JPH0565698A - Production of electrolytically chromated steel sheet excellent in corrosion resistance and weldability - Google Patents

Abstract

PURPOSE:To produce an electrolytically chromated steel sheet having superior adhesive strength and external appearance of plating, inhibiting the formation of tin sludge, and excellent in corrosion resistance and weldability. CONSTITUTION:A first layer of metallic chromium of 30 to 300mg/m<2> is formed on a steel sheet. After water washing, the steel sheet is immediately subjected to cathode electrolytic treatment in an aqueous solution of the acid conc. at 120g/l expressed in terms of sulfuric acid containing 5 to 50g/l chromium sulfate and 3 to 15g/l tin ions at a current density not higher than 50 to 150A/dm<2>, by which a second layer consisting of tin in the amount of [(1000/X)+50 to (30000/X)+50]mg/m<2> (where X means the amount of metallic chromium in the first layer) expressed in terms of metallic tin and chromium oxide in the amount of 2 to 30mg/m<2> expressed in terms of chromium. Further, a metallic chromium layer of 3 to 30mg/m<2> and a chromate film consisting of hydrated oxide of 1 to 30mg/m<2> are formed on the second layer. Moreover, a nonionic surfactant in which oxyethylene chains are added to naphthyl groups is incorporated into the above-mentioned aqueous solution by 1 to 8g/l.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to a first steel plate on the surface of a steel plate.
An electrolytic chromate-treated steel sheet excellent in corrosion resistance and weldability, in which a second layer made of metallic tin and chromium oxide is formed on a metallic chromium layer as a layer, or the second layer
The present invention relates to a method for producing an electrolytic chromate-treated steel sheet, which has a chromate coating composed of metallic chromium and hydrated chromium oxide formed on the surface of a layer and is excellent in corrosion resistance and weldability.

[0002]

2. Description of the Related Art An electrolytic chromate-treated steel sheet having a coating formed of a metal chromium layer as a lower layer and a chromium hydrated oxide layer mainly containing chromium oxide as an upper layer on the surface of a steel sheet is a tin plate. Since it is cheaper than, it is used in a wide range of fields as a material for cans such as beverage cans, pail cans, 18 liter cans, and oil cans. Conventionally, a can material using this type of steel sheet has been practically used mainly as a two-piece can made by drawing and an adhesive can (3 piece can) using an organic resin or special cement. The usage rate is very small. The reason is that the electrolytic chromate treated steel sheet has extremely poor weldability. The cause is as follows. That is, because of the non-conductivity and non-heat transfer properties of the metal chrome layer as the lower layer and the chromium hydrated oxide layer as the upper layer which form the plating layer, the heat generation form of the heat generated by the welding current becomes non-uniform, This is because the steel locally generates heat and welding defects such as dust and blowholes are likely to occur.

For this reason, conventionally, in the case of intentionally welding an ordinary electrolytic chromate-treated steel sheet, a complicated method of polishing and removing the chromate-treated film to be the welded portion and then welding was adopted. However, in recent years, the demand for welded cans with high strength and reliability is increasing, so improvement in the weldability of electrolytic chromate-treated steel sheets is required, and the development of electrolytic chromate-treated steel sheets that can be welded without polishing removal of the coating film is desired. It is rare.

As one of the conventional techniques aimed at improving the weldability of electrolytic chromate-treated steel sheets, a metal chromium layer is typified by JP-B-63-35718 and JP-A-60-262975. There is a coating of tin to improve weldability. However, in these prior arts, in order to coat tin on the metal chromium layer, a special pretreatment or tin plating is performed, so that the metal chromium that is the lower layer of tin lacks uniformity and tends to have poor corrosion resistance. Furthermore, it was an essential condition to perform chromate treatment on the tin layer. This decrease in corrosion resistance can be compensated by adding a large amount of tin plating, but not only against the idea of developing a cheap material as a development goal, but also for the thread-like rust resistance, There was a problem that it was not effective and, conversely, filiform rust was likely to occur.

Therefore, the inventors of the present invention have conducted extensive research to solve these problems, and have already shown in Japanese Patent Application No. 1-104258, "Electrolytic chromate treated steel sheet excellent in corrosion resistance and weldability and its manufacturing method". As described above, the invention of a novel material and a manufacturing method thereof has been reached.

[0006]

However, as in the above-mentioned Japanese Patent Application No. 1-104258, the plating layer as the second layer made of tin and chromium oxide is formed on the surface of the metal chromium layer as the first layer. In the production of a new material having the above-mentioned structure, there is a problem that good adhesion of a plating layer made of tin and chromium oxide on a metal chromium layer, or good appearance without unevenness cannot be obtained with good stability. is there. In addition, in a plating bath for plating such tin and chromium oxide, tin sludge (tin oxide precipitate) is rapidly generated during plating electrolysis, resulting in accelerated bath deterioration and There is also the problem of impairing stable operation.

