JPS6231066B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to a method for manufacturing a steel sheet for containers that exhibits excellent weldability using electric resistance welding and also exhibits excellent corrosion resistance required for beverage cans, general cans, and the like. (Prior Art) In recent years, can manufacturing methods and can designs for beverage cans and food cans have significantly advanced and diversified, and materials for containers that are compatible with these are required to be low-cost and high-performance. In particular, electric resistance welding can manufacturing methods, such as the Sudronik welding can manufacturing method, have a high material yield, high strength during joining, and an extremely low incidence of can leakage due to poor joining, and can be applied to design cans of various shapes. It has many advantages and is beginning to be widely used. Conventionally, Sn-plated steel sheets with a Sn coating of #10 or higher (Sn coating of 1.12 g/m ² ), preferably #25 or higher (Sn coating of 0.28 g/m ² ) are used as welded can making materials. It's here. However, its biggest drawback is that its price is extremely high due to the soaring price of Sn metal. Therefore, various attempts have been made to reduce costs by reducing the amount of Sn deposited, but in this case, the problem is that corrosion resistance and weldability deteriorate. Recently, alternative materials for containers have been published in JP-A-57-23091, JP-A-57-200592, and JP-A-57-110685.
Steel plates with various plating layers or coating layers have been developed, as shown in Japanese Patent Publication No. The manufacturing method is a combination of Ni plating, thin Sn plating, alloying diffusion treatment (heat melting treatment), and chromate coating treatment on the steel plate surface. Steel sheets manufactured using this manufacturing method have a reduction in pinholes due to the superimposed effect of the two-layer coating, and a reduction in the plating layer.
An alloy layer of Ni and Sn is formed densely and ATC (Alloy
Corrosion resistance is also being improved by lowering the tin couple value. In particular, the Ni underplating suppresses the alloy layer consisting of Fe and Sn (FeSn ₂ alloy layer) that grows during the high-temperature heating process during welded can making or high-temperature sterilization after filling, and improves weldability and Improve the appearance of welded parts. (Problems to be Solved by the Invention) However, when these steel plates for containers are examined in detail, it is difficult to say that sufficient performance is necessarily ensured. When a double-layer plated steel plate consisting of a Sn-plated plate with a Ni undercoat is exposed to a corrosive environment, the dissolution rate of Sn decreases due to the above-mentioned effect, as shown in FIG. 1, and its initial corrosion resistance is excellent. Figure 1 shows a comparison of sn elution rates in model corrosive fluids. (Note-1) Model corrosive liquid (1.5% citric acid +
1.5% salt) Measurement conditions 27℃, _N2 atmosphere (Note 2) Test piece coating composition 〇... Base (Fe-20% Ni) alloy plating (200mg/
m ² ) → Sn plating (800 mg/m ² ) → Heat melting treatment → chromate treatment (9 mg/m ² ) △...Ni plating on base 25 mg/m ² → Sn plating (800
mg/m ² ) → Chromate treatment (8 mg/m ² ) □… Base (Fe-10%Ni) diffusion coating layer (Ni plating amount 50 mg/m ² → diffusion treatment) → Sn plating (800
mg/m ² ) → Heat melting treatment → Chromate treatment (8mg/m ² ) ×…Sn plating (850mg/m ² ) → Heat melting treatment →
Chromate treatment (9 mg/m ² ) ▲… Base (Ni-16%P) alloy plating (60 mg/
m ² ) → Sn plating (850 mg/m ² ) → chromate treatment However, if exposed to a corrosive environment for a long time, the Sn will be dissolved and consumed and the alloy layer will be exposed, no matter how dense the alloy layer is, pinholes will form. There are not all
Local batteries are formed in the Ni and Sn alloy layer and corrosion is accelerated. In this case, the Ni and Sn alloy layer has an extremely noble potential (cathode) compared to the steel base (base iron), so the exposed part of the iron (pinhole part)
Since the base iron is preferentially leached from the steel, corrosion resistance deteriorates, and in some cases, drilling corrosion may occur. In addition, such a phenomenon may expose the alloy layer or the base metal due to processing scratches during can manufacturing, and similarly to the above, this causes deterioration in corrosion resistance due to elution of the base metal, and eventually causes perforation corrosion. Furthermore, welding operations have become faster and faster in recent years, and better weldability than ever before is required. Weldability is determined by the amount of unalloyed Sn plating (free Sn), and it is important to suppress the alloying reaction during the paint baking process and increase the remaining amount of free Sn. However, as mentioned above, today's steel sheets for containers are coated with a Ni-based base plating, which is effective to some extent, but the diffusion rate of Ni and Sn is quite fast, resulting in excellent weldability. It is difficult to secure free Sn to improve the Sn content, and good high-speed weldability has not always been obtained, especially for steel plates with low Sn adhesion. The present invention has been made to solve these problems and to provide a steel plate for containers having better corrosion resistance and weldability. (Structure and operation of the invention) The present invention provides an Fe-P, Fe-Mo or Fe-P-Mo alloy base plating with a P or Mo or composite content of 1 to 60% on the surface of a steel sheet at a rate of 3 to 3 per side.
It was applied at a coating weight of 300mg/ ^m2 , and on top of this, 300mg/m2 was applied per side.
This is a method for producing steel sheets for containers with excellent corrosion resistance and weldability, in which Sn plating of mg/m ² or more is applied, or a chromate coating is applied on top of the plated Sn plating or heat melting treatment. In the first place, the present inventors believe that (1) as mentioned above, in cases where there are corrosion conditions or defects that expose the alloy layer and the base metal, it is necessary to It is possible to form a dense alloy metal with Sn without forming an alloy layer with Sn (for example, Ni-Sn alloy, Ni-Sn-Fe alloy, Ni-P-Sn alloy, etc.), and without forming an alloy layer with Sn. In addition to providing a base plating layer that can reduce pinholes (reducing ATC value), the alloy layer with Sn that is generated also
The base plating layer is closer in potential to the base iron than the Ni and Sn alloy plating layer, and suppresses preferential iron elution from the base iron even in a corrosive environment (2) During thermal diffusion processes such as heating, the base plating layer Various studies were conducted on the base plating layer, which has a much slower reaction rate than the Ni base plating layer and allows more free Sn to remain even after heat treatment. As a result, we used an Fe alloy mainly consisting of Fe metal, which has no potential difference compared to the steel substrate, as the base plating layer, and created a dense alloy layer with Sn. It has been found that a Fe-P or Fe-Mo alloy plating layer is effective in preventing the diffusion reaction of. The present invention was thus completed. The present invention will be explained in detail below. Cooled steel sheets manufactured through the rolling and annealing processes in the normal steelmaking process are subjected to pretreatment such as degreasing and pickling to clean and activate the surface, and then the Fe-P Or Fe-Mo
Or perform Fe-P-Mo alloy base plating. The effect of this base plating layer is as shown in Table 1, Figures 2 and 3. During heat treatment in the process, the alloy layer formed with Sn is dense, has few pinholes, and has a low ATC value (Figure 2), and the potential of the alloy is similar to that of Ni.
Compared to the Sn alloy layer, it is extremely close to the potential of the plating original plate, and reduces the couple current (corrosion current) between it and the base metal (Table 1). Furthermore,

