JPS629196B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electro-tinned steel sheet with improved corrosion resistance and a method for manufacturing the same. Electrically tinned steel sheets are used for food and beverage containers. This tin-plated steel sheet is degreased and pickled, then tin-plated, and then heated for a short time above the melting point of tin to brighten the tin surface and at the same time
Form a tin alloy. This iron-tin alloy greatly affects corrosion resistance. On the other hand, in recent years, continuous casting materials have been used instead of ingot materials for the base steel of electrically tinned steel sheets due to customer needs or economical reasons. Continuously cast materials do not have a surface rim layer that is similar to pure iron like ingot rimmed steel, but tend to have a uniform composition including the surface layer, and contain many impurity elements added to the surface layer. This is a major obstacle to corrosion resistance. As described above, the corrosion resistance of the alloy layer of a tin-plated steel plate using a continuous casting material without a rim layer is poor, and various troubles may occur. As a method for evaluating the corrosion resistance of tin-plated steel sheets
ATC test is used. ATC test on steel
This shows the coating properties of the Fe-Sn alloy. Tin-plated steel sheets made from continuous casting generally have a higher ATC value and poorer corrosion resistance than those made from rimmed steel. Furthermore, it has poor corrosion resistance in actual citric acid-based foods, often causing problems with corrosion inside the can. The reason for the poor corrosion resistance is not only the coverage of the iron-tin alloy formed when tin is melted, but also the impurities on the surface layer that accelerate corrosion of the steel and cause expansion can or pitting corrosion.The ATC value is It decreases as the amount of iron-tin alloy increases. Compared to rimmed steel, continuous casting materials generally exhibit higher values even with the same amount of iron-tin alloy. Therefore, simply increasing the amount of iron-tin alloy
It is not a measure to improve the ATC value. JP-A-57-108291 describes a method for improving the corrosion resistance of electro-tinned steel sheets using continuous casting materials. In this method, iron plating is applied before tin plating to modify the steel surface layer so that the surface layer is similar to the surface layer of rimmed steel, which is close to pure iron, but the surface layer of rimmed steel is cold rolled, Annealed and temper-rolled tin-plated steel plates are thick at 20 to 40 μm, and in order to improve corrosion resistance to the same level as rimmed steel, iron plating is required to the thickness of the rim layer of rimmed steel. Iron plating to this thickness requires a large amount of electricity in electric iron plating, and also deteriorates the shape of the plate due to electrodeposition stress, which is unfavorable both economically and in terms of quality. In JP-A No. 54-108291, a small amount of iron plating is applied, but if the amount of iron plating is small, the steel on the surface of the base steel cannot be sufficiently covered with iron plating, so continuous It is not possible to modify the surface layer of the cast material that contains impure elements. In this application, in addition to the iron-tin alloy, more than 50% by weight is Cu-
By providing a Cu layer with a Sn alloy and a Ni layer with a Ni-Sn alloy of 50% or more by weight, the above-mentioned drawbacks are overcome and the corrosion resistance of tin-plated steel sheets using continuous casting material is improved. . On the other hand, there is a method for improving the ATC value of electrically tin-plated steel sheets, which was published in Japanese Patent Publication No. 1983-20940. In this invention, one of Ni, Cu and Ni-Sn alloy is applied to the surface of the steel plate.
In this method, a seed is preplated to a thickness of 0.005 to 0.5 μm, heated in a non-oxidizing atmosphere until the entire amount of the preplated metal or alloy permeates and diffuses into the steel sheet, and then tin plating is performed. Since the electric tinning line does not have a heating device for permeating and diffusing the above-mentioned metal or alloy into the steel sheet before tinning, this must be done in the annealing process. However, after annealing, the original sheet for tin-plated steel sheet (tin plate) is generally subjected to temper rolling in order to finish the sheet to a hardness and surface roughness appropriate for the intended use, and further to improve the shape. Cu is deposited on the steel plate surface during temper rolling.
Even if a trace amount of Ni is present, there are drawbacks such as shortening the life of the roll and making it difficult to straighten the shape, resulting in various obstacles to practical use. In this application, in order to avoid Cu and Ni penetration diffusion into the steel, Cu and Ni are then plated with Sn.
In a normal electric tinning line, Sn is alloyed by heating in a reflow process that melts and brightens, and at the same time reacts with the tin layer on exposed steel that is not sufficiently coated with Cu and Ni to form Fe-Sn.
