JP2003221675A - Galvanized steel sheet superior in press formability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a galvanized steel sheet superior in press formability. <P>SOLUTION: The galvanized steel sheet has a zinc phosphate-based coating on the surface, wherein x and y satisfy the following expressions (1): 1.5x+1.0y≤6.3 and (2): x≥0.5, when a coating mass of the zinc phosphate-based film is expressed as x g/m<SP>2</SP>, and a length of a long side of crystals forming the zinc phosphate-based film is expressed as y μm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet which can be mainly used for automobile bodies and home electric appliances, and more particularly to a galvanized steel sheet having excellent press formability.

[0002]

2. Description of the Related Art Zinc-based plated steel sheets are widely used because the strength of automobile bodies is not likely to deteriorate due to long-term use in a corrosive environment.
In Japan, zinc-nickel alloy-plated steel sheets and zinc-iron alloy-plated steel sheets, which are zinc-based alloy plating, are mainly used. Zinc-nickel alloy plated steel sheet
Generally manufactured by electroplating,
Since Ni is expensive, the cost is high, and the Ni content must be controlled within an extremely narrow range (usually 12 ± 1% by mass), which makes it difficult to manufacture. Further, in the zinc-iron alloy plated steel sheet, as in the case of the zinc-nickel alloy plated steel sheet, since the influence of the Fe content on the quality is large, it has to be controlled within an extremely narrow range, which makes it difficult to manufacture. is there.

On the other hand, with the globalization of automobile manufacturers and the sharing of parts in recent years, it has been required to be able to use surface-treated steel sheets that are easily available around the world. Therefore, the difficult-to-manufacture alloy-plated steel sheet that has been mainly used in Japan in the past is being changed to an easily galvanized electrogalvanized steel sheet or hot-dip galvanized steel sheet.

So-called pure galvanized steel sheets formed by galvanizing only can be manufactured at low cost by either electroplating or hot dip coating, but rarely used for automobile bodies. . The reason for this is that a large amount of zinc is likely to accumulate on the electrode during spot welding, which shortens the life of the electrode (poor spot weldability), the adhesion of zinc plating to the die during press forming, and the steel plate surface This is because there was a problem that galling and press cracking occurred and the press formability was poor.

As a method for solving the problems of such a galvanized steel sheet, a steel sheet having a zinc phosphate coating on the surface of galvanization has been proposed and is already used in Europe. Originally, the use of galvanized steel sheets is advancing due to the difficulty in obtaining alloy-plated steel sheets that are difficult to manufacture in Europe and the low manufacturing cost of low-density electrogalvanized steel sheets (low electrical cost). The welding machine, etc. are also designed to be applicable to galvanized steel sheets. Further, also for galvanized steel sheets, surface-treated steel sheets having a zinc phosphate-based coating on the surface of galvanization are adopted to improve press formability.

[0006] In Japan, alloy-plated steel sheets have been conventionally used, and since the alloy-plated steel sheets usually have good press formability and spot weldability, press cracking and welding such as occurs in galvanized steel sheets. Very few sex problems occur. However, when a galvanized steel sheet is press-formed using the press die used for this alloy-plated steel sheet, press cracking is likely to occur.

Therefore, in order to press-form a galvanized steel sheet without causing the problem of cracking, there is no method other than changing the press die, that is, changing the design design of the automobile body (model change). There is a problem that the steel sheet cannot be applied to the current press die as it is.

As a method for solving the problem of press formability of galvanized steel sheet, as described above, a zinc phosphate-based film is formed on the surface of galvanized steel sheet, as in Europe. The method of making is useful. By this method, the press formability is greatly improved, and it is possible for a considerable number of parts to be press-formed using this press die without changing the press die used for conventional alloy plated steel sheets. become. The reason for this is that the zinc phosphate coating prevents direct contact between the press die and zinc plating,
It is considered that this is because the zinc phosphate-based film can hold oil in the gaps between the crystals in addition to functioning as a buffer layer, so that more oil is supplied during press molding.

However, even when a zinc phosphate-based coating is provided, it often occurs in galvanizing depending on the pressing conditions, or even when the same pressing conditions are used, and a slight variation factor. There is a problem that galling and press cracking may occur.

