JPH0610360B2 - High corrosion resistance zinc plated steel sheet - Google Patents

Description

Description: [Industrial field of application] The present invention is a highly corrosion-resistant surface-treated steel sheet used for building materials, outer panels of automobiles, etc., which is a zinc-dispersed plated steel sheet excellent in weldability and workability. It is about.

[Prior Art] Zinc-based plated steel sheets have been used in various fields including construction materials for a long time because they are inexpensive and have excellent corrosion resistance. In recent years, particularly in the automobile industry, etc., in addition to higher corrosion resistance, There has been a demand for a plated steel sheet having formability and weldability. In response to this, zinc alloy plating and multi-layer plating steel plates including zinc plating combined with these,
Zinc-dispersed plated steel sheets in which oxides are dispersed have been developed.

Among these plated steel sheets, the zinc-dispersed plated steel sheet has the shortest history, but it is reported that the dispersed plated layer improves the corrosion resistance. For example, JP-A-54-14
6228, the main component of Zn is 2.0 to 1 of silica.
It has been disclosed that an electrogalvanized steel sheet containing 5.0% has good corrosion resistance, and JP-A-60-211094 discloses that a zinc-Fe alloy plated layer has alumina, silica,
Zn-C containing 0.01 to 3 wt% of titanium and titania
A multi-layer plated steel sheet having an o-based alloy plating is disclosed as a high-corrosion-resistant surface-treated steel sheet.

[Problems to be Solved by the Invention] However, when a dispersion-plated layer of zinc containing silica is examined, the corrosion resistance of this dispersion-plated layer increases with the content of silica, but at the same time, there is a problem in workability and weldability. It turned out to occur. Among them, the silica content in the plating film and the amount of plating applied greatly affect the weldability in electric spot welding, and the zinc-dispersed plating layer containing a high concentration of silica cannot withstand severe processing. Was confirmed.

The present invention has been made to solve such a problem, and an object thereof is to provide a zinc-dispersed plated steel sheet having excellent workability and weldability while exhibiting high corrosion resistance due to the inclusion of silica. is there.

[Means and Actions for Solving the Problem] Means for achieving this object include silica particles on one or both surfaces of a non-plated steel plate, a zinc-plated steel plate, or a zinc alloy-plated steel plate. Adhesion of 10 g / m ² or more containing 0.1% by weight or more and less than 3% by weight in terms of silica 1
It has a zinc-silica-dispersed plated layer of 00 g / m ₂ or less as a first layer, and further contains silica particles in an amount of 3% by weight or more and 30% by weight or less in terms of silica on the first layer.
g / m ² or more 20 g / m ² or less of zinc - silica dispersion plating layer is highly corrosion-resistant zinc-plated steel sheet having a second layer, a zinc alloy such as zinc and iron zinc alloy plated steel sheet, nickel, cobalt or chromium It is preferable to be an alloy of one or more of the above.

In the zinc-dispersed plated layer containing silica, the content of silica is preferably low with respect to workability and weldability, but the content of silica is preferably high with respect to corrosion resistance. In order to make these contradictory properties compatible with each other, attention was paid to the difference in the influence of the first layer and the second layer on the workability of the entire plating layer in the multilayer plating. Examination of this difference shows that the peeling of the plating layer during processing depends considerably on the first layer, and that the ductility of the first layer has a large effect on the peeling during processing of the entire plating layer. It has been clarified that the silica contained in the oil affects the lubricity and contributes. Based on this, it is conceivable to lower the silica content of the first layer and increase the silica content of the second layer to simultaneously satisfy workability and corrosion resistance. However, this alone cannot satisfy the weldability. The dispersed plating layer having a high silica content lowers the lower limit of the proper welding current density, but if the plating layer is thick, the upper limit thereof is lowered, and thus it becomes difficult to bond it to another steel plate having a high lower limit of the proper welding current density. In order to avoid this, it is necessary to reduce the film thickness of the second layer having a high silica content. The above is the basic idea of the present invention, and as a result of repeated research on the layer structure and performance of the coated plating layer based on this,
It was the invention.

