JPS61288082A - Chromated steel sheet containing cr and having superior paintability and workability - Google Patents

Abstract

PURPOSE:To improve the paintability and workability of a steel sheet contg. prescribed percentages of C, Cr, acid-sol. Al, Ti, Nb, etc. by forming a coating layer consisting of prescribed amounts of a metallic Cr layer and a Cr oxide hydrate layer on the steel sheet. CONSTITUTION:A coating layer consisting of 1-300mg/m<2> metallic Cr layer and 5-50mg/m<2> (expressed in terms of metallic Cr) Cr oxide hydrate layer is formed on a steel sheet contg. Cr. The steel sheet consists of, by weight, <=0.02% C, 0.5-20% Cr, 0.005-0.1% acid-sol. Al, 0.03-0.5% one or more among Ti, Nb, Zr and V, <=0.003% B and the balance Fe.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is a chromate-based treated coated Cr-containing steel sheet that has extremely excellent paintability and processability, and has particularly improved needle corrosion resistance after painting and paint adhesion after painting ( The present invention relates to a steel plate coated with a paint base that has extremely excellent performance in terms of so-called secondary paint adhesion), secondary processing cracking properties, etc.

(Prior art) As a steel plate for containers that is used after painting, for example,
As disclosed in Publication No. 4-95941, a surface-treated steel sheet consisting of a two-layer coating composition of a metallic chromium layer and a chromium oxide layer mainly composed of water-conserving oxides on a cold thin steel sheet, so-called TFS-CT, is used. Good results have been obtained in terms of adhesion, post-painting corrosion resistance, economic efficiency, etc.

The steel plate, which has been treated with TFS-CT on the plated original plate made of ordinary steel components, takes advantage of its excellent painting performance and can be used to bond the can body by adhesive method, or to improve paint adhesion after processing and corrosion resistance after painting. It is often used as a material for can lids, crowns, etc.

(Problem to be solved by the invention) Recently, the range of application of steel sheets has been expanded and diversified, and in response to high performance characteristics and consumer's preference for luxury products, steel sheets have been improved in appearance and during storage. There is a demand for surface-treated steel sheets with improved performance such as resistance to rust.

For example, in response to the increasing number of deformed cans such as necked-in cans, it is desired to improve corrosion resistance after painting on parts that have undergone more severe processing than before, or to improve paint adhesion after long-term storage. ing.

In addition, the material for can lids is required to be easier to open than before, and in response to the reduction in the thickness of the can lid material and the reduction in the remaining thickness of the score processed area, we are responding to the need to reduce the corrosion resistance of the coating after processing, and the adhesion of the paint. There is a need to improve gender. Furthermore, for uses such as can bottom lids, which are coated with clear lacquer, it is required to have a whitish appearance with a metallic luster, as well as to be resistant to needle corrosion after coating and to have better adhesion to the paint. There is a need for improvements in various aspects of the performance of Makoto Crown, including the prevention of red rust that occurs from the edges during storage, as well as the reduction of red rust that occurs during storage on the machining parts used for the can body and can lid.

In addition to the above-mentioned containers, there is also a high demand for high-performance materials that have high paintability, excellent needle corrosion resistance after painting, and excellent formability for steel plates for automobiles and the like.

As a result of various studies in response to these demands, we found that steel sheets with a hard chromate treatment coating layer, mainly steel sheets with a TFS-CT treatment layer, which is often used as a base steel sheet for conventional painting, contain elements that improve corrosion resistance. Because the plated plate is made of aluminium-killed steel, the potential of the plated plate is less base than that of the coating layer, and during post-painting processing, rust occurs from the scratched parts that reach the base metal, and the iron is leached out. There is a problem that the adhesion of corrosion-resistant paint deteriorates.

It has also been found that when the end face after painting is exposed to an atmospheric environment for a long period of time, preferential corrosion of iron occurs from the iron end face, which is less noble in potential, and promotes the formation of red rust.

The improvement in the appearance of t1 is presumed to be due to the fact that the original plate exhibits a dark appearance due to the etching action of the chromate bath in which the original plate is used in the process of forming a chromate-based treated coating layer such as TFS-CT. .