Since the hydrated chromium oxide is always present on the surface of the metallic chrome plating layer formed by electrochromic plating, when different metal plating is further applied after electrochromic plating, this hydrated chromium oxide is used. It is known that a dissimilar metal plating layer having good adhesion and good appearance cannot be obtained due to the presence of a substance. Therefore, for example, when performing tin plating on the surface of the metal chromium plating layer,
As disclosed in 63-35718 and JP-A-61-130500, the tin content (tin concentration) in the tin plating solution.
To lower the normal concentration or increase the acidity to reduce the electrolytic efficiency of tin and perform electrotin plating, and as a result, a large amount of hydrogen gas is generated on the chromium plating surface during tin plating. Hydrogen gas removes hydrated chromium oxides on the surface of metallic chromium and activates the surface, and at the same time tin plating is performed, and special treatment such as obtaining a tin plating film with excellent adhesion is required. is there.

Also in the production of the electrolytic chromate-treated steel sheet of the present invention, when the second layer plating on metal chromium is carried out, the same idea as in the tin plating method on metal chromium of the prior art similar to the above is used. A large amount of hydrogen gas may be generated at the same time as plating. However, although such a known technical idea certainly improves the plating adhesion of the second layer, it is not possible to stably obtain a surface having a uniform appearance and a good appearance.

Therefore, an object of the present invention is to produce an adhesive layer in the production of an electrolytic chromate-treated steel sheet having a plating layer made of tin and chromium oxide on the surface of a metal chromium plating layer, which is excellent in corrosion resistance and weldability. Good and
A method capable of obtaining a plating layer composed of tin and chromium oxide having a good appearance without unevenness, and at the same time suppressing the formation of tin sludge (tin oxide precipitate) in a plating bath for plating of tin and chromium oxide To provide.

[0010]

In view of the above-mentioned problems, the present inventors have formed a metal chromium layer as the first layer and a plating layer made of tin and chromium oxide as the second layer on the surface of the steel sheet. In manufacturing the electrolytic chromate-treated steel sheet, the inventors conducted extensive studies on the cause of poor adhesion or unevenness of the second layer plating and the cause of tin sludge formation in the second layer plating bath. As a result, the following findings were obtained. The poor adhesion results from the fact that the chromium oxide on the metallic chromium is not sufficiently removed, and can be improved by generating a large amount of hydrogen gas at the same time as the second layer plating.
However, the unevenness is caused by the generation of this hydrogen gas,
That is, the desorption of hydrogen gas from the surface of the treated steel sheet is involved, and the unevenness cannot be resolved unless the stirring of the interface of the treated steel sheet is promoted and the desorption of the generated hydrogen gas is accelerated. As with ordinary tin plating, tin sludge (tin oxide precipitate) is generated by liquid phase oxidation by dissolved oxygen in the tin and chromium mixed plating bath or by oxygen generated on the plating electrode (anode). In addition, direct oxidation on the plated electrode is not a little involved, and in the present treatment method, chromium present at the same time as tin ions is involved in the oxidation of tin.

The present invention has been made on the basis of the above-mentioned findings, and a second layer of metallic tin and chromium oxide is formed on the surface of a metallic chromium layer as a first layer on a steel sheet.
An electrolytic chromate treated steel sheet having a layer formed thereon and excellent in corrosion resistance and weldability, or further, on the surface of the second layer,
Regarding an electrolytic chromate-treated steel sheet excellent in corrosion resistance and weldability in which a chromate coating composed of a metal chromium layer and a hydrated chromium oxide is formed, improvement in adhesion of the second layer plating layer, prevention of unevenness, and second It is an invention of a novel manufacturing method that simultaneously enables sludge suppression in a plating bath for forming a layer.

