JPH01316491A - Zinc coated stainless steel sheet - Google Patents

Abstract

PURPOSE:To produce a zinc coated stainless steel sheet having superior corrosion resistance by forming Zn coating layers of a specified thickness on both sides of a stainless steel sheet. CONSTITUTION:At least one Zn and/or Zn alloy coating layer of 3.0-50mum thickness is formed on each of both sides of a stainless steel sheet to obtain a zinc coated stainless steel sheet having superior corrosion resistance. The Zn alloy contains <=65wt.% Al, <=10wt.% Si, <=20wt.% each of Ni and Fe. In order to obtain satisfactory adhesion to a paint film, a phosphate film if further formed by 0.5-5g/m<2> with a chemical treating soln. contg. zinc phosphate or a chromate film is further formed by 10-200g/m<2> by chromating.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a zinc-coated stainless steel sheet with excellent corrosion resistance.

<Conventional technology> Currently, Z
Ordinary steel plate plated with n or Zn alloy is used. These have the sacrificial anticorrosive effect of Zn and the effect of preventing subsequent corrosion of the steel plate by covering the outer surface with corrosion products of Zn.

However, in recent years, the environment in which automobiles can be used has become much more severe due to, for example, salt sprayed as an antifreeze agent on roads in winter, acid rain, and the like.

In response to this, various methods have been proposed such as the development of a matte layer with excellent corrosion resistance, and various chemical conversion treatment techniques with similar excellent corrosion resistance, but these are not sufficient to prevent the deterioration of the environment as described above. Furthermore, in recent years, there has been a tendency for the durability required for automobiles to increase, so materials with even better corrosion resistance are required.

On the other hand, in the field of building materials, painted hot-dip galvanized steel sheets, such as colored galvanized iron, are hot-dip galvanized, and after chemical conversion treatment are made into painted steel sheets, which are used as interior materials, interior materials, and building exterior materials such as roofs. has been done. From the perspective of weather resistance, recently the paint for building exterior materials has been changed from conventional epoxy or silicone polyester resins to fluorine resins, which have less deterioration due to ultraviolet rays, resulting in products that guarantee the coating film for 30 years. molten Zn plating with Zn-5%Al, which has better corrosion resistance, and even Zn-
Products with improved red rust resistance have been developed by changing to Zn alloy plating such as 55% AJ2.

Furthermore, coated stainless steel has been developed to improve red rust resistance.

However, in recent years, environmental pollution has become significant, and the progress of corrosive environments such as acid rain has become a problem in Europe and the United States.In Japan, this, combined with the problem of salt damage in coastal areas, has made the environment for exterior materials harsher, causing major ripples. It is showing.

Additionally, in winter, salt is sprayed on roads to prevent them from freezing, but this combined with the aforementioned acid rain is creating a harsher environment for building exterior materials.

In such a harsh corrosive environment, deterioration of the paint film can be guaranteed by selecting a resin such as fluororesin, but
If the paint film breaks for some reason, the conventional paint melting Z
Since n (alloy) plated steel sheets and painted stainless steel sheets do not have sufficient red rust resistance and significantly impair their aesthetic appearance, there has been a long-awaited appearance of painted steel sheets for building materials that are extremely resistant to red rust.

<Problem to be solved by the invention> In other words, for example, deep scratches are made on the surface of the loading platform of a food truck when loading and unloading cargo, and a corrosive aqueous solution (e.g., salt water) accumulates in the scratched area. The problem was that severe corrosion occurred, resulting in holes in the steel plate. Similarly, the above-mentioned pitting corrosion occurs when the doors of a car, especially the lower part of the car body, are scratched by stones or the like when the car is driven.

As a countermeasure to this problem, FRP (fiber) is installed on the truck bed.
A material using reinforced plastics (Re1nforced Plastics) has been developed, but although the problem of corrosion resistance has been improved, the wear resistance is poor, and there are problems such as the material itself deteriorating due to long-term use due to ultraviolet rays from sunlight. There was a point.

