公开(公告)号：US20180057916A1

公开(公告)日：2018-03-01

申请号：US15551301

申请日：2016-01-25

Applicant: JFE Steel Corporation

Inventor： Yoshie OBATA ,  Yoshiyasu KAWASAKI ,  Keiji UEDA ,  Shinjiro KANEKO ,  Takeshi YOKOTA ,  Kazuhiro SETO

IPC: C22C38/14 ,  C21D8/02 ,  C21D9/46 ,  C23C2/06 ,  C22C38/02 ,  C22C38/06 ,  C22C38/04 ,  C22C38/00 ,  C22C38/12

CPC classification number: C22C38/14 ,  C21D8/0236 ,  C21D8/0268 ,  C21D9/46 ,  C21D2211/001 ,  C21D2211/004 ,  C21D2211/005 ,  C21D2211/008 ,  C21D2211/009 ,  C22C38/00 ,  C22C38/001 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/12 ,  C22C38/16 ,  C22C38/18 ,  C22C38/60 ,  C23C2/02 ,  C23C2/06 ,  C23C2/40

Abstract: A steel having a composition containing C: more than 0.20% and 0.45% or less, Si: 0.50% to 2.50%, Mn: 2.00% or more and less than 3.50%, and one or two selected from Ti: 0.005% to 0.100% and Nb: 0.005% to 0.100% is hot-rolled and cold-rolled. The steel sheet is heated to 800° C. to 950° C. and cooled to a cooling-end temperature of 350° C. to 500° C. at a cooling rate of 5° C./s or more to form a steel sheet having a microstructure including martensite and bainite phases such that the total proportion of the martensite and bainite phases is 80% or more by volume. The steel sheet is heated to 700° C. to 840° C. and maintained at 700° C. to 840° C., cooled to a cooling-end temperature of 350° C. to 500° C. at a cooling rate of 5 to 50° C./s, and maintained within the above temperature range for 10 to 1800 s.

公开(公告)号：US20180023161A1

公开(公告)日：2018-01-25

申请号：US15547659

申请日：2016-01-27

Applicant: JFE STEEL CORPORATION

Inventor： Hidekazu MINAMI ,  Shinjiro KANEKO ,  Takeshi YOKOTA ,  Kazuhiro SETO

IPC: C21D9/46 ,  C22C38/02 ,  C22C38/60 ,  C22C38/06 ,  C22C38/12 ,  C22C38/14 ,  C22C38/04

Abstract: A steel sheet has a microstructure that contains ferrite in an area ratio of 20% or more, martensite in an area ratio of 5% or more, and tempered martensite in an area ratio of 5% or more. The ferrite has a mean grain size of 20.0 μm or less. An inverse intensity ratio of γ-fiber to α-fiber in the ferrite is 1.00 or more and an inverse intensity ratio of γ-fiber to α-fiber in the martensite and the tempered martensite is 1.00 or more.

公开(公告)号：US20170327919A1

公开(公告)日：2017-11-16

申请号：US15520531

申请日：2015-10-29

Applicant: JFE STEEL CORPORATION

Inventor： Yoshiyasu KAWASAKI ,  Hiroshi MATSUDA ,  Takeshi YOKOTA ,  Takako YAMASHITA ,  Kazuhiro SETO

IPC: C21D9/46 ,  B32B15/01 ,  C23C2/40 ,  C23C2/12 ,  C23C2/06 ,  C22C38/38 ,  C22C38/28 ,  C22C38/16 ,  C22C38/12 ,  C22C38/08 ,  C22C38/06 ,  C22C38/02 ,  C22C38/00 ,  C23G1/00 ,  C21D6/00 ,  C21D8/02 ,  C25D3/22

CPC classification number: C21D9/46 ,  B32B15/012 ,  B32B15/013 ,  C21D6/001 ,  C21D6/002 ,  C21D6/005 ,  C21D6/008 ,  C21D8/0205 ,  C21D8/0226 ,  C21D8/0236 ,  C21D8/0263 ,  C21D8/0273 ,  C21D2211/001 ,  C21D2211/005 ,  C21D2211/008 ,  C22C38/00 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/008 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/28 ,  C22C38/38 ,  C22C38/58 ,  C22C38/60 ,  C23C2/02 ,  C23C2/06 ,  C23C2/12 ,  C23C2/28 ,  C23C2/40 ,  C23G1/00 ,  C25D3/22

