JPH0768634B2 - Zinc-based plated steel sheet with excellent corrosion resistance, coating performance and workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is excellent in corrosion resistance, coating film performance and workability when exposed to a severe corrosive environment in which an aqueous solution of NaCl, CaCl ₂ or the like exists, and is a building material. Or zinc-based alloy plated steel sheet used for automobiles, automobiles, etc.

(Prior Art and Problems Thereof) So-called cold-rolled steel sheets, which are not provided with an anticorrosion coating layer, have been conventionally used for automobile steel sheets. This cold-rolled steel sheet is processed into various parts for automobiles by an automobile company, assembled, subjected to a phosphate treatment, and then painted. That is, cold-rolled steel sheets used in automobiles are protected from corrosion by a coating film. However, in recent years, the demand for improved durability of automobiles, especially due to corrosion, has increased,
Conventional painting alone cannot always meet this requirement. For example, in Canada, where salt is sprayed to prevent roads from freezing in the winter, 1985 targets "no pitting" and "no rusting for 5 years" as guidelines for car body corrosion in 1985. This guideline is known as the "Canada Code", and as a result, various measures are being taken as a goal for car body rust prevention.

At present, electrogalvanized steel sheets are widely used because they improve the corrosion resistance of cold-rolled steel sheets and the corrosion resistance after painting and can be mass-produced without impairing workability. However, since zinc in galvanized steel is more anodic than base steel, it exhibits good corrosion resistance in general corrosive environments, but as mentioned above, it is harsh to spray salts (NaCl, CaCl _2, etc.). In a corrosive environment, the corrosion rate of zinc against the base metal is high, and the sacrificial corrosion effect of zinc is lost in a short period of time.

The easiest way to improve corrosion resistance is to increase the plating amount. However, an increase in the plating amount causes a marked decrease in productivity and an increase in cost in electroplating, which is not only economically undesirable, but also has the following problems in terms of workability and weldability. That is, when a plated steel sheet is processed into an automobile part, particularly in a drawing process, a plating layer is peeled off or a part of it is scraped off (so-called powdering) and deposited on a press die, resulting in a flaw in the product. There is. If such powdering occurs, not only the productivity will be significantly reduced by the maintenance of the mold, but also the performance of the product will be adversely affected. Therefore, it is necessary to reduce the plating amount. For the assembly of various members processed 10,000 times, almost all resistance welding (spot welding) is used, and good or bad weldability is emphasized. The weldability is greatly affected by the plating amount, and if the plating amount increases to a certain extent or more, defects such as insufficient strength of the welded portion and poor appearance are likely to occur, and further, the life of the welding electrode is significantly reduced. Therefore, from the viewpoint of workability and weldability, it is desirable that the amount of plating is as low as possible. Furthermore, galvanized steel sheets for automobiles are finally coated, but zinc is easily corroded by the corrosive aqueous solution that has penetrated the coating film defects and the coating film, so the coating surface "blister" (so-called Prister) However, there is a drawback that the coating film is generated and the coating film floats from the substrate and peels off. or,
When a coating film defect occurs due to flying stones while the automobile is running, corrosion under the coating film spreads from that portion, and the coating film is likely to peel off.

For the purpose of eliminating the drawbacks of galvanized steel sheet, the electric potential is more noble than zinc (eathodic) and less noble than base steel (Anodic).
It has an anodic anticorrosion effect on the base steel, has a low corrosion rate due to salts, and has coating properties (especially corrosion resistance after coating, secondary paint adhesion ... coating film when the coating part is exposed to a corrosive environment. Based on the idea of excellent adhesiveness, workability, and weldability, for example, Zn-Fe system (Japanese Patent Publication No. 60-11117), Zn-Ni system (Japanese Patent Publication No. 58-11795), Zn-Fe
Many zinc-based alloy-plated steel sheets such as -Ni-based, Zn-Ni-Co-based, Zn-Fe-Cr-based, etc., and multi-layer plating combining them have been developed. These zinc alloy plated steel sheets are
Although it has excellent performance as a whole compared to galvanized steel sheet, it has further improved corrosion resistance, especially for pitting corrosion (Pitting Corrosion) in the severe corrosive environment where the above-mentioned salts are sprayed. Is desired.

The improvement in corrosion resistance is most easily achieved by increasing the amount of plating, but as already mentioned for galvanized steel sheets, even in the case of Zn-based alloy plated steel sheets, an increase in plating cost, powdering during processing, It is desirable that the amount of plating is as low as possible because it causes problems such as deterioration of weldability.

