JP5861662B2 - Zinc-based electroplated steel sheet and method for producing the same - Google Patents

Description

  The present invention relates to a zinc-based electroplated steel sheet excellent in corrosion resistance of a flat plate part and a collar part and a method for producing the same.

Zinc-based electroplated steel sheets are widely used for home appliances, building materials, and the like because they are excellent in the uniformity and appearance of plating films in addition to high corrosion resistance.
However, since zinc is one of the exhaustible resources and the price is expected to rise in the future, it is necessary to reduce the amount of zinc plating and to develop a surface treatment film that replaces zinc plating in order to reduce the amount of zinc used. Has been.

  Here, a technique for improving the corrosion resistance of the plating layer is mentioned as one of the techniques for reducing the galvanized adhesion amount. This is because if the corrosion resistance of the plating layer is improved, the plating layer can be made thinner, which leads to a reduction in the amount of zinc attached.

  Conventionally, as a method for producing a highly corrosion-resistant electrogalvanized film, alloying of metals such as Ni and Co, which are more precious than Fe, and Zn has been studied. However, many of these alloy platings show high corrosion resistance in the initial stage of use, but once corrosion starts, corrosion of zinc and the material (underlying) steel sheet is promoted, so that perforation corrosion occurs early. There was a problem that occurred.

Here, in order to solve the above-described problem, in Patent Document 1 and Non-Patent Document 1, studies are made on zinc-based composite electroplating containing an active metal that is lower than Fe.
That is, in Patent Document 1, 0.2 mol / L or more of Zn ions, one or more metal ions selected from Al, Sc, Y, La, Ce, Nd, Zr and V, and 0.0005 to 0.1 mol / L It is described that a zinc-based composite electroplated steel sheet having excellent corrosion resistance and appearance uniformity can be obtained by electrolysis at a relative flow rate of 0.6 m / s or more with a steel sheet containing a nitrate ion. ing.

Non-Patent Document 1 describes a method of obtaining an electrodeposited Zn film containing V element by adding VO ²⁺ which hydrolyzes at a pH lower than Zn ²⁺ to an electrolytic solution in a plating bath. . The V content of this electrodeposited Zn film increases as the pH and current density of the plating bath increase. Further, when the plating bath is stirred, the V content of the electrodeposited film decreases, but the distribution of V elements is uniform. It is stated that the property is improved.

JP 2011-111633 A

Hiroaki Nakano, Satoru Ogami, Daisuke Kanzaki, Shigeo Kobayashi, Hisatsu Fukushima "Zn-V oxide composite electrodeposition from aqueous sulfate" iron and steel; 93, 703 (2007)

  However, in the technique described in Patent Document 1, since the plating bath contains nitrate ions, the pH of the bath solution is likely to increase rapidly during electrolysis, and the plating bath composition, the conditions of the liquid flow rate, etc. are slight. There was a problem that the resulting plating film composition would change drastically even if it was only changed.

  On the other hand, in Non-Patent Document 1, when there is no stirring, the distribution of V in the plating film is unevenly distributed, and a uniform plating film cannot be obtained. In addition, although the surface becomes uniform when stirring is performed, there is a problem that the V content in the film is remarkably lowered.

  That is, in the prior art, it is very difficult to obtain a uniform electroplated film containing V, and there remains a problem that good flat plate corrosion resistance and further heel corrosion resistance cannot be obtained.

  The present invention was developed in view of the above-mentioned present situation, and an object thereof is to provide a zinc-based electroplated steel sheet having excellent flat plate portion corrosion resistance and heel portion corrosion resistance together with an advantageous manufacturing method for obtaining the steel plate. To do.

In order to solve the above-mentioned problems, the inventors used a plating bath that does not contain nitrate ions but contains Zn ions and V ions, and uses a cathode having a relative flow rate of the material steel plate and the plating solution of 0.5 m / s or more. Electrolytic treatment was performed.
As a result, the following knowledge was obtained.

