The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 14, 2001
Filed:
Apr. 10, 2000
Fusato Kitano, Tokyo, JP;
Takeshi Fujita, Tokyo, JP;
Tadashi Inoue, Tokyo, JP;
Michihiro Hiasa, Tokyo, JP;
Takeo Ishii, Toyota, JP;
NKK Corporation, Tokyo, JP;
Abstract
The present invention provides a method of manufacturing a cold rolled steel sheet and a hot-dip zinc-coated steel sheet having excellent surface properties, an excellent resistance to natural aging and an excellent dent resistance of panel and, thus, adapted to the manufacture of steel sheet for outer panels of vehicles. The method comprises the steps of preparing steel consisting of 0.005 to 0.012% by weight of C, 0.01 to 0.4% by weight of Si, 0.15 to 1.0% by weight of Mn, 0.01 to 0.08% by weight of P, at most 0.02% by weight of S, 0.01 to 0.1% by weight of sol. Al, at most 0.004% by weight of N, and at least one element selected from the group consisting of 0.01 to 0.2% by weight of Nb and 0.04 to 0.1% by weight of Ti, and satisfying the condition 1.2≦(12/93) (Nb%/C%)+(12/48) (Ti*%/C%)≦2.5, applying a hot rolling and a cold rolling to the steel, soaking the cold rolled steel sheet at T(° C.) meeting a formula Ac3≧T(° C.)≧157log(X)+737, and cooling the steel sheet after the soaking step at a cooling rate meeting a formula R(° C./sec)≦−35+162/X. Ti*% (noted above)=Ti%−(48/14)N%−(48/32)S%. When Ti* in the above equation is not larger than 0, Ti* is regarded as 0.