Jfe Steel Corporation

Nkk Corporation

Nkk Cororation

Michitaka Sakurai

Kenji Takahashi

Yoshihiko Ono

Kaneharu Okuda

Yusuke Fushiwaki

Junichi Inagaki

Shoichiro Taira

Toru Imokawa

Masaaki Yamashita

Takayuki Urakawa

Minoru Tanaka

Katsutoshi Takashima

Yoshikazu Suzuki

Toyofumi Watanabe

Noriaki Kohsaka

Shuji Nomura

Satoshi Hashimoto

Takeshi Fujita

Kaoru Sato

Yoshimasa Funakawa

Yoshiyasu Kawasaki

Kohei Hasegawa

Toshio Ishii

Hideyuki Kimura

Masayasu Nagoshi

Katsuya Hoshino

Shusaku Takagi

Yasuaki Okita

Yoshiharu Sugimoto

Shunsuke Yamamoto

Shunichi Sugiyama

Kenji Tahara

Masaru Sagiyama

Hidetaka Kawabe

Chiyoko Tada

Yuki Takeda

Akira Gamou

Shotaro Terashima

Yoshie Obata

Wataru Tanimoto

Yoichi Miyakawa

Akira Hiraya

Yoshimasa Himei

Masahiro Iwabuchi

Toshihiko Ooi

Kenji Tsuzumi

Shunsaku Node

Yasuhisa Tajiri

Jun-ichi Inagaki

Shingo Arakawa

Nobuo Baba

To obtain a high-strength hot-dip galvanized steel sheet having excellent surface appearance even in the case where a steel strip containing Mn at a predetermined ratio or more to Si is subjected to hot-dip galvanizing treatment, a method of producing a hot-dip galvanized steel sheet using a continuous hot-dip galvanizing apparatus comprises: subjecting a steel strip to annealing, by conveying it in an annealing furnace; and subjecting the steel strip discharged from a cooling zone to hot-dip galvanizing using a hot-dip galvanizing line, to obtain a hot-dip galvanized steel sheet. The steel strip has a chemical composition containing, in mass %, Mn: 1.7% or more and 3.5% or less and Si: 0.2% or more and 1.05% or less and satisfying [Si]/[Mn]≤0.30. The chemical composition, a dew point of an atmosphere in the soaking zone, and a delivery temperature of the heating zone satisfy Formula (1).

Method of producing high-strength hot-dip galvanized steel sheet

Provided is a hot-pressed member that combines both high strength of 1850 MPa or more in TS and excellent delayed fracture resistance. A hot-pressed member comprises: a predetermined chemical composition; a microstructure in which a prior austenite average grain size is 8 μm or less, a volume fraction of martensite is 95% or more, and a volume fraction of granular carbide of 0.1 μm or more in grain size is 0.10% to 4.0%; a Ni diffusion region of 2.0 μm or more in a depth direction in a surface layer; and a tensile strength of 1850 MPa or more.

Hot-pressed member, cold-rolled steel sheet for hot pressing, and manufacturing methods therefor

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.

Hot-pressed member, cold-rolled steel sheet for hot-pressed member, and method for producing the same

A high-strength steel sheet contains, in mass %, C: 0.07 to 0.14%, Si: 0.65 to 1.65%, Mn: 1.8 to 2.6%, P: 0.05% or less, S: 0.005% or less, Al: 0.08% or less, N: 0.0060% or less, Ti: 0.005 to 0.030%, B: 0.0002 to 0.0030%, and either or both of Cr: 0.01 to 0.40% and Mo: 0.01 to 0.50% and satisfies the expression (1); where: an average grain size of a ferrite phase is 1.5 &#x3bc;m or less; an area ratio of the ferrite phase is 2% or more and 15% or less; an area ratio of a tempered martensite phase is 75% or more and 96% or less; and a total length per unit area of an interface between an untempered martensite phase and the ferrite phase and an interface between the untempered martensite phase and the tempered martensite phase is 6.3&#xd7;10&#x3bc;m/mto 5.0&#xd7;10&#x3bc;m/m.

High-strength steel sheet and manufacturing method therefor

A high-strength steel sheet having a composition containing C: 0.09% to 0.17%, Si: 0.6% to 1.7%, Mn: 3.5% or less, P: 0.03% or less, S: 0.005% or less, Al: 0.08% or less, N: 0.006% or less, Ti: 0.05% or less, and B: 0.0002% to 0.0030% on a mass basis, the remainder being Fe and inevitable impurities. The steel sheet also has a microstructure containing less than 20% (including 0%) of a ferrite phase, 75% or more (including 100%) of a tempered martensite phase, 10% or less (including 0%) of an untempered martensite phase, and less than 5% (including 0%) of a retained austenite phase in terms of area fraction. The tempered martensite phase has a Vickers hardness of 280 to 340 and a tensile strength of 950 MPa to 1,120 MPa.

High strength steel sheet and method for manufacturing the same

A high strength steel sheet is formed of steel having the composition containing by mass % over 0.015% and less than 0.100% C, less than 0.50% Si, over 1.0% and less than 2.0% Mn, 0.05% or less P, 0.03% or less S, 0.01% or more and 0.3% or less sol. Al, 0.005% or less N, less than 0.35% Cr, 0.0010% or more and 0.0050% or less B, less than 0.15% Mo, less than 0.030% Ti, and iron and unavoidable impurities as a balance, wherein the steel satisfies 2.1&#x2266;[Mneq]&#x2266;3.1, the microstructure of the steel includes a ferrite and a second phase, a volume fraction of the second phase is set to 2.0 to 12.0%, a total ratio of a volume fraction of martensite and a volume fraction of retained &#x3b3; to the volume fraction of second phase is 60% or more, and the number of carbides which are present within ferrite particles, have an aspect ratio of 3.0 or less and have a diameter of 0.25 to 0.90 &#x3bc;m is set to 10000 pieces/mmor less.

