Nisshin Steel Co., Ltd.

Nippon Steel Nisshin Co., Ltd.

Shigeyasu Morikawa

Takahiro Fujii

Hirofumi Taketsu

Masaya Yamamoto

Shinya Furukawa

Mitsuo Asabuki

Tadashi Nakano

Masanori Matsuno

Keiji Izumi

Takao Tsujimura

Yasumi Ariyoshi

Kouichiro Ueda

A chemically processed steel sheet comprises a steel base coated with an Al&#x2014;Si alloy plating layer, whose Si content is preferably adjusted to 5&#x2013;13 mass % as a whole and to 7&#x2013;80 mass % at a surface, and a converted layer generated on the surface of the plating layer. The converted layer contains both soluble and scarcely-soluble compounds. The soluble compound, such as a manganese oxide or hydroxide, or a valve metal fluoride, is once dissolved into water in an atmosphere and then re-precipitated as scarcely-soluble compounds at defective parts of the converted layer. The scarcely-soluble compounds act as a barrier for corrosion prevention of a base steel. Due to the re-precipitation, i.e., self-repairing faculty, excellent corrosion resistance of the converted layer is still maintained even after defects are introduced therein during plastic deformation of the steel sheet.

Chemically processed steel sheet excellent in corrosion resistance

A chemically processed steel sheet comprising a steel base coated with an Al&mdash;Si alloy plating layer, whose Si content is preferably adjusted to approximately 5-13 mass % as a whole and to approximately 7-80 mass % at a surface, and a converted layer generated on the surface of the plating layer. The converted layer contains both soluble and scarcely-soluble compounds. The soluble compound such as a manganese oxide or hydroxide or a valve metal fluoride is once dissolved to water in an atmosphere and then re-precipitated as scarcely-soluble compounds at defective parts of the converted layer. The scarcely-soluble compounds act as a barrier for corrosion-prevention of a base steel. Due to the re-precipitation, that is self-repairing faculty, excellent corrosion resistance of the converted layer is still maintained even after defects are introduced therein during plastic deformation of the steel sheet.

A new processed steel sheet comprising of a steel base coated with a Zn or its alloy plating layer and a converted layer, which contains both of at least an insoluble or scarcely-soluble metal compound and at least a soluble metal compound. The insoluble or scarcely-soluble compound may be one or more of valve metal oxides or hydroxides, and the soluble compound may be one or more of valve metal fluorides. The converted layer may be also composed of one or more of complex compounds of Mn and Ti. The insoluble or scarcely-soluble compound acts as a barrier for insulation of a steel base from an atmosphere, while the soluble compound exhibits a self-repairing faculty to repair defective parts of the converted layer. Due to the converted layer, the processed steel sheet is remarkably improved in corrosion resistance, without the presence of chromium compounds which would put harmful influences on the environment.

Chemically processed steel sheet improved in corrosion resistance

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Sakai, Japan

Shigeyasu Morikawa