Furthermore, plated base plates with a low C content are generally used to improve workability, but they suffer from the adverse effects of unavoidable impurities in steel such as P and S, cause embrittlement of grain boundaries, and cause secondary processing cracks. is becoming more likely to occur.

Therefore, the present invention solves these problems, improves corrosion resistance after painting, improves paint adhesion after aging, prevents rust from forming on the end surface, has excellent workability, and improves its appearance. The objective is to provide a high-performance coating base steel sheet that has excellent properties.

(Tth means for solving the problem) The gist of the present invention is (1) weight s''
c", C; 0.02% or less, Cr", 0.5-20
1 acid soluble ht; 0.005-0.10%, TI
, Nb, Zr *One or more types of V: 0.03
~0.51 'If: 0.0030% or less, the balance is iron and inevitable impurities in a Cr-containing steel plate,
This is a Cr-containing steel plate treated with a chromate system and has excellent paintability and workability, and has a coating layer consisting of a metal Cr layer of 1 to 3001 MP/m2 and a hydrated oxidized Cr layer of 5 to 5°η in terms of metal Cr.

(for production) The details of the present invention will be explained below.

The molten steel melted in a melting furnace such as a converter or an electric furnace is made into a slab through continuous casting, ingot making, and blooming methods, followed by hot rolling, cold rolling, and annealing process, C: 0.02. -Hereinafter, acid soluble A
t: 0.005-0.10%, Cr: 0.5-20
%, Ti, Nb, Zr, VOW1 or H2Ii or more:
A Cr-containing plated original plate containing 0.03 to 0.5% and 0.0030% or less of B is manufactured.

As the C content increases, chromium carbide is precipitated, which deteriorates the workability and corrosion resistance of steel. Therefore, the C content is 0.0
2% or less, preferably 0.005 inch or less.

When the amount of At remaining in the steel is less than 0.005%, it is difficult to prevent the formation of bubbles due to oxygen gas, and the occurrence of surface defects in the steel. This significantly increases the corrosion rate and becomes the starting point for deterioration of the corrosion resistance of steel materials. In addition, excess acid-soluble AL exceeding 0.10% causes At-based oxides to be scattered on the steel surface and becomes a starting point for deterioration of corrosion resistance. This is not preferable since there are many factors that impede the uniformity of processing. Therefore, 5olAt contained in steel is o,oos~0.10% as the amount that can ensure stable performance.
, preferably 0.01 to o.oss.

The addition of Cr brings the potential of the steel sheet exposed to a corrosive environment closer to the negative direction, and brings it closer to the potential of the chromate-based treated coating layer, that is, the metallic Cr layer, and the chromium oxide layer mainly composed of hydrated chromium oxide. The corrosion resistance of the steel plate itself is improved, and the steel plate is subjected to a chromate-based coating treatment such as TFS-CT treatment to improve performance such as needle corrosion resistance after painting and coating performance as a base steel sheet for painting. That is, Cr
The inclusion of chromate brings the potential of the original plate close to the chromate-based treated covering layer, thereby reducing the coupled corrosion current between the original plate and the covering layer.

At the same time, the corrosion resistance of the original plate itself is improved, and the rate of self-corrosion of the original plate itself when exposed to a corrosive aqueous solution is also reduced.

As a result, when the product of the present invention is exposed to a corrosive environment after painting, it has the following effects. In other words, when exposed to a corrosive environment with defects such as coating defects, defects in the coating that reach the base metal during handling, or defects in the coating during processing, Cr is found to be contained only as an impurity. Products using steel plates as base plates suffer from significant corrosion under the paint film, with corrosion originating from the base metal (base plate) in areas with paint film flaws. For example, the base iron has a lower potential in the corrosive aqueous solution than the chromate treatment layer, and the kaggle corrosion current between the two is large, resulting in preferential dissolution and corrosion of the base iron. As a result, the corrosion of the base metal perforates deeply in the depth direction of the defect, creating a risk of perforation corrosion, and the base metal spreads not only in the depth direction but also in the lateral direction of the defect under the coating film. , the paint film peels off from the defective area.

