JP2959024B2 - Ni-plated steel sheet for can and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a material for cans in which seams of a can body are welded by welding in can making of food cans and the like, and as a material for cans such as corrosion resistance after painting and corrosion resistance after processing. The present invention relates to Ni-plated steel sheets for welded cans, which ensure the weldability in addition to the various characteristics described above.

[Prior Art] Ni-plated steel sheet is one of the materials currently used for cans. Ni is a metal with good corrosion resistance, and also has the required processing characteristics and weldability for can materials. Many can bodies, such as food cans, are made by rolling a square can material and seaming both ends, and soldering, welding, bonding, and the like are used for this seam. Soldering is used only for Sn-plated steel sheets, and the welding method and the bonding method are recently used methods.However, when comparing these two methods, the welding method is superior in various aspects, and organic materials are used. In the conventional bonding method, the adhesive has a limitation in heat resistance and a reduction in productivity due to the bonding time, and is limited in use and process. In the welding method, the seams are overlapped and sandwiched between copper wire electrodes,
Electric resistance heating welding is performed while pressing with a roll. At this time, for example, in the case of a Cr-plated steel sheet, the hardness of the coating surface is large, the area covered with the oxide or hydroxide of Cr is large, and the actual contact area is smaller than the apparent contact area. For this reason, the contact electric resistance between the joint surfaces increases, and a high voltage must be applied to obtain a desired welding current. When a high voltage is applied, the current flows locally and a splash called dust is generated in this local area, so that a good weld surface cannot be obtained. Ni-plated steel sheets to which this welding method can be applied are suitable for can materials.
For example, JP-A-36-15252 proposes a Ni-plated steel sheet in which Ni is plated at 0.02 to 0.3 μm. Recently, proposals have been made to improve corrosion resistance and weldability.
In JP-A-62-139898, 10 mmg / m2 to ²⁰⁰ mmg / m
A surface-treated steel sheet is disclosed, which is plated with Cr of ² and further plated with Sn, Cu, or Ni of ²⁰ to 500 mmg / m ² in a state having locally convex portions thereon, and having a chromate layer in the upper layer again. ing.
In this method, corrosion resistance is ensured by a double plating layer, and defects in the weldability of Cr are compensated for by the upper plating layer.

[Problems to be Solved by the Invention] However, when the Ni plating layer is present, the electrode potential of Ni is much more noble than the electrode potential of Fe, and Fe is very easily eluted by contact electrolytic corrosion. This phenomenon is particularly severe in the case of vegetable juices and meats containing salt in the contents of the can, and the can may be perforated. JP-A-62-13
As in 9898, when a Cr plating layer is present between the Ni plating layer and the steel substrate, the potential gradient is alleviated and the tendency is slightly improved. A crack is formed, exposing the steel at the tip. For this reason,
There remains a problem that the corrosion resistance after processing required for can materials is insufficient, and pitting corrosion cannot be prevented.

In order to solve this problem, the present invention has been made, and aims to provide a steel plate for a welding can having excellent corrosion resistance and pitting corrosion resistance together with various properties as a material for a can, such as weldability. is there.

Means for [Means for Solving the Problems] To achieve the object, the surface of the steel sheet is covered with Cr thermal diffusion layer, 0.05 g / m ² or more 1 g / m ² on the diffused layer
It is a steel plate for a welding can having the following Ni plating layer and having a chromate layer on the Ni plating layer, and in such a film configuration, preferably, the Cr heat diffusion layer is 0.02 g / m ² or more. 0.
2 g / m and a welding steel sheet for cans is ² or less, chromate layer C
a welding steel sheet for cans containing 0.005 g / m ² or more 0.03 g / m ² or less r. Furthermore, a method of producing such a steel sheet for welding is also a means of achieving the object, and the method is to apply a Cr plating to the surface of the steel sheet before heat treatment, and to generate a Cr heat diffusion layer when performing the heat treatment of the steel sheet. This is a method of manufacturing a steel plate for a welding can that is subjected to Ni plating after temper rolling, and then subjected to chromate treatment.
Other methods of generating the Cr thermal diffusion layer include a method of applying a Cr / Fe alloy plating and performing a heat treatment, and a method of applying a Cr plating and then applying a Fe
Plating method, and Cr / Fe
There is a method of applying alloy plating.

