Jfe Steel Corporation

Hiromi Yoshitomi

Masaki Koba

Tatsuya Nakagaito

Yoshitsugu Suzuki

Yoshihiko Ono

Hiroshi Hasegawa

Hiroshi Matsuda

Yasuaki Okita

Yoshimasa Funakawa

Katsutoshi Takashima

Satoshi Maeda

Yoichi Makimizu

Yoshikazu Suzuki

Hiroyuki Masuoka

Takuya Hirashima

Gentaro Takeda

Yoshimasa Himei

Yasuhiro Nishimura

Gosuke Ikeda

Seisuke Tsuda

Nao Kawabe

To provide a galvanized steel sheet having high strength; specifically, with a tensile strength of 1160 MPa or more and excellent resistance spot weldability. A chemical composition of a base steel sheet contains one or more of Ti, Nb, V, and Zr: 0.02% or more and 0.20% or less in total, and an amount of diffusible hydrogen in a zinc or zinc alloy coating layer is 0.40 mass ppm or less.

Galvanized steel sheet and method for producing same

A high-strength galvanized steel sheet of the present invention includes a steel sheet having a specific chemical composition, and a steel structure containing, in terms of area ratio, 4% or more and 20% or less of retained austenite, 30% or less (including 0%) of ferrite, 40% or more of martensite, and 10% or more and 50% or less of bainite; and a galvanized layer provided on the steel sheet, in which an amount of diffusible hydrogen in the steel is less than 0.20 mass ppm, a tensile strength is 1100 MPa or more, a relationship between a tensile strength TS (MPa), an elongation El (%), and a sheet thickness t (mm) satisfies a (1) formula below, and a yield ratio YR is 67% or more.TS&#xd7;(El+3&#x2212;2.5)&#x2265;13000 &#x2003;&#x2003;(1)

High-strength galvanized steel sheet, high strength member, and method for manufacturing the same

A high-strength galvanized steel sheet includes a steel sheet having a chemical composition containing a predetermined component element, a mass ratio of a content of Si to a content of Mn in the steel (Si/Mn) being 0.1 or more and less than 0.2, and the balance: Fe and incidental impurities, and a steel structure in which an average grain size of inclusions containing at least one of Al, Si, Mg, and Ca and existing in an area extending from a surface to a position of &#x2153; of a sheet thickness is 50 &#x3bc;m or less, and an average nearest distance between ones of the inclusions is 20 &#x3bc;m or more; and a galvanized layer provided on a surface of the steel sheet, in which an amount of diffusible hydrogen contained in the steel is less than 0.25 mass ppm, and a tensile strength is 1100 MPa or more.

A high-strength galvanized steel sheet includes a steel sheet containing a predetermined component element, a mass ratio of a content amount of Si to a content amount of Mn in the steel (Si/Mn) being 0.2 or more, and a steel structure in which an average grain size of inclusions existing in an area extending from a surface to a position of &#x2153; of a sheet thickness is 50 &#x3bc;m or less, and an average nearest distance between ones of the inclusions is 20 &#x3bc;m or more; and a galvanized layer provided on a surface of the steel sheet, in which an amount of diffusible hydrogen contained in the steel is less than 0.25 mass ppm, oxides containing predetermined elements in an outer layer portion of the steel sheet account for 0.010 g/mor more per one surface, and a tensile strength is 1100 MPa or more.

A high-strength galvanized steel sheet of the present invention includes a steel sheet having a chemical composition containing a predetermined component element, and a steel structure in which an average grain size of inclusions containing at least one of Al, Si, Mg, and Ca and existing in an area extending from a surface to a position of &#x2153; of a sheet thickness is 50 &#x3bc;m or less, and an average nearest distance between ones of the inclusions is 20 &#x3bc;m or more; and a galvanized layer provided on a surface of the steel sheet and having a coating weight per one surface of 20 g/mor more and 120 g/mor less, in which an amount of diffusible hydrogen contained in the steel is less than 0.25 mass ppm, and a tensile strength is 1100 MPa or more.

Provided are a high-yield-ratio high-strength galvanized steel sheet and a method for manufacturing thereof. The high-yield-ratio high-strength galvanized steel sheet has a steel sheet having a specified chemical composition and a metallographic structure including, in terms of area ratio, in terms of area ratio, 15% or less of ferrite, 20% or more and 50% or less of martensite, and bainite and tempered martensite in a total amount of 30% or more, and a galvanized layer formed on the steel sheet having a coating weight of 20 g/mto 120 g/mper side, in which a yield strength ratio is 65% or more, a tensile strength is 950 MPa or more, and Mn oxides are contained in the galvanized layer in an amount of 0.015 g/mto 0.050 g/m.

