JPH0425350B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention provides a seam-welded can surface with excellent weldability and corrosion resistance after painting, which is particularly suitable for joining can bodies by electric resistance welding, for food cans, beverage cans, and general cans. This relates to treated steel sheets. <Prior art and its problems> Tin-plated steel sheets, commonly referred to as tinplate, have been widely used as a material for food cans. Previously, solder was used to join these can bodies, but due to the toxicity of lead contained in solder, pure tin solder has come to be used in recent years. 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 increases 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. Since plated tin cans are expensive to manufacture, they have been forced into a difficult competitive position, even though 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 tinplate mentioned above, chromium-type stain-free steel is a conventionally used material for cans. This is an electrolytic chromate treatment that forms metallic chromium and a chromium hydrated oxide layer on the surface, and is highly economical, but the thick chromium hydrated oxide film on the surface has high resistance. Therefore, the weldability is poor and the strength of the welded part is insufficient, 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. For example, there is a nickel-plated steel plate represented by ``Nitzkelite'' released by the American National Steel Company, which has a nickel plating with an area weight of approximately 0.5 g/m <sup>2</sup> on the steel plate. In addition, the surface is treated with conventional chromate treatment, resulting in poor paint adhesion and poor weldability at high speeds of 30 m/min or higher, so it has not been widely used. Yet another type is represented by ``Tein Alloy'' released by John's Rollin Steel Company in the United States. This is about
After 0.6g/ ^m2 thin tin plating is treated with hot tin,
Although it has undergone conventional chromate treatment, its rust resistance, paint adhesion, and weldability are insufficient. Can materials suitable for electric resistance welding must have excellent weldability and corrosion resistance after painting. To explain this requirement specifically, there is sufficient welding strength during welding,
Moreover, it has an appropriate welding current range that does not cause welding defects such as so-called "splashing" in the welded part, and when used to coat the contents of a can, the coating film can take full advantage of its corrosion resistance. Has adhesion,
Furthermore, in the areas where coating film defects inevitably occur, corrosion must be prevented by the excellent corrosion resistance of the material itself. In order to create a material for welded cans that satisfies weldability and post-painting corrosion resistance at such a low cost, the present inventors first prepared a metal tin layer with a large number of convex portions on the surface of a steel plate, and A surface-treated steel sheet for seam welded cans (Japanese Patent Application No. 1983-063883) having a chromate coating consisting of chromium hydrated oxide or metallic chromium and chromium hydrated oxide was provided. 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 includes a metal tin layer having a large number of convex portions and concave portions having the following properties (i) to (iii) on the surface of a steel plate, and ^an area of each convex portion of 1 μm ² to 800000 μm. The area percentage occupied is 20 to 80%. The thickness of the metal tin in the convex portion is 0.007 μm to 0.7 μm. The surface treated steel sheet for seam welded cans has a chromate film layer made of metal chromium and chromium hydrated oxide on the metal tin layer. , the amount of metallic chromium on the metallic tin protrusion is X ^M mg/m ² and the amount of hydrated chromium oxide is X ^O
mg/m ² , the amount of metallic chromium on the metallic tin recess is Y ^M mg/
m ² , and the amount of chromium hydrated oxide is Y ^O mg/m ² , the metal tin layer is set so that X ^M ≧2, 18≧X ^M +X ^O ≧4 Y ^M ≧4, Y ^M +Y ^O ≧8 By distributing the upper chromate film layer, a surface-treated steel sheet for seam welded cans with very good weldability and post-painting corrosion resistance is provided. Further, the present invention provides a metal tin layer having a large number of convex portions and concave portions having the following properties (i) to (iii) on the surface of the steel plate, and an area of each convex portion of 1 μm ² to 800000 μm ^{2 and} an area percentage occupied by the convex portions. is 20 to 80%. The thickness of the metal tin in the convex portion is 0.007 μm to 0.7 μm. A chromate film layer made of metal chromium and chromium hydrated oxide is provided on the metal tin layer, and the chromate film layer is The amount of metallic chromium on the metal tin protrusion is X ^M mg/m ² , the amount of hydrated chromium oxide (hereinafter referred to as chromium equivalent amount) is X ^O mg/m ² , and the amount of metallic chromium on the metal tin concave portion is Y ^M mg/m 2 m ² , the amount of chromium hydrated oxide is Y ^O
When manufacturing a ^surface -treated steel sheet for seam ^welded cans that satisfies ^the following conditions: ^{mg / m 2} , Before forming the metallic tin layer having a large number of convex portions and concave portions and performing electrolytic treatment to form a chromate film on the metallic tin layer, the steel plate on which the metallic tin layer has been formed is immersed in a chromate treatment solution. The present invention provides a method for manufacturing a surface-treated steel sheet for seam-welded cans, characterized by the following. The present invention will be explained in more detail below. The inventors previously proposed a steel plate shown in Japanese Patent Application No. 59-63883 as a light tint with excellent weldability and post-painting corrosion resistance. This steel plate provides an innovative product as a thin tint with excellent weldability and corrosion resistance after painting, and has the characteristics of low cost. It came to be used instead of.
