JPH03197693A - Very thin sn plated steel sheet for can and its production - Google Patents

Abstract

PURPOSE:To produce an Sn plated steel sheet for cans having superior characteristics such as weldability as a steel sheet for cans with a small amt. of Sn at a low cost by successively forming a Cr thermal diffusion layer, an Sn plating layer and a chromate layer having fine protrusions on the surface of a steel sheet. CONSTITUTION:When an Sn plated steel sheet for producing cans such as food cans is produced, the surface of a cold-rolled steel sheet is plated with Cr or further plated with Fe or plated with a Cr-Fe alloy before heat treatment. The plated steel sheet is annealed by heat treatment and a Cr thermal diffusion layer contg. 0.02-0.2g/m<2> Cr per one side of the steel sheet is formed. The steel sheet is then temper-rolled, an Sn plating layer is formed by such a small amt. as 0.05-1.0 g/m<2> and anodic electrolysis, and cathodic electrolysis are carried out in the conventional chromating soln. contg. chromic acid or dichromate to form a chromate layer having >=10 fine protrusions per 1mum<2> by 3-30 mg/m<2> (expressed in terms of metallic Cr). A steel sheet for cans having superior weldability and superior corrosion resistance after coating and working can be produced with a small amt. of expensive Sn at a low cost.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a material for cans that uses welding to seam the joints of can bodies during the manufacturing of food cans, etc., and even if the Sn plating layer is extremely thin, it has good corrosion resistance after painting. This invention relates to a steel plate for cans that has excellent properties as a can material, such as corrosion resistance after processing, as well as excellent weldability.

[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, since Sn is a limited resource, the history of the development of Sn-plated steel sheets is also the history of technology for saving 'X S n.

The can body is made by applying anti-corrosion paint to a plated steel strip for can material, then cutting a rectangular can material to that size, rolling it up, and seaming both ends. This seam technology was also developed in response to saving Sn in Sn-plated steel sheets, and started with soldering, and now welding methods, adhesive methods, etc. are in practical use.

Tin-free steel is a Cr-plated steel plate, and has a total (S)
However, unfortunately, only adhesive methods using organic materials can be used for seaming, and welding methods are not practical. Adhesive methods have limitations in the heat resistance of the adhesive and productivity problems associated with bonding time. There may be a decrease in the temperature, etc., and there are restrictions on 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 a roll. The contact electrical resistance between the surfaces is too large, so a high voltage must be applied. When high voltage is applied, excessive current flows locally and splashes called dust occur, making it impossible to obtain good welding. At present, it has been found that this problem can be resolved by adding a small amount of Sn to the outermost layer of the plating, and the minimum amount of Sn is 0.05g/
It is said to be m3. That is, in the development of ultra-FISn-plated steel sheets for cans, efforts are being focused on maintaining the minimum amount of Sn during welding, in addition to improving properties such as corrosion resistance and workability for can materials.

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. Taking this point into consideration, Sn-plated steel sheets that are plated with only Sn and then chemically treated are
So-called #10 tin, which has been reduced to 1.1 g/m'', is in practical use.On the other hand, as a plating film structure that does not impair weldability as well as the other properties mentioned above even if the Sn content is further reduced. , it is being considered to provide a Ni or Cr plating layer under the Sn layer.
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/m''. is proposed.

[Problems to be Solved by the Invention] However, although the diffusion layer of Cr and Fe or the diffusion layer of Cr, Ni, and Fe can suppress the formation of 5n-Fe alloy, there is a limit to the degree of suppression. Almost half of the Sn content is alloyed.

For this reason, it has been difficult to further reduce the amount of Sn without impairing weldability.

This invention was made to solve this problem.
Another object of the present invention is to provide an ultra-thin Sn-plated steel sheet for cans that does not impair weldability or other properties as a can material even if the amount of Sn is reduced.

[Means for solving the problem] The means for achieving this object is that the surface layer of the steel plate is a Cr thermal diffusion layer, and a Cr thermal diffusion layer of 0.05 g/ro" or more
/rr? It has the following Sn plating layer, and the top layer is μm”
It is an ultra-thin Sn-plated steel sheet for cans having a chromate layer with 10 or more protrusions per layer, preferably a Cr thermal diffusion layer of 0.02 g/+1? It is an ultra-thin Sn-plated steel sheet for cans having a chromate layer having a metal Cr content of 3, g/m2 or more, and preferably 3 Q + g/m2 or more.
/m2 or less, and a method for manufacturing such an ultra-thin Sn-plated steel sheet for cans, which is the following method (a).

