JPS59107096A - Surface treated steel sheet for seam welded can with superior corrosion resistance, weldability and coatability - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance, weldability and coatability of a steel sheet by forming Ni layers of a specified thickness on the surface of the sheet by plating and Ni-Sn alloy layers of a specified thickness having a specified composition on the Ni layers by plating and by further forming chromate layers of a specified thickness. CONSTITUTION:Ni layers of 0.01-0.15mum thickness are formed by plating on the surfaces of a steel sheet for a surface treated steel sheet for a steam welded can. Ni-Sn alloy layers of 0.01-0.2mum thickness having a composition satisfying Sn/(Sn+Ni)=0.5-0.8 by weight are formed on the Ni layers by plating. Chromate layers of 1-30mg/m<2> thickness are further formed on the Ni-Sn alloy layers so as to improve the corrosion resistance, especially the adhesive strength to paint and the corrosion resistance after coating.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface-treated steel sheet for seam welded cans that has an Nl plating layer, a Ni-Sn alloy plating layer, and a chromate coating layer and has excellent corrosion resistance, weldability, and paintability. .

Tinplate and TFS (tin free steel) are currently available materials for cans, but when these are used as materials for seam welded cans, there are problems as described below. #25 tin is used as a material for seam welding beverage cans (carbonated drinks, juices, soups, etc.).

There are no problems with weldability, corrosion resistance, or paintability. but,#
No. 25 tinplate is made of expensive tin plated with approximately 0.5 μm per side, and cannot be said to be a suitable material for the seam welding can manufacturing method, whose main feature is reduction in can manufacturing costs.

When thin tinplate with a reduced tin coating is used as a material for seam welded cans, its corrosion resistance is extremely poor and it cannot be put to practical use.

TFS is an inexpensive material for cans and has excellent paintability and corrosion resistance, but it has problems with seam weldability.

That is, when seam welding is performed, TFS not only causes "splashing" and causes the repair coating at the welded part to become solid pieces, but also tends to cause welding defects due to insufficient welding strength.

"Scatter" is a phenomenon in which molten metal scatters, and it occurs when a high electrical resistance material such as Cr water oxide is present.

However, even if the formation of Cr hydrated oxides is reduced and TFS is seam welded, which consists almost entirely of a metallic Cr layer, Cr oxides will be formed during the temperature rising process during welding, and "scattering" will still occur. Therefore, TFS cannot be used as a material for welded cans.

There is a method of exposing the base iron by grinding in order to seam weld TFS, but there are problems in putting it to practical use, such as grinding debris scattering and adhering to the surface corresponding to the inner surface of the can after the can is made.

As described above, all currently used can materials are insufficient as seam welded can materials.

An object of the present invention is to provide a surface-treated steel sheet for seam-welded cans that is excellent in corrosion resistance, weldability, and paintability required as a material for seam-welded cans, and is inexpensive.

According to the present invention, 0.01 to 0.15μ of N is applied to the surface of the steel plate.
The i-plated layer and the upper layer have a weight ratio of Sn/(Sn + Ni)
has an alloy composition of 0.5 to 0.8, and has a thickness of 0.5 to 0.8.
and a Ni-Sn alloy plating layer of 0.01 to 0.20 p.

Further, by forming a chromate coating layer of 1 to 30 my/i on the upper layer, the above object can be achieved.

Although the Ni-Sn alloy plating film itself has excellent corrosion resistance and weldability, pinholes are present in the film when the plating thickness is 0.01 to 0.20 μm. Simply applying Ni-Sn alloy plating to the surface of a steel plate will not cause Ni-S in a corrosive environment.
This is because the n-alloy plating film acts as a more dangerous metal than iron, and the potential difference between them is large.

