JPS627890A - Zinc or zinc alloy plated steel sheet having superior corrosion resistance, paintability and workability - Google Patents

Abstract

PURPOSE:To improve the workability and pitting corrosion resistance of the resulting titled steel sheet, the corrosion resistance at the worked part and the paintability, especially the corrosion resistance after painting by forming a Zn or Zn alloy layer on a steel sheet having a specified composition by plating. CONSTITUTION:One side or both sides of a steel sheet having a composition contg., by weight, <0.01% C, 0.005-0.10% acid-sol. Al, 0.02-0.15% P, 0.1-0.8% Cu and 0.03-0.5% one or more among Ti, Nb, Zr and V are plated with Zn or a Zn alloy. The steel composition may further contain <=1% Ni. An Ni or Ni alloy undercoat layer may be formed as an intermediate layer between the steel sheet and the resulting Zn or Zn alloy layer. The plated steel sheet has superior corrosion resistance in a corrosive environment contg. Cl<->, superior paintability and workability, so it is suitable for use as a steel sheet for an automobile, a building material or the like.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides improvements in corrosion resistance, coating performance, and workability when exposed to a severe corrosive environment in the presence of an aqueous solution of NaC, '(:aCC20). This product relates to zinc or zinc-based alloy plated steel sheets used for building materials, automobiles, etc.

(Prior art and its problems) Conventionally, so-called cold-rolled steel sheets without a rust-preventing coating layer have been used as steel sheets for automobiles. This cold-rolled steel sheet is processed and assembled into various parts of automobiles at automobile companies, then subjected to 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, there has been a growing demand for improved durability of automobiles, particularly for improved durability due to corrosion, and conventional painting alone cannot necessarily meet this demand. For example, in Canada, where salt is sprayed to prevent roads from freezing in the winter, the 1985 guidelines for car body corrosion are ``No drilling for 10 years''.
And we are aiming for "no rust for 5 years". This guideline is known as the ``Strengthening Code'', and for this reason, various measures are being taken as a goal for car body rust prevention.

At present, Denki-A, which improves the corrosion resistance of cold-rolled steel sheets and the corrosion resistance after painting, and which can be mass-produced without compromising workability, is being developed.
Lead-plated steel sheets are widely used.

However, since the zinc in galvanized steel sheets is more anodic than base steel, it exhibits good corrosion resistance in general corrosive environments;
In a severe corrosive environment where zinc is sprayed (e.g. CaO2), the corrosion rate due to the sacrificial anti-corrosion effect of zinc on the base iron is high, and the sacrificial anti-corrosion effect of zinc is lost in a short period of time, making it impossible to obtain a long-term anti-corrosion effect.

The easiest way to improve corrosion resistance is to increase the amount of plating. However, an increase in the amount of plating causes a significant decrease in productivity and an increase in cost in electroplating, which is not only economically undesirable, but also poses the following problems in terms of workability, weldability, etc.

In other words, when processing plated steel sheets into automobile parts, especially during drawing, the plating layer! ! There is a phenomenon in which the powder is separated or a part of it is scraped off (so-called powdering) and deposited on the press mold, causing defects in the finished product. If such powdering occurs, not only will productivity be significantly reduced due to maintenance of the mold, but it will also have an adverse effect on the performance of the finished product, so it is necessary to reduce the amount of plating. On the other hand, resistance welding (spot welding) is mostly used to assemble various processed parts.
Emphasis is placed on the quality of weldability. Weldability is greatly affected by the amount of plating, and when the amount of plating increases beyond a certain level,
Defects such as insufficient strength of welded parts and poor appearance are likely to occur.
Furthermore, 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 be as low as possible. Furthermore, although galvanized steel sheets for automobiles are eventually painted, the zinc is easily corroded by the corrosive aqueous solution that has penetrated the paint film and the defective parts of the paint film, resulting in "blistering" on the paint film surface. This has the disadvantage that the paint film lifts up and peels off from the substrate.

Furthermore, if a paint film defect occurs due to a flying stone or the like while the car is running, corrosion under the paint film spreads from that area, which tends to cause paint film peeling.

