JPS61288080A - Surface treated steel sheet for seam welded can and its manufacture - Google Patents

Abstract

PURPOSE:To improve the weldability of a steel sheet and the corrosion resistance after painting by immersing the steel sheet having a formed metallic tin layer with many recesses and projections in a chromating soln. before electrolysis so as to limit the distribution of a chromate film according to the recesses and projections. CONSTITUTION:Before a chromate film is formed by electrolysis on a metallic tin layer with many recesses and projections formed on the surface of a steel sheet, the steel sheet is immersed in a chromating soln. to form a chromate film consisting of metallic chromium and chromium oxide hydrate on the metallic tin layer. The thickness of the chromate film is regulated according to the recesses and projections so as to satisfy formulae XM>=2, XM+XO=4-18, YM>=4 and YM+YO>=8 [where XM is the amount (mg/m<2>) of metallic chromium on the projections, XO is the amount (mg/m<2>) of chromium oxide hydrate on the projections, YM is the amount (mg/m<2>) of metallic chromium on the recesses and YO is the amount (mg/m<2>) of chromium oxide hydrate on the recesses].

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is suitable for single-meal cans, beverage cans, and general cans, and has excellent weldability and post-painting corrosion resistance particularly suitable for joining can bodies by electric resistance welding. This invention relates to an excellent surface-treated steel sheet for seam-welded cans.

<Prior art and its problems> Tin-plated steel sheets, commonly referred to as Burisato, have been widely used as materials for food cans. In the past, soldering was the only method used to join this can body, but
Pure tin solder has come into use in recent years due to the toxicity of lead contained in solder. However, pure tin solder has a technical problem in solder bonding due to poor wettability during bonding, and furthermore, the use of expensive pure tin solder causes an increase in manufacturing costs.

On the other hand, in recent years, food containers have been faced with the entry of low-priced competing materials such as polyethylene, aluminum, glass, and paper, and the amount of expensive tin deposited is 2.8 to 11.2 g.
Thickly plated tin cans such as /rn' are expensive to manufacture, so they have been forced into a difficult competitive position, although they have excellent corrosion resistance.

In order to eliminate the above-mentioned drawbacks of tin cans, a method of joining can bodies by electric resistance welding instead of soldering has recently been developed and has become popular. For this purpose, a can material suitable for electric resistance welding is required.

In addition to the above-mentioned tin, chrome-type tin-free steel is a conventionally used material for cans.

This is an electrolytic chromate treatment that forms a layer of metallic chromium and chromium hydration oxide on the surface, and is highly economical, but the thick chromium hydration oxide coating on the surface has high resistance. Moreover, it has poor weldability and lacks strength in the welded part, making it unsuitable as a material for welded cans.

Since all other conventional can materials are unsuitable as materials for welded cans, various attempts have been proposed. There is a steel plate, but this is made by applying nickel plating to a coating weight of approximately 0.5 g/rn' on the steel plate, and then applying a conventional chromate treatment to the surface, which results in poor paint adhesion and 30
It has not been widely used because it has poor weldability at high speed welding of m/win or higher.

Still another type is ``Tin Alloy'' released by Jones Rollin Steel Company in the United States. This is a tin plating with a thin coating weight of about 0.6 g/rn' which is subjected to a hot pot treatment and then a conventional chromate treatment, but the rust resistance, paint adhesion, and weldability are insufficient.

Can materials suitable for electric resistance welding must have excellent weldability and corrosion resistance after coating. To explain this requirement specifically, the welding strength is sufficient during welding, the welding current range is appropriate to avoid welding defects such as so-called "splatter", and the contents of the can are coated. When used as a paint film, it has the adhesion of a paint film that can take full advantage of the corrosion resistance of the paint film,
Furthermore, in the areas where paint film defects inevitably occur, corrosion must be prevented by the excellent corrosion resistance of the material itself.As a material for welded cans that satisfies weldability and post-painting corrosion resistance at such a low cost, The present inventors have previously discovered a seam-welded can having a metal tin layer having a large number of convex portions on the surface of a steel plate, and a chromate coating consisting of chromium water-retention oxide or metal chromium and chromium water-retention oxide on the metal tin layer. surface-treated steel sheet (Japanese Patent Application No. 59-063883).

The surface-treated steel sheet for seam welded cans obtained by the above method has a particularly large tin saving effect by forming the metal tin layer in a convex shape, has an appropriate welding current range with a small amount of tin, and is a material for seam welded cans. As a result, both weldability and post-painting corrosion resistance were excellent. However, depending on the contents of the can, post-coating corrosion resistance is required under very severe conditions, and it has been found that some cans do not have sufficient post-coating corrosion resistance under these conditions.