1) Cr is plated on the surface of the steel sheet before heat treatment, a Cr heat dissipation layer is generated during heat treatment of the steel sheet, temper rolling is performed, Sn plating is applied, and further anodic electrolysis is performed in a chromate treatment solution. A method for manufacturing an ultra-thin Sn-plated steel sheet for cans, which is followed by cathodic electrolysis.

(B) Plating Cr on the surface of the steel plate before heat treatment, plating Fe on top of it, generating a Cr heat dissipation layer during heat treatment of the steel plate, performing temper rolling, and then applying Sn plating, A method for manufacturing an ultra-thin Sn-plated steel sheet for cans, which comprises performing anodic electrolysis in a chromate treatment solution and then cathodic electrolysis.

(A) CrFe alloy is plated on the surface of the steel sheet before heat treatment, a Cr heat dissipation layer is generated during heat treatment of the steel sheet, temper rolling is performed, Sn plating is applied, and further, CrFe alloy is plated on the surface of the steel sheet before heat treatment. A method for manufacturing an ultra-thin Sn-plated steel sheet for cans, which performs anodic electrolysis followed by cathodic electrolysis.

(2) Cr is plated on the surface of the steel plate before heat treatment, and then Cr-Fe alloy is plated on top of that, and Cr is plated on the surface of the steel plate before heat treatment.
A method for producing an ultra-thin Sn-plated steel sheet for cans, in which a heat dissipation layer is generated, temper rolling is performed, Sn plating is applied, and further, anodic electrolysis is performed in a chromate treatment solution, followed by cathodic electrolysis. .

[Function] When a Cr plating layer or a Cr heat diffusion layer exists between the steel base and the Sn plating layer, it provides corrosion resistance to the plated steel sheet and suppresses 5n-Fe alloying during paint baking. , well known. 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,
In a non-diffused Cr plating layer, the steel substrate is exposed under this crack, but in a thermal diffusion layer, Cr is deposited deep inside.
Cr is diffused, and even if a crack occurs in the upper part of the layer, Cr still exists under the crack and prevents the steel from being exposed.For this reason, even after the rolling and drawing processes during can manufacturing, the coating remains intact. Maintains continuity and corrosion resistance.

During seam welding, the Sn plating layer reduces the contact resistance during electric resistance heating welding due to the softness and low melting point peculiar to Sn, allowing for good welding.It also forms a corrosion-resistant coating after filling the can. functions as

The amount of Sn plating is necessary only to ensure weldability, and in order to ensure this necessary amount of Sn, the alloying suppressing effect of the Cr thermal diffusion layer is utilized. However, even with this Cr thermal diffusion layer, it is sometimes difficult to sufficiently prevent the diffusion of Sn and Fe from seizing the can material. Table 1 shows the relationship between the Cr thermal diffusion layer and 5n-Fe diffusion.The thermal diffusion layer is formed by changing the amount of Cr plating, Sn is plated on top of the thermal diffusion layer, and this is heated to 205°C for 10 minutes. This is the result of measuring the amount of metallic tin remaining without alloying after dry firing for a minute.

Table 1 The alloying suppressing effect of the Cr thermal diffusion layer is clear.

This effect is sufficient even when the amount of Cr is 0.01 g/m'', but considering variations in processing conditions in practice, in order to reliably maintain corrosion resistance after tightening, 0.02 g
A Cr content of /m2 or more is desirable, and the thicker this heat diffusion layer is, the better in terms of corrosion resistance, but the hardness of this layer is higher than that of steel or N.
i, and if it is too thick, it will lack flexibility when the welding surfaces are brought into contact, which is unfavorable for weldability.

Furthermore, even if the thickness exceeds 0.2 g/m'', its effectiveness will be slow, so when considering economic efficiency, the amount should be 0.2 g/m.
g/m" or less is desirable.

However, even with such a Cr thermal diffusion layer, 3
0 to 40% Sn ends up being alloyed by dry firing.