[Action] It is well known that a Cr-Fe alloy generally has corrosion resistance. The presence of the Cr thermal diffusion layer can maintain good corrosion resistance even after processing. In other words, in a Cr plating layer that has not diffused, when subjected to severe processing, a crack occurs in the plating film, and under this crack, the steel base is exposed, but in the thermal diffusion layer, Cr is diffused deeply. Even if a crack occurs at the top of the layer, there is still Cr under the crack to prevent the steel from being exposed. For this reason, the elution of Fe is suppressed and the corrosion resistance is maintained even after the winding process at the time of can making. Further, this Cr thermal diffusion layer has an action of suppressing pitting corrosion in addition to its corrosion resistance. When there is a plating layer with a noble potential for steel, such as Ni, not only cracks during processing but also film defects such as pinholes constitute the steel base and battery, and the dissolution of the base steel is promoted. The steel substrate is deeply eroded. The elution amount is proportional to the potential gradient, but the potential of the Cr diffusion layer is located between steel and Ni, and this gradient is moderated to suppress erosion of the substrate. Even if the Cr plating layer is not diffused, its potential is located between the steel and Ni, so one step is relaxed where the Cr plating film exists, but it is continuous like the Cr diffusion layer. There is no relaxation. The effect of the continuous relaxation is particularly remarkable where cracks and pinholes are present.

However, weldability cannot be obtained only with the Cr heat diffusion layer. That is, this layer is hard, has a small actual contact area when the welded portions are brought into contact with each other, and has a large contact electric resistance since oxides or hydroxides having insulating properties are easily generated. this
If the Ni plating layer is on the Cr diffusion layer, this defect is compensated. In addition, Ni is a metal having good corrosion resistance, and the corrosion resistance is extremely enhanced. Although the Ni plating layer is effective even if it is thin, it is necessary to make up for the defect in weldability of the Cr thermal diffusion layer.
A thickness of 0.05 g / m ² is required. Further, even if the thickness exceeds 1 g / m ² , the effect does not change much and the metal is quite expensive. Therefore, the upper limit is appropriately 1 g / m ² . In addition to the corrosion resistance and weldability described above, the properties required for can materials include the adhesion of the paint in the can. The chromate layer on the Ni plating layer improves the adhesion of the paint, and may be a chromate layer generally used for Sn-plated steel sheets. However, in order to ensure the adhesion of paint,
The content is preferably 0.005 g / m ² or more in terms of Cr, and if it is too large, the amount of oxides and hydroxides increases and the weldability may be impaired. Therefore, the content is preferably 0.03 g / m ² or less.

The effect on the corrosion resistance after processing of the Cr diffusion layer is 0.
Although appearing at about 001 g / m ² , in consideration of the variation in working conditions in practical use, the Cr content is desirably 0.002 g / m ² or more in order to surely maintain the corrosion resistance after the winding work. As for the corrosion resistance, the thicker the Cr heat diffusion layer, the better. However, the hardness of this layer is higher than that of steel or Ni. If it is too thick, it will lack flexibility when the welded surfaces are brought into contact, and impair weldability. Furthermore, considering the economics and effects, the amount is 0.
It is desirable that it be ² g / m ² or less.

In order to manufacture the above steel plate for a welding can, it is necessary to first form a Cr heat diffusion layer. For this purpose, if Cr or a Cr-Fe alloy is attached to the surface of the steel sheet before the heat treatment, Cr is thermally diffused when the steel sheet is heat-treated. This method is more economical than plating a steel sheet which has been subjected to heat treatment and temper rolling and has adjusted mechanical properties, as is generally performed, and is not affected by the second heat treatment. Only needs to be done. In addition, since heat treatment is generally performed in a reducing atmosphere, oxides and the like on the Cr plating layer are also removed.
The steps of undergoing heat treatment in the steel sheet adjustment stage include an annealing step after cold rolling and an overaging step, and only some of the latter undergo the treatment. The former is heated to around 700 ° C, and the latter is heated to around 500 ° C. Since Cr diffuses sufficiently in any of the heat treatments, either heat treatment step can be used.

When the heat treatment is performed after plating the Cr-Fe alloy, a diffusion layer having a gentle Cr concentration gradient is formed even when the heat treatment temperature is low or the treatment time is short. Plating Cr on it
When heat treatment is performed after plating of Fe, Cr in the deep part of the diffusion layer
The concentration can be ensured. Cr is plated, and Cr
Even when the heat treatment is performed after plating the Fe alloy, the Cr concentration in the deep part of the diffusion layer can be ensured. These adhesion methods may be selected in consideration of the use of the material for the can, the sheet thickness, the annealing conditions, and the like.

When Ni plating is applied after temper rolling, the contact area can be increased at the time of welding as described above, and even if a crack occurs in the Cr heat diffusion layer due to temper rolling, it can be covered. I can do it. The uppermost layer is subjected to the chromate treatment in order to secure the adhesion of the paint as described above, and may be performed using a dichromic acid bath or a chromic acid bath as is generally performed.

Example 1 Example 1 The surface of a cold-rolled steel sheet is plated with Cr or a Cr—Fe alloy with a different amount of adhesion, and is subjected to a heat treatment at 680 ° C. for 3 seconds to have an elongation of 2
%, After temper rolling, Ni was plated with a different amount of adhesion, and a chromate treatment was performed thereon. The corrosion resistance, paint adhesion, and weldability of these test pieces and the test piece of the conventional example that was not subjected to heat treatment after Cr plating were examined.