<Structure of the Invention> The present invention provides a surface for a seam welded can having a metallic tin layer having a large number of convex portions and concave portions on the surface of a steel plate, and a chromate film layer made of metallic chromium and chromium water-conserving oxide on the metallic tin layer. In the treated steel sheet, the amount of metal chromium on the metal tin protrusion is X'mg/m', and the amount of hydrated chromium oxide is X0mg/rr.
1', the amount of metallic chromium on the metallic tin recess is Y'mg/rn'
, when the amount of chromium hydrated oxide is YOmg/rn', xPI≧2.18:2X' +XO≧4yM≧4,y”
By distributing the chromate film layer on the metal tin layer so that +YO≧8, a surface-treated steel sheet for seam welded cans with very good weldability and corrosion resistance after painting is provided.

In the present invention, in order to increase the effect of saving tin, a metal tin layer having a large number of convex portions on the surface is formed.
g rr+”■) The area percentage occupied by the convex portion is 20 to 80%
m) It is preferable to form the convex portion so that the thickness of the metal tin is 0.0071L to 0.7L.

The present invention will be explained in more detail below.

The structure of a surface-treated steel sheet for seam-welded cans having a large number of convex and concave portions on the surface as shown in Japanese Patent Application No. 59-063883 is schematically shown in FIG. 1a or 1b. There is. In FIG. 1, 1 is a steel plate, 2 is a metal tin layer, 3 is a chromate film layer, 4 is a metal tin protrusion, and 5 is a metal tin recess. In order to save tin, the metal tin recess 5 does not contain much metal tin, so the upper chromate film 3 plays an important role in corrosion resistance after painting.

Therefore, the inventors thoroughly investigated the relationship between the structure of this chromate film and the corrosion resistance after painting, and found that those with extremely excellent corrosion resistance after painting have metallic chromium above a certain value, and the chromate film has metallic tin. It was common in concave areas.

In other words, when we investigated the distribution of the chromate film on the metal tin layer using various samples using AES line analysis, we found that the chromate film was roughly divided into those with a uniform chromate film as shown in Figure 2d, and those with a uniform chromate film as shown in Figure 2C. As shown in the figure, there are cases where there is a large amount of chromate film on areas with a small amount of metallic tin, and those showing the distribution shown in Fig. 2C had very excellent corrosion resistance after painting.

FIGS. 2a and 2b schematically represent the AES line analysis results of FIGS. 2c and 2d, respectively. In the case of a metallic tin layer having a large number of convex portions 4 and concave portions 5 on the surface of the steel plate, the convex portions 4 containing a large amount of metallic tin do not have much problem in corrosion resistance after coating due to the sacrificial anticorrosive action of tin.

However, for the concave portions 5 other than the convex portions 3 that contain less tin, it is necessary to cover the corrosion resistance after painting with a chromate film, and the chromate film plays an important role. On the other hand, if there is too much chromate film on the metal tin convex part, weldability will be poor and an appropriate welding current range will not be obtained.
It is believed that a surface-treated steel sheet for seam-welded cans with excellent corrosion resistance after painting can be obtained when the distribution is as shown in Fig. 2 and Fig. 2C, without impairing the weldability of the convex metal tin.

Therefore, the present inventors further investigated the structure of this chromate film,
The effects of distribution and amount on weldability and post-painting corrosion resistance were investigated in detail. In other words, the amount of metallic chromium on the metallic tin protrusion 4 is x'''g/rn', and the amount of hydrated chromium oxide is xOII.
g/rr1', and the amount of metal chromium on the metal tin recess 5 is Y
"tmg/rn', the amount of chromium hydrated oxide is YOmg/r
When rI', these X'', Y''.

Corrosion resistance and weldability after painting were investigated in detail by varying X″+xo and y″+YO. The results are shown in FIG. 3 and PI3.

The amount of metal chromium (X”) on the convex metal tin streetcar is 2 g/l
n” or the total amount of metal chromium hydrated oxide (X
When X'+XO) was less than 4 mg/m', the corrosion resistance after painting was poor, and when X'+XO was more than 18 tag/rre, weldability was poor.

Furthermore, since there is almost no metallic tin in the metallic tin recess 5, the condition for good corrosion resistance is that the amount of metallic chromium (YM +yo) is 8IIg.
/rr1'' or more was found to be necessary.

