Claims
- 1. A cold rolled steel sheet comprising:
- not more than 0.004 wt % C, not more than 0.1 wt % Si, not more than 0.5 wt % Mn, not more than 0.025 wt % P, not more than 0.025 wt % S, not more than 0.0040 wt % N, 0.01.about.0.04 wt % Ti, 0.003.about.0.008 wt % Nb, 0.0001.multidot.0.001 wt % B, 0.01.about.0.1 wt % Al and the remainder being substantially Fe; and
- fine precipitates of Ti having a grain size of not more than 0.05 .mu.m uniformly dispersed in said steel in an amount of not less than 30 ppm as a Ti conversion amount.
- 2. A cold rolled steel sheet comprising:
- not more than 0.004 wt % C, not more than 0.1 wt % Si, not more than 0.5 wt % Mn, not more than 0.025 wt % P, not more than 0.025 wt % S, 0.01.about.0.04 wt % Ti, 0.001.about.0.008 wt % Nb, 0.0001.about.0.001 wt % B, 0.01.about.0.1 wt % Al and the remainder being substantially Fe;
- wherein said steel sheet has a surface roughness satisfying either one of the following (a) and (b);
- (a) surface roughness (SRa) and yield stress (Y.S.) satisfy the following relationship:
- SRa.gtoreq.(32.4/Y.S.)-1.1;
- (b) an area ratio of convex portions on a surface of said steel sheet (SSr) of not more than 60% and an average area per one convex portion (SGr) of not less than 2.times.10.sup.4 .mu.m.sup.2.
- 3. The cold rolled steel sheet of claim 1, wherein the amount of Nb present is less than 1/5 (93/48) of the amount of Ti present.
- 4. The cold rolled steel sheet of claim 2, wherein the amount of Nb present is less than 1/5 (93/48) of the amount of Ti present.
- 5. The cold rolled steel sheet of claim 1, wherein the amount of Nb present is less than 1/4 of the amount of Ti present.
- 6. The cold rolled steel sheet of claim 2, wherein the amount of Nb present is less than 1/4 of the amount of Ti present.
Priority Claims (4)
Number |
Date |
Country |
Kind |
62-150313 |
Jun 1987 |
JPX |
|
62-152977 |
Jun 1987 |
JPX |
|
62-152978 |
Jun 1987 |
JPX |
|
62-152979 |
Jun 1987 |
JPX |
|
Parent Case Info
This is a division of application Ser. No. 07/204,619, filed Jun. 9, 1988, now U.S. Pat. No.4,889,566.
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4141761 |
Abraham et al. |
Feb 1979 |
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4504326 |
Tokunaga et al. |
Mar 1985 |
|
4586966 |
Okamoto et al. |
May 1986 |
|
4615749 |
Satoh et al. |
Oct 1986 |
|
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EPX |
228756 |
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EPX |
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Divisions (1)
|
Number |
Date |
Country |
Parent |
204619 |
Jun 1988 |
|