In a first invention, a steel plate is electrochromized to form 30 to 300 m on at least one surface of the steel plate.
forming a first layer consisting of an amount of metallic chromium deposited in the range of g / m ² , then washing the steel sheet on which the first layer has been formed with water, and then immediately after washing with water, forming the first layer Chrome sulfate in the range of 5 to 50 g / l and
3 contains tin (Sn) ions within the range of 15 g / l, in an aqueous solution of an acid concentration in the range of from 45 to 120 g / l sulfuric acid in terms of, 50A / dm ² Ultra 150A / dm ² or less in the range By applying cathodic electrolysis treatment according to the current density inside, (1000 / X) +50 to (30000 / X) +50 mg in terms of metallic tin on the surface of the first layer.
/ m ² (where X is the amount of metallic chromium deposited in the first layer) within a range of 2 to 2 in terms of tin and chromium in terms of tin and chromium.
By forming the second layer composed of the chromium oxide having an adhesion amount within the range of 30 mg / m ² , deterioration of the plating bath composed of the aqueous solution is suppressed and at the same time, on the surface of the first layer,
It is characterized by forming the second layer having excellent adhesion and a good surface appearance without unevenness. Second
The invention of (1) is characterized in that a chromate film made of a hydrated oxide having an adhesion amount in the range of 1 to 30 mg / m ² is formed on the surface of the second layer. The third invention is
A metal chromium layer having a deposition amount in the range of 3 to 30 mg / m ² is formed on the surface of the second layer, and then a metal chromium layer in the range of 1 to 30 mg / m ² is formed on the surface of the metal chromium layer. It is characterized by forming a chromate film composed of an attached amount of hydrated oxide. A fourth aspect of the invention is characterized in that the aqueous solution contains 1 to 8 g / l of a nonionic surfactant having an oxyethylene chain added to a naphthyl group.

The present invention will be specifically described below. In the present invention, first, the surface of the steel sheet is electroplated with chromium. The steel plate on which electrochromic plating is performed is not particularly limited, but normally a cold rolled cold rolled steel plate may be used.
Further, the pretreatment method before electrochromic plating may be arbitrarily determined according to the surface condition of the steel sheet used, and various treatments may be performed as necessary.

The electrochrome plating method is not limited to a specific treatment method, and a conventionally known chromium plating bath or plating method may be used. That is, mainly one or more of chromic anhydride or chromate,
In addition, a chromium plating solution containing one or more of sulfuric acid, sulfate, and fluoride as an auxiliary agent may be electrolyzed so that a predetermined amount of chromium adheres to the steel plate as a cathode.

The electrolytic current density of the electrochromic plating is not particularly limited, but preferably 70 A / dm ² or more. This is for the following reason. That is, the hydrated chromium oxide on the surface layer of the chromium-plated steel sheet subjected to the second layer plating treatment in order to perform uniform plating (second layer plating without unevenness) with good adhesion of the plated layer as the second layer. It's best to keep the amount of things as small as possible. For that purpose, it is more effective if the amount of hydrated chromium oxides unavoidably present at the time of completion of chromium plating can be suppressed to the minimum level. In the known chrome plating technology, various methods for suppressing the amount of hydrated chrome oxide are known, but the hydration that is unavoidable also exists by the method of performing electrochrome plating at a current density of 70 A / dm ² or more. The amount of chromium oxide can be reduced to the lowest level. If the treatment is performed at a high current density of 70 A / dm ² or more, the additional effect of shortening the chromium plating equipment can be expected.

The form of metallic chromium in the electrochromic plating is not specified at all, and includes granular metallic chromium and plate metallic chromium. Therefore, it does not matter if the granular metal chromium is intentionally formed by performing the reverse electrolysis treatment using the treated steel plate as an anode immediately before or during the electrochromic plating treatment.

The adhesion amount of metallic chromium is 30 to 300 mg / m ²
Should be limited to within the range. Adhesion amount of metallic chromium is 30 mg
If it is less than / m ² , the effect of suppressing the alloying of tin, which will be described later, does not sufficiently appear, and moreover, a large amount of metallic tin that is present to impart weldability is required, and depending on the paint baking conditions, the thread-like rust resistance decreases. There is a problem in corrosion resistance. on the other hand,
Even if the amount of deposited metallic chromium exceeds 300 mg / m ² , the effect of suppressing alloying of tin is not improved and the cost is increased.

In this way, after the electrochromic plating is performed, a sufficient washing treatment with water is carried out, and the surface is not dried, and then chromium sulfate in the range of 5 to 50 g / l and 3 to 15 g / l are continuously added. In an aqueous solution containing tin (Sn) ions in the range of l, converted to sulfuric acid in the range of 45 to 120 g / l, a cathode is applied to the steel sheet at a current density in the range of more than 50 A / dm ^{2 and not} more than 150 A / dm ^2. An electrolytic treatment is performed to perform second layer plating of a predetermined amount of tin and a predetermined amount of chromium oxide. Washing with water after chrome plating should be thoroughly performed to eliminate unevenness on the surface of metal chrome. The temperature of the wash water is 50 ° C.
The following is good, and preferably 30 ° C or lower. This is because the surface temperature of the electrochromic plating increases due to the Joule heat of the steel sheet during electroplating or the temperature of washing water, and it becomes difficult to remove the hydrated chromium oxide on the surface layer during the subsequent second layer plating. It is effective in not changing its structure in the direction.