 The plating and chromate conditions were as follows.

Cr plating: CrO ₃ 200 g / (NH ₄ ) F 3 g / Bath temperature 50 ° C Current density 40 A / dm ² Cr / Fe alloy plating: CrO ₃ 200 g / FeCl ₂ .4H ₂ O 150 g / m ² Bath temperature 45 ° C. pH 1.8 current density 40A / dm ² Ni _{plating: NiSO 4 · 6H 2 O 240g} / NiCl 2 · 6H 2 O 45g / H 3 BO 3 30g / bath temperature 45 ° C. pH 2.7 current density 10A / dm ² chromating A: Na ₂ Cr ₂ O ₇ 20 g / bath temperature 40 ° C pH 5.5 Current density 5 A / dm ² Chromate treatment B: CrO ₃ 20 g / Na ₂ SO ₄ 0.6 g / bath temperature 40 ° C pH 5.5 Current density 40 A / dm ² Test No. 1 , 3, 5, 7, 9, 11, and 13 were treated with chromate treatment A, and Test Nos. 2, 4, 6, 8, 10, and 14 were treated with B.

In Test Nos. 1, 5, 9, and 13, after Cr plating,
Heat treatment for 0 seconds, and in test Nos. 2, 6, 10, 14
Perform e-alloy plating and heat treatment at 430 ° C for 6 hours. In Test Nos. 3, 7, 11, and 15, after applying Cr plating, apply a half of Fe plating and then heat treat at 530 ° C for 5 hours. In Test Nos. 4, 8 and 12, Cr.
Heat treatment was performed at 80 ° C. for 30 seconds.

As the corrosion resistance test, corrosion resistance after processing, corrosion resistance under coating,
An iron dissolution test and a pitting corrosion test were performed, a T-peel test was conducted as a paint adhesion test, and a contact electric resistance was examined for weldability.

Corrosion resistance after processing is to examine the corrosion resistance after winding processing at the time of can-making.
After being immersed in an aqueous solution containing 5% and 1.5% citric acid at 38 ° C. for 96 hours, iron rusting was examined. When bending into two, no spacer is inserted between them, so-called close contact bending is OT, 1T when a plate of the same thickness as the test piece is inserted, up to 5T indicated by the spacer thickness ratio below Is determined by the T value according to which bending method did not cause rust. Here, 30 samples were tested and all were 1T
The case where it was better was evaluated as ○, the case where 2T was mixed was evaluated as Δ, and the case where 3T was mixed was evaluated as x.

The iron dissolution test examines the corrosion resistance of the contents of cans such as fruits and juices. Paint the test material with an epoxy-based paint in a can (20 μm), bake at 205 ° C for 10 minutes, and then add 1.5% citric acid and sodium chloride. It was immersed in an aqueous solution containing 1.5% at 38 ° C. for 96 hours, and the amount of iron eluted in the immersion liquid was measured.

In the investigation of corrosion resistance under a coating film, a UCC test and a blister test were conducted, and the worse of the results of both tests was evaluated.

In the UCC test, the paint in the can is baked in the same way as the iron dissolution test, and the coating is scratched with a knife to reach the base in a cross shape. The situation was observed. The deterioration was observed by visually observing the state of the coating film turning over and the state of corrosion of the substrate, and the state where no corrosion was observed was evaluated as ○, the state where corrosion was slightly observed but was practically acceptable, and the state where corrosion was observed at first glance It evaluated by x.

In the blister test, similarly to the iron dissolution test, a specimen in which a coating film in a can is baked is first heated to 120 ° C. in 0.1% salt and exposed to a pressure of ² kg / cm ² for 1.5 hours. After this, further 0.1
% Saline solution at 38 ° C. for 96 hours, and observe the state of deterioration of the coating film. In the observation, the ratio of the area of the portion where the blister is generated in the coating film to the whole is determined. ○ 5 when the rate is less than 5%
2020% was evaluated as Δ, and when it exceeded 20%, evaluated as ×.

The pitting corrosion test is similar to the iron dissolution test.
After soaking for a period of time, the state of corrosion was examined. The tip of the needle is 1.5 μmR,
The pressing load is 17g heavy, the corrosion liquid is citric acid 1.5%, salt 1.
It was a 5% aqueous solution. In this test, corrosion occurs as if holes were dug along the flaw. This is shown in FIG.

(A) is a top view of the test piece after the test, 1 is a test piece, 2 is a flaw made by a needle, and 3 is a hole made by corrosion. It is determined that the shape of the hole 3 is such that the narrower the opening and the greater the depth, the greater the tendency of pitting corrosion. (B) The figure is an enlarged and schematic view of the hole 3, wherein the major axis and minor axis of the opening are a or b, the depth is d, and the tendency of pitting is 2d / (a + b), that is, And the average pore diameter of the opening. If this ratio exceeds 1.5, it is determined that the material is likely to cause pitting corrosion.