On the other hand, products using Cr-containing steel sheets as plating base plates, as in the present invention, improve the corrosion resistance of the base plate itself and bring the potential of the base plate close to the chromate-based treatment layer, as described above. Even when paint film defects or cracks that reach the base metal occur and are exposed to a corrosive aqueous solution, corrosion from the base metal is significantly improved, and paint adhesion due to perforation corrosion or corrosion under the paint film is improved as shown in Figure 1. This is a significant improvement as shown in . Therefore, the Cr content added to the steel plate to achieve the above purpose is 0.5 to 20 inches, preferably 3 to 20 inches.
It is 18 inches. If the Cr content is less than 0.5%, the effect of improving the corrosion resistance and coating performance after painting, which is the objective of the present invention, cannot be obtained, and if the Cr content exceeds 20%, the effect of improving the corrosion resistance of the steel sheet itself cannot be obtained. saturation, the workability of the steel sheet deteriorates due to hardening due to the influence of Cr addition, and furthermore, the uniformity of the chromate-based coating treatment to improve the coating performance of the steel sheet is not sufficiently ensured. This results in disadvantages such as:

In addition, from the point of view of the above-mentioned molding processability, r of 11% or less Cr
In the transformation region composition of the phase and α phase, coarsening of crystal grains is difficult to occur due to these transformations during steel sheet manufacturing, and a phenomenon called "ridging" is less likely to occur when subjected to severe forming processing. (Particularly preferred. In the present invention, the addition of Cr in the steel is preferably 3% or more, in order to ensure the appearance of metallic luster and to prevent the occurrence of red rust from the end face of the steel sheet. In order to prevent corrosion by etching during chromate coating treatment, etc. 5% or more is good.

Furthermore, in the present invention, in addition to the above steel components, 0.03 to 0.5
T1 at 0chi. One or more of Nb, Zr, and V are contained in the steel to combine with C in the steel to make the contained Cr effective and further improve moldability and corrosion resistance.

If the content of steel components such as TI is less than 0.03%, the effect of preventing the precipitation of chromium carbide and improving formability and corrosion resistance is small;
%, the effect reaches saturation and is not economical (at the same time, precipitation of these components tends to harden the material and deteriorate moldability).

The content of these elements is preferably in the range of 0.075 to 0.20%. In addition, in order to improve the workability, corrosion resistance, and other properties of Or-containing steel, Mo may be added in an amount similar to that added to stainless steel (approximately 1% or less).

In the present invention, in addition to the above-mentioned steel components, K O,003-
The following B is added. The addition of B causes secondary processing cracks to occur when subjected to impact at low temperatures when subjected to severe surface forming processing and used in cold regions. This is because, as mentioned above, in order to improve formability, the C content is limited to an extremely small amount, and that small amount of C is fixed by additive elements such as Cr@TieNb in the steel. It is thought that for this reason, unavoidable impurities in steel such as P and S precipitate at the grain boundaries and embrittle the grain boundaries.

Instead of these impurities, B precipitates at the grain boundaries and forms P and S.
This suppresses the precipitation of such substances and prevents cracks caused by secondary processing. Therefore, B is o to prevent secondary processing cracks.
, ooa* or less, preferably 0.001% or less.

If the amount of B added exceeds 0.003 inch, the steel plate becomes hard and the formability deteriorates, which is not preferable.

Incidentally, even if B is added to about 0.00010S, the effect of preventing secondary processing cracking can be obtained.

In addition to the above, B also has the effect of preventing the growth and coarsening of crystal grains in the heat affected zone when subjected to high heat effects such as during welding and brazing operations.

In the present invention, if such a steel plate is used as it is as a base steel plate for painting, the paint adhesion will be insufficient when exposed to corrosive aqueous solution for a long period of time due to needle corrosion after painting, etc., as shown in Figure 1. Therefore, for these steel plates, using an aqueous solution containing Cr'' ions, 5o4-2, r ions, etc.
It is necessary to provide a chromate-based coating treatment layer formed by a metal Cr layer and a water-containing chromium oxide layer by cathodic electrolytic treatment.

