KR890002987B1 - Surface treated steel plates with a weldability and method therefor - Google Patents

Abstract

The surface treated steel sheet has a chromium layer plated in amount 30-300 mg/m2 on the surface of steel sheet, a tin layer or a layer of tin-nickel alloy containing 20-60 wt.% plated in amount 10-500 mg/m2 on the chromium layer, and a layer formed on the surfaces of the tin or the alloy layers and made of hydrated chromium oxide in amount 2- 18 mg/m2.

Description

Surface Treatment Steel Plate for Weld Pipe Making and Manufacturing Method Thereof

The present invention relates to a surface-treated steel sheet for weld steel pipe having excellent weldability, coating performance and corrosion resistance, and a method of manufacturing the same.

In particular, metal chromium as the first layer on the surface of the steel sheet, tin or tin-nickel alloy as the second layer thereon, and chromium water and oxide as the third layer thereon (hereafter referred to as chromium conversion amount). It relates to a surface treatment signage for welding canal production by electrical resistance, and a method of manufacturing the same.

BACKGROUND ART Conventionally, as a surface-treated steel sheet for steel cans, electrolytic chromic acid treated steel sheets having two layers of an electro-tin plated steel sheet and metal chromium and chromium hydroxide are generally used.

Among these, the tin-plated steel sheet has excellent corrosion resistance, surface gloss, solderability, surface lubricity, and low contact electrical resistance, and therefore, a solder tube DI tube has been used as a mainstream of materials for steel production for a long time because of its good welding resistance due to electrical resistance. (Tubes formed by drawing and drawing processing) and tin have been most widely used, but tin used for plating has become expensive every year, making it an expensive material for canning.

On the other hand, all-chromic acid-treated steel sheet is a cheaper material than electro-tin plated steel sheet, which was developed about 20 years ago, and after that, the use of electro-tin plated steel sheet as an alternative material for manufacturing canisters has been increased every year. come.

However, when using an electrolytic chromic acid treated steel sheet having an excellent corrosion resistance and paint adhesion property as an adhesive forging material as a welding canning material, the metal chromium surface and chromium are heated by heating at the time of coating (no coating film is applied to the welding portion). Since the hydrated oxide deteriorates to chromium oxide having high electrical resistance, it was necessary to remove the surface coating by means such as mechanical grinding before welding.

The removal of the coating before welding not only increases the unit cost of manufacturing the tube, but also has a hygienic problem due to deterioration of corrosion resistance of the welded portion and scattering of the removed chromium powder, and can be welded without removing the surface coating. Tolerable materials have been strongly desired.

酸基), 초산기(硝酸基), 염소 이온등의 음이온을 의도적으로 첨가하지 않은 크롬산, 중크롬산 등을 주성분으로 하는 수용액중에서 편면(片面)당 0.5∼30mg/m²의 금속크롬, 금속크롬 환산으로 2∼50mg/m²의 크롬수산화산물을 주성분으로 하는 전해크롬산 처리강판(일본국 특개소 55-18542) (3)크롬도금 강판에 20%이하의 조질(調質)압연을 행하는 것을 특징으로 하는 전해크롬산 처리강판(일본국 특개소 55-48406)등이 제안되고 있다.Here, as an attempt to improve the weldability of the electrolytic chromic acid treated steel sheet-based material, for example, (1) a metal chromium layer of ³ to 40 mg / m ^{2 on} the surface of the steel sheet, ² to 15 mg / m in terms of metal chromium on the upper portion thereof Electrolytic chromic acid treated steel sheet having a porous shape of a non-metallic chromium layer mainly composed of chromium oxide of ² (Japanese Patent Application Laid-Open No. 55-31124), (2) Sulfuric Acid Group (

酸基), acetate group (硝酸基), chlorine ions and the like in terms of metal chromium, chromium metal in 0.5~30mg / m ² per in an aqueous solution mainly composed of chromic acid, dichromate and so on which are not intentionally added to an anionic one surface (片面) Electrolytic chromic acid treated steel sheet mainly containing ² to 50 mg / m ² chromium hydroxide product (Japanese Patent Application Laid-Open No. 55-18542) (3) Crude-plated steel sheet is characterized in that temper rolling of less than 20% is carried out. Electrolytic chromic acid treated steel sheets (Japanese Patent Laid-Open No. 55-48406) and the like have been proposed.

