JPS6350431B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the invention of a steel plate for welded and painted cans, and an object thereof is to provide a new steel plate for welded and painted cans that is excellent in both weldability and paint adhesion and has excellent corrosion resistance after painting. Soldered cans have traditionally been commonly used as can bodies for canned goods, but in recent years there has been a rapid shift from soldered cans to welded and adhesive cans, and thick tin cans with unpainted inner surfaces are also being used. Substitution of cans (white cans) to tinplate with a thinner inner coating and cans made of stain-free steel (TFS) has become almost commonplace.
Under these circumstances, the required performance for can materials has changed substantially, and when the above-mentioned inner surface coating is assumed, the greatest required performance is paint adhesion and post-processing corrosion resistance. However, as mentioned above
TFS is a surface-treated steel sheet with very good paint adhesion and is widely used in adhesive cans, but it has poor corrosion resistance after processing and is extremely poor in welding workability, so strong joint strength is required. This TFS is suitable for welded can types such as spray cans.
The current situation is that it cannot be used. Therefore such TFS
There is a need for a material for cans that maintains average paintability, has excellent corrosion resistance after processing, and has excellent welding workability. In view of the above-mentioned circumstances, the inventors have conducted extensive studies and succeeded in obtaining a steel plate for cans that does not have the disadvantages mentioned above, and have already filed an application (Patent Application No. 1973-
150577). In other words, since the above steel plate is for cans, the metals are limited to Fe and Sn, and the entire surface layer is completely alloyed to create an oxide film with excellent paintability (adhesion). In order to improve the surface composition and workability, the alloy layer has a finer or amorphous crystal structure, and in order to suppress the occurrence of cracks and improve corrosion resistance, it acts cathodically on the steel base and A surface layer with a highly polarized composition is formed. As a result of repeated detailed studies on the Sn--Fe system as described above, the present inventors have clarified the following. FeSn ₂ is a columnar crystal with high porosity and is prone to processing cracks. A Sn-rich oxide film is formed on Sn and FeSn ₂ , and this film has poor adhesion. By forming a thin Sn plating on iron and heat-treating it sufficiently, it is possible to obtain an alloy layer with an even higher Fe ratio than FeSn ₂ , and on the surface of this alloy with a high Fe atomic ratio, an oxide film containing iron and tin is formed. is formed, and the adhesion of the film is good. When alloyed to the composition of FeSn, it becomes an amorphous alloy layer with a high coverage, and this FeSn layer is difficult to crack during processing. An alloy layer with a high Fe ratio behaves similar to iron in terms of welding workability, suppresses heating oxidation during welding, and has a potential closer to that of iron than FeSn ₂ , making it easier to cathode polarize. In the present invention, the amount of tin in the Fe--Sn alloy layer coated on the steel plate is 0.05 to 0.7 g/ ^m2 , and furthermore, the entire amount of tin is formed into the Fe--Sn alloy, and the main body of the alloy layer is This invention relates to a steel plate for welded cans, which is made of FeSn and has an atomic ratio of 40 to 80% Fe, and has a chemical conversion coating on the alloy layer with a Cr content of 0.5 to 5 mg/ ^m2 . . To further explain these relationships, the relationship between the composition of the formed alloy surface layer and the Fe atomic ratio in the oxide film formed on that surface is based on the Fe atomic ratio of the alloy surface layer.
The Fe atomic ratio in the oxide film changes greatly in the range of 40 to 80% atomic ratio, preferably 45 to 60%, and in this case, the adhesion of the oxide film is determined when the Fe atomic ratio in the alloy surface layer is 40 to 80%. The adhesion of the oxide film can be made sufficiently high within the range,
Compared to the conventional FeSn ₂ with an Fe atomic ratio of about 33%, a remarkable improvement in adhesion can be achieved. Therefore, the present invention appropriately utilizes this relationship, and if the previously unknown characteristics of the alloy layer with a high Fe ratio are utilized as described above, the drawbacks of conventional can materials of this type can be overcome. Wipe out,
