Invention Grant
- Patent Title: High strength cold rolled steel sheet with low yield ratio and method of manufacturing the same
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Application No.: US14648778Application Date: 2013-12-04
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Publication No.: US10144996B2Publication Date: 2018-12-04
- Inventor: Katsutoshi Takashima , Yuki Toji , Hideyuki Kimura , Kohei Hasegawa
- Applicant: JFE Steel Corporation
- Applicant Address: JP
- Assignee: JFE Steel Corporation
- Current Assignee: JFE Steel Corporation
- Current Assignee Address: JP
- Agency: DLA Piper LLP (US)
- Priority: JP2012-275627 20121218
- International Application: PCT/JP2013/007135 WO 20131204
- International Announcement: WO2014/097559 WO 20140626
- Main IPC: C21D6/00
- IPC: C21D6/00 ; C21D8/02 ; C21D9/46 ; C22C38/00 ; C22C38/02 ; C22C38/04 ; C22C38/06 ; C22C38/08 ; C22C38/12 ; C22C38/14 ; C22C38/16 ; C22C38/38 ; C22C38/18

Abstract:
A high strength cold rolled steel sheet with a low yield ratio has a chemical composition containing C: 0.05% to 0.10%, Si: 0.6% to 1.3%, Mn: 1.4% to 2.2%, P: 0.08% or less, S: 0.010% or less, Al: 0.01% to 0.08%, N: 0.010% or less, and the remainder being Fe and incidental impurities, on a percent by mass basis, and a microstructure in which the average grain size of ferrite is 15 μm or less, the volume fraction of ferrite is 70% or more, the volume fraction of bainite is 3% or more, the volume fraction of retained austenite is 4% to 7%, the average grain size of martensite is 5 μm or less, and the volume fraction of martensite is 1% to 6%, wherein the average C concentration (percent by mass) in the retained austenite is 0.30% to 0.70%, yield ratio is 64% or less, and the tensile strength is 590 MPa or more.
Public/Granted literature
- US20150322552A1 HIGH STRENGTH COLD ROLLED STEEL SHEET WITH LOW YIELD RATIO AND METHOD OF MANUFACTURING THE SAME Public/Granted day:2015-11-12
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