In the T-peel test, an epoxy phenol resin was applied at 50 mg / m ² before the treatment, baked at 205 ° C. for 10 minutes, and a nylon film was narrowed and thermocompression-bonded between the two coated specimens cut to 5 mm width. The test piece was used as a measurement specimen, and the force required to peel it off at 20 μm / min was measured.

The weldability was evaluated by measuring the contact electrical resistance between the same type of materials. ^Two test pieces were stacked and inserted between copper electrodes having a diameter of 5 mm, and a current was applied under a pressure of 4000 kg / cm ² , and a contact resistance was determined from a current flowing at this time and a potential difference between the test pieces.
Table 1 shows the test materials and test results.

In Examples, the test N having a smaller Cr content than the preferable range
o.3 has a slightly higher iron elution amount and test No. 7 in which the chromate layer is less than the preferred range, T-peel test value is slightly smaller, and test No. 10 in which the chromate layer is more than the preferred range, the contact resistance Although somewhat large, satisfactory results were obtained in all items including these.

In contrast, in the comparative example, the test with a small amount of Ni plating was performed.
In No.11, the weldability was not sufficiently improved, and in the test with a small amount of Cr thermal diffusion layer, in No.12, the corrosion resistance after processing, corrosion resistance under the coating film and iron elution test were slightly inferior, and the tendency of pitting was clear Appears. In Test No. 13 with a small chromate layer, the corrosion resistance under the coating film and the T-peel test were inferior, and in Test No. 14 with too many chromate layers, the contact resistance increased. This phenomenon is similar to that of Test No. 15 in which the amount of Cr is extremely large.

In the conventional example, the Cr plating layer is a non-diffusion layer and has a large tendency to pit. Inevitably, the corrosion resistance after processing and the corrosion resistance under the coating film are inferior, and the iron elution amount is large.

[Effects of the Invention] As described above, according to the present invention, Ni is deposited on the Cr thermal diffusion layer.
There is a coating structure in which a plating layer exists and a thin chromate layer covers the plating layer. Therefore, in addition to the corrosion resistance of Ni and Cr, the Cr thermal diffusion layer alleviates the sharp potential gradient between Ni and Fe to prevent pitting, and the Ni plating layer lowers the contact resistance and improves weldability. The chromate layer enhances paint adhesion.
As described above, the effect of the present invention in which each layer exhibits various characteristics and satisfies various characteristics as a material for a welding can, even if it is a thin film, is inevitably significant.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of pitting for explaining the tendency of pitting. 1 ... test piece, 2 ... flaw, 3 ... pitting corrosion.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-274091 (JP, A) JP-A-63-499 (JP, A) JP-A-62-139898 (JP, A) JP-A-61-1986 159596 (JP, A) JP-A-59-232296 (JP, A) JP-A-57-192286 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C25D 5/26 C25D 5 / 14 C25D 5/50

Claims (7)

(57) [Claims] Surface of 1. A steel sheet is covered with Cr thermal diffusion layer has a 0.05 g / m ² or more 1 g / m ² or less of the Ni plating layer on the diffusion layer, chromate on the Ni plating layer Steel plate for welding cans having layers. Wherein Cr thermal diffusion layer is 0.02 g / m ² or more in weight Cr 0.2 g / m ²
The steel plate for a welding can according to claim 1, which is: 3. The chromate layer has a Cr equivalent of 0.005 g / m ² or more and 0.0
3 g / m ² or less welded steel sheet for cans according to claim 1, wherein. 4. The steel plate before heat treatment is plated with Cr.
A method for producing a steel sheet for a welded can, characterized in that a Cr heat diffusion layer is generated during heat treatment of this steel sheet, temper rolling is performed, Ni plating is performed, and then chromate treatment is performed. 5. A steel sheet before heat treatment is coated with a Cr-Fe alloy, a heat-spreading layer is formed when heat-treating the steel sheet, temper-rolled, then Ni-plated, and then chromate-treated. A method for producing a steel plate for a welding can, wherein the method is performed. 6. The steel sheet before heat treatment is plated with Cr.
Next, Fe plating is applied, and when this steel sheet is subjected to heat treatment, Cr
A method for producing a steel sheet for a welding can, characterized in that a heat diffusion layer is generated, temper rolling is performed, Ni plating is performed, and then a chromate treatment is performed. 7. The steel plate before heat treatment is plated with Cr.
Next, a Cr-Fe alloy plating is performed, and when this steel sheet is subjected to heat treatment, a Cr heat diffusion layer is generated, and after temper rolling, Ni plating is performed, and then a chromate treatment is performed. Production method.