In order to eliminate the drawbacks of galvanized steel sheets, we developed galvanized steel sheets, which have a more noble potential (ethodic) than zinc but are more base than steel (anodic), have an anodic corrosion protection effect on bare steel, and reduce the corrosion rate due to salts. It is small, and also has excellent coating performance (especially corrosion resistance after coating, secondary paint adhesion... deterioration of coating film adhesion when the painted part is exposed to a corrosive environment)', workability, and weldability. Based on the idea of superiority, for example, Z
n-Fe series (Japanese Patent Publication No. 80-11117), Zn-
Ni-based (Special Publication No. 58-11'795), Zn-
Fe-Ni series, Zn-Ni-Co series, Zn-Fe-Cr
Many zinc-based alloy-plated steel sheets have been developed, such as zinc-based alloy-plated steel sheets, etc., and multilayer plating that combines them. Although these zinc-based alloy plated steel sheets generally have superior performance compared to galvanized steel sheets, they have poor corrosion resistance, especially pitting corrosion in the harsh corrosive environment where salts are sprayed. Pittin
4 Corrosion), further improvement is desired.

Improving 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, there are problems such as increased coating costs, powdering during processing, and welding. It is desirable to have as little fear of men as possible, as this may lead to problems such as sexual deterioration.

Furthermore, Japanese Patent Laid-Open No. 57-2 discloses a zinc-based alloy plated steel plate with improved processed parts and plating adhesion.
3054, Japanese Unexamined Patent Publication No. 57-85983, etc.

However, a detailed study of conventional zinc-based alloy plated steel sheets reveals that, although they have excellent workability and plating adhesion, they require further improvement in corrosion resistance, especially the corrosion resistance of the coating material itself and severe forming. It was found that it is necessary to improve the moldability when processing is performed, and also to improve the corrosion resistance of the molded part.

(Means for Solving the Problems) The present invention was made in response to these circumstances, and aims to further improve the corrosion resistance and workability of the plated original plate itself by further appropriate adjustment of steel components. It has been discovered that the interaction or synergistic effect of plating layers can improve pitting corrosion resistance, improve corrosion resistance in processed areas, and improve paint film performance, especially post-painting corrosion resistance in defective areas. It is.

Furthermore, in the present invention, by providing a Ni-based undercoating layer in the intermediate layer between the above-mentioned metal + original plate and the zinc or zinc-based alloy plating layer, the performance can be further improved due to the rough cutting effect of the wJ acid component coating layer. This is what I discovered.

Therefore, the gist is (1) In % by weight.

C: Less than 0.01%, acid soluble A: 0.005-0
．． 10%, P, 0.02-0.15%, Cu
; A zinc or zinc-based alloy plating layer is applied to one or both sides of a steel plate containing 0.01% and one or more of Ti, Nb, Zr, and V, and 0.03 to 0.5% of the above. A zinc-plated steel sheet with excellent corrosion resistance, coating performance, and workability.

(2) In weight percent, C, less than 0.01%, acid soluble A; 0.005 to 0.
10%, P; 0.02-0.15%, Cu;
0.01%.

Ni: Contains 1% or less, and also contains Ti and Nb.

Excellent corrosion resistance, coating performance, and workability, made by applying a zinc or zinc-based alloy plating layer to one or both sides of a steel plate containing 0.03 to 0.5% of one or more of Zr and V. Galvanized steel sheet.

(3) In weight percent.

C, less than 0.01%, acid soluble A fL: 0.005~
0.10%, P, 0.02-0.15%, Cu
: Contains 0.01%, 1 of Ti, Nb, Zr, V
Corrosion resistance, coating performance, and processing obtained by applying a Ni-based base coating layer and a zinc or zinc-based alloy plating layer on one or both sides of a steel plate containing 0.03 to 0.5% of one or more of the following types: Zinc-plated steel sheet that is highly durable.

(4) In heavy use%.

C; less than 0.01%, acid soluble A2.0.005-0.
10%, P; 0.02-0.15%, Cu;
0.01%.

Contains Ni; 1% or less, and further contains T i , N b
.

Made by applying a Ni-based base coating layer and a zinc or zinc-based alloy plating layer on one or both sides of a steel plate containing 0.03 to 0.5% of one or more of Zr and V. A galvanized steel sheet with excellent corrosion resistance, painting performance, and workability.

It is.

The present invention will be explained in detail below.

A steel plate having the above-mentioned steel components manufactured through a normal steel plate manufacturing process is used as a plating base plate.

C is an element that adversely affects corrosion resistance and moldability, and is less than 0.01%, preferably less than o, ooe%.

That is, if the C content is 0. When α1% or more, precipitation of cementite or carbide such as titanium carbide at grain boundaries increases, and the corrosion resistance of the plated original plate itself deteriorates due to intergranular corrosion in a corrosive environment or non-uniformity of the steel plate structure. .

