公开(公告)号：EP4026922A1

公开(公告)日：2022-07-13

申请号：EP20861319.0

申请日：2020-09-03

申请人： NIPPON STEEL CORPORATION

发明人： YOKOYAMA, Takafumi ,  SHIOKAWA, Kazuki ,  OBUCHI, Tatsuya ,  HAYASHI, Kunio

IPC分类号： C21D9/46 ,  C22C38/00 ,  C22C38/60 ,  C22C38/02 ,  C22C38/04 ,  C22C38/14 ,  C21D8/02 ,  C21D1/19 ,  C21D1/22 ,  B22D11/00 ,  B22D11/043 ,  B22D11/06 ,  C21D1/25 ,  C21D1/76 ,  B22D11/055

摘要： Provided are a steel sheet having a predetermined chemical composition and having the following steel structure, and a method of manufacturing the steel sheet.
(1) In area ratio%, ferrite: 0 to 5%, martensite: 90 to 100%, a ratio of tempered martensite to total martensite: 80 to 100%, and retained austenite: 0.5 to 6.0% are contained.
(2) The number density of inclusions satisfying the maximum diameter ≥ 3 µm is 40 inclusions/mm 2 or less.
(3)When the number density of the inclusions satisfying the maximum diameter ≥ 3 µm in each section is calculated, the number density in the section where the number density of inclusions is in the top 10% is 80 inclusions/mm 2 or less.
(4) Formula (A) is satisfied. V γ ′ /V γ ≥ 0.1 Vγ: Initial retained austenite, Vy': Retained austenite after deep cooling at -196°C
(5) The tensile strength is 1470 MPa or more.

公开(公告)号：EP3604582A1

公开(公告)日：2020-02-05

申请号：EP17903051.5

申请日：2017-03-31

申请人： Nippon Steel Corporation

发明人： YOKOYAMA, Takafumi ,  OKAMOTO, Riki ,  YAMAGUCHI, Yuji ,  SHIOKAWA, Kazuki ,  NAKAHIRA, Yuichi ,  KAWATA, Hiroyuki

IPC分类号： C22C38/00 ,  C23C2/06 ,  C21D9/46

摘要： A cold-rolled steel sheet is provided that has a tensile strength of 980 MPa or more, and has a prescribed chemical composition. The microstructure is composed of, in area%, ferrite: 1 to 29%, retained austenite: 5 to 20%, martensite: less than 10%, pearlite: less than 5%, and the balance: bainite and/or tempered martensite. The total sum of the lengths of phase boundaries where ferrite comes in contact with martensite or retained austenite having a circle-equivalent radius of 1 µm or more is 100 µm or less per 1000 µm 2 . The cold-rolled steel sheet is excellent in workability and low-temperature toughness, and in particular is excellent in low-temperature toughness after introduction of plastic strain.