The inventors have investigated the causes of press cracking of a galvanized steel sheet having a zinc phosphate-based coating, regarding the base material component,
The effects of galvanizing, zinc phosphate coating and its components on press formability were investigated in the laboratory. When carrying out this investigation, since the sample size that can be manufactured is small, the actual machine press test cannot be performed, but only the galvanizing amount is changed by using the steel plate taken from the same coil, or it is taken from the same plated coil Since the investigation can be performed by changing only the zinc phosphate-based coating amount using a galvanized steel sheet, there is an advantage that influences of factors other than the intended investigation parameters such as the base material composition can be eliminated. In addition, the important point in this laboratory test must have a good correlation with the press formability of the actual machine.

However, in the plane sliding property test conducted by the inventors mainly in the laboratory so far, press cracks may occur when no significant difference is observed or when the friction coefficient μ is rather low. there were. Various tests were conducted on the laboratory test method that correlates with the actual press result, and it was found that the evaluation by the draw bead test method had a good correlation with the press formability in the actual machine. That is,
After the draw bead test was performed, the powdering occurrence on the sample surface and the evaluation based on the drawing force showed a good correlation with the press formability of the actual machine. Therefore, using the draw bead test method, the effects of base material components, zinc plating amount, zinc phosphate coating and its components on press formability were investigated in the laboratory. As a result, even if the base metal component, the zinc plating amount, and the zinc phosphate-based coating film component were all the same, the press formability was high due to the zinc phosphate-based coating film amount and the size of the zinc phosphate-based coating crystal. I have found that it will change.

On the other hand, in order to improve the press formability of a galvanized steel sheet having a zinc phosphate coating, for example,
Japanese Unexamined Patent Publication No. 11-343581 discloses a technique for controlling the surface roughness Ra of the steel sheet and the phosphate coating amount. That is,
According to the description of this publication, the lubricity decreases as the phosphate film amount increases, but when the arithmetic mean roughness Ra is large,
It has been found that even if the amount of phosphate film is large, the peeled phosphate film (which hinders lubricity) is captured in the recesses, which does not hinder lubricity and improves press formability. As a result, the arithmetic mean roughness Ra and the phosphorus conversion adhesion amount of the phosphate coating are specified.

The plated steel sheet described in JP-A-11-343581 is an alloy-plated steel sheet having a relatively hard plating layer, or a galvanized steel sheet having a soft plating layer, and the surface of the steel sheet is sufficiently coated with oil. In this case, it is considered that the press moldability is excellent because the oil retaining ability of the phosphate is effectively exhibited and the lubricity is good. However, the above-mentioned plated steel sheet cannot reduce powdering itself, and in particular, depending on the conditions such as pressing under a high surface pressure, the peeled phosphate coating cannot be captured well in the recess, resulting in press cracking. Became.

Further, JP-A-8-13154 discloses a method in which a zinc phosphate film contains Ni and Mn and has a fine zinc phosphate film. This zinc phosphate coating is a composite coating containing ordinary zinc phosphate crystals and fine zinc phosphate crystals on top of it, and as a result, a steel sheet with excellent coatability, that is, paint adhesion and corrosion resistance after coating, can be obtained. That is. That is, this is a method for improving the paint adhesion of the prior art, in which the surface pressure is high and the radius of curvature R
There is no knowledge of press formability in difficult-to-form parts that are subject to severe bending and unbending such as with small beads. In fact, the adhesiveness to the coating material is influenced by the adhesiveness between the outermost surface of the zinc phosphate crystal and the interface of the coating film, and it is considered that the adhesiveness of the coating material is improved when the outermost surface layer of the steel sheet has fine crystals. Especially in the case of press forming where bending and unbending is performed, how much the steel sheet can follow the bending process affects the press formability, and it is necessary that the total zinc phosphate film be fine, and the amount of film (thickness ) Is naturally important, but in the case of the composite zinc phosphate coating disclosed in Japanese Patent Laid-Open No. 8-13154, crystals having a normal shape are present in the lower layer forming this coating, so severe press molding is required. In
Sufficient press formability cannot be obtained.

From the above, the above-mentioned conventional technique has excellent press formability under the condition of being press formed under a high surface pressure, for example, under the condition that the steel sheet is severely bent and unbent during press forming. I was not satisfied.