In this case, a material with even more Cr metal was required, but if the amount of Cr metal was simply increased, weldability deteriorated, leading to complaints. Therefore, in actual production lines, the amount of Sn and the amount of metal Cr must be controlled within very strict ranges, resulting in low workability and efficiency. Therefore, the present inventors considered a thin coating that has conventional weldability performance and is stable and excellent in paint adhesion and post-painting corrosion resistance. First, we investigated the difference in surface film structure as the cause of the difference in corrosion resistance after painting with the same Cr content. The structure of a surface-treated steel plate 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 Figures 1a and 1b. ing. In Figure 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. Since the metallic tin recess 5 contains almost no metallic tin in order to save tin, 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 its corrosion resistance after painting.
Those with excellent corrosion resistance after painting had metallic chromium above a certain value and had a large chromate film in the metallic tin recesses. 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 a large amount of chromate film is deposited on areas with a small amount of metallic tin, and those showing the distribution shown in Fig. 2c have extremely 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 painting due to the sacrificial corrosion protection 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 portion, weldability will be poor and an appropriate welding current range will not be obtained. Therefore, we believe that if the chromate film has a distribution as shown in Figures 2a and 2c, a surface-treated steel sheet for seam welded cans with excellent corrosion resistance after painting can be obtained without impairing the weldability of the convex metal tin. It will be done. Therefore, the present inventors further investigated in detail the influence of the structure, distribution, and amount of this chromate film on weldability and post-painting corrosion resistance. That is, the amount of metal chromium on the metal tin convex portion 4 is X ^M mg/m ² , the amount of hydrated chromium oxide is X ^O mg/m ² , the amount of metal chromium on the metal tin recess 5 is Y ^M mg/m ² , The amount of chromium hydrated oxide
When Y ^O mg/m ² , this X ^M , Y ^M , X ^M +X ^O , Y ^M
Corrosion resistance and weldability after painting were investigated in detail by varying +Y ^O. The results are shown in FIGS. 3 and 4. The amount of metal chromium (X ^M ) on the convex metal tin portion 4 is 2
If the total amount of metallic chromium and chromium hydrated oxide (X ^M + X ^O ) is less than 4 mg/m ^{2 ,} the corrosion resistance after painting may be poor, and if X ^M + X ^O is less than 18
When the content exceeded mg/m ² , weldability deteriorated. Furthermore, since there is almost no metallic tin in the metallic tin recess 5, the conditions for good corrosion resistance are that the amount of metallic chromium (Y ^M ) is 4 mg/m ² or more, and the total amount of metallic chromium and chromium hydrated oxide (Y ^M +Y ^O ) It was found that 8 mg/m ² or more is required. By creating a chromate film with the above structure, the incidence of defective products is significantly reduced, and the coating has a thin coating that has better paint adhesion and post-painting corrosion resistance than ever before, without worsening weldability. We were able to manufacture tinplate on an actual line. 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 it is, is to tin plate, form a convex tin layer, and then, before chromate treatment,
By immersing it in the same chromate solution, the convex tin part is oxidized and a large amount of tin oxide is formed, thereby lowering the current efficiency of chromium in the convex tin part and forming a large chromate film in the concave part of the metal tin. be. 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, 2
Although the effect of the present invention can be recognized even if electrolysis is turned off for more than one pass, providing more passes than necessary is
This is negative in terms of equipment costs, and even more
If the number of passes increases, the current efficiency of chromium becomes too small, which is not good. Furthermore, the current density of chromate treatment is 10A/dm ²
