Honda Motor Co., Ltd.

Nippon Steel Corporation

Daido Steel Co., Ltd.

Yoshikazu Umeno

Koki Tanaka

Kazuhiko Honda

Kaoru Yamazaki

Masaki Shinkawa

Hiroaki Yoshida

Yoshitaka Okitsu

Katsuyoshi Kaneko

Toshiyuki Katsumi

Takahiro Tanae

Toshiaki Otsuka

Masanao Fujiwara

Disclosed are a weldable steel of high strength and high toughness and a method of producing members of machine parts. The steel consists essentially of, by weight %, C: 0.10-0.16%, Si: 0.05-0.50%, Mn: 1.3-2.3%, Cu: up to 0.5%, Ni: up to 0.5%, Cr: up to 0.5%, Mo: up to 0.3% and Ti: 0.025-0.035%, and the balance of Fe and inevitable impurities, and satisfying the condition that the weld-cracking susceptibility, Pcm, defined by the formula 1A below is less than 0.35, and the condition that the manganese equivalent, Mneq, defined by the formula 2A below is larger than 2.0.Pcm=C(%)+Si(%)/30+Mn(%)/20+Ni(%)/60+Cr(%)/20+Mo(%)/15+Cu(%)/20&#x2003;&#x2003;1AMneq=Mn(%)+Cu(%)+Ni(%)/2+Cr(%)+Mo(%)&#x2003;&#x2003;2A

Weldable steel of high strength and high toughness, and method of producing members using the same

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

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Wako, Japan

Yoshikazu Umeno