Abstract: A high-strength steel sheet with excellent formability and high yield ratio that has TS of 980 MPa or more and YR of 68% or more is obtained by providing a predetermined chemical composition and a steel microstructure that contains, in area ratio, 15 to 55% of polygonal ferrite, 8% or more of non-recrystallized ferrite, and 15 to 30% of martensite, and that contains, in volume fraction, 12% or more of retained austenite, in which the polygonal ferrite has a mean grain size of 4 μm or less, the martensite has a mean grain size of 2 μm or less, the retained austenite has a mean grain size of 2 μm or less, and a value obtained by dividing an Mn content in the retained austenite (in mass %) by an Mn content in the polygonal ferrite (in mass %) equals 2.0 or more.

公开(公告)号：US20170314091A1

公开(公告)日：2017-11-02

申请号：US15520236

申请日：2015-10-29

Applicant: JFE STEEL CORPORATION

Inventor： Yoshiyasu KAWASAKI ,  Hiroshi MATSUDA ,  Takeshi YOKOTA ,  Takako YAMASHITA ,  Kazuhiro SETO

IPC: C21D9/46 ,  B32B15/01 ,  C23C2/40 ,  C23C2/12 ,  C22C38/38 ,  C22C38/28 ,  C22C38/16 ,  C22C38/12 ,  C22C38/08 ,  C22C38/02 ,  C22C38/00 ,  C21D8/02 ,  C21D6/00 ,  C23G1/00 ,  C25D3/22

CPC classification number: C21D9/46 ,  B32B15/012 ,  B32B2255/06 ,  B32B2255/205 ,  C21D6/001 ,  C21D6/002 ,  C21D6/005 ,  C21D6/008 ,  C21D8/0205 ,  C21D8/0226 ,  C21D8/0263 ,  C21D8/0278 ,  C22C38/00 ,  C22C38/001 ,  C22C38/002 ,  C22C38/008 ,  C22C38/02 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/28 ,  C22C38/38 ,  C22C38/60 ,  C23C2/02 ,  C23C2/06 ,  C23C2/12 ,  C23C2/28 ,  C23C2/40 ,  C23G1/00 ,  C25D3/22

Abstract: Disclosed is a steel sheet having a predetermined chemical composition and a steel microstructure that contains, in area ratio, 35% or more and 80% or less of polygonal ferrite and 5% or more and 25% or less of martensite, and that contains, in volume fraction, 8% or more of retained austenite, in which the polygonal ferrite, the martensite, and the retained austenite have a mean grain size of 6 μm or less, 3 μm or less, and 3 μm or less, respectively, and each have a mean grain aspect ratio of 2.0 or less, and in which a value obtained by dividing an Mn content in the retained austenite in mass % by an Mn content in the polygonal ferrite in mass % equals 2.0 or more.

公开(公告)号：US20170306435A1

公开(公告)日：2017-10-26

申请号：US15517467

申请日：2015-10-29

Applicant: JFE STEEL CORPORATION

Inventor： Yoshiyasu KAWASAKI ,  Hiroshi MATSUDA ,  Takako YAMASHITA ,  Takeshi YOKOTA ,  Kazuhiro SETO

IPC: C21D9/46 ,  C21D8/02 ,  C22C38/28 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C22C38/60 ,  C25D3/22

CPC classification number: C21D9/46 ,  C21D8/0205 ,  C21D8/0226 ,  C21D8/0236 ,  C21D8/0278 ,  C22C38/00 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/008 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/28 ,  C22C38/60 ,  C23C2/02 ,  C23C2/06 ,  C23C2/12 ,  C23C2/28 ,  C25D3/22

Abstract: A high-strength steel sheet with excellent formability and high yield ratio that has TS of 590 MPa or more and YR of 68% or more is obtained by providing a predetermined chemical composition and a steel microstructure that contains, in area ratio, 35 to 80% of polygonal ferrite, 5% or more of non-recrystallized ferrite, and 5 to 25% of martensite, and that contains, in volume fraction, 8% or more of retained austenite, in which the polygonal ferrite has a mean grain size of 6 μm or less, the martensite has a mean grain size of 3 μm or less, the retained austenite has a mean grain size of 3 μm or less, and a value obtained by dividing an Mn content in the retained austenite (in mass %) by an Mn content in the polygonal ferrite (in mass %) equals 2.0 or more.