It forms an alloy. Cu and Ni react with Sn in the upper layer to form Cu-Sn alloy and Ni-Sn alloy, and Cu and Ni suppress the reaction with steel. For this reason, Cu-Sn alloys and Ni-Sn alloys alone do not adhere well to the base steel, and when light processing is performed, the intermediate layer of Cu-Sn alloys and Ni-Sn alloys, as well as unalloyed Cu and Ni may peel off. For example, it peels off along with the tin layer on the processed parts of can lids, squeezed cans, etc.
The formation of an Fe-Sn alloy strengthens the adhesion between the tin layer and the base steel. On the other hand, in the case of Special Publication No. 54-20940, before tin plating, Ni, Cu or Ni-Sn alloy is permeated and diffused by heating at a high temperature of about 700℃ in an annealing process, and this diffusion layer acts as a barrier and tin It becomes difficult to form an iron-tin alloy during the reflow process after plating. Furthermore, the pre-plated metal is heated until it disappears, and Cu-Sn alloy or Ni which is effective for corrosion resistance is heated.
-The formation of Sn alloys is difficult to occur, which not only makes it impossible to achieve excellent corrosion resistance, but also tends to cause problems during temper rolling. The present application overcomes the above-mentioned drawbacks and improves the corrosion resistance of continuous casting materials. Next, the present application will be specifically explained. Cu-Sn alloying rate of 50% by weight between steel plate and tin
The above Cu layer has a Cu content of 0.001g/ ^m2 or more, and Ni-
Ni layer with Sn alloying rate of 50% by weight or more is the amount of Ni
0.001g/m2 or ^more , and the amount of Cu in the Cu layer and the amount of Ni in the Ni layer
Mixed in a total amount of 0.2g/ ^m2 or less, and
There is a Fe-Sn alloy layer in the mixed layer of Cu and Ni layers.
It is a tin-plated steel sheet having a layer in which the amount of Sn is mixed in the range of 0.001 to 1.5 g/m ² . Cu--Sn alloy and Cu have an effect on the corrosion resistance of the base steel surface, and the presence of Ni and Ni--Sn alloy further improves the corrosion resistance. Corrosion resistance is improved when the amount of Cu is 0.001g/m2 or ^more , and
Corrosion resistance is further improved when 0.001 g/m ² or more of Ni is present. If the total amount of Ni and Cu is 0.2 g/m ² or more, no further corrosion resistance can be obtained. Cu and Ni
Corrosion resistance is improved by alloying 50% by weight or more with Sn. Fe-Sn alloys are mainly composed of FeSn ₂ , but if this amount is too large, cracks may occur in the alloy layer during processing in the can manufacturing process, and in recent years, tin-plated steel sheets have become thinner. In view of the current progress, the limit is 1.5g/ ^m2 . Also, Fe
- If the Sn alloy is not present on the surface of the steel in terms of tin content of 0.001g/m2 or ^more , the adhesion between the base steel and the tin layer will not be sufficient, making it unsuitable for processing purposes.
The alloy has a suitable Sn content of 0.001 to 1.5 g/m ² . Hereinafter, the method for manufacturing a tin-plated steel sheet of the present invention will be specifically explained. (1) After degreasing and pickling a cold-rolled, annealed, and temper-rolled steel plate, it is plated with copper or nickel at a density of 0.001 to 0.19 g/m ² . As the copper plating bath, a pyrophosphoric acid bath, a sulfuric acid bath, and a hofusing bath are used. Copper plating can be applied by electroplating, and immersion plating is also acceptable. Electroplating is suitable for nickel plating,
As the electric nickel plating bath, any of a nickel sulfate plating bath, a nickel chloride plating bath, a sulfamic acid bath, and a nickel ammonium sulfate bath can be used. After copper plating (or nickel plating), continue with nickel plating (or copper plating). Total amount of Cu and Ni is 0.2
Nickel (or copper) so that g/ ^m2 or less
Perform plating. In the next step, copper plating reacts with tin, causing some or all of the Cu to form a Cu-Sn alloy. Corrosion resistance will not be improved unless the total amount of Cu and Cu-Sn alloy is 0.001g/m2 ^or more, so the amount of copper plating should be 0.001g/m2 or more.