When the plated steel sheet is processed, the destruction of the plated layer occurs in the forms of cracking, powdering and peeling of the plated layer. Of these, the most problematic is the peeling of the plating layer, and the peeling mainly occurs at the interface between the base and the plating layer. In normal working, the main force acting between the steel plate and the plating layer is shear stress, and the magnitude thereof increases as the difference in ductility between the base material and the plating layer increases, if the working degree is constant. That is, if the difference in ductility between the layers contacting at the interface is large, peeling of the plating layer is likely to occur.

Generally, the zinc plating layer has a lower ductility than a steel sheet, but the inclusion of silica further reduces the ductility. Therefore, in order to eliminate the peeling of the multi-layered plating layer due to the processing of the plated steel sheet, the first layer in contact with the steel sheet base material should be a low-silica dispersed plating layer, and the base material should be zinc plated rather than non-plated steel sheet. It is better if it is a steel plate.
Alloy plating of iron, zinc, nickel zinc, cobalt, etc. is also preferable.

Even if the substrate is a non-plated steel sheet, if the silica content is 3% by weight, the ductility is not significantly reduced and the multi-layer plated layer does not peel off. From this, the silica content of the first layer is preferably less than 3% by weight, while the first layer also plays a part in the high corrosion resistance of the multi-layer plating layer, so that the amount of silica exhibiting the corrosion resistance, that is, 0. It is preferable to contain 1% by weight or more of silica. Another role of the first layer is to relieve shear stress due to the difference in ductility between the green body and the second layer, which requires a certain amount of coating thickness. . This thickness can be obtained by setting the adhesion amount to 10 g / m ² or more. However, if the entire multi-layer becomes too thick by increasing the adhesion amount of the first layer, powdering tends to occur during press working. There is a tendency, and there is a risk of excessive quality from the viewpoint of corrosion resistance. Therefore, the amount of the first layer deposited need not exceed 100 g / m ² .

In the second layer, stress relaxation with the substrate is done by the first layer, so that increasing the silica content no longer causes workability problems. On the other hand, since spherical silica particles are dispersed in the surface layer, friction with the die is reduced during pressing to exert a lubricating effect. That is, in press working, it acts to prevent cracks in the plated coating. Utilizing the above-mentioned layer structure and the characteristics of silica, the second layer has a higher content of silica and is intended to have improved corrosion resistance and workability. Regarding the corrosion resistance, the plating amount is 1
If it is g / m ² or more, a silica content of 3% by weight exhibits a corrosion resistance effect. Regarding workability, even if the adhesion amount is less than 1 g / m ² and the silica content is less than 3% by weight, a lubricating effect appears, but a corrosion resistance, In order to satisfy both the workability, a deposition amount of 1 g / m ² or more and a silica content of 3% by weight or more are required. On the other hand, if an attempt is made to increase the silica content to 30% by weight or more, there is a problem in operation such as a significant decrease in the plating current efficiency in electroplating during electroplating, and the limit is 30% by weight. Further, in the best electric spot welding used in the bonding of the plated steel sheet, since narrowing the proper welding current range when the amount of plating deposition is too large, the adhesion amount in the second layer exceeds 20 g / m ² is not preferable.

Among the base steel sheets, zinc alloy plated steel sheets have innumerable types of zinc alloys, and most of the alloy types can be used because of the ductility relationship described earlier, but for zinc, iron, nickel, and cobalt alloy plating, Since mass production technology has been established and there are practical results in terms of adhesion and brittleness of the plating layer, it is necessary to attach the multiple layers of the first and second layers described above on these zinc alloy plated steel sheets. If it does, it will definitely exhibit its excellent characteristics.

