Jfe Steel Corporation

Wataru Tanimoto

Masayasu Nagoshi

Katsuya Hoshino

Hiroyuki Masuoka

Naoto Yoshimi

Masahiko Tada

Hiroshi Kajiyama

Yoichi Makimizu

Shinji Ootsuka

Kyoko Fujimoto

Sakae Fujita

Shoichiro Taira

Takahiro Kubota

Kazuhiko Higai

Yoshiharu Sugimoto

Hideo Kijima

Hisato Noro

Nobuo Baba

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

An object of the present invention is to make it possible, without necessitating an alkali pretreatment, to form a zinc oxide layer having excellent sliding properties on a hot dip galvanized steel sheet not subjected to alloying after galvanizing and thus having a relatively low degree of surface activity. Another object of the present invention is to make it possible to manufacture a hot dip galvanized steel sheet having higher area ratio of Zn oxide layer formed on a coating surface and larger thickness of the Zn oxide layer. Specifically, the present invention provides a method for manufacturing a hot dip galvanized steel sheet comprising: subjecting a steel sheet to hot dip galvanizing and subsequent temper rolling; bringing the steel sheet into contact with acidic solution having pH buffering capacity; retaining the steel sheet for 1 second to 60 seconds after the contact with the acidic solution; and rinsing the steel sheet with water, to form a zinc oxide layer on a coating surface of the steel sheet, characterized in that the method further comprising: carrying out the temper rolling by either rolling the steel sheet first with a dull roll having Ra&#x2267;2.0 &#x3bc;m at rolling reduction rate &#x2266;5% and then with a bright roll having Ra&#x2266;0.1 &#x3bc;m at rolling reduction rate &#x2266;3% or rolling the steel sheet first with a bright roll having Ra&#x2266;0.1 &#x3bc;m at rolling reduction rate &#x2266;3% and then with a dull roll having Ra&#x2266;2.0 &#x3bc;m at rolling reduction rate &#x2266;5%.

Method for manufacturing hot dip galvanized steel sheet

A zinc-based metal plated steel sheet is excellent in tribological properties during press forming. An oxide layer containing crystalline 3Zn(OH)&#xb7;ZnSO&#xb7;xHO is formed on a plated surface. The oxide layer has a thickness of 10 nm or more. The crystalline oxide layer is composed of 3Zn(OH)&#xb7;ZnSO&#xb7;3-5HO.

Zinc-based metal plated steel sheet

A zinc-based metal plated steel sheet is excellent in tribological properties during press forming. An oxide layer containing crystalline 3Zn(OH).ZnSO.xHO is formed on a plated surface. The oxide layer has a thickness of 10 nm or more. The crystalline oxide layer is composed of 3Zn(OH).ZnSO.3-5HO.

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

The press formability of a galvanized steel sheet including an oxide film, which has a thickness of 10 nm to 100 nm, as a surface layer is nondestructively speedily evaluated. A specific method for solving problems is characterized by including the steps of irradiating X-rays to a galvanized steel sheet, dispersing a fluorescent X-ray, which is excited and emitted in the applying, with an analyzing crystal exhibiting the difference in diffraction angle between a primary oxygen K&#x3b1; x-ray and a secondary zinc L&#x3b2; x-ray of 2 degrees or more, detecting the X-ray, which is dispersed in the dispersing and which mainly contains the primary oxygen K&#x3b1; x-ray, with a detector, separating an X-ray at an energy level within the range of &#xb1;25% to &#xb1;75% relative to the reference (100%) that is the energy level of the primary oxygen K&#x3b1; x-ray from the X-ray, which is detected in the detecting and which mainly contains the primary oxygen K&#x3b1; x-ray, by adjusting the window width of a pulse-height analyzer, measuring the intensity of the X-ray separated in the separating, and evaluating the press formability of the galvanized steel sheet on the basis of the intensity of the X-ray measured in the measuring.

Method for evaluating press-formability of galvanized steel sheet

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Tokyo, Japan

Wataru Tanimoto