In these electrolytic chromic acid treated steel sheets, the technical concept for achieving the improvement of weldability is demonstrated as follows.

That is, in the citation examples (1) and (3), since the metal chromium layer itself inhibits passage of the welding current immediately after the start of welding, in order to increase the exposed area of the base steel on the surface of the steel sheet. In addition, even if the plating amount of the metal chromium is reduced, even when the plating amount of the metal chromium is large, the steel sheet is cracked by slight stretching by temper rolling.

However, in order to improve the weldability, simply making the amount of metal chromium or giving extension to the steel sheet to cause cracks in the metal chromium layer not only inevitably lowers the corrosion resistance of the electrochromic acid treated steel sheet, In the case of coating and using an electrolytic chromic acid treated steel sheet, iron oxide with high electrical resistance is easily generated during heating, and thus weldability has a problem of adverse effect.

In addition, in the above-mentioned citation example (2), the metal chromium plating amount can be reduced by the qualitative improvement of the chromium hydroxide, and it is described that the weldability was improved. Neither (3) nor (3) was attempted to improve weldability, focusing on the need to suppress chromium oxide itself having high electrical resistance generated during coating heating.

On the other hand, as a material for welding canning of a tin plating system, a tin plating steel sheet having a reduced tin plating amount is known on the surface of a steel sheet as compared with the tin plating amount of a conventional electroplated steel sheet.

However, when used as a material for welding canning, since it is heated at the time of coating, tin, which is a low melting point metal, is likely to cause alloying of base steel and iron and tin, and includes a problem in that tin cannot be reduced, which contributes to improvement of weldability.

The present invention relates to the problem of the generation of chromium oxide with high electrical resistance during coating heating of such a conventional electrolytic chromic acid treated steel sheet material, and the tin and base steels of the tin plating material having a small tin plating amount. It is to provide a surface-treated steel sheet for welding canning that simultaneously solves the problem of tin alloying.

If the conventional electrolytic chromic acid-treated steel sheet can be welded after coating heating, it has already been explained that commercially satisfactory welding is not possible unless the surface coating is ground and grounded. Chromium oxide with high electrical resistance is formed on the surface of metal chromium. (2) Chromium hydride oxides are dehydrated by heating to form chromium oxides having higher electrical resistance. (3) Iron oxide with high electrical resistance is generated on the surface of the base steel exposed through the pin holes present in the metal chromium layer.

Among the causes of lowering these weldability, (1) and (3) were found to be particularly large.

However, the cause (1) originates from the essence of metal chromium, which is that chromium oxide having high electrical resistance is generated by heating the metal chromium, and there is a great difficulty in solving the problem. It was found that oxidation of the surface of metal chromium can be greatly suppressed by the presence of a tin-nickel alloy insect.

At the same time, even better, the formation of tin or tin-nickel alloy layer on the metal chromium causes the tin or tin-nickel alloy to adhere on the surface of the base steel exposed through the pores of the metal chromium layer. Even effectively.

In addition, since the tin plating layer or the tin-nickel alloy layer is intercalated with metal chromium in the lower layer, alloying with the base steel is remarkably suppressed, and even after the coating is heated, the good weldability of the tin or tin-nickel alloy plating layer itself is maintained. This is advantageous in that the weldability after actual heating of the coating is much higher than that in the case where the tin or tin-nickel alloy plating layer is directly formed on the steel sheet.

That is, the present invention is 30 to 300 mg / m ² chromium plating layer on the surface of the steel sheet, 10 to 500 mg / m ² tin plating layer or tin-nickel alloy plating layer per side on the chromium plating layer, and at the same time in chromium conversion thereon The present invention provides a surface-treated steel sheet for welding canning, wherein a chromium hydroxide oxide layer of ^{2 to} 18 mg / m ² is formed per side.

The tin-nickel alloy plating layer of 10 to 500 mg / m ² described above contains 20 to 60% by weight of nickel.

