Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1993-09-03
1995-01-24
Zimmerman, John
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
148533, 148537, 148320, 148333, 148651, B32B 1518, C21D 702, C21D 952
Patent
active
053842065
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a cold-rolled steel strip having a high strength and a good formability, and also to a method of producing the same.
A high-strength cold-rolled steel strip with which the present invention is concerned is press-formed for use in an automobile, electronic home appliances, a building, and so on. Such strip includes both a cold-rolled steel strip with no surface treatment in a narrow sense and a cold-rolled steel strip with a surface treatment such, for example, as Zn-plating and alloyed Zn-plating, for rust prevention purposes. A steel strip according to the present invention is one having both strength and workability, and therefore when this strip is to be used, it can be made smaller in thickness than conventional steel strips, and hence can be lightweight. Therefore, it is thought that it can contribute to the protection of the environment of the earth.
BACKGROUND ART
With the recent progress of a vacuum degassing treatment of molten steel, it has now become easy to make very low-carbon steel through melting, and there has now been an increasing demand for very low-carbon steel strips having a good workability. Among such strips, a very low-carbon steel strip, having Ti and Nb added thereto in combination, which is disclosed for example in Japanese Patent Unexamined Publication No. 59-31827 and Japanese Patent Unexamined Publication No. 59-38337, possesses a very good workability, also has coating-baking hardenability (BH), and is excellent in molten zinc platability, and therefore is now holding an important position.
On the other hand, in order to enhance the strength while maintaining the workability, various attempts have heretofore been made. Particularly, in the case of steel with a tensile strength of 35 to 50 kgf/mm.sup.2 with which the present invention is concerned, P, Si and so on have been added to the steel to increase the strength utilizing a solid solution-strengthening mechanism thereof. For example, Japanese Patent Unexamined Publication No. 59-31827 and Japanese Patent Unexamined Publication No. 59-38337 disclose a method of producing a high-strength cold-rolled steel strip in which Si and P are mainly added to a very low-carbon steel strip having Ti and Nb added thereto, thereby increasing the tensile strength up to the 45 kgf/mm.sup.2 class. Japanese Patent Publication No. 57-57945 discloses a representative prior art technique relating to a method of producing a high-strength cold-rolled steel strip in which P is added to Ti-added, very low-carbon steel. Japanese Patent Unexamined Publication No. 56-139654 discloses a high-strength steel strip based on Nb-added, very low-carbon steel, as well as a method of producing the same.
As described above, P and then Si have heretofore been extensively used as a strengthening element. This is because it has been thought that by adding a small amount of P and Si, the strength can be increased since they have a very high solid solution-strengthening ability, that ductility and deep drawability are not so lowered, and that the cost of the addition is not so increased. Actually, however, when it is intended to achieve the increase of the strength only with these elements, not only the strength but also a yield strength are simultaneously increased markedly, so that a defect in plane shape occurs, and its use for a panel of an automobile is sometimes limited. In the case of applying molten zinc-plating, Si causes a plating defect, and also P and Si greatly lowers the alloying speed, which results in a problem that the productivity is lowered.
On the other hand, it is also known to use Mn and Cr as a solid solution-strengthening element. Japanese Patent Unexamined Publication No. 63-190141 and Japanese Patent Unexamined Publication No. 64-62440 disclose a technique in which Mn is added to a Ti-contained, very low-carbon steel strip, and Japanese Patent Publication No. 59-42742 and the above-mentioned Japanese Patent Publication No. 57-57945 disclose a technique in which Mn and Cr are added to Ti-added,
REFERENCES:
patent: 4473414 (1984-09-01), Irie et al.
patent: 4878960 (1989-11-01), Sakai et al.
patent: 5019460 (1991-05-01), Yasuda et al.
patent: 5069981 (1991-12-01), Oishi et al.
patent: 5156690 (1992-10-01), Asano et al.
Takechi, Recent Developments in Production Technology of Automotive High Strength Steel Sheets, Iron and Steel, 1982, No. 9, pp. 116-129.
Akisue Osamu
Ushioda Kohsaku
Yoshinaga Naoki
Nippon Steel Corporation
Zimmerman John
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