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.