For tin plating containing chromium oxide on chromium, it is effective to generate hydrogen gas during plating and simultaneously remove the hydrated oxide by this gas and perform plating at the same time. There are problems that the surface appearance is unstable and that the second layer plating solution deteriorates due to sludge formation. The present inventors, as a result of continuing studies on these problem solving methods, prevent the deterioration of the second layer plating solution, and
At the same time, we have newly found a second layer plating method that can stably obtain a good plating appearance.

The chromium sulfate content (chromium sulfate concentration) in the second layer plating solution of the present invention is in the range of 5 to 50 g / l. When the content of chromium sulfate is less than 5 g / l, no chromium oxide is formed and tin is also precipitated in powder form. On the other hand, when the content of chromium sulfate exceeds 50 g / l, the surface color tone of the steel sheet becomes slightly pale and there is no problem in performance, but it is not economical.

The tin ion content (tin ion concentration) in the second layer plating solution of the present invention is 3 to 15 g / l, preferably
It should be in the range of 3 to 8 g / l. If the tin ion content is less than 3 g / l, the electrolysis efficiency of tin is extremely lowered, which is inefficient, and at the same time, the tin ion concentration control becomes difficult,
Not preferable. On the other hand, when the tin ion content exceeds 15 g / l, the precipitated tin becomes powdery, and the adhesion and the appearance are extremely deteriorated. The supply of tin ions used is not limited to a specific tin compound, and stannous oxide, tin chloride, tin sulfate, tin borofluoride, or other tin compounds can be used.

The acid concentration in the tin plating solution of the present invention should be 45 g / l or more, preferably 60 g / l or more in terms of sulfuric acid. If the acid concentration is less than 45 g / l in terms of sulfuric acid, the sludge generation rate in the second layer plating solution will increase, the plating solution will deteriorate faster, and the continuous processability of the second layer plating will deteriorate and the processing cost will increase at the same time. .. On the other hand, the acid concentration is 45 in terms of sulfuric acid.
Above g / l, the generation of sludge is suppressed and a continuous and stable second layer plating process is possible. Sludge is white fine particles in which tin ions (Sn ²⁺ ) in the plating solution are oxidized and precipitated as (Sn ⁴⁺ ) tin oxide. When a large amount of this is present in the plating solution, it sometimes adheres to the surface of the steel plate, causing a flaw on the plating surface or an arc spot defect in the electric power feeding portion. In particular, it was found that chromium ions due to the addition of chromium sulfate are mixed in the second layer plating solution of the present invention, and the chromium ions have some action to promote sludge formation. Therefore, in the case of the chromium oxide-containing tin plating treatment on the metal chromium layer, it is important to suppress the generation of sludge during the plating treatment while performing the plating with good adhesion and excellent appearance. When the acid concentration is 45 g / l or more in terms of sulfuric acid as in the present invention, sludge formation is suppressed, but this is because the solubility of tin oxide is increased, and it tends to be present in the tin plating solution as tin ions. It is thought to be because. The upper limit of the acid concentration is 120 g / l. If the acid concentration becomes too high, it is expected that the corrosiveness will increase and the deterioration of the plating equipment will be accelerated.

The cathode current density of the second layer plating is 50 A / dm ²
It should be a super-150A / dm ² or less. Current density is 50 A / dm ²
Below, the amount of hydrogen gas generated per unit time is small,
Stirring of the steel sheet surface due to the generated hydrogen gas becomes insufficient, and the release of hydrogen gas from the steel sheet surface is delayed, and at the same time, the removal of hydrated chromium oxide becomes insufficient, resulting in partial poor tin plating adhesion and partial The unevenness of the plating occurs due to the difference in the amount of the tin plating deposited, and the second layer plating having a good appearance cannot be stably obtained. By treating with a current density of more than 50 A / dm ² , the above problems are solved and a good appearance is obtained. On the other hand, if the current density exceeds 150 A / dm ² ,
The amount of hydrogen gas generated is too large to prevent the electrodeposition of tin.

The temperature of the plating bath for the second layer is preferably set within the range of 30 to 50 ° C.

The amount of tin deposited during the second layer plating of the present invention is
In terms of metallic tin, (1000 / X) + 50mg / m ² to (30000 / X) +50
It is within the range of mg / m ² . The amount of tin deposited is (1
If it is less than 000 / X) +50 mg / m ² , an alloy of metallic tin and steel is formed by the heat at the time of baking the paint, and as a result, metallic tin is reduced and the weldability becomes insufficient. On the other hand, when the amount of deposited tin exceeds (30000 / X) + 50 mg / m ² in terms of metallic tin,
Metallic tin remains unnecessarily, which is economically disadvantageous. For this reason, the amount of tin deposited during the second layer plating is limited. Also, the amount of chromium oxide deposited in the second layer should be within the range of 1 to 30 mg / m ^{2 in} terms of chromium. If the amount of chromium oxide adhered is less than 1 mg / m ^{2 in} terms of chromium, the corrosion resistance decreases. On the other hand, if the amount of deposited chromium oxide exceeds 30 mg / m ^{2 in} terms of chromium, the weldability will deteriorate.