As the amount of Sn is reduced, the amount of alloying becomes impossible to ignore, and especially when the amount of Sn plating becomes less than 0.1 g/m, the remaining amount of Sn decreases to the amount that is said to be necessary for welding. There is a possibility that it will be less than 0.05g/m1.However,
The amount of Sn required for this welding is based on the presence of a chromate layer, and can be further reduced by modifying the chromate layer. Corrosion resistance is ensured by coating, but in order to ensure the adhesion of these paints and corrosion resistance under the coating,
The chromate layer has become essential. The chromate layer consists of metal Cr and Cr oxide or hydroxide covering it. Oxide or hydroxide is an insulating material with higher electrical resistance than metal, and oxide is extremely hard and both are The melting point is extremely high, which increases the electrical contact resistance of the welding surface. Such a chromate layer generally exists in an amount of 5 to 30 mg/m2 in terms of Cr, and 50 tsg/m2 of Sn is added as an amount to compensate for this presence during welding.
quantity is required. However, if the chromate layer has 10 or more protrusions per μ♂, when a reduction blade is applied during welding and a large force is applied locally to the tips of these protrusions, the oxide or hydroxide film in this area will be destroyed. is destroyed, and metal Cr is exposed. If metal Cr comes into contact with each other, the electrical resistance decreases by a factor of 10-12 or less, so the contact resistance of the welding surface decreases. Furthermore, since the stress difference between the protruding portion and the flat portion is very large, cracks are likely to occur between the protruding portions and the flat portion, further increasing the chance of metal-to-metal contact. This effect is due to the fact that the lower layer is
This is especially true when the n-plated layer is softer than the chromate layer. These effects combine to significantly reduce the contact resistance, so if the amount of Sn is 0.02 g/m2 or more during welding, welding can be performed easily.
．． A plating amount of 0.05 g/m2 or more is sufficient.It goes without saying that weldability improves as the amount of Sn increases, but the effect of increasing the amount gradually decreases, so from the perspective of saving Sn, 1.0 g/m2 or more is sufficient.
It is appropriate to set the upper limit to "/m".

The larger the number of protrusions in the chromate layer, the lower the contact resistance, and the μ
If there are 10 or more of them per m1, the effect can be reliably obtained. Figure 1 shows the relationship between the number of protrusions and the contact resistance value for a sample in which 0.05 g/m'' of Sn was plated on Cr thermal diffusion and chromate treatment was performed to form protrusions using the method described later. The vertical axis is the contact resistance value,
The horizontal axis is the number of protrusions and is graduated at intervals of the square root of the number. It is thought that the stress gradient is inversely proportional to the distance between protrusions, and the location where the stress difference occurs is proportional to the number of protrusions.Figure 1 shows that the contact resistance value increases when the number of protrusions is small, and that the contact resistance value increases when the number of protrusions is 10/10. It is shown that the contact resistance value is extremely small above μm2. In order to create protrusions that reduce contact resistance in this way, it is desirable that the chromate layer has a metallic Cr content of 3 mg/m" or more.
When the thickness is about m2, it is difficult not only to form protrusions but also to maintain under-coating corrosion resistance. Although protrusions are formed even if the density exceeds 30 yag/m2, it is preferable not to exceed 30 yag/m2, considering the negative effect of an increase in oxides, etc.

In order to manufacture the above ultra-thin Sn-plated steel sheet for cans, it is first necessary to form a Cr thermal diffusion layer. For this purpose, if Cr is attached to the surface of the steel plate before heat treatment, Cr will be thermally diffused when the steel plate is heat treated. This method requires fewer steps and is more energy efficient than plating a steel plate that has been heat-treated and temper-rolled to adjust its mechanical properties, as is done in -m. The material is not affected by the second treatment,
When the heat treatment is an annealing treatment performed after cold rolling, the steel plate for cans is generally heated to around 700°C, and in overaging treatment, it is heated to around 500°C. Since a Cr thermal diffusion layer is sufficiently formed by either treatment, either heat treatment may be used.

There are many methods for attaching Cr to a steel sheet other than those described here. The simplest method is to plate Cr, but the Cr concentration increases in the upper layer of the diffusion layer, and the Sn plating performed later
Plating tends to reduce adhesion efficiency. This is Cr
This is thought to be because oxides and hydroxides are likely to be generated when the concentration is high due to the oxygen affinity of Sn, and reduction current is consumed during Sn plating. Plating Cr and then plating Fe on top of it increases the number of steps, but since the Cr concentration is highest in the middle layer of the heat diffusion layer and is diluted in the upper layer, it contributes to improving the adhesion efficiency of Sn plating and prevents cracks. The Cr concentration at the tip is also ensured. When Cr-Fe alloy plating is applied, sufficient diffusion occurs even if the heat treatment temperature is low or the heat treatment time is short, and the Cr concentration in the diffusion layer is also relatively constant. Cr
When plating Cr-Fe alloy on it,
The Cr concentration gradient within the diffusion layer is more relaxed than when Fe is plated on top of Cr. The method of depositing Cr is selected depending on the application, the thickness of the steel plate, the heat treatment conditions, etc., but whichever method is used, the above-mentioned Cr thermal diffusion layer with excellent post-processing corrosion resistance can be obtained.

