JPS6136595B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the invention of a surface-treated steel sheet for welded cans,
The aim is to provide a steel plate that can be welded without polishing, has corrosion resistance after painting that is equal to or better than chrome-type stain-free steel (TFS), and has excellent paint adhesion. With the spread of cans with internal coatings, the amount of tin used in the tin plate used to obtain these can bodies was reduced, and TFS, a chrome type with excellent paint adhesion, became popular in place of tin plate. has been done. On the other hand, a new welding method has been developed as a can manufacturing technology, and can materials suitable for this welding are being reconsidered. In other words, one of the characteristics required for this welding can material is that it can be welded without polishing, but in the current welding can making method using copper wire electrodes, chrome type TFS can be welded without polishing. It is very difficult to do so. Therefore, materials such as nickel-plated steel sheets and ultra-thin tin-plated steel sheets treated with chromate containing metallic chromium have been developed as materials that eliminate this drawback, but these materials effectively combine both weldability and post-painting corrosion resistance. Its performance is still insufficient as a material to replace #25 tin. And this #25
Tinplate has considerably poor paint adhesion. The present invention has been devised after repeated studies in view of the above-mentioned circumstances ^. We propose a treated steel sheet for welded cans in which the layer is plated discontinuously and in particulate form with tin at a coverage of 2 to 90%. That is, to further explain the present invention, the present inventors first considered safety for the human body and conducted research by limiting the metal to be plated to tin, but when the amount of tin to be plated was reduced. The following properties arise. When tin preferentially dissolves, the underlying steel or alloy layer is likely to be exposed due to the small amount of tin, and it is structurally difficult to suppress iron elution due to sacrificial dissolution of tin over a long period of time. If a small amount of pure tin remains in the material, such as 0.1 to 0.6 g/m ² , preferential dissolution of pure tin will result in insufficient contact between the material and the coating film, which will have an adverse effect on the corrosion resistance after coating. Therefore, when the amount of tin to be plated is small, it is necessary to use a material with an extremely small amount of pure tin or no pure tin, and it is essential that the coating state on the steel substrate is good. Therefore, in the present invention, taking these relationships into consideration, the material is based on the fact that all tin is made into an iron-tin alloy by heating after plating. The above-mentioned iron-tin alloy layer changes depending on the alloying temperature.
The composition is different. That is, when the temperature is below 400°C, it is confirmed by X-ray diffraction that it is Fen ₂ , but when it is above 500°C, it becomes FeSn. However, at 400-500℃, both often exist together, and regarding these relationships, the alloy composition state formed by various alloying temperatures and holding times when the alloy tin amount is 0.66 g/ ^m2 is as follows. As shown in Table 1.