In order to further improve the corrosion resistance of the electrolytic chromate-treated steel sheet obtained by the above-mentioned method after coating, 1 to 30 mg / m ² of hydrated chromium oxide is formed on the surface of the second layer. A chromate film may be formed. Alternatively, a known chromate treatment is further applied to the surface of the second layer to form 3 to 30 mg / m ² of metallic chromium, and a chromate coating consisting of 1 to 30 mg / m ² of hydrated chromium oxide is further formed thereon. May be formed. Further, the following processing may be performed for the same purpose. That is, from 0.2
Aqueous solution containing 5.0g / l hexavalent chromium and / or 0.3
To 10 g / l of polyacrylic acid, an aqueous solution containing a copolymer of acrylonitrile and itaconic acid, the first layer and the second layer
It is a method of immersing a steel sheet on which a layer is formed and then drying the aqueous solution attached to the steel sheet. The reason why the hexavalent chromium concentration is limited to the above range is that if it is less than 0.2 g / l, the effect on the corrosion resistance is small, and if it exceeds 5.0 g / l, the coating adhesion becomes poor. The reason for limiting the content (concentration) of the water-soluble resin (polyacrylic acid, an aqueous solution containing a copolymer of acrylonitrile and itaconic acid) to the above range is that the desired effect is obtained when the content is less than 0.3 g / l. If not, on the other hand, if it exceeds 10 g / l, the effect is saturated and it is not economical.

Further, in the present invention, in order to obtain a chromium oxide-containing tin plating layer on glossy metallic chromium, an naphthyl group-containing oxyethylene chain ([CH ₂ CH ₂ It is preferable that the nonionic surfactant to which O −] _n ) is added be contained in an amount of 1 to 8 g / l. There are many types of surfactants, but in the present invention, only nonionic surfactants having a structure in which an oxyethylene chain is added to a naphthyl group are effective and have a glossy and even appearance. Stable tin plating is obtained. The cause is unclear, but an ionic surfactant having a structure in which an oxyethylene chain is added to the naphthyl group and having a structure in which the naphthyl group is sulfonated provides stable tin plating with a good appearance. Absent. Furthermore, the content of surfactants according to the invention should be from 1 to 8 g / l. When the content of the surfactant is less than 1 g / l, the effect of the brightening agent does not appear, and bright tin plating cannot be obtained. On the other hand, if the content exceeds 8 g / l, the tin plating electrolysis efficiency decreases sharply, which is economically disadvantageous.

[0028]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. [Example 1] A cold-rolled steel sheet having a thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, then with 175 g / l chromic anhydride, and with 5 g / l sodium silicofluoride and 1 g
In a known chromium plating solution containing 1 / l sodium sulfate, the steel sheet was subjected to cathodic electrolysis treatment at a current density of 100 A / dm ² , and the first layer of 100 mg / m ² metallic chromium was applied to the surface of the steel sheet. Formed on. After that, 20g / l chromium sulfate and 8g / l
1 g of stannous sulfate was added to the steel sheet in a 60 g / l sulfuric acid solution.
Cathodic electrolysis is performed under the conditions of 45 ° C and 60 A / dm ² , and 150 m
A second layer consisting of g / m ² tin and 6 mg / m ² chromium oxide was formed to prepare a steel sheet specimen within the scope of the invention.

Example 2 A cold-rolled steel sheet having a plate thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, and then with 175 g / l of chromic anhydride, 5 g / l of a caustic agent. In a well-known chromium plating solution to which sodium chloride and 1 g / l sodium sulfate were added, the steel plate was subjected to cathodic electrolysis treatment at a current density of 50 A / dm ² to obtain 80 mg / m ² of metallic chromium
A layer was formed on the surface of the steel sheet. Then, in a 60 g / l sulfuric acid solution containing 15 g / l of chromium sulfate, 8 g / l of stannous sulfate and 2 g / l of 6-ethoxylate α-naphthol, the steel sheet was treated at 45 ° C and 80 A / dm ² A cathodic electrolysis treatment was performed under the conditions to form a second layer consisting of 130 mg / m ² tin and 5 mg / m ² chromium oxide on the first layer. Then, in this way, the steel plate on which the first layer and the second layer were formed, 20 g /
soak for 1 second in an aqueous solution of sodium dichromate
The aqueous solution adhering to the steel sheet is dried to 3 mg / m on the second layer.
^A third layer of hydrated chromium oxide of No. 2 was formed and a steel plate specimen within the scope of this invention was prepared.