【table】

[Table] (2) The formation of the FeSn ₂ alloy layer is suppressed by preventing the diffusion of the base iron and the plating layer during the heating process, and the surface layer is
It has a barrier effect that increases the amount of Sn remaining (Figure 3). (Note) Measurement method - Test piece preparation method Firing conditions Firing at 210°C for 20 minutes Conditions for electrolytic stripping of free Sn The test piece after firing was exposed to 0.5% Na ₂ CO ₃
Electrolytic degreasing is carried out cathodically in 5% NaOH, followed by anodic stripping in 5% NaOH to expose the alloy layer, followed by washing with water and drying.・Couple current measurement method Test liquid 1.5% citric acid + 1.5% salt Measurement conditions The test piece after Sn removal and the mated original plate are coupled in the test solution,
The couple current was measured with a non-resistance ammeter after 20 hours at 27°C in a nitrogen atmosphere. The test area was 2 x 2 cm. Figure 2 shows a Sn-plated steel plate with an Fe-P or Fe-Mo base alloy plating layer (coating amount per side: 780
mg/m ² ). (Note) Measurement conditions Test liquid Tomato juice was diluted 1:1 with distilled water, boiled, and 0.19g/SnCl ₂ 2H ₂ O was added (Sn ²⁺ 100ppm) used as the test liquid after ripening Measurement conditions Free Sn of the test piece Electrolytic stripping is performed in sodium hydroxide to expose the alloy layer, which is then coupled with Sn in the above test solution, and the couple current is measured after 20 hours at 27°C in a nitrogen gas atmosphere. Moreover, FIG. 3 shows the amount of free Sn remaining after heat treatment of a Sn-plated steel sheet having a Fe-P or Fe-Mo base alloy plating layer. Note (1) Fe-P and Fe-Mo alloy base plating treatment was applied at a coating amount of 75mg/ ^m2 per one side, and after washing with water.
After applying Sn plating amount of 550mg/ ^m2 per side,
The amount of free Sn was measured by performing the following heat treatment on the premise of baking the paint. Heating conditions: Firing was performed at 210°C for 20 minutes. Note (2) Measuring method of free Sn: Calculate the amount of free Sn from the electrolytic exfoliation curve during Sn removal described above (the amount of Sn before and after removing Sn was measured with fluorescent X-rays, and the difference was confirmed as the amount of free Sn) That is, the content of P or Mo in the Fe alloy is 1 to 60%, preferably 5 to 30%, and the amount of the underlying plating layer is 3 to 300 mg/m ² (per one side).
Preferably, the desired effect of the present invention can be obtained within the range of 10 to 200 mg/m ² , and a steel plate for containers having excellent corrosion resistance and weldability can be obtained. Here, if the content of P, Mo, or their composite is less than 1%, the density and low ATC value of the base alloy plating layer produced by reacting with Sn cannot be obtained, and furthermore, the base metal may deteriorate during the heating process. This does not prevent the diffusion of Sn and makes it impossible to obtain steel sheets for containers with excellent weldability and corrosion resistance. In addition, when the content of P or Mo exceeds 60% each, the effect of densification of the alloy plating layer and the
As the anti-diffusion effect of Sn saturates, the potential of the alloy layer with Sn containing the base coating layer becomes more cathodic than that of the base metal, increasing the amount of Fe eluted from the defective parts of the alloy layer, and eventually causing drilling corrosion. The upper limit of P and Mo content was limited to 60%. In addition, if the amount of the base coating layer is less than 3 mg/m ² (per side), the effect of the base plating layer will not be obtained.
Moreover, when it exceeds 300 mg/m ² , the effect reaches saturation, and the alloy layer including the base plating layer formed between Sn and Sn becomes thicker, degrading workability. Next, the method for obtaining such a base plating layer is not particularly specified, and electroplating method,
This is carried out by chemical plating (electroless plating method) or by heat mechanical dispersion treatment in the annealing process of the steel plate after applying a compound of P and Mo, and the conditions for these treatments are not particularly specified. An example of how to provide these base plating layers is as follows. (1) Fe-P alloy base plating treatment by electroplating method