Iron elution from pinholes is promoted and iron dissolution is significant.
Corrosion resistance is not sufficient. When an N1 plating layer exists between the steel plate surface and the Ni-Sn alloy plating layer, Ni acts as a front seat between iron and the Ni-Sn alloy plating layer in a corrosive environment, so the iron and Nl Plating layer and Ni-Sn
The potential difference between each layer of the alloy plating film layer becomes smaller, and the double plating reduces the number of pinholes that expose the base metal, which significantly reduces iron dissolution and improves corrosion resistance. Understood.

The surface-treated steel sheet of the present invention is also used by being coated in the same way as other can materials in order to prevent the dissolution of the base iron and the plating layer itself, but the Ni-Sn alloy plating film itself has poor paint adhesion, especially Paint adhesion (secondary paint adhesion) is poor when exposed to high-temperature aqueous solutions for some time, and corrosion resistance after painting is insufficient.

In the present invention, after Ni plating and Nt-Sn alloy plating is applied to the steel plate surface, chromate treatment is performed for the purpose of further improving corrosion resistance, especially paint adhesion, and post-painting corrosion resistance. Since it is a gas-resistant material, if the amount of chromate coating is excessive, it will cause "scattering" during seam welding, resulting in poor weldability.

Therefore, the amount of Ni plating that provides excellent corrosion resistance, weldability, and paintability (paint adhesion and corrosion resistance after painting),
As a result of various studies on the amount of n-alloy plating and the amount of chromate coating, it was found that a Ni plating layer of 0.01 to 0.15μ on the saw plate surface,
The upper layer has a weight ratio Sn/(Sn + Ni) of 0.
It has an alloy composition of 5 to 0.8, and a thickness of 0.01 to
0.20p Ni-Sn alloy plating layer and 1~30μ/lr layer on top of it. It was found that the formation of a chromate film layer was good.

In the present invention, the purpose of Ni-Sn alloy plating is to improve weldability and impart corrosion resistance, and one alloy composition has a weight ratio of Sn.
/(8n+Ni) = in the range of 0.5 to 0.8,
It was found that these properties were significantly improved.

The prior art is disclosed in Japanese Patent Publication No. 36-15252 "Ultra-Thin Nickel Plated Steel Sheet".

This steel plate is intended for solder cans, and issues include corrosion resistance, solderability, lacquerability, and workability.The alloy composition of the Ni-Sn alloy plating is not specified, and it is stated that the layer is mainly Nid. Whereas there is.

The steel sheet of the present invention targets seam welded cans that have been developed in recent years due to improvements in welding technology, and has a major feature of specifying the alloy composition range of the plating layer, and is based on the invention disclosed in the above-mentioned publication. The present invention is completely different both conceptually and technically.

Ni-Sn alloy plating can be carried out using any of a chloride-fluoride bath, a sulfate-fluoride bath, a silicofluoride bath, a pyrophosphoric acid bath, and a chloride bath, and the bath temperature is 30 to 70°C. , current density 0.1-50 A/drr?
It can be done with

Unlike the mixed structure of intermetallic compounds such as N15Snl, Ni, and Sn4 as shown in the equilibrium phase diagram, the Ni-Sn alloy plating layer has a 1 weight ratio Sn/(Sn + Ni).
In the range of 0.5 to 0.8, almost the entire layer is a single layer, and in this range excellent performance in weldability and corrosion resistance is exhibited.

The value of Sn / (Sn + N'l) is 0.5 to 0.8
The reason for limiting it to is as follows. 8n/(Sn +
If Ni ) is less than 0.5, cracks will occur in the plating layer, resulting in a significant decrease in corrosion resistance, and oxides will be more likely to be formed on the surface of the plating layer during welding, making it easier to cause "splatter". . If Sn/(Sn+Ni) is greater than 0.8, the plated layer will be rough.

i! contains many defects such as pinholes! The corrosion resistance becomes deposited and the melting point of the kNi-Sn alloy becomes lower than 1000°C. Below 100°C, the plating layer melts during welding, causing heat loss due to the latent heat of fusion and requiring a large amount of current. Therefore, it is not practical. In the present invention, the reason why the value of %S1/(Sn-4-Ni) is limited to 0.5 to 0.8 is that, as is clear from the above, extremely excellent performance in weldability and corrosion resistance can be obtained. This is because compositions other than these do not have a significant effect on weldability and corrosion resistance.

