JPH03197695A - Very thin sn plated steel sheet for can and its production - Google Patents

Abstract

PURPOSE:To produce an Sn plated steel sheet for welded cans having superior weldability while maintaining corrosion resistance required by a material for cans with a small amt. of Sn by successively forming a Cr thermal diffusion layer, an Ni plating layer and an Sn plating layer on the surface of a steel sheet. CONSTITUTION:The surface of a cold-rolled steel sheet is uniformly plated with Cr, the plated steel sheet is annealed by heat treatment and a Cr thermal diffusion layer is formed by 0.01-0.2g/m<2> (expressed in terms of Cr) per one side of the steel sheet. The steel sheet is then temper-rolled, plated with 0.01-0.2g/m<2> Ni and further plated with 0.05-1.0g/m<2> Sn. A steel sheet for cans having superior corrosion resistance after coating and working as a material for cans such as food cans subjected to welding along the joints of the bodies is produced at a low cost.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a material for cans that uses welding to seam the seams of can bodies during the production of food cans, and is useful as a material for cans in terms of corrosion resistance after painting and processing. This invention relates to a steel sheet for cans that has excellent weldability in addition to the various characteristics described above.

[Prior art] Currently, the most widely used material for cans is S.
There are n-plated steel sheets and tin-free steel. Sn-plated steel sheets have been used since the last century, and the properties of Sn-plated steel sheets as a material for cans are extremely excellent. However, as is well known, Sn is a limited resource, so the history of the development of Sn-plated steel sheets is also the history of technology for saving Sn.

The can body is made by rolling a rectangular can material and seaming both ends. This seaming technology was also developed in response to the need to save Sn in Sn-plated steel sheets, and it started with soldering, and now welding, gluing, etc. It is put into practical use.

Tin-free steel is a Cr-plated steel plate, and has a total (S)
Unfortunately, the seams can only be seamed using adhesive methods using organic materials, and welding methods are not practical. However, there are some limitations in usage and process. In the welding method, the joints are overlapped and sandwiched between copper wire electrodes, and electrical resistance heat welding is performed while applying pressure with rolls. At this time, with tin-free steel, there is a lot of oxide, which is an insulator, on the coating surface, and the electrical contact resistance between the joint surfaces is too high, so a high voltage must be applied. A splash called flow dust is generated. At present, it is known that the presence of a small amount of Sn in the outermost layer of the plating eliminates the problem of 1.: It is said that the minimum amount of Sn is 0.05 g/m" In the development of steel sheets for cans,
In addition to improving its properties as a material for cans, such as corrosion resistance and workability, efforts are being focused on leaving a minimum amount of Sn during welding.

Generally, the paint inside the can is baked before welding, and at this time the Sn plated on the steel plate becomes alloyed with the diffused Fe and loses the characteristics of metal Sn.Only Sn is plated and a chemical conversion treatment is applied on top of it. Taking this point into consideration, the Sn-plated steel sheet
So-called #10 tin tin with Sn content reduced to 1.1 g/m'' is in use.On the other hand, there are plating film configurations that do not impair weldability as well as the other properties mentioned above even if the Sn amount is further reduced. Therefore, it is being considered to provide a Ni or Cr plating layer under the Sn layer.For example, Japanese Patent Laid-Open No. 63
-499, Cr or Cr-Ni is diffused on the surface of the steel plate, and this diffusion layer suppresses the formation of 5n-Fe alloy during paint baking, reducing the amount of Sn plating to 0.1 g/m2. is proposed.

[Problems to be Solved by the Invention] However, although the diffusion layer of Cr and Fe or the diffusion layer of Cr, N1, and Fe can suppress the generation of Sn-Feb gold, the degree of suppression is limited. Since there is a limit to the amount of Sn, and about half of the amount of Sn is alloyed, there remains the problem that further savings cannot be made.