[0016]

An object of the present invention is to provide a galvanized steel sheet having excellent press formability. It is an object of the present invention to provide a galvanized steel sheet having a zinc phosphate-based coating that exhibits excellent press formability, especially under press conditions in which the steel sheet undergoes severe bending and bending back during press forming.

[0017]

Means for Solving the Problems The inventors of the present invention have made extensive studies on a method for solving the problems in the prior art. As a result, the surface of a galvanized steel sheet has a crystalline zinc phosphate-based coating, and When the adhesion amount of the zinc-based coating is xg / m ² and the length of the long side of the crystal forming the zinc phosphate-based coating is yμm, x and y are expressed by the following equations (1) and (2). It was found that a galvanized steel sheet having excellent press formability can be obtained when the above condition is satisfied. Note 1.5 x + 1.0y ≤ 6.3-----(1) x ≥ 0.5-----(2) In addition, 0.3 to 1.5 mass% of Ni in the zinc phosphate-based coating is used.
It has been found that the addition of 3.0 to 5.0 mass% of Mn makes it possible to obtain a galvanized steel sheet which is excellent not only in press formability but also in paint adhesion and corrosion resistance after coating.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION A galvanized steel sheet is used as a material for the surface-treated steel sheet of the present invention. The “zinc-plated steel sheet” in the present invention means a so-called pure zinc-plated steel sheet, but the zinc-plated film usually contains, as plating impurities, elution components (Fe and other steel components) from the steel sheet. Since it is generally inevitable to include impurities (Ni, Sn, Al, etc.) due to other types of plating and combined use of equipment such as cells, these components are also included. The galvanization may be performed by an electroplating method or a hot dipping method, and is not particularly limited.

Further, according to the present invention, the galvanized surface glue
The amount of zinc phosphate coating applied is xg / m ²And then x
It must satisfy ≧ 0.5. Zinc phosphate type
The coating is preferably hopite crystalline. Phosphoric acid
The amount of zinc-based coating applied is 0.5 g / m²The reason for the above is
Wearing amount is 0.5g / m²If it is less than, oil retaining power is maintained even in the oiled state.
Cannot be fully exhibited, and the contact between the die and the zinc plating
It is inevitable that the zinc phosphate coating will improve press formability.
This is because the upper effect becomes insufficient.

The inventors investigated the properties of the surface coating on press formability in the above-mentioned draw bead test with respect to various parameters and analyzed the results. As a result, the adhesion amount of the zinc phosphate-based coating and the zinc phosphate-based coating were investigated. It was found that the size of the crystal has a great influence on the occurrence of powdering after the draw bead test. Therefore, only the amount of the zinc phosphate-based coating adhered and the size of the zinc phosphate-based coating crystal were extracted as parameters to obtain the regression coefficient. That is, the adhesion amount of the zinc phosphate-based coating was xg / m ² , the length of the long side of the zinc phosphate-based coating crystal was y μm, and this was plotted with the powdering occurrence result in the formula shown below. (1) was determined. Note 1.5x + 1.0y ≤ 6.3-----(1)

That is, in the case where the amount of the zinc phosphate-based film deposited is small, if within the range of the formula (1), the press formability is good even if the crystal size is large to some extent. When the crystal size is small, it means that the press formability is good even if the amount of adhesion is large to some extent within the range of the formula (1).

The reason why the amount of zinc phosphate-based coating adhered and the size of zinc phosphate-based coating crystal are correlated with the occurrence of powdering and the pulling force after the draw bead test is considered as follows. In the case of a plane sliding property test, the mold slides on the surface of the steel sheet as it is.In the case of a galvanized steel sheet, galling occurs due to direct contact between zinc and the mold, so the surface is oiled. The presence of a cushioning agent or a buffering agent to prevent direct contact improves the plane sliding property.
Therefore, if the oil can be sufficiently retained, the slipperiness on a flat surface is improved.

However, in the case of the draw bead test, when the beads pass through the steel sheet, the steel sheet is bent and unbent. Therefore, the steel plate needs to follow along the circumference of this bead.