Furthermore, the precipitation of cementite or carbide inhibits the uniform precipitation of the zinc and zinc-based alloy plating layer, increases pinholes and non-plating in the plating layer, and deteriorates the corrosion resistance of the plated steel sheet.

Furthermore, in the formation of a uniform coating layer of the Ni-based base coating layer in the present invention, pinholes, blemishes, and spots may be generated, especially when the Ni-based base coating layer is provided as a diffusion coating layer. This will help prevent the spread.

In addition, an increase in C causes deterioration of mechanical properties and deterioration of forming processability, and when severe forming processes are performed, these C precipitates can cause cracks and cracks in the original plate. Such occurrence causes cracks to reach the surface of the plating layer or the coating film, deteriorating the corrosion resistance of the plated steel sheet or after painting.

Next, as corrosion resistance improving elements in the present invention, P and Cu are added in combination, Ni is added in some cases, and Tt, Nb, Zr,
One or more types of V(7) may be added.

That is, by controlling the steel composition to an extremely low C content as described above, the corrosion resistance is improved and the corrosion rate is reduced.

On the other hand, in steel sheets to which Ti or the like is added to improve workability, drilling corrosion is likely to occur due to the S component inevitably included in the steel. Therefore, in order to reduce the corrosion rate, suppress pitting corrosion, and improve corrosion resistance, P and Cu are added as desired components.

P is an element that improves corrosion resistance in a corrosive atmosphere containing CI- ions, and is particularly effective as an element that prevents pitting corrosion in extremely low C-containing steel, and has a particularly large effect on improving corrosion resistance when coexisting with Cu.

In addition, when a steel plate is used with a zinc or zinc-based alloy plating layer applied to only one side, it also has the effect of promoting uniform formation of phosphate crystals on the iron side on which the plating layer is not applied.

Therefore, the amount added is 0.02-0.15%, 0-0
If it is less than 2%, the effect of improving corrosion resistance cannot be obtained, and 0.15%
Exceeding this results in deterioration of workability. The preferred amount of P added is Q, in the range of 0.35 to 0.07%.

Next, the addition of Cu has a large effect on improving corrosion resistance.
In a corrosive atmosphere containing CI- ions, the potential is made noble (cathodic).

The effect of reducing the corrosion rate is extremely large. A great effect can be obtained by adding 0.01%. 0.1
If it is less than 0.8%, the effect of improving corrosion resistance will be small, and if it exceeds 0.8%, corrosion resistance will be further improved.
becomes concentrated and scale scratches etc. are likely to occur. In the present invention, the addition of Cu is preferably 0.5% or less.

Next, Nf is selectively added at 1% or less,
Adding Ni alone has a small effect on improving corrosion resistance, but adding P and C
By co-adding with u, the effect of improving corrosion resistance is large.
It is highly effective in resolving the problems of Cu in the steel plate manufacturing process, and in order to increase the amount of Cu added, it is added in an amount of 1% or less, preferably 0.5% or less.

Generally, Ti, Nb, and Zr are added to the steel plate with the above components.

Contain one or more types of V in an amount of 0.03 to 0.50%.

It combines with carbon in steel to prevent the negative effects of carbon. That is, by precipitating fine carbide such as Ti, corrosion resistance and mechanical properties are improved in combination with the effect of extremely low C content. Therefore, if the amount of addition of steel components such as Ti is less than 0.03%, the effect of improving formability and corrosion resistance is small, and if it exceeds 0.50%, the effect reaches saturation and becomes uneconomical. At the same time, the precipitation of these components tends to cause the material to become hard and deteriorate moldability. The preferred range is 0.075-0.
It is 20%.

In addition, in the present invention, in order to prevent deterioration of corrosion resistance due to defects (precipitation of inclusions, surface defects) during the manufacturing process, the amount of acid-soluble An is regulated within the range of 0.005 to 0.10%. . In other words, the acid-soluble A content (S) remaining in the steel
O B/A) A small amount of food with an amount of less than 0.005% is due to oxidation and
It is difficult to prevent the generation of bubbles due to moth gas, which significantly increases the incidence of surface defects in steel and becomes the starting point for deterioration of the corrosion resistance of steel materials. In addition, excess acid-soluble A exceeding 0.10%
n causes An-based oxides to be dotted on the steel surface, leading to deterioration of corrosion resistance or the formation of non-plating, pinholes, etc. on the plated surface applied to the steel plate, and the integrity of the plated layer. spoil one's sexuality. Therefore, the amount of acid soluble should be within the above range,
Preferably it is 0.03 to 0.08%.