High strength steel sheet and method of manufacturing the same

A method of manufacturing a high strength cold rolled steel sheet includes hot-rolling and cold-rolling a steel slab annealing the steel sheet at an annealing temperature of 750&#xb0; C. to 830&#xb0; C.; subjecting the steel sheet to first cooling at an average cooling rate of 3&#xb0; C./sec to 40&#xb0; C./sec in a temperature range from the annealing temperature to 480&#xb0; C.; subjecting the steel sheet to second cooling at an average cooling rate of 8&#xb0; C./sec to 80&#xb0; C./sec in a temperature range from 480&#xb0; C. to Tc (&#xb0; C.) given by formula (6):Tc=435&#x2212;40&#xd7;[% Mn]&#x2212;30&#xd7;[% Cr]&#x2212;30&#xd7;[% V]&#x2003;&#x2003;(6)wherein [% A] is the content (% by mass) of alloying element A; and subjecting the steel sheet to third cooling at an average cooling rate of 0.3&#xb0; C./sec to 30&#xb0; C./sec in a temperature range from Tc (&#xb0; C.) to 200&#xb0; C.

High strength cold rolled steel sheet and method for manufacturing the same

A high-strength galvanized steel sheet has a low YP, good stretch flangeability, and excellent corrosion resistance and contains, on a percent by mass basis, more than 0.015% to less than 0.10% of C, 0.5% or less of Si, 1.0% to 1.9% of Mn, 0.015% to 0.050% of P, 0.03% or less of S, 0.01% to 0.5% of sol. Al, 0.005% or less of N, less than 0.40% of Cr, 0.005% or less of B, less than 0.15% of Mo, 0.4% or less of V, and less than 0.020% of Ti, in which 2.2&#x2266;[Mneq]&#x2266;3.1 and [% Mn]+3.3[% Mo]&#x2266;1.9, and [% Mn]+3.3[% Mo])/(1.3[% Cr]+8[% P]+150B*)&#x3c;3.5 are satisfied.

High-steel galvanized steel sheet and method for manufacturing the same

A multiphase steel sheet has a steel composition containing, in percent by mass, more than 0.015% to less than 0.100% of carbon, less than 0.40% of silicon, 1.0% to 1.9% of manganese, more than 0.015% to 0.05% of phosphorus, 0.03% or less of sulfur, 0.01% to 0.3% of soluble aluminum, 0.005% or less of nitrogen, less than 0.30% of chromium, 0.0050% or less of boron, less than 0.15% of molybdenum, 0.4% or less of vanadium, 0.02% or less of titanium, wherein [Mneq] is 2.0 to 2.8, the balance being iron and incidental impurities.

A high tensile-strength galvanized steel sheet includes C: at least 0.05% but less than 0.12%, Si: at least 0.01% but less than 0.35%, Mn: 2.0% to 3.5%, P: 0.001% to 0.020%, S: 0.0001% to 0.0030%, Al: 0.005% to 0.1%, N: 0.0001% to 0.0060%, Cr: more than 0.5% but not more than 2.0%, Mo: 0.01% to 0.50%, Ti: 0.010% to 0.080%, Nb: 0.010% to 0.080%, and B: 0.0001% to 0.0030%, the remainder being Fe and unavoidable impurities, wherein the high tensile-strength galvanized steel sheet has a microstructure that contains 20% to 70% by volume ferrite having an average grain size of 5 &#x3bc;m or less. The high tensile-strength galvanized steel sheet has a tensile strength of at least 980 MPa, and excellent formability and weldability.

High tensile-strength galvanized steel sheet and process for manufacturing high tensile-strength galvanized steel sheet

The invention provides a galvannealed steel sheet which has an oxide layer having 10 nm or larger thickness on the plateau of the coating layer flattened by temper rolling. With the use of the galvannealed steel sheet, no powdering occurs during press-forming, and stable and excellent sliding performance is attained. By selecting the area percentage of the plateau of the flattened coating layer to a range from 20 to 80%, making the coating layer single layer of &dgr; phase, and letting &zgr; phase exist in the &dgr; phase, further improved sliding performance and anti-powdering property are obtained.

Galvannealed steel sheet and method for manufacturing the same

A zinciferous coated steel sheet comprises a steel sheet, a zinciferous coating layer formed on the steel sheet, a Fe--Ni--Zn--O film formed on the zinciferous coating layer, and an oxide layer formed on a surface portion of the Fe--Ni--Zn--O film. The method comprises providing an electrolyte of an acidic sulfate aqueous solution, carrying out an electrolysis treatment in the electrolyte under a current density ranging from 1 to 150 A/dm.sup.2, and carrying out an oxidation treatment to a surface of the zinciferous coated steel sheet.

Zinciferous coated steel sheet and method for producing the same

Zinciferous plated steel sheet and method for manufacturing same

A method for manufacturing a zinciferous plated steel sheet, comprises: forming a zinciferous plating layer on a steel sheet; and forming an Fe--Ni--O film on the zinciferous plating layer. The Fe--Ni--O film is formed by carrying out electrolysis with the steel sheet as a cathode in an aqueous solution, dipping the steel sheet in an aqueous solution, or spraying a mist on a surface of the zinciferous plating layer.

Alloying-treated iron-zinc alloy dip-plated steel sheet excellent in

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Fukuyama, Japan

Michitaka Sakurai