公开(公告)号：US20190062863A1

公开(公告)日：2019-02-28

申请号：US16075747

申请日：2017-01-12

Applicant: JFE STEEL CORPORATION

Inventor： Yuji TANAKA ,  Sarka MIKMEKOVA ,  Takako YAMASHITA ,  Yoshie OBATA

IPC: C21D9/46 ,  C21D8/02 ,  C21D6/00 ,  C23C2/02 ,  C23C2/40 ,  C23C2/06 ,  B32B15/01 ,  C22C38/04 ,  C22C38/06 ,  C22C38/02 ,  C22C38/00

Abstract: A high-strength cold rolled steel sheet has both high strength, i.e. a tensile strength of 900 MPa or more, and high workability, i.e. a total elongation of 20% or more, and also has a low yield ratio of less than 60%. The high-strength cold rolled steel sheet comprises: a predetermined chemical composition; and a steel structure having, in area ratio, ferrite: 30% to 75%, martensite: 15% to 40%, and retained austenite: 10% to 30%. In the case where a distribution of crystal grain circularity of the retained austenite is represented by a histogram with a class range of more than 0.1×(n−1) and 0.1×n or less and a class value of 0.1×n (n is an integer from 1 to 10), a mode of the crystal grain circularity of the retained austenite is 0.7 or more.

公开(公告)号：US20190048436A1

公开(公告)日：2019-02-14

申请号：US16075750

申请日：2017-01-12

Applicant: JFE STEEL CORPORATION

Inventor： Yuji TANAKA ,  Sarka MIKMEKOVA ,  Takako YAMASHITA ,  Yoshie OBATA

IPC: C21D9/46 ,  C21D8/02 ,  C21D6/00 ,  C22C38/06 ,  C22C38/04 ,  C22C38/00 ,  C22C38/02

Abstract: A high-strength cold rolled steel sheet has both high strength, i.e. a tensile strength of 900 MPa or more, and high workability, i.e. a total elongation of 20% or more, and also has a high yield ratio of 60% or more. The high-strength cold rolled steel sheet comprises: a predetermined chemical composition; and a steel structure having, in area ratio, ferrite: 30% to 75%, martensite: 15% to 40%, and retained austenite: 10% to 30%. In the case where a distribution of crystal grain circularity of the retained austenite is represented by a histogram with a class range of more than 0.1×(n−1) and 0.1×n or less and a class value of 0.1×n (n is an integer from 1 to 10), a mode of the crystal grain circularity of the retained austenite is 0.6 or less.