Other components that are unavoidably contained in steel are not particularly defined, but each is preferably used within the following ranges.

S is the form for corrosion resistance! is large, preferably 0.025% or less.

Since Si inhibits the uniform coverage of the plating layer or Ni-based base coating treatment, the content should be 0.30% or less, preferably 0.1%.
It is 0% or less.

Furthermore, Mn is used in a range of 0.1 to 1.5%. Mn has the effect of preventing drilling corrosion, and is effective in improving corrosion resistance and uniformly forming a phosphate crystal coating on the iron surface when used in single-sided plated steel sheets, but when the amount added increases, it deteriorates the material. Preferably, it is 0.3 to 0.6% since it tends to become slightly hard.

Although the steel sheets having the above-mentioned steel compositions have superior corrosion resistance and workability compared to conventional steel sheets, they are insufficient in terms of the corrosion resistance currently required for automobile steel sheets.

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

Zn is a metal whose corrosion potential is anodic with respect to steel plates and has a sacrificial anticorrosion effect on steel plates,
The anticorrosion effect of the Zn plating layer is quite remarkable.

However, as mentioned above, as a metal + steel plate for automobiles,
Highly corrosion resistant with no holes for 10 years and no rust for 5 hours, as well as coating performance.

It is necessary to have excellent weldability, and from the standpoint of overall performance, Z
With nn plating, sufficient performance could not be obtained.

After conducting various studies on the cause of this problem, we found that the couple corrosion current between the galvanized layer and the plated original plate/substrate was extremely large, and it was found that there were defects in the plating, scratches during processing, cracks in the plating layer caused by processing, or Significant dissolution of the galvanized layer occurs due to the sacrificial anticorrosion effect of the galvanized layer on end faces, etc., and sufficient corrosion resistance cannot be obtained unless the plated layer is made thicker. In the areas where the coating film is defective, steel sheets with a galvanized layer made using conventional plated original plates will produce many corrosion products of Zn due to the dissolving action of Zn due to the remarkable sacrificial anticorrosion ability of Zn, resulting in coating film blistering (so-called It was found that the formation of blisters and peeling of the paint film were significantly more likely to occur, and that the paint film adhesion and post-painting corrosion resistance were significantly inferior.

As can be seen from FIG. 1, which shows an example of the couple corrosion current between the Zn plating layer, the Zn-16% Fe alloy plating layer, and the plating original plate of the present invention in a 5% NaC-containing aqueous solution, it is possible to use the plating original plate of the present invention. According to the present invention, the couple corrosion current between the galvanized layer and the base steel is reduced, the corrosion rate of zinc is reduced by reducing the sacrificial corrosion protection effect of the galvanized layer, and the corrosion resistance and coating performance are significantly improved. Because the plated original plate has excellent corrosion resistance and workability, even if the sacrificial corrosion protection ability of the galvanized layer decreases, it will ensure sufficient corrosion resistance at plating defects and edge areas, and will prevent cracks from occurring during processing. Become.

Furthermore, even if the plating layer disappears, the corrosion resistance of the plated original plate extends the corrosion-resistant life.

As described above, the present invention provides excellent performance improvement effects such as corrosion resistance and coating performance due to the rough cutting effect of the plated original plate and the plated layer.Furthermore, since there is no need to thicken the plated layer, weldability is improved. Because it has excellent plating adhesion during processing, it can be applied to rust-proof steel plates for automobiles.

Furthermore, in the present invention, Zn has a lower corrosion rate than the Zn plating layer and has a sacrificial corrosion protection effect on the base steel.
By providing an n-based alloy plating layer, it is possible to further improve corrosion resistance and coating performance.

In the Zn-based alloy plating in the present invention, N is added to Zn.
An alloy plating layer containing one or more of Co, Cr, Fe, and Mo is applied. In other words, since the alloy plating layer has a higher potential than the zinc plating layer, its corrosion rate is low, and the corrosion resistance life of the plating layer is extended when exposed to a corrosive environment for a long period of time, which is combined with the effect of improving the corrosion resistance of the original plate. This further extends its corrosion resistance life. Furthermore, since the rate of dissolution of the plating layer in defective parts of the coating film is low, less corrosion products are produced, which has the advantage that blistering and coating peeling are less likely to occur.