In addition, the "tin-nickel alloy" used in this invention means containing the vacancy of tin and nickel obtained by the cathode electrolysis from the plating bath containing tin ion and nickel ion, and necessarily stoichiometry Tin-nickel alloys (e.g., NiSn, Ni ₃ Sn, Ni) having a compositional ratio of characteristics according to (mainly a division of physical chemistry that studies the quantitative relationship between the molecular structure of a substance and its physical properties) ₃ Sn ₂ , Ni ₃ Sn _4, etc.).

Usually, since the thing called "alloy" including the vacancy obtained by plating is generally performed, the expression used as an alloy was used.

In the implementation of the surface-treated steel sheet for weld canning according to the present invention, it is important to uniformly coat a tin or tin-nickel alloy layer on the chromium plating layer and to bring the chromium surface into good contact with each other. The surface-treated steel sheet for welding production can be obtained.

Conventionally, tin plating on chromium plating becomes very difficult, for example, JP 48-35136 "Chrome-Tin Two-Layer Plating Method" or JP 33-1455 "Chrome and Chromium". Various methods have been proposed for the method such as "plating various metals on an alloy surface".

However, none of the above methods is suitable as a method of carrying out tin plating in the present invention.

That is, in Japanese Unexamined Patent Application No. 48-35136, tin plating is performed with a normal gloss current density after strike plating at a high current density at the initial stage of tin plating energization, but the tin deposited as a strike current density is As described in the form of dark gray and tree branches and hairs, as in the present invention, when the amount of tin is extremely small, there is an unreasonable point that it is not possible to continuously form the layer by the gloss current density and conceal the strike plating layer.

In Japanese Unexamined Patent Publication No. 33-1455, anodizing is performed in an aqueous solution of caustic alkali. However, chromium plating of the first layer is dissolved by anodizing and chromium plating surface can be sufficiently activated in caustic alkali. In the case of using a conventional tin plating bath, no uniform or coherent precipitation of tin can be achieved, and there is an unreasonable defect that the plating layer is easily scratched after plating.

The surface-treated steel sheet for weld canning of the present invention is to solve the problems in the conventional chromium-tin two-layer plating technology, and the present invention as described above will be described in more detail as follows.

The amount of metal chromium which is a 1st layer is prescribed | regulated to 30-300 mg / m <^2> per side.

This metal chromium layer plays a role of corrosion resistance as the material for steel making, suppression of oxidation of the base steel and improvement of weldability, and it is difficult to secure these characteristics at less than 30 mg / m ² .

As the amount of metal chromium increases, the properties and the oxidation inhibitory effect of the base steel tend to be improved. However, when the amount of the metal chromium exceeds 300 mg / m ² , the effect becomes saturated, and the manufacturing cost is also high, which is uneconomical. The upper limit is 300 mg / m ² , more preferably 70 to 150 mg / m ² .

The tin or tin-nickel alloy plated layer, which is the second layer, is defined to be 10 to 500 mg / m ² per single side, and when the tin or tin-nickel alloy plating amount is less than 10 mg / m ² , the main improvement in weldability of the present invention is achieved. It doesn't work.

This is because tin or tin-nickel alloy plating cannot sufficiently cover the metal chromium which is the first layer.

In addition, when the tin or tin / nickel alloy plating amount exceeds 500 mg / m ² , the effect of improving weldability is not saturated anymore, and when it is more than that, it becomes disadvantageous in manufacturing cost.

Here, the tin-nickel alloy plating layer of 10 to 500 mg / m ² contains 20 to 60% by weight of nickel.

The nickel content stably obtained by tin / nickel alloy plating is 20 to 60% by weight, and the weldability decreases slightly as nickel is vacated in tin, but such tin-nickel alloy plating also has a metal chromium present in the lower layer. Due to the film formation peculiar to the present invention, it has much better weldability as compared with the conventional electrolytic chromic acid treated steel sheet.

In addition, for foods rich in protein such as fish meat and meat, the tin and nickel alloys are very stable, so that the so-called sulfided black stools in the inner surface of steel tubes seen in conventional tin-coated steel sheets are less likely to occur. Have.

Even if the tin-nickel alloy plating in the range of 20 to 60% of nickel content is obtained, the characteristics of the object of the present invention can be obtained, but the relationship between the plating conditions and the plating alloy composition ratio is unstable, It is unsuitable for industrial products, such as unstable chromium oxide production.