[Table] However, the inventors of the present invention added tin to 0.15 to 0.15 per side.
1.2 g/m ² , preferably 0.2 to 0.9 g/m ² , and the plated tin is alloyed by heating, and the upper layer is coated discontinuously with tin. By electrodepositing and then performing a conventional chemical conversion treatment, it satisfies the weldability and post-painting corrosion resistance required for welded cans intended for internal painting, and also has excellent paint adhesion. A surface-treated steel sheet is obtained, but if the amount of tin in the alloyed layer is less than 0.15 g/m ² , the underlying iron will be exposed more and the alloy coating effect will not be obtained, so it is difficult to effectively suppress Fe elution. is not obtained. Moreover, if it exceeds 1.2 g/m ² , it is not economical and cracks are likely to occur in the alloy layer during bending or other processing, so that a desirable coating effect cannot be obtained. Regarding the alloy composition, although FeSn ₂ has a sufficient effect, using FeSn improves paint adhesion and provides better corrosion resistance. As shown in the test results. Furthermore, in the present invention, tin is electrodeposited discontinuously and in the form of particles on the alloy layer as described above, thereby significantly suppressing corrosion under the paint film and improving paint adhesion. The tin coverage on this alloy layer is from 2 to 90%; if it is less than 2%, the under-coating corrosion performance will be insufficient, while if it exceeds 90%, the paint adhesion will deteriorate. An example of the small amount of electrodeposited tin that is formed is shown in the accompanying drawing, which is a scanning electron micrograph at a magnification of 20,000 times. In this photograph, the scattered white particles are tin particles. In any case, it is formed as discontinuous particles. It has been confirmed that particles formed in the form of tin with the above-mentioned tin coverage can be welded favorably without polishing in actual operation when manufacturing welded cans using a Sudronik welding machine or the like. The size of the tin particles described above varies depending on the respective plating conditions. The relationship between the tin coverage on the alloy layer mentioned above, corrosion under the paint film, and paint adhesion (T-peel strength) is summarized in Figure 2. Good retention of under-paint corrosion,
T-peel strength of 1.0Kg/5mm or more can also be ensured. Specific manufacturing examples according to the present invention will be described below along with comparative examples thereof as appropriate. Production Example 1 An annealed material with a thickness of 0.21 mm that was continuously annealed and temper rolled by a conventional method was electrolytically degreased and electrolytically pickled, and then tin was added within the range of 0.51 to 0.55 g/m ² per side. This material was then heated in a reducing atmosphere at a maximum temperature of 350 to 400°C to form all the tin into an iron-tin alloy. Also, for this case, the current density of tin is 1A/dm ²
The plate was plated for 0.5 seconds, and then cathodically treated for 1 second at a current density of 5 A/dm ² in an aqueous solution of 20 g of sodium dichromate to deposit hydrated chromium oxide. As a comparative example, a sample was prepared in which iron-tin alloying was performed in the same manner as above, but the subsequent tin plating process was not performed. That is, the tin plating amount, alloying temperature, and tin plating of the surface-treated plates specifically obtained as such production examples and comparative examples are summarized as follows:
As shown in Table 2 below. 〓〓〓〓〓

[Table] Production Example 2 The same annealed material as in Production Example 1 was electrolytically degreased and electrolytically pickled, then plated with tin at 0.50 to 0.57 g/ ^m2 per side, and then plated in a reducing atmosphere at a maximum temperature of 500 to 600℃. The entire amount of tin was heated to form an iron-tin alloy. This material was then temper-rolled with an elongation of 2.0%, plated with tin for 0.5 seconds at a current density of 1 A/ ^dm2 , and then plated with tin at a current density of 1 A/dm2 for 0.5 seconds, and then in an aqueous solution of 20 g/d of sodium chromate at 5 A/d.
A cathodic treatment was performed at m ² for 1 second to electrodeposit the hydrated chromium oxide. On the other hand, as a comparative example, one was prepared in which the tin plating step after alloying was removed. Some examples of concretely obtained steel plates are shown in Table 3 below, as in Production Example 1.

[Table] Comparative manufacturing example 1 After electrolytically degreasing and electrolytically pickling the annealed material in the same manner as in manufacturing examples 1 and 2, it was plated with tin at 0.54 g/m ² (per side), and then sodium dichromate 20
Manufactured No. 11 by cathodic treatment at 5 A/dm ² for 1 second in an aqueous solution to electrodeposit chromium hydrated oxide.
steel plate was obtained. Comparative Production Example 2 After electrolytically degreasing and electrolytically pickling the annealed material in the same manner as in Production Examples 1 and 2, tin was added at a concentration of 0.30 to 0.55 per side.
g/m ² Plating (Tin plating) This product was heated in a reducing atmosphere at a maximum temperature of 350 to 600°C to convert all of the tin into an iron-tin alloy. Also, tin for this thing.
0.15-0.40g/ ^m2 Re-plated (tinning) and then 5% in an aqueous solution of 20g/m of sodium dichromate
Refined No. 12~ by cathodic treatment with a current density of A/dm ² for 1 second to electrodeposit chromium hydrated oxide.
Got 15. The tin plating amount and alloying temperature are as shown in Table 4 below.

[Table] Manufacturing example 3 After electrolytically degreasing an unannealed material with a thickness of 0.22 mm, it was plated with tin at a rate of 0.55 g/ ^m2 per side, and this material was heated to a maximum temperature of 600
It was heated in a reducing atmosphere at 0.degree. C. to convert all the tin into an iron-tin alloy. (Also used for annealing) After temper rolling, electrolytic degreasing and electrolytic pickling, tin was plated at a current density of 0.5 A/dm ² for 0.5 seconds, and then an aqueous solution of 20 g of sodium dichromate was applied. A cathodic treatment was carried out for 1 second at a current density of 4 A/dm ² to electrodeposit chromium hydrated oxide to obtain Production No. 16. In addition, as a comparative example, a product was prepared as Production No. 17, which was made into an iron-tin alloy in the same manner as above, but without the subsequent tin plating step. If these are shown along with the amount of tin plating and the alloying temperature, the following 5th
As shown in the table. 〓〓〓〓〓

[Table] Comparative Production Example 3 After performing electrolytic degreasing and electrolytic pickling on a product that had been subjected to temper rolling in the same manner as in Production Example 3,
The tin was replated at 0.40 g/m ² per side (tinning) and then cathodized in an aqueous solution of 20 g/m of sodium dichromate for 1 second at a current density of 4 A/dm ² to produce chromium hydrate oxidation. Manufactured by electrodeposition of materials
Steel plate No. 18 was obtained. (Comparative material) Production example 4 In Production example 3, a mixed solution of 30 g of chromic anhydride and 2 g of ammonium fluoride was used instead of sodium dichromate, and cathodic treatment was performed for 1 second at a current density of 15 A/dm ² . , metal chromium and chromium hydrated oxide were electrodeposited, and steel plate No. 19 was obtained. (Inventive material) Comparative production example 4 In comparative production example 3, a mixed solution of 30 g of chromic anhydride and 2 g of ammonium fluoride was used instead of sodium dichromate, and cathodic treatment was performed for 1 second at a current density of 15 A/dm ^2. Metallic chromium and hydrated chromium oxide were electrodeposited, and a steel plate of production No. 20 was obtained as a comparison material. Each steel plate and #25 tin plate and TFS obtained by each production example or comparative production example as described above
(Tein-free steel) was tested for its T-peel strength (Test A), corrosion under the coating (where no crosscuts were applied), corrosion width of the crosscut and pitting corrosion (Test B), and also tested for non-abrasive weldability. The results of the study are summarized in Table 6 below.

[Table] 〓〓〓〓〓

[Table] The conditions for each test in Table 6 above are as follows. Test A: Apply epoxy phenol paint at 50mg/ ^dm2 ,
After baking at 205℃ for 10 minutes and cutting the samples into 5 x 100 mm pieces, the coated surfaces were thermocompressed with nylon film and the strength was measured when peeled off at 20 mm/min (unit: kg/5mm). Test B: 50mg/dm ² of epoxy phenol paint on each material
It was coated, baked at 205℃ for 10 minutes, and then immersed in a mixture of 0.55% citric acid and 1.5% salt at 35℃ for 96 hours, and then visually observed. ◎ is good, 〇 is very good, △ Judgment was made based on whether there was a problem or "x" means a problem, and the maximum corrosion width was measured as the corrosion width. Non-polishing weldability: Judgment was made by visual observation in the same way as above, ◎ as good, 〇 as very good, △ as having some difficulties, and × as having some difficulties. namely production Nos. 1, 2 and 5 according to the invention,
Items 6, 7, 16, and 19 show favorable results in all test results.For example, even though they are slightly inferior to #25 tin in terms of cross-cut pitting corrosion and non-polishing weldability, they are superior in cross-cut corrosion width. is much better, T
The pineal strength is also 10 to 20 times higher. It was also confirmed that it was significantly superior to TFS in terms of cross-cut pitting corrosion and non-abrasive weldability, and was superior in all respects to other comparative materials. According to the present invention as explained above, it is possible to appropriately provide a product that satisfies all the necessary characteristics as a surface-treated steel sheet for welded cans and has excellent performance, and is an invention that has great industrial effects. be.

[Brief explanation of the drawing]

The drawings illustrate embodiments of the invention,
FIG. 1 is a scanning electron micrograph showing the state of tin-plated particles according to an example of the present invention at a magnification of 20,000 times.
The figure is a diagram summarizing the relationship between discontinuous particulate tin coverage, paint adhesion, and under-paint corrosion. 〓〓〓〓〓

Claims (1)

[Claims] 1 An iron-tin alloy layer with an Sn content of 0.15 to 1.2 g/m ² (per side) is formed on the steel plate, and discontinuous and particulate tin plating with a coverage of 2 to 90% is formed on the alloy layer. Surface-treated steel sheet for welded cans.