公开(公告)号：US11447848B2

公开(公告)日：2022-09-20

申请号：US17041372

申请日：2018-03-30

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi Yokoyama ,  Kohichi Sano ,  Riki Okamoto ,  Hiroyuki Kawata ,  Eisaku Sakurada ,  Yuji Yamaguchi ,  Kazuki Shiokawa ,  Yuichi Nakahira ,  Kohei Ueda ,  Masahiro Nakata ,  Satoshi Uchida

IPC: C21D8/02 ,  C21D9/00 ,  C22C38/58 ,  C21D9/46 ,  C22C38/00 ,  C22C38/02 ,  C22C38/06 ,  C22C38/42 ,  C22C38/44 ,  C22C38/46 ,  C22C38/48 ,  C22C38/50 ,  C22C38/52 ,  C22C38/54 ,  C23C2/06 ,  C23C2/40

Abstract: A steel sheet wherein a steel structure of an inside of the steel sheet contains, by volume fraction, soft ferrite: 0% to 30%, retained austenite: 3% to 40%, fresh martensite: 0% to 30%, a sum of pearlite and cementite: 0% to 10%, and a remainder including hard ferrite. In the steel sheet, in a ⅛ to ⅜ thickness range, a proportion of retained austenite having an aspect ratio of 2.0 or more is 50% or more, and a soft layer having a thickness of 1 to 100 μm from a surface in a sheet thickness direction is present. When an emission intensity at a wavelength indicating Si is analyzed in the sheet thickness direction from the surface by a radio-frequency glow discharge analysis method, a peak of the emission intensity appears in a range of more than 0.2 μm and 5.0 μm or less from the surface.

公开(公告)号：US11377710B2

公开(公告)日：2022-07-05

申请号：US16981653

申请日：2018-03-30

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi Yokoyama ,  Kohichi Sano ,  Riki Okamoto ,  Hiroyuki Kawata ,  Eisaku Sakurada ,  Yuji Yamaguchi ,  Kazuki Shiokawa ,  Yuichi Nakahira ,  Kohei Ueda ,  Masahiro Nakata ,  Satoshi Uchida

IPC: C22C38/18 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/10 ,  C22C38/08 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C23C2/40 ,  C23C2/28 ,  B32B15/01 ,  C21D6/00 ,  C21D8/02 ,  C21D9/46 ,  C22C38/06 ,  C22C38/60 ,  C23C2/06 ,  C22C38/42 ,  C22C38/44 ,  C22C38/46 ,  C22C38/48 ,  C22C38/50 ,  C22C38/52 ,  C22C38/58 ,  C25D3/56 ,  C23C2/26 ,  C23C30/00 ,  B32B15/04 ,  B32B15/18 ,  C21D8/00 ,  C22C38/20 ,  C22C38/34 ,  C22C38/30 ,  C22C38/32 ,  C22C38/40 ,  C22C38/26 ,  C22C38/28 ,  C22C38/38 ,  C22C38/22 ,  C22C38/24 ,  C22C38/54

Abstract: A steel sheet has a chemical composition with a steel structure containing, by volume fraction, soft ferrite: 0-30%, retained austenite: 3-40%, fresh martensite: 0-30%, pearlite and cementite: 0-10%, and a remainder including hard ferrite. In the steel sheet, a number proportion of retained austenite having an aspect ratio of 2.0 or more in the total retained austenite is 50% or more, and a soft layer having a thickness of 1-100 μm is present. In the soft layer, a volume fraction of ferrite grains having an aspect ratio of less than 3.0 is 50% or more, and a volume fraction of retained austenite is 50% or more of the volume fraction of the retained austenite of the inside of the steel sheet. A peak of an emission intensity at a wavelength indicating Si appears in a range of more than 0.2 μm to 5 μm or less from the surface.

公开(公告)号：US11326234B2

公开(公告)日：2022-05-10

申请号：US16499834

申请日：2017-03-31

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi Yokoyama ,  Riki Okamoto ,  Yuji Yamaguchi ,  Kazuki Shiokawa ,  Yuichi Nakahira ,  Hiroyuki Kawata

IPC: C22C38/04 ,  C21D8/02 ,  C21D9/46 ,  C22C38/00 ,  C22C38/02 ,  C22C38/06 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/54 ,  C22C38/60 ,  C23C2/06

Abstract: 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 μm2. 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.