Example 3 A cold-rolled steel sheet having a plate thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, and then with 175 g / l of chromic anhydride, 5 g / l of caustic fluoride. In a well-known chrome plating solution to which sodium chloride and 1 g / l sodium sulfate were added, the steel plate was subjected to cathodic electrolysis treatment at a current density of 30 A / dm ² , and 120 mg / m ² of metallic chromium
A layer was formed on the surface of the steel sheet. Then, in a 50 g / l sulfuric acid solution containing 15 g / l of chromium sulfate, 10 g / l of stannous oxide, and 5 g / l of 6-ethoxylate α-naphthol, the steel sheet was treated at 40 ° C. and 100 A / dm ² A cathodic electrolysis treatment was performed under the conditions to form a second layer consisting of 500 mg / m ² tin and 3 mg / m ² chromium oxide on the first layer. Then, in this way, the steel sheet on which the first layer and the second layer are formed is used.
40 ° C, 5 A / dm in g / l sodium dichromate solution
Subjected to cathodic electrolysis treatment with ² conditions, 6 mg on the second layer
A third layer of hydrated chromium oxide of / m ² was formed to prepare a steel plate specimen within the scope of this invention.

Example 4 A cold-rolled steel sheet having a plate thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, and then with 175 g / l of chromic anhydride, 5 g / l of a caustic agent. In a well-known chromium plating solution to which sodium chloride and 1 g / l sodium sulfate were added, the steel sheet was subjected to cathodic electrolysis treatment at a current density of 30 A / dm ² , and then anodic electrolysis at a current density of 1 A / dm ^2. The treatment was followed by a cathodic electrolysis treatment at a current density of 30 A / dm ² to form a 50 mg / m ² protrusive first layer of metallic chromium on the surface of the steel sheet. Then 25 g / l chromium sulphate and 15 g / l stannous sulphate and 3 g / l 6
In a 250 g / l phenolsulfonic acid (50 g / sulfuric acid equivalent) solution containing ethoxylate α-naphthol, apply 40 ° C to the steel plate,
Cathodic electrolysis treatment under the condition of 90A / dm ² gives 300mg / m 2.
^{A second} layer consisting of ² tin and 11 mg / m ² chromium oxide was formed on the first layer. Then, in this way, the steel sheet on which the first layer and the second layer are formed, in an aqueous solution containing 15 g / l of anhydrous chromium and 0.3 g / l of sodium sulfate,
The steel sheet was subjected to cathodic electrolysis under the conditions of 45 ° C and 10 A / dm ² to obtain 5 mg / m ² of metallic chromium on the second layer and its upper layer.
A third layer and a fourth layer of 16 mg / m ² of hydrated chromium oxide were formed and a steel plate specimen within the scope of the present invention was prepared.

Example 5 A cold-rolled steel sheet having a plate thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, and then with 175 g / l of chromic anhydride, 5 g / l of a caustic agent. In a well-known chrome plating solution to which sodium chloride and 1 g / l sodium sulfate were added, the steel plate was subjected to cathodic electrolysis treatment at a current density of 70 A / dm ² and 110 mg / m ² of metallic chromium
A layer was formed on the surface of the steel sheet. Then, in a 45g / l sulfuric acid solution containing 10g / l chromium sulphate and 10g / l stannous sulphate added, the steel sheet was subjected to cathodic electrolysis at 40 ° C and 70A / dm ² to give 170mg / l. the second layer of chromium oxide of tin and 4 mg / m ² of m ² was formed on the first layer. Then, in this way, the steel sheet on which the first layer and the second layer are formed is used.
Immerse in an aqueous solution of g / l chromic anhydride for 1 second and dry the aqueous solution adhering to the steel sheet to form a third layer of ² mg / m ² of hydrated chromium oxide on the second layer. A steel plate specimen within the scope of the invention was prepared.

[Comparative Example 1] A cold-rolled steel sheet having a thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, and then with 175 g / l chromic anhydride, 5 g / l of a caustic fluoride. The first layer of 100 mg / m ² metallic chromium was obtained by subjecting the steel sheet to cathodic electrolysis at a current density of 100 A / dm ² in a known chromium plating solution to which sodium chloride and 1 g / l sodium sulfate were added. Was formed on the surface of the steel sheet. Then, in a 60g / l sulfuric acid solution containing 20g / l chromium sulfate and 40g / l stannous sulfate added, the steel sheet was subjected to cathodic electrolysis treatment at 45 ° C and 70A / dm ² to give 300mg / l. forming a second layer of chromium oxide of tin and 9 mg / m ² of m ^2, and to prepare a specimen of the outside of the steel plate of the present invention.

Comparative Example 2 A cold-rolled steel sheet having a plate thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, and then with 175 g / l of chromic anhydride, 5 g / l of caustic fluoride. In a well-known chromium plating solution to which sodium chloride and 1 g / l sodium sulfate were added, the steel plate was subjected to cathodic electrolysis treatment at a current density of 50 A / dm ² to obtain 80 mg / m ² of metallic chromium
A layer was formed on the surface of the steel sheet. Then, in a 30 g / l sulfuric acid solution containing 15 g / l of chromium sulfate, 12 g / l of stannous sulfate and 2 g / l of 6-ethoxylate α-naphthol, the steel plate was treated at 45 ° C. and 60 A / dm ² . A cathodic electrolysis treatment was performed under the conditions to form a second layer of 200 mg / m ² tin and 5 mg / m ² chromium oxide on the first layer. Then, in this way, the steel sheet on which the first layer and the second layer were formed was 20 g / l.
Dipped in the aqueous solution of sodium dichromate for 1 second to dry the aqueous solution adhering to the steel plate, and 3 mg / m 2 on the second layer.
^A third layer of hydrated chromium oxide of No. 2 was formed to prepare a steel plate specimen outside the scope of the present invention.

Comparative Example 3 A cold-rolled steel sheet having a plate thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, and then with 175 g / l of chromic anhydride, 5 g / l of caustic fluoride. In a well-known chrome plating solution to which sodium chloride and 1 g / l sodium sulfate were added, the steel plate was subjected to cathodic electrolysis treatment at a current density of 30 A / dm ² , and 120 mg / m ² of metallic chromium
A layer was formed on the surface of the steel sheet. Then, in a 60g / l sulfuric acid solution containing 15g / l chromium sulfate and 8g / l stannous oxide added, the steel sheet was subjected to cathodic electrolysis treatment at 45 ° C and 40A / dm ² to obtain 150mg / l. the second layer of chromium oxide of tin and 3 mg / m ² of m ² was formed on the first layer. Then, in this way, the steel sheet on which the first layer and the second layer are formed
The steel sheet was subjected to cathodic electrolysis in an aqueous solution of 20 g / l chromic anhydride and 0.3 g / l sodium sulfate at 40 ° C. and 10 A / dm ² , and 4 mg / m ² on the second layer. A metallic chromium layer and a third layer consisting of 10 mg / m ² of hydrated chromium oxide were formed to prepare a steel plate specimen outside the scope of the present invention.

[Comparative Example 4] A cold-rolled steel sheet having a thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, and then with 175 g / l chromic anhydride, 5 g / l of caustic fluoride. A first layer of 100 mg / m ² of metallic chromium was obtained by subjecting a steel sheet to cathodic electrolysis at a current density of 30 A / dm ² in a known chromium plating solution to which sodium chloride and 1 g / l of sodium sulfate were added. Was formed on the surface of the steel sheet. Then, in a 250g / l phenolsulfonic acid (50g / sulfuric acid equivalent) solution containing 25g / l of chromium sulfate, 10g / l of stannous sulfate and 3g / l of 6-ethoxylate α-naphthol added to the steel sheet. 45 ℃, 160A / d
Cathodic electrolysis was performed under the condition of m ² to form a second layer composed of tin and chromium oxide on the first layer, and a steel sheet specimen outside the scope of the present invention was prepared. At this time, the surface of the second layer had an uneven surface with partial plating.

[Comparative Example 5] A cold-rolled steel sheet having a thickness of 0.22 mm was degreased and pickled under normal conditions, then washed with water, and then with 175 g / l chromic anhydride, 5 g / l of caustic fluoride. In a well-known chromium plating solution to which sodium chloride and 1 g / l sodium sulfate were added, the steel sheet was subjected to cathodic electrolysis treatment at a current density of 70 A / dm ² to obtain 100 mg / m ² of metallic chromium
A layer was formed on the surface of the steel sheet. Then, in a 60g / l sulfuric acid solution containing 10g / l of chromium sulfate, 10g / l of stannous sulfate and 2g / l of 6-ethoxylate-α-naphtholsulfonic acid, the steel sheet was heated at 40 ° C and 60A / dm subjected to cathodic electrolysis treatment with ² conditions, to form a second layer of chromium oxide of tin and 4 mg / m ² of 200 mg / m ² on the first layer. Then
In this way, the steel sheet on which the first and second layers were formed was immersed in an aqueous solution of 20 g / l chromic anhydride and 0.3 g / l sodium sulphate at 40 ° C. and 10 A / dm ² conditions. Was subjected to cathodic electrolysis treatment to form a 4 mg / m ² metallic chromium layer and a 10 mg / m ² hydrated chromium oxide third layer, and a steel plate specimen outside the scope of the present invention was prepared.

