Toyota Jidosha Kabushiki Kaisha

Sumitomo Metal Industries, Inc.

Toyoda Iron Works Co., Ltd.

Nisshin Steel Co., Ltd.

Nippon Steel & Sumitomo Metal Corporation

Shuntaro Sudo

Masanobu Ichikawa

Akira Obayashi

Masaya Yamamoto

Masahiro Nakata

Hirofumi Taketsu

Keiji Izumi

Kunihiro Fukui

Tamotsu Toki

Kazuhito Imai

Yukihiro Yoshikawa

Toshinobu Nishibata

Kunihiro Sumitomo Metal Industries Ltd Fukui

Yukihiro Sumitomo Metal Industries Ltd Yoshikawa

Kazuhito Sumitomo Metal Industries Ltd Imai

Tamotsu Sumitomo Metal Industries Ltd Toki

A hot press-formed member having stable strength and toughness is manufactured from a high strength steel sheet by hot press forming. In the cooling stage during hot press forming, the cooling rate is at least the critical cooling rate until the Ms point is reached and it is then in the range of 25-150&#xb0; C./s in the temperature range from the Ms point to 200&#xb0; C. The Vickers hardness of the hot pressed member is less than the value of (maximum quenching hardness&#x2014;10) and at least the value of (maximum quenching hardness&#x2014;100).

Hot forming method and a hot formed member

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

An Al-coated steel sheet is improved in anti-scratching property during press-working and corrosion-resistance to a stored fuel by direct formation of an alkali-soluble resin film on an Al-coated steel sheet. An alkali-soluble resin, which can be dissolved in an alkali liquid of pH 9.0 or higher, is preferably urethane or acrylic resin with an acid value of 40-90 having a carboxyl group in its molecule. Alkali metal may be substituted for 1-50% hydrogen atom of the carboxyl group. A powdery synthetic resin at a ratio of 1-25 mass % and/or powdery silica at a ratio of 1-30 mass % may be dispersed in the resin film. The resin film is preferably of 0.2-5.0 &#x3bc;m in thickness. After the Al-coated steel sheet is painted with the resin, it is shaped to upper and lower halves of a fuel tank and washed with an alkali to dissolve off the resin film. The upper and lower halves are welded together and coated with a paint at their external surfaces to fabricate a fuel tank.

Fuel tank made from aluminum coated steel sheet

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Shuntaro Sudo