In order to obtain these effects, in the present invention, N1 (8 to 30%) and Co (8%) are added to Zn, respectively.
~30%), Fe (8~30%), Cr (1~8%),
Mo (3-30%) is added alone. In addition, in the case of combined addition of two or more of these types, the lower limit of each individual addition amount or more is contained with respect to Zn, and the upper limit is less than the upper limit of each individual addition amount, and the total is 30% or less Good.

If it exceeds 30%, the effect of reducing the corrosion rate is saturated and the number of pinholes in the alloy plating layer tends to increase, which is not necessarily advantageous in terms of corrosion resistance, and may cause problems such as cracks being easily generated in the alloy plating layer during processing. This is undesirable.

In addition, the galvanized steel sheet in the present invention has improved phosphate treatment properties with an amount of adhesion (approximately 174 or less of the amount of adhesion of the zinc or zinc-based alloy plating layer) that does not deteriorate the corrosion resistance of the outermost layer. Zn-Fe with a high Fe content (Felp degree of 80% or more) that improves coating performance
, Zn-Fe-Ni.

A Zn-Fe-P based coating layer may also be provided.

Accordingly, in the present invention, in order to further improve the corrosion resistance performance and coating film performance, a Ni-based base coating layer is provided as an intermediate layer between the plating base plate and the zinc or zinc alloy plating layer.

This Ni-based base coating layer reduces pinholes and improves corrosion resistance due to the superimposed effect with the Zn or Zn-based alloy plating layer.

In addition, the metal or alloy constituting the Ni-based base coating layer is
The diffusion rate is relatively fast compared to the Zn or Zn-based alloy plating layer,
During paint baking, a Zn-Ni alloy layer is easily formed during work, etc., and corrosion resistance can be improved by reducing pinholes that reach the base metal.

This Ni-based base coating layer is made of Ni.

Ni-Co alloy, Ni-P alloy, Ni-Fe alloy,
The Ni diffusion treatment layer has a thickness of 0.01 to 1 pot.

This is because if the thickness is less than 0.01 μm, the uniform coating effect of the base coating layer is insufficient, and the pinhole reduction effect described above tends not to be obtained. Moreover, if the thickness exceeds 1 mil, the above-mentioned effect will be saturated and the base coating layer will tend to crack due to processing, which is not preferable.

Furthermore, among these Ni-based base coating layers, the method of providing a Ni diffusion coating layer is particularly excellent. This diffusion layer is formed by providing a base coating layer as described above and then providing a diffusion treatment layer using a heat annealing process of the cold-rolled steel sheet. This creates a highly concentrated and electrically stable plating base plate, giving the base plate a high degree of corrosion resistance. At the same time, the coupled corrosion current with the galvanized layer is reduced, reducing the corrosion rate due to sacrificial melting at plating defects, end faces, etc. of the plating layer. The conclusion! , Corrosion under the coating film is significantly suppressed, resulting in an extension of the corrosion-resistant life of the plated steel sheet, or a reduction in the corrosion rate of the galvanized layer, etc. in defective areas and edges of the coating film that reach the base metal even after painting, resulting in improved corrosion resistance after painting. Further improvement in paint adhesion after sowing can be expected.

Next, in the present invention, there are no particular restrictions on the method and amount of coating of the Ni-based base coating layer, zinc plating layer, or zinc alloy plating layer applied to the plated original plate, but the coating layer may be For example, the following method may be used for providing the coating, and the following range for the amount of adhesion is preferable.

Namely, 1 Ni-based base treatment methods include: (1) Nickel base treatment; electroplating using a sulfuric acid solution, nickel chloride, and boric acid bath; (2) Nickel-cobalt alloy base treatment. <Electroplating method using a nickel sulfate-cobalt sulfate-nickel chloride-cobalt chloride-boric acid bath containing iron ions (
3) Nickel-iron alloy base treatment: Electroplating method using a nickel sulfate-iron sulfate-boric acid bath containing nickel and iron ions of the desired composition (4) Nickel-P alloy base treatment: Targeted composition The electroplating method using a sulfuric acid, Kelu, nickel chloride-sodium hypophosphorous acid-phosphoric acid bath containing nickel and P ions is performed by applying the above-mentioned Ni and Ni alloy to the plating original plate by electroplating, or An aqueous solution containing Nf ions or Ni ions and other alloying element ions is applied to the surface of the plated original plate, and a heating diffusion treatment is performed on each plated original plate.