Further, as a method for forming a large amount of chromate film on the metal tin recesses, there may be a method of reducing the current efficiency of chromium on the metal tin protrusions or increasing the chromium current efficiency on the metal tin recesses. In other words, if the current efficiency of chromium in the metal tin recesses is higher than that in the metal tin convex parts, more chromium will be electrodeposited in the recesses.

The simplest method, which can be carried out using existing equipment as is, is to perform tin plating to form an I'-shaped tin layer, then immerse it in the same chromate solution before performing the chromate treatment. By oxidizing the convex trowel to form a large amount of tin oxide, the current efficiency of chromium in the convex trowel is lowered, and a large amount of chromate film is formed in the concave portions of the metal tin.

The best method for the immersion treatment before the chromate electrolytic treatment is to turn off the downpass of the first chromate treatment layer. Soak for a longer time and conduct electrolysis for 2 or more passes.
Although the effect of the present invention can be recognized as an FF, providing more OFF paths than necessary is negative from the equipment cost perspective, and if the number of OFF paths increases, the current efficiency of chromium becomes too small. not good.

Therefore, in the chromate treatment, after turning off the downpass of the first chromate treatment layer and performing the chromate immersion treatment,
By chromate electrolytic treatment, the corrosion resistance after painting of the surface-treated steel sheet for seam welded cans (Japanese Patent Application No. 59-063883), which has a metallic tin layer with a large number of convex portions, which the present inventors had previously proposed, was improved. We were able to obtain the great effect of improving the system with almost no cost or management cost.

In the present invention, the effect of metallic tin is to improve weldability.

The metal tin layer has a large number of convex portions, and it is preferable that the metal tin is dispersed in a convex or uneven shape, and I) the area of each convex portion is Igm'' to 800,000 ILrr1
``i) The area percentage occupied by the convex portion is 20 to 80% m) The thickness of the metal tin of the convex portion is preferably 0.00 full m to 0.71 Lra.

The reason for limiting the area of each convex part to 1 μg to 800,000 ILrn' is that if it is less than 1 ILrn', the effect of expanding the contact area during welding is insufficient and there is no effect of improving weldability, and if it exceeds 800,000 ILIT+', this The effect becomes saturated and tin is used unnecessarily, resulting in an economic disadvantage.

At the same time, the reason why the area percentage of the convex portion is limited to 20 to 80% is that if it is less than 20%, the effect of expanding the contact area during welding is insufficient and there is no effect of improving weldability, and if it exceeds 80%, the convex portion is This is because the economic advantage of having a private company is lost.

At the same time, the thickness of the metal tin on the convex part was set to 0.00? pm～0
．． The reason for limiting it to 0.007 g m
This is because if it is less than that, sufficient weldability improvement effect cannot be obtained.
O,? This is because the effect of improving weldability is saturated when the weldability exceeds uLra, resulting in an economical disadvantage. The thickness of the metal tin may be arbitrarily selected within the above range depending on the type of base metal and the baking conditions after painting.

Methods for dispersing metallic tin in a convex or uneven shape are not limited to these methods, but the following methods can be exemplified.

(1) Electrodeposition via a Mask Tin is electrodeposited in a convex or uneven shape by electroplating via a masking sheet having micropores of an arbitrary shape.

(2) Coagulation using flux After electrolytic tin plating on the flat surface, flux (ZnCI
2. After applying an aqueous solution such as NH4CI to the surface in an arbitrary distribution state, a molten tin treatment is performed, and the difference in leakage of molten tin between areas where flux is applied and areas where flux is not applied is used to form convex or Coagulates and solidifies tin in an uneven shape.

(3) Coagulation on an inert surface After applying inertization treatment (old diffusion treatment, etc.) to prevent leakage of molten tin on the surface, apply tin electroplating on a flat surface, perform molten tin treatment, and coagulate and solidify tin. let

Below this metal tin layer is a nickel diffusion layer (inactive layer) 32.
can be provided so that the weight ratio Ni/(Ni+Fe) is 0.50 or less and the thickness is 5000 Å or less. The nickel diffusion layer is formed as an inert layer for processing a flat tin layer into a convex shape or for forming a thin metallic tin layer having local convexities. If the nickel diffusion layer deviates from the above range, it becomes difficult to form the convex portions satisfactorily as described above.

The AES analysis method, welding method, and post-painting corrosion resistance evaluation method used to understand the quality characteristics of surface-treated steel sheets for seam-welded cans are shown below.

(1) AES Measurement The distribution and quantification of metallic chromium on the surface of a surface-treated steel sheet for seam-welded cans, and the distribution and quantification of the sum of metallic chromium and chromium hydrated oxide were investigated by AES.

