Jfe Steel Corporation

Kawasaki Steel Corporation

Yoshitsugu Suzuki

Yoichi Makimizu

Shinjiro Kaneko

Tatsuya Nakagaito

Yasunobu Nagataki

Yoshiyasu Kawasaki

Saiji Matsuoka

Hiroshi Hasegawa

Yusuke Fushiwaki

Mai Miyata

Minoru Tanaka

Gentaro Takeda

Yoshimasa Funakawa

Takashi Kawano

Mai Aoyama

Masaki Koba

Hiromi Yoshitomi

Hideyuki Kimura

Hideki Nagano

Hideyuki Takahashi

Masahiro Yoshida

Takashi Ueno

Osamu Furukimi

Satoshi Maeda

Kei Sakata

Yoshikazu Suzuki

Yoichiro Yamanaka

Yoichi Tobiyama

Chiaki Kato

Yoshiharu Sugimoto

Kazunori Osawa

Haruo Nakamichi

Akio Shinohara

Daisuke Harako

Masanari Tomozawa

Hiroshi Matsuda

Katsumi Yamada

Yohei Sato

Kohei Hasegawa

Akira Matsuzaki

Satoru Ando

Yuki Toji

Noriaki Kohsaka

Hiroyuki Masuoka

Shusaku Takagi

Kenji Kawamura

Junichiro Hirasawa

Naoto Yoshimi

Kazuaki Kyono

Koichiro Fujita

Hirokazu Sugihara

Akihiko Furuta

Yoshimasa Himei

Shinji Otsuka

Toshihiko Ooi

Masaru Miyake

Toshiyuki Okuma

Koji Maitake

It is provided a surface-treated steel sheet that can be produced without using hexavalent chromium and has excellent film wet adhesion and coating secondary adhesion as well as high film corrosion resistance and coating corrosion resistance. It is a surface-treated steel sheet having: a steel sheet; a metallic Cr layer disposed on at least one surface of the steel sheet; and a Cr oxide layer disposed on the metallic Cr layer, and the surface-treated steel sheet has a water contact angle of 50° or less and a total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface to Cr of 5% or less.

Surface-treated steel sheet and method of producing the same

It is provided a surface-treated steel sheet that can be produced without using hexavalent chromium and has excellent sulfide staining resistance and coating secondary adhesion. It is a surface-treated steel sheet having: a Sn plating layer; a metallic Cr layer disposed on the Sn plating layer; and a Cr oxide layer disposed on the metallic Cr layer, on at least one surface of a steel sheet, and the surface-treated steel sheet has a water contact angle of 50° or less and a total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface to Cr of 5% or less.

A high-strength galvanized steel sheet and a method for producing the steel sheet. The steel sheet has a composition that includes C: 0.030% to 0.250%, Si: 0.01% to 3.00%, Mn: 2.00% to 10.00%, P: 0.001% to 0.100%, S: 0.0001% to 0.0200%, N: 0.0005% to 0.0100%, Ti: 0.005% to 0.200%, on a mass basis, and Fe and inevitable impurities. Additionally, the steel sheet has concentration of solute Mn at a depth of 5 &#x3bc;m or less from a surface of the steel sheet that is 1.50% by mass or less, and a value obtained by dividing the average mass percentage of Mn in retained austenite by the average mass percentage of Mn in ferrite is 2.0 or more.

Method for manufacturing high-strength galvanized steel sheet and high-strength galvanized steel sheet

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.

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

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.

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

Provided are a high-strength galvannealed steel sheet, and a manufacturing method therefor. The manufacturing method is for a high-strength galvannealed steel sheet which includes a zinc coated layer with a coating weight of 20 to 120 g/mper side on a surface of a steel sheet having a chemical composition containing, in mass %, C: 0.03 to 0.35%, Si: 0.01 to 1.00%, Mn: 3.6 to 8.0%, Al: 0.001 to 1.00%, P: 0.100% or less, and S: 0.010% or less, with the balance being Fe and inevitable impurities. The method includes: setting a cold rolling reduction ratio to 20% or more and 35% or less when cold rolling is performed on the steel sheet, and setting a maximum steel sheet temperature to be reached in an annealing furnace to 600&#xb0; C. or higher and 700&#xb0; C. or lower when annealing is further performed on the steel sheet.

High-strength galvannealed steel sheet

High-strength galvannealed steel sheet including any of a) an oxide containing Fe and Mn, b) an oxide containing Fe and Mn and an Fe oxide, c) an oxide containing Fe and Mn and a Mn oxide, d) an oxide containing Fe and Mn, an Fe oxide, and a Mn oxide, and e) an Fe oxide and a Mn oxide is present in a zinc coated layer. The total amount of oxide is 0.01 to 0.100 g/m; the ratio by mass % of Mn to Fe, e.g., Mn/Fe, contained in the oxide is 0.10 to 10.00; an oxide of at least one selected from Fe and Mn is present in an amount of 60% or more; and an oxide of at least one selected from Fe and Mn is present in a surface layer portion of a steel sheet in an amount of 0.040 g/mor less (not including zero).