This invention was made to solve this problem.
Furthermore, it is an object of the present invention to provide a steel plate for welded cans that does not impair weldability and other properties as a can material even if the amount of Sn is reduced.

Means for Solving Problem 1] The means for achieving this objective is to cover the surface of the steel plate with a Cr heat diffusion layer, to have an Nj plating layer on the heat diffusion layer, and to cover the Ni plating layer. 0.05g/m2 or more1.
This is a multilayer plated steel plate for welded cans having an Sn plating layer of 0 g/m" or less, and with such a plating film structure, preferably the thickness of each layer is Cr thermal diffusion layer on one side in terms of Cr. Welded steel plates for welded cans having a Ni plating layer of 0.01g/m2 or more and 0.2g/lo'' or less per side, or steel plates for welded cans that have a Ni plating layer of 0.01g/m2 or more and 0.2g/lo'' or less per side. Furthermore, the method for producing these welded steel sheets for cans is also a means to achieve this objective, and involves uniformly plating Cr on the surface of the steel sheet before heat treatment.
A Cr-plated steel sheet is used, and a Cr heat dissipation layer is generated when this Cr-plated steel sheet is heat treated. This method of manufacturing a steel sheet for welded cans is characterized by applying Ni plating after temper rolling, and then applying a thin Sn plating.

[Function] It is well known that the lowermost Cr heat diffusion layer provides corrosion resistance to the plated steel sheet and suppresses S ri -Fe alloying during paint baking. In addition to these effects, the presence of this heat diffusion layer allows good corrosion resistance to be maintained even after processing. When subjected to severe processing, cracks occur in the plating film, and in a non-diffused Cr plating layer, the steel base is exposed beneath the cracks, but in a heat diffusion layer, Cr is diffused deep into the layer. Even if a crack occurs at the top of the steel, Cr particles exist below the crack to prevent the steel from being exposed.

For this reason, the anticorrosive layer continues even after the tightening process or drawing process during can manufacturing and maintains the anticorrosion effect. However, a drawback of this Cr thermal diffusion layer is that when Sn plating is applied thereon, the adhesion efficiency of the plating decreases. A Ni plating layer is highly effective in preventing this decrease in efficiency. On the surface of the metal Cr or Cr diffusion layer, oxides or hydroxides are likely to be generated, the precipitation of Sn is suppressed, and the surface diffusion of the precipitated Sn is not easy. On the other hand, Ni
During plating, Cr oxides and the like are easily reduced, and since Ni has high surface diffusivity, a highly uniform coating is formed even on the Cr diffusion layer.

In addition, there are few oxides on the Ni surface (and Sn also forms a uniform film on the surface of the Ni plating layer, improving plating efficiency. Therefore, even if the Sn film on Ni is thin, it can efficiently coat the entire surface. Also, if this Ni plating layer exists between the Cr thermal diffusion layer and the Sn plating layer,
Even if it is very thin, it is extremely effective for paint baking at just 5nF.
e Alloying is suppressed and most of the Sn remains in the state of metal Sn even after the coating is baked at 200° C. for 10 minutes. For this reason,
There is no need to plate an extra amount of Sn to be alloyed, and weldability can be ensured with a small amount. In addition to this, the Ni plating layer also has the effect of compensating for the Cr thermal diffusion layer, which tends to crack when subjected to processing.

At the seam weld, the Sn plating layer reduces the contact resistance during electric resistance heating welding due to the softness and low melting point unique to Sn, enabling good welding, and also serves as a corrosion-resistant coating after filling the can contents. Function.

The amount of Sn plating is sufficient to ensure weldability, but if it is too small, there is a risk of dusting during welding.
05 g/m" or more is required. Also, the higher the amount of Sn, the better the weldability, but the effect of increasing the amount gradually decreases, so from the perspective of saving Sn, the upper limit is set at 1.0 g/m2. Therefore, the surface of the steel plate is covered with a Cr heat diffusion layer, and a Ni plating layer is formed on the heat diffusion layer, and a coating rate of 0.05 g/m1 per side is formed on the Ni plating layer.
A steel sheet for cans that is multi-layer plated with the above Sn plating layer satisfies the characteristics of can materials such as paintability and corrosion resistance, even with a plating film structure with a small amount of Sn, and has sufficient properties. It has excellent weldability.