The measurement was carried out at a vacuum level of 1. The distribution was roughly investigated using line analysis under the conditions of OXI O-9 Torr and beam voltage of 10.0, and especially exact quantitative values were obtained by combining line analysis and depth direction analysis and using the calibration curve method. All analyzed samples were run on the same day.

The distribution and quantification of metallic chromium was determined by immersing the obtained plated plate in hot alkali (7,5N NaOH, 90°C) for 10 minutes, and then using the above method to determine the distribution and quantification of the sum of metallic chromium and chromium hydrated oxide. The plated plate obtained was used as it was in the above method.

(2) Evaluation of weldability Using a copper wire of about 1.5 + s + sφ as a welding electrode, the test material specimens were overlapped under constant pressure while moving, and electrical resistance welded at a welding speed of 40 × 1 minute. and
The weldability of the material was evaluated based on the size of the appropriate range of welding current and pressure, which is determined based on the conditions that the welded part has sufficient strength and there is no occurrence of so-called "splashing".

The strength of the welded part was tested by a so-called beer test, in which a V-shaped cut was made from the end of the cylinder that sandwiched the welded part, and the triangular part was held with pliers and pulled toward the other end. The required strength was not to cut.

(3) Apply 50 layers of epoxy/phenol paint to the corrosion-resistant specimen after painting.
After painting to a thickness of dm', cross-cuts were made, and Erichsen overhangs of 5 parts were made.The ends and back side were sealed and used as test pieces for corrosion resistance after painting. This test piece was immersed for one week at 55° C. using commercially available grapefruit juice, tomato juice, and milk as test liquids, and then the corrosion state of the processed part was comprehensively evaluated.

The evaluation symbols for the weldability test and post-painting corrosion resistance are shown in Tables 1 and 2, respectively.

Table 1 Table 2 Practical example Next, the present invention will be specifically explained by giving examples.

After electrolytically degreasing and pickling an ordinary tin plate, metallic tin was made to exist in a convex shape according to the following method, and chromate treatment was performed on it.

(Example 1) Metallic tin was electrodeposited in a convex shape in a halogen bath through a masking sheet having micropores with a diameter of 3 gm. At this time, the area of the convex part is 9 rugos, and the surface m percentage of the convex part is 55%.
The thickness of the metal tin in the convex portion was 0.11 mm thick.

Further 20g/l CrCJ3+0.18g/text H2
S04 (7) After immersing in chromate solution for 0.4 seconds, l
It was subjected to cathodic treatment at OA/dm'', immersed in the same solution for 5 seconds, and then taken out.

(Comparative Example 1) Metallic tin was electrodeposited in a convex shape by the same method as in Example 1, and immediately cathodically treated at 5 A/dm'' in a CrO315 g/Jl solution without pre-plating immersion treatment.
It was immersed in rO350g/b, 60°C solution for 3 seconds.

(Comparative Example 2) A convex metal tin layer was obtained by the same method as in Example 1, and further Cr
After 0.5 second immersion in a chromate treatment solution of 0.3100 g/l +H2SO40.7 g/4, cathodic treatment at 35 A/dm'' was performed.

(Example 2) Nickel sulfate 250g/M, nickel chloride 45g/1 sentence,
After nickel plating using a solution containing 30 g/l of phosphoric acid and annealing, a molten tin treatment was performed to coagulate and solidify the tin, thereby obtaining a convex metallic tin layer. The area of the convex part at this time is 200ILrr1
'', the area percentage of the convex portion was 70%, and the thickness of the metal tin of the convex portion was O.15JAII.

Further, after immersion in a solution of 0350g/4+NaF 5g/fL for 0.6 seconds, a cathode treatment of 30A/dtn' was performed.

(Comparative Example 3) A convex metallic tin layer was obtained by the same method as in Example 2, and using the same chromate treatment solution as in Example 2, a layer of 30 A/d m" was immediately applied without dipping before plating. Cathode treatment was applied.

(Comparative Example 4) A convex metal tin layer was obtained by the same method as in Example 2, and further Cr
O320g/l +Na2 Cr2 073g/l +
No pre-plating immersion treatment was performed in a solution containing 82 SO40.2 g/l, and cathodic treatment at 30 A/drn' was immediately performed.

The amount of metallic chromium XM on the metallic tin protrusion (4 in FIG. 1) of the steel sheets obtained in Examples 1 to 2 and Comparative Examples 1 to 4, the total chromium amount of metallic chromium and chromium hydrate (X'' +xO),
Amount of metallic chromium Y″ on the metallic tin recess (5 in Figure 1), total amount of chromium of metallic chromium and chromium hydrated oxide (y” + YO
), welding test results, and post-painting corrosion resistance test results are shown in Table 3.