Test pieces were cut out from each of the test pieces prepared as described above, and the following evaluations were performed. In addition, the following evaluation was performed on the plating of the second layer after the treatment. The results are shown in Table 1.

[0039]

[Table 1]

(1) Evaluation of Second Layer Plating Adhesion After lightly rubbing the surface of the test piece with a tissue paper, evaluation was made based on whether stains due to plating peeling were observed or not on the tissue paper. ◯: No stain was found on the tissue paper, ×: Soil was found on the tissue paper.

(2) Evaluation of plating appearance Visual judgment was performed. ◯: Good appearance (uniform color tone and no unevenness), ×: uneven appearance is observed.

(3) Stability of Second Layer Plating Solution Under each second layer plating condition, continuous treatment was carried out for 5 hours, and then a certain amount of the second layer plating solution was sampled, and then sludge was filtered and dried. After that, the weight was measured to quantify the sludge concentration in the tin plating solution. ○: Sludge concentration of 0.3 g / l or less, △: Sludge concentration of more than 0.3 to less than 0.5 g / l, ×: Sludge concentration of 0.5 g / l or more.

As is clear from Table 1, Comparative Examples 1-5
In each case, any of the adhesion of plating, the appearance of tin plating, and the stability of the tin plating solution was poor. On the other hand, in each of Examples 1 to 5, the plating adhesion was excellent, the plating appearance was good, and the stability of the tin plating solution was excellent. From the above, according to the manufacturing method of the present invention, in the plating treatment for forming the second layer made of metallic tin and chromium oxide on the metallic chromium layer as the first layer on the surface of the steel plate, It can be seen that a plating layer having excellent adhesion and a good surface appearance without unevenness can be obtained. Furthermore, since it is possible to suppress the formation of tin sludge, it is found that it is useful for preventing the deterioration of the plating bath.

[0044]

As described above, according to the manufacturing method of the present invention, it is possible to obtain an electrolytically treated chromate-treated steel sheet having good plating adhesion and good appearance without unevenness.
Further, the generation of tin sludge in the plating solution containing tin ions is suppressed, and thus the industrially useful effect is brought about.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toyofumi Watanabe 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (4)

[Claims] 1. A steel sheet is electrochromed to form a first layer of deposited chromium on at least one surface of the steel sheet in an amount of 30 to 300 mg / m ² ; The steel sheet on which the first layer has been formed is washed with water, and immediately after washing with water, the steel sheet on which the first layer has been formed is
To 50 to 50 g / l chromium sulphate and 3 to 15 g / l tin (Sn) ion, 45 to 120 in terms of sulfuric acid.
Over 50 A / dm ² in aqueous solutions with acid concentrations in the g / l range.
By performing cathodic electrolysis treatment with a current density within the range of 150 A / dm ² or less, (1000 / X) +50 to (30000 / X) +50 mg / m ² (in terms of metallic tin) on the surface of the first layer ( However, X
Is the amount of chromium metal deposited in the first layer) and forms a second layer consisting of an amount of tin in the range of 2 and 30 mg / m ² of chromium oxide in terms of chromium. By so doing, it is possible to suppress the deterioration of the plating bath made of the aqueous solution and form the second layer on the surface of the first layer, which has excellent adhesion and has a good surface appearance without unevenness. And a method for producing an electrolytic chromate-treated steel sheet having excellent corrosion resistance and weldability. 2. On the surface of said second layer 1 to 30 mg / m ²
The method for producing an electrolytic chromate-treated steel sheet having excellent corrosion resistance and weldability according to claim 1, characterized in that a chromate film made of a hydrated oxide having an adhesion amount within the range is formed. 3. On the surface of said second layer, 3 to 30 mg / m ²
And forming a chromium chrome coating film comprising a hydrated oxide in an amount of 1 to 30 mg / m ² on the surface of the metal chromium layer. The method for producing an electrolytic chromate-treated steel sheet having excellent corrosion resistance and weldability according to claim 1. 4. The aqueous solution contains 1 to 8 g / l of a nonionic surfactant having an oxyethylene chain added to a naphthyl group.
The method for producing an electrolytic chromate-treated steel sheet having excellent corrosion resistance and weldability according to claim 1, 2 or 3, wherein the steel sheet is contained.