Nippon Steel Sumitomo Metal Corporation

Sumitomo Metal Industries, Inc.

Toyoda Iron Works Co., Ltd.

Toyota Jidosha Kabushiki Kaisha

Kazuhito Imai

Tamotsu Toki

Nobusato Kojima

Atsushi Tomizawa

Naoaki Shimada

Kazuya Ishii

Toyomitsu Nakamura

Masanobu Ichikawa

Yukihiro Yoshikawa

Hiroyuki Takahashi

Masaru Takahashi

Kunihiro Fukui

Hitomi Nishibata

Akira Obayashi

Shuntaro Sudo

Toshinobu Nishibata

A galvanized steel sheet for hot forming, the galvanized steel sheet including a galvanized film provided on a surface of a steel sheet,

Galvanized steel sheet for hot forming

A heat treated galvannealed steel material having excellent post-painting corrosion resistance and a high strength which is suitable for use as an automotive part and a method for its manufacture are provided. A galvannealed steel material having a galvannealed coating on at least one side thereof is heat treated by heating at least a portion thereof to a temperature range in which hardening is possible. The coating remaining on the surface of at least a part of the portion which underwent heat treatment has a coating weight of at least 20 g/mand at most 80 g/mper side and an Fe content of at least 15% and at most 35%, an &#x3b7; phase is present in the coating, and the centerline average roughness Ra of the surface of the coating is at most 1.5 &#x3bc;m.

Heat treated galvannealed steel material and a method for its manufacture

A method of producing a hot press-formed member having good corrosion resistance comprises subjecting a zinc-based plated steel sheet to heat treatment by heating to a temperature region of 600-750&#xb0; C. at a rate of temperature increase up to 600&#xb0; C. of at most 50&#xb0; C. per second followed by cooling to 550&#xb0; C. or below to form a steel blank which has a zinc oxide layer in its uppermost surface portion and below it a zinc-iron alloy phase having an Fe content of at least 25 mass %. This steel blank is heated to a temperature of at least its Acpoint, then press formed immediately at a temperature of at least its Acpoint, and then rapidly cooled. The hot press-formed member has a surface region with zinc oxide and iron-zinc solid solution phases and not containing an intermetallic compound phase or a pure zinc phase.

Method for manufacturing a hot press-formed member

A method of manufacturing a bent metal member comprises supporting the outer surface of a tubular metal material having a Zn-Fe alloy coating layer at two locations spaced in the axial direction of the metal material. The metal material is fed in its axial direction and heated at a position between the two locations to a temperature range of at least the Acpoint at a heating speed such that the rate of temperature increase is at least 3.0&#xd7;10&#xb0; C. per second, held so that the time for which the surface of the metal material is at a temperature of 8.0&#xd7;10&#xb0; C. or higher is at most 2 seconds, and then rapid cooled. A bending moment is imparted to the healed portion in two or three dimensions to manufacture a bent metal member having on its surface a Zn-based layer which contains an &#x3b7;, phase.

Bent metal member and a method for its manufacture

Hot press forming of a steel material is made possible by coating the surface of the steel material with a plated layer of zinc or a zinc alloy and forming thereon a barrier layer which prevents the vaporization of zinc even when heated to 700-1000&#xb0; C. Corrosion resistance can also be guaranteed without requiring post treatment, and hot press forming of high tensile steel sheet and stainless steel sheet is made possible. The barrier layer is formed by forming an upper plated layer, by surface oxidation, by contact with an oxidizing agent, by contact with Zn and an oxidizing agent, by anodic electrolysis, by cathodic electrolysis, or by coating with a ZnO sol.

Hot press forming method

A hot press-formed article having improved corrosion resistance and coating adhesion when coated is obtained by hot press forming of a zinc-based plated steel material. It has a zinc-based plating layer comprising an iron-zinc solid solution phase and atop it a zinc oxide layer. The average thickness of the zinc oxide layer which is the outermost layer is at most 2 &#x3bc;m. A hot press-formed article having a good appearance and excellent corrosion resistance, coating adhesion, post-coating corrosion resistance, and weldability has a layer () consisting essentially of an iron-zinc solid solution phase atop a base material steel sheet (). It also has a zinc oxide layer () with an average thickness of at most 5 &#x3bc;m as an uppermost layer, but it does not have a substantial amount of an iron-zinc intermetallic compound phase. The total amount of Al contained in the iron-zinc solid solution layer () and the zinc oxide layer () is at most 0.5 g/m, and/or the total amount of Al oxides contained in these layers is at most 5 mg/m.

Hot press-formed article

Growing community of inventors

Amagasaki, Japan

Kazuhito Imai