公开(公告)号：US20220118741A1

公开(公告)日：2022-04-21

申请号：US17425847

申请日：2019-12-26

Applicant: JFE Steel Corporation

Inventor： Katsutoshi Takashima ,  Minoru Tanaka ,  Kenji Tsuzumi ,  Shingo Arakawa ,  Michitaka Sakurai

IPC: B32B15/01 ,  B21B3/02 ,  C22C38/32 ,  C22C38/28 ,  C22C38/26 ,  C22C38/16 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C21D9/46 ,  C21D8/02 ,  C21D6/00

Abstract: A hot-pressed member has a predetermined chemical composition. In the hot-pressed member, a steel sheet has a microstructure in which a prior austenite average grain diameter is 8 μm or less, and martensite is present in a volume fraction of 95% or greater in a region within 30 μm of a surface; a Ni diffusion region having a thickness of 0.5 μm or greater exists in a surface layer; a standard deviation of Vickers hardness values is 35 or less; Mndif (mass %) in a sheet thickness direction ≤0.20, where Mndif (mass %) is a degree of Mn segregation; and a tensile strength is 1780 MPa or greater.

公开(公告)号：US11293074B2

公开(公告)日：2022-04-05

申请号：US16617133

申请日：2018-03-30

Applicant: JFE STEEL CORPORATION

Inventor： Katsutoshi Takashima ,  Chikaumi Sawanishi ,  Takashi Kobayashi ,  Yoshimasa Funakawa

IPC: C21D9/46 ,  B21D22/02 ,  B32B15/01 ,  C21D1/18 ,  C21D6/00 ,  C21D8/02 ,  C22C38/00 ,  C22C38/02 ,  C22C38/06 ,  C22C38/08 ,  C22C38/10 ,  C22C38/16 ,  C22C38/26 ,  C22C38/28 ,  C22C38/32 ,  C22C38/38

Abstract: Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing as high as TS: 1780 MPa or more, excellent resistance to resistance welding cracking, and excellent delayed fracture resistance after resistance welding by having a specific chemical composition, and a microstructure such that a prior austenite average grain size is 7 μm or less, a volume fraction of martensite is 90% or more, and at least 5 Nb-based precipitates having a grain size of less than 0.08 μm are present on average per 100 μm2 of a cross section parallel to a thickness direction of the member within a range of 100 μm in the thickness direction from a surface of the member, and such that a Ni diffusion region having a thickness of 0.5 μm or more is present in a surface layer of the member.

公开(公告)号：US20200230735A1

公开(公告)日：2020-07-23

申请号：US16488703

申请日：2018-03-01

Applicant: JFE Steel Corporation

Inventor： Koichi Taniguchi ,  Chikaumi Sawanishi ,  Katsutoshi Takashima ,  Hiroshi Matsuda ,  Rinsei Ikeda

IPC: B23K11/11 ,  B23K11/16 ,  B23K11/00

Abstract: Provided is a resistance spot welding method. The resistance spot welding method for joining a sheet set including a plurality of lapped steel sheets includes: holding the sheet set between a pair of electrodes; and energizing the sheet set under application of electrode force to thereby join the steel sheets together. At least one of the plurality of lapped steel sheets is a surface-treated steel sheet including a metal coating layer on a surface thereof. The energizing includes: a primary energizing step of performing energization to form a nugget portion; a non-energizing step in which, after the primary energizing step, the energization is suspended for an energization suspension time Tc (cycles); and a secondary energizing step of, after the non-energizing step, performing energization for reheating while the nugget portion is prevented from growing. During the energizing, the relations of a particular formula are satisfied.

公开(公告)号：US10435762B2

公开(公告)日：2019-10-08

申请号：US15129938

申请日：2015-03-13

Applicant: JFE Steel Corporation

Inventor： Katsutoshi Takashima ,  Yoshihiko Ono ,  Kohei Hasegawa

IPC: C21D9/46 ,  C21D8/02 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/18 ,  C22C38/28 ,  C22C38/32 ,  C22C38/38 ,  C22C38/00

Abstract: A high-strength cold-rolled steel sheet has a composite structure containing 0.15 to 0.25% by mass of C, 1.8 to 3.0% by mass of Mn, and 0.0003 to 0.0050% by mass of B, and having a ferrite volume fraction of 20% to 50%, a retained austenite volume fraction of 7% to 20%, a martensite volume fraction of 1% to 8%, and the balance containing bainite and tempered martensite, and in the composite structure, ferrite has an average crystal grain diameter of 5 μm or less, retained austenite has an average crystal grain diameter of 0.3 to 2.0 μm and an aspect ratio of 4 or more, martensite has an average crystal grain diameter of 2 μm or less, a metal phase containing both bainite and tempered martensite has an average crystal grain diameter of 7 μm or less, the ratio of the volume fraction of tempered martensite to the volume fraction of a metal structure other than ferrite is 0.60 to 0.85, and the average C concentration in retained austenite is 0.65% by mass or more.

公开(公告)号：US20190201999A1

公开(公告)日：2019-07-04

申请号：US16323570

申请日：2017-08-21

Applicant: JFE Steel Corporation

Inventor： Katsutoshi Takashima ,  Hiroshi Matsuda ,  Rinsei Ikeda ,  Yoshiyasu Kawasaki

IPC: B23K11/16 ,  F16B5/08 ,  C22C38/38 ,  C22C38/28 ,  C22C38/26 ,  C22C38/16 ,  C22C38/08 ,  C22C38/06 ,  C22C38/02 ,  C22C38/00 ,  C21D9/46 ,  C21D8/02 ,  C21D6/00 ,  B32B15/01

CPC classification number: B23K11/16 ,  B23K11/0026 ,  B23K11/115 ,  B23K11/166 ,  B23K11/20 ,  B23K2101/006 ,  B23K2101/18 ,  B23K2101/34 ,  B23K2103/04 ,  B23K2103/18 ,  B32B15/01 ,  B32B15/013 ,  C21D6/001 ,  C21D6/002 ,  C21D6/005 ,  C21D6/008 ,  C21D8/0205 ,  C21D8/0226 ,  C21D8/0236 ,  C21D8/0263 ,  C21D9/46 ,  C21D2211/001 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/26 ,  C22C38/28 ,  C22C38/38 ,  C23C2/00 ,  F16B5/08

Abstract: Provided is an automotive member, or particularly, a steel sheet having a tensile strength exceeding 900 MPa. The automotive member has a resistance weld for fixing two or more steel sheets containing a predetermined composition, in which a maximum hardness (HVBM) in a heat-affected zone of the resistance weld is at least 1.1 times hardness (HVW) of a nugget in the resistance weld formed in a softest steel sheet of a sheet set during resistance welding, and furthermore, an average grain size of a steel sheet structure of the heat-affected zone within 2 mm in a direction at a right angle to a sheet thickness from an end part of the nugget of the high-strength steel sheet is 3 μm or less, and a minimum hardness (HVmin) in the heat-affected zone is at least 90% of hardness (HVα) of the high-strength steel sheet before the resistance welding.

公开(公告)号：US12195819B2

公开(公告)日：2025-01-14

申请号：US17632566

申请日：2020-07-16

Applicant: JFE STEEL CORPORATION

Inventor： Katsutoshi Takashima ,  Takeshi Yokota

IPC: C21D9/46 ,  C21D8/02 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C23C2/02 ,  C23C2/28 ,  C23G1/08

Abstract: The high-strength thin steel sheet has a chemical composition containing C, Si, Mn, P, S, Al, and N, with the balance being Fe and inevitable impurities, and a complex structure containing ferrite, tempered martensite, and bainite, where a volume fraction of a total of tempered martensite and bainite containing five or more carbides with a particle size of 0.1 μm or more and 1.0 μm or less in a grain with respect to a total of the tempered martensite and the bainite is 85% or more, and C mass % and Mn mass % in a region of 20 μm or less in a thickness direction from a surface of the steel sheet are each 20% or less with respect to C mass % and Mn mass % in a region of 100 μm or more and 200 μm or less from the surface of the steel sheet.

公开(公告)号：US11850821B2

公开(公告)日：2023-12-26

申请号：US17425847

申请日：2019-12-26

Applicant: JFE Steel Corporation

Inventor： Katsutoshi Takashima ,  Minoru Tanaka ,  Kenji Tsuzumi ,  Shingo Arakawa ,  Michitaka Sakurai

IPC: C21D6/00 ,  B32B15/01 ,  B21B3/02 ,  C21D8/02 ,  C21D9/46 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/16 ,  C22C38/26 ,  C22C38/28 ,  C22C38/32 ,  C23C2/02 ,  C23C2/26 ,  C23C2/28 ,  C25D3/22

CPC classification number: B32B15/015 ,  B21B3/02 ,  C21D6/001 ,  C21D6/002 ,  C21D6/005 ,  C21D6/008 ,  C21D8/0205 ,  C21D8/0226 ,  C21D8/0236 ,  C21D8/0263 ,  C21D9/46 ,  C22C38/001 ,  C22C38/002 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/16 ,  C22C38/26 ,  C22C38/28 ,  C22C38/32 ,  C23C2/02 ,  C23C2/024 ,  C23C2/0224 ,  C23C2/26 ,  C23C2/28 ,  C21D2211/008 ,  C25D3/22

Abstract: A hot-pressed member has a predetermined chemical composition. In the hot-pressed member, a steel sheet has a microstructure in which a prior austenite average grain diameter is 8 μm or less, and martensite is present in a volume fraction of 95% or greater in a region within 30 μm of a surface; a Ni diffusion region having a thickness of 0.5 μm or greater exists in a surface layer; a standard deviation of Vickers hardness values is 35 or less; Mndif (mass %) in a sheet thickness direction ≤0.20, where Mndif (mass %) is a degree of Mn segregation; and a tensile strength is 1780 MPa or greater.

公开(公告)号：US11420247B2

公开(公告)日：2022-08-23

申请号：US16618243

申请日：2018-03-30

Applicant: JFE STEEL CORPORATION

Inventor： Katsutoshi Takashima ,  Takashi Kobayashi ,  Yoshimasa Funakawa ,  Seiji Nakajima

IPC: B32B15/00 ,  B21D22/02 ,  B32B15/01 ,  C21D1/18 ,  C21D6/00 ,  C21D8/02 ,  C21D9/46 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/24 ,  C22C38/26 ,  C22C38/32 ,  C22C38/42 ,  C22C38/44 ,  C22C38/50 ,  C23C30/00

Abstract: Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing of 1780 MPa or more, excellent delayed fracture resistance, and high cross tensile strength after resistance spot welding by properly adjusting its chemical composition and its microstructure such that a prior austenite average grain size is 8 μm or less, a volume fraction of martensite is 90% or more, and at least 10 cementite grains having a grain size of 0.05 μm or more are present on average per 200 μm2 of a cross section parallel to a thickness direction of the member, and such that at least 10 Ti-based precipitates having a grain size of less than 0.10 μm are present on average per 100 μm2 of the cross section parallel to the thickness direction of the member in a range of 100 μm in the thickness direction from a surface of the member.

公开(公告)号：US11377709B2

公开(公告)日：2022-07-05

申请号：US16616602

申请日：2018-03-30

Applicant: JFE STEEL CORPORATION

Inventor： Katsutoshi Takashima ,  Takashi Kobayashi ,  Yoshimasa Funakawa ,  Seiji Nakajima

IPC: B32B15/00 ,  C21D9/46 ,  B21D22/20 ,  B21K29/00 ,  B32B15/01 ,  C21D1/18 ,  C21D6/00 ,  C21D8/02 ,  C22C38/00 ,  C22C38/02 ,  C22C38/08 ,  C22C38/16 ,  C22C38/22 ,  C22C38/26 ,  C22C38/28 ,  C22C38/32 ,  C22C38/38 ,  C23C2/06 ,  C23C2/12 ,  C23C2/40 ,  C25D3/22 ,  C25D3/54 ,  C25D3/56

Abstract: Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing, excellent delayed fracture resistance, and high tensile shear stress after resistance spot welding by properly adjusting its chemical composition and its microstructure such that at least 20 Nb-based precipitates having a grain size of less than 0.10 μm are present on average per 100 μm2 of a cross section parallel to a thickness direction of the member, a prior austenite average grain size is 8 μm or less, an average aspect ratio of prior austenite grains is 2.5 or less, and a volume fraction of martensite is 90% or more, and such that a standard deviation of Vickers hardness measured every 200 μm on a surface of the member is 40 or less.

公开(公告)号：US11339452B2

公开(公告)日：2022-05-24

申请号：US16762501

申请日：2018-11-07

Applicant: JFE STEEL CORPORATION

Inventor： Katsutoshi Takashima ,  Takayuki Futatsuka ,  Kentaro Sato ,  Shimpei Yoshioka ,  Yoshihiko Ono ,  Yoshimasa Funakawa

IPC: C22C38/58 ,  C22C38/54 ,  C22C38/52 ,  C22C38/50 ,  C22C38/48 ,  C22C38/46 ,  C22C38/44 ,  C22C38/42 ,  C22C38/06 ,  C22C38/02 ,  C22C38/00 ,  C22C38/60 ,  B32B15/01 ,  C21D6/00 ,  C21D8/02 ,  C21D9/46 ,  C23C2/06 ,  C23C2/12 ,  C21D1/18 ,  C22C38/04 ,  C22C38/12 ,  C23C2/26 ,  C23C2/40 ,  C23C2/28 ,  C23C30/00 ,  B32B15/04 ,  B32B15/18 ,  C22C38/26 ,  C22C38/18 ,  C22C38/28 ,  C22C38/34 ,  C22C38/24 ,  C22C38/14 ,  C22C38/30 ,  C22C38/20 ,  C22C38/32 ,  C22C38/40 ,  C22C38/10 ,  C22C38/22 ,  C22C38/38 ,  C22C38/16

Abstract: Disclosed is a hot-pressed steel sheet member having a tensile strength of 1780 MPa or more and excellent bending collapsibility. The hot-pressed steel sheet member includes: a specific chemical composition; a microstructure in which an average grain size of prior austenite grains is 8 μm or less, a volume fraction of martensite is 90% or more, and a solute C content is 25% or less of a total C content; and a tensile strength of 1780 MPa or more.