Nippon Steel Corporation

Honda Motor Co., Ltd.

Toshiyuki Katsumi

Koki Tanaka

Kazuhiko Honda

Ikuo Kikuchi

Kaoru Yamazaki

Yoshitaka Okitsu

Kimitaka Hayashi

Katsuyoshi Kaneko

Yoshikazu Umeno

Takahiro Tanae

A surface treated steel sheet has a surface treatment film including a metallic compound containing titanium, a metallic compound containing magnesium, a cationic urethane resin having at least one cationic functional group selected from primary to tertiary amino groups and quaternary ammonium bases, and a cationic phenol polycondensate which is a polycondensate of a phenol compound with an aldehyde and has a cationic functional group, wherein the titanium content in the surface treatment film is in the range of 1 mass % to 4 mass % based on a total solid content; the magnesium content in the surface treatment film is in the range of 0.2 mass % to 2 mass % based on a total solid content; the cationic urethane resin content in the surface treatment film is in the range of 20 mass % to 35 mass % based on a total solid content; the cationic phenol polycondensate content in the surface treatment film is in the range of 25 mass % to 40 mass % based on a total solid content; and the mass ratio of the cationic urethane resin to the cationic phenol polycondensate is in the range of 33.3:66.7 to 49:51.

Surface treated steel sheet

The present invention: provides a good-workability and high-strength cold-rolled steel sheet excellent in post-painting corrosion resistance to the extent of securing excellent resistance to salt warm water immersion which is a good-workability and high-strength cold-rolled steel sheet excellent in post-painting corrosion resistance characterized in that: said steel sheet contains, in mass, 0.16 to 0.19% C, 1.10 to 1.30% Si, 1.50 to 1.60% Mn, not more than 0.1% P and 0.015 to 0.050% Al, with the balance consisting of Fe and unavoidable impurities; the average of the amount of Si incrassating on the surface of said steel sheet is not more than 20 times the Si concentration in said steel sheet; and the area percentage of the portions where the ratio of the Si concentration on the surface of said steel sheet to the Si concentration in said steel sheet is not less than 10 is not more than 95%.

Good-workability and high-strength cold-rolled steel sheet excellent in post-painting corrosion resistance

Growing community of inventors

Kimitsu, Japan

Toshiyuki Katsumi