It is possible to obtain a new surface-treated steel sheet that is superior in weldability to TFS, has the same or better paint adhesion, and has better corrosion resistance after painting than TFS tinplate. In order to accurately exhibit the characteristics of alloying and alloy layers as described above, it is necessary to uniformly deposit tin in the tin plating process prior to alloying, and in the present invention, tin is deposited uniformly at 0.05 to 0.7 g/m ² ,Preferably
The required tin amount of 0.1 to 0.3 g/m ² is uniformly deposited to achieve uniform alloying. In other words, the amount of tin plating is 0.05
g/m ² , it is not possible to form a stable coating and a uniform alloy layer, and therefore an appropriate composite oxide film cannot be obtained. This means that favorable results cannot be obtained in terms of adhesion, welding workability, and post-painting corrosion resistance. Moreover, if the amount of tin plating exceeds 0.7 g/m ² , a large amount of tin is required, which is not only uneconomical, but also requires a higher or longer heating temperature and heating time for alloying. Moreover, if the amount of tin plating exceeds 0.7 g/m ² , the corresponding Sn--Fe alloy layer becomes too thick and tends to cause processing cracks. Of course, in order to obtain the desired amount of tin plating, the initial stage of a normal plating method may be used, but in the present invention, an alloy layer obtained by forming a relatively thin plating layer and alloying it. Since the density and uniformity of the metal are important, it is preferable that the pre-plating prior to alloying be improved over the conventional method. For example, SnSO ₄ ,
It is advantageous to employ methods such as those using a plating bath consisting of H ₂ SO ₄ and a nonionic activator. However, as mentioned above, such a tin-plated plate
The heating method for obtaining an alloy layer with an Fe ratio of 40 to 80% may be either a continuous method or a batch method, but the heating time is appropriately determined in consideration of the Sn amount and heating temperature. One example is 0.2, which has a relatively small amount of Sn.
g/ ^m2 , the relationship between the Fe atomic ratio in the alloy surface layer obtained by the heating temperature and heating time is as follows:
As shown in the figure, the Sn content is relatively high at 0.7
The case of g/m ² is as shown in Fig. 3, and the case of 0.5 g/m ² , which falls between them, is as shown in Fig. 2. In the case of Figure 1, the heating temperature is 250℃
However, even if it takes a long time, alloying with an Fe atomic ratio of 40% or more cannot be achieved, so the heating temperature must be higher than that. If the heating temperature is 350℃, it will take more than 8 seconds.
Alloying with an Fe atomic ratio of 40% or more can be obtained in 3.5 seconds or more at 400℃ and 1 second or more at 450℃, but
10 seconds or more at 400℃, 4 seconds or more at 450℃
Fe atomic ratio becomes 80% or more. In the case of Figure 2, even if it takes a long time at the heating temperature of 350℃, the Fe atomic ratio is still 40%.
Since alloying cannot be achieved at a higher temperature, it is necessary to heat the alloy at a higher temperature. An alloy with an Fe atomic ratio of 40% or more can be obtained at a heating temperature of 400°C for 50 seconds or more, at 410°C for 32 seconds or more, at 430°C for 20 seconds or more, and at 450°C for 8 seconds or more, but at 480°C case 48
If the time is longer than 26 seconds at 450°C, the Fe atomic ratio will increase.
It will be more than 80%. In the case of FIG. 3, if the heating temperature is below 400°C, it is not possible to obtain an alloy with an Fe atomic ratio of 40% or more even if it takes a long time, so it is necessary to set the heating temperature to a higher temperature. At heating temperature 450℃
Alloying with an Fe atomic ratio of 40% or more can be obtained in 38 seconds or more, 22 seconds or more at 500°C, and 11 seconds or more at 600°C, but if it takes more than 40 seconds at 600°C, the Fe atomic ratio will decrease.
80% or more. Furthermore, a chemical conversion film is formed on the alloyed layer as described above, and the amount of Cr in this chemical conversion film is 0.5.
mg/ ^m2 to 5mg/ ^m2 . That is, if the amount of Cr in the chemical conversion coating does not reach 0.5 mg/m ² , the treatment effect will not be recognized, and even if the weldability is appropriate, the corrosion resistance and paint adhesion will not necessarily be sufficient. Furthermore, if the Cr content is 5 mg/m ² or more, even if corrosion resistance is sufficient, favorable results will not be obtained in terms of paintability and weldability after processing. Specific manufacturing examples according to the present invention and comparative examples thereof are described below. That is, the plating conditions for some examples actually produced by the present inventors are shown in Table 1 below.