Furthermore, JP-A-57-2305 discloses a steel sheet having improved workability and plating adhesion of a zinc-based alloy-plated steel sheet.
4 and JP-A-57-85963.

However, a detailed examination of the conventional zinc-based alloy-plated steel sheet shows that it has excellent workability and plating adhesion, but it has a further improvement in corrosion resistance, in particular, a further improvement in corrosion resistance of the original plating plate itself and severe forming. It has been found that it is necessary to improve the forming workability when the processing is performed, and further, to improve the corrosion resistance of the forming processing part.

(Means for Solving Problems) The present invention has been made in view of these situations, and by further appropriately adjusting the steel composition, further improvement in corrosion resistance and workability of the plating base plate itself and the plating layer It has been found that the effects of improving the pitting corrosion resistance, improving the corrosion resistance of the processed portion, and improving the coating performance, especially the corrosion resistance after coating in the defective portion of the coating film, can be obtained by the interaction or synergistic effect.

Further, according to the present invention, by providing a Ni-based undercoating layer on the intermediate layer between the above-mentioned plated original plate and the zinc or zinc-based alloy plated layer, it is possible to further improve the performance due to the additive effect of the steel component and the plated layer. Is found.

Therefore, the gist is (1)% by weight, C; less than 0.01%, acid-soluble Al; 0.005-0.10%, P; 0.02-0.15
%, Cu; 0.1% to 0.8% or less, and Ti, Nb, Zr, V 1
Type or two or more types of steel sheet containing 0.03 to 0.5% zinc or zinc based alloy plated layer on one or both sides, which has excellent corrosion resistance, coating performance and workability, (2) Weight %, C; less than 0.01%, acid-soluble Al; 0.005-0.10%, P; 0.02-0.15
%, Cu; 0.1-0.8%, Ni; 1% or less, Ti, Nb, Zr,
A zinc-based plated steel sheet excellent in corrosion resistance, coating performance and workability, which is obtained by applying a zinc or zinc-based alloy plating layer to one or both sides of a steel sheet containing 0.03 to 0.5% of one or more types of V, ( 3)% by weight, C; less than 0.01%, acid-soluble Al; 0.005-0.10%, P; 0.02-0.15
%, Cu; 0.1 to 0.8%, and one or more of Ti, Nb, Zr, and V; 0.03 to 0.5% on one side or both sides of a steel sheet containing Ni.
Zinc-plated steel sheet with excellent corrosion resistance, coating performance and workability by applying zinc-based or zinc-based alloy plating layer on top of base type undercoating layer, (4)% by weight, C; less than 0.01%, acid soluble Al; 0.005-0.10%, P; 0.02-0.15
%, Cu; 0.1-0.8%, Ni; 1% or less, and Ti, Nb, Z
Corrosion resistance and coating performance obtained by applying a Ni-based undercoating layer and a zinc or zinc-based alloy plating layer on the Ni-based undercoating layer on one or both sides of a steel sheet containing 0.03 to 0.5% of one or more types of r and V And a zinc-based plated steel sheet with excellent workability.

The present invention will be described in detail below.

A steel plate corresponding to the steel plate manufactured through a normal steel plate manufacturing process is used as a plating original plate.

C is an element that adversely affects corrosion resistance and moldability.
It is less than 0.01%, preferably 0.006% or less. That is, when the C content is 0.01% or more, the precipitation of carbide such as cementite or titanium carbide on the crystal grain boundaries increases, and the grain boundary corrosion in the corrosive environment or the nonuniformity of the structure of the steel sheet causes the plating original plate to become uneven. The corrosiveness of itself deteriorates.

Further, the precipitation of these cementite or carbide hinders the uniform precipitation of zinc and a zinc-based alloy plating layer,
This increases the number of pinholes and non-plating in the plated layer, which deteriorates the corrosion resistance of the plated steel sheet.

Further, even for the formation of a uniform coating layer of the Ni-based undercoating layer in the present invention, it causes pinholes and non-plating. Especially, when the Ni-based undercoating layer is provided as a diffusion coating layer, uniform diffusion is not possible. It becomes a cause to prevent.

Further, the increase of C causes deterioration of mechanical properties and deterioration of moldability, and when severe molding is performed, cracks and cracks of the original plate originating from these C precipitates are generated. It causes the generation of cracks reaching the surface of the plating layer or the surface of the coating film due to the occurrence of the cracks, and deteriorates the corrosion resistance of the plated steel sheet or after coating.

