Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2002-02-11
2004-06-22
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C148S246000, C148S253000, C148S255000, C148S261000, C148S262000, C148S273000, C148S276000, C428S624000, C428S628000, C428S659000, C428S687000, C428S472300
Reexamination Certificate
active
06753095
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a phosphate treated zinc coated steel sheet having excellent workability applied for use in vehicles, household appliances, building materials, and the like.
BACKGROUND ART
Conventionally, it is common for zinc coated steel sheet applied for use in vehicles, household appliances, building materials, and the like to undergo a phosphate treatment, a chromate treatment, and a further organic coating treatment so that the added value such as corrosion resistance, workability, and the like is improved. Recent years have seen a trend in which, because of environmental concerns, chromate treated steel sheet, in particular, is out of favor due to the possibility of hexavalent chromium being contained therein, and the demands on phosphate treatment have increased. Moreover, from the viewpoint of workability, because Zn—Ni based alloy plated steel sheet exhibits excellent properties, it is widely used, however, the drawback arises that, because the alloy plating includes Ni, the production costs are high. Therefore, attempts have been made to improve the added value by carrying out a phosphate treatment on electrically zinc coated steel sheet, hot-dip zinc coated steel sheet, and alloyed hot-dip zinc coated steel sheet, which each have low production costs.
However, in the conventional phosphate treatment for electrically zinc coated steel sheet, hot-dip zinc coated steel sheet, and alloyed hot-dip zinc coated steel sheet, a sufficient workability is not necessarily obtained as compared with Zn—Ni based alloy plated steel sheet. In particular, the workability is not sufficient when it is used in the performing of a drawing process in which the amount of inflow of steel sheet is regulated using a bead press whose use has increased in recent years.
In contrast to this, Japanese Patent Laid-Open Publication No. Hei 7-138764 discloses a zinc phosphate treated zinc coated steel sheet that contains at least one of Fe, Co, Ni, Ca, Mg, Mn, and the like and has excellent press performance. However, in this technology as well, sufficient performance is not obtained in the above bead press drawing process.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the above problems and provide a phosphate treated zinc coated steel sheet having excellent workability. A further object is to provide a phosphate treated zinc coated steel sheet having excellent corrosion resistance and weldability.
As a result of their investigations into improving the workability of phosphate treated zinc coated steel sheet, the present inventors noticed that the shape of the surface phosphate crystals plays an extremely important role and thus achieved the present invention. Namely, the present invention provides a great improvement in the workability of the drawing in the bead press process by having a shape in which granulated crystals are mainly used.
The present invention also provided improved corrosion resistance by simultaneously supplying magnesium which has excellent corrosion resistance to the phosphate treatment coat. Moreover, by controlling the amount of the coating, it is also possible to improve the weldability.
Namely, the present invention is as follows.
(1) A phosphate treated zinc coated steel sheet with excellent workability, having a phosphate treated coating comprising mainly granulated crystals on a surface of azinc coated steel sheet.
(2) A phosphate treated zinc coated steel sheet with excellent workability, having a phosphate treated coating on a surface of a zinc coated steel sheet in which an average ratio of a major axis to a minor axis of crystals in the phosphate treated coating is not less than 1.00 and not more than 2.90. In this case, the average ratio is an average value of that crystal whose length ratio of the major axis to the minor axis is closest to 1.00 and that crystal whose length ratio of the major axis to the minor axis is the largest from among crystals seen when an SEM photograph (at a magnification of 5000×) is taken.
(3) A phosphate treated zinc coated steel sheet also with excellent corrosion resistance, wherein Mg is contained in the phosphate treated coating according to the above (1) or (2) in an amount of not less than 10 mg/m
2
.
(4) A phosphate treated zinc coated steel sheet also with excellent weldability, wherein an adhered amount of the phosphate treated coating according to any one of the above (1) to (3) is from 0.5 g/m
2
to 3.0 g/m
2
.
(5) A phosphate treated zinc coated steel sheet also with excellent intermediate rust prevention property, wherein a rust prevention oil layer is provided on the phosphate treated coating according to any one of the above (1) to (4).
(6) A method for producing a phosphate treated zinc coated steel sheet with excellent workability and corrosion resistance, wherein a phosphate treatment is performed on a zinc coated steel sheet using a phosphate treatment solution in which, among metallic ions included in the phosphate treatment solution, an amount of Mg ions is at least 6 g/l and an amount of Zn ions is at least 0.5 g/l.
(7) A method for producing a phosphate treated zinc coated steel sheet with excellent workability and corrosion resistance, wherein a phosphate treatment is performed on a zinc coated steel sheet using a phosphate treatment solution in which, among metallic ions included in the phosphate treatment solution, an amount of Mg ions is at least 6 g/l and an amount of Zn ions is 0 or more and less than 0.5 g/l, and an amount of nitric acid ions included in the phosphate treatment solution is at least 40 g/l.
(8) A method for producing a phosphate treated zinc coated steel sheet with excellent workability and corrosion resistance, wherein, after the phosphate treatment according to the above (6) or (7), a heavy magnesium phosphate coating is formed on a surface thereof by coating and drying in a coating amount of not more than 0.5 g/m
2
.
(9) A phosphate treated zinc coated steel sheet with excellent workability, having a phosphate treated coating on a surface of a zinc coated steel sheet, the phosphate treated coating being characterized in that when measuring an X-ray diffraction pattern using CuK&agr; ray characteristic X-rays, the strength ratio (Ia/Ib) of the largest strength value of the maximum peak (Ia) at which 2&thgr;=not less than 9.540° and not more than 9.800° and the largest strength value of the maximum peak (Ib) at which 2&thgr;=not less than 19.200° and not more than 19.660° is not less than 3.0.
There is no particular limitation on the zinc coated steel sheet used in the present invention, and an excellent workability improvement effect can be obtained when both pure zinc coating and alloy coating are used. However, in view of production costs, electrical zinc coating, hot-dip zinc coating, alloyed hot-dip zinc coating, and the like are preferable.
Other than as to the shape of the crystals of the phosphate coating formed on top of the zinc coating, there is no particular limitation, and generally examples thereof may include a zinc phosphate coating forming what are known as hopeit crystals, a zinc phosphate coating modified by an element such as Fe, Ni, Co, Mn, Mg, Ca, Cu, and the like, and complex phosphate treated coatings in which a post treatment is performed on the above zinc phosphate coatings.
As is shown in
FIG. 1
, the conventional phosphate treated coating on the surface of zinc coated steel sheets is formed from needle crystals with a length of several &mgr;m, however, in the present invention, it is extremely important that the crystals are formed in a granulated crystal shape.
The shape of the crystals can be easily observed by surface SEM. Specifically, if the surface of a steel sheet (after solvent degreasing if it is an oil coated material) is observed by SEM (at an accelerating voltage of 15 Kv, with no inclination, and at a magnification of 5000×), it is possible to easily distinguish between granulated crystals and needle crystals. In the present invention, it is important tha
Isizuka Kiyokazu
Ito Daisuke
Ooba Shigekazu
Sanada Keiichi
Shindou Hidetoshi
Koehler Robert R.
Nippon Steel Corporation
Wenderoth , Lind & Ponack, L.L.P.
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