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Title:
HIGH-STRENGTH HOT-ROLLED STEEL SHEET AND METHOD FOR MANUFACTURING SAME
Document Type and Number:
WIPO Patent Application WO/2014/171062
Kind Code:
A1
Abstract:
Provided is a high-strength hot-rolled steel sheet having excellent mass-production punchability and tensile strength (TS) of at least 900 Mpa, and a method for manufacturing same. A steel slab having a composition containing, by mass%, more than 0.07% and no more than 0.2% C, at least 2.0% Si, 1.0-3.0% Mn, no more than 0.1% Al, 0.05-0.3% Ti, and 0.05-0.3% V, is heated to at least 1100°C, the total rolling reduction of the rough rolling and the final two passes is at least 30%, and finish rolling is performed with the rolling ending temperature being within a range of (Ar3 transformation point)-(Ar3 transformation point + 120°C), and after finish rolling is completed, cooling is started within 2 seconds, and winding is performed at a winding temperature of 300-500°C at an average cooling speed of at least 40°C/s. Using this method, a high-strength hot-rolled steel sheet having a tensile strength of at least 900 Mpa and significantly improved mass-production punchability is achieved, the steel sheet having a composition with a bainite phase of more than 90% by volume, the average bainite lath interval being no more than 0.45 µm, and the proportion of Fe-type carbides precipitated on the bainite laths among all Fe-type carbides being at least 10%.

Inventors:
NAKAJIMA KATSUMI (JP)
YAMAZAKI KAZUHIKO (JP)
KAMI CHIKARA (JP)
Application Number:
PCT/JP2014/001508
Publication Date:
October 23, 2014
Filing Date:
March 17, 2014
Export Citation:
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Assignee:
JFE STEEL CORP (JP)
International Classes:
C22C38/00; C21D8/02; C21D9/46; C22C38/14; C22C38/58; C22C18/04
Domestic Patent References:
WO2013051238A12013-04-11
Foreign References:
JP2012062562A2012-03-29
JP2012062561A2012-03-29
JP2012062558A2012-03-29
JP2012062557A2012-03-29
JP2005298924A2005-10-27
JP2006161139A2006-06-22
JP2012251201A2012-12-20
JP2008069425A2008-03-27
JP3889766B22007-03-07
JP2006274318A2006-10-12
JP2004315857A2004-11-11
JP2012062562A2012-03-29
Other References:
See also references of EP 2987883A4
Attorney, Agent or Firm:
KUMASAKA, Akira et al. (JP)
Akira Kumasaka (JP)
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