JPH0431037B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for manufacturing a chromium-plated steel sheet for welded cans used in the fields of food cans such as beverage cans and food cans, and miscellaneous cans such as 18 cans and pail cans. It is something. <Conventional technology> In general, the main materials used for cans are tinplate and chrome-plated steel sheets called tain-free steel, but tinplates have been changed from soldered cans to welded cans in order to save resources, reduce costs, and improve appearance. This is rapidly changing, and instead of thick tin coatings of 2.8 g/m ² or more, thin tin coatings of 1.0 g/m ² or less are being developed. However, from a cost perspective, even thin tinplate is not superior to stain-free steel sheet. On the other hand, bonding of stain-free steel can bodies has traditionally been carried out mainly using adhesive methods;
This is because it cannot be soldered and because the surface coating has a high resistance and a high melting point, it cannot be welded. However, when using these adhesive cans to sterilize the can contents at high temperatures, there is a risk that the adhesive may tear and cause the can to explode. It is expected. For example, as a material that provides weldable stain-free steel and its manufacturing method,
-19752 and Japanese Patent Publication No. 57-36986 are already known. However, these attempts were made to improve weldability by reducing the amount of metallic chromium or non-metallic chromium, and were still insufficient in terms of the corrosion resistance required for can materials. The present inventors have previously proposed JP-A-61-213399 and JP-A-61-281899 as a method for manufacturing stain-free steel with excellent weldability and corrosion resistance after painting. However, with this method, which involves anodizing between the chromium plating processes, it is possible to uniformly and stably deposit a large number of protruding metallic chromium particles, greatly improving weldability, but with the same amount of metallic chromium,
Products with different weldability and corrosion resistance were obtained depending on the amount of chromium oxide, and it was not always possible to obtain good products stably. <Problems to be Solved by the Invention> The present invention provides a method by which a chromium-plated steel plate having excellent weldability and corrosion resistance can be stably obtained. <Means for solving the problem> The present invention provides electrolytic chromium plating on a steel plate, and then electrolytic treatment using the plated steel plate as an anode.
Next, after electrolytic chromium plating treatment is performed again, electrolytic treatment is performed again using the steel plate as an anode, and then electrolytic chromic acid treatment is applied to produce a surface weight of 40 with some of the metallic chromium protruding on the surface of the steel plate. ~150
A method for producing a chromium-plated steel sheet for welded cans with excellent corrosion resistance, characterized by forming a metallic chromium layer of mg/ ^m2 and a chromium oxide layer of uniform thickness with a basis weight of 5 to 25 mg/ ^m2 . be. <Function> The present inventors analyzed and investigated surface chromium using various stain-free steels on which a large number of protruding metallic chromium particles having different weldability and corrosion resistance were precipitated. As a result, it was found that the uniformity of the chromium oxide layer was a major factor influencing the variation in weldability and corrosion resistance. Figure 2 shows an example of examining the uniformity of the chromium oxide layer of two samples with different weldability and corrosion resistance. Weldability was investigated by measuring contact resistance. Resistance welding uses resistance heating when current is passed through a Cu wire electrode, but if the contact resistance is large, heat will concentrate on the surface, causing splash. Therefore, in order to improve weldability, it is necessary to reduce contact resistance. Moreover, the corrosion resistance was evaluated by a dry-wet repeated test described later. Sample A, B
Both are stain-free steels with many protruding metallic chromium deposits. Although these two samples had the same amount of metallic chromium and the same amount of chromium oxide, sample A had low contact resistance, good weldability, and good rust resistance. On the other hand, sample B had higher contact resistance than sample A, poor weldability, and somewhat poor rust resistance. The uniformity of the chromium oxide layer in samples A and B was examined using an optical microscope and an X-ray microanalyzer (EPMA). Using an optical microscope, the thickness unevenness of the chromium oxide layer was investigated by observing the surface of the steel plate at 400 times magnification. EPMA peeled off only the chromium oxide layer on the surface of the stain-free steel, performed line analysis of Cr on the obtained thin film, and examined the distribution of Cr using counts. The dark areas observed in the optical micrograph of sample B are areas where the chromium oxide layer is thick, and even though sample B has the same amount of chromium oxide as sample A, there are locally thick areas of the chromium oxide layer. Furthermore, line analysis using EPMA also shows that Cr is unevenly distributed. On the other hand, sample A has no locally thick chromium oxide layer observed with an optical microscope, and the distribution of Cr using EPMA is uniform. These results show that it is important to make the chromium oxide layer uniform in order to improve weldability and corrosion resistance. The non-uniformity of the chromium oxide layer means that
This means that there are both thick and thin parts of the chromium oxide layer, and not only the corrosion resistance and paint adhesion deteriorate in the thin part of the chromium oxide layer, but also the conductivity deteriorates even in the thick part of the chromium oxide layer. Due to the poor quality, splashes are likely to occur. Therefore, if the chromium oxide layer is non-uniform, it is disadvantageous in terms of corrosion resistance and weldability, and the appearance is likely to be stained. If the chromium oxide layer is uniform, not only will it be possible to stably obtain a product that satisfies both corrosion resistance and weldability, but also the coverage of the chromium oxide layer will improve, so the amount of chromium oxide can be uniformly reduced. , weldability can be further improved. Therefore, we investigated a method for stably depositing a uniform chromium oxide layer. After plating to deposit a large number of protruding metallic chromium, we applied an electric current of 0.1 to 15 C/ ^dm2 using a steel plate as an anode. The present inventors have discovered that a method of electrolytically treating the material and then electrolytically treating it with chromic acid is very effective, leading to the present invention. Next, the reason for limiting the basis weight of the present invention will be explained. The reason for setting the amount of metallic chromium to 40 to 150 mg/ ^m2 is that if the amount of metallic chromium is less than 40 mg/ ^m2 , the metallic chromium layer will have a porous structure and will not be able to sufficiently cover the steel plate surface, resulting in poor corrosion resistance after painting. Inferior. Furthermore, even if the amount of metallic chromium exceeds 150mg/ ^m2 , further improvement in corrosion resistance after painting cannot be expected, and it is not economical.