Next, P and Cu are added in combination as a corrosion resistance improving element in the present invention, Ni is added in some cases, and one or more of Ti, Nb, Zr and V are added in combination with these components. To be done.

That is, by controlling the steel composition to have an extremely low C content as described above, there are advantages that the corrosion resistance is improved and the corrosion rate is decreased.

On the other hand, in a steel sheet to which Ti or the like that improves workability is added, piercing corrosion is likely to occur due to the S component that is unavoidably contained in the steel. Therefore, in order to reduce the corrosion rate and suppress the piercing corrosion to improve the corrosion resistance, P and Cu are added as essential components.

P is effective as an element for improving corrosion resistance in a corrosive atmosphere containing Cl ⁻ ions, particularly as an element for preventing piercing corrosion in a steel containing extremely low C, and particularly when coexisting with Cu, the effect of improving corrosion resistance is particularly large.

In addition, when a zinc or zinc-based alloy plating layer is applied to only one side of a steel sheet for use, it also has an effect of promoting uniform generation of phosphate crystals on the iron surface without the plating layer.

The addition amount is 0.02 to 0.15%. If it is less than 0.02%, the effect of improving the corrosion resistance cannot be obtained, and if it exceeds 0.15%, the workability is deteriorated. The preferred amount of P added is 0.035 to 0.0
It is in the range of 7%.

Next, the addition of Cu has a great effect on improving the corrosion resistance.
^- in corrosive atmosphere containing ions, the potential of the noble (cathodic reduction), is extremely large effect of reducing the corrosion rate. In the first place, a large effect is stably obtained when the addition amount exceeds 0.1% and 0.8% or less. If 0.1% or less, the effect of improving the corrosion resistance cannot be obtained stably, and if it exceeds 0.8%, the corrosion resistance is further improved.However, in the hot rolling process of the steel plate manufacturing process, cracks due to red hot brittleness and Cu on the steel plate surface are caused.
Are concentrated and scale scratches and the like are likely to occur. In the present invention, the addition of Cu is preferably 0.5% or less.

Next, Ni is selectively added, and 1% or less of Ni is added.
The effect of improving the corrosion resistance is small when added alone, but the effect of improving the corrosion resistance is large due to the co-addition with P and Cu, and the effect of solving the problem of Cu in the steel sheet manufacturing process is great, and the amount of Cu added is 1 % Or less, preferably 0.5% or less.

Furthermore, 0.03 to 0.50% of one or more of Ti, Nb, Zr, and V is contained in the steel sheet having the above components, and is combined with C in the steel,
Prevent the adverse effect of C. That is, by precipitating fine carbide such as Ti, the corrosion resistance and the mechanical properties are improved together with the effect of the extremely low C content. Therefore,
If the addition amount of steel components such as Ti is less than 0.03%, the effect of improving the formability and corrosion resistance is small, and if it exceeds 0.50%, the effect reaches saturation and becomes uneconomical. It tends to harden the material and deteriorate the moldability. The preferred range is
It is 0.075 to 0.20%.

Further, in the present invention, in order to prevent deterioration of corrosion resistance due to defects (precipitation of inclusions, surface defects) in the steelmaking process, the amount of acid-soluble Al is regulated within the range of 0.005 to 0.10%.
That is, the amount of acid-soluble Al (SolAl) remaining in the steel is 0.005
When the content is less than%, it is difficult to prevent the generation of bubbles due to the oxidizing gas, the surface defect occurrence rate of steel is remarkably increased, and the corrosion resistance of the steel material is deteriorated. Excessive acid-soluble Al exceeding 0.10% causes Al-based oxides to be scattered on the steel surface, causing no corrosion at the starting point of corrosion resistance deterioration or the plated surface applied to this steel sheet, pinholes, etc. Occurs, and the soundness of the plating layer is impaired. Therefore, the amount of acid-soluble Al is in the above range, preferably 0.03 to 0.08%.

Other components that are inevitably contained in the steel are not particularly specified, but they are preferably used in the following ranges.

S has a great adverse effect on the corrosion resistance and is preferably 0.025% or less.

Si hinders the uniform coverage of the plating layer or the Ni-based undercoating treatment, so it is 0.30% or less, preferably 0.10% or less.

