Jfe Steel Corporation

Nkk Corporation

Shoichiro Taira

Masayasu Nagoshi

Kenji Takahashi

Yoshihiko Ono

Kaneharu Okuda

Yoshiharu Sugimoto

Michitaka Sakurai

Takashi Kawano

Yusuke Fushiwaki

Katsuya Hoshino

Akira Gamou

Yoichi Miyakawa

Masaaki Yamashita

Wataru Tanimoto

Kazutoshi Hanada

Kaoru Sato

Masaki Tada

Satoru Ando

Junichi Inagaki

Hiroyuki Masuoka

Naoto Yoshimi

Shinichi Furuya

Shinji Ootsuka

Toru Imokawa

Shuji Nomura

Etsuo Hamada

Masahiro Iwabuchi

Kazuki Nakazato

Shigeyuki Aizawa

Shunsaku Node

Hirotsugu Kondo

Yuta Terasaki

A method for producing a galvanized steel sheet includes an oxide layer forming step of bringing a galvanized steel sheet into contact with an acidic solution containing sulfate ions, then holding the galvanized steel sheet in contact for 1 to 60 seconds, and then washing the galvanized steel sheet with water; and a neutralization treatment step of holding a surface of an oxide layer, which has been formed in the oxide layer forming step, in contact with an alkaline aqueous solution for 0.5 seconds or longer, and then performing washing with water and drying. The alkaline aqueous solution contains P ions at a P concentration of 0.01 g/L or more and carbonate ions at a carbonate ion concentration of 0.1 g/L or more.

Galvanized steel sheet and method for producing the same

Provided is a method for producing a galvanized steel sheet that includes an oxide layer forming step of bringing a galvanized steel sheet into contact with an acidic solution containing sulfate ions, then holding the galvanized steel sheet in contact for 1 to 60 seconds, and then washing the galvanized steel sheet with water; and a neutralization treatment step of holding a surface of an oxide layer, which has been formed in the oxide layer forming step, in contact with an alkaline aqueous solution for 0.5 seconds or longer, and then performing washing with water and drying. The alkaline aqueous solution contains 0.1 g/L or more of carbonate ions.

There is provided a method for manufacturing a galvanized steel sheet that has low sliding resistance in press forming and good degreasing property even under severe alkaline degreasing treatment conditions due to low temperature and short process line length. An oxide layer formed on the surface of a galvanized steel sheet is subjected to neutralization treatment using an alkaline aqueous solution containing 0.01 g/L or more of P ions and 0.01 g/L or more of colloid dispersed particles, wherein the alkaline aqueous solution preferably contains at least one phosphorus compound selected from phosphates, pyrophosphates, and triphosphates and at least one type of colloid dispersed particles selected from Ti, silica, Pt, Pd, Zr, Ag, Cu, Au, and Mg.

Method for manufacturing galvanized steel sheet

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

The high strength galvanized steel sheet contains C: more than 0.015% and lower than 0.100%, Si: 0.3% or lower, Mn: lower than 1.90%, P: 0.015% or more and 0.05% or lower, S: 0.03% or lower, sol.Al: 0.01% or more and 0.5% or lower, N: 0.005% or lower, Cr: lower than 0.30%, B: 0.0003% or more and 0.005% or lower, and Ti: lower than 0.014% in terms of mass %, and satisfies 2.2&#x2266;[Mneq]&#x2266;3.1 and 0.42&#x2266;8[% P]+150B*&#x2266;0.73. The steel microstructure contains ferrite and a second phase, in which the second phase area ratio is 3 to 15%, the ratio of the area ratio of martensite and retained &#x3b3; to the second phase area ratio is more than 70%, and 50% or more of the area ratio of the second phase exists in the grain boundary triple point.

High strength galvanized 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.

The invention provides a hot dip galvanized steel sheet which has: a hot dip galvanizing layer having a flat part on a surface thereof; and a film formed on the flat part. The film is composed of a compound containing Zn, Fe, and O, having an average film thickness A in a range from 10 to 100 nm determined by an element analysis of the film, and has {[Fe]/([Zn]+[Fe])} in the film in a range from 0.002 to 0.25, where [Zn] and [Fe] designate the content (% by atom) of Zn and Fe in the film, respectively. Since the hot dip galvanized steel sheet of the invention has excellent press-formability, bondability, and phosphatability, it is suitable for automobiles and electrical appliances.

Hot dip galvanized steel sheet and method for manufacturing same

A method of manufacturing a hot dip galvannealed steel sheet, including the steps of: subjecting a steel sheet to hot dip galvanizing to manufacture a hot dip galvanized steel sheet; heating the hot dip galvanized steel sheet for alloying; subjecting the hot dip galvanized steel sheet to temper rolling; bringing the temper-rolled hot dip galvanized steel sheet into contact with an acid solution containing at least one ion selected from the group consisting of Zr ions, Ti ions, and Sn ions to thereby form an acid solution film on the surface of the steel sheet; after completion of the contact, a state where the acid solution film is formed on the surface of the steel sheet is held for at least 1 second; and washing with water the hot dip galvanized steel sheet after holding, to thereby form a Zn oxide layer having a thickness of 10 nm or more on the surface of the galvanized steel sheet. The hot dip galvannealed steel sheet has an oxide layer having an average thickness of 10 nm or more on the surface of the plated steel sheet.

Method of manufacturing hot dip galvannealed steel sheet and hot dip galvannealed steel sheet

A hot-dip galvanized steel sheet includes a plating layer substantially composed of the &#x3b7; phase and an oxide layer disposed on a surface of the plating layer. The oxide layer has an average thickness of 10 nm or more and includes a Zn-based oxide layer and an Al-based oxide layer. A method for producing the hot-dip galvanized steel sheet includes a hot-dip galvanization step, a temper rolling step, and an oxidation step.

Zinc hot dip galvanized steel plate excellent in press formability and method for production thereof

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.

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Fukuyama, Japan

Shoichiro Taira