g/m ² or more is required. Ni, Ni-Sn alloy is Ni
It is effective to further improve corrosion resistance when the amount is 0.001 g/m ² or more, but the total amount with the Cu amount is 0.2
If it exceeds g/m ² , it becomes difficult to form an Fe-Sn alloy, so it is suitable that the total amount of copper plating and nickel plating is 0.2 g/m ² or less. Copper plating and nickel plating may be performed in any order. After copper plating and nickel plating, tin plating is continued. The amount of tin plating is determined depending on the application, and the amount of tin plating on tin-plated steel sheets is usually
2.8, 5.6, 8.4 and 11.2g/ ^m2 , but 2.8
g/m ² or less, for example 1 g/m ² or less, can also be applied. As the tinning bath, a sulfuric acid bath, an alkaline bath, a halogen bath, and a borofusating bath can be used. After tin plating, the tin is heated at 150 to 400°C in a reflow process to melt and brighten the tin. As the heating method, electric resistance heating, high frequency heating, and a combination thereof can be used. In an actual continuous line, heating is performed in seconds, so the heating temperature can be controlled based on the maximum temperature reached. This heating causes the formation of Cu--Sn alloy, Ni--Sn alloy and Fe--Sn alloy. By this heating, more than 50% by weight of the plated Cu and Ni is formed into an alloy with Sn, that is, a Cu-Sn alloy, and a Ni
-Since it is necessary to form a Sn alloy,
Heating above 150℃ is required. At the same time Fe-Sn
Alloy formation occurs, but when heated above 400℃ Fe
- 150 to 400℃ as the formation of Sn alloy becomes excessive.
is preferred. If the melting point of tin is 231.9℃ or higher, Cu-Sn
The rate of formation of the alloys, Ni--Sn alloys and Fe--Sn alloys is higher, resulting in higher alloying rates of Cu and Ni. After heating, it is rapidly cooled, subjected to a specified chemical treatment, and then coated with oil. (2) The tin-plated steel sheet of the present invention can also be produced by eutectoid plating of Cu and Ni on a steel sheet instead of plating Cu and Ni in the method (1) above. A pyrophosphoric acid bath can be used as the eutectoid plating bath. The amount of eutectoid plating is Cu amount 0.001g/
^m2 or more, Ni amount is 0.001g/ ^m2 or more, and the total amount is
It is 0.2g/ ^m2 or less. After eutectoid plating, tin plating is performed as in (1) above and heated at 150 to 400°C. After heating, chemical treatment is performed and oil is applied. Hereinafter, the present invention will be specifically explained with reference to Examples. Example 1 A cold-rolled steel plate of 0.22 mm aluminum killed continuous cast steel that had been annealed and temper-rolled was electrolytically degreased in a 7% sodium hydroxide solution, washed with water, electrolyzed in a 3% sulfuric acid solution, and washed with water. Copper plating of 0.03 g/m ² was performed using the copper pyrophosphate plating bath composition and conditions shown below, and after washing with water, nickel plating of 0.01 g/m ² was performed using the following nickel sulfate plating bath composition and conditions. After applying and washing with water, 5.6g/m ² in a tin sulfuric acid plating bath.
Tin plating is carried out and heated for 3 seconds to a maximum temperature of 270°C using the resistance heating method to melt the Sn, as well as Cu-Sn alloy, Ni-Sn alloy and Fe-Sn alloy.
An alloy was formed. This was followed by a chemical treatment in a commonly used sodium dichromate solution, dried and oiled. The produced Cu-Sn alloy has a Cu content of 0.03g/
m ² , Ni-Sn alloy has a Ni content of 0.01 g/m ² and Cu,
Both Ni and Sn formed an alloy. The Sn content of the Fe-Sn alloy was 0.8 g/m ² . X-ray diffraction results show that Cu-Sn alloy is Cu ₆ Sn ₅ and Ni-Sn alloy is Ni ₃ Sn ₄
It was hot. Copper plating bath composition and processing conditions Copper pyrophosphate 80g / Potassium pyrophosphate 350g / Ammonia water 3c.c. / Processing conditions Current density 2A/dm ² Processing electricity amount 0.8C/dm ² Bath temperature 55℃ Nickel metal Composition of bath and treatment conditions Composition of nickel sulfate 200g / Boric acid 10g / Treatment conditions Current density 1A/dm ² Processing electricity amount 0.4C/dm ² Bath temperature 45°C Example 2 A cold-rolled steel sheet similar to Example 1 was After pretreatment, the same nickel plating bath as in Example 1 was used at a current density of 1 A/dm ² and a processing amount of electricity of 1 C/dm ^{2 .}
After applying nickel plating of 0.025 g/m ² and washing with water, using the same copper plating bath as in Example 1, the current density was 0.1 A/dm ² and the amount of electricity processed was 0.1 C/dm ^2.