[Table] The heat treatment conditions for alloying these materials are shown in Table 2 below.

[Table] Furthermore, when performing chemical conversion treatment on the above products, NaHCO ₃ was added in advance to 20% of the production example ~.
Cathode current density in a solution with a bath temperature of 50℃ at g/
Pretreatment was carried out under the conditions of 8 A/dm ² , and the other components were subjected to chemical conversion treatment as they were. The conditions for this chemical conversion treatment are as shown in Table 3 below.

[Table] Test results on the amount of tin in the alloy layer, its atomic ratio, the amount of Cr in the chemical conversion coating, as well as the weldability, paint adhesion and corrosion resistance of the steel sheets obtained in each of the above manufacturing examples. Table 4 below shows the case of conventional TFS (manufacturing example).

[Table] Note: * indicates pure tin remains on the surface layer. The test method and judgment criteria in Table 4 above are as follows. (1) Welding workability Judged by the nugget formation status observed by cross-sectional microscopic observation of the weld, the welding current range necessary to maintain airtightness by the Weld-Lob method, the tendency to generate dust, and the oxidation property of the weld. 〇 indicates excellent weldability. ing,
× indicates poor weldability. (2) Paint adhesion After retorting, epoxyphenol paint 50
After applying mg/dm ² , bake at 210℃ for 10 minutes,
The coating film crack area at the 2t bent section or the peeling status of cellophane tape at the processed section after circular press molding was measured. The measured value for 0t bending is the iron exposed area ratio (%), and for circular presses, ◎ means no peeling, 〇 means little peeling, and × means severe peeling. (3) Primary corrosion resistance Bare wet test was conducted at 24°C with R/H of 95% or more at 50°C.
This is the occurrence of red rust due to a wet test over a long period of time, and the indoor exposure was after being left at room temperature for 3 months. Each judgment is ◎ cannot be determined with the naked eye, ○ is slightly visible with the naked eye, and × is severe red rust. It is. (4) Secondary corrosion resistance After painting according to (1) above, the cross-cut area
Corrosion status in 0.1N citric acid at 35℃ for 48 hours and in 0.1N citric acid after extruding Erichsen 5 mm
The adhesive was immersed at 50°C for 75 hours, and the peeling status of the cellophane tape was determined. Regarding the judgment results, ◎ means no peeling, ○ means little peeling, and × means severe peeling. In other words, according to these results, the test results of the production examples and the products according to the present invention are all good, whereas the other comparative examples have poor weldability, paint adhesion, and corrosion resistance. It is clear that the results are considerably inferior to those of the present invention. According to the present invention as explained above, it is possible to obtain a steel sheet having good properties in terms of weldability, paint adhesion, and corrosion resistance after painting as this type of can material. By alloying the entire target, the pure tin layer with a low melting point is dissolved and the melting point becomes high, which effectively prevents electrode contamination during welding. It is an invention that has great industrial effects, as it improves corrosion resistance and can sufficiently increase paint adhesion through chemical conversion treatment to obtain a product that is favorable in all tests.

[Brief explanation of drawings]

The drawings show the technical contents of the present invention, and FIGS. 1 to 3 show Sn amounts of 0.2 g/m ² and 0.5, respectively.
Fig. 3 is a chart showing the relationship between the Fe atomic ratio in the alloy surface layer and the heating time in the case of g/m ² and 0.7 g/m ² .

Claims (1)

[Claims] 1 The amount of tin in the Fe-Sn alloy layer coated on the steel plate is
0.05 to 0.7 g/m ² , and the entire amount of tin is formed into the Fe-Sn alloy, and the alloy layer is mainly FeSn.
A steel sheet for welded coated cans, characterized in that the Fe content is 40 to 80% in terms of atomic ratio, and a chemical conversion coating having a Cr content of 0.5 to 5 mg/m ² is provided on the alloy layer.