Regarding the amount of Ni plating, even an extremely thin plating layer
It exhibits effects on plating efficiency, suppression of 5n-Fe alloying, and corrosion resistance, but is practically stable.1. In order to obtain such effects, it is preferable that the Ni plating amount is 0.01 g/m or more.Although the corrosion resistance increases as the amount of Ni plating increases, the effect of improving Sn plating efficiency and the effect of suppressing 5n-Fe alloying is less than 0.2 g.
/m2 is already saturated, so from the viewpoint of resource saving and economics, a value of 0.2 g/m" or less is appropriate.

Regarding the lowest Cr heat diffusion layer, metal C is applied to the surface of the steel plate.
Since the Cr plating layer is formed and then diffused by heating, the Cr concentration is large (the Fe concentration is small) in the upper part of the diffusion layer. Therefore, even if the Cr plating amount is small, the 5n- Although Fe alloying is suppressed, in order to obtain a practically stable effect, it is preferable that the amount is 0.01 g/m" or more. If the amount of Cr is too large,
If it exceeds m2, the hard alloy layer becomes thick and the joint surface lacks flexibility, which is not preferable for weldability.

The effect of suppressing 5n-Fe alloying also becomes saturated when it exceeds 0.2 g/m2, so from the viewpoint of resource saving and economics,
2 g/m'' or less is practical.

Heat treatment and temper rolling are used to give steel sheets the mechanical properties necessary for can material, but if Cr plating is performed before heat treatment, the heat treatment can also serve as Cr diffusion, resulting in energy savings. , Also, ll of the steel plate by second heat treatment! If the heat treatment is an annealing treatment performed after cold rolling, the mechanical properties will not be affected.
Steel plates for cans are first heated to around 700°C, and during overaging treatment they are heated to around 500°C. Since the Cr thermal diffusion layer is sufficiently formed by either heat treatment, either heat treatment may be adopted.

[Example 1 (Example 1) 0 Cr was added to the surface of a cold rolled steel plate using an N84F addition bath.
．． 05g/m'' plated, heat treated at 680°C for 30 seconds, and temper rolled with an elongation rate of 2%, and then plated with Ni with varying amounts of coating.This test piece was used as a test piece. The surface was subjected to Sn plating at 0.7 g/r[11] to examine the plating efficiency, and at the same time, the plated surface was observed using a scanning electron microscope.

The plating conditions were as follows.

Cr plating CrO3200g/m"(NHa>F3g/m" Bath temperature
50℃ Current density 40 A/d m2Ni plating Ni SOa・6Hz 0 240g/m”NIC1
2-6H2045g/m2 83 B Os 30g/m”p
H2,6 Bath temperature 50°C Current density 40 A/d m"Sn plating: Sn" 30 g/m"phenol sulfonic acid 70 g/to" brightener
5 g/m” Bath temperature 5
0°C current density 20 A/d tn” The measurement results of plating efficiency are shown in Figure 1, where the vertical axis is Sn.
Plating efficiency, the horizontal axis is the amount of Ni plating. There is a clear relationship between the two, and the amount of Ni plating is 0.01.
The Sn plating efficiency suddenly improves as the temperature approaches 0.
．． At 0.2 g/m2, it reaches 80%. After that, even if Ni increases, the efficiency increases slowly.

When observing the Sn plating surface, those with an efficiency of 80% or more were smooth, but those with an efficiency of 40% or less were rough and had whiskers.

(Example 2) The surface of a cold-rolled steel sheet was plated with 0.1 g/m'' of Cr, and the plate was plated with 0.02 g/+N2 of Ni on the surface of the cold-rolled steel sheet, which was subjected to or without temper rolling after thermal diffusion. in addition,
Sn plating was applied by changing the amount, and finally chromate treatment was performed. Plating was performed in the same manner as in Example 1, and a commonly used sodium dichromate bath was used for chromate treatment. At the same time, for comparison, we made a steel plate without Ni plating and a steel plate directly plated with Sn, and used these as test pieces. After baking for 10 minutes, the amount of Sn alloyed at this time was examined. These results are shown in Table 1.

Test floors 1 to 5 were Ni-plated, and the amount of alloyed Sn was zero regardless of the presence or absence of heat treatment, the presence or absence of temper rolling, and the amount of Sn. The fact that there was no relationship with the presence or absence of temper rolling is considered to be because even if some cracks were generated in the Cr heat diffusion layer due to temper rolling, the Ni plating layer compensated for them.

On the other hand, Cr thermal diffusion layer or Cr-N without Ni plating
i Test Na6. Sn plating was applied directly on the heat diffusion layer.
In Test No. 7 and No. 8, approximately 30 to 40% of Sn was alloyed, and in Test No. 8, in which neither Cr plating nor Ni plating was applied, as much as 70% of Sn was alloyed.

Table 1 (Example 3) Corrosion resistance and weldability were examined for test pieces that were plated with varying amounts of Cr plating, Ni plating, and Sn plating and then subjected to chromate treatment. Plating was carried out in the same manner as in Example 1, and for chromate treatment, 50 g/1 of chromic anhydride was used.
A well-known bath in which 1 g/g of ammonium fluoride was added to 2 was used. For comparison, the sample materials include a comparative example outside the scope of the invention and a conventional Cr thermal diffusion layer or a Cr-Ni thermal diffusion layer with S
A conventional example in which n was plated was included.

In the corrosion resistance investigation, we conducted a post-processing corrosion resistance test, an iron elution test, and an under-coating corrosion resistance test.

Corrosion resistance after processing is to examine the corrosion resistance after the seaming process during can manufacturing, by folding the test piece in half and adding 1.
96% at 38°C in an aqueous solution containing 5% and 1.5% citric acid.
After immersion for a period of time, rusting of the iron was examined. When folding in two, so-called close folding without inserting any smoother between them is OT, and I is when a plate of the same thickness as the test piece is inserted.
The T value is determined based on the bending method up to 5T and up to which bending method rust does not occur. Here, 30 samples were tested, and the cases where all were better than IT were evaluated as Δ when 012T was mixed, and the cases where 3T was mixed were evaluated as ×.

The iron elution test examines the resistance to corrosion caused by the contents of cans such as fruits and juices.The test material is coated with 20 μm of epoxy paint inside the can, baked at 205℃ for 10 minutes, and then coated with 1.5% quench VI. Add to an aqueous solution containing 1.5% salt at 38°C.
The samples were immersed in water for 96 hours, and the amount of iron eluted into the immersion solution was measured.

As the under-coating corrosion resistance test, a UCC test and a blister test were conducted, and the under-coating corrosion resistance was evaluated based on the worse result of both tests. In the UCC test, the paint inside the can is baked in the same manner as in the iron elution test, then scratches reaching the base are made in a cross pattern with a knife on the paint film, and after being immersed under the same conditions as in the iron elution test, the deterioration around the scratches is measured. To determine the state of deterioration, visually observe the peeling of the paint film and the corrosion of the substrate, and look at the state where no corrosion is observed and the state where some O1 corrosion is observed but can withstand practical use by Δ, -. Corrosion is observed and the condition is ×
It was evaluated by

In the blister test, as in the iron elution test, a test piece with a baked-in can coating was first heated to 120°C in 0.1% salt and exposed to a pressure of 2 kg/ant for 1.5 hours. After this, the coating film was immersed in 01% saline solution at 38° C. for 96 hours, and the state of deterioration of the coating film was observed. The observation determines the ratio of the area of the blistered portion of the paint film to the total area. When the ratio was less than 5%, it was evaluated as ◯, when it was 5 to 20%, it was Δ, and when it was over 20%, it was evaluated as ×.