The galvanized steel sheet of the present invention is one in which a hard zinc phosphate crystal is formed on the surface layer of soft zinc plating. Zinc plating is soft, so it easily follows draw bead processing. However, since the zinc phosphate-based crystal is hard and cannot be deformed, the zinc phosphate-based crystal passes through the bead as it is or after being ground. For this reason, the larger the crystal, the harder it is to follow, the larger force is required for the deformation of the steel sheet, and the larger force is required when the steel sheet is crushed, and the pulling force becomes large.

Further, since there is soft zinc plating under the hard zinc phosphate-based coating, the zinc phosphate powder generated by crushing the hard zinc phosphate-based coating further scrapes the underlying zinc, causing further powdering. . If galling occurs, the pulling force will increase further. In press molding of an actual machine, since the powder of this hard zinc phosphate-based film is accumulated in the press die, galling occurs.

It is considered that due to the above phenomenon, galling is likely to occur when the size of the zinc phosphate-based coating crystal is large or when the amount of the zinc phosphate-based coating deposited is large.

As means for reducing the size of the zinc phosphate-based coating crystal, (1) a method for achieving fineness by surface adjustment performed before zinc phosphate treatment, or (2) a phosphate treatment liquid Examples include a method of adding a cationic additive other than zinc.

In the method (1), a titanium colloid solution is generally used as the surface conditioner, and zinc phosphate crystals are formed by using the titanium colloid as a nucleus. Therefore, by finely dispersing the titanium colloid in the surface modifier, a large number of small nuclei can be formed on the surface of the steel sheet, and the zinc phosphate crystals can be made small.
However, titanium colloid has the property that when the hardness is high in an aqueous solution, they are adsorbed to titanium colloid in the presence of Ca, etc., causing large growth and precipitation, and thus when the dispersion state is poor. In addition, since the number of nucleation points of the zinc phosphate crystal is reduced because the surface of the steel sheet is scattered, each crystal grows large. Therefore, by adding a dispersant for stably dispersing this titanium colloid or adjusting the pH, a large number of zinc phosphate crystal nuclei can be formed on the surface of the steel sheet, and the zinc phosphate crystals can be made smaller. . The inventors have tried various surface modifiers and found that the size of zinc phosphate crystals formed varies depending on the type of the surface modifier even when the same phosphate treatment solution is used.

In the above method (2), any cation may be used as long as it does not adversely affect the coating adhesion and the corrosion resistance. The reason why the zinc phosphate crystals become smaller by the addition of cations is not clear, but the obtained zinc phosphate crystals are called "hopite" by X-ray diffraction.
1 shows the crystal structure of Zn ₃ (PO ₄ ) ₂ .4H ₂ O. The added cations are detected in the film obtained by adding cations to the phosphate treatment solution, but when identified by X-ray diffraction, Zn ₃ (PO
₄ ) ₂・ 4H ₂ O peak only appears, therefore Zn ₃ (P
O ₄₎ part of Zn ₂ · 4H ₂ O crystal structure is considered substituted structures added cations. On the other hand, comparing the peak intensities of Zn ₃ (PO ₄ ) ₂・ 4H ₂ O with and without the addition of cations, the cation-added film has a lower peak intensity and lower crystallinity. Conceivable. That is, it is considered that the addition of cations to the phosphate treatment reduces the crystallinity of zinc phosphate and makes the crystals finer. As cations to be added, the present inventors
In the case of using Mg proposed in Japanese Patent Laid-Open No. 73163, a steel sheet having excellent perforation resistance can be obtained.

Further, 0.3 to 1.5 mas in the zinc phosphate coating
When s% Ni and 3.0 to 5.0 mass% Mn are contained, a galvanized steel sheet excellent in press formability, paint adhesion, and corrosion resistance after coating can be obtained. Ni and Mn contained in the zinc phosphate-based coating are zinc phosphate crystals (Zn ₃ (PO ₄ ) ₂
4H ₂ O / Hopeite), it is not clear in what form it exists, but even if it contains Ni and Mn, only Hopeite is detected in the X-ray diffraction pattern.
Is considered to exist in the form of replacing Zn.