When anodic electrolysis is performed for a short time in a chromate treatment solution, followed by cathodic electrolysis, countless fine protrusions are formed. The chromate treatment solution may be a well-known chromic acid or dichromate-based solution.The treated surface is brought into a non-uniform state by short-time anodic electrolysis, and then cathodic electrolysis is performed to cause non-uniform precipitation of Cr. The anodic oxidation time may be extremely short, and even if it does not reach 0.5 seconds, a sufficient effect can be obtained.

[Example] After attaching Cr and Ni to the surface of a cold-rolled steel sheet, heat treatment was performed, followed by temper rolling with an elongation rate of 2%, followed by plating with Sn, and anodizing in a chromate treatment solution. Subsequently, cathodic treatment was performed. For these test pieces, corrosion resistance,
Paint adhesion and weldability were investigated. The test was also conducted on a comparative example outside the scope of the present invention and a conventional example based on conventional technology, and these were compared. In addition, in the conventional example, Cr-Ni plating, heat treatment, and Sn plating were applied in the same way as in the example, and cases where the thermal diffusion layer was a Cr-Ni thermal diffusion layer were also included, but in the chromate treatment, anodic electrolysis was not performed and the cathode Only electrolytic treatment was performed.

The processing conditions for preparing the test piece were as follows.

Cr plating: CrO3200g/1 (NH4)F3g/41 bath temperature
50℃, flow density 40 A/d m”Cr Fe
Alloy plating: CrO3200g/J Fe Cl2 150g/j! bath temperature
50℃ pH 1,7 Current density 40 A/d m”Sn plating: Sn” 30g/l Phenols I
Lefonic acid 70g/J brightener 5
g/l Bath temperature 50°C Current density 20 A/d m” Chromate treatment A: CrOs 50 g/4
1(NH4)F 1g/ρ bath temperature
40°C Cathode treatment current density 20-50A Anodization current density 5-30A Anodization time 0.3-0.4 seconds Romate treatment B: Na2 Crz 07 50 g/Jl
pH 5.5 Bath temperature 40°C Cathode treatment current density 5-IOA Anodization current density 5-30A Anodization time 0.3-0.4 seconds Corrosion resistance tests include post-processing corrosion resistance, corrosion resistance under coating, and iron elution test. A T-beer test was carried out as a paint adhesion test, and contact electrical resistance was tested for weldability.

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.
After immersing the steel in an aqueous solution containing 5% citric acid and 1.5% citric acid at 38°C for 96 hours, rusting of the iron was examined. When folding in two, so-called close folding without inserting any spacer in between is OT, and I is when a plate of the same thickness as the test piece is inserted.
Depending on the bending method up to 5T, the T value is determined based on the bending method up to which point no rust occurs. Here, 30 samples were tested, and when all were better than IT, the case where 012T was mixed was evaluated as Δ, and the case where 3T was mixed was 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°C for 10 minutes, and then exposed to 1.5% citric acid. Immerse it in an aqueous solution containing 1.5% salt and 1.5% common salt at 38°C for 96 hours, and measure the amount of iron eluted into the immersion solution.

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 the re-test. In the UCC test, the paint inside the can is baked in the same way as the iron elution test, and then a cross-shaped scratch is made on the paint film that reaches the base layer with a knife.After immersing it under the same conditions as the iron elution test, The deterioration status was observed. The state of deterioration is determined by visually observing the peeling of the paint film and the corrosion of the substrate. Evaluate with X.

In the blister test, a test piece with a baked-in can coating was first heated in 0.1% salt to 120°C and exposed to a pressure of 2 kg/C11l for 1.5 hours in the same manner as in the iron elution test. On the next page, the coating film was immersed in 0.1% saline solution at 38° C. for 96 hours, and the deterioration status 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. Rate is less than 5% 015-20%
The value was evaluated as Δ, and the case where it exceeded 20% was evaluated as ×.

In the T beer test, epoxy phenolic resin for cans was
After baking at 205℃ for 10 minutes, a test piece with a width of 51 mm was prepared, and the coated surfaces of the two test pieces were thermocompressed using nylon film as an adhesive medium, and then heated at a speed of 20 g/min. The adhesive strength of the coating film was measured.

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 5 mm, and current was applied under a pressure of 4000 kg/-, and the contact resistance was determined from the current applied at this time and the potential difference between the test pieces.