The thickness of Ni-Sn alloy plating is 0.01 to 0.207
The reason why T is limited to 1 is that if it is less than 0.01μ, it will not produce any significant effects on weldability and corrosion resistance, and if it exceeds 0.2μ, the effects on weldability and corrosion resistance will be saturated, resulting in economic disadvantages. This is because it occurs.

If this Ni-Sn alloy plating is applied to the surface of a steel plate.

Improved weldability and corrosion resistance. However, it is very difficult to completely eliminate pinholes in the plating layer, and iron elution from these pinholes is unavoidable, and in a corrosive environment, Ni-Sn alloy plating is considered a more harmful metal than iron. Because the potential difference is large, iron dissolution from pinholes is promoted, and corrosion resistance is insufficient.

In the present invention, the purpose of applying Ni plating between the steel plate and the Ni-Sn alloy plating is to improve corrosion resistance. In a corrosive environment, the degree of shellness is intermediate between that of iron and Ni-Sn alloy plating, and the potential difference between the iron and Ni plating layer and the Ni-Sn alloy plating layer becomes small, and the difference between Nl plating and N
By forming a double layer of i-Sn alloy plating, the number of pin poles that expose the bare metal is reduced, thereby significantly reducing iron dissolution and improving corrosion resistance.

Ni plating may be carried out by a conventional electroplating method using a Watt bath, a sulfamic acid bath, etc. for 1 hour, or by a chemical plating method. In the present invention, the thickness of the Nl plating layer is 0.01
The reason why it is limited to ~0.15μ is that if it is less than 0.01μ, it will not show a remarkable effect on improving corrosion resistance, and if it is less than 0.01μ,
This is because, if it exceeds this, the effect of improving corrosion resistance will be saturated, resulting in economic disadvantages.

In the present invention, after Ni plating (Nl-Sn alloy plating) is applied to the surface of a steel sheet, chromate treatment is performed for the purpose of further improving corrosion resistance, paint adhesion, and post-painting corrosion resistance. When painted on Nl-Sn alloy plating,
Ni-Sn alloy plating has poor paint adhesion, especially when exposed to high-temperature aqueous solutions for a long time, and does not have sufficient corrosion resistance after painting. Moreover, it can improve paint adhesion and improve corrosion resistance after painting.

The chromate treatment bath is an aqueous solution of chromic acid anhydride, chromate, dichromate or a mixture thereof.

The p degree is 5 to 70 f/l, and the pH should be appropriately adjusted. Treatment methods include immersion method and electrolysis method.

Either spray method will work.

The reason why the amount of chromate film is limited to 1 to 30 ■/ltl is that if it is less than 1 ■/n1, the base surface cannot be sufficiently covered, and the effect of improving corrosion resistance, paint adhesion, and post-painting body corrosion resistance is insufficient. Moreover, if it exceeds 30 ri/i, it is effective in improving corrosion resistance, paint adhesion, and corrosion resistance after painting, but the high electrical resistance of the coating itself inhibits the bonding of iron to iron at the welded part. This is because "scattering" occurs.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

[Example 1] After electrolytically degreasing and pickling a tin plate, Ht plating with a thickness of 0.03μ was performed using a Watt bath at a bath temperature of 55°C and a current density of 5 Altrd, and further using a chloride-fluoride bath. pH 2.5, bath temperature 70°C, current density 5 k/dtr
? 0.04p Ni-Sn alloy plating was performed.

After that, F) Q? /l chromic acid bath with a current density of 1
Chromate treatment was performed at 0 A/gff1''.

[Example 2] After electrolytically degreasing and pickling a tinplate original plate, a Watts bath was used at a bath temperature of 60°C and a current density of 10 A/dn? 0.06μ
Ni plating is carried out, and then p is plated using a birophosphate bath.
H8.0, bath temperature 65°C, current density g 3 A/dn? Ni-Sn alloy plating was performed at a rate of 0.02/J.