At the time of cathodic electrolysis, Zn is deposited by electrolysis, and V oxides (V ₂ O ₃ , VO _2, V ₂ O _5, etc.) are generated due to an increase in interfacial pH caused by hydrogen gas generation during electrolysis. The composite plating is formed. In the formed composite plating film, the amount of V varies depending on the applied current density. However, the lower the current density, the more difficult the pH of the interface increases, and the amount of V in the plating film decreases, while the current density increases. The more the amount of V is, the more the plating film becomes. That is, although the plating film manufactured by such a procedure shows the more excellent flat plate part corrosion resistance, so that there is much V content, when V content increases too much, a plating film will become inactive and galvanization of The sacrificial anticorrosive ability possessed has the problem that the buttock corrosion resistance deteriorates.

Therefore, the inventors recalled that the cathodic electrolysis is divided into two stages in order to optimize the V content, and conducted extensive studies. As a result, in the previous stage of the cathodic electrolysis treatment, by performing electrolysis at a slightly lower current density, first, a plating film having a sacrificial anticorrosive ability with a low V content is formed in the lower layer to ensure the buttock corrosion resistance, In the subsequent stage, by performing electrolysis at a higher current density, an inactive plating film containing a large amount of V is formed in the upper layer, thereby ensuring flat plate portion corrosion resistance, and excellent flat plate portion corrosion resistance and heel portion corrosion resistance. It was found that a zinc-based electroplated steel sheet was obtained.
The present invention has been made based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. A zinc-based electroplated steel sheet having a zinc-based plating film, wherein V in the plating film is 0.5 atm% or more and less than 8 atm% in the range from the interface between the plating film and the base steel sheet to a height of 0.1 μm. A zinc-based electroplated steel sheet characterized by being 8 atm% or more in the range from the outermost surface of the plating film to a depth of 0.1 μm.

2. A method for producing a zinc-based electroplated steel sheet in which a zinc-based electroplated film is formed on the surface of the material steel sheet by electrolyzing the steel sheet as a cathode in a zinc-containing plating bath,
The plating bath contains Zn ions of 0.2 mol / L or more, V ions of 0.1 mol / L or more, and the relative flow rate of the plating solution in the plating bath with respect to the material steel plate is 0.5 m / s or more, Furthermore, the manufacturing method of the zinc-type electroplating steel plate characterized by performing the electroplating process which consists of a two-stage process of the front | former stage process and a back | latter stage process shown below.
In the above pretreatment, cathodic electrolysis is performed at a current density of 10 A / dm ² or more and less than 60 A / dm ² .
In the latter stage treatment, cathodic electrolysis is performed at a current density of 60 A / dm ² or more.

According to the zinc-based electroplated steel sheet of the present invention and the method for producing a zinc-based electroplated steel sheet according to the present invention, it is possible to maintain excellent flat plate portion corrosion resistance and heel portion corrosion resistance with a small amount of Zn adhesion, and the Zn adhesion amount as a whole is reduced. While keeping it low, a zinc-based electroplated steel sheet having flat plate corrosion resistance and buttock corrosion resistance comparable to pure Zn: 20 g / m ² can be obtained efficiently.

It is the figure which showed the test piece which measures a buttock corrosion resistance.

Hereinafter, the present invention will be specifically described.
In the present invention, the plating film containing zinc as a main component needs to be 0.5 atm% or more and less than 8 atm% in the range where V in the plating film is 0.1 μm height from the interface between the base steel sheet and the plating film. is there.
This means that when the V content is less than 0.5 atm%, good buttock corrosion resistance cannot be obtained as compared with pure Zn plating. On the other hand, when the V content is 8 atm% or more, the plating film becomes inactive, and the sacrificial corrosion resistance becomes inferior without being able to show good sacrificial corrosion resistance.
In addition, in this invention, the plating film which has zinc as a main component means that zinc contains 50atm% or more in the component of a plating film.

Further, the plating film containing zinc as a main component needs to be 8 atm% or more in the range where V in the plating film is 0.1 μm deep from the outermost surface of the plating film. This is because sufficient flat plate portion corrosion resistance cannot be obtained when the V content is less than 8 atm%.
In addition, although there is no restriction | limiting in particular in the upper limit of V content rate, From a viewpoint of productivity, it is preferable to set it as about 20 atm%.

The plating film component in the present invention is mainly composed of zinc as described above, but the other components may be component compositions and ratios used in conventionally known plating films.
In addition, the V content rate of the plating film other than the above-described V content rate is not particularly limited.

