JPH073417A - High corrosion resistance alloyed hot dip galvanized steel sheet - Google Patents

Abstract

(57) [Summary] [Purpose] Highly corrosion resistant alloyed hot-dip galvanized steel sheet. [Structure] 1) In a galvannealed steel sheet having a Zn-Fe alloy layer as a first layer and a Zn-Fe-Ni-Al alloy layer as a second layer on a steel sheet, The composition of the Zn-Fe-Ni-Al alloy layer is Fe8-
15%, Ni 0.1-2%, Al 1% or less. 2) An alloyed hot-dip galvanized steel sheet having excellent red rust resistance, characterized in that Sb, Pb, and Mg are contained in the second layer of claim 1 individually or in a combination within 1%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized steel sheet with high corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, galvannealed steel sheets have been known as steel sheets for automobiles or building materials which are excellent in coating film adhesion and corrosion resistance after coating. Further, recently, the inventors of the present invention have provided a method for producing an alloyed hot-dip Zn-plated steel sheet in which Japanese Patent Application No. 2-271956 pre-Ni plating is followed by rapid low-temperature heating for hot-dip Zn plating and alloying treatment. That is, after the Ni pre-plated layer is plated on the surface of the steel sheet at 0.2 to ² g / m ² , the plate temperature is set at 430 to 50 in a non-oxidizing or reducing atmosphere.
After rapid heating to 0 ° C. at a heating rate of 30 ° C./s or more, hot-dip plating is performed in a Zn plating bath containing 0.05 to 0.25% Al, and 10 to 40 at 470 to 550 ° C. immediately above wiping. Second, it is a method of performing alloying treatment, and the plated steel sheet obtained by this method has a structure including a Zn-Fe-based alloy layer as the first layer and a Zn-Fe-Ni-Al-based alloy layer as the second layer. As a characteristic, it is disclosed that the bare corrosion resistance of the processed portion under the salt spray test environment (SST) and the corrosion resistance of the damaged portion of the coating material are excellent.

[0003]

However, recently,
The demands from users on the corrosion resistance of car bodies or building materials are becoming more and more stringent, especially in salt spray tests for drying,
Severe corrosion cycle test (C
There has been a demand for improving the corrosion resistance of galvannealed steel sheets in CT).

The alloyed hot dip galvanized steel sheet produced by the method proposed by the present inventors in Japanese Patent Application No. Hei 2-271956 has a bare corrosion resistance of a worked portion under a salt spray test environment (SST) and a scratched portion of a coated material. Although it is a steel plate with excellent corrosion resistance, it exhibits sufficient performance with respect to coating adhesion and blister resistance of paint scratches even in severe corrosion tests such as CCT.
At the mating part such as the hem part, the coating is hard to penetrate and becomes the same as the bare material, so the red rust resistance deteriorates in a severe corrosive environment such as CCT, and the red rust resistance of the mating part in CCT is There is still room for improvement, and improvements were desired.

[0005]

Then, the inventors of the present invention subsequently conducted various experiments and analyzed in detail the relationship between the red rust resistance of the heme mating portion and the plating layer structure in CCT.
As a result, the structure of the plating layer that makes the red rust resistance of the hem mating portion in CCT good is clarified, and when finding a hot-dip Zn-plated steel sheet having the plating layer structure of the present invention or completing the present invention described below. Is.

That is, in an alloyed hot dip galvanized steel sheet having a Zn-Fe alloy layer as a first layer and a Zn-Fe-Ni-Al alloy layer as a second layer on a steel sheet,
The composition of the Zn—Fe—Ni—Al-based alloy layer of the layer is Fe 8
.About.15%, Ni 0.1 to 2%, Al 1% or less, and alloyed hot-dip galvanized steel sheet having excellent red rust resistance and Sb, Pb, Mg alone or in the second layer. An alloyed hot-dip Zn-plated steel sheet excellent in red rust resistance, characterized in that it is contained within 1% in a composite.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the alloyed molten Zn obtained according to the present invention.
It is the figure which showed typically the structure of the plating layer of a plated steel plate. The plating layer of the present invention is the first layer of Zn as shown in FIG.
-Fe alloy layer is extremely thin and uniform Zn- as the second layer-
It has a plating layer structure composed of an Fe-Ni-Al alloy layer.

FIG. 2 shows the Ni content (wt%) in the second layer.
It is a figure showing the relation between and corrosion resistance.

A laminated test material simulating a car body hem portion having a structure in which a flat plate and a bent plate, which are electrodeposition coated except for an unpainted portion of 5 mm × 50 mm, are sandwiched by a 0.5 mm spacer. Use, corrosion cycle test (S
ST35 ° C 6hr → Dry 50 ° C 45% 3hr → Wet 50
The rate of occurrence of red rust after 4 W was evaluated at 95 ° C. 14 hours → dry 50 ° C. 95% 1 hour). A rating of 3 or higher was passed.

(Corrosion Resistance Evaluation Criteria) CCT Two-Week Combined Material Rating Red Rust Occurrence Rate (%) in Unpainted Area 5 ... Less than 10 4 ... 10-30 3 ... 30-50 2 ... 50 to 90 1 ... 90 to 100 Red rust resistance is good when Ni in the plating layer is in the range of 0.1% to 2%. If the Ni content in the plating layer is less than 0.1%, the effect of improving red rust resistance is not recognized. Further, if it exceeds 2%, the red rust property deteriorates. It seems that when the corrosion of Zn progresses, the potential becomes too noble and local corrosion easily occurs.