[Table] (2) Fe-Mo alloy base plating treatment by electroplating method

[Table] (3) Fe-P alloy base plating using thermal diffusion treatment method After immersing in 50 g of ammonium phosphate solution at 50°C for 3 seconds, apply ammonium phosphate solution to a predetermined coating amount using high-pressure gas squeezing method. After applying to the steel plate surface,
Heat treatment at 730°C for 30 seconds in a non-oxidizing atmosphere (4) Fe-Mo alloy base plating treatment using thermal diffusion treatment Using 35g/ammonium molybdate aqueous solution, apply the specified amount of adhesion using electrostatic coating method. It is applied to the surface of a steel plate and treated by a heat treatment method such as heating at 715°C for 20 seconds in a reducing atmosphere. In this way, a steel plate is subjected to a base plating made of Fe--P or Fe--Mo alloy and then Sn plating, or further after Sn plating, heating and melting treatment (melt treatment) is performed. Regarding the Sn plating conditions and the heat melting treatment conditions after Sn plating in this case,
Usual plating conditions and heat-melting treatment conditions may be employed, and there are no particular restrictions on the plating bath composition, plating conditions, heat-melting treatment conditions, etc. For example, (1) Metsu bath composition (ferostane bath); phenolsulfonic acid
10 to 30 g/(converted to sulfuric acid) SnSO ₄ 40 to 80 g/ ENSA (additive, manufactured by Dupont) 5 to 15 g/ (2) Plating bath composition (halogen bath); Stannous chloride 50 to 100 g/ Fluoride Soda 15-35g/potassium sulfur hydride 40-60g/sodium chloride 30-60g/naphtholsulfonic acid 1-5g/current density 5-100A/ ^dm2 , bath temperature 30-60°C. In addition, heat melting treatment improves the appearance by increasing the metallic luster of the Sn plating layer, and improves the appearance of the base alloy plating layer and Sn.
This is done to further improve corrosion resistance by making the alloy layer more uniform and dense. The heating and melting treatment is carried out after Sn plating, washing with water, as it is, or applying an aqueous solution flux, at 40 to 350°C, preferably 250 to 300°C, in air or in a non-acidic atmosphere (for example, _N2 atmosphere). The Sn plating layer is melted. The flux can be treated by dipping or spraying, for example, in plating baths and ferrostan baths, phenolsulfonic acid
2 to 10 g/(in terms of sulfuric acid) of SnSO ₄ is applied and melted. In addition, the steel sheet of the present invention having a Fe-P or Fe-Mo alloy base plating layer and a Sn plating layer or a heat-melted Sn plating layer on the surface thereof has a high Sn plating layer during storage.
In order to prevent the formation of an oxide film on the surface of the plating layer and improve coating performance, chromate treatment is performed.The chromate treatment involves removing residues on the steel surface by washing with water after Sn plating or further heating and melting treatment. This is done after preliminary removal of the oxide film on the surface of the plating layer using ammonium carbonate, soda carbonate, etc. In other words, chromate treatment is performed after Sn plating or further heat-melting treatment to remove residues on the surface. salt (ammonium dichromate,
This is carried out using a mixed aqueous solution of one or more of sodium dichromate, etc.) and an aqueous solution to which SO ₄ ^-2 ions, F ^- ions, etc. are added. The chromate treatment aqueous solution or treatment conditions in this case are not particularly limited, but for example, the following chromate baths are used and the treatment is carried out under chromate conditions. (1) Chromate bath composition;
60g/CrO ₃ -0.3g/SO ₄ ^-2 Current density 7.5A/dm ² baths Temperature 60℃ Chromate coating amount (Cr conversion); 14.5mg/m ² (2) Chromate bath composition
30g/sodium dichromate Current density 10A/dm ² baths Temperature 50℃ Chromate coating amount 6.5mg/m ^2Especially to improve coating performance (paint adhesion, corrosion resistance after coating), use CrO ₃ −SO ₄ ^-2 system or CrO ₃ −
Using a chromate bath containing anions such as F ^- , a chromate coating layer consisting of a metallic chromium layer and hydrated chromium oxide is applied at a rate of 10 mg/m ² or less, preferably 5 mg/m 2 or less.
It is preferable to precipitate up to m ² at the same time. The chromate-covered layer is most suitable for applications in which the shape of the can is required to have good flexibility and is subject to severe processing, as well as applications in which excellent coating performance is required. In addition, the steel sheet for containers manufactured by the method of the present invention has a very large diffusion prevention effect of the base plating layer, base iron, and Sn plating layer, so the residual amount of free Sn is large, and the Sn adhesion amount is, for example, 1.12 g/m Excellent weldability is achieved even at a low deposition amount of less than ² (deposition amount per one side), preferably 0.70 g/m ² (deposition amount per one side). That is, in the present invention, even if the amount of Sn attached is low, even after the heat treatment for baking the paint, there is a large amount of free Sn remaining, so excellent weldability can be obtained. moreover,