If it is more than that, the effect will be greater. It is thought that when the current density is low, the effect of pre-soaking is lost because it is less affected by the condition of the substrate. Therefore, the present inventors have previously proposed that the chromate treatment is performed by turning off the downpass of the first chromate treatment layer, performing chromate immersion treatment, and then performing chromate electrolysis treatment at a current density of 10 A/dm ² or more. Surface-treated steel sheet for seam welded cans having a metallic tin layer with a large number of convex portions (Japanese Patent Application No. 59-063883)
We were able to obtain the great effect of improving the post-painting corrosion resistance of the paint with almost no equipment or management costs. In the present invention, the effect of metallic tin is to improve weldability. It is preferable that the metal tin layer has a large number of convex portions, and the metal tin is dispersed in a convex or uneven shape. Preferably, the area of each convex portion is 1 μm ² to 800000 μm ² The area percentage occupied by the convex portion is 20 to 80%, and the thickness of the metal tin of the convex portion is 0.007 μm to 0.7 μm. The reason for limiting the area of each convex part to 1 μm ² to 800000 μm ² is that if it is less than 1 μm ² , the effect of expanding the contact area during welding is insufficient, and there is no effect of improving weldability.
If it exceeds 800,000 μm ² , this effect will be saturated and tin will be used unnecessarily, resulting in an economic disadvantage. At the same time, the reason for limiting the area percentage of the convex portion 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 This is because the economic advantage of maintaining a At the same time, the thickness of the metal tin on the convex part is 0.007 μm ~
The reason why it is limited to 0.7μm is that if it is less than 0.007μm, the effect of improving weldability cannot be sufficiently obtained.
This is because if the welding property is exceeded, the effect of improving weldability is saturated, resulting in an economic 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) Coagulation using flux After applying electrolytic tin plating to a flat surface, flux (an aqueous solution of ZnCl ₂ , NH ₄ Cl, etc.) is applied to the surface in an arbitrary distribution state, and then a molten tin treatment is performed to form the flux. Utilizing the difference in wettability of molten tin between areas coated with and areas not coated, tin is coagulated and solidified in a convex or uneven shape. (2) Agglomeration on an inert surface After the surface is subjected to inactivation treatment (Ni diffusion treatment, etc.) against wetting of molten tin, electrolytic tin plating is applied to the surface, followed by molten tin treatment to agglomerate the tin. Let solidify. A nickel diffusion layer (inactive layer) 32 can be provided under this metal tin layer so that its weight ratio Ni/(Ni+Fe) is 0.50 or less and its 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 metal 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. Below are the AES analysis method, welding method, and
A method for evaluating corrosion resistance after painting was shown. (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 total sum of metallic chromium and chromium hydrated oxide, were investigated by AES. Measurements were carried out at a vacuum level of 1.0×10 ^-9 Torr and a beam voltage.
The distribution was roughly investigated using line analysis under the condition of 10.0KV, and especially exact quantitative values were obtained by combining line analysis and depth direction analysis, using the calibration curve method, and performing all analysis samples on the same day. The distribution and quantification of metallic chromium was determined by immersing the obtained test plate in hot alkali (7.5N NaOH, 90°C) for 10 minutes, and using the above method. The obtained test plate was directly subjected to the above method. (2) Evaluation of weldability Using a copper wire with a diameter of approximately 1.5 mm as a welding electrode, we overlapped the test material specimens under constant pressure while moving the wire, and performed electric resistance welding at a welding speed of 40 m/min. The weldability of the material was evaluated based on the size of the appropriate range of welding current and pressure, which was determined based on the conditions that the welded part had sufficient strength and there was no occurrence of so-called "splashing". The strength of the welded part was determined by a so-called peel test, in which a V-shaped cut was made from the end of a cylinder that held the welded part in place, and the triangular part was grasped with pliers and pulled toward the other end. The required strength was that the welded part would not break. (3) Corrosion resistance after painting 50% of epoxy/phenol paint was applied to the sample material.