Examples 1 and 2 have an appropriate welding current range with a small amount of tin because the metal tin is formed in a convex shape, and the amount of metal chromium and the amount of chromium water-containing oxide on the convex portion of the metal tin, as well as the amount of metal tin Since the amount of metallic chromium and the amount of chromium hydroxide on the recesses are within the appropriate range of the present invention, the corrosion resistance after painting is also very good.
A steel sheet satisfying all of the requirements for a surface-treated steel sheet for seam-welded cans as described above was obtained.

In Comparative Example 1, the amount of hydrated chromium oxide on the metal tin protrusions was large, so there was no appropriate welding current range, and the amount of metal chromium on the metal tin recesses was also small, so the corrosion resistance after painting was poor.

In Comparative Example 2, the number of chromium eiwa oxide sites on the metal tin recesses was small, so the corrosion resistance after painting was slightly inferior.

Comparative Example 3 had a chromate film that did not contain any metallic chromium, and therefore had poor etching resistance after painting.

In Comparative Example 4, the amount of hydrated chromium oxide on the metal tin protrusion was large, so there was no appropriate welding current range.

<Effects of the Invention> As is clear from the above, the surface-treated steel sheet for seam-welded cans according to the present invention has a convex metal tin layer on the steel sheet, so it has a large metal tin saving effect and can be used for sufficient welding. In addition, the upper layer has a chromate film made of metallic chromium and chromium hydrated oxide that is effective for corrosion resistance after painting, and it can be welded because it matches the irregularities of metallic tin and strictly limits the distribution of the chromate film. The present inventors have developed a material for seam welded cans that satisfies all of the conditions required for materials for welded cans listed above. We were able to provide surface-treated steel sheets.

[Brief explanation of drawings]

1a and 1b are diagrammatic cross-sectional views of a surface-treated steel sheet for seam-welded cans having a convex metallic tin layer. FIGS. 2a and 2b are AES line analysis diagrams of C' and Sn of a surface-treated steel sheet for seam welded cans having a convex metal tin layer. FIGS. 2c and 2d are respectively Fig. 2b is a schematic diagram of Fig. 2b. Fig. 3 and Fig. 4 are graphs showing the effects of the amount of metallic chromium and the amount of chromium hydrate on weldability and post-painting corrosion resistance on metal tin convex portions and concave portions, respectively. Explanation of symbols 1... Steel plate, 2... Metal tin, 3... Chromate film. 4... Metal tin convex part, 5... Metal tin concave part FIG, 1a mu FIG, 2a FIG , 2cFIG
, 2b FIG, 2d, F
IG, 3 ε (X') (mg i m21

Claims (2)

[Claims] (1) A surface-treated steel sheet for seam welded cans having a metallic tin layer having a large number of convex portions and concave portions on the surface of the steel sheet, and a chromate film layer made of metallic chromium and chromium hydrated oxide on the metallic tin layer, The chromate film layer has an amount of metal chromium on the metal tin convex portion of X^Mmg/m^2 and an amount of chromium hydrated oxide (hereinafter referred to as chromium equivalent amount) of X^0mg/m^
2. The amount of metal chromium on the metal tin recess is Y^Mmg/m
＾2, When the amount of chromium hydrated oxide is Y＾0mg/m＾2, satisfy X＾M≧2, 18≧X＾M+X＾0≧4 Y＾M≧4, Y＾M+Y＾0≧8 A surface-treated steel sheet for seam welded cans, characterized by: (2) A metal tin layer having a large number of convex portions and concave portions on the surface of the steel plate, and a chromate film layer made of metal chromium and chromium hydrated oxide on the metal tin layer, and the chromate film layer is Amount of metallic chromium on the metallic tin protrusion X^Mmg/m
^2.The amount of chromium hydrated oxide (hereinafter referred to as chromium equivalent amount) is
0mg/m^2, the amount of metal chromium on the metal tin recess is Y
^Mmg/m^2, the amount of chromium hydrated oxide is Y^0mg/
When manufacturing a surface-treated steel sheet for seam welded cans that satisfies the following when m^2: A metal tin layer having many convex and concave portions is formed on the surface of the steel plate, and before electrolytic treatment is performed to form a chromate film on the metal tin layer, the steel plate on which the metal tin layer has been formed is immersed in a chromate treatment solution. A method for manufacturing a surface-treated steel sheet for seam-welded cans, characterized by: