公开(公告)号：US20210017620A1

公开(公告)日：2021-01-21

申请号：US16982003

申请日：2018-03-30

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Riki OKAMOTO ,  Kohichi SANO ,  Hiroyuki KAWATA ,  Kohei UEDA ,  Eisaku SAKURADA

IPC: C21D9/46 ,  C21D8/02 ,  C21D6/00 ,  C23C2/06 ,  C23C2/40 ,  C22C38/18 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/10 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/60 ,  C22C38/00 ,  B32B15/01

Abstract: This steel sheet has a predetermined chemical composition, in which 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 includes hard ferrite, a number proportion of the retained austenite having an aspect ratio of 2.0 or more in the total retained austenite is 50% or more, a soft layer having a thickness of 1 to 100 μm from a surface in a sheet thickness direction is present, in ferrite contained in the soft layer, a volume fraction of grains having an aspect ratio of 3.0 or more is 50% or more, a volume fraction of retained austenite in the soft layer is 80% or less of the volume fraction of the retained austenite in the inside of the steel sheet, and a peak of an emission intensity at a wavelength indicating Si appears in a range of more than 0.2 μm and 10.0 μm or less from the surface.

公开(公告)号：US20220145417A1

公开(公告)日：2022-05-12

申请号：US17434981

申请日：2020-03-12

Applicant: NIPPON STEEL CORPORATION

Inventor： Kengo TAKEDA ,  Hitoshi NIKAIDO ,  Hiroyuki KAWATA ,  Takafumi YOKOYAMA

IPC: C21D9/46 ,  C22C38/58 ,  C22C38/54 ,  C22C38/52 ,  C22C38/50 ,  C22C38/48 ,  C22C38/44 ,  C22C38/10 ,  C22C38/06 ,  C22C38/02 ,  C22C38/00 ,  C21D8/02 ,  C21D6/00

Abstract: Provided are: a steel sheet having a high strength and excellent stretch formability; and a method of producing the same. The steel sheet has prescribed chemical composition and structure, in which the integration degree of the (111) orientation of ferrite is 3.0 or higher, and the integration degree of the (252) orientation of martensite and tempered martensite is 5.0 or lower. The method of producing the steel sheet includes: the step of continuously casting a molten steel having the prescribed chemical composition, and performing 5 to 40% rolling reduction at a temperature of 800° C. to lower than 1,200° C. in a period after the continuous casting until cooling to room temperature; the hot rolling step of performing hot rolling with a finishing temperature of 650 to 950° C.; the step of coiling the resulting hot-rolled steel sheet at a coiling temperature of 400 to 700° C.; the step of retaining the hot-rolled steel sheet at (coiling start temperature+20° C. to 100° C.) for 5 to 300 minutes; the step of cold rolling the hot-rolled steel sheet at a rolling reduction ratio of 10.0 to 90.0%; and the step of annealing the resulting cold-rolled steel sheet at 700 to 900° C.

公开(公告)号：US20220127691A1

公开(公告)日：2022-04-28

申请号：US17312871

申请日：2018-12-11

Applicant: NIPPON STEEL CORPORATION

Inventor： Hiroyuki KAWATA ,  Eisaku SAKURADA ,  Kohichi SANO ,  Takafumi YOKOYAMA

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

Abstract: A high-strength steel sheet includes a chemical composition including: by mass %, C: 0.080 to 0.500%, Si: 2.50% or less, Mn: 0.50 to 5.00%, P: 0.100% or less, S: 0.0100% or less, Al: 0.001 to 2.500%, N: 0.0150% or less, O: 0.0050% or less, and the balance: Fe and inevitable impurities. The high-strength steel sheet satisfying a predetermined formula has a microstructure in a region from ⅛t to ⅜t from a steel sheet surface. The microstructure includes: by volume %, 20% or more of acicular ferrite, 20% or more of an island-shaped hard structure including residual austenite, 2% to 25% of residual austenite, and 20% or less of aggregated ferrite.