For example, the above-mentioned Ni film, after coating, or nickel nishiorate-surfactant aqueous solution, or nickel acetate-antimony phosphate-surfactant aqueous solution can be applied with a roll coater.
After drying, each is heated and diffused in a non-oxidizing atmosphere (for example,
A heat treatment is performed at a temperature of 650 to 900° C. for 30 to 180 seconds.

This diffusion cover layer is made of cold-rolled steel plate (AsCol).
d material) or a cold-rolled and annealed steel plate (full-finish material), after surface cleaning such as degreasing and pickling, and activation treatment, Ni-based coating is applied by electroplating or aqueous solution coating. A heating diffusion treatment may be performed with a coating layer provided. However, it is preferable to provide a Ni-based coating layer on a cold-rolled steel sheet and perform a diffusion treatment during annealing and recycling of the original sheet.

The processing strain of the cold-rolled material further promotes mutual diffusion between the Ni-based I layer and the steel sheet, so the desired diffusion layer is generated in a short heat treatment, which is advantageous from an economical and industrial perspective. .

Further, the gold plating layer on zinc or aluminum is formed by hot-dip plating after surface cleaning and activation treatment of the plating original plate of the present invention or after providing a Ni-based undercoating layer.

It is provided on one side or both sides according to the purpose by an electric coating method, a vacuum evaporation method, or the like.

When providing a galvanized layer by hot-dip plating, either the flux method or the gas reduction method may be used, and the coating is performed using a plating bath containing a small amount of A to ensure plating adhesion. In addition, when providing a zinc or zinc-based alloy plating layer by electroplating, the coating layer is provided using an electrolytic plating bath used in normal electroplating. For example, coating a galvanized layer by electrolyzing a (zinc sulfate-sodium sulfate) aqueous solution, (zinc sulfate-nickel sulfate-ammony sulfate)
Coating of Zn-Ni alloy plating layer by electrolysis of system aqueous solution,
Coating of Zn-Ni-Co alloy plating layer by electrolysis of (zinc sulfate-nickel sulfate-cobalt sulfate-ammony sulfate) system aqueous solution, coating treatment of Zn-Fe alloy plating layer by electrolysis of (zinc sulfate-iron sulfate) system aqueous solution etc. are carried out using a soluble anode or an insoluble anode. The thickness of each of these zinc or zinc-based alloy plating layers is 1.5 g or more, preferably three colors or more, from the viewpoint of corrosion resistance by ensuring uniform coverage. In addition, in terms of adhesion, formability, weldability, etc. of the coating layer, the thickness of the galvanized layer is 25μ, preferably 15g or less, and 151L, preferably 8p or less in the case of a zinc alloy plating layer. As mentioned above, when a plated steel sheet composed of a steel sheet having the steel composition of the present invention and a zinc-based plating layer, or a NN layer and a zinc-based plating layer is exposed to a 1g eclipse environment, As shown above, due to the combined effect of the plated original plate and the coating layer.

(1) The corrosion life of the plating layer is extended by reducing the dissolution rate due to the sacrificial anticorrosion effect of the plating layer at plating defects, processing flaws during molding, or end surfaces, and when the plating layer is used after being painted. The effect of improving paint adhesion over time by reducing corrosion under the paint film and improving corrosion resistance after painting can be obtained.

(2) In order to use a steel sheet with an extremely low C content in the steel composition, in combination with the addition of other corrosion-resistant elements, the corrosion resistance of the plated original plate itself is improved, and carbide precipitation is suppressed. Corrosion resistance is improved by reducing the occurrence of unplated surfaces in the unplated layer, and by improving processability, it is possible to improve corrosion resistance by preventing the occurrence of cracks that reach the surface of the plating layer or the coating film.

As described above, the present invention achieves an extremely excellent effect due to the combined effect of the plated base plate and the coating layer, which makes it possible to reduce the adhesion thickness of the plated layer, thereby improving the weldability required for rust-proof steel sheets for automobiles. Also, roughening effects such as reduction in powdery peeling (so-called powdering) of the plating coating layer during molding can also be obtained.

(Example) Examples of the present invention will be described below along with comparative examples.

Using a steel sheet whose composition is changed mainly around the contents of P, Cu, Ni, Ti, Nb, etc. shown in Table 1, a zinc-based plating layer or an N1-based base coating layer and a zinc-based coating layer are coated using the coating method shown below. A plating layer was provided.

