JPH0526878B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a laminated galvanized steel sheet, and particularly to a laminated galvanized steel sheet comprising a non-intermetallic compound coating as a lower layer and an intermetallic Fe-Zn alloy coating as an upper layer. . More specifically, the present invention relates to improving the performance of Fe-Zn plated steel sheets, which are intermetallic compound-based plated steel sheets that exhibit brittle behavior against impact deformation after general coating. , relates to a laminated galvanized steel sheet that exhibits suitable performance as a pre-coated steel sheet or a rust-proof galvanized steel sheet for automobiles. (Prior art) In recent years, in response to requests from steel sheet consumers to improve productivity, steel manufacturers or their related manufacturers have begun using so-called pre-coated steel sheets, which are coated with a coil coater or the like before forming. has become popular. As steel plates for producing such pre-coated steel plates, steel plates plated with Zn or Zn alloy are used because corrosion resistance and paintability are required. However, a plated steel plate that satisfies both rust prevention function and workability has not been found among known Zn-based plated steel plates. From various viewpoints, Fe-Zn plated steel sheets based on Zn-based intermetallic compounds have excellent weldability,
Although it has corrosion resistance, from a thermodynamic phase diagram, its composition is an intermetallic compound, and after being painted as a pre-coated steel sheet,
The disadvantage is that the plated layer is likely to peel off due to impact deformation when press working or the like is performed by the steel sheet customer. Such defects observed in intermetallic compound plating appear as a phenomenon in which the plating layer peels off during shearing or punching when used for precoated steel sheets, for example. In addition, when used as a rust-proof steel plate for automobiles, the plating on the impact part will peel off when it is impacted by stone chips etc. while driving.
It has the disadvantage that rust prevention ability is significantly reduced locally. Here, "intermetallic compound plating" refers to at least 50% in the thermodynamic phase diagram due to its composition.
It is a general term for plating in which intermetallic compounds account for % of the weight ratio, and a typical example is plating of Zn-based alloys. Found in both electroplating and hot melt plating. In addition, it is generally said that in non-intermetallic compound plating such as pure Zn plating or Zn-Al plating, the above-mentioned peeling does not occur unless the film thickness becomes excessively large. (Problems to be Solved by the Invention) An object of the present invention is to provide a plated steel sheet for precoating, particularly an intermetallic compound-based Fe-Zn-based plated steel sheet. The present inventors considered a drastic solution to the above-mentioned problems caused by intermetallic compound plating, conducted research on a matted steel plate that has impact peeling resistance after painting and rust prevention ability, and Later, he invented a galvanized steel plate with excellent impact resistance and corrosion resistance, and first applied for a patent application in 1983.
A patent application was filed as No. 234299. Japanese Patent Publication No. 1986-128286
See publication. That is, on the surface of the steel plate, Fe, Ni,
One or more of Cu, Sn, Cd, and Pb are coated in a non-intermetallic metal state in an amount of 1.5 to 50 g/ ^m2 , and then an intermetallic compound-based plating such as Fe-Zn is applied as an upper layer. It is a laminated type plated steel plate that is coated with 2 to 80 g/m ² of. (Means for Solving the Problems) According to the results of further study by the present inventors, if Cu or Ni is used among the metals constituting the lower layer of the multi-layer plating, the lower layer The present invention was completed based on the discovery that it is possible to further significantly reduce the amount of plating deposited, and that there are other effective metals other than the above-mentioned metals that exhibit effects at low amounts of plating. Therefore, the gist of the present invention is as follows:
Ni or Cu5mg/m ² as a lower layer on the surface of the steel plate
100mg/ ^m2 or more, less than 200mg/m2, Mn20mg/m2 ^or more and less than 200mg/ ^m2
Below, Co20mg/m ² or more and 200mg/m ² or less, and
Coated with at least one type of Cr of 20 mg/m ² or more and 200 mg/m ² or less in a non-intermetallic compound, and further coated with 7% or more and less than 40% Fe-Zn alloy plating with 2 to 80 g/m ² of Cr. This is a laminated plated steel plate characterized by the fact that it is provided with only a certain amount. Here, the above-mentioned "in a state that is not an intermetallic compound"
This means that there are no restrictions on the plating means or treatment methods as long as they do not substantially form intermetallic compounds.Therefore, in addition to single metal coatings, solid solution alloys are not included in the thermodynamic phase diagram. Also included are alloys formed by a combination of two or more metals and laminated systems of single metals. Therefore, methods include vapor deposition, electroplating, chemical plating, cementation, etc., but electroplating is generally preferred. This lower coating has the effect of preventing brittle fracture at the interface between the intermetallic alloy plating upper layer and the steel plate that occurs during impact and high-speed deformation after coating, and increasing the adhesion between the plating layer and the steel interface. Such metallizations include Ni, Cu, Mn, Co and
At least one metal is selected from the group consisting of Cr, and the coating amount of each metal is as follows. Ni: 5 to 100 mg/m ² (less than), preferably 5 to 50
mg/m ² Cu: 5 to 100 mg/m ² (less than), preferably 5 to 50