Moreover, about Mn, it is used in the range of 0.1 to 1.5%.
Mn has the effect of preventing piercing corrosion, and is effective in terms of improving corrosion resistance and evenly forming a phosphate crystal film on the iron surface when used on a single-sided steel sheet, but increasing the amount of addition increases the material Since it tends to be slightly hardened, 0.3 is preferable.
~ 0.6%.

Although the steel plates having the above-mentioned steel components have excellent corrosion resistance and workability as compared with the conventional steel plates, they are insufficient in view of the corrosion resistance currently required for automobile steel plates.

Therefore, a Zn or Zn-based alloy plating layer is applied in order to provide better corrosion resistance and coating film performance.

Zn is a metal whose corrosion potential is base (Anodic) with respect to a steel sheet and has a sacrificial anticorrosion action on the steel sheet, and the anticorrosion effect of the Zn plating layer is considerably remarkable.

However, as mentioned above, plated steel sheets for automobiles are required to have excellent coating performance and weldability as well as a high level of corrosion resistance of "no piercing for 10 years" and "no rusting for 5 years". From the viewpoint of overall performance, the Zn plating layer using the conventional plating original plate could not provide sufficient performance.

As a result of various studies on the cause of this, the couple corrosion current between the zinc plating layer and the plating base plate / base iron was extremely large, and the plating defect part, the scratched part during processing, the plating layer cracked part due to processing, or The galvanized layer is remarkably melted by the sacrificial anticorrosive action of the galvanized layer on the end face, etc., and sufficient corrosion resistance cannot be obtained unless the plating amount is made thick. In the coating film defect portion reaching up to, a steel plate having a galvanized layer using a conventional plating original plate, a large amount of Zn corrosion products are generated due to the dissolution action of Zn due to the remarkable sacrificial anticorrosion ability of Zn, and coating blisters (so-called , Blisters) and peeling of the coating film are apt to occur, and the adhesiveness of the coating film and the corrosion resistance after coating are remarkably inferior.

As is known from FIG. 1 showing an example of a couple corrosion current in a 5% NaCl aqueous solution of a Zn plating layer or a Zn-16% Fe alloy plating layer and a plating base plate of the present invention, by using the plating base plate of the present invention , The couple corrosion current between the galvanized layer and the base metal is reduced, the corrosion rate of zinc is reduced by reducing the sacrificial anticorrosive action of the galvanized layer, and its corrosion resistance and coating performance are significantly improved.

Since the present invention has excellent corrosion resistance and workability of the plated original plate, even if the sacrificial anticorrosive ability of the zinc plating layer is reduced, the corrosion resistance of the plating defect portion and the end face portion is sufficiently secured, and cracks during processing are also generated. Less likely to occur.

Even if the plating layer disappears, the corrosion resistance of the original plating plate extends the corrosion resistance life.

As described above, the present invention provides an excellent effect of improving the corrosion resistance, coating performance, etc. of the original plating plate and the plating layer due to the additional effect, and since it is not necessary to thicken the plating layer, weldability, It has excellent plating adhesion during processing and can be applied to rustproof steel sheets for automobiles.

Furthermore, in the present invention, the corrosion rate is further smaller than that of the Zn plating layer, and by providing the Zn-based alloy plating layer having a sacrificial anticorrosion effect on the base iron, it is possible to further improve the corrosion resistance performance and the coating film performance. Is.

Zn-based alloy plating in the present invention, Zn, Ni, Co,
An alloy plating layer containing one or more of Cr, Fe and Mo is applied. In other words, the alloy plating layer, which is more noble than the zinc plating layer, has a low corrosion rate, prolongs the corrosion resistance life of the plating layer when exposed to a corrosive environment for a long time, and combines it with the effect of improving the corrosiveness of the original plate. The corrosion resistance life is further extended. In addition, since the dissolution rate of the plated layer in the coating film defect portion is low, the generation of corrosion products is small, and the formation of blisters and the peeling of the coating film are less likely to occur.

Therefore, in order to obtain these effects, in the present invention, Ni (8-30%), Co (8-30%),
Fe (8-30%), Cr (1-8%), Mo (3-30%) are added alone. In addition, in the case of the composite addition of two or more of these, not less than the lower limit value of each individual addition amount is contained with respect to Zn, and the upper limit is not more than the upper limit value of each individual addition amount and the total amount is 30% or less. Is good. When it exceeds 30%, the effect of reducing the corrosion rate is saturated, and the pinholes in the alloy plating layer tend to increase, which is not necessarily advantageous in terms of corrosion resistance, and there is a problem that cracks are easily generated in the alloy plating layer during processing. It is not preferred.