In addition, even if tin and zinc alloys vaccinated in tin are formed in place of the tin and nickel alloys described above, the characteristics of weldability can be obtained.However, vacancy in tin can be applied to a special bath such as zinc cyanide bath. It is limited in manufacturing.

Even if nickel plating is repeatedly formed on the tin plating or vice versa, tin and nickel tend to diffuse and form a tin-nickel alloy, but the manufacturing process is complicated.

Next, the third layer of chromium hydroxide is defined as ² to 18 mg / m ² , and the purpose of the third layer is the same as the role of chromium hydroxide in the conventional electrolytic chromic acid treated steel sheet, It is to secure corrosion resistance and coating performance by hole blocking of plated pores which cannot be achieved even by the above method.

At less than ² mg / m ² , weldability is excellent, but corrosion resistance and coating performance are not obtained.

If it exceeds 18 mg / m ² , the corrosion resistance and the copper performance are good, but the weldability is lowered to 18 mg / m ² or less, and more preferably 4 to 12 mg / m ² .

In carrying out the present invention, first, the surface of the steel sheet is degreased by a known method and washed with an acid, followed by chromic anhydride as a main agent, and a small amount of sulfuric acid, phosphate, hydrofluoric acid, fluoride, silicide (硅 佛) In a known chromium plating bath (also referred to as an electrolytic chromic acid treatment bath) containing one or more of a fluoride and a boron fluoride. A 300 mg / m ² metal chromium layer is obtained.

On this first layer of metal chromium, chromium hydride oxide, which is an intermediate reduction product of chromium precipitation, is inevitably formed.

This chromium hydrated sulfide inhibits the uniform coating property and adhesion of the second layer of tin or tin / nickel alloy plating to the metal chromium surface. Therefore, the chromium plating conditions should be selected so as to be the best. In the chromium plating technique, the following plating conditions for reducing the generation of chromium hydroxide are well known and are easy to implement. (1) Chromic anhydride concentration: Normal chromium plating is performed at 50 to 300 g / l, but higher concentrations such as 80 to 300 g / l tend to produce less chromium hydroxide. (2) Types and concentrations of auxiliaries: Typical examples are sulfuric acid, and silicic acid hydrofluoric acid, butyric acid and their alkali metals alone or in combination with sulfuric acid are also added.

In general, the fluorine-based adjuvant tends to produce less chromium hydroxide than the sulfuric acid adjuvant.

The amount of the adjuvant varies slightly depending on the kind thereof, but is about 1 to 5% by weight of the chromic acid concentration. (3) Bath temperature: Although generally performed at 30-60 degreeC, making it higher at 50-60 degreeC tends to produce less chromium hydride oxide. (4) Cathode Current Density: Although usually performed at ¹⁰ to 100 A / dm ² , the higher at ³⁰ to 100 A / dm ² tends to produce less chromium hydroxide.

In the known chromium plating technique described above, the chromium hydride is immediately immersed in the same bath for several seconds by selecting conditions under which the production of chromium hydride is reduced and, if necessary, after energizing the chromium. It is easy to make the amount of chromium hydride oxide into about 3-10 mg / m < ² > because it melt | dissolves in part, and chromium plating of the 1st layer of this invention is performed in this way.

Following the chromium plating which is a 1st layer, the tin or tin-nickel alloy plating of 10-500 mg / m <^{2> which} is a 2nd layer is performed.

In the tin or tin-nickel alloy plating, if there is much chromium hydroxide remaining on the surface after chromium plating, the uniform coating of tin or tin-nickel alloy plating and the adhesion to the chromium surface are inhibited, and a small amount of tin Or since the weldability improvement effect by a tin-nickel alloy plating layer cannot be achieved, it has already demonstrated that it needs to be made small. Even if 3-10 mg / m <^2> exists as chromium hydration oxide amount, the tin or tin-nickel alloy plating of a 2nd layer can be fully performed by the method demonstrated below.

First, as a method of forming the tin plating layer of the second layer, in the known tin plating bath used for the production of the electroplated steel sheet, the tin ion concentration is selected to be about 1/3 or less of the concentration normally used. Doing.