  In the present invention, the method for measuring the V content is not particularly limited, and a general method for measuring the V content can be used. Examples thereof include a quantitative analysis method for elements using AES, EPMA, or the like.

In the present invention, it is necessary to contain Zn ions in the bath at 0.2 mol / L or more and V ions at 0.1 mol / L or more. This is because if both the Zn ion and the V ion are less than the above range, each ion at the cathode interface is deficient and a good plating film cannot be obtained. Preferably, Zn ion: 0.5 mol / L or more, V ion: 0.2 mol / L or more.
The upper limit concentration of both Zn ions and V ions is not limited, but Zn ions: about 2.0 mol / L and V ions: about 1.0 mol / L are preferable, respectively.

  Furthermore, in the present invention, the relative flow rate of the plating solution and the steel plate to be plated needs to be 0.5 m / s or more. This is because a plating film having a uniform V content cannot be formed at a flow rate of less than 0.5 m / s. The flow rate is preferably 1.0 m / s or more. The upper limit of the relative flow velocity is not particularly limited, but is preferably about 6.0 m / s.

Cathodic electrolysis is a two-stage process consisting of a pre-stage process and a post-stage process, the current density of the pre-stage process is set to 10 A / dm ² or more and less than 60 A / dm ^2, and the current density of the post-stage process is set to 60 A / dm ² or more. There is a need.
This is because if the current density of the pre-treatment is less than 10 A / dm ² , the pH at the cathode interface is difficult to increase and a plating film lower layer having a uniform V content cannot be obtained. On the other hand, if the current density of the pretreatment is 60 A / dm ² or more, the lower layer of the plating film becomes inactive, and good buttock corrosion resistance cannot be obtained. Further, if the current density of the post-treatment is less than 60 A / dm ² , an upper layer having a high V content is not formed on the upper layer of the plating film, and good plate portion corrosion resistance cannot be obtained. The upper limit of the current density of the latter stage treatment is not particularly limited, but is preferably about 300 A / dm ² .

Furthermore, it is preferable that the electric density of the pre-treatment is 3500 to 34200 C / m ² and the electric density of the post-treatment is 3500 to 34200 C / m ² . If the electric density of the pre-treatment is 3500 C / m ² or more, the amount of adhesion of the lower layer can be secured, and no problem occurs in the corrosion resistance of the buttock. On the other hand, if the electric quantity density of the pretreatment is 34200 C / m ² or less, it has an effect of reducing the amount of galvanized adhesion. In addition, if the electric density of the post-treatment is 3500 C / m ² or more, the amount of adhesion of the upper layer can be secured, and no problem occurs in the corrosion resistance of the flat plate portion. On the other hand, if the electric quantity density in the post-treatment is 34200 C / m ² or less, it has the effect of reducing the amount of galvanized adhesion.

  Here, the pH of the plating bath is preferably 1.5 to 3.0. If the pH is 1.5 or more, the cathode interface pH can be sufficiently increased, and V can be taken into the plating film. On the other hand, if the pH is 3.0 or less, the pH of the interface does not rise too much during electrolysis, and a plating film having a uniform V content is formed.

The bath temperature is not particularly limited, but is preferably about 40 to 65 ° C. from the viewpoint of constant temperature retention.
Further, the Zn adhesion amount is not particularly limited, but is preferably 3 g / m ² or more and 10 g / m ² or less per side. If it is 3 g / m ² or more, sufficient corrosion resistance can be obtained, and if it is less than 10 g / m ² , the amount of Zn can be reduced and the amount of zinc used can be reduced. In addition, it is preferable that the thickness of the plating film in this invention shall be 0.2 micrometer or more. On the other hand, the upper limit is not particularly limited, but is preferably about 5 μm from the viewpoint of the amount of zinc used.

  After the zinc-based electroplating treatment, if necessary, various chemical conversion coatings (coating type, reaction type and electrolytic type) of chromate or chromate-free type are provided for the purpose of further improving various performances such as corrosion resistance, scratch resistance and workability. Further, a resin coating treatment or the like can be performed thereon. Needless to say, the effects of the present invention can also be obtained for steel sheets subjected to these treatments.