In the plated steel sheet of the present invention, the phosphate treatment property should be improved by the amount of adhesion (about 1/4 or less of the amount of zinc or zinc-based alloy plating layer) that does not deteriorate the corrosion resistance of the outermost surface layer. Higher Fe content (80% or more of Fe concentration), which improves the coating performance, Zn-Fe, Zn-Fe-Ni, Zn-Fe-P
A system coating layer may be provided.

Thus, in the present invention, in order to further improve the corrosion resistance and the coating film performance, a Ni-based undercoating layer is provided as an intermediate layer between the plating original plate and the zinc or zinc alloy plating layer. This Ni-based undercoat layer reduces pinholes and improves corrosion resistance due to the effect of overlapping with the Zn or Zn-based alloy plating layer.

Further, the metal or alloy forming the Ni-based undercoat layer is Zn
Alternatively, the diffusion rate is relatively high with respect to the Zn-based alloy plating layer, the Zn-Ni-based alloy layer is likely to be formed during coating and baking work, and the effect of improving the corrosion resistance can be obtained by reducing pinholes reaching the base iron.

Thus, this Ni-based undercoat layer is made of Ni, Ni-Co alloy, Ni-P
Alloy, Ni-Fe alloy, Ni diffusion treatment layer, the thickness is 0.01-1
μ is good. If the thickness is less than 0.01 μm, the uniform coating effect of the undercoating layer tends to be insufficient, and the above-mentioned pinhole reducing effect tends not to be obtained. On the other hand, when the thickness exceeds 1 μ, the above effect is saturated and the undercoat layer tends to crack due to processing, which is not preferable.

Among these Ni-based undercoat layers, the method of providing a Ni diffusion coating layer is particularly excellent. The diffusion layer is provided with the undercoating layer as described above, and then the diffusion treatment layer is provided by utilizing the heating and annealing process of the cold-rolled steel sheet and the like. It becomes a plated original plate with high concentration and is electrically noble, and a high degree of corrosion resistance can be obtained for the original plate. At the same time, the couple corrosion current with the zinc plating layer is reduced, and the corrosion rate due to sacrificial dissolution is reduced at the plating defect portion, the end surface, etc. of the plating layer. As a result, the corrosion resistance of the plated steel sheet is extended or the undercoat corrosion is significantly suppressed due to the decrease in the corrosion rate of the galvanized layer, etc. at the coating defect portion or the end surface that reaches the base metal even after coating. Further improvement of corrosion resistance and paint adhesion after aging can be expected.

Next, in the present invention, the method for providing the Ni-based undercoating layer, the zinc plating layer or the zinc alloy plating layer applied to the original plating plate and the amount of deposition thereof are not particularly limited, but the coating layer For example, the following method is used as the method for providing the layer, and the following range is preferable for the attached amount.

That is, as the Ni-based undercoating method, (1) nickel undercoating; electroplating method using nickel sulfate-nickel chloride-boric acid-based bath (2) nickel-cobalt alloy undercoating; nickel having a desired composition, Electroplating Method Using Nickel Sulfate-Cobalt Sulfate-Nickel Chloride-Cobalt Chloride-Boric Acid-Based Bath Containing Cobalt Ion (3) Nickel-iron alloy substrate treatment; sulfuric acid containing nickel and iron ions having a desired composition Electroplating Method Using Nickel-Iron Sulfate-Boric Acid Bath (4) Nickel-P Alloy Substrate Treatment; Nickel Sulfate-Nickel Chloride-Sodium Hypophosphite-Phosphorus Containing Nickel and P Ion of Desired Composition An electroplating method using an acid bath is performed.

When the Ni-based undercoat is used as the Ni-based diffusion-treated layer, the above Ni and Ni alloys are applied to the plating original plate by the electroplating method or an aqueous solution containing Ni ions or Ni ions and other alloying element ions. Is applied to the surface of the original plating plate and subjected to a heat diffusion treatment.

For example, after the above Ni plating or nickel acetate-surfactant aqueous solution, or nickel acetate-antimony phosphate-surfactant aqueous solution is applied and dried by a roll coater, and then each heat diffusion treatment in a non-oxidizing atmosphere (for example, 650 ~ 900
A heat treatment is performed at a temperature of ℃ for 30 to 180 seconds).