Mn-containing galvannealed steel sheet and method for producing the same

A high-strength hot-dip coated hot-rolled steel sheet excellent in terms of surface appearance quality and coating adhesiveness and a method for manufacturing. The method includes performing hot rolling followed by pickling on steel to form a pickled steel sheet, the steel having a chemical composition containing, by mass %, C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.3% or more and 2.5% or less, P: 0.08% or less, S: 0.02% or less, Al: 0.001% or more and 0.20% or less, and Fe and inevitable impurities. The method further includes performing rolling with a rolling reduction ratio of 1% or more and 10% or less, and a hot-dip coating treatment. The obtained steel sheet has an arithmetic average roughness Ra of 2.0 &#x3bc;m or less on the surface of the steel sheet, and a tensile strength of 590 MPa or more.

High-strength hot-dip coated hot-rolled steel sheet and method for manufacturing the same

A method for producing a high-strength galvanized steel sheet having excellent fatigue resistance properties. The method includes an oxidation processing in which a steel sheet is heated at a temperature of 400 to 750&#xb0; C. in an atmosphere having an Oconcentration of 1000 ppm by volume or more and a HO concentration of 1000 ppm by volume or more, and the steel sheet is heated at a temperature of 600 to 850&#xb0; C. in an atmosphere having an Oconcentration of less than 1000 ppm by volume and a HO concentration of 1000 ppm by volume or more. The method also includes reduction-annealing in which the steel sheet is heated at a heating rate of 0.1&#xb0; C./sec or more to a temperature of 650 to 900&#xb0; C. in an atmosphere having a Hconcentration of 5 to 30 vol % and a HO concentration of 10 to 1000 ppm by volume.

Method for producing high-strength galvanized steel sheet

A method of producing a galvannealed steel sheet includes: annealing a steel strip by conveying the steel strip through a heating zone including a direct fired furnace, a soaking zone, and a cooling zone in this order in an annealing furnace; hot-dip galvanizing the steel strip discharged from the cooling zone; and heat-alloying a galvanized coating formed on the steel strip. Mixed gas of humidified gas and dry gas is supplied into the soaking zone from at least one gas supply port located in a region of lower &#xbd; of the soaking zone in a height direction so that a dew point measured in a region of upper &#x2155; of the soaking zone in the height direction and a dew point measured in a region of lower &#x2155; of the soaking zone in the height direction are both 20&#xb0; C. or more and 0&#xb0; C. or less.

Method of producing galvannealed steel sheet

Provided are a cold-rolled steel sheet which can preferably be used for manufacturing a high-strength galvanized steel sheet and methods for manufacturing the steel sheets. The cold-rolled steel sheet has a specified chemical composition, in which the Mn concentration in a surface layer of the steel sheet satisfies relational expression (1) and relational expression (2) below. 8&#x2264;(C/C)&#xd7;Mn . . . (1) (C/C)&#xd7;Mn&#x2264;2.5 . . . (2) where C: maximum Mn concentration in a region within 0.5 &#x3bc;m of the surface of a steel sheet in the thickness direction; C: average Mn concentration in a region from a position located 5 &#x3bc;m from a surface of a steel sheet in the thickness direction to a position located 5 &#x3bc;m from an opposite surface in the thickness direction; C: minimum Mn concentration in a region from 0.5 &#x3bc;m to 5 &#x3bc;m from the surface of a steel sheet in the thickness direction; and Mn: Mn content (mass %).

Cold-rolled steel sheet, coated steel sheet, method for manufacturing cold-rolled steel sheet, and method for manufacturing coated steel sheet

Provided is a hot-dip Al&#x2014;Zn&#x2014;Mg&#x2014;Si coated steel sheet having good corrosion resistance in flat parts and edge parts, and also having excellent worked part corrosion resistance. The hot-dip Al&#x2014;Zn&#x2014;Mg&#x2014;Si coated steel sheet includes a base steel sheet and a hot-dip coating on a surface of the base steel sheet. The hot-dip coating includes an interfacial alloy layer present at an interface with the base steel sheet and a main layer present on the interfacial alloy layer, and contains from 25 mass % to 80 mass % of Al, from greater than 0.6 mass % to 15 mass % of Si, and from greater than 0.1 mass % to 25 mass % of Mg. The Mg content and Si content in the hot-dip coating satisfy formula (1):/(&#x2212;0.6)&#x3e;1.7&#x2003;&#x2003;(1)where Mrepresents the Mg content (mass %) and Mrepresents the Si content (mass %).

Hot-dip Al&#x2014;Zn&#x2014;Mg&#x2014;Si coated steel sheet and method of producing same

A method for producing high-strength galvanized steel sheets having excellent coating adhesion, workability and appearance. The method comprises hot rolling a slab comprising, by mass %, C: 0.05 to 0.30%, Si: 0.1 to 2.0% and Mn: 1.0 to 4.0%, then coiling the steel sheet into a coil at a specific temperature T, and pickling the steel sheet, cold rolling the hot-rolled steel sheet resulting from the hot rolling, annealing the cold-rolled steel sheet resulting from the cold rolling under specific conditions, and galvanizing the annealed sheet resulting from the annealing in a galvanizing bath containing 0.12 to 0.22 mass % Al.

Method and facility for producing high-strength galavanized steel sheets

Growing community of inventors

Tokyo, Japan

Yoshitsugu Suzuki