Excellent corrosion resistance can be obtained due to the pinhole prevention effect of the metal Cr, even though some pinholes are generated due to the low amount of Sn deposited. In particular, due to the effect of improving paint adhesion, when the can is subjected to damage during transportation, the low Sn adhesion makes it difficult for the paint to peel off, which is extremely desirable from the viewpoint of corrosion resistance. (Effects of the Invention) As described above, the steel sheet for containers obtained by the method of the present invention has improved corrosion resistance due to the formation of a dense alloy layer due to the appropriate base plating layer for the Sn plating layer.
Compared to cases where other metals or other alloys are used as the base plating layer, the potential of the alloy layer is less likely to be cathodic than the base metal, so Fe is prioritized from the defective parts of the plating layer. There is less concern about melting and even perforation corrosion, and when heat treatment is applied, the diffusion prevention effect between the base steel and the Sn plating layer is large, resulting in improved weldability and corrosion resistance due to the residual effect of free Sn. Excellent performance can be obtained over time. In addition, as the base plating layer of the present invention, Fe-P,
Although Fe-Mo alloy was explained, Fe-P-Mo
Similar effects can be obtained with ternary alloys. This is because there are many difficult points in the plating process in an actual industrial line for ternary alloys, such as component adjustment and bath management, so explanations are omitted in this invention.
Since almost the same technique and the same effect as the present invention can be obtained, it is included in the scope of the present invention. (Example) Examples of the present invention will be described below. After degreasing and pickling the steel plate by electrolytic method using the usual method, (a) iron sulfate-sodium hypophosphite-phosphoric acid aqueous solution (b) iron sulfate-sodium molybdate-sodium citrate aqueous solution were used to degrease the steel plate at 10 A/min each. Electroplating was performed at a current density of ^dm2.The content of each P or Mo was adjusted by the content of hypophosphorous acid or the content of sodium molybdate in the solution, and the amount of deposit was adjusted by the number of coulombs. A predetermined base coating layer was obtained.
In addition, in (dip coating → thermal diffusion treatment method) (c) iron chloride -
After immersing in a sodium hypophosphite aqueous solution and (d) an ammonium molybdate aqueous solution, the amount of adhesion was adjusted by a roll squeezing method, and a base plating layer was obtained by annealing and diffusion. After washing with water, the current density in the Ferrostan bath is 30A/d.
m ² , Sn plating was applied to each coating amount, and in some cases, heating and melting treatment was performed. Then 30g/dichromate bath (no metallic chromium precipitation) or
A predetermined amount of chromate coating was obtained using a 60 g/CrO ₃ -0.3 g/SO ₄ ^-2 bath (metallic Cr precipitation) at a temperature of 60° C. and varying the current density and electrolysis time. The welding performance and corrosion resistance of the container steel sheets obtained in this way were compared with a known steel plate with a base plating layer and a Sn-plated steel plate (tin plate) without a base plating layer, and the welding performance and corrosion resistance performance were examined in the following manner. The results are shown in Table 2. (1) Welding performance After dry baking the plated plate in a simulated cycle equivalent to heat treatment of 210℃ x 20 minutes and then 190℃ x 10 minutes for paint baking, using a Sudronik welding machine,
Frequency 400Hz, lap width 0.5mm, welding speed 50m/
Seam welding was performed at min., the occurrence of dust in the welded area and the formation of nuggets in the cross section of the welded area were investigated, and the welding performance was comprehensively judged. (2) Under-coating corrosion (UCC) Apply 55% epoxy phenol paint to the plating board.
After applying ² mg/dm2 and baking at 210℃ for 10 minutes, a cross cut reaching the base metal was placed on the surface of the sample plate, and immersed in a 1.5% citric acid-1.5% NaCl aqueous solution at 55℃ for 4 days. Judgment was made based on the degree of rust spread and the peeling status of the paint film after peeling off the cellophane tape (cross-cut areas and flat areas). (3) Pitting corrosion resistance (pitting corrosion status of defective parts of painted plate) Painted under the same conditions as in 2 above, a cross cut reaching the base metal was inserted, and 50% was applied during the corrosion test shown in Table 2.
After being immersed at ℃ for 12 days, the corrosion resistance was evaluated by observing the corrosion state in the depth direction of the cross-cut portion using a cross-sectional microscope.