Thereafter, chromate treatment was carried out using a dichromate bath at a current density of 15 A/d+/.

[Example 3] After electrolytically degreasing and pickling a tinplate original plate, it was treated with a sulfamic acid bath at a bath temperature of 50°C and a current density of 10 A/d-.
02μ Ni plating, and further using a chloride-fluoride bath at pH 2.5, bath temperature ff60'c, and current density 1.
0.18μ Ni-Sn alloy plating was performed at 0 Alctrd. Then, using a 75 fil dichromate bath, the current density was 15 A/drr? Chromate treatment was performed.

[Example 4] After electrolytically degreasing and WR washing a tinplate original plate, a Watt bath was used at a bath temperature of 55°C and a current density of 5 A/ctrr? 0, 1
3 pO)Ni plating was performed using a chloride-fufluoride bath at p)t 2.5, bath temperature 75°C, current density 1.
0 A/dFr? 0.10μ Ni-Sn alloy plating was performed. Thereafter, chromate treatment was carried out using a 501/l chromic acid bath at a current density of 15 A/d-.

[Comparative Example 1] After electrolytically degreasing and pickling a tinplate original plate, p)I 2.5. was applied using a chloride-fluoride bath. Bath temperature 60℃.

0.06μ Ni-Sn alloy plating was performed at a current density of 10 A/dd. Thereafter, chromate treatment was performed using a 451/l chromic acid bath.

[Ratio example 2] After electrolytically degreasing and pickling a tin plate, use a Watt bath at a bath temperature of 55°C and a current density of 5A/dw? 0.03μ Nl plating was performed using a chloride-fluoride bath at pH 2.5, bath temperature 70°C, current density F 5 fi,
/dd 0.0471 Ni-Sn alloy plating was performed.

[Comparative Example 3] After electrolytically degreasing and pickling a tinplate original plate, a sulfamino acid bath was used at a bath temperature of 50°C% and a current density of 10 A/d- and a current density of 0.
Ni plating with a thickness of 0.3μ was performed using a pyrophosphoric acid bath at a pH of 8.0, a bath temperature of 1260°C, and a current density of 3 A/
Ni-Sn alloy plating of 0.04 p was carried out at 0.04 p gm". Chromate treatment was then carried out using a % 75 fiL chromium 6N/bath at a current density of 15 A/rLtt?.

A 164.7 x 80 fin specimen was cut out from the steel plate treated as described above and subjected to a seam weldability test. Also,
A paint secondary adhesion test was conducted using a 1100×100+ test piece.

(1) Seam weldability test Seam welding was performed using a Sudronik pear can making machine at a welding speed of 8 m/start, a contact pressure of 30 Kff, and an overlap of 0.4 to determine the appropriate current range.

Q) Paint secondary adhesion test and corrosion resistance after painting Epoxy phenol paint 50η/i after painting % 2% NaCt
After treatment in a 1,4% acetic acid solution at 125°C for 60 minutes, the secondary adhesion of the paint was evaluated using a cross-cut tape peel test, and the corrosion resistance after painting was evaluated based on the corrosion state of the paint surface. As is clear from Table 1 showing the test results, 1 surface-treated steel sheets according to the present invention (Examples 1 to 4)
shows superior performance compared to comparative materials (Comparative Examples 1 to 3) in weldability, secondary paint adhesion, and corrosion resistance after painting.

Claims (1)

[Claims] There is a Ni plating layer of 0.01 to 0.15μ on the surface of the steel plate, and the upper layer has a weight ratio of Sn / (Sn + Ni) of 0.5.
It has an alloy composition of ~0.8 and a thickness of 0.01~0
．． 2μ Ni-Sn alloy plating layer and further upper layer 1~
A surface-treated steel sheet for seam welded cans with excellent corrosion resistance, weldability, and paintability, characterized by having a chromate coating layer of 30η/1a.