Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1995-09-28
1999-03-16
Zimmerman, John J.
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
428681, 427433, 148320, 148625, B32B 1518, C22C 3800, C21D 100
Patent
active
058828036
DESCRIPTION:
BRIEF SUMMARY
This application is the National Stage of International Application No. PCT/JP95/00196, filed on 13, Feb. 1995.
1. Technical Field
This invention relates to high-strength hot dip galvannealed steel sheets mainly usable in bending, press forming, deep drawing or the like for vehicle bodies, and to a method of producing the same.
2. Background Art
Recently, it has been strongly demanded to reduce the weight of a vehicle body in order to improve fuel consumption from a viewpoint of regulations for automobile emission gas and the like based on environmental pollution. And also, improvement of safety in automobiles is an important matter. As a counter-measure to these problems, it is required to develop high-strength hot dip galvannealed steel sheets having a tensile strength of not less than about 400 MPa and excellent press formability.
In cold rolled steel sheets, however, the press formability or average r-value and balance between strength and ductility (hereinafter referred to as TS-El) are generally degraded as the strength increases, and also it tends to deteriorate surface properties such as plating properties and the like. Therefore, in order to use this steel sheet for an automobile, it is important to improve plating properties and press formability in addition to increase of strength.
Up to the present, there have been proposed various methods for improving press formability accompanied with increase of strength.
For example, JP-A-63-100158 discloses a high-strength cold rolled steel sheet having excellent formability in which an extreme-low carbon steel having a reduced amount of C is combined with Ti, Nb and the like as a carbonitride forming component to improve workability and aging and further contains amounts of Si, Mn, P not damaging workability to mainly increase strength. Particularly, Si is a component useful for increasing strength without degrading workability represented by average r-value, elongation and the like. However, when a great amount of Si is included, deterioration of surface properties can not be avoided and a problem of considerably degrading plating properties arises.
Therefore, in order to increase the strength of the hot dip galvannealed steel sheet, as disclosed in JP-A-5-255807 (high-strength cold rolled steel sheets having excellent formability and high-strength hot dip galvannealed cold rolled steel sheets as well as a method of producing the same), restricting Si to not more than 0.03% and mainly using P and Mn as a strengthening components is prevalent. However, when a great amount of P is added, the problem arises that galvannealed alloying is delayed and particularly, that secondary working embrittlement is apt to be caused in the extreme-low carbon steel. And also, Mn has less influence upon plating properties, but an Mn content of not less than 1% starts deterioration of the plating properties when restricting Si to not more than 0.1%, and when Mn is included in a great amount, another problem arises that the transformation point is lowered to cause inconvenience in bringing about the deterioration of material that the hot rolled sheet is hardened and is not recrystallized during annealing.
Thus, there is a limit in increasing strength only by the addition of P and Mn while maintaining good workability and plating properties.
DISCLOSURE OF INVENTION
The inventors have made various studies and found that high-strength hot dip galvannealed steel sheets possessing good plating properties and press formability and having a tensile strength of not less than 400 MPa are obtained by utilizing Si as a strengthening component and specifying an interrelation between Si and Mn.
That is, the essential point of the invention is as follows:
A high-strength hot dip galvannealed steel sheet having excellent plating properties comprising a steel sheet wherein all percentages are expressed by mass or weight, having a composition consisting essentially of the following equation (1), and the remainder being Fe and incidental impurities, and a hot dip galvannealed layer formed
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Translation of JP 03-294463 (Dec. 1991).
Kato Chiaki
Kato Toshiyuki
Sakata Kei
Seto Kazuhiro
Umino Shigeru
Kawasaki Steel Corporation
LaVilla Michael
Miller Austin R.
Zimmerman John J.
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