Title:
HIGH TENSILE STEEL SHEET OF LOW ACOUSTICAL ANISOTROPY EXCELLING IN WELDABILITY, AND PROCESS FOR PRODUCING THE SAME
Document Type and Number:
WIPO Patent Application WO/2006/011257
Kind Code:
A1
Abstract:
A high tensile steel sheet of low acoustical anisotropy excelling in weldability, whose tensile strength is on the order of 570 MPa or greater; and a process for producing a steel sheet, based on an accelerated cooling-halfway stopping process realizing high productivity. There is provided a high tensile steel sheet comprising a steel structure of 0.055% ≤ Nb+2Ti ≤ 0.105%, value of A = (Nb+2Ti)×(C+N×12/14) being in the range of 0.0025 to 0.0055, content of bainite being ≥ 30 vol% and content of pearlite plus island shaped martensite being < 3 vol%. In the production thereof, steel is heated to ≥ 1200&ring C, and preliminarily rolled at ≥ 1020&ring C. Thereafter, the preliminarily rolled steel is further rolled so that the cumulative draft at temperature of >920°C but <1020°C is ≤15% while the cumulative draft at temperature of 860° to 920°C falls within the range of 20 to 50%, and an accelerated cooling of 2° to 30°C/sec cooling rate is started from ≥800°C. The accelerated cooling is stopped at 600° to 700°C, and thereafter cooling is performed at a rate of ≤ 0.4°C/sec.
Inventors:
KUMAGAI TATSUYA (JP)
FUJIOKA MASAAKI (JP)
FUJIOKA MASAAKI (JP)
Application Number:
PCT/JP2005/002663
Publication Date:
February 02, 2006
Filing Date:
February 14, 2005
Export Citation:
Assignee:
NIPPON STEEL CORP (JP)
KUMAGAI TATSUYA (JP)
FUJIOKA MASAAKI (JP)
KUMAGAI TATSUYA (JP)
FUJIOKA MASAAKI (JP)
International Classes:
B21B1/38; B21B3/00; C21D8/02; C22C38/00; C22C38/58; (IPC1-7): C22C38/00; B21B1/26; B21B3/00; C21D8/02; C22C38/14; C22C38/58
Foreign References:
| JP2002053912A | 2002-02-19 | |||
| JPH01301819A | 1989-12-06 | |||
| JP2000256737A | 2000-09-19 | |||
| JP2003160833A | 2003-06-06 | |||
| JP2000219934A | 2000-08-08 |
Attorney, Agent or Firm:
Aoki, Atsushi (ISHIDA & ASSOCIATES Toranomon 37 Mori
Bldg., 5-1, Toranomon 3-chom, Minato-ku Tokyo 23, JP)
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