In addition, with regard to building materials, as mentioned above, conventional painted hot-dip Zn (alloy) plated steel sheets and painted stainless steel sheets do not have sufficient red rust resistance when the paint film is damaged or deteriorates, resulting in a significant loss of aesthetic appearance. There was a problem with losses.

An object of the present invention is to solve the above problems and provide a zinc-coated stainless steel sheet with excellent corrosion resistance.

Means for Solving the Problems> In order to achieve the above object, according to the present invention, 1f! selected from Zn and Zn alloy is coated on both sides of a stainless steel plate. The coating layer consisting of the above is 3.0 to 50 per side.
A zinc-coated stainless steel sheet is provided, characterized in that the zinc-coated stainless steel sheet is formed with at least one layer having a thickness of μm.

Further, according to the present invention, the surface of at least one zinc coating layer of the zinc-coated stainless steel sheet has a basis weight of 0.5.
A zinc-coated stainless steel sheet is provided, characterized in that a phosphate coating of ~5 glrd is formed.

Furthermore, according to the present invention, the surface of at least one zinc coating layer of the zinc coated stainless steel sheet has a basis weight of 10.
A zinc-coated stainless steel sheet is provided, characterized in that a chromate film of ~200 mg/m2 is formed.

Furthermore, there is provided a painted zinc-coated stainless steel sheet, characterized in that an organic coating film is formed on the surface of the phosphate coating or chromic acid coating of the zinc-coated stainless steel sheet.

Here, when the coating layer is an alloy, A! So 65w
The content is preferably t% or less, 10wt% or less for SL, and 20wt% or less for each of Ni and Fe, and the coating layer may be alloyed.

The present invention will be explained in more detail below.

In the present invention, a coating layer made of one or more selected from Zn and Zn alloys is formed on both sides of the stainless steel plate, thereby significantly improving the corrosion resistance life.

This is based on the findings from the experimental results described below. That is, both surfaces were coated with Zn with a layer thickness of 6 μm by electroplating under known conditions, and then chemically treated with a zinc phosphate-based immersion type chemical conversion treatment solution so that the coating weight was 2.5 g/m2. A 0.6 mm thick 5UH409 cold-rolled steel plate and an AJZ guild cold-rolled steel plate were coated with cationic electrodeposition coating on one side so that the film thickness was 20 μm, and a cross cut was made on the painted surface with a knife. A one-year atmospheric exposure test and the following combined corrosion test (OCT) were conducted in the Chiba Ikuhama coastal area.

Composite corrosion test: As a result, when 5UH409 cold-rolled steel plate was used as the test material, although blisters were observed at the cross-cut section after the atmospheric exposure test, no red rust was observed;
When J2 killed cold-rolled steel sheet was used, blistering and red rust were observed. Regarding the pitting corrosion of the steel plate that occurs at the cross-cut part after 90 OCT cycles, almost no pitting corrosion occurred when using the 5UH409 cold rolled steel plate, whereas the Aλ guild cold rolled steel plate When using , the maximum pitting corrosion depth is 0.
It was 20++++u.

Furthermore, one side and both sides were coated with a layer of Zn with a thickness of 6 μm by electroplating under known conditions, and further chemical conversion treatment was performed using a zinc phosphate-based immersion type chemical conversion treatment solution so that the coating weight was 2.5 g/m2. , 5UH409 with a thickness of 0.6 mm, coated with a cationic electrodeposition coating on one side (the plated side for single-sided plated materials) so that the coating thickness is 20 μm.
Using cold-rolled steel sheets, we conducted a one-year atmospheric exposure test in a coastal area and a salt water spray test (300 hours) using a 5% NaCJZ aqueous solution at 35°C. As for the single-sided plated material, red rust was observed on the non-plated side. On the other hand, almost no red rust was observed on the double-sided plated material. In other words, this shows that the generation of red rust was prevented by coating the non-painted surface with Zn.

That is, for this reason, coating on both sides is indispensable, especially against corrosion from the lower back side of the vehicle body, where paint is difficult to adhere to. Further, when a stainless steel plate is used for a part of the vehicle body, the above-mentioned double-sided coating is essential from the viewpoint of electrolytic corrosion between the stainless steel and ordinary steel.