The Ni content in the zinc phosphate-based coating is set to 0 in order to improve the adhesion with the electrodeposition coating and the corrosion resistance after electrodeposition coating.
It is preferably 3 mass% or more. Further, if the Ni content is too high, the surface appearance is dark and uneven appearance is likely to occur, resulting in high cost. Therefore, it is preferable to set the content to 1.5 mass% or less.

The content of Mn in the zinc phosphate coating is
In order to improve the press moldability, it is preferably 3.0 mass% or more. Further, the higher the Mn content, the more the effect of improving the press formability tends to become large, but the adhesion with the electrodeposition coating and the corrosion resistance after electrodeposition coating tend to deteriorate, so it is set to 5.0 mass% or less. It is preferable.

Further, when it is necessary to improve the perforation resistance, 0.5 to 10 mass% of M is contained in the zinc phosphate-based coating as proposed by the inventors in Japanese Patent Laid-Open No. 2001-73163.
It is preferable to include g.

The above is merely an example of the embodiment of the present invention, and various modifications can be made within the scope of the claims.

[0035]

EXAMPLES Next, examples of the present invention will be described.
Table 1 for electrogalvanized or hot-dip galvanized steel
A zinc phosphate-based film was formed with the surface conditioner shown in Table 1 and the zinc phosphate-based treatment solution shown in Table 2, and the performance was evaluated by the test methods shown below.

[0036]

[Table 1]

[0037]

[Table 2]

[Flatness Sliding Property] A test piece having a length of 300 mm and a width of 20 mm was subjected to solvent degreasing on its surface, and rust-preventing oil (Z5 manufactured by Idemitsu Kosan Co., Ltd.) was applied at 1.5 g / m ^2. Under the conditions, a plane sliding property test was performed and the friction coefficient μ was measured. Die shape: 10 mm L x 20 mm W long plane pressing load: 24.5 N / mm ² Drawing speed: 1000 mm / min Sliding length: 100 mm Test temperature: Room temperature

[Draw bead (powdering) test]
For a test piece with a length of 300 mm and a width of 20 mm, the surface of the test piece was degreased with a solvent, rust preventive oil (Z5 manufactured by Idemitsu Kosan Co., Ltd.) was applied at 1.5 g / m ² , and a draw bead test was conducted under the following conditions. The pulling load was measured and the powdering property was evaluated. The powdering property was evaluated on a scale of 5 from 1 to 5 according to the following criteria after repeating the step of sticking a tape on the surface after the draw bead test and peeling the tape twice. Die shape: Round type, convex R5mm, concave R2mm Pressing load: 4.9kN Extraction speed: 1000mm / min Sliding length: 100mm

(Powdering Judgment Criteria) Rating 5: No tapering even with two tape peelings 4: Only slight tapering with only the first tape peeling of the two tape peelings 3: Tape twice There is some powdering only by the first tape peeling of the peeling 2: There is remarkable powdering only by the first tape peeling of the two times of tape peeling 1: There is significant powdering even by the second tape peeling

[Paint Adhesion] The paint adhesion was evaluated by a water resistant secondary adhesion test. Each surface-treated steel sheet was subjected to normal alkali degreasing and then surface conditioning according to the automobile body manufacturing process, and then immersed in a phosphate treatment solution SD2500 (manufactured by Nippon Paint Co., Ltd.) for 2 minutes. After that, a V20 electrodeposition paint (bath temperature: 28 to 30 ° C) manufactured by Nippon Paint Co., Ltd. was used to apply an electrodeposition voltage of 250 V for 180 seconds to perform electrodeposition coating,
It was baked at 165 ° C. for 20 minutes to form an electrodeposition coating film (film thickness: 20 μm). Next, OTO-870H intermediate coating for automobiles (manufactured by Nippon Paint Co., Ltd.) and OTO650 overcoat coating for automobiles (manufactured by Nippon Paint Co., Ltd.) were each applied to a thickness of 40 μm, and then applied to pure water at 50 ° C for 10 After immersing for a day, it was taken out, and immediately after a cross cut with a knife of 2 mm width was put in, a peeling test using a cross-cut tape was conducted to observe the peeling state of the coating film. And, if the coating film residual rate after the peeling test is 95 to 100%, it is good "○", and if the coating film residual rate is 85% or more and less than 95%, it is "△" and the same coating film residual rate. Of less than 85% was evaluated as “poor”.

[Corrosion resistance after coating] Each surface-treated steel sheet was subjected to normal alkali degreasing and then surface conditioning according to the automobile body manufacturing process, and then a phosphate treatment liquid SD2500 (manufactured by Nippon Paint Co., Ltd.) And soaked for 2 minutes. Then, using V20 electrodeposition paint (bath temperature: 28 to 30 ° C) manufactured by Nippon Paint Co., Ltd., an electrodeposition voltage of 250 V was applied for 180 seconds to carry out electrodeposition coating, followed by baking at 165 ° C for 20 minutes. Electrodeposition coating (film thickness: 15 μm
) Was formed to obtain a test material. The sample after electrodeposition coating is subjected to a cross-cut with a knife, then a combined cycle corrosion test is performed under the cycle conditions shown below, and the post-coating corrosion resistance is evaluated by measuring the swollen width and plate thickness reduction amount shown below. did. Since the corrosion resistance after electrodeposition coating is greatly affected by the Zn plating amount, all Zn plating adhesion amounts of 40 g / m ² were prepared and evaluated in this test.

Cycle conditions Salt spray (35 ° C, 6h) → dry (50 ° C, 3h) → wet (50
℃, 14h) → Left (35 ℃, 1h)

Evaluation Method of Corrosion Resistance After Painting by Bulging Width After conducting a combined cycle corrosion test for 30 cycles under the above cycle conditions, each test material was taken out, and the unilateral swelling width from the cross cut portion was measured from the maximum of 5 points, The average value was taken as the swollen width, and when the swollen width was 0 mm or more and less than 6 mm, it was evaluated as “◯”, when it was 6 mm or more and less than 10 mm, it was evaluated as “Δ”, and when it was 10 mm or more, it was evaluated as “x”.

Evaluation method of post-painting corrosion resistance (perforation resistance) based on the amount of reduction in sheet thickness After 90 cycles of combined cycle corrosion test under the above cycle conditions, each test material was taken out and the electrodeposition coating film was peeled off. The maximum corrosion depth was measured, and when the measured maximum corrosion depth value was 0 mm or more and less than 0.1 mm, "○", 0.1
In case of more than mm and less than 0.3mm, it is "△", and 0.3m
The case of m or more was evaluated as "x".

Table 3 shows the results of these evaluations.

[0047]

[Table 3]

As is clear from the evaluation results shown in Table 3,
It can be seen that all of the examples have excellent press formability without galling in the draw bead test that undergoes bending and bending back as occurs in a real press having beads.

[0049]

Industrial Applicability According to the present invention, it is possible to provide a galvanized steel sheet excellent in press formability as a surface-treated steel sheet mainly used as a steel sheet for automobile bodies and a steel sheet for home appliances.

[Brief description of drawings]

FIG. 1 shows various galvanized steel sheets having different amounts x of zinc phosphate-based coating and length y of long sides of crystals forming the zinc phosphate-based coating, and x and y of each galvanized steel sheet. The value of
It is the figure which plotted the rating of the powdering property with respect to the value when substituting for 1.5x + 1.0y.

FIG. 2 is a diagram showing only one crystal of a zinc phosphate-based film extracted and the length y of its long side.

[Explanation of symbols]

1 Crystal of zinc phosphate coating

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Chiaki Kato             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. F term (reference) 4K026 AA02 AA13 AA22 BA04 BB06                       BB08 CA26 DA03                 4K044 AA02 AB02 BA10 BA17 BB03                       BC03 BC08 CA04 CA11 CA16                       CA18

Claims (2)

[Claims] 1. In a galvanized steel sheet having a zinc phosphate-based coating on its surface, the adhesion amount of the zinc phosphate-based coating is x.
g / m ² , where x and y satisfy the following formulas (1) and (2), where y μm is the length of the long side of the crystal forming the zinc phosphate coating. Galvanized steel sheet with excellent press formability. Note 1.5x + 1.0y ≤ 6.3-----(1) x ≥ 0.5-----(2) 2. The zinc phosphate coating is 0.3 to 1.5 mass.
% Of Ni and 3.0 to 5.0 mass% of Mn, The galvanized steel sheet having excellent press formability according to claim 1.