mg/m ² Mn: 20 to 200 mg/m ² , preferably 20 to 150 mg/m ² Co: 20 to 200 mg/m ² , preferably 20 to 150 mg/m ² Cr: 20 to 200 mg/m ² , preferably If the lower layer coverage is less than the indicated lower limit of 20 to 150 mg/ ^m2 ,
It is insufficient to cover the entire surface, and a sufficient effect on improving workability cannot be expected. The upper limit of the amount of coating of the lower layer is mainly set from the viewpoint of economic efficiency, and the effect is sufficient below the upper limit. In addition, as mentioned above, the lower layer coating may be a single metal of the above metal or a solid solution based on at least one of the above metals, and although it is possible to contain some intermetallic compounds, a large amount It is necessary that the parts are coated in a metallic state and that the entire coating has the toughness of a metal. That is, it is necessary that substantially no intermetallic compounds are formed. When using two or more metals, each metal may be laminated. In either case, the amount of each metal coated is within the above range. The upper layer Fe-Zn alloy plating may be electroplated, vacuum evaporation, or ion plating. Upper layer Fe−
For Zn alloy plating, when the Fe content is less than 7%, η
Corrosion resistance after painting decreases due to eutectoid phase, while 40%
If it exceeds this, the ferrite phase eutectoids and causes corrosion resistance deterioration. If the upper layer is thinner than 2 g/m ² , the rust-preventing effect will be poor, while if it exceeds 80 g/m ² , it will tend to deteriorate workability and weldability when unpainted. Therefore, in the present invention, the upper layer coating is
The Fe-Zn alloy should have an Fe content of less than 7% and 40% or less, and the amount of coating should be limited to 2 to 80 g/m ² . More preferably, it is 20 to 60 g/ ^m2 . In addition, the present invention solves the brittleness of intermetallic compound-based Fe-Zn alloy plating by intervening an intermediate layer.
It is based on improvement, and does not insist on a mere two-layered plating as in the past. In other words, the Fe-Zn lower layer is further coated with Fe-Zn.
Various multilayer platings have been proposed with various coatings such as Zn, Ni-Zn, Fe-P, and Fe as upper layers, but all of these platings suffer from the peeling defects mentioned above due to the brittleness of the lower layer plating. It is internalized. Therefore, the present invention also includes cases in which a coating layer of at least one of Ni, Cu, Mn, Co, and Cr is provided as the bottom layer in this type of multilayer plating. (Function) The thus obtained laminated plated steel sheet according to the present invention is then subjected to a conventional chemical conversion treatment, and then coated with a high hardness paint or a large coating film thickness. Demonstrates significantly superior performance compared to plated steel sheets. Hereinafter, the effects of the present invention will be explained in more detail based on Examples. Example SPCC grade mild steel cold rolled steel plate (thickness 0.5mm)
It was cut into pieces of 150 x 100 mm, electrolytically degreased in a sodium orthosilicate solution, and then Cu,
Electroplating of Ni, Mn, Co, Cr and Sn was performed up to the given coverage. The electrolysis area was 1 ^dm2 . After washing the steel sheets with the lower layer plated in this way, electrolytic plating of Fe--Zn alloy was performed under the electrolytic conditions shown in Table 2. The amount of the upper layer plating was 40 g/m ² in all cases. Separately, single-phase Fe-Zn plating was similarly performed under the conditions shown in Table 2. In this case as well, the adhesion amount is 40% per single phase area.
g/ ^m2 . After plating, each sample was treated with a commercially available zinc phosphate treatment agent (Bonderite #3300, manufactured by Nippon Parker Co., Ltd.), and then chromate sealing (Percolene #62, manufactured by Nippon Parker Co., Ltd.) was applied. Acrylic baking paint (primer coating thickness: 6 μm, top coat coating thickness: 18 μm) was applied using a bar coater method. The pencil hardness of the coating film was 2H. Next, each sample was subjected to a Dupont impact test (energy 7.2 J, steel ball diameter 12 mm) at 0°C, and when the painted and plated surfaces were subjected to convex deformation, the state of peeling of the plated layer at the convexities was investigated. . The obtained results are summarized in a graph and shown in the attached drawing. In the figure, various types of base plating and their adhesion amounts, alloy plating, and impact resistance after painting are shown in graphs. The amount of plating on the lower layer was determined by a separate chemical analysis. Regarding the impact resistance rating on the vertical axis, a score of 5 means that there is no peeling of the coating film or plating, and a score of 0 means that the plating layer has peeled off in most of the deformed parts.
The evaluation is divided into stages. A rating of 4 or higher was judged to be a nearly satisfactory level. Therefore, for Ni and Cu, 5 mg/m ² or more,
For Mn, Cr, and Co, 20 mg/m ² or more is sufficient, and the upper limit may be determined as appropriate in consideration of economic efficiency. In this specification, electroplating is used as the lower layer plating, but it goes without saying that vapor deposition, electroless plating, etc. can also be used for some metals.

【table】

【table】

[Table] (Note) *: Current density indicates cathode current density.

[Brief explanation of the drawing]

The accompanying drawing is a graph summarizing experimental data of examples of the present invention.

Claims (1)

[Claims] 1 Ni or Cu5 as a lower layer on the surface of the steel plate
mg/ ^m2 or more and less than 100mg/ ^m2 , Mn20mg/ ^m2 or more and less than 200
mg/m ² or less, Co 20 mg/m ² or more and 200 mg/m ² or less, and Cr 20 mg/m ² or more and 200 mg/m ² or less in a non-intermetallic compound, and further as an upper layer, 7% or more 40 1. A laminated plated steel sheet characterized by being coated with less than 2% Fe-Zn alloy plating in an amount of 2 to 80 g/m ² .