Weldability was evaluated by measuring the electrical contact resistance between similar materials. Two test pieces were stacked and inserted between copper electrodes with a diameter of 511 cm, and current was applied under a pressure of 4000 kg/co (2000 kg/co), and the contact resistance was determined from the current applied at this time and the potential difference between the test pieces.

The sample materials and test results are shown in Table 2.

In the example, test magnets 1 to 18 in the preferred condition range are
Of course, fully satisfactory results were obtained in all items, and in test Na19, which had a slightly lower amount of Cr plating, the amount of iron elution and contact resistance were slightly higher than in other examples, and the amount of Ni plating was small. Similarly, in Test @Magnetic 20, the amount of iron eluted was somewhat large, but both tests had results that were acceptable for practical use.

Table 1 Cr-Ni (85:15) On the other hand, in comparison with the Examples, in the comparative examples, the corrosion resistance after processing was poor in test holes 21 and 23, in which the Cr plating layer was not thermally diffused, and the amount of Cr plating was extremely high. Test Fox 22, which is often used in Japan, has poor weldability. The amount of Sn is the lower limit and the amount of Sn is the lower limit and
In test No. 24 where no layer was present, the amount of iron eluted increased and the weldability decreased to the very limit of practical use. Furthermore, Cr
If neither the heat diffusion layer nor the Ni plating layer is present, the test magnet will be 25.
As shown in No. 26, the characteristics are further deteriorated. That is, if there is no Cr thermal diffusion layer or Ni layer, the amount of Sn is 0.05 g/m
Although it is dangerous to reduce the thickness to 2, even with a thin plating layer, the existence of the Ni layer on the Cr thermal diffusion layer makes this possible while ensuring stable thermal characteristics.

Compared to the example, in the conventional example, the thermal diffusion Cr layer or the Cr
Even if there is a -Ni thermal diffusion layer, if the Sn amount is about 0.1 g/m2, the corrosion resistance of processed parts, iron elution, and weldability are slightly inferior.

[Effects of the Invention] As described above, according to the present invention, N is formed on the Cr thermal diffusion layer.
Since it has a film structure with an i-plated layer and a Sn-plated layer on top of it, the amount of Sn required is dramatically smaller than before, and the amount of Cr and Ni is also small, making it an excellent material for cans. This is a steel plate for welded cans that has excellent weldability while maintaining the necessary corrosion resistance. As described above, it must be said that the effects of this invention, which achieves excellent performance and resource saving, are significant.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of Ni and the alloy suppressing effect, which explains the present invention in detail.

Claims (4)

[Claims] (1) The surface of the steel plate is covered with a Cr heat diffusion layer, and on this diffusion layer there is a Ni plating layer, and on the Ni plating layer, there is a
．． A steel plate for welded cans having a Sn plating layer of 05 g/m^2 or more and 1.0 g/m^2 or less. (2) Cr thermal diffusion layer is 0.01g in terms of Cr per side
2. The steel plate for welded cans according to claim 1, wherein the steel sheet has a tensile strength of 0.2 g/m^2 or more and 0.2 g/m^2 or less. (3) Ni plating layer is 0.01g/m^2 or more 0.2g
3. The steel plate for welded cans according to claim 1 or claim 2, wherein the steel sheet has a thickness of /m^2 or less. (4) Cr is uniformly plated on the surface of the steel sheet before heat treatment to produce a Cr-plated steel sheet, and when this Cr-plated steel sheet is heat treated, a Cr heat dissipation layer is generated, and after temper rolling, N
Apply i-plating and apply 0.05g/m^2 or more on it1.
A method for manufacturing a steel plate for welded cans, characterized by applying Sn plating of 0 g/m^2 or less.