The amount is preferably 40 to 150 mg/ ^m2 . Furthermore, if the amount of chromium oxide is less than 5 mg/ ^m2 , the surface cannot be sufficiently coated, resulting in poor corrosion resistance after painting.
If it exceeds m ² , weldability will drop sharply, which is not preferable. Next, the manufacturing method of the present invention will be explained in detail. The main manufacturing process of the chrome-plated steel sheet for welded cans in the present invention is [Chrome plating (1) → Anodization (1) →
Chrome plating (2) → anodizing (2) → electrolytic chromic acid treatment] is performed in this order. Chrome plating (1) and chrome plating (2) can be done using normal electrochrome plating methods.
(1) and chrome plating (2) may be plated using the same solution or may be plated using different solutions. The anodic treatment (1) sandwiched between is chrome plated (1)
It may be carried out in the solution of chromium plating (2) or in the solution of chromium plating (2), or it may be carried out using another solution. Further, the amount of electricity in the anodization (1) is preferably in the range of 0.1 to 10 C/dm ² . FIG. 1 schematically shows the generation mechanism of metallic chromium and chromium oxide according to the manufacturing process in the present invention. Chrome plating is performed to produce a metallic chromium layer, but at the same time a chromium oxide layer is formed on the metallic chromium layer. When performing chromium plating, a large amount of auxiliary agent is added to increase the efficiency of precipitation of metallic chromium, so the chromium oxide layer formed at the same time as plating becomes non-uniform (Figure 1). Anodizing has the effect of dissolving the chromium oxide layer and uniformly thinning it. Anodizing (1) uniformly thins the uneven chromium oxide layer generated during chromium plating (1). Figure 1). When the chromium oxide layer becomes thinner,
Since there are many pinholes in the chromium oxide layer, in the next chromium plating (2), metallic chromium precipitates in the pinholes of the chromium oxide layer and becomes protrusive, and many protruding metallic chromium are precipitated. (Figure 1). After obtaining a metallic chromium layer with many protrusions in the process up to chrome plating (2), it is further anodized (2).
and electrolytic chromic acid treatment. The anodization (2) may be performed in a solution for chromium plating (2) or in an electrolytic chromic acid treatment solution. Alternatively, a tank of another solution, such as an electrolyte such as a Na ₂ CO ₃ solution, may be used. However, from the point of view of equipment costs, and considering that the anion that dissolves at the same time as chromium oxide in anodizing (2) is an auxiliary agent for chromium plating (2), it is difficult to It is preferable to do it inside. The electrolytic chromic acid treatment performed after anodizing (2) uses a solution containing one or more of chromic acid, chromate, or dichromate in an amount of 10 to 100 g in terms of chromic acid,
The electrolysis may be carried out using a solution to which fluorine, a fluorine compound, sulfuric acid, sulfate, or the like is added as an auxiliary agent, under electrolytic conditions that mainly precipitate chromium oxide. The effect of anodization (2) in the present invention is as follows. In chromium plating (2), a large amount of auxiliary agent is added to increase the efficiency of precipitation of metallic chromium, so that protruding metallic chromium is formed and at the same time non-uniform chromium oxide is formed. (Figure 1). If electrolytic chromic acid treatment is performed after this, the chromium oxide layer generated during chromium plating (2) will continue to grow and become an uneven chromium oxide layer, but if anodized treatment (2) is performed, as shown in Figure 1. The chromium oxide layer dissolves and becomes a thin, uniform chromium oxide layer. After this, when electrolytic chromic acid treatment is performed, the uniform chromium oxide layer grows as it is, forming an appropriate amount of chromium oxide layer uniformly. It is thought that it will be done. (Figure 1). It is desirable that the amount of electricity in the anodization (2) is 0.1 to 15 C/dm ² . If the amount of electricity in the anodization (2) is less than 0.1 C/dm ² , the smoothing effect of the chromium oxide layer by the anodization will not be sufficient, and the chromium oxide layer will not be uniform. Moreover, even if it exceeds 15C/ ^dm2 , not only can no further smoothing effect of the chromium oxide layer be expected, but
The amount of eluted metal chromium increases, which is economically disadvantageous. In addition, as a counter electrode for anodizing, it is possible to use a lead-based electrode, which is normally used as an insoluble anode for chromium plating, but if used for a long period of time, chromium will precipitate on the surface of the lead-based alloy electrode, causing the anode to deteriorate. Since the process becomes unstable, it is better to use an electrode whose surface is coated with platinum or gold, which is less likely to cause the precipitation of metallic chromium.
Anodization can be performed stably. <Examples> Next, the present invention will be described with reference to Examples and Comparative Examples. After degreasing and pickling a cold-rolled steel plate with a thickness of 0.22 mm, it was chromium plated using the solution shown in Table 1, and the uniformity of the chromium oxide film on the obtained specimen was evaluated by EPMA and copper sulfate tests. Weldability, contact resistance, and corrosion resistance were investigated using wet and dry repeated tests. The results are shown in Table 2. Examples 1 to 3 that satisfy the present invention are Comparative Examples 1 to 3.
It can be seen that compared to No. 2, it is a stain-free steel that has a uniform chromium oxide layer on a metal chromium layer with many protrusions, and has excellent weldability and corrosion resistance. In addition, each test method is shown below. (EPMA line analysis: Analysis of chromium oxide layer using an X-ray microanalyzer) The surface of tain-free steel is carbon-deposited and immersed in a 5% Br ₂ -methanol solution for 24 hours. The thin film of the chromium oxide layer that had floated was scooped onto platinum and dried to prepare a sample for an X-ray microanalyzer. This sample was subjected to line analysis of Cr using an X-ray microanalyzer manufactured by Shimadzu Corporation at an analysis speed of 48 μm/min at an acceleration voltage of 20 KV and a sample current of 0.02 μA to detect the chromium oxide layer. We investigated the distribution. (Copper sulfate test) After degreasing the sample, it was immersed in a 50 g/copper sulfate solution for 1 minute, and then the precipitated copper was quantified using fluorescent X-rays. (Contact resistance) After heat treatment at 210℃×20min, the sample was
The contact resistance was measured by stacking the sheets and applying pressure from above and below at 40 Kgf using roller electrodes using copper wires. (Dry and Wet Repeated Test) Rust formation was observed after 1, 2, 3, 4, and 7 days using a tester that alternately repeated high-humidity and dry conditions, and an overall judgment was made. 〔judgement〕