Further, the plated steel sheet of the present invention had very good plating adhesion and red rust resistance in the worked part, and further, red rust resistance in the paint scratched part.

The Fe content in the plating layer is set to 8% or more because if it is less than 8%, the chemical conversion treatment property and the coating film adhesion are poor. Further, the Fe content is set to 15% or less because
This is because if it exceeds 15%, it becomes an overalloy and the plating adhesion of the processed part deteriorates.

When Al in the uppermost Zn layer exceeds 1%, the effect of improving the corrosion resistance of the processed portion becomes weak. This is because Al constitutes a local battery with Zn in the plating layer,
It is considered that the corrosion resistance is deteriorated due to the action of elution.

The total thickness of the plating layer is not particularly limited, but is preferably 1 μm or more from the viewpoint of corrosion resistance and 50 μm or less from the viewpoint of workability.

The above results have been described only in the case where the second layer contains 1% or less of Al. However, in addition to Al, Ni, Sb, Pb as alloying elements alone or in a composite amount of 3% or less are contained. The results were similar in these cases.

As the base steel sheet, both hot-rolled steel sheet and cold-rolled steel sheet can be used, and various types such as Al-killed steel sheet, Al-Si killed steel sheet or ultra-low carbon steel sheet such as Ti addition, P-Ti addition, various high-tensile steel sheets, etc. Things can be applied.

The method for producing the plated steel sheet of the present invention is not particularly limited. Desirably, the method of pre-Ni plating the steel sheet proposed by the present inventors, followed by rapid low temperature heating in a non-oxidizing or reducing atmosphere, hot dip plating, and then alloying treatment is most suitable. .

[0019]

The plated layer obtained by the present invention is the first thin Zn-Fe-alloy layer and the second Zn-Fe-layer near the base iron interface.
The second layer is composed of a Ni-Al alloy layer, and the second layer is Ni 0.1-0.1
2%, Fe 8 to 15%, Al 1% or less, the reason why the red rust resistance of the uncoated portion of the composite material is good is not yet clear, but Ni should be contained in the second plating layer. Causes Z due to Ni in the corrosion process of the plating layer.
There is a possibility that the stabilizing action of the corrosion product (basic zinc chloride) contributes.

[0020]

EXAMPLES Table 1 shows examples of the alloyed hot-dip galvanized steel sheet of the present invention. * Indicates comparative materials other than the present invention. A pickling material of hot-rolled steel sheet SGHC (1.6 mm) was used as a base, and it was prepared by a method of rapid low temperature heating after pre-Ni plating. The pre-Ni plating was performed by electroplating in a sulfuric acid acidic bath, and the Ni adhesion amount was changed to 0.2 to ² g / m ² . The pretreatment heating was performed at 40 ° C./s up to 450 ° C. in an N ₂ atmosphere containing O ₂ 60 ppm and H ₂ 3%. After hot-dip galvanizing at 450 ° C. for 3 seconds in a Zn plating bath in which the amount of Al changed, N ₂ wiping was performed to make the adhesion amount 60 g / m ^2, and then alloying treatment was performed at 470 to 520 ° C. for 5 to 40 s. The evaluation of the corrosion resistance of the unpainted part of the laminated material was carried out according to the aforementioned evaluation criteria. The plating adhesion of the processed portion was evaluated by the tape test blackening degree by performing a 60 degree V-bending test. The evaluation criteria are as follows. Three or more pass.

[0021]

[Table 1]

(Evaluation Criteria) Rating Plating adhesion of processed part (tape blackening rate) 5 ... less than 1% 4 ... 1% or more and less than 5% 3 ... 5% or more and less than 10% 2.・ 10% or more and less than 20% 1 ... more than 20% No. As shown in 1-7, the plated steel sheet having the plated layer structure of the present invention has excellent red rust resistance in the uncoated portion of the laminated material. Also, the plating adhesion of the processed part is good.

On the other hand, when the plating layer structure deviates from the scope of the present invention (No. 8-10), the performance is inferior to that of the steel sheet of the present invention.

[0024]

INDUSTRIAL APPLICABILITY As described above, the steel sheet of the present invention is a steel sheet excellent in red rust resistance of the unpainted portion of the laminated structural material such as the hem, which has not been hitherto available, and is useful for vehicle bodies, building materials and the like. Therefore, its industrial significance is extremely large.

[Brief description of drawings]

FIG. 1 is a plating layer structure of a galvannealed steel sheet of the present invention.

FIG. 2 is a diagram showing a relationship between Ni% in a plating layer and corrosion resistance.

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Claims (2)

[Claims] 1. An alloyed hot dip galvanized steel sheet having a Zn—Fe based alloy layer as a first layer and a Zn—Fe—Ni—Al based alloy layer as a second layer on a steel sheet, wherein The composition of the Zn—Fe—Ni—Al alloy layer is Fe 8 to 1
5%, Ni 0.1-2%, Al 1% or less, highly corrosion resistant alloyed hot-dip galvanized steel sheet with excellent red rust resistance. 2. The second layer according to claim 1, further comprising Sb, P
A highly corrosion-resistant alloyed hot-dip galvanized steel sheet having excellent red rust resistance, characterized in that b and Mg are contained within 1% individually or in combination.