High-yield-ratio high-strength galvanized steel sheet and method for manufacturing the same

A high-strength galvanized steel sheet having improved post-work impact resistance, a method for producing the high-strength galvanized steel sheet, and a high-strength member produced using the steel sheet. The high-strength galvanized steel sheet includes a steel sheet having a microstructure including ferrite and carbide-free bainite, martensite and carbide-containing bainite, and retained austenite, the total area fraction of ferrite and carbide-free bainite being 0% to 55%, the total area fraction of martensite and carbide-containing bainite being 45% to 100%, and the area fraction of retained austenite being 0% to 5%. Additionally, a galvanizing layer is disposed on the steel sheet. The density of gaps that cut across the entire thickness of the galvanizing layer in a cross section of the galvanizing layer, which is taken in the thickness direction so as to be perpendicular to the rolling direction, is 10 gaps/mm or more.

High-strength galvanized steel sheet, high-strength member, and method for producing high-strength galvanized steel sheet

A high-strength galvanized steel sheet is excellent in the external appearance of plating and the hydrogen brittleness resistance, and has a high yield ratio, and a method for manufacturing the same. The high-strength galvanized steel sheet including a steel sheet having a specific component composition and a specific steel structure, the amount of diffusible hydrogen in the steel sheet being 0.20 mass ppm or less; and a galvanizing layer provided on a surface of the steel sheet, the galvanizing layer having a content amount of Fe of 8 to 15% in mass %, and an attachment amount of plating per one surface of 20 to 120 g/m, wherein the amount of Mn oxides contained in the galvanizing layer is 0.050 g/mor less; and the high-strength galvanized steel sheet has a yield strength of 700 MPa or more and a yield strength ratio of 65% or more and less than 85%.

High-strength galvanized steel sheet and method for manufacturing same

A high-strength galvanized steel sheet includes a steel sheet having a steel composition having a specific component composition, a steel structure containing martensite and bainite at more than or equal to 70% (including 100%), ferrite at less than 20% (including 0%), and retained austenite at less than 5% (including 0%) in terms of area ratio, the amount of diffusible hydrogen in steel being less than or equal to 0.20 mass ppm; and a galvanizing layer provided on a surface of the steel sheet, having a content amount of Fe of 8 to 15% in mass %, and having an coating weight per one surface of 20 to 120 g/m, wherein the amount of Mn oxides contained in the galvanizing layer is less than or equal to 0.050 g/m, and a tensile strength is more than or equal to 1100 MPa and a yield ratio is more than or equal to 0.85.

Provided are a high-strength galvanized steel sheet and a method for producing the high-strength galvanized steel sheet. The high-strength galvanized steel sheet includes a base steel sheet having a specific composition and a microstructure including ferrite and carbide-free bainite, martensite and carbide-containing bainite, and retained austenite, the total area fraction of ferrite and carbide-free bainite being 0% to 65%, the total area fraction of martensite and carbide-containing bainite being 35% to 100%, and the area fraction of retained austenite being 0% to 15%, the content of diffusible hydrogen in the base steel sheet being 0.00008% by mass or less (including 0%) and a galvanizing layer disposed on the base steel sheet. The density of gaps in the galvanizing layer, that the gaps cutting across the entire thickness of the galvanizing layer, is 10 gaps/mm or more.

High-strength galvanized steel sheet and method for producing the same

A high-strength cold-rolled steel sheet has a component composition containing, on a percent by mass basis, C: 0.12% or more and 0.25% or less, Si: less than 0.5%, Mn: 2.0% or more and 3.0% or less, P: 0.05% or less, S: 0.005% or less, Al: 0.01% or more and 0.10% or less, and N: 0.010% or less, the balance being Fe and incidental impurities, the total area percentage of martensite and tempered martensite satisfying 20% or more and 90% or less, the area percentage of ferrite satisfying 10% or less, the area percentage of bainite satisfying 10% or more and 80% or less, the area percentage of a martensite-austenite constituent in the bainite being 1% or more and 10% or less, the area percentage of cementite having an average grain size of 1 &#x3bc;m or less in the bainite being 0.1% or more and 5.0% or less.

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Tokyo, Japan

Hiromi Yoshitomi