Kawasaki Steel Corporation

Kawatetsu Galvanizing Co., Ltd.

Toshio Irie

Susumu Sato

Toshio Ichida

Osamu Hashimoto

Hajime Ogata

Isao Takahashi

Susumu Satoh

Hajime Kimura

Kazuaki Kyono

Shigeo Kurokawa

Kazuo Mochizuki

Saiji Matsuoka

Akio Tosaka

Takashi Obara

Toshiyuki Kato

Hisatada Nakakoji

Koichi Hashiguchi

Hiroshi Shimanaka

Kozo Tsunoyama

Shunichi Tsugawa

Ko Matsumura

Yasuo Yokoyama

Kyoko Yamaji

Hiroto Nakamura

Akira Yasuda

Toshio Suzuki

Toshio Sadayori

Yoshihiro Matsumoto

Shigeru Kobayashi

Takahisa Yoshihara

Toshitomo Sugiyama

Masatoshi Shinozaki

Motoyuki Konishi

Akira Matsuda

Hisatada Nakakouji

Yoshiharu Ohashi

Toshikuni Tanda

Katsuo Yamaguchi

Kazuo Hamachi

Tomoyuki Ichi

Nobuo Matsuno

Yozo Ogawa

Sachiko Otsuka

Yasuhiro Akeda

Yasuhei Sakamoto

Hideshi Fujisawa

Morimasa Kuroda

Koji Seto

Yoshihiko Kameishi

Method for the production of steel sheet coated with a fluororesin film

The present invention relates to the production of a cold rolled steel sheet having good ageing resistance and small anisotropy and adapted for deep drawing, which properties can satisfy concurrently the demands for the deep drawability and ageing resistance of the cold rolled steel sheet to be pressed and used for automotive exterior plate. The present invention has concurrently and satisfactorily solved the problems in the above described good ageing resistance and anisotropy, which problems had not hitherto been solved in the conventional method, by a method wherein a cold rolled steel sheet having such a limited composition that contains not more than 0.004% of C, 0.002-0.010% of a total amount of at least one element selected from Nb, Ti, V, Zr and W, and further occasionally contains not more than 0.0050% of B, is subjected to a continuous annealing at a temperature within the range of 700-950.degree. C. in the production of the cold rolled steel sheet according to the conventional method. The steel sheet obtained in the present invention can be advantageously used as a thin steel sheet adapted to be pressed, for example, into an automotive exterior plate.

Method of producing a cold rolled steel sheet having a good ageing

A method of manufacturing formable as-rolled thin steel sheets having excellent ridging resistance and other properties is disclosed, which comprises rolling a low carbon steel to a given thickness without cold rolling and recrystallization annealing steps. In this rolling, at least one rolling pass is carried out within a given temperature range at high draft and high strain rate.

Method of manufacturing formable as-rolled thin steel sheets

The invention relates to a method of manufacturing a high-strength steel sheet by annealing the steel sheet after cold rolling. In order to obtain the low-yield ratio, high-strength steel sheet having high strength and good ductility, resistance to secondary cold-work embrittlement and spot weldability at low cost, the steel sheet containing 0.03-0.15% of P and specified amounts of C, Mn and Al as basic components and optionally containing, as a selective component, at least one element selected from a group of Si, Cr, Mo and B and a group of Nb, Ti, and V in such amounts as to meet the relation formula restricting the total content of Mn, Si, P, Cr and Mo is subjected to annealing under the conditions that the sheet is heated at a temperature of from Ac.sub.1 transformation point to 950.degree. C. for from 10 seconds to 10 minutes and cooled in such a control manner that an average cooling rate between 600.degree. C. and 300.degree. C. is not less than a specified critical cooling rate CR pertaining to the chemical composition and within a range of 15.degree.-200.degree. C./sec (FIGS. 1 and 4). The invention is suitable for the production of bumper, door guard bar, and the like in the automotive vehicles.

Low yield ratio high-strength annealed steel sheet having good ductility

Method of manufacturing a low yield ratio high-strength steel sheet

A tin-free steel strip comprising a steel strip, 40 to 150 mg/m.sup.2 of a metallic chromium layer on the steel surface, and 5 to 25 mg/m.sup.2 of a chromium compound containing layer thereon wherein the metallic chromium layer contains a plurality of protrusions, exhibits improved corrosion resistance and weldability and is thus useful in the manufacture of welded cans. Preferably, 1.times.10.sup.11 to 1.times.10.sup.14 protrusions having a diameter of 5 to 1000 nm at the base thereof are present per square meter of the metallic chromium layer surface. The tin-free steel strip is produced by chromium plating a steel strip in an aqueous solution containing CR.sup.6+ preferably to a weight of 40 to 140 mg/m.sup.2, subjecting the chromium plated strip to anodic electrolysis, preferably at an eectricity quantity of 0.1 to 10 C/dm.sup.2, and subjecting the strip to a cathodic treatment in an aqueous solution containing Cr.sup.6+ and a chromium plating aid so as to deposit additional metallic chromium, preferably in a weight of 10 to 60 mg/m.sup.2.

Tin-free steel strips useful in the manufacture of welded cans and

A process for producing a formable thin steel sheet excellent in ridging resistance. Said process comprises finishing a low carbon steel at a strain rate of not less than 300 (s.sup.-1) in a temperature range of 800.degree. to 300.degree. C. in at least one pass when the low carbon steel is rolled into a specified thickness, and subsequently performing recrystallization annealing.