In other words, the galvanized layer by the electric coating method is made by coating a cold-rolled steel plate (full finish material) with (3% Na OH +
A 0.3% surfactant) degreasing bath was used.

After degreasing and washing with water, heat at 50℃ using 10% H2SO4 aqueous solution.
anodic pickling for 1 second at a current density of 2'OA/d*2,
Electrolytic pickling and water washing were carried out for 1 second each with cathodic pickling to perform surface cleaning and activation treatment. After that, (350g/
A galvanized layer of a predetermined thickness was provided at 60° C. and a current density of 40 A/d+i2 using an electrolytic bath based on zinc sulfate (Bog/l sodium sulfate).

On the other hand, for the galvanized layer formed by the hot-dip plating method or the zinc alloy plated layer that has a eutectic structure with zinc and whose main component is zinc, the cold-rolled As Co1d material is used and a non-oxidation furnace method is used. Using a hot-dip galvanizing apparatus, a Zn-0,2%A cross-plating bath and a zinc-based alloy plating bath shown in Table 1 were used to form a zinc-based plating layer of a predetermined thickness. Furthermore, when providing a Ni-based base coating layer, if the base coating layer is formed by the electroplating method, the Ni-based base coating layer is coated with a predetermined thickness using the same method as the electroplating method described above using a Ni-based electrolytic bath composition. A coating layer was applied to provide a zinc-based plating layer.

In the case of Ni-based diffusion coating layer, use ASCod material,
After cleaning and activating the surface using the same method as for electroplating, heat diffusion is performed using a non-oxidizing furnace for hot-dip plating.
A diffusion layer was provided at the same time as the Gaud material was annealed, and then a zinc-based plating layer was applied.

Thereafter, the untreated material was treated with chromate treatment using a CrO3-5i02 bath, and the full-dip type was also subjected to phosphate treatment, each with a predetermined coating amount, and the following evaluation tests were conducted.

As can be seen from Table 2 showing the performance evaluation test results, the steel plate of the present invention has extremely superior properties in terms of corrosion resistance and painting performance compared to the steel plate of the comparative example.

O Evaluation Test Method (I) Corrosion Resistance of Unpainted Material ■ Corrosion resistance evaluation material after salt spray test A scratch that reaches the base steel is made and the corrosion resistance life is determined by the pitting depth after 360 hours of salt spray test. was evaluated. 1 move i-face P-semi(z, the following pass-1
There are 11".

0...Plate thickness reduction in the corroded part of the hole is 0.25mm or less () , , , , , //
0.35mm or less Δ・・・・・・ //
0.40mm or less×・・・・・・
// When exceeding the recommended 0.40ts■ Corrosion resistance by cyclic corrosion test (A) Using evaluation material with a plate thickness of 0.8mm.

Medium salt wood spray (5% NaC 35℃ x 4 hours) → (1?
) Drying (70℃, humidity 60% for 2 hours) =! ii) Humidity (49°C, humidity 98% for 2 hours) Cooling (-20°C)
x 2 hours) → I'r salt spray (・1t ~ (iQ> is 1 cycle)) Cyclic corrosion test under the conditions of The lifespan was evaluated.

■・・・Maximum drilling corrosion depth Less than 0.3■○・
・・・・・・ // 0.40mm
Less than Δ...-tt O, 50rg! 11
Less than×・・・・・・／／ 0
, 50 m r11 or more ~ Pouring occurs ■ Corrosion resistance by cyclic corrosion test (B) Using evaluation material with a plate thickness of 0.8 mra, 470 x 470
200 x 200 rs from mar blank size
Using a rectangular tube drawn material with rs angle and drawing depth of 100cm, the corrosion resistance life of the machined part was evaluated by the cyclic corrosion test described in section 2 above and the measurement of the drilling corrosion depth after 50 cycles. .

The evaluation criteria were as follows.

O...Maximum drilling corrosion depth Less than 0.20mm○.../l 0.25
Less than mm Δ・・・・・・tt
Less than 0.30 rarn×・・・・・・ //
0.30mm or more (II) Corrosion resistance performance of coating materials Coating performance by cyclic corrosion test (A
) A phosphate crystal coating layer with a coating weight of 2 to 2.5 g/m' was formed on each evaluation material, and then a cationic electrodeposition coating was applied to a thickness of 20 g, and then scratches reaching the base steel were removed. After 75 cycles under the cyclic corrosion test conditions described in item (1) above, the width of the coating film blistering in the scratched area and the maximum perforation corrosion depth in the scratched area were measured.