This multi-layer zinc-dispersed plating is applied to one side or both sides, because there are cases where the same corrosion resistance is required on both surfaces of the high-corrosion-resistant surface-treated steel sheet, and there are cases where one-sided corrosion resistance is required. This is because the selection depends on the request.

When the application of the plated steel sheet places particular importance on coatability, it is possible to add a third element such as iron or manganese to the second layer for the purpose of improving coatability, and the above-mentioned action is unchanged. Absent.

In addition, the method for forming the multi-layered zinc-dispersed plated layer is a vapor deposition method,
Although there are several methods such as the fusion method, the electroplating method has good productivity and the control of the amount of adhesion and the component ratio is easy. An example of a method using an electric plating bath is pending (Japanese Patent Application No. 62-
028359) and the bath composition based on the invention is as follows.

Plating bath _{composition: ZnSO 4 · 7H 2 O;} 250~500g / l Na 2 SO 4; 5~50 g / l CH 3 COONa; 12~50 g / l of colloidal _{silica; 0.5~30 g / l NaNO 3;} 100 ~ 3000 ppm pH; 1.0-5.0 Within this composition range, the lower layer of colloidal silica is used for the first layer having a small silica content, and the higher layer of colloidal silica is used for the second layer. / D
Plating with m ² .

[Examples of the Invention] Non-plated cold-rolled steel sheets, zinc-plated steel sheets, zinc-iron alloy-plated steel sheets, zinc-nickel alloy-plated steel sheets, zinc-cobalt alloy-plated steel sheets, zinc-iron-nickel-alloy plated steel sheets, etc. The surface is coated with zinc-dispersed first and second layers with different amounts of deposited plating and silica content to obtain 10 kinds of multi-layer zinc-dispersed plated steel sheets, and their corrosion resistance, plating layer workability, and welding I investigated the sex.

Both the zinc-plated steel sheet and the zinc alloy-plated steel sheet had a plating adhesion amount of 2 g / m ² , and in Example 8 a zinc-plated steel sheet was used. In Example 5, cobalt was 1.5%, and in Example 6, iron 11
%, Nickel 12% in Example 10, chromium 1% in Example 11, iron 11% and nickel 12% in Example 12, respectively, and non-plated cold-rolled steel sheets in other examples. Using.

An example of the plating conditions for the first layer and the second layer was as follows.

First layer: plating bath _{composition: ZnSO 4 · 7H 2 O;} 500g / l Na 2 SO 4; 30 g / l CH 3 COONa; 25 g / l of colloidal _{silica; 1.5g / l NaNO 3; 900ppm} pH; 2.1 plating current density: 60A / dm ² second layer: plating bath _{composition: ZnSO 4 · 7H 2 O;} 250g / l Na 2 SO 4; 25 g / l CH 3 COONa; 40 g / l of colloidal silica; 15g / l NaNO ₃ 400ppm pH; 3.8 Plating current density: 60A / dm ² Under these plating conditions, the first layer was a dispersion plating layer with a silica content of 2.5% by weight, and the second layer was a dispersion plating layer with a silica content of 5% by weight. Obtained.

In the investigation of corrosion resistance, workability, and weldability, the following tests were conducted and evaluated.

The corrosion resistance was evaluated by the salt spray test by the time until the occurrence of red rust.

As for workability, a draw bead test was conducted, and no or slight peeling of the plating layer was evaluated as good, and one with a large amount of peeling was regarded as poor.

Regarding the weldability, electric spot welding was performed, and the upper and lower limits of the proper welding current and the continuous spotting property were examined. Regarding the upper limit and the lower limit of the proper welding current, the lower limit current at which the diameter of the fusion mark, that is, the nugget, which is fused is obtained as 4 times the square root of the plate thickness, and the upper limit at which the phenomenon called dust that the molten metal scatters begins to occur. The current and were measured. In this case, the larger the difference between the upper limit current value and the lower limit current value, which is generally used, is from 6 kA to 13 kA, the better. The continuous hitting property is an electrode durability test, and when the same electrode is repeatedly used, the tip of the electrode changes and the nugget diameter gradually becomes smaller. The number of consecutive hits (the number of hits) was calculated up to 80% of that. The welding current in this case is 10 kA /
It was once.