This diffusion coating is a cold rolled steel plate (As Cold
Material) or a steel sheet (full finish material) that has been annealed after cold rolling, for surface cleaning such as degreasing and pickling,
After the activation treatment, the Ni-based coating layer may be provided by the electroplating method or the aqueous solution coating method to perform the heat diffusion treatment. However, the Ni-based coating layer is provided on the as-cold-rolled steel sheet, and the diffusion treatment is performed simultaneously with the annealing of the original plate. Since it is promoted, a target diffusion layer is produced by a short heat treatment, which is economically and industrially advantageous.

Further, the zinc or zinc-based alloy plating layer is prepared by subjecting the plating original plate of the present invention to surface cleaning, activation treatment or after providing a Ni-based undercoating layer, by a hot dipping method, an electroplating method, a vacuum deposition method, or the like. It is provided on one side or both sides according to its use.

When the galvanized layer is formed by the hot dip plating method, either the flux method or the gas reduction method may be used, and the galvanizing bath containing a small amount of Al is used for coating in order to secure the plating adhesion. When the zinc or zinc-based alloy plating layer is provided by the electroplating method, the coating layer is provided by using the electrolytic plating bath used in the usual electroplating method. For example, as one example, coating of a zinc plating layer by electrolysis of a (zinc sulfate-sodium sulfate) -based aqueous solution, coating of a Zn-Ni alloy plating layer by electrolysis of a (zinc sulfate-nickel sulfate-ammonium sulfate) -based aqueous solution, Coating of Zn-Ni-Co alloy plating layer by electrolysis of (zinc sulfate-nickel sulfate-cobalt sulfate-ammonium sulfate) aqueous solution, coating treatment of Zn-Fe alloy plating layer by electrolysis of (zinc sulfate-iron sulfate) aqueous solution Etc. using a soluble or insoluble anode. Thus, the thickness of each of these zinc or zinc-based alloy plating layers is 1.5 μm or more, preferably 3 μm or more, from the viewpoint of corrosion resistance by ensuring uniform coverage. In addition, the thickness of the coating layer is 25μ for the galvanized layer, preferably 15μ, from the aspects of adhesion, forming workability, weldability, etc. of the coating layer.
In the case of a zinc alloy plating layer, it is 15μ or less, preferably 8μ or less.

As described above, the plated steel sheet composed of the steel sheet having the steel component of the present invention and the zinc-based plating layer, or the Ni-based underlayer and the zinc-based plating layer, when exposed to a corrosive environment, has been described above. As described above, due to the combined effect of the original plating plate and the coating layer, (1) the plating layer is corroded by reducing the dissolution rate due to the sacrificial anticorrosive action of the plating layer at the plating defect, the processing flaw portion or the end surface portion during molding. When the product is used with extended life and painted, the effect of improving paint adhesion after aging and corrosion resistance after painting is obtained by reducing undercoat corrosion.

(2) In the steel composition, in order to use a steel sheet in which the C content is regulated to an extremely low content, in addition to the effect of adding other corrosion resistance improving elements, the effect of improving the corrosion resistance of the original plating plate itself and the plating layer by suppressing the precipitation of carbide It is possible to obtain the effect of improving the corrosion resistance by reducing the occurrence of non-plating and the effect of improving the corrosion resistance by the effect of preventing the generation of cracks reaching the surface of the plating layer or the coating film by improving the workability.

Thus, the present invention, by the combined effect of the original plating plate and the coating layer, it is possible to obtain an extremely excellent effect, it is possible to reduce the adhesion thickness of the plating layer, the weldability required for automotive rust-preventive steel sheet, It is also possible to obtain a complementary effect such as reduction of powdery peeling (so-called powdering) of the plating coating layer during molding.

(Example) Below, the Example of this invention is demonstrated with a comparative example.

Using steel plates with steel components that are changed mainly in the contents of P, Cu, Ni, Ti, Nb, etc. shown in Table 1, a zinc-based plating layer or a Ni-based undercoat layer and zinc are applied by the following coating method. A system plating layer was provided.

That is, the galvanized layer by the electroplating method uses a cold rolled steel sheet (full finish material) in a (3% NaOH + 0.3% surfactant) type degreasing bath, and after degreasing and washing with water, a 10% H ₂ SO ₄ aqueous solution is used. Anodic pickling for 1 second at a current density of 20 A / dm ² at 50 ℃
Cathodic pickling was carried out by electrolytic pickling and water washing for 1 second each for surface cleaning and activation. Then, using a (350 g / zinc sulfate-80 g / sodium sulfate) -based electrolytic bath, 60
A zinc plating layer having a predetermined thickness was provided at a current density of 40 A / dm ^{2 at} ℃.

