of Si, Mn, Al, P, S and N are adjusted within proper ranges, and which further contains
0.01 to 0.15% of Ti and 0.0010 to 0.0050% of B. The steel material is subjected
to the hot-rolling under the conditions of a rolling finishing temperature for
the finish rolling of 820 to 880°C. The resulting product is cooled at a
cooling rate of 15 to 50°C/s and a cooling finishing temperature of 500 to
600°C, and is then wound-up in a coli-like shape. In this manner, the steel
sheet can have a structure which is uniform in the thickness-wise direction and
is composed of a bainitic ferrite phase. The steel sheet has excellent uniformity
in the thickness-wise direction so that the fluctuation in the hardness in the
thickness-wise direction falls within the range up to 10% above or below the average
value, and has a tensile strength of 440 to 640 MPa and an elongation of 20% or more.
The steel sheet may be subjected to a further thermal treatment, thereby producing
a highly-strong, highly-tough, thick and large-sized structural member having
a tensile strength of 980 MPa or more and a vTrs of -60˚C or lower.
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Inventors:
SETO KAZUHIRO (JP)
NAKAMURA NOBUYUKI (JP)
KOBAYASHI AKIO (JP)
NAKAMURA NOBUYUKI (JP)
KOBAYASHI AKIO (JP)
Application Number:
PCT/JP2008/060805
Publication Date:
January 08, 2009
Filing Date:
June 06, 2008
Export Citation:
Assignee:
JFE STEEL CORP (JP)
SETO KAZUHIRO (JP)
NAKAMURA NOBUYUKI (JP)
KOBAYASHI AKIO (JP)
SETO KAZUHIRO (JP)
NAKAMURA NOBUYUKI (JP)
KOBAYASHI AKIO (JP)
International Classes:
C22C38/00; C21D8/02; C21D9/46; C22C38/14
Foreign References:
| JP2005060796A | 2005-03-10 | |||
| JP2005220415A | 2005-08-18 | |||
| JP2008019453A | 2008-01-31 | |||
| JP2002309344A | 2002-10-23 | |||
| JP2002309345A | 2002-10-23 |
Other References:
See also references of EP 2184373A4
Attorney, Agent or Firm:
OCHIAI, Kenichiro (JFE TECHNO-RESEARCH CORPORATION7th floor Yanagiya building., 1-10,Nihonbashi 2-chome, Chuo-ku, Tokyo 27, JP)
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