After painting to a thickness of mg/dm ² , put a cross cut,
Furthermore, the one with 5mm Eriksen overhang,
The edges and back side were sealed and a test piece was prepared for corrosion resistance after painting. This test piece was immersed for one week at 55°C using commercially available grapefruit juice, tomato juice, milk, and coffee 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】

[Table] <Example> Next, the present invention will be specifically explained with reference to Examples. After electrolytically degreasing and pickling an ordinary tin plate, metal tin was made to exist in a convex shape according to the following method, and chromate treatment was applied thereto. (Example 1) Nickel sulfate 250g/l, nickel chloride 45g/l
1, nickel plating using a solution containing 30g/l of boric acid, and then tin plating using a solution containing 55g/l of ferrous sulfate, 35g/l of phenolsulfonic acid (65%), and an appropriate amount of brightener. A convex metallic tin layer was obtained by heating and melting the tin at a temperature higher than the melting point of tin to coagulate and solidify the tin. The area of each convex portion at this time is ² to 170 μm2,
The area percentage of the protrusions was 55%, and the thickness of the metal tin in the protrusions was 0.10 to 0.50 μm. Further, the thickness of the metal tin in the recess was 0 to 0.005 μm. Furthermore, after immersion in a solution of 40 g/l of CrO ₃ and 0.38 g/l of H ₂ SO ₄ for 0.4 seconds, cathodic treatment at 20 A/dm ² was performed. (Comparative Example 1) A convex metallic tin layer was obtained by the same method as in Example 1, and immediately subjected to cathodic treatment at 5 A/dm ² without pre-plating immersion treatment in a 15 g/l CrO ₃ solution. ,
It was immersed in a CrO ₃ 50g/l solution at 60°C for 3 seconds. (Comparative Example 2) A convex metallic tin layer was obtained in the same manner as in Example 1, and after immersed in a chromate treatment solution of 100 g/l of CrO ₃ + 0.7 g/l of H ₂ SO ₄ for 0.5 seconds, a cathode of 35 A/dm ² was formed. I processed it. (Example 2) Nickel sulfate 250g/l, nickel chloride 45g/l
1. Nickel plated using a solution of 30 g/l of boric acid, annealed at 700°C in a 10% H ₂ + 90% N ₂ atmosphere,
Diffuse and penetrate the Ni glare. Reduction rate of this steel plate
After 1.5% temper rolling, degreasing and pickling, 50g/l of stannous chloride and sodium fluoride.
Tin plating using 45g/l, sodium hydrogen fluoride 10g/l, sodium chloride 54g/l, yellow blood soda 0.8g/l, and an appropriate amount of brightener, followed by heating and melting treatment above the melting point of tin. to coagulate and solidify tin,
A convex metallic tin layer was obtained. At this time, the area of each convex portion is 2 to 235 μm ² , and the area percentage of the convex portion is 70%.
The thickness of the metal tin in the convex portion was 0.08 to 0.27 μm. Further, the thickness of the metal tin in the recess was 0 to 0.001 μm. Furthermore, in a solution of 50g/l of CrO ₃ and 5g/l of NaF.
After immersion for 0.6 seconds, cathode treatment at 30 A/dm ² 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, it was immediately heated to 30 A/d without dipping before plating.
m ² cathodically treated. (Comparative Example 4) A convex metallic tin layer was obtained by the same method as in Example 2, and further CrO ₃ 20 g/l + Na ₂ Cr ₂ O ₇ 3 g/l +
A cathodic treatment of 30 A/dm ² was immediately performed without performing a pre-plating dipping treatment in a H ₂ SO ₄ solution of 0.2 g/l. Amount of metallic chromium on the metallic tin protrusions (4 in Fig. 1) of the steel plates obtained in Examples 1 to 2 and Comparative Examples 1 to 4
X ^M , total amount of chromium in metallic chromium and chromium hydrated oxide (X ^M +X ^O ), amount of metallic chromium on the metallic tin recess (5 in Figure 1) Y ^M , total amount of metallic chromium and chromium hydrated oxide Table 3 shows the amount of chromium (Y ^M +Y ^O ), the welding test results, and the post-painting corrosion resistance test results.