Cold-rolled steel sheet (thickness: 0.7 mm) is used as the plating plate, and this is subjected to electrolytic degreasing treatment, water washing and pickling treatment (sulfuric acid concentration: 70 g / L, liquid temperature: 25 to 40 ° C., immersion for 5 seconds). Was given. Next, a zinc-based electroplating treatment was performed using a plating bath and plating conditions shown in Table 1 to produce a zinc-based electroplated steel sheet.
The zinc-based electroplated steel sheet thus obtained was measured for Zn, V, Fe, and O element concentrations using AES (Auger electron spectroscopy) depth direction analysis (acceleration voltage: 3 kV, Ar ion sputtering). Then, the V content in the vicinity of the outermost surface of the plating film upper layer and in the vicinity of the interface with the underlying steel sheet in the lower layer of the plating film was confirmed and evaluated as follows.

Lower layer (in the zinc-based plating film, the range from the interface with the underlying steel plate to a height of 0.1 μm)
×: 8 atm% or more ○: 0.5 atm% or more and less than 8 atm% −: Less than 0.5 atm% Upper layer (in the zinc-based plating film, the range from the outermost surface to a depth of 0.1 μm)
○: 8 atm% or more ×: Less than 8 atm%

In addition, X-ray fluorescence analysis was performed, and using a calibration curve obtained by standard plate measurement with a known adhesion amount, the Zn adhesion amount (g / m ² ) per one side of the zinc-based electroplating film was measured.
Furthermore, the following evaluation items were evaluated.
<Evaluation items>
I Flat Plate Corrosion Resistance The obtained zinc-based electroplated steel sheet was evaluated for corrosion resistance by a salt spray test in accordance with JIS Z 2371-2000. The test piece was 150 mm × 50 mm, and the cut end face and back face were sealed. In addition, flat plate part corrosion resistance was evaluated by 5% red rust generation time.
◎: More than 36h ○: More than 24h and less than 36h ×: Less than 24h

II Corrugation resistance on the galvanized steel sheet The obtained zinc-based electroplated steel sheet was clawed with a cutter knife as shown in FIG. 1 with a force reaching the base steel sheet, and was subjected to a salt spray test similar to the flat plate corrosion resistance. The corrosion resistance of the part was measured. The test piece was 150 mm × 50 mm, and the cut end face and back face were sealed. The buttock corrosion resistance was evaluated by the 5% red rust occurrence time around the buttock.
◎: More than 36h ○: More than 24h and less than 36h ×: Less than 24h

  From the above results, it can be seen that the zinc-based electroplated steel sheets (test Nos. 9 to 24) according to the present invention have high flat plate portion corrosion resistance and heel portion corrosion resistance.

  The zinc-based electroplated steel sheet of the present invention is not only excellent in surface appearance, but also excellent in flat plate portion corrosion resistance and collar portion corrosion resistance, and can be used without any problem even without coating. Therefore, it can be used in a wide range of applications such as home appliances, automobiles, and building materials.

Claims (2)

  A zinc-based electroplated steel sheet having a zinc-based plating film, wherein V in the plating film is 0.5 atm% or more and less than 8 atm% in the range from the interface between the plating film and the base steel sheet to a height of 0.1 μm. A zinc-based electroplated steel sheet characterized by being 8 atm% or more in the range from the outermost surface of the plating film to a depth of 0.1 μm. A method for producing a zinc-based electroplated steel sheet in which a zinc-based electroplated film is formed on the surface of the material steel sheet by electrolyzing the steel sheet as a cathode in a zinc-containing plating bath,
The plating bath contains Zn ions of 0.2 mol / L or more, V ions of 0.1 mol / L or more, and the relative flow rate of the plating solution in the plating bath with respect to the material steel plate is 0.5 m / s or more, Furthermore, the manufacturing method of the zinc-type electroplating steel plate characterized by performing the electroplating process which consists of a two-stage process of the front | former stage process and a back | latter stage process shown below.
In the above pretreatment, cathodic electrolysis is performed at a current density of 10 A / dm ² or more and less than 60 A / dm ² .
In the latter stage treatment, cathodic electrolysis is performed at a current density of 60 A / dm ² or more.

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