Through the above test, evaluations were conducted focusing on paint film adhesion over time and post-painting corrosion resistance, targeting defective parts of the paint film.

@・・・Maximum swell width on one side from scratch part 5
+sm or less, and the maximum drilling corrosion depth is 0.1mm or less.
．． 0 mm or less, and the maximum drilling corrosion depth is 0.2 mm.
Below Δ・・・Maximum bulge width on one side from scratch part 8
．． 5 mm or less, and the maximum drilling corrosion depth is 0.3 mm.
Less than ×・・・Maximum bulge width on one side from scratch part 8
．． Exceeding 51 mm or maximum drilling corrosion depth exceeding 0.3 arm (5) Painting performance by cyclic corrosion test (B) 0.8 ■ Using a cationic electrodeposition material with the above Φ term of board thickness,
After 20% deformation by bulge processing and 50 cycle tests under the conditions of the cyclic corrosion test described in item (1) above, an evaluation test was conducted targeting corrosion from the defective parts of the coating film due to processing.

The evaluation criteria were as follows: ■...Punching corrosion depth less than 0.05mm O.../-0, less than 10mff1Δ...
... tt Less than 0.15mmX , , , , tt 0
．． After making scratches reaching 15 mm or more and spraying 5% NaC water once a day on the evaluation material and conducting an outdoor exposure test for two years, the depth of perforation corrosion was measured and the evaluation material was tested. The corrosion state from the end face was observed and the corrosion resistance was evaluated according to the following evaluation criteria.

■・・・Maximum drilling corrosion depth less than 0.25mm,
No corrosion spots from the end face, ○...Maximum drilling corrosion depth 0.25mm or more ~ 0
, Less than 40 mm, slight corrosion occurs from the end surface Δ... Maximum drilling corrosion depth 0.40 mra or more ~
If it is less than 0.60111ff1, corrosion from the end face will occur considerably. Shape: None (: Molding processability: 0.8a+m
A rectangular tube was drawn with a size of 0Offill and a drawing depth of 125 mm, and the forming processability was evaluated by relatively comparing the occurrence of cracks and the occurrence of galling on the surface.

O...Excellent O... Fairly good condition Δ・・・・・・Significantly inferior ×・・・・・・Very poor

[Brief explanation of drawings]

FIG. 1 is a graph showing an example of the couple corrosion current of a Zn plating layer, a Zn-16% Fe alloy plating layer, and the plating material of the present invention in a 5% NaC aqueous solution. Agent: Patent attorney Masaaki Akizawa, Mitsugai (2 people)

Claims (4)

[Claims] (1) In weight%, C: less than 0.01%, acid-soluble Al: 0.005 to 0.1
0%, P; 0.02-0.15%, Cu; 0.1-0.
8%, and further contains 0.03 to 0.5% of one or more of Ti, Nb, Zr, and V. Corrosion resistance obtained by applying a zinc or zinc-based alloy plating layer on one or both sides of a steel plate,
Galvanized steel sheet with excellent painting performance and workability. (2) In weight%, C: less than 0.01%, acid-soluble Al: 0.005 to 0.1
0%, P; 0.02-0.15%, Cu; 0.1-0.
8%, Ni; Contains 1% or less, and further contains Ti, Nb, Zr
, zinc or zinc-based alloy plating layer on one or both sides of a steel plate containing 0.03 to 0.5% of one or more of V, which has excellent corrosion resistance, coating performance, and workability. type plated steel plate. (3) In weight%, C: less than 0.01%, acid-soluble Al: 0.005 to 0.1
0%, P; 0.02-0.15%, Cu; 0.1-0.
8% and one or more of Ti, Nb, Zr, and V; on one or both sides of a steel plate containing 0.03 to 0.5%, a Ni-based base coating layer and a zinc or A zinc-plated steel sheet with excellent corrosion resistance, coating performance, and workability, which is coated with a zinc-based alloy plating layer. (4) In weight%, C: less than 0.01%, acid-soluble Al: 0.005 to 0.1
0%, P; 0.02-0.15%, Cu; 0.1-0.
8%, Ni: 1% or less, and further contains Ti, Nb, Z
Corrosion resistance obtained by applying a Ni-based base coating layer and a zinc or zinc-based alloy plating layer on one or both sides of a steel plate containing 0.03 to 0.5% of one or more of r and V. , galvanized steel sheet with excellent painting performance and workability.