As the metal coating layer to be attached to the stainless steel plate, Zn
It is necessary to use a metal chosen from Zn and Zn alloys. This is because the sacrificial corrosion protection effect on stainless steel and the chemical conversion treatment property and paintability after coating are excellent. On the other hand, when using AfL or Aft alloy, for example, the chemical conversion treatment properties and coating adhesion are poor, and when molten Af or A11 alloy plating is applied, the interface with the base steel is brittle. The drawback is that intermetallic compounds are likely to form, making it more likely to break during press working.

As for the plating layer, if Al1 exceeds 65wt% or Si exceeds 20wt%, the workability of the plating layer will decrease and the appearance of the painted surface will be impaired. % and towt% or less.

In addition, Ni and Fe in the plating layer are each 20wt.
%, the rust from the plating layer changes from white rust to black rust, which impairs the appearance of the cross-cut area.
The content of Fe and Fe is preferably 20 wt% or less.

Even when alloying the plating layer and the base steel by post-plating heat treatment, A1, Ni, Si, Fe in the plating layer
If it is within the above-mentioned range, all problems in aesthetics and molding due to rust in the cross-cut portions can be solved, and therefore, this alloying treatment is also included in the scope of the present application.

The metal coating layer attached to the stainless steel plate is 1f! selected from Zn or Zn alloy. Alternatively, two or more types can be used, and the coating layer is not limited to a single layer but may be a laminate. This is because even if these metal layers are laminated, there is no effect on the basic characteristics.

The thickness of such a metal coating layer is 3.0 to 50 mm.

If the thickness of the metal coating layer is less than 3.0 μm, no sacrificial anticorrosion effect will be observed, and if it exceeds 50 μm, peeling will easily occur after molding, which is not preferable.

As for the stainless steel on which a metal coating layer is formed, when coated with a thin metal layer as described above, martensitic,
The purpose of the present invention can be achieved regardless of whether ferritic or austenitic stainless steel is used, so there is no limitation.

The steel material that serves as the base material for paint-plated stainless steel sheets, such as 7wt% Cr steel, naturally has better corrosion resistance than ordinary steel sheets, but from the viewpoint of the corrosion resistance of the base material,
The Cr content is preferably 30 wt% or more, and 30 wt% or more.
If it exceeds 10~, the workability of stainless steel will be impaired.
Stainless steel containing 30 wt% Cr is preferred. In addition, as other alloying elements, from the viewpoint of formability, Mo is 5 wt% or less, Cu, Si, Mn%Nb%Ti%V%
It is desirable that Zr be added in an amount of 1 wt% or less.

In addition, steel types with lower Cr content than stainless steel, such as 7%
Naturally, Cr steel and the like are also included in the present invention because the corrosion resistance of the steel plate itself is improved compared to ordinary steel plates.

Methods for attaching the metal coating layer to the stainless steel plate include electroplating, hot-dip plating, vacuum deposition, thermal spraying, etc., and the present invention can be achieved using any of these methods.

From the point of view of paint film adhesion, the coating weight is 0.5 to 58/rr? A chromate film with a basis weight of 10 to 200 mg/rd must be formed by forming a film with a phosphate or by chromate treatment. This is based on the following experimental results obtained. That is, after each side was coated with Zn with a layer thickness of 6JJJll by electroplating under known conditions, the coating weight was adjusted to 0.3 to 7g/m2 using a known zinc phosphate-based immersion type chemical conversion treatment solution. is subjected to various chemical conversion treatments, and the coating thickness is 20 μs on one side.
Plate thickness 0.6m with cationic electrodeposition coating so that
Using +n 5UH409 cold rolled steel plate, 1
When we marked squares at mm intervals and peeled them off with tape (burrow test), we observed the peeling status of the paint film and found that it was 0.5g/rr? Less than or 5g/
When the temperature exceeded rn'', peeling occurred in some parts.

