JP2904060B2 - Surface-treated steel sheet with excellent punching workability and formability - Google Patents

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 is excellent in stamping workability and formability, and in particular, when forming a chassis or a case of home electric appliances, it has excellent formability (deep drawability or overhang). Surface-treated steel sheet that has all the required properties such as corrosion resistance, fingerprint resistance, grounding properties, etc. as well as having extremely low burr height formed on the end face of the steel sheet when punched. It is about.

[0002]

2. Description of the Related Art Surface-treated steel sheets, which are made of cold-rolled steel sheets, are subjected to galvanization, and further subjected to inorganic coating or resin coating, are used in automobile parts and household electric appliances. Although widely used, various characteristics are required according to each application. In particular, a surface-treated steel sheet used for a chassis of home electric appliances or the like is required to have all properties such as formability, punching workability, corrosion resistance, fingerprint resistance, and grounding property.

[0003] Among these required properties, the punching workability is evaluated by the size of burrs generated in a sheared portion when the surface-treated steel sheet is punched, and the fact that such burrs are small is a very important property in practical use. Becomes If the burrs are too large, the dimensional accuracy of the sheared portion will be deviated, and it will be difficult to adjust the dimensions at the time of assembling the product. This often causes the steel sheet surface to be damaged, or adversely affects the electric circuit due to the adhesion of metal powder caused by wear of the burrs. In addition, a large problem arises in that the electrodeposition paint becomes poorly adhered at the burrs and the corrosion resistance deteriorates.

[0004] Further, since these surface-treated steel sheets are often used as components of a driving system or a chassis or a case material of household electric appliances, corrosion resistance is also important from the viewpoint of ensuring the quality of product appearance. Characterized. Furthermore,
When assembling into a product after punching a surface-treated steel sheet, not a little manual work process is added,
Fingerprint resistance is also required in order to prevent contamination due to the attachment of fingerprints. Conventionally, as a measure for improving such corrosion resistance and fingerprint resistance, a resin coating method has been mainly employed. However, when a steel plate for a chassis is used as a box of an electric device, conductivity is also an important required characteristic because grounding is usually performed in the box, and in order to secure the conductivity, corrosion resistance and The resin coating for improving fingerprint resistance cannot be made sufficiently thick.

[0005] Under these circumstances, what has been put to practical use at present with the above-mentioned required characteristics is that a zinc-based electroplating is applied to the surface of a cold-rolled steel sheet, and a grounding property is further placed thereon. This is a method of improving fingerprint resistance by forming an extremely thin organic resin coating film that does not hinder, but it is not possible to increase both grounding property and fingerprint resistance to a satisfactory degree.

On the other hand, in recent years, the formability and punching workability required for a steel sheet for a chassis tend to be more and more severe due to simplification of the process and reduction in the number of parts by a chassis press maker, thereby reducing costs. Conventionally, SPCD or box-annealed low-carbon Al-killed cold-rolled steel sheets of SPCD grade have been applied to this type of application.
This is because although the workability of the low-carbon Al-killed steel sheet is slightly inferior, carbon is coarsely precipitated as fragile cementite in the crystal grain boundaries and in the grains during the box annealing process for 10 hours or more, and this cementite is removed during punching. This is because it has the advantage that the amount of burrs generated is small, the abrasion of the mold is reduced, and the shearing load is also reduced since it becomes the starting point of crack generation.

[0007] However, the demands of consumers for workability in recent years have become increasingly severe, and in fact, such a low carbon Al-killed cold-rolled steel sheet cannot satisfy such demands.

Therefore, regarding the punching workability, a method of introducing a work strain by rolling or the like to the surface layer portion of the annealed steel sheet to harden it (Japanese Patent Application Laid-Open No. 1-255625), and hardening the steel sheet surface by nitriding treatment or carburizing treatment Methods (JP-A-1-255626, JP-A-2-133561, JP-A-3-199343, and JP-A-3-202442) have been tried.