On the other hand, the hot-dip galvanizing method or the zinc alloy plating layer having a eutectic structure with zinc containing zinc as the main component is formed by using the cold rolled As Cold material,
Zn-
A 0.2% Al-based plating bath and a zinc-based alloy plating bath shown in Table 1 were used to form zinc-based plating layers each having a predetermined thickness.
Furthermore, in the case of providing a Ni-based undercoat layer, in the case of the undercoat layer by electroplating, the same method as the above electroplating method is used, and a Ni-based electrolytic bath composition of a predetermined thickness is used.
A Ni-based undercoat layer was applied to provide a zinc-based plating layer.

In the case of the Ni-based diffusion coating layer, As Cold material is used, and the surface is cleaned and activated by the same method as in the case of electroplating.
The material was annealed simultaneously with the annealing of the material to provide a diffusion layer. After that, a zinc-based plating layer was applied.

Then, the untreated material was subjected to a chromate treatment using a CrO ₃ —SiO ₂ system bath and a phosphate treatment for a full dip type, and a predetermined coating amount was provided for each, and the following evaluation test was performed.

As can be seen from Table 2 showing the results of the performance evaluation test, the steel sheet of the present invention has extremely excellent properties in corrosion resistance and coating performance as compared with the comparative example steel sheet.

○ Evaluation test method (I) Corrosion resistance of unpainted material Corrosion resistance after salt spray test Scratch flaws reaching the base metal were put into the evaluation material, and the corrosion resistance life was determined by the pitting depth after 360 hours of salt spray test. evaluated. The evaluation criteria are as follows.

◎ …… Decrease in thickness of pierced corrosion part 0.25mm or less ○ …… 〃 0.35mm or less △ …… 〃 0.40mm or less × …… When it exceeds 〃0.40mm Corrosion resistance (A) 0.8mm Using the plate thickness evaluation material, (i) salt spray (5% NaCl 35 ° C x 4 hours) → (ii) dry (70 ° C humidity 60% 2 hours) → (iii) wet (49 ° C humidity 98% 2) Time) → (iv) cooling (-20 ° C x 2 hours) →
(I) Salt spray ((i) to (iv) is 1 cycle) The cyclic corrosion test under the conditions of 60 cycles was performed to measure the pitting corrosion depth, and the corrosion resistance was evaluated according to the following evaluation criteria. .

◎ …… Maximum perforation corrosion depth less than 0.3 mm ○ …… 〃 less than 0.40 mm △ …… 〃 less than 0.50 mm × …… 〃 more than 0.50 mm ~ perforation occurred Corrosion resistance by cyclic corosion test (B) 0.8 mm plate Using a thick evaluation material, a blank size of 470 × 470 mm to a square cylinder drawing material of 200 × 200 mm square and a drawing depth of 100 mm, and using the cyclic corosion test of the above item,
The corrosion resistance life of the processed part was evaluated by measuring the pitting corrosion depth after 50 cycles.

The evaluation criteria were as follows.

◎ …… Maximum perforation corrosion depth less than 0.20 mm ○ …… 〃 less than 0.25 mm △ …… 〃 less than 0.30 mm × …… 〃 0.30 mm or more ~ (II) Corrosion resistance of coating materials Coating performance by cyclic corosion test ( A) A phosphate crystal coating layer with a coating weight of ^{2 to} 2.5 g / m ² was formed on each of the evaluation materials, and then 20 μm thick of cationic electrodeposition coating was applied, and then scratch flaws reaching the base steel were put in. Then, the coating film swell width of the scratch portion and the maximum pitting corrosion depth of the scratch portion were measured after 75 cycles under the cyclic corosion test conditions described in the above item.

By the above-mentioned test, the coating film defective portion was evaluated mainly with respect to the paint adhesion after aging and the corrosion resistance after coating.

◎ ... Maximum swell width on one side from scratch of 5mm or less and maximum pitting corrosion depth of 0.1mm or less ○ …… Maximum swell width of 7.0mm or less on one side from scratch and maximum pitting corrosion depth of 0.2mm or less △ ...... Maximum swell width of 8.5 mm or less on one side from the scratch part and maximum piercing corrosion depth of 0.3 mm or less × …… Maximum swell width of one side from the scratch part is over 8.5 mm or maximum piercing corrosion depth is over 0.3 mm Cyclic roller Coating performance by the John test (B) After using the cationic electrodeposition material of the above item of 0.8 mm thickness to perform 20% deformation processing by bulging, after 50 cycles test under the conditions of the cyclic corosion test of the above item An evaluation test was carried out for corrosion from the coating film defect portion due to processing.

The evaluation criteria were as follows: ∙ Corrosion depth of pierce less than 0.05mm ∃ 〃 less than 0.10mm △ …… 〃 less than 0.15mm × …… 〃 0.15mm or more Coating performance by outdoor exposure test Cation of the above item After using scratches that reach the base metal using electrodeposited material, spray 5% NaCl water once a day on the evaluation material, conduct an outdoor exposure test for 2 years, and then determine the pitting corrosion depth. The corrosion state from the end face of the measurement and evaluation material was observed, and its corrosion resistance was evaluated according to the following evaluation criteria.

◎ …… The maximum pitting corrosion depth is less than 0.25 mm, almost no corrosion from the end face part ○ …… The maximum piercing corrosion depth is 0.25 mm or more and less than 0.40 mm, some corrosion from the end face part △ …… Corrosion from the end face is possible when the maximum piercing corrosion depth is 0.40 mm or more and less than 0.60 mm ........ The maximum piercing corrosion depth is 0.60 mm or more and partial pitting corrosion occurs, or the end face is caused by corrosion from the end face. The initial shape of the product has almost no molding processability. From a blank size of 0.8 mm × 480 × 480 mm, a rectangular tube drawing of 200 × 200 mm size, drawing depth of 125 mm was performed with a wrinkle holding pressure of 20 T. The forming processability was evaluated by relatively comparing the occurrence of surface galling.

◎ …… Excellent ○ …… Satisfactory good △ …… Satisfactory inferior × …… Very inferior

[Brief description of drawings]

FIG. 1 is a graph showing an example of a couple corrosion current in a 5% NaCl aqueous solution of a Zn plating layer, a Zn-16% Fe alloy plating layer and a plating base plate of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C25D 5/26 M (72) Inventor Teruaki Izaki 1-1-1 Edemitsu, Hachimanto-ku, Kitakyushu, Fukuoka Nippon Steel Co., Ltd. Yawata Works (56) Reference JP 59-23894 (JP, A) JP 57-171692 (JP, A) JP 55-141555 (JP, A) JP JP-A-57-104656 (JP, A) JP-A-55-24943 (JP, A) JP-A-55-110794 (JP, A) JP-A-56-166390 (JP, A) JP-A-58-45396 (JP , A)

Claims (4)

[Claims] 1. By weight%, C; less than 0.01%, soluble Al; 0.005
.About.0.10%, P; 0.02 to 0.15%, Cu; 0.1% to more than 0.8% and further contains Ti, Nb, Zr, V of 1 or 2 or more and 0.
A zinc-based plated steel sheet with excellent corrosion resistance, coating performance and workability, which is obtained by applying a zinc or zinc-based alloy plating layer on one or both sides of a steel sheet containing 03 to 0.5%. 2. C, less than 0.01% by weight, soluble Al; 0.005
~ 0.10%, P; 0.02-0.15%, Cu; over 0.1% and 0.8% or less,
Ni: Contains 1% or less, and further contains one or two of Ti, Nb, Zr and V.
A zinc-based plated steel sheet with excellent corrosion resistance, coating performance and workability, which is obtained by applying a zinc or zinc-based alloy plating layer on one or both sides of a steel sheet containing 0.03 to 0.5% of a kind or more. 3. By weight%, C; less than 0.01%, soluble Al; 0.005
.About.0.10%, P; 0.02 to 0.15%, Cu; 0.1% to more than 0.8% and further contains Ti, Nb, Zr, V of 1 or 2 or more and 0.
Zinc-based plated steel sheet with excellent corrosion resistance, coating performance and workability, which is obtained by applying a Ni-based undercoating layer and a zinc or zinc-based alloy plating layer on the Ni-based undercoating layer on one or both sides of a steel sheet containing 03 to 0.5%. 4. By weight%, C; less than 0.01%, soluble Al; 0.005
~ 0.10%, P; 0.02-0.15%, Cu; over 0.1% and 0.8% or less,
Ni: Contains 1% or less, and further contains one or two of Ti, Nb, Zr and V.
Zinc-based plating with excellent corrosion resistance, coating performance and workability by applying a Ni-based undercoating layer and a zinc or zinc-based alloy plating layer on the Ni-based undercoating layer on one or both sides of a steel sheet containing 0.03 to 0.5% steel sheet.