Production of formable thin steel sheet excellent in ridging resistance

Steel strips having a Zn-Fe-P alloy electroplated thereon exhibit improved corrosion resistance, particularly perforation corrosion resistance, as long as the plating contains 5 to 30% by weight of iron and 0.0003 to 0.5% by weight of phosphorus.

Corrosion-resistant steel strip having Zn-Fe-P alloy electroplated

Highly corrosion resistant plated steel strips or sheets adapted for phosphate treatment and cathodic electrodeposition and intended for use in automobiles, are produced by electroplating at least one surface of a steel strip with an alloy consisting essentially of 0.0003 to 15% by weight of phosphorous, balance essentially iron, in a plating bath containing Fe.sup.2+ ions in an amount of from 0.3 mol/liter to the solubility limit and hypophosphorous acid and/or a hypophosphite in an amount of 0.001 to 25 g/liter expressed as NaH.sub.2 PO.sub.2.H.sub.2 O at a pH of 1.0 to 5.0, a temperature of 30.degree. to 60.degree. C., and a current density of from more than 20 to 200 A/dm.sup.2, preferably 40 to 150 A/dm.sup.2. A top coat can be applied thereover, of one element selected from the group consisting of Ni, Zn, Mn, and Ti, deposited on the Fe-P plating layer to a build-up of 5 to 50 mg/m.sup.2. A lower layer of zinc or a zinc alloy can also be electrodeposited on at least one surface of the steel strip, prior to formation of the Fe-P layer. A surface film can be formed by chemically treating the Fe-P plating layer with a phosphate.

Corrosion resistant surface-treated steel strip and process for making

Surface-treated steel strips suitable for electric resistance welding are prepared by forming a first layer of iron-nickel alloy on a steel strip, said first layer having a weight ratio of Ni/(Fe+Ni) in the range between 0.02 and 0.50 and a thickness of 10 to 5,000 angstroms, forming a second layer of tin or iron-tin-nickel alloy on said first layer by tin plating to a coating weight of 0.1 to 1 g/m.sup.2 of tin and optionally, causing the tin to reflow, and forming a third layer on said second layer by effecting an electrolytic chromate treatment, said third layer consisting essentially of metallic chromium and hydrated chromium oxide in a total amount of 5 to 20 mg/m.sup.2 calculated as elemental chromium. More preferably, the electrolytic chromate treatment is controlled such that at least 2 mg/m.sup.2 of metallic chromium is present in the third layer.

Surface-treated steel strips adapted for electric resistance welding

Method of producing a thin steel sheet having baking hardenability and

Process of manufacturing a cold rolled steel sheet having excellent

A dual phase-structured hot rolled steel sheet having a composition consisting of 0.03-0.15% by weight of C. 0.6-1.8% by weight of Mn, 0.04-0.2% by weight of P, not more than 0.10% of Al, not more than 0.008% by weight of S, and the remainder being substantially Fe, and having a microstructure consisting of ferrite and martensite dispersed therein, the area fraction of said ferrite being at least 70% and that of said martensite being at least 5% at the section of the steel sheet, has a high tensile strength and a low yield ratio of not higher than 70%, and has excellent formability. The steel sheet can be produced in a simple manner by cooling directly a hot rolled sheet at an ordinary cooling rate without the use of a particular cooling pattern.

Dual phase-structured hot rolled high-tensile strength steel sheet and a

Surface-treated steel strips suitable for electric resistance welding are prepared by forming a first layer of iron-nickel alloy on a steel strip, this first layer having a weight ratio of Ni/(Fe+Ni) in the range between 0.02 and 0.50 and a thickness of 10 to 5,000 angstroms, forming a second layer of tin or iron-tin-nickel alloy on the first layer by tin plating to a coating weight of 0.1 to 1 g/m.sup.2 of tin and optionally, causing the tin to reflow. A third layer is formed on the second layer by effecting an electrolytic chromate treatment, this third layer consisting essentially of metallic chromium and hydrated chromium oxide in a total amount of 5 to 20 mg/m.sup.2 calculated as elemental chromium. Preferably, the electrolytic chromate treatment is controlled so that at least 2 mg/m.sup.2 of metallic chromium is present in the third layer.

Process for preparing surface-treated steel strips adapted for electric

The present invention provides high tensile strength cold rolled steel sheets having excellent formability, which consist of 0.002-0.015% of C, not more than 1.2% of Si, 0.04-0.8% of Mn, 0.03-0.10% of P, 0.02-0.10% and not less than N%.times.4 of Al, C%.times.3-{C%.times.8+0.020%} of Nb and the remainder being substantially Fe, as the high tensile strength steel sheets which reduce the weight of automobiles and the like. The steel sheet is produced by hot rolling a steel slab having the above described composition to obtain a hot rolled coil, in the hot rolling the total reduction rate being at least 90%, the rolling speed in the finishing rolling being at least 40 m/min and the coiling-up temperature being at least 600.degree. C.; cold rolling the above described hot rolled coil in a conventional process to obtain a cold rolled steel strip having a final gauge; subjecting the above described cold rolled steel strip to a continuous annealing at a temperature of 700.degree.-900.degree. C. for 10 sec-5 min and then cooling the annealed strip to 500.degree. C. at a rate of at least 60.degree. C./min. The steel sheets having the above described composition, except that Si is not more than 0.5%, are suitable for the continuous hot-dip galvanizing.

Method for producing high tensile strength cold rolled steel sheets

Growing community of inventors

Chiba, Japan

Toshio Irie