【table】

[Table] <Effects of the Invention> As described above, the present invention has made it possible to stably produce stain-free steel, that is, chromium-plated steel plate, which has excellent weldability and corrosion resistance, and therefore has great industrial benefits. .

【table】

【table】 [Brief explanation of drawings]

Figure 1 is a diagram schematically showing the generation mechanism of metallic chromium and chromium oxide in the order of the manufacturing process of the present invention, and Figure 2 shows the uniformity and weldability of the chromium oxide layer,
It is a figure showing the relationship of corrosion resistance. The optical micrograph in FIG. 2 is a metallographic diagram of the surface of the chromium-plated steel plate.

Claims (1)

[Claims] 1 After performing electrolytic chromium plating on a steel sheet, electrolytic treatment is performed using the plated steel sheet as an anode, then electrolytic chromium plating is performed again, electrolytic treatment is performed again using the steel sheet as an anode, and then electrolytic treatment is performed using the steel sheet as an anode. By applying chromic acid treatment, a metallic chromium layer with a basis weight of 40 to 150 mg/m ² and a uniform thickness of chromium oxide with a basis weight of 5 to 25 mg/m ² are formed on the surface of the steel sheet, with some of the metallic chromium protruding. A method for manufacturing a chromium-plated steel plate for welded cans with excellent corrosion resistance, characterized by forming a chromium-plated steel plate with a substance.