In the former method, although the punching workability is improved to some extent, there is a problem that the mechanical properties such as elongation and r-value, which are the inherent characteristics required of the steel sheet, are remarkably deteriorated. The method requires special equipment and steps for nitriding and carburizing treatments, and it is hard to say that it is advantageous in terms of equipment and productivity.

Further, by adding Mn and S, M
A method for producing a large amount of nS precipitates (JP-A-1-230
No. 748 and No. 6-73457) have been proposed, but this method causes hot working cracks at the time of working with an increase in the S, increases a point defect called a blowhole or a blister inside, A problem arises in that point-like surface defects called slivers frequently occur.

In order to reduce the cost of home electric appliances, punching and assembling steps are being omitted for chassis parts and the like. There are some trends. For example, the pulley shaft to be attached to the chassis plate surface was previously manufactured by a separate process of mechanical cutting, but was inserted into the punched hole and caulked, but recently, the integral molding method of overhang and deep drawing has been adopted. It is becoming mainstream. Therefore, excellent formability is also required for steel sheets used for applications such as chassis. From a metallurgical point of view, punchability is affected by the presence of cementite and MnS, which are the starting points of crack initiation, and the hardness of the steel sheet itself. It was difficult to balance sex.

Further, in order to improve the efficiency of the annealing step and to improve the surface properties and internal quality, the transition from the conventional box annealing to the continuous annealing capable of short-time annealing is rapidly progressing. There is an urgent need to develop a steel sheet that has both good stamping workability and excellent formability.

On the other hand, a so-called IF cold-rolled steel sheet to which carbon and nitride forming elements such as Ti and Nb are added and C and N are fixed has excellent workability such as high elongation and r value and low yield stress. It is widely used for difficult-to-machine parts such as automobile bodies, and this IF-based cold-rolled steel sheet exerts its properties more than fully by adopting a continuous annealing method. However, although workability is good, there is a problem that punching workability is inferior to low carbon Al-killed cold-rolled steel sheet, and the burr height of the end face after punching becomes large. Not suitable.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a conventional IF-based cold-rolled steel sheet by appropriately adjusting the chemical composition of the steel material. In addition to ensuring excellent moldability and mechanical properties as obtained in the above, the punching workability is good and there is no burr problem, and furthermore, the corrosion resistance and resistance without impairing the conductivity required for grounding An object of the present invention is to provide a surface-treated steel sheet having improved fingerprint properties.

[0015]

The structure of the surface-treated steel sheet according to the present invention which can achieve the above-mentioned objects is mas
In s%, C ≦ 0.008% Si ≦ 1.0% 0.25% ≦ Mn ≦ 1.0% P ≦ 0.10% 0.010% ≦ S ≦ 0.025% Al ≦ 0.10% N ≦ 0.010% Ti ≦ 0.20%, and 4 ≦ Ti * / C where Ti * = Ti − [(48/14) N + (48/3)
2) zinc-based electroplating having a coating weight of 3 to 40 g / m ^{2 on} at least one surface of a cold-rolled steel sheet that satisfies S] and the balance is Fe and inevitable impurities;
The gist lies in that a resin coating film having an adhesion amount of 0.1 to 2.5 g / m ² is formed thereon.

In the above-mentioned surface-treated steel sheet according to the present invention, as a criterion for ensuring excellent formability and punching workability, the r value is 1.6 or more, and the burr height after punching is 20 mm or less. Certain ones are particularly preferred, and by using a resin coating containing a silicon-based inorganic oxide, it is possible to obtain a surface-treated steel sheet having even more excellent corrosion resistance and fingerprint resistance. The surface-treated steel sheet having the above configuration can be very effectively used as a material of a chassis of an electric appliance by utilizing its features.

[0017]

In the surface-treated steel sheet according to the present invention, the type and amount of each element contained in the cold-rolled steel sheet to be used are defined,
The content of Ti is determined in consideration of the relationship with the content of C, N, and S. This is because the present invention has a base composition of ultra-low carbon IF steel having excellent press formability, and improves the punching workability which has been pointed out as a disadvantage while maintaining its characteristics. The reasons for determining the contents and their contents will be described in detail later, but the important technical features are as follows.