Regarding the formation of the Cr thermal diffusion layer, at test point 1.2, Cr plating was applied and thermal 9JS treatment was performed at 700°C for 20 seconds, and at test point 3.4.10 and IX, Cr-Fe alloy plating was applied. At test points 5.6.12 and 13, Fe was plated after Cr plating.
After plating, heat treatment was performed at 670°C for 50 seconds, and at test point 7.8.9, CrF was applied after plating with Cr.
E-alloy plating was applied and heat treatment was performed at 430°C for 10 hours. In addition, chromate treatment has a test NIL of 1 to 5.10.
and 11 were conducted under the conditions for chromate treatment, trials @ 6-9. 12 and 13 were conducted under the conditions for chromate treatment B, and trials No. 14-16 were conducted under the cathode treatment conditions of chromate treatment FIA. .

The number of protrusions was measured at 10 locations on each test piece using a scanning electron microscope with a magnification of 200,000 times, and the average value was determined.

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

In the examples, test Na 6, which has a small amount of Cr adhesion and a lower limit of the amount of Sn plating, has a slightly larger amount of iron elution and contact resistance than other examples. In addition, although the contact resistance was somewhat large in sample @N&9 in which the amount of metal Cr in the chromate layer was small, satisfactory results were obtained in all items including these.

On the other hand, in the comparative example, test NLIO with a small amount of Sn plating and test No. 11 with a small amount of Cr plating were inferior in items other than the T-peel test, and test No. 12 with an extremely large amount of Cr plating had poor contact resistance. Test N1L13 with slightly more metal Cr in the chromate layer and fewer protrusions
In this case, the adhesion of the coating film is poor and the corrosion resistance on the coating film is poor, and as for weldability, the chromate layer is thin, which compensates for the small number of protrusions. Test magnet 13, which was not subjected to anodic electrolysis, had a small number of protrusions and was inferior in weldability.

In the conventional example, whether the heat diffusion layer is made of Cr or Cr/Ni, anodic electrolysis is not performed, so weldability is poor.

[Effects of the Invention] As described above, according to the present invention, S is formed on the Cr thermal diffusion layer.
It has a film structure in which an n-plated layer is present, and a chromate layer having many protrusions covers the n-plated layer. Therefore, despite the significant reduction in Sn, it was possible to satisfy various properties as a steel sheet for cans, including weldability. 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 number of protrusions and contact resistance for explaining the present invention in detail.

Claims (7)

[Claims] (1) The surface layer of the steel plate is a Cr heat diffusion layer, and there is
．． Ultra-thin S for cans, characterized by having an Sn plating layer of 05 g/m^2 or more and 1.0 g/m^2 or less, and a chromate layer having 10 or more protrusions per μm^2 on the top layer.
n-plated steel plate. (2) Cr amount in the Cr heat diffusion layer is 0.02g per side
2. The ultra-thin Sn-plated steel sheet for cans according to claim 1, which has a thickness of 0.2 g/m^2 or more and 0.2 g/m^2 or less. (3) The ultra-thin Sn-plated steel sheet for cans according to claim 1 or 2, wherein the amount of metallic Cr in the chromate layer is 3 mg/m^2 or more and 30 mg/m^2 or less. (4) Apply Cr plating to the surface of the steel sheet before heat treatment, generate a Cr heat dissipation layer during heat treatment of this steel sheet, perform temper rolling, then apply Sn plating, and then apply anodic electrolysis in a chromate treatment solution. 1. A method for manufacturing an ultra-thin Sn-plated steel sheet for cans, which comprises performing cathodic electrolysis. (5) Cr is plated on the surface of the steel plate before heat treatment, Fe plating is applied thereon, a Cr heat dissipation layer is generated during heat treatment of this steel plate, after temper rolling, Sn plating is applied, and . A method for producing an ultra-thin Sn-plated steel sheet for cans, which comprises performing anodic electrolysis in a chromate treatment solution followed by cathodic electrolysis. (6) Plating Cr/Fe alloy on the surface of the steel plate before heat treatment, generating a Cr heat dissipation layer during heat treatment of the steel plate,
A method for producing an ultra-thin Sn-plated steel sheet for cans, which comprises skin-pass rolling, Sn plating, anodic electrolysis in a chromate treatment solution, and then cathodic electrolysis. (7) The surface of the steel plate before heat treatment is plated with Cr, and then a Cr/Fe alloy is plated on top of it, and when the steel plate is heat treated, Cr is plated.
Ultra-thin S for cans, characterized in that a heat dissipation layer is generated, temper rolling is performed, Sn plating is applied, and further, anodic electrolysis is performed in a chromate treatment solution, followed by cathodic electrolysis.
Method for manufacturing n-plated steel sheet.