公开(公告)号：US20230021370A1

公开(公告)日：2023-01-26

申请号：US17911974

申请日：2021-03-17

Applicant: NIPPON STEEL CORPORATION

Inventor： Takahiko KOHTAKE ,  Koutarou HAYASHI ,  Yoshihiro SUWA

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

Abstract: A steel sheet has a predetermined chemical composition containing, in mass %, C: more than 0.18% and less than 0.30%, Mn: more than 2.50% and 4.00% or less, and other elements. The steel micro-structure at a position at a depth of ¼ of the sheet thickness from the surface in an L cross section of the steel sheet is, in area %, tempered martensite: 25 to 90%, ferrite: 5% or less, retained austenite: 10 to 50%, and bainite: 5% or less. At a position at a depth of ¼ of the sheet thickness from the surface of the L cross section, the proportion of a total area of retained austenite grains having an area of 1 μm2 or more and having a grain shape circularity of 0.1 or more is less than 50% with respect to the entire area of retained austenite. The steel sheet satisfies the formula CMnγ/CMnα≥1.2.

公开(公告)号：US20220002831A1

公开(公告)日：2022-01-06

申请号：US17421309

申请日：2020-01-08

Applicant: NIPPON STEEL CORPORATION

Inventor： Nobusato MORISHIGE ,  Ryutaro YAMAGATA ,  Ichiro TANAKA ,  Takashi KATAOKA ,  Haruhiko ATSUMI ,  Yoshihiro SUWA ,  Kazumi MIZUKAMI

IPC: C21D9/46 ,  C21D8/12 ,  C21D8/00 ,  C21D6/00 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  H01F1/147

Abstract: Grain-oriented electrical steel sheet excellent in coating adhesion and magnetic properties is provided. The method for manufacturing grain-oriented electrical steel sheet excellent in coating adhesion and magnetic properties includes a process of heating to 1280° C. or more and hot rolling a slab containing, by mass %, Bi and a predetermined composition of constituents and having a balance of Fe and impurities so as to obtain hot rolled steel sheet, a process, after hot rolling annealing the hot rolled steel sheet, of cold rolling it one time or cold rolling it two times or more with process annealing performed interposed so as to obtain cold rolled steel sheet, a process of rapidly heating then decarburization annealing the steel sheet, a process of coating the surface of the cold rolled steel sheet after decarburization annealing with an annealing separator containing predetermined compounds including sulfates or sulfides and having MgO as its main constituent, then performing finish annealing, a process of performing strictly controlled finish annealing, and a process of coating an insulating coating, then performing flattening annealing.

公开(公告)号：US20210262073A1

公开(公告)日：2021-08-26

申请号：US17049493

申请日：2019-04-23

Applicant: NIPPON STEEL CORPORATION

Inventor： Shinichiro TABATA ,  Yoshihiro SUWA ,  Kazuo HIKIDA ,  Kazuhisa KUSUMI

IPC: C22C38/58 ,  C22C38/02 ,  C22C38/54 ,  C22C38/50 ,  C22C38/42 ,  C22C38/44 ,  C22C38/46 ,  C22C38/48 ,  C22C38/06 ,  C22C38/00 ,  C22C38/12 ,  C21D9/46

Abstract: A steel member according to an aspect of the present invention has a predetermined chemical composition, in which a metallographic structure includes, by a volume %, 60.0% to 85.0% of martensite, 10.0% to 30.0% of bainite, 5.0% to 15.0% of residual austenite, and 0% to 4.0% of a remainder in microstructure. A length of a maximum minor axis of the residual austenite is 30 nm or longer. A number density of a carbide which exist in the steel member and has a circle equivalent diameter of 0.1 μm or more and an aspect ratio of 2.5 or less is 4.0×103 pieces/mm2 or less.