【table】

[Table] (4) Salt water retort resistance Epoxyphenol paint applied to plating board 55
mg/dm ² was coated and baked at 210°C for 10 minutes, the sample was subjected to contact bending and retorted in a 5% NaCl aqueous solution at 120°C for 60 minutes. Cellotape was removed immediately after the salt water retort treatment, and the state of paint film removal on the bent portion and flat plate portion was evaluated. After conducting the above performance test, the performance of the example and comparative materials was judged, and the criteria for the judgment were as shown below. ◎...Very good 〇...Relatively good △...Slightly poor ×...Very poor Note that P... and Mo... indicate the amount of P or Mo attached. As described above, the product of the present invention has extremely superior performance as a material for containers, such as corrosion resistance and welding performance, compared to the comparative plated product.

[Brief explanation of the drawing]

Figure 1 shows the Sn elution rate of various steel sheets for containers. FIG. 2 shows the ATC value of a Sn-plated steel sheet having an Fe-P or Fe-Mo base alloy plating layer. Third
The figure shows Fe-P or FeMo base alloy plating layer.
The figure shows the amount of free Sn remaining after heat treatment of Sn-plated steel sheets.

Claims (1)

[Claims] 1. Fe-P, Fe-Mo or
Fe-P-Mo alloy base plating 3 to 300 per side
300 mg/ ^m2 per side.
A method for manufacturing a steel sheet for containers with excellent corrosion resistance and weldability, which is characterized in that it is plated with Sn of mg/m ² or more, or further heat-melted, and then further treated with a chromate coating.