That is, the acid concentration, the type and role of the additive as the tin plating bath are basically the same as the known tin plating baths, such as the first tin sulfate bath and the first tin chloride bath, but the tin ion concentration is lowered by lowering the tin ion concentration. Is about 60% or less.

Thus, by lowering the current efficiency, hydrogen generation on the chromium plating surface becomes active, and the chromium hydroxide surface is peeled off and the chromium plating surface is remarkably activated, so that tin is uniformly coated with a good surface appearance.

For example, in the case of stannous sulphate bath, the tin ion concentration is usually used in a concentration of 20 to 30 g / l or more. However, when applying a bath on chromium plating, the tin concentration can be carried out by setting the tin concentration to 10 g / l or less. As conditions, it is as follows, for example.

1 st tin sulfate: 2 to 10 g / l (as tin ion concentration)

Phenolic Sulfonate (as 60% solution) 10-30 g / l

-나프톨 설폰산 또는 에톡시화

-나프톨 : 2∼8g/lEthoxylation

Naphthol sulfonic acid or ethoxylation

Naphthol: 2 to 8 g / l

pH: 0.5 ~ 1.5

Bath temperature: 30 ~ 60 ℃

Cathode Current Density: 3 ~ 20A / dm ²

Or as an example for stannous chloride,

Stannous chloride: 2 to 10 g / l (as the tin ion concentration)

Sodium fluoride: 20-30 g / l

Sodium Chloride: 40-50g / l

Gelatin: 0.5-3 g / l

pH: 2-3

Bath temperature: 50 ~ 60 ℃

Current density: 3 ~ 50A / dm ²

Particularly important as a method for forming tin plating on the chromium plating of the first layer without removing chromium hydride oxides is that the tin ion concentration is 2 to 10 G / l in an acid spatula plating bath having a pH of 0.5 to 3. will be.

-나프톨 설폰산,

-나프톨등의 첨가제 종류는, 공지의 산성 주석도금욕과 동일하며 특별히 규정하지는 않는다.Acidity adjustment, ethoxylation of sulfuric acid, phenolsulfonic acid, etc.

Naphthol sulfonic acid,

The kind of additives, such as naphthol, is the same as a well-known acidic tin plating bath, and is not specifically prescribed.

As described above, the tin ion concentration is about 1/3 or less of the ordinary tin plating bath, and a uniform and adhesive tin plated layer is obtained at 10 g / l or less.

Below 2 g / l, the precipitation current efficiency becomes extremely bad and is not practical.

If the pH is 3 or less, activation of the chromium surface by the acid is achieved to obtain good tin plating, but even better is pH 2 or less.

Below pH 0.5 it is unreasonable because the surface of chromium is excessively activated or causes some chromium dissolution.

According to the tin plating bath composition and conditions as described above, the tin layer can be easily uniformly coated on the chromium plating, but before the tin plating is applied, the chromium hydroxide formed on the chromium surface immediately after the chromium plating is removed. It goes without saying that the tin plating layer rate can be uniformly coated thereon.

Cathodic electrolysis in an acidic solution is most effective as a condition for removing the chromium hydride oxide on the chromium plating.

That is, in a sulfuric acid, hydrochloric acid, and an aqueous solution of sulfuric acid and hydrochloric acid of pH 0.5-2, it is performed as temperature 30-70 degreeC, cathode current density 2-50 A / dm <^2> , processing time 05.-5 second.

After forming chromium plating as the first layer, a method of removing chromium hydride oxide inevitably formed on the surface of chromium plating and subsequently performing plating to be performed is proposed in Japanese Patent Application No. 33-1455. As described above, there is a method of dipping or anodizing in a hot alkali aqueous solution, but in the production of the surface-treated steel sheet for welding canalization of the present invention, the above-mentioned cathodic electrolysis in the warm acidic aqueous solution is most effective and workability Found good.

In this method, strong acids, such as sulfuric acid and hydrochloric acid, are used, and pH needs to be adjusted to 0.5-2.

Although the pH is less than 0.5, it is effective in terms of removal of chromium hydride oxide, but it is unreasonable because dissolution of metal chromium is likely to occur due to the action of acid.

In addition, when the pH exceeds 2, only time is required for removal.