[Table] Underlined items indicate items outside the scope of the present invention.
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 chromium hydrated oxide on the convex portion of the metal tin, as well as the amount of metal Since the amount of metallic chromium and the amount of chromium hydrated oxide on the tin recesses are within the appropriate range of the present invention, a product with excellent corrosion resistance after painting and satisfying all of the above-mentioned requirements as a surface-treated steel sheet for seam-welded cans can be obtained. It was done. 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 amount of hydrated chromium oxide on the metal tin recesses was small, so the corrosion resistance after painting was slightly inferior. Since Comparative Example 3 was a chromate film containing no metallic chromium, the corrosion resistance after painting was poor. In Comparative Example 4, there was no appropriate welding current range because the amount of hydrated chromium oxide on the metal tin protrusion was large. <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. Furthermore, the upper layer has a chromate film made of metallic chromium and chromium hydrated oxide, which is effective for corrosion resistance after painting.Moreover, the distribution of the chromate film is strictly limited to match the irregularities of the metallic tin, resulting in excellent weldability. The present inventors have developed a surface for seam welded cans that satisfies all of the conditions required for materials for welded cans listed above. We were able to provide 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. Figures 2a and 2b show Cr surface treated steel sheets for seam welded cans having a convex metal tin layer.
and Sn AES line analysis diagram. Figures 2c and 2d are schematic diagrams of Figures 2a and 2b, respectively. FIG. 3 and FIG. 4 are graphs showing the effects of the amount of metallic chromium and the amount of chromium hydrate on the weldability and post-painting corrosion resistance on the metallic tin convex portions and concave portions, respectively. Explanation of the symbols: 1... Steel plate, 2... Metal tin, 3... Chromate film, 4... Metal tin protrusion, 5... Metal tin recess.

Claims (1)

[Claims] 1. A metal tin layer having a large number of convex portions and concave portions having the following properties (i) to (iii) on the surface of the steel plate, and the area of each convex portion is 1 μm ² to 800000 μm ² The area occupied by the convex portions The percentage is 20 to 80% The thickness of the metal tin in the convex portion is 0.007 μm to 0.7 μm In the surface-treated steel sheet for seam welded cans that has a chromate film layer consisting of metal chromium and chromium hydrated oxide on the metal tin layer. , ^the chromate film layer has an amount of ^metal chromium on ^the metal tin convex ^portion of When the amount of metallic chromium is Y ^M mg/m ² and the amount of hydrated chromium oxide is Y ^O mg/m ² , X ^M ≧2, 18≧X ^M +X ^O ≧4 Y ^M ≧4, Y ^M +Y ^O ≧ 8. A surface-treated steel sheet for seam welded cans, which satisfies the following. 2 A metal tin layer having a large number of convex portions and concave portions with the following properties (i) to (iii) on the surface of the steel plate, and the area of each convex portion is 1 μm ² to 800000 μm ² The area percentage occupied by the convex portions is 20 to 80% The thickness of the metal tin on the convex portion is 0.007 μm to 0.7 μm. A chromate film layer made of metal chromium and chromium hydrated oxide is provided on the metal tin layer, and the chromate film layer is on the metal tin convex portion. The amount of metallic chromium is X ^M mg/m ² , the amount of hydrated chromium oxide (hereinafter referred to as chromium equivalent amount) is X ^O mg/m ² , the amount of metallic chromium on the metal tin recess is Y ^M mg/m ² , chromium water The amount of oxide is Y ^O
When manufacturing a ^surface -treated steel sheet for seam ^welded cans that satisfies ^the following conditions: ^{mg / m 2} , Before forming the metallic tin layer having a large number of convex portions and concave portions and performing electrolytic treatment to form a chromate film on the metallic tin layer, the steel plate on which the metallic 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: