Claims
- 1. A method of producing a high-strength cold-rolled steel sheet suitable for working, comprising the steps of:
- preparing a steel consisting essentially of not more than 0.006 wt % of C, not more than 0.5 wt % of Si, not more than 2.0 wt % of Mn, and not less than 0.01 wt % but not more than 0.10 wt % of Ti, the Ti, C and N contents being determined to meet the condition of Ti<(48/12) C wt %+(48/14) N wt %, said steel also comprising not less than 0.0010 wt % but not more than 0.0100 wt % of Nb, not less than 0.0002 wt % but not more than 0.0020 wt % of B, not less than 0.03 wt % but not more than 0.20 wt % of P, not more than 0.03 wt % of S, not less than 0.010 wt % but not more than 0.100 wt % of Al, not more than 0.008 wt % of N, not more than 0.0045 wt % of O, and the balance substantially Fe and incidental inclusions;
- subjecting said steel to an ordinary casting, reheating at not less than 1,100.degree. C. but not higher than 1,250.degree. C., and a subsequent hot-rolling;
- subjecting the hot-rolled steel to a cold rolling conducted at a sheet temperature not higher than 300.degree. C. under such a condition that the sum of the rolling reductions of passes which meet the following conditions between said sheet temperature T(.degree.C.) and the strain rate .epsilon. (S.sup.-1) is 50% of greater:
- T.times..epsilon..gtoreq.50,000.degree. C. S.sup.-1
- and
- subjecting the cold-rolled steel to a continuous annealing, whereby a high-tension cold-rolled steel sheet is obtained having superior workability and which simultaneously exhibits both a Lankford value (r) not lower than 2.1, and a tensile strength (T.S.) not lower than 40 kfg/mm.sup.2, an elongation (El) not less than 40% and a coning height not smaller than 40 mm.
- 2. A method according to claim 1, wherein the P content is not less than 0.04 wt % and not more than 0.15 wt % and the O content is not more than 0.0040 wt %.
- 3. A method according to claim 1, wherein galvannealing is conducted in place of said continuous annealing.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2-159856 |
Jun 1990 |
JPX |
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Parent Case Info
This application is a continuation-in-part of application Ser. No. 07/686,698 filed Apr. 17, 1991, now abandoned.
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
4576657 |
Satoh et al. |
Mar 1986 |
|
4857117 |
Sakata et al. |
Aug 1989 |
|
Foreign Referenced Citations (1)
Number |
Date |
Country |
0193221 |
Nov 1984 |
JPX |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
686698 |
Apr 1991 |
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