If the above temperature is less than 30 ° C, it takes time to obtain the removal effect and is not practical.

In addition, when the temperature exceeds 70 ° C, dissolution of metal chromium is likely to occur.

The most effective cathodic electrolytic condition in such a warm acid solution is defined as a current density of ^{2 to} 50 A / dm ² and a time of 0.5 to 5 seconds.

Under both the current density and the time, the removal effect of chromium hydride becomes insufficient under the lower limit condition.

The higher the current density, the more remarkable the effect is, but it is saturated and no more than 50 A / dm ² is required.

In addition, the longer the time is, the greater the effect of removing the chromium hydride oxide, but more than 5 seconds, dissolution of chromium chromium is likely to occur, which is not practical.

In the case where the chromium hydride oxide on the chromium plating is removed under the above conditions, the subsequent tin plating conditions do not need to be specifically selected such as lowering the tin ion concentration. One main bath is used as it is.

For example, as the first tin bath,

Stannous sulfate: 30 g / l (as tin ion concentration)

Phenolic sulfonic acid (as a 60% solution): 30 g / l

나프롤 설폰산 또는 에톡시화

나프톨 : 6g/lEthoxylation

Naprol sulfonic acid or ethoxylation

Naphthol: 6 g / l

Bath temperature: 30 ~ 60 ℃

Cathode Current Density: ² ~ 30A / dm ²

As the first tin chloride bath,

Tin Tin Chloride: 30g / l

Sodium fluoride: 30 g / l

Sodium Chloride: 50g / l

Gelatin: 3 g / l

Bath temperature: 50 ~ 60 ℃

Current density: ^{2 to} 50 A / dm ^2, etc. are used.

Next, when forming a nickel nickel alloy as a 2nd layer, a well-known pyrroline acid salt system, a chloride system, a fluoride system, a tin nickel alloy plating bath is used, In this case, chromium is used before plating. It is not necessary to remove the hydroxide oxide.

For example, as a phylloline salt plating bath,

Stannous chloride: 2 to 40 g / l (as the tin ion concentration)

Nickel chloride: 4 to 20 g / l (as nickel ion concentration)

Glysan: 10-30 g / l

Potassium Pyrrolate: 80 ~ 200g / l

pH: 8-10

Bath temperature: 40 ~ 60 ℃

Current density: 1 ~ 30A / dm ²

In the alkaline tin / nickel alloy plating bath having a pH of 8 to 10 as described above, tin / nickel alloy plating having a nickel content of 20 to 60 wt% is obtained by setting the tin ion / nickel ion concentration ratio to 0.1 to 3.

If the concentration of tin ions and nickel ions is lower than the lower limit, the precipitation current efficiency is extremely lowered. If the concentration is higher than the upper limit, the loss of tin and nickel contained in the plating liquid is large, which is not practical.

As the chloride plating bath,

Stannous chloride: 2 to 70 g / l (as the tin ion concentration)

Nickel chloride: 4 to 80 g / l (as nickel ion concentration)

Ethylene Glycol: 30-100g / l

Hydrochloric acid (37%): 20 to 60 g / l

pH: 0.5 ~ 3

Bath temperature: 30 ~ 60 ℃

Current density: 1 ~ 30A / dm ²

In the acidic tin / nickel alloy plating bath having a pH of 0.5 to 3 as described above, tin / nickel alloy plating having a nickel content of 20 to 60 wt% is obtained by setting the tin ion / nickel ion concentration ratio to 0.1 to 0.8.

As in the case of the alkali bath, below the lower limit of the tin ion and nickel ion concentrations, the precipitation current efficiency is extremely lowered. If the concentration exceeds the upper limit concentration, the loss of tin and nickel contained in the plating liquid becomes large and practical. no.

In the alkali bath and the acid bath, the pH adjuster and the additive are the same as the known baths, and are not particularly specified.

According to the composition and the conditions of the bath described above, tin-nickel alloy plating having a nickel content of 20 to 60% by weight can be obtained.

The tin-nickel alloy plating composition deviating from 20 to 60% by weight as a nickel content can also be obtained by selecting the composition electrolytic conditions of the bath, but the tin ions of the known pyrroline salt baths and chloride baths listed first as examples. The nickel content which is stably obtained by changing the nickel ion concentration ratio is generally 20 to 60% by weight, and the tin-nickel alloy plating layer which is the second layer of the present invention can be easily carried out.

As the chromium hydroxide oxide that is the third layer, a conventional chromate treatment is used.

For example, it is formed by cathodic electrolysis in aqueous solution, such as chromic acid and dichromate (sodium dichromate, kali dichromate, ammonium dichromate).

In addition, in the above bath, in order to improve the precipitation efficiency of chromium hydride oxide, it is also possible to add a small amount of auxiliary agent commonly used in chromium plating such as sulfuric acid and fluoride, but in this case, metal chromium is also easily precipitated and weldability It is necessary to prevent the precipitation of the metal chromium by selecting conditions such as the addition amount and the current density to be lowered because of the adverse effect.

농도 5∼30g/l, 온도 30∼70℃, 음극 전류밀도 1∼20A/dm², 전기량 1∼40클롱/dm²으로 처리된다.If chromic acid or dichromate is used and no supplements are added

Concentration is processed in 5~30g / l, temperature 30~70 ℃, cathode current density 1~20A / dm ^2, the stored electricity quantity from 1 to 40 Klong / dm ^2.

When chromic acid is used and an auxiliary agent is added, the CrO ₃ concentration is 10 to 50 g / l, the auxiliary agent is 0.2 to 1% by weight with respect to the chromic acid concentration, the temperature is 30 to 60 ° C, the cathode current density is 1 to 10 A / dm ² , and the amount of electricity is 1 to Treated as 20c / dm ² .

As described above, the surface-treated steel sheet for welding canalization of the present invention has much better weldability than the conventional electrolytic chromic acid treated steel sheet, but is superior to weldability and characteristics thereof, that is, corrosion resistance, coating performance, and surface tint. In addition, it can be sufficiently used for steel caps, DRD pipes (molded pipes by the two-draw method), cement side seam, etc., which are applications other than welded pipes.

Hereinafter, the present invention will be described in detail with reference to the following Examples.

EXAMPLE

Degreasing (NaOH: 70g / l, temperature 80 ℃, current density: 5A / dm ² , time: 5 seconds) by conventional method, pickling (H ₂ SO ₄ : 70g / l, temperature: 25 ℃, soaking for 5 seconds) ) Using a steel sheet (thickness: 0.22 mm).

Formation of the first layer (metal chromium), removal of the chromium hydride oxide, formation of the second layer (tin or tin-nickel alloy) and the third layer (chromium hydride oxide) are carried out under the treatment conditions shown in the first table. The second table shows the results of the characteristic evaluation.

[Table 1]

Example Processing Conditions of the Invention

(Note 1) In Comparative Example 3, the surface of the steel sheet was first tin plated (the condition is indicated in the second layer column), and the electrolytic chromic acid treatment (the condition is indicated in the first layer column) was applied thereon.

[Table 2]

Example characteristic evaluation result of this invention

(Note 1) In Comparative Example 3, the first layer near the surface of the steel sheet is made of tin and the second layer thereon is made of metal chromium.

Examples 1 and 2 formed tin plating which is 2nd layer, without removing chromium hydration oxide after the chromium plating which is a 1st layer, and tin ion concentration used the bath which is about 1/3 or less of a normal bath. In Examples 3 and 4, after the chromium hydride oxide was removed by cathodic electrolysis in an warm acidic aqueous solution, tin plating was applied in a normal bath. Examples 5, 6, and 7 are those in which tin-nickel alloy plating is formed as the second layer, and thus nickel can be contained in this manner, and exhibits good characteristics, and in any of the examples, it is much better than Comparative Example 1, which is a conventional electrolytic chromic acid-treated steel sheet. Excellent weldability is shown.

In Comparative Example 2, there is no metal chromium which is the first layer. The weldability is much inferior to any of Examples in which the first layer has metal chromium. In Comparative Example 3, the film composition order was reversed, the first layer was tin plated, and the second layer was metal chromium. The weldability is much worse than that of the embodiment, and it can be well understood as a feature of the present invention that the first layer must be made of metal chromium and the second layer must be tin.

The test method of the characteristic evaluation shown in Table 2 is as follows.