In addition, for comparison, a plating amount on a cold-rolled steel sheet, a comparative example of a plated steel sheet having a multilayer zinc alloy plated layer outside the range of silica content, and a silica-containing single-layer zinc-dispersed plated layer of the prior art. It has a plated steel sheet (conventional example 1) and a multi-layer dispersed plated layer in which a zinc-cobalt (Co3%) alloy dispersed plated layer having a silica content of 3% is provided on a zinc-iron alloy plated layer (Fe12%). A plated steel sheet (conventional example 2) was tested and evaluated in the same manner as in the example.

The results are shown in Table 1.

As can be seen in Comparative Examples 1 and 2, with only the zinc plating layer,
Although there is a difference in the amount of plating applied, red rust occurs in tens of hours in the salt spray test. Further, these have good workability, and have a proper welding current range of 4 to 5 kA, which is excellent.
If the adhesion amount is increased as shown in, the continuous dot performance becomes inferior.
This is the basic characteristic of the zinc-plated steel sheet, and in Conventional Examples 1 and 2 in which silica is dispersed in this zinc-plated layer, the corrosion resistance is clearly improved. Particularly, in Conventional Example 1 in which a large amount of silica is dispersed, the effect is extremely remarkable, but on the other hand, the ductility of the dispersion-plated layer is large and the workability is not good, and the proper welding current density is too low and the range is further reduced. It is narrowing. In Conventional Example 2, the silica content of the dispersion-plated layer is suppressed to a low level, but the lubrication effect is poor and the workability is poor. In contrast to these examples, in each of the examples, the salt spray time exceeds 100 hours, and particularly in the case of a high silica content, not only the corrosion resistance exceeds 1000 hours but also the workability is good and the proper welding current is obtained. Does not fall too much, and the range is 3-4
It has a wide kA and a continuous hitting property of 4000 or more.
In comparison, Comparative Example 3 in which the second layer is too thick and Comparative Example 4 in which the first layer is not present and the second layer is too thick have insufficient workability and weldability, and Comparative Example 5 in which there is no second layer and In Comparative Example 6 where the second layer is too thin, the corrosion resistance is insufficient.

[Effects of the Invention] As described above, according to the present invention, the steel sheet has a silica-containing highly corrosion-resistant dispersed plating layer including a relatively thick first layer that relaxes shear stress and a workable thin second layer. Since it is coated with, the workability is excellent due to the stress relaxation effect and the lubricating effect, and the high corrosion-resistant plated steel sheet is excellent in weldability due to the combination of the silica content and the film thickness. As described above, the effect of the present invention to provide a plated steel sheet having incompatible characteristics is great.

Claims (2)

[Claims] 1. A non-plated steel sheet, a zinc-plated steel sheet, or a zinc alloy-plated steel sheet, on one side or both sides of which, silica particles are contained in an amount of 0.1% by weight or more and less than 3% by weight in terms of silica. It has a zinc-silica-dispersed plating layer having an adhesion amount of 10 g / m ² or more and 100 g / m ² or less as a first layer, and further, silica particles on the first layer are 3% by weight or more in terms of silica 3 or more.
A highly corrosion-resistant zinc-based plated steel sheet, comprising a zinc-silica-dispersed plated layer containing 0% by weight or less and having an adhesion amount of 1 g / m ₂ or more and 20 g / m ² or less as a second layer. 2. The zinc alloy of the zinc alloy plated steel sheet is zinc and iron,
The highly corrosion-resistant zinc-based plated steel sheet according to claim 1, which is an alloy with one or more of nickel, cobalt, and chromium.