That is, in order to improve the punchability while maintaining the excellent formability inherent in the IF-based cold-rolled steel sheet, it is necessary to use a precipitate, which is a starting point of crack generation at the time of punching, specifically Ti The book states that the presence of ₄ C ₂ S ₂ is indispensable, and that by properly controlling its size and dispersion state, it is possible to obtain a cold-rolled steel sheet that simultaneously satisfies excellent formability, punching workability, and surface properties. Based on the new findings identified by the inventors. Precipitates and inclusions present in ultra-low carbon IF steel sheets include TiC, Ti
₄ C ₂ S ₂ , TiS, TiN, FeTiP, TiO _2, etc., and Nb (C, N) etc. in the Nb-added system. Of these precipitates and inclusions, especially the formability and punching workability Ti ₄ C ₂ has a remarkable favorable effect on the surface properties.
It was confirmed that the S _2. And the Ti ₄ C ₂ S ₂
It was also confirmed that the other precipitates and inclusions had the following tendencies.

TiC, Nb (C, N): Since the size as a precipitate is very small, there is a tendency that the formability is largely deteriorated, and the effect of improving the punchability is small. Fe
TiP: The size is about the same as that of Ti ₄ C ₂ S _2, and although it has an effect of improving the punching property, it greatly deteriorates the formability.

TiS, TiN: It seems that the effect of improving punchability is expected to be slightly larger than Ti ₄ C ₂ S _{2 in} terms of size. However, since it is soft, there is little substantial improvement effect. When the S content is increased, Ti ₄ C ₂
Although the amount of S ₂ increases, a certain amount (C is Ti ₄ C ₂ S ₂
Until Ti) is generated, and TiS is not generated until C is consumed.
iS is not preferable because it causes surface defects. Further, in practical steel, it is difficult to control the amount of N, and it is very difficult to properly control the amount of TiN.

TiO ₂ : The size is one order of magnitude larger than that of Ti ₄ C ₂ S _2, which is not preferable because not only the effect of improving the punching property is small but also a cause of surface defects. MnS: T
The same effect of improving punchability as i ₄ C ₂ S ₂ can be expected.

For the reasons described above, the present invention controls the amount of Ti ₄ C ₂ S ₂ produced and the state of dispersion in the ultra-low carbon Ti-added IF steel sheet to improve formability and punching properties.
Furthermore, they have succeeded in obtaining a cold-rolled steel sheet satisfying all the surface properties. Incidentally, as a technique for improving the formability and punching property of an ultra-low carbon IF steel sheet, Japanese Patent Application Laid-Open No.
No. 73457, there is a method of adding Ti and Nb in a complex manner. According to the present inventors' investigation, when Nb is added in a range of 0.003 to 0.03%, Nb (C , N) is generated and C in the steel is consumed, so that Ti ₄ C ₂ S ₂ effective for improving the punching property cannot be generated. Moreover, in this method, 0.05% or more of S is essential for improving the punching property.
Has a problem that the generation rate of surface defects is increased by the generation of GaN. Hereinafter, the reasons for determining the component composition of the steel used in the present invention will be described in detail.

C contributes to the improvement of the strength of the steel material as a strengthening element, but if it is too much, the elongation and the r-value etc. decrease and the workability deteriorates. 008%.

Si is an effective element for increasing the strength without lowering the ductility, but if it is too much, the oxide film formed during annealing increases, adversely affecting the chemical conversion treatment often performed thereafter, Further, when performing electroplating, there arises a problem that the plating thickness becomes non-uniform and plating unevenness occurs, so the amount of Si should be suppressed to 1.0% or less. In particular, when the cold-rolled steel sheet is hot-dip galvanized, it is desirable to suppress the Si content to 0.3% or less, because the formation of an oxide film tends to cause an unplated portion.

Since P has a function of strengthening the steel by forming a solid solution in the steel, it is effective to contain P in an appropriate amount according to the required strength. However, if it is too much, segregation occurs and workability is deteriorated. Since this has an adverse effect, the upper limit is 0.10%.

N, if its content increases, has an adverse effect on mechanical properties such as elongation and r-value, so it must be suppressed to 0.010% or less. Al acts effectively as a deoxidizing agent, but if it is too much, it becomes a source of nonmetallic inclusions and adversely affects mechanical properties and workability.
It must be kept below 10%.

S is added to the steel sheet of the present invention together with Ti described later.
Is an extremely important element in In other words, excellent punchability
In order to obtain, an appropriate amount of Ti_Four C
_Two S _Two It is necessary to generate and distribute
Must contain at least 0.010% or more of S
No. However, excessive content exceeding 0.025%
And the incidence of surface defects increase.
I have to get it.

FIG. 1 shows C: 0.0052%, S
i: 0.01%, Mn: 0.4%, P: 0.014%,
Al: 0.03%, Ti: 0.08%, N: 0.006
5 shows the punching workability and r value when the S content was changed from 0.002% to 0.037% for a cold-rolled steel sheet having a basic composition containing 0.1%. In this figure,
Box-annealed Al-killed cold-rolled steel sheet (C: 0.044%, A) which is considered to have excellent punching properties and mechanical properties.
1: 0.045%) is also shown as a comparative example.
FIG. 2 shows the relationship between the S content and the incidence rate of surface defects.

The physical property test method was as follows. That is,
120 kg of 40 kg steel ingot melted and cast in a laboratory
After heating to 0 ° C., it is roughly rolled to 30 mm ^t . Then
After heating this slab to 1200 ° C., the plate thickness: 4 mm
^t , finishing temperature: 920 ° C or higher, winding temperature: 680 ° C
Hot-rolled under the conditions described above and ground to 3.2 mm ^t .
The sample was cold-rolled to 8 mm ^t , subjected to continuous annealing at a soaking temperature of 800 ° C. for 1 minute, and then temper-rolled at 1% to obtain a test cold-rolled steel sheet. The r-value was determined by measuring the width and thickness of a 10 mm × 110 mm test piece when tensile strains of 0% and 15% were applied. In addition, the punching workability is 0.
An 8 mm ^t cold-rolled steel sheet was punched out with a clearance of 9% to 10 mmφ to measure and evaluate the burr height. The surface flaw was evaluated by visually observing the surface of each of the obtained cold-rolled steel sheets and determining the surface flaw occurrence rate at a fixed length.

As is clear from FIGS. 1 and 2, if the S content is less than 0.010%, the height of burrs at the time of punching becomes extremely large, and the object of the present invention cannot be achieved. On the other hand, when the S content exceeds 0.025%, the generation of surface flaws becomes remarkable, and the object of the present invention is not satisfied. However, the S content is 0.010% or more and 0.025%.
It can be seen that in the following range, surface flaws and burr heights can be suppressed as much as possible and a high level of r value can be secured.

When the punched portion of the steel sheet is observed microscopically, a shear fracture surface is first formed on the front and back surfaces of the steel sheet as the punch descends after the contact between the punch and the steel sheet, and the rest is locally strongly sheared. Upon receiving this, voids are generated and cracks are formed, and the cracks unite from the front and back surfaces to complete the processing. Therefore, in order to reduce burr after punching, it is effective to promote the formation of voids and the progress of cracks described above. However, since Ti ₄ C ₂ S ₂ is a relatively large precipitate, It is considered that when the steel sheet is subjected to strong shear deformation, the formation and development of voids and cracks in the vicinity of the precipitate are promoted, and as a result, burrs are reduced.

On the other hand, Ti combines with C and S to form Ti ₄ C ₂
In addition to producing S ₂ and Ti, it also binds with N, so that an amount that can completely fix N in the above range is necessary. In order to impart formability and aging resistance, it is sufficient to fix C. Quantity of T
i is also needed. From this viewpoint, in the present invention, as described above, the amount of Ti added is 4 ≦ Ti * / C, where Ti * = Ti − [(48/14) N + (48/3)
2) S].

However, the effect of adding Ti as described above is about 0.2.
Saturating at 0%, and adding more than that is not only economically wasteful, but also has the negative effect of increasing the recrystallization temperature, so the upper limit was set to 0.20%.

Mn is also an element that forms coarse precipitates of MnS as described above and contributes to the improvement of punching workability.
% Or more. But too much,
Since the steel sheet becomes too hard and adversely affects workability, the upper limit is set to 1.0%.

The surface-treated steel sheet according to the present invention is prepared by melting a steel material which satisfies the above requirements for the component composition and casting it according to a conventional method, followed by hot rolling, pickling, cold rolling, annealing temper rolling and the like. The cold rolled steel sheet obtained by sequentially performing
At least one surface is coated with an appropriate amount of electro-galvanized coating and further coated with an appropriate amount of resin, thereby improving corrosion resistance and providing excellent fingerprint resistance without deteriorating grounding properties. It has improved properties and appearance.

That is, ordinary steel sheets for chassis are often used without painting, and when cold-rolled steel sheets are used as they are, red rust is generated in a short time even in an air atmosphere, and erosion due to rust causes a reduction in strength. In addition, rust powder that falls off during use adversely affects the drive unit and the electric circuit system. Therefore, surface treatment is indispensable to prevent such rusting, and in the present invention, zinc-based electroplating is employed as a material exhibiting an excellent rust-preventing effect without adversely affecting the formability and punching workability. I do.

The zinc-based plating includes a hot-dip galvanizing method in which a steel sheet is immersed in a hot-dip zinc bath.
There are electroplating method in which zinc is deposited on the steel sheet surface by energizing in an electrolytic solution containing zinc ions, and vapor deposition plating method in which zinc or the like adheres to the steel sheet surface in a vapor state. In the present invention, an electroplating method is adopted as a material capable of forming a uniform and beautiful plating layer without defects such as defects. In order to effectively exhibit the rust-preventive effect of the zinc-based electroplating, the coating weight of the electroplating layer should be 3 g / m ² or more. If the coating weight is insufficient, satisfactory corrosion resistance is guaranteed. It becomes impossible or the resin coating film formed thereon must be made too thick, resulting in a problem that the grounding property is impaired. From the viewpoint of corrosion resistance, there is no particular upper limit for the zinc-based electroplating coating amount, but even if the coating amount is excessively increased beyond 40 g / m ² , no further improvement in corrosion resistance can be obtained. and a plating time only to unnecessarily prolonged, and because in some cases come out also a risk of plating peeling with reduced plating adhesion to punching or the like, 40 g / m ²
Was set as a temporary upper limit.

The zinc-based electroplating employed in the present invention means, in addition to pure zinc plating, a zinc-based plating containing a metal such as Ni, Co, Fe, etc. together with zinc, or an underlayer of these zinc-based plating or pure zinc-plating. Refers to plating on which the same or different pre-plating is applied, and includes various zinc alloy platings having a zinc content of 50% by weight or more.

Although the purpose of the rust prevention of the steel sheet itself is achieved by forming the zinc-based electroplating layer, in order to put it into practical use as a material for a chassis or the like, the rusting of the zinc-based plating layer itself is prevented. At the same time, it is necessary to improve the fingerprint resistance, and as a means for that, in the present invention, a resin coating is further applied on the zinc-based electroplated layer. The preferred coating weight of the resin coating is in the range of 0.1 to 2.5 g / m ² , and if the coating weight is insufficient, satisfactory corrosion resistance and fingerprint resistance cannot be obtained. In addition, there arises a problem that the conductivity of the surface layer is reduced and the grounding property is extremely deteriorated.

The type of the resin component constituting the resin coating film is not particularly limited, but the most common one is an epoxy resin,
Ethylene copolymer resin containing an ethylenically unsaturated carboxylic acid as a polymerizable component, a polyester resin, a polyvinyl resin, an acrylic resin, a urethane resin, a polyamide resin, and the like, which can be used alone, If necessary, two or more kinds can be used as a mixture.
In addition, functional groups in these resins are modified by a conventional method or reinforced by the use of a cross-linking agent, and furthermore, a silicon-based organic or inorganic compound is used in combination with, for example, further improving fingerprint resistance and the like. What was modified by introducing a wax component to a functional group in the resin together with a small amount of a wax component to improve the surface mold galling during press processing,
Are also recommended as preferred resin components.

The resin coating film desirably exhibits good corrosion resistance and fingerprint resistance as a surface protective film even after pressing or the like. In this sense, a particularly preferred base resin is
One or a mixture of two or more of epoxy resins, ethylene copolymer resins, polyester resins, and urethane resins.

In the resin coating film, in addition to the base resin, 5% by weight of a silicon-based inorganic oxide such as silica particles is used.
It is preferable that the content be more than that, because the corrosion resistance of the coating film can be further enhanced. However, if the content of silica particles and the like is too large, they will act as a lubricant, increasing the coefficient of friction of the coating film, lowering lubricity, and thus deteriorating the corrosion resistance after processing. 30% by weight or less, more preferably 1%
It is desired that the content be suppressed to about 0% by weight or less.

The effect of the combined use of silica particles is most effectively exhibited by using the particles having a particle diameter of 1 to 20 μm. That is, as the silica particles become smaller, the coating becomes denser and the adhesiveness is improved, and as a result, the corrosion resistance and coating properties of the coating are improved, but even if extremely fine particles of less than 1 μm are used, they are more. Is not necessarily obtained, the lower limit of about 1 μm is sufficient,
Conversely, if the thickness exceeds 20 μm, the surface of the coating film is roughened, a dense coating is not formed, and the corrosion resistance is deteriorated. From these viewpoints, a more preferable particle size of the silica particles is in the range of 4 to 6 μm.
Known as colloidal silica, for example, "Snowtex-XS or SS" (all manufactured by Nissan Chemical Industries, Ltd.)
Available as commercial products.

The method for producing the surface-treated steel sheet according to the present invention is not limited at all, and one or both sides of a cold-rolled steel sheet produced by the above-described method are subjected to a zinc-based electroplating treatment according to a conventional method. A resin coating may be applied thereon by any method such as a roll coating method, a dip coating method, and a spray coating method. At this time, in order to enhance the adhesion between the zinc-based electroplated layer and the resin coating film, it is also effective to subject the surface of the zinc-based electroplated steel sheet to a chemical conversion treatment such as a chromate treatment or a phosphate treatment and then apply the resin coating. Which are, of course, included in the technical scope of the present invention.

[0045]

EXAMPLES Hereinafter, the structure, operation, and effects of the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples, and can be adapted to the above and following points. It is also possible to implement the present invention with appropriate modifications within the scope, and all of them are included in the technical scope of the present invention.

Example 40 kg of the components shown in Table 1 which were vacuum-dissolved in a laboratory
After heating the steel ingot to 1200 ° C., it was roughly rolled to 30 mm ^t , and then this slab was heated to 1200 ° C., and the sheet thickness was 4 m.
m ^t, finishing temperature 920 ° C. or higher, and hot rolled under conditions of a coiling temperature 680 ° C.. Then pressure cold-rolled from the ground to 0.8 mm ^t to 3.2 mm ^t, was subjected to continuous annealing for 1 minute soaking at 800 ° C., it was carried out 1% temper rolling.

The surface of each of the obtained cold-rolled steel sheets is subjected to electrogalvanization by an electroplating method according to a conventional method so that the amount of zinc applied is 20 g / m ^2, and the amount of Cr applied thereon is calculated as metal Cr. After subjecting to a chromate treatment to 10 mg / m ² , a resin in which an ethylene-based, ester-based or urethane-based resin is used as a base resin, and colloidal silica having a particle diameter of 4 to 6 μm is blended at 10% by weight in terms of solid content. The paint was applied so that the resin adhesion amount was 1.0 g / m ² to obtain a surface-treated steel sheet.

With respect to each of the obtained surface-treated steel sheets, the tensile properties, r values, punching workability, corrosion resistance, fingerprint resistance, and grounding property were evaluated by the following methods, and the results shown in Table 2 were obtained. Although not shown in Table 2, the corrosion resistance, fingerprint resistance, and grounding property of each surface-treated steel sheet were good because the amount of the zinc-based electroplating layer and the amount of the resin coating film were appropriate. Met.

A part of the cold-rolled steel sheet shown in Table 1 was used as the steel sheet to be treated, and the surface thereof was electroplated by an electroplating method according to a conventional method so that the zinc deposition amount was 1 to 50 g / m ^2. Galvanized, and the amount of deposited Cr
After a chromate treatment was performed so as to be 10 mg / m ^{2 in} terms of conversion, a resin coating was performed so that the resin adhesion amount was 0.05 to 3.0 g / m ² to obtain a surface-treated steel sheet. With respect to each of the obtained surface-treated steel sheets, corrosion resistance, fingerprint resistance, and grounding property were evaluated, and the results shown in Table 3 were obtained.

Tensile properties : Using a JIS No. 5 tensile test piece, the yield point (YP), strength (TS), elongation (El), and work hardening index (n value) were each evaluated.
The aging resistance (AI) was evaluated based on the amount of increase in the yield point after the treatment in min. r value : Using a test piece of 10 mm × 110 mm, the width and plate thickness when tensile strains of 0% and 15% were applied were measured and determined.

Punching workability : A blank having a clearance of 9% was punched into a circular shape having a diameter of 10 mm, and the height of burrs formed on the punched end face was measured by a micrometer and evaluated. …: Burr height of less than 20 μm, ×: Burr height of 20 μm or more Corrosion resistance : A salt water spray test was performed according to the method described in JIS Z 2371, and evaluation was made at 1% white rust generation time. ○: 240 hours or more, ×: less than 240 hours

Fingerprint resistance : A test piece was immersed in a 50% aqueous petrolatum solution at 40 ° C. and taken out, and the change in color tone between the petrolatum-adhered portion and the non-adhered portion was measured and evaluated using a color difference meter. When the color difference (ΔE) between the petrolatum-adhered portion and the non-adhered portion is “3 or less”, the fingerprint resistance is determined to be good. …: ΔE: 3 or less, ×: ΔE: 3, super- grounding property : Conductivity on the surface of the test piece was evaluated by measuring the surface resistance with a tester with the terminal interval being 100 mm. …: Surface resistance of less than 200Ω, ×: Surface resistance of 200Ω or more Overall evaluation :…: good, ×: bad

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

From Tables 1 and 2, the following can be considered. Steel types A, B, and I are mild steels and steel type E is a high-strength steel, all of which satisfy the requirements of the present invention, and have strength (TS), elongation (El), r-value, On average, good results were obtained in all of I (aging resistance), burr height, surface defects, and surface properties.

On the other hand, the steel type C is a comparative example having a larger C content than the steel type A and exceeding the specified range of the present invention, and has a low elongation and r value. Surface defects such as blisters and slivers. Further, since the steel type F has a larger Si content than the steel type E and exceeds the specified range, when electroplating is performed, the formation of an oxide film causes uneven plating.

Since the amount of Si exceeds the specified range, the steel type F has poor surface properties, and also impairs the chemical conversion treatment performed thereafter and the uniformity of electroplating. Steel type G is a comparative example in which the amount of S is insufficient with respect to steel type A, has high burrs generated by punching, does not meet the object of the present invention, and steel type H has a Ti * / C ratio of the present invention. , The satisfactory elongation, r-value and aging resistance are not obtained. Since the amount of N of steel type J exceeds the specified range with respect to steel type I, elongation and r value are poor.
Further, the steel type K has a smaller Mn content than the steel type A and does not satisfy the amount specified in the present invention, so that the punching workability is poor and the purpose of reducing the burr height cannot be fulfilled.

Steel type L is a comparative example in which the amount of Mn is too large relative to steel type E, and the elongation and r value are poor. Steel type M is a comparative example in which the P amount is too large relative to steel type E. Low elongation and r-value. Steel type N is a comparative example in which the amount of Al is too large with respect to steel type A, and elongation and r value are low and surface defects are observed. It's getting worse.

Table 3 can be considered as follows. No.
Examples 1 to 5 are examples in which both the component composition of the steel material and the adhesion amount of the electrogalvanized layer and the resin coating film satisfy the stipulated requirements of the present invention, and in any of the corrosion resistance, the fingerprint resistance, and the grounding property. Very good results have been obtained.

On the other hand, no. No. 6 was poor in corrosion resistance and fingerprint resistance because both the zinc-based electroplating layer and the resin film had insufficient adhesion amounts. No. 7 has poor grounding property due to too much resin adhesion. No. 8 was poor in corrosion resistance and fingerprint resistance because no resin coating was applied. No. 9 cannot satisfy the arrowhead corrosion resistance and fingerprint resistance because of insufficient resin adhesion amount.

[0062]

The present invention is constituted as described above, and regulates the component composition of the base steel material, in particular, the content of S, Mn, Ti, etc., as well as the S, N, C and Ti contents. By properly controlling the relationship between the two and forming a zinc-based electroplating layer and resin coating with the proper amount of adhesion on the surface, it is excellent in all of the strength characteristics, moldability, punching workability, corrosion resistance, fingerprint resistance In addition, the surface treated steel sheet has excellent properties and grounding properties, and can provide a surface-treated steel sheet which is extremely useful as a chassis material for home electric appliances.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the S content in a steel material on the burr height and r value formed during punching.

FIG. 2 is a graph showing a relationship between an S content in a steel material and a surface flaw generation index of a cold-rolled steel sheet.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ichiro Tsukaya 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Kobe Steel, Ltd. Inside the Kakogawa Works (72) Inventor Yukihiro Utsumi 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Kobe Steel, Ltd. Kakogawa Works (56) References JP-A-8-337841 (JP, A) JP-A-8-739982 (JP, A) JP-A-7-102344 (JP, A) JP-A-6-158175 (JP, A A) JP-A-5-230595 (JP, A) JP-A-59-89729 (JP, A) Patent 2672751 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 38 / 00 301 B05D 7/14 B32B 15/08 C09D 183/04 C25D 5/26

Claims (4)

(57) [Claims] 1. Mass% C ≦ 0.008% Si ≦ 1.0% 0.25% ≦ Mn ≦ 1.0% P ≦ 0.10% 0.010% ≦ S ≦ 0.025% Al ≦ 0.10% N ≦ 0.010% Ti ≦ 0.20%, and 4 ≦ Ti * / C where Ti * = Ti − [(48/14) N + (48/3)
2) zinc-based electroplating having a coating weight of 3 to 40 g / m ^{2 on} at least one surface of a cold-rolled steel sheet that satisfies S] and the balance is Fe and inevitable impurities;
Excellent surface treated steel sheet punching workability and moldability, characterized in that in which a resin coating film adhesion amount 0.1~2.5g / m ² was formed thereon. 2. The surface-treated steel sheet according to claim 1, wherein the r value is 1.6 or more, and the burr height after punching is 20 mm or less. 3. The surface-treated steel sheet according to claim 1, wherein the resin coating film contains a silicon-based inorganic oxide. 4. The surface-treated steel sheet according to claim 1, which is used as a chassis of an electric appliance.