公开(公告)号：US20210095356A1

公开(公告)日：2021-04-01

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: C21D9/46 ,  B32B15/01 ,  C22C38/18 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/10 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C21D8/02 ,  C21D6/00 ,  C23C2/40 ,  C23C2/28

Abstract: A steel sheet according to an aspect of the present invention has a predetermined chemical composition, in which 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 inside of the steel sheet, a number proportion of the retained austenite having an aspect ratio of 2.0 or more in the total retained austenite is 50% or more, a soft layer having a thickness of 1 μm to 100 μm from the surface is present in a sheet thickness direction, among ferrite contained in the soft layer, a volume fraction of grains having an aspect ratio of less than 3.0 is 50% or more, a volume fraction of retained austenite in the soft layer is 50% or more of the volume fraction of the retained austenite of the inside of the steel sheet, and a peak of an emission intensity at a wavelength indicating Si appears in a range of more than 0.2 μm from the surface to 5 μm or less from the surface.

公开(公告)号：US20250146095A1

公开(公告)日：2025-05-08

申请号：US18837473

申请日：2023-02-17

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Kengo TAKEDA ,  Katsuya NAKANO ,  Taku MIYAKAWA

IPC: C21D9/46 ,  C21D8/02 ,  C22C38/02 ,  C22C38/04

Abstract: This steel sheet includes, in mass % C: 0.15% to 0.50%, Si: 0.01% to 1.00%, Mn: 1.00% to 3.00%, P: 0% to 0.0200%, S: 0.0001% to 0.0200%, Al: 0.001% to 0.100%, and N: 0% to 0.0200%, with the remainder being Fe and impurities, in which a metallorgraphic structure has an area fraction of 0% to 10.0% of retained austenite and 0% to 5.0% of pearlite, ferrite, and bainite in total, with the remaining structure being martensite and tempered martensite, a maximum diameter of MnS predicted by extreme value statistics is 30 μm or less, a surface roughness Ra is 5 μm or less, and a surface layer has a Vickers hardness of greater than or equal to a tensile strength TS (MPa) of the steel sheet×0.25.

公开(公告)号：US20220282351A1

公开(公告)日：2022-09-08

申请号：US17426592

申请日：2020-03-12

Applicant: NIPPON STEEL CORPORATION

Inventor： Kengo TAKEDA ,  Hiroyuki KAWATA ,  Takafumi YOKOYAMA ,  Katsuya NAKANO

IPC: C21D9/46 ,  C21D8/02 ,  C22C38/00 ,  C22C38/42 ,  C22C38/44 ,  C22C38/46 ,  C22C38/48 ,  C22C38/50 ,  C22C38/52 ,  C22C38/54 ,  C22C38/60

Abstract: Provided are: a steel sheet having a high strength and excellent hydrogen embrittlement resistance; and a method of producing the same. The steel sheet has prescribed chemical composition and structure, in which a standard deviation σ of Mn concentration satisfies σ≥0.15 Mnave (wherein, Mnave represents an average Mn concentration) and a region with a Mn concentration of higher than (Mnave+1.3σ) has a circle-equivalent diameter of less than 10.0 μm. The method of producing the steel sheet includes: the hot rolling step that includes finish rolling a slab having a prescribed chemical composition under prescribed conditions; the step of coiling the thus obtained hot-rolled steel sheet at a coiling temperature of 450 to 700° C.; and the step of cold rolling the hot-rolled steel sheet and subsequently annealing this steel sheet at 800 to 900° C.

公开(公告)号：US20220275493A1

公开(公告)日：2022-09-01

申请号：US17634229

申请日：2020-09-03

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Kazuki SHIOKAWA ,  Tatsuya OBUCHI ,  Kunio HAYASHI

IPC: C22C38/60 ,  C22C38/58 ,  C22C38/54 ,  C22C38/50 ,  C22C38/48 ,  C22C38/44 ,  C22C38/42 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/08 ,  C22C38/04 ,  C22C38/02 ,  C22C38/06 ,  C22C38/00 ,  C22C38/10 ,  C21D9/46 ,  C21D8/02

Abstract: 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/mm2 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/mm2 or less.
(4) Formula (A) is satisfied. Vγ′/Vγ≥0.1  (A) Vγ: Initial retained austenite, Vγ′: Retained austenite after deep cooling at −196° C.
(5) The tensile strength is 1470 MPa or more.