(1) weldability test

The weldability is expressed by the magnitude of the appropriate welding current range obtained as the difference between the lower current limit required for uniform nugget formation and sufficient welding strength and the upper current limit at which a portion of the steel sheet is dissolved. The larger the range, the better the weldability. This proper welding current range correlates well with the contact electric resistance value when two sheets of steel sheets for welding cans are superimposed (for example, Japan Steel Association's 106th Lecture Competition, Fla. No. 507, 1983 13, 69 The lower the contact electrical resistance, the larger the proper welding current range. Thus, this contact electrical resistance measurement was performed as a weldability test of the surface-treated steel sheet for weld canning of the present invention. This contact electrical resistance value was measured by the method described below. A sample plate (20 mm × 100 mm) overlapped with two sheets of copper electrodes (diameter: 65 mm; thickness 2 mm) of two copper electrodes replaced to contact each one of the circular scanning points was sandwiched between the electrodes. Pressurized by load 5A flowed a DC current between two disk electrodes, rotated at a circumferential speed of 5m / min, and moved the sample plate to measure the voltage between the electrodes to obtain a contact electric resistance value (unit: milo). In addition, the sample plate continued the measurement after heat-processing for 20 minutes at 210 degreeC.

(2) Corrosion resistance test after painting

The sample was coated with 60 mg / dm ² of epoxy-femol inner surface paint, and sintered at 210 ° C. for 12 minutes, and then made a “+” shape of a scratch from the coated surface to the steel sheet with a sharp razor blade, which was then 1.5% citric acid-1,5 After immersing in a corrosion solution of% salt and elapsed at 50 ° C. for 7 days, the coating film near the scratch was peeled off with a cellophane tape, and the corrosion state including the corrosion width was evaluated by the following 5-step method.

5: very good 4: good

3: slightly bad 2: bad

1: very poor

(3) Paint adhesion test

After coating, the sample sintered and painted in the same manner as the corrosion resistance test was made by drilling a disc with a diameter of 80 mm and drawing into a cup with a draw ratio of 2, and peeling the coating film of the outer side wall of the cup with a cellophane tape. It evaluated by the step method.

5: no peeling 4: slightly peeling

3: less peeling 2: almost peeling

1: front peeling

Claims (2)

30 to 300 mg / m ² chromium plating layer per side on the surface of the steel plate, 10 to 500 mg / m ² tin plating layer per side on the chromium plating layer or tin and nickel alloy plating layer having 20 to 60 wt% nickel content, A surface-treated steel sheet for weld can manufacturing, wherein a chromium hydroxide oxide layer of ^{2 to} 18 mg / m ² per side is formed thereon in terms of chromium. After chromium plating at 30 to 300 mg / m2 per single side on the surface of the steel sheet, sulfuric acid, hydrochloric acid, and aqueous solutions of sulfuric acid and hydrochloric acid at pH 0.5-2: 30-70 DEG C, cathode current density: 0.5-A 5 seconds of treatment removes the remaining chromium hydride on the surface of chromium plating, followed by tin plating of 10 to 500 mg / m 2 per side or tin and nickel alloy plating of 20 to 60 wt% nickel. A method for producing a surface-treated steel sheet for welding canning, characterized in that to form 2-18 mg / m 2 chromium hydride oxide in chromium conversion. After chromium plating of 30 to 300 mg / m2 per single side on the surface of the steel sheet, 10 to 500 mg / m2 tin plating was applied using an acidic tin plating bath having a pH of 0.5 to 3 containing tin ions concentration of 2 to 10 g / l. Alkali tin / nickel alloy plating bath or tin ion concentration of pH 8 to 10 with tin ion concentration of 2 to 40 g / l and tin ion / nickel ion concentration of 0.1 to 3 containing nickel ion concentration of 4 to 20 g / l. Nickel content of 10-500mh / m2 using an acidic tin / nickel alloy plating bath with a pH of 0.5 to 3 with a tin ion / nickel ion concentration ratio of 0.1 to 0.8 containing ˜70 g / l and a nickel ion concentration of 4 to 80 g / l 20 to 60% by weight tin-nickel alloy plating, and further, 2 to 18 mg / m2 of chromium hydrate oxide is formed in chromium conversion.