After applying 0.004g/ ^m2 copper plating and washing with water,
Tin plating with a concentration of 5.6 g/m ² is carried out in a sulfuric acid tin plating bath and heated for 3 seconds to a maximum temperature of 240°C using the resistance heating method to melt the Sn and melt the Cu-Sn.
alloys, Ni-Sn alloy and Fe-Sn alloy were formed. This was followed by chemical treatment in a commonly used sodium dichromate solution and oiling. The produced Cu-Sn alloy has a Cu content of 0.004g/m ² and a Ni-
The Sn alloy had a Ni content of 0.025 g/m ² , and both Cu and Ni were alloyed with the total amount of Sn. Fe-Sn alloy is 0.7g/m ²
It was hot. The X-ray diffraction results show that the Cu-Sn alloy is
The Cu ₆ Sn ₅ and Ni-Sn alloys were Ni ₃ Sn ₄ . Example 3 A cold-rolled steel sheet similar to that in Example 1 was pretreated, and then Cu and Ni were treated using the following pyrophosphoric acid bath.
Perform eutectoid plating with 0.02 g/m ² of Cu and 0.03
g/m ² of Ni was deposited. After washing with water, tin plating at 5.6 g/m ² in a sulfuric acid tin plating bath and heating for 10 seconds to reach a maximum temperature of 220°C, just below the melting point of Sn, to form a Cu-Sn alloy. Ni-
Sn alloy and Fe-Sn alloy were formed. This was followed by chemical treatment in a commonly used sodium dichromate solution and oiling. The produced Cu-Sn alloy is 0.014g/ ^m2 , the Ni-Sn alloy is 0.02g/ ^m2 , the alloying rate of Cu is 57%, the alloying rate of Ni is 67%, and the Fe-Sn alloy is 0.02g. / ^m2 . X-ray diffraction results show that the Cu-Sn alloy is Cu ₆ Sn ₅ , Ni
-The Sn alloy was Ni ₃ Sn ₄ . Composition of eutectoid plating with Cu and Ni and processing conditions Composition Nickel pyrophosphate 300g / Copper pyrophosphate 15g / Potassium pyrophosphate 350g / Rothsiel salt 25g / Processing conditions Current density 1A/dm ² Processing electricity amount 3C/dm ² baths Temperature: 60°C Comparative Example A cold-rolled steel sheet similar to that used in Example 1 was pretreated, then tinned at 5.6 g/m ² in a sulfuric acid tinning bath, and the tin was melted using a resistance heating method. At the same time, an Fe-Sn alloy was formed. This was followed by chemical treatment in a commonly used sodium dichromate solution and oiling. The produced Fe-Sn alloy is
It was 0.9g/ ^m2 . The tin-plated steel plates obtained in Examples 1 to 3 and Comparative Example were subjected to an ATC test and the following corrosion resistance test. Corrosion resistance test A 50mm x 20mm specimen was coated with Fe―Sn alloy layer and Cu―
Sn that did not form a Sn alloy was electrolytically removed in a 1N sodium hydroxide solution at 40°C while maintaining the voltage at 0.35V. The end face of this specimen was sealed and immersed in a 1M citric acid solution at 25°C, and the iron corrosion rate was determined from the amount of hydrogen generated. iron corrosion rate mg/d
Expressed in m ² /hr. As shown in Table 1, the tin-plated steel sheet of the present invention exhibited excellent corrosion resistance and significantly improved the corrosion resistance of continuous casting materials. 【table】

Claims (1)

[Claims] 1 Between the steel plate and the tin layer, a Cu layer with a Cu-Sn alloying rate of 50% by weight or ^more is Cu, a Ni layer with a Ni-Sn alloying rate of 50% by weight or more is Ni The amount is 0.001g/ ^m2 or more, and the amount of Cu in the Cu layer and Ni
The total amount of Ni in the layers is 0.2g/ ^m2 or less, and Fe-Sn is mixed in the layer where the Cu layer and Ni layer are mixed.
A tin-plated steel sheet characterized in that the alloy layer has a mixed layer containing Sn in a range of 0.001 to 1.5 g/m ² .