Similarly, after coating both sides with Zn, a known reactive chromate treatment solution is used to reduce the area weight to 5 to 220.
Using a 5UH409 cold-rolled steel plate with a thickness of 0.6 m + n, which has been subjected to various chemical conversion treatments to give a coating thickness of 20 mg/rn, and one side of which has been coated with cationic electrodeposition coating to a coating thickness of 20 units, When I did the Gopan eye test, the basis weight was 10mg.
/rr? When the amount was less than 200 mg/rn'' or more than 200 mg/rn'', peeling occurred in some areas.

Here, the chromate treatment may be of a reaction type, a dipping type, or a coating type, but the present invention can be achieved with any of these methods. Further, there are immersion type and spray type phosphate treatment, and the present invention can be achieved with either method.

In addition, examples of resins used for paint coating include epoxy, vinyl chloride, acrylic, polyester, and fluorine resins, and polyester and fluorine resins are suitable for exterior use such as building materials. The resin is not particularly limited, as it should be selected depending on the intended use.

Additionally, epoxy or polyester resin may be used as a brimer before applying a top coat of polyester or fluorine resin, but this does not detract from the spirit of the present application and is therefore included within the scope of the present application. .
The thickness of the coating film is preferably 10 or more in total from the viewpoint of its durability.

<Examples> The present invention will be specifically described below based on Examples, but the present invention is not limited thereto.

(Example 1) Using 5UH409 and 5US430 cold-rolled steel sheets with a thickness of 0.6 mm, various metal layers were applied to stainless steel sheets by known electroplating, hot-dip plating, and plasma spraying methods (using Ar gas) as shown in Table 1. Coated on both sides with 5% NaC at 50°C.
Salt water spray test (SST) in which u aqueous solution is sprayed for 100 hours
was conducted and evaluated as follows.

A: No occurrence of red rust B: Occurrence of red rust Small C: Occurrence of red rust Medium D = Occurrence of red rust Large It can be seen that no occurrence of red rust was observed in Examples 1 to 4 of the present invention.

In addition, a salt water jet test was similarly performed and evaluated without forming an adhered metal layer.

It can be seen that in Comparative Examples 1 and 2, which were non-coated materials, the occurrence of red rust was large.

The results are also shown in Table 1.

Table 1 (Example 2) 0.6+nm thick 5UH409, 5US430 and 5
Using a US304 cold-rolled steel plate, various metal layers were coated on both sides of the stainless steel plate by known electroplating, hot-dip plating, vacuum evaporation, or plasma spraying (using Ar gas) as shown in Table 2, and then zinc phosphate was coated on both sides of the stainless steel plate. After either treatment or chromate treatment, one side is coated with cationic electrodeposition (
20 units thick). The results are shown in Table 2.

Evaluation 2 Using the above samples, corrosion resistance and coating adhesion were evaluated as follows.

(1) Corrosion resistance A one-year atmospheric exposure test in a coastal area by making cross cuts with a knife on the painted surface and a combined corrosion test as shown below (
OCT) was performed for 60 days.

Composite corrosion test: Evaluation method: ■The cross-cut portion after the atmospheric exposure test was visually observed and evaluated based on the following criteria.

A: No red rust was observed at all B: Red rust occurred in some areas C: Red rust occurred on the entire surface ■Evaluation was made based on the maximum depth of pitting corrosion that occurred at the cross-cut portion after the composite corrosion test.

(2) Paint film adhesion Square grids were marked on the painted surface at 1 m+n intervals and peeled off with tape at 11f (row grid test), and the peeling status of the paint film at that time was evaluated as follows.

A: No abnormality B: Slight C: Slight peeling D= Significant peeling E: Fully peeled In Examples 5 to 24 of the present invention, almost no corrosion of the steel plate itself was observed at the cross-cut portion, and good corrosion resistance was obtained. I understand. Moreover, the coating film adhesion is also good.

Similarly, as shown in Table 2, a metal layer was coated or not coated, and the former was further subjected to the chemical conversion treatment shown in Table 2, followed by cationic electrodeposition coating on one side (20 units thick). ) was carried out.

The results are also shown in Table 2.

It can be seen that the corrosion resistance is insufficient in those with a coating layer thickness of less than 3.0 units or in Comparative Examples 3.5 and 10 of non-coated materials.

Furthermore, a metal layer was coated in the same manner as shown in Table 2,
After carrying out the chemical conversion treatment shown in Table 2, cationic electrodeposition coating (20 units thick) was applied to one side. The results are also shown in Table 2.

In the chemical conversion treatment after the Zn and Zn alloy coating layer, is the zinc phosphate basis weight less than 0.5 g/m' or the chromate film adhesion amount 10 mg/rr? If it is less than that, the coating film adhesion is insufficient. In addition, the basis weight of zinc phosphate is 5
g/m' or the amount of chromate film attached is 200r
It can be seen that Comparative Examples 4, 6.7, and 11, which exceeded ag/rd, also had insufficient coating film adhesion.

In addition, a 0.6 mm thick AJ2 killed ordinary steel plate was coated with a metal layer as shown in Table 2, subjected to chemical conversion treatment, and then cationic electrodeposition coating (20-thickness) was applied to one side. .

The results are shown in Table 2, and it can be seen that the corrosion resistance of Comparative Examples 8 and 9 is insufficient.

(Example 3) Zn (alloy) plating was applied in a laboratory by electroplating or hot-dip plating using a 0.5 mm thick cold rolled annealed plate whose composition is shown in Table 3.

For Zn plating, for Zn having a basis weight of 6 or less, electroplating was performed in a sulfate bath after alkaline electrolytic degreasing and pickling (using hydrochloric acid). In addition, Zn batting material for 6 or more houses, Z
For n-5%AJ2 and Zn-55%A1 plating materials, we use a hot-dip plating simulator in the laboratory to perform one-sided 60μ plating, and then control the coating weight by mechanical cutting or acid dissolution. did.

Thereafter, phosphate treatment or coating type chromate treatment was performed under the conditions shown in Table 4. In addition, for comparison purposes, a sample without chemical conversion treatment was also prepared.

Next, resin coating was also performed using a roll coater. Brimer is coated with 5 layers of silicone polyester resin or epoxy resin, each with 180%
℃, and held at 200℃ for 1 minute for baking. Next, a top coat was applied, and when the brimer was made of silicone polyester, the top coat was made of silicone polyester, and when the brimer was made of epoxy resin, it was coated with 20% of fluororesin, and baked at 210°C and 250°C, respectively. The coated steel plate thus prepared was evaluated by conducting the following tests.

(1) Base grain - Erichsen test The coated film surface was scratched in the shape of a base grain based on JIS K5400, and then the Erichsen test was performed based on JIS Z2247, the overhanging surface was pasted with Sellotape and peeled off by 8 mm, The peeling status of the paint film was evaluated on a five-level scale.

Ago/100 B: 1/100~t O/100 Call/100~40/100 D: 41/100~70/100 Enea 1/100' or more (2) Base item - boiling water test of Erichsen test piece ( JIS K5400 and JIS
Based on 22247, the foundation test (8m
The overhanging material (m) was immersed in boiling water for 2 hours, and then the overhanging surface was pasted with cellophane tape and peeled off, and the peeling status of the coating film was evaluated on a 5-grade scale in the same manner as in (1).

(3) Salt spray test Cross-cut the coating film of the painted steel plate with a cutter knife, and
A salt spray test was conducted for 5000 hours based on IS 22371, and the state of red rust on the cross-cut portion was visually evaluated in five grades.

A: No red rust B: Slight red rust C: Slight red rust D= Moderate red rust E: Large red rust The test results are shown in Table 5. In the example of the present invention, there was no occurrence of red rust in the salt water spray test of the cross-cut part, and the red rust resistance was extremely excellent, and the coating film also showed excellent red rust resistance in the base-to-two-branch adhesion test and the base-to-Erichsen boiling water test. No peeling was observed, and the adhesion of the coating film was extremely excellent.

On the other hand, in the comparative example, the red rust resistance is significantly inferior at 5 pcc, and the red rust resistance is similarly inferior even with stainless steel because the area weight of the plating is small. In addition, if no chemical conversion treatment is applied, the adhesion of the coating film is significantly inferior.

(Example 4) Using a 0.5-inch thick cold-rolled annealed SUH409 plate, the hot-dip plating bath composition was changed as shown in Table 6 in a hot-dip plating simulator, and plating was performed for about 25 μs each. A bending test (bending radius 0.5 mm, bending angle 180") was performed on the plated material to examine the bending workability of the plating layer. In addition, the plating material was subjected to coating-type chromate treatment under the conditions shown in Table 4, and In the coater, epoxy resin (5 μs) was used as a brimer, and fluororesin (5μs) was used as a top coat.
20μs) and 200℃, 25μs respectively.
It was held at 0° C. for 1 minute and baked. Thereafter, the coated film surface was cross-cut with a cutter knife, and a 5,000-hour salt spray test was conducted based on JIS22371, and the color of red rust at the cross-cut portions was observed.

The rust at the cross-cut portions was not red rust in any case, but when the Ni and Fe contents in the plating layer exceeded 20 wt% each, the rust changed to blackish rust, significantly impairing the appearance of the coating film. In addition, the Si content in the plating layer is 10 wt%.
When the bending temperature was exceeded, peeling of the plating occurred at the bent portion, and the bending workability of the plating decreased.

(Example 5) 0.5mm of S IJ H409 or 5US304
Approximately 25 plating layers shown in Table 7 were deposited in a hot-dip plating simulator using a thick cold-rolled annealed plate.
Alloying treatment was carried out at various temperatures from 0 to 700°C, coating type chromate treatment was carried out under the conditions shown in Table 2, and epoxy resin as a brimer and fluororesin as a top coat were coated with a roll coater and baked. Next, cross-cut the coating surface with a cutter knife to JIS 2
A salt water spray test was conducted based on 2371, and the rusting state of the cross cut portion was observed. When the average content of Fe in the plating layer after alloying treatment exceeded 20 wt%, the rust at the cross-cut portions became dark brown, significantly impairing the aesthetic appearance of the coating film.

Thus, according to the present invention, there is no significant deterioration in appearance due to the formation of red rust, which is seen in conventional painted hot-dip Zn (alloy) plated steel sheets, and Zn (alloy) has excellent coating film adhesion even after forming. We can provide plated stainless steel (alloy) and are expected to find application in a wide range of fields such as building materials and automobiles.

<Effects of the Invention> Since the present invention is configured as described above, corrosion resistance is extremely excellent, and sufficient coating film adhesion can be obtained by appropriate chemical conversion treatment. In addition, Zn or Zn on both sides
Since it is coated with an alloy, it also has excellent galvanic corrosion resistance with ordinary steel sheets. Further, there is no significant deterioration in appearance due to the occurrence of red rust, which is seen in conventional painted hot-dip Zn (alloy) plated steel sheets.

Therefore, the present invention has a wide range of industrial applications, and can be used, for example, in automobile bodies, truck beds, and building materials.

Claims (6)

[Claims] (1) Zinc-coated stainless steel, characterized in that at least one coating layer made of one or more selected from Zn and Zn alloys is formed on both sides of a stainless steel plate with a thickness of 3.0 to 50 μm per side. steel plate. (2) The surface of at least one zinc coating layer of the zinc-coated stainless steel sheet according to claim 1 has a basis weight of 0.5 to 5.
A zinc-coated stainless steel sheet characterized in that a phosphate film of g/m^2 is formed. (3) The surface of at least one zinc coating layer of the zinc-coated stainless steel sheet according to claim 1 has a basis weight of 10 to 20.
A zinc-coated stainless steel sheet characterized by having a chromate film of 0 mg/m^2 formed thereon. (4) A zinc-coated stainless steel sheet, characterized in that an organic coating film is not formed on the surface of the zinc-coated stainless steel sheet according to claim 2 or 3. (5) When the coating layer is an alloy, 65wt of Al
5. The zinc-coated stainless steel sheet according to claim 1, wherein the content of Si is 10 wt% or less, and each of Ni and Fe is 20 wt% or less. (6) Claims 1 to 3, wherein the coating layer is alloyed.
5. The zinc-coated stainless steel sheet according to any one of 5.