That is, although the Cr-containing friend steel sheet used in the present invention improves its corrosion resistance, when the surface of the steel sheet is directly painted, a thin stable oxide film is formed on the surface of the steel sheet. Due to the effects of this, sufficient adhesive strength cannot be obtained between the paint and the steel plate, and when exposed to a corrosive aqueous solution for a long period of time, the steel plate surface may be damaged by the corrosive aqueous solution that enters through the paint film or from the defective parts of the paint film. is corroded, and the paint is extremely likely to peel off. That is, simply applying a paint treatment directly to the surface of a steel plate does not provide paint adhesion, post-painting needle corrosion resistance, secondary paint adhesion, etc.

In the present invention, various measures were taken to improve coating performance such as paint adhesion and post-painting corrosion resistance for this steel plate, and as a result, as shown in Fig. 1, an example of the effect is shown in Fig. 1. It was found that by providing a chromate-based coating treatment layer consisting mainly of a chromium oxide layer, the coating performance was significantly improved.

FIG. 1 shows the relationship between various processing conditions and coating properties, and the processing conditions and evaluation criteria for each treatment are as follows.

1) Various processing conditions ■NazCr207 series 309/l N120r20
．． (p) 14.5) 70°C 8 A/dg2-3. s
l@e negative i treatment■phosphoric acid type 25b9s45
0℃1oVdJ-3a@c Cathode treatment■CrO3-8O4 system CrO3100!1/1. SO4
”-1j'/l 50℃60A/dm -0.5s
e c cathode treatment ■Cr0s-F- system CrO851
/l-8O4'-0,0717140℃ F-1,81
/1 60 A/dm' -0,5sec
Test conditions: 1.5 chicitric acid + 1.5% salt 55°C
X Evaluation of tape peeling after immersion in 96 hours Paint film peeled area: ◎...5 inches or less ○...
10% or less Δ... 20% or less ×... 40% or less Insert and crimp.

Test conditions: The test pieces were pulled in a T-shape using a tensile testing machine, and strong urea was added between the test pieces to determine the bond strength at 9 o'clock, which is the normal phosphor treatment used on steel plates to improve coating performance. In acid-based treatments, chromic acid-based treatments, etc., it is difficult to uniformly form a treated film on the surface of a steel plate, making it difficult to improve coating performance as the objective of the present invention.

On the other hand, the coating layer of the present invention (which simultaneously forms a chromium oxide layer mainly composed of metallic Cr and a hydrated oxide) is made of Cr.
A chromate-based film treatment can be obtained by cathodic electrolytic treatment using an aqueous solution containing SO44O7, F- ions, or a mixture thereof. With this method, even if the stable oxide film on the surface of the steel sheet is not sufficiently removed by pre-treatments such as degreasing and pickling, the chromate-based treatment can be oxidized by cathodic electrolytic treatment in a chromic acid bath containing anions. Since the film is removed by reduction, a chromate treatment film consisting of a metal C7 layer and a chromium oxide layer is uniformly formed on the steel surface. As a result, the adhesion between the chromium oxide layer and the paint is sufficiently ensured.Even if the film is exposed to a corrosive aqueous solution for a long time, the chromate treatment film prevents the corrosive aqueous solution from penetrating through the paint film or paint film defects. It prevents corrosion products from reaching the steel substrate, prevents the formation of corrosion products on the steel surface, and significantly improves paint adhesion.

Mat1 glow discharge optical emission spectrometry (GDS-G・IOW
Figure 2 shows an example of the cross-sectional analysis results after the above chromate treatment by Dlseharg@5pactroscopy (Figure 2 (IL) is the original plated plate (16% Cr), and (b) is the chromate treatment with CrOs-F system. ), Cr-added steel has a low Cr concentration on its surface due to the dechromization phenomenon, which causes deterioration of corrosion resistance. concentration can be maintained. As a result, corrosion resistance after painting is significantly improved.

Therefore, in order to obtain the desired effect of the present invention, a chromate-based treatment film is applied, in terms of the amount of metal Cr, with a metal Cr layer of 1 to 300'1197 m2 on each side, and an oxidation film mainly consisting of water-use chromium oxide. It is necessary to provide Cr layers 5-50-4. That is, the metal Cr layer is IWIg/rn
If it is less than that, it will be difficult to form a chromate-based treated film uniformly.
The effect of improving electrical equipment performance cannot be obtained.

On the other hand, when the metal Cr layer reaches 300 to 2, the metal Cr
This is undesirable because the layer may develop cracks during processing, and these cracks may become starting points for cracks that reach the surface of the coating layer, deteriorating the coating performance. Therefore, metal C
The r layer is 1-300-42 degrees, preferably 5-60 degrees.

On the other hand, if the chromium oxide layer is less than 5 T197 m2, the uniform coverage by the chromium oxide layer is poor, and the effect of improving paintability, especially paint adhesion, which is the object of the present invention, cannot be obtained. If the corrosion rate or the chromium oxide layer exceeds 50119/n2, the effect of improving paintability will be saturated and problems with the appearance, which is the objective of the present invention, will occur, which is not preferable. That is, the Cr oxide layer has 5
If it exceeds 0 to 42, the appearance becomes yellowish or blackish, and a good surface appearance cannot be obtained.

Therefore, the Cr oxide layer has a thickness of 5 to 50 to 4, preferably 7
．． 5 to 2011f7m. In particular, when the painted steel sheet of the present invention is intended for uses other than container materials as described above, for example, for applications where press forming is performed such as rust-proofing steel sheets for automobiles, it is possible to prevent scratching by dies. In order to prevent the occurrence, the metal Cr layer has a thickness of 5 to 25 to 4,
The Cr oxide layer, which is mainly composed of water-use oxides, is 7.5 to 151'
97m2, and the total area is 12.5~35'97m
A range of 2 is preferred.

The method for applying the chromate treatment film of the present invention to the surface of Cr-containing steel is as follows. That is, Cr-containing steel is first subjected to degreasing and pickling treatment prior to chromate treatment. The degreasing treatment is not particularly specified, and includes the immersion method using sodium orthosilicate and caustic soda washing solution, and the degreasing method. A ray treatment method, an electrolytic degreasing treatment, or a combination thereof is performed.

Next, after washing with water, surface cleaning-1 activation treatment by pickling is performed, but cathodic electrolytic treatment is preferred from the viewpoint of uniformity and adhesion of the chromate-based treated film.

In other words, in order to obtain a product with a good appearance that retains the gloss of the surface appearance, it is necessary to use 0.5 to 10 ts.
Cathodic TlEs pickling in a H2SO4 based bath is most preferred.

That is, in the case of cathodic electrolytic treatment, a passivation film is formed on the surface of the steel sheet due to treatment in a sulfuric acid bath, which is not preferable from the viewpoint of uniformity and adhesion of the chromate-based treatment film. Even in the case of pickling using the immersion method, it is difficult to remove the oxide film, so the performance of the chromate-based treated film is inferior.

On the other hand, activating the surface of the steel sheet by reducing the oxide film on the surface of the steel sheet through cathodic electrolytic treatment is superior in terms of appearance, performance and uniformity of the chromate treatment film. Therefore, the current density in electrolysis is 1 to 30
It is preferable to carry out at a current density of Vdm2, preferably 3 to 10 A7dm, at room temperature to 70°C, for 0.1 to 5 seconds. Within this range, the uniformity of each chromate-based treatment film
It is preferable from the viewpoint of processability and adhesion of the chromate-based treated film.

In addition, from the point of view of uniformity and adhesion of the chromate film treatment, a short pretreatment pickling may be performed using an aqueous solution containing F- ions such as fluorosulfuric acid or fluoronitric acid solution. .

In this case, in order to ensure a good appearance, strict process control is required such as treatment temperature, treatment time, and water washing in terms of bringing the pickling bath into the subsequent chromate treatment bath. However, the following processing methods are used. For example, (a) F-ion-containing treatment bath bath composition Cros 85 j' / 1802
-0.0711/1 Na 2S IF 62.7 II/ 1NH4F
0.41/1 Current density 60A/dm2 Bath temperature 40℃ 伽）S04 Ion-containing treatment bath Bath composition Crys 10011 / lso
2-x, og/1 Current density: 60 A/dm2 Bath temperature: 60°C Through the above treatments, a chromate-treated film with excellent uniform adhesion can be obtained to ensure the desired paintability of the present invention. However, as mentioned above, the chromate treatment bath containing F- ions also has the effect of removing the oxide film on the surface of Cr-added steel in the chromate bath, and the uniformity of the chromate-based film is excellent. - When using an ion-containing bath, the improvement in paintability is even more effective.

(Example) Examples of the present invention will be described below.

Using steel sheets with steel components whose Cr content was mainly varied as shown in Table 1, 0.3 t of surfactant was added to a 3% NaOH aqueous solution, degreased using a degreasing bath, washed with water, and then treated with 10 S H2
804 aqueous solution at room temperature with a current density of 15 Addm.
．． After performing cathodic electrolytic degreasing for 5 seconds and washing with water to clean and activate the surface, a chromate treatment coating layer was applied under the conditions shown in Table 1, and various performance evaluation tests were conducted.

The performance evaluation was carried out using the methods shown below, and the evaluation results are shown in Table 1.

As a result, the product of the present invention has extremely superior properties as a steel plate for painting compared to comparative materials.

○Evaluation test method■ Appearance after clear lacquer coating After applying 2.5μ thick epoxy-phenol-based clear lacquer to a steel plate with a chromate-based coating, the appearance condition was visually judged◎...・・Whitish appearance with a metallic luster O ・・・Whitish appearance with slightly inferior metallic luster × ・・・・・Blackish appearance ■ Pitting corrosion resistance of coating material for paint film defects - Painting Evaluation of post-corrosion resistance - After coating the product of the present invention with epoxy-phenol paint to a thickness of 5 μm, scratches reaching the bare metal were added assuming car film defects (1.5% NaCL + 1.5 chicitric acid)
By immersing it in the system aqueous solution at 27°C for 15 days, the screen 2. The depth of erosion due to puncture corrosion from the cracked area by the solution was measured using a cross-sectional microscope, and the needle corrosion property after painting was evaluated.

The test material was an original plate with a thickness of 0.21 vm.

◎・・・・・・Punching corrosion depth 0.05m or less...
・・・ tt O, 10■ or less Δ・・・・・・
z O, 15■ or less 4 paints
．． After painting to a thickness of 2 μ, put 100 1×1× pans on the coating surface so that they reach the base metal, and then add the sample (1,5
To NaCL + 1.55 to citric acid) in an aqueous solution,
After soaking at 55°C for 96 hours, dry and immediately peel off the cellophane tube, and evaluate the adhesion of this secondary paint from the peeled area of the paint film.・・・・・・Peeling area 10% or less Δ°−−−−−120% or less After coating the present invention with a thickness of .25cm with a 6.5μ thick coating containing Zn-free pigment, extrusion processing to a depth of 3 cages was performed using Erichsen processing. 1.5%N
After being immersed in an aCA+ 1.0% citric acid + 0.5 tyrinic acid aqueous solution at 55°C for 96 hours, a cellophane tape peeling test was performed immediately after drying, and the time after processing was determined from the measurement results of the peeled area of the paint film. Paint performance was evaluated in terms of paint adhesion.
I Less than 50 cm ×・・・・・・ l 5
Exceeding 0% to full surface peeling ■ Corrosion resistance by long-term corrosion test of wing covering material ■ Paint performance after long-term corrosion test when using paint for deaf materials, when applying epoxy base coat paint to the present invention with a thickness of 0.6 tm After applying a 5μ thick coating and then applying a 13μ thick silicone preester paint, 1 was bent and subjected to a salt spray test for 1,000 hours, and the appearance was observed and cellophane peeling was performed to determine the coating performance. was evaluated.

◎・・・・・・No occurrence of red rust or beginning of paint film peeling○・
...I and 15% or less Δ...
... Red rust occurrence 10 inches or less or paint film peeling 20 inches or less X... # More than 10 inches or paint film peeling 20%
Super ■ Corrosion resistant caotine electrodeposition coating made of C, C, and T electrodeposition coating materials applied to a thickness of 20μ, with scratches reaching the base metal, ■Salt water spray (5% NaCL 35℃ x 4 hours) →■
Dry (70℃, humidity 60℃, 2 hours) →■Wet (49℃)
℃"Humidity 98℃ 2 hours) → ■ Cooling (-20℃ x 2 hours) → ■ Salt water spray ■ ~ ■ carried out 125 cycles of cyclic corrosion test under the conditions of 1 cycle, and the corrosion resistance was evaluated according to the following evaluation criteria. Conducted with ◎...Punching corrosion depth is 0.3 m or less, and the coating film width at the scratch area is 3.5 mm or less on one side.
・Punching corrosion depth: more than 0.3■~0.40 wsxmm Width of blistering of coating film at scratch part: 3.5 m or less on one sideΔ...Punching corrosion depth: more than 0.3■~0. 40 m
m or less, the coating film blistering width at the scratch part is more than 3.5 tm on one side and less than 5 tm ×...Punching corrosion depth is more than 0.40°C, or the coating film blistering width at the scratch part is 5 mm on one side After applying 5.5μ of corrosion-resistant epoxy phenol-based paint to the sheared edge of ultra-fine coated materials on a 0.22m thick paint,
After the sample was sheared by punching, its end face was relatively evaluated for end face corrosion resistance using the following evaluation method and evaluation criteria using a wet cycle test.

Humidity cycle test conditions: Stored in a humidity chamber at 49°C, RH 98° or higher for 1 hour, then dried and left at room temperature for 2 hours. This is 1
After 5 cycles, the occurrence of red rust on the end face was evaluated.

◎・・・・・・Incidence of red rust Almost none O・・・・・・
・ # 5 or less Δ・・・・・・I
10 inches or less×・・・・・・ I More than 10 inches■
Forming workability ■Evaluation of drawing workability Using the evaluation material of the present invention with a board thickness of 1.0, a square tube drawing process was performed on a 470 mm square blank material using a 200 m square punch with a wrinkle pressing force of 10 tons. friend.

The lubricating oil is φ620 made by Nippon Oil Co., Ltd. Regarding the forming processability, the drawing depth limit, the smoothness of the appearance of the rectangular tube drawing material (the occurrence of ridging), and the damage caused by galling etc. on the appearance are relative. Please make an evaluation.

◎・・・Extremely good○・・・Relatively goodΔ・・・Relatively poorX・・・Extremely poor ■Secondary processing side deviation evaluation test Plate thickness 0. Using 8 samples, the blank diameter was 133.2 dew, and the aperture ratio was changed from 1-stage aperture (2, 22) to 2-stage aperture (2, 8).
9) → 3-stage aperture (3, 6), -40
A conical punch was pressed into the workpiece at a temperature of 0.degree. C., and the secondary workability of the workpiece was evaluated based on whether or not longitudinal cracks occurred in the workpiece.

◎...No vertical cracks occurred, good secondary workability ×...Vertical cracks occurred, poor secondary workability, measurement impossible...Cracks occurred during 3-stage drawing, secondary workability evaluation impossible ( (Poor workability) (Effects of the invention) As shown above, the steel sheet of the present invention can be used for many purposes such as container materials, antirust steel sheets for automobiles, painted steel sheets for building materials (so-called colored stainless steel, etc.) It can be used as a steel plate for industrial use.

[Brief explanation of drawings]

Figure 1 is a diagram comparing the paint adhesion of the surface coating layers of six types and the degree of corrosion resistance after painting, Figure 2 (a). (b) shows the cross-sectional analysis results of the plated original plate and after chromate treatment by glow discharge emission spectroscopy. Figure 1

Claims (1)

[Claims] In weight%, C: 0.02% or less, Cr: 0.5-20%, acid-soluble Al: 0.005-0.10%, one of Ti, Nb, Zr, and V Or two or more types; 0.03~
A Cr-containing steel sheet containing 0.5%, B; 0.0030% or less, with the remainder consisting of iron and unavoidable impurities, is coated with a metallic Cr layer of 1 to 300 mg/m^2, and a hydrated oxidized Cr layer in terms of metallic Cr. A chromate-treated coated Cr-containing steel sheet with excellent paintability and workability, characterized by having a coating layer of 5 to 50 mg/m^2.