公开(公告)号：US20220119908A1

公开(公告)日：2022-04-21

申请号：US17427870

申请日：2020-02-06

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Hiroyuki KAWATA ,  Kunio HAYASHI ,  Yuji YAMAGUCHI ,  Satoshi UCHIDA

IPC: C21D9/46 ,  C21D8/02 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/42 ,  C22C38/44 ,  C22C38/46 ,  C22C38/48 ,  C22C38/50 ,  C22C38/52 ,  C22C38/54 ,  C22C38/60 ,  C23C2/06 ,  C23C2/12 ,  C23C2/28 ,  C23C2/40

Abstract: Provided are a hot dip galvanized steel sheet comprising a base steel sheet and a hot dip galvanized layer on at least one surface of the base metal steel sheet, wherein the base steel sheet has a predetermined chemical composition, and contains, by volume fraction, ferrite: 0% to 50%, retained austenite: 0% to 30%, tempered martensite: 5% or more, fresh martensite: 0% to 10%, and pearlite and cementite in total: 0% to 5%, when there are remaining structures, the remaining structures consist of bainite, a concentration of B atoms at prior austenite grain boundaries is 2.0 atm % or more, and an average effective crystal grain size is 7.0 μm or less, and a method for producing the same.

公开(公告)号：US20240327962A1

公开(公告)日：2024-10-03

申请号：US18711903

申请日：2022-11-29

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Chisato YOSHINAGA ,  Takuya KUWAYAMA ,  Kengo TAKEDA ,  Takuya MITSUNOBU ,  Seiji FURUSAKO ,  Tatsuya OBUCHI

IPC: C22C38/04 ,  C21D6/00 ,  C21D8/02 ,  C22C38/02 ,  C22C38/06 ,  C23C2/06 ,  C23C2/20 ,  C23C2/28 ,  C23C2/40

CPC classification number: C22C38/04 ,  C21D6/005 ,  C21D8/0205 ,  C21D8/0226 ,  C21D8/0236 ,  C21D8/0273 ,  C22C38/02 ,  C22C38/06 ,  C23C2/06 ,  C23C2/20 ,  C23C2/28 ,  C23C2/40 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/003 ,  C21D2211/005 ,  C21D2211/008 ,  C21D2211/009

Abstract: Provided are a hot dip galvanized steel sheet having a predetermined chemical composition, and a steel microstructure comprising, by vol %, ferrite: 0 to 50%, tempered martensite: 1% or more, retained austenite: 5% or more, fresh martensite: 0 to 15%, total of pearlite and cementite: 0 to 5%, and balance: bainite, when measuring by GDS, a maximum value of Al concentration of an Al rich layer present at an interface of the base steel sheet and the hot dip galvanized layer is 2.0 mass % or more and an Sis/Sib right under the interface is 0.90 or less, a number density of recessed parts with a depth of more than 2 μm at the interface is 2.0/100 μm or less per interface length, and a tensile strength is 980 MPa or more, and a method for producing the same.

公开(公告)号：US20240182997A1

公开(公告)日：2024-06-06

申请号：US18410064

申请日：2024-01-11

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Hiroyuki KAWATA ,  Kunio HAYASHI ,  Yuji YAMAGUCHI ,  Satoshi UCHIDA

IPC: C21D9/46 ,  B32B15/01 ,  C21D8/02 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/18 ,  C22C38/42 ,  C22C38/44 ,  C22C38/46 ,  C22C38/48 ,  C22C38/50 ,  C22C38/52 ,  C22C38/54 ,  C22C38/60 ,  C23C2/02 ,  C23C2/06 ,  C23C2/28 ,  C23C2/40

CPC classification number: C21D9/46 ,  B32B15/013 ,  C21D8/0226 ,  C21D8/0263 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/008 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/18 ,  C22C38/42 ,  C22C38/44 ,  C22C38/46 ,  C22C38/48 ,  C22C38/50 ,  C22C38/52 ,  C22C38/54 ,  C22C38/60 ,  C23C2/02 ,  C23C2/0224 ,  C23C2/06 ,  C23C2/28 ,  C23C2/40 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/003 ,  C21D2211/005 ,  C21D2211/008 ,  C21D2211/009

Abstract: A hot dip galvanized steel sheet includes a base steel sheet and a hot dip galvanized layer on at least one surface of the base metal steel sheet, wherein the base steel sheet has a predetermined chemical composition, and contains, by volume fraction, ferrite: 0% to 50%, retained austenite: 0% to 30%, tempered martensite: 5% or more, fresh martensite: 0% to 10%, and pearlite and cementite in total: 0% to 5%, when there are remaining structures, the remaining structures consist of bainite, a concentration of B atoms at prior austenite grain boundaries is 2.0 atm % or more, and an average effective crystal grain size is 7.0 μm or less, and a method for producing the same.