JPH1129897A - Electrolytic chromic acid-treated steel sheet being excellent in plating adhesion and corrosion resistance and weldable without grinding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the adhesion strength of an Sn plating in an electrolytic chromic acid-treated steel sheet which is improved in welderability without impairing the corrosion resistance by forming the Sn plating. SOLUTION: At least one side of the steel sheet is constituted by having a Ni diffused layer with a Ni concentration of >=1 to <20 wt.% on the surface and the Sn plating with an amount of adhesion of 20 to 500 mg/m<2> per one surface of the steel sheet formed without reflowing on the Ni diffused layer. Furthermore, the outermost layers of both sides of the steel sheet are constituted by being covered with surface coating films by a metallic Cr layer with an amount of adhesion per one surface of the steel sheet of 30 to 200 mg/m<2> and a Cr hydration oxide layer with an amount of adhesion per the same of 4 to 18 mg/m<2> in terms of Cr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic chromic acid-treated steel sheet used as a three-piece welded can body such as a gallon can or a pail, and more particularly to an electrolytic chromic acid treated for welding without removing a film by grinding. It relates to a steel plate.

[0002]

2. Description of the Related Art Tin bodies and electrolytic chromic acid-treated steel sheets are used for can bodies such as gallon cans and pail cans. Above all, tinplate is excellent in corrosion resistance and weldability due to thick Sn plating, but expensive due to the large amount of Sn used, and is not preferable from the viewpoint of resource saving.

On the other hand, electrolytic chromic acid-treated steel sheets are low in cost and have excellent paint adhesion because they do not use Sn, but the nonmetallic Cr layer (Cr hydrated oxide layer) on the coating surface of the steel sheet is nonconductive. It is difficult to perform welding as it is because it is a volatile substance, and it is necessary to grind the surface of the weld in advance. The grinding powder generated in the grinding process deteriorates the working environment and adheres to the can after welding, so that it is regarded as a problem particularly in a can for food use. Therefore, in order to solve such a problem, the weldability of the electrolytic chromic acid-treated steel sheet was improved,
Various attempts have been made to realize welding without grinding.

[0004] For example, in Kokoku 3-69999 discloses, on the surface of the steel sheet, in 40~150mg / m ² of metallic Cr layer and the metal Cr terms become non-metallic Cr layer of 5 to 25 mg / m ² and the metal Cr It has been proposed to form a partially projecting coating.
This proposal certainly improves the weldability, but the metal Cr
However, a problem remains that a thin portion of the metal Cr layer is locally formed and the corrosion resistance is deteriorated due to the projection of a part of the metal Cr layer.

In Japanese Patent Publication No. Hei 5-27720, a metal Cr layer of 45 to 90 mg / m ² is deposited on a steel sheet surface.
It has been proposed to form a hardly soluble Cr hydrated oxide layer of 1 to 10 mg / m ² as Cr. However, the weldability is insufficient, and the corrosion resistance is deteriorated because the thickness of the Cr hydrated oxide layer is reduced compared to the conventional one.

Accordingly, in order to improve the weldability of the electrolytic chromic acid-treated steel sheet without deteriorating the corrosion resistance, it is necessary for the steel sheet surface to contain even a small amount of Sn. Then, 50 ~ 900mg /
has a Sn plating m ^2, has a Cr hydrous oxide layer of 5 to 50 mg / m ² on at 7~100mg / m ² of the metal Cr layer and Cr in terms of its,
In addition, it is not covered with Sn plating and has a diameter of 0 in circle.
A steel plate having a steel plate exposed portion of 5 to 20 μm has been proposed.

Here, it is stated that Sn is not required to be heated and melted after Sn plating, that is, so-called reflow is required.
If reflow is performed after Sn plating, the amount of Sn is originally small, and the amount of metallic Sn is reduced due to the progress of alloying between Sn and the base steel during reflow. Moreover, since paint baking is usually performed before welding, metal treatment is performed by heat treatment at that time.
The amount of Sn further decreases. As a result, the weldability becomes insufficient.

On the other hand, when reflow is not performed after Sn plating, although there is an effect of improving weldability, the problem is that the adhesion between Sn plating and the base steel is significantly reduced. Here, when the electrolytic chromic acid treatment is performed directly on the steel sheet, the adhesion at the interface between the precipitated metal Cr layer and the base steel sheet is generally good. This is because the structures of Fe and Cr are both body-centered cubic and similar in structure with similar lattice constants.Therefore, the Cr plating film grows epitaxially on the steel sheet, and the crystallographic interface This is considered to be due to good consistency. On the other hand, since the structures of Sn and Fe are completely different, the adhesion at the interface between the steel sheet and the Sn plating is generally poor.
In the case of reflow after Sn plating, adhesion is improved by forming a Sn-Fe alloy phase between Sn and the base steel by reflow treatment, but as described above, weldability is insufficient when reflow is performed. Becomes a problem.

Furthermore, Japanese Patent Publication No. 6-96790 discloses that a steel sheet having a diameter of 0.2 to 2.0 μm and a height of 0.1 μm or more is coated on a steel sheet surface.
Made from the grain has a Sn layer of 20 to 200 mg / m ^2,. 30 to thereon
A steel sheet having a 150 mg / m ² metal Cr layer and a Cr hydrated oxide layer of ² to 40 mg / m ² in terms of Cr has been proposed. According to this proposal, although a certain effect can be obtained in terms of improving the weldability, the problem that the adhesion of the Sn plating is poor still remains in this case.

[0010]

SUMMARY OF THE INVENTION The present invention seeks to improve the adhesion of Sn plating in an electrolytic chromic acid-treated steel sheet which has improved weldability without forming Sn plating and impairing corrosion resistance.

[0011]

According to the present invention, at least one surface of a steel sheet has a surface Ni concentration of 1 wt% or more and less than 20 wt%.
Ni diffusion layer and was formed without reflowing on the Ni diffusion layer, the amount of deposition per steel sheet one side of 20 to 500 mg / m ² Sn
It has a plating, further the outermost layer of the steel sheet both sides, coating weight of 30 to 200 mg / m ² of the metal Cr layer and the coating weight of Cr hydrous oxide of 4~18mg / m ² of Cr in terms of per steel sided An electrolytic chromic acid-treated steel sheet which is excellent in plating adhesion and corrosion resistance and which can be welded without grinding, characterized by being covered with a surface coating of a layer.

Here, the Sn plating adhesion amount is 50 to 300 mg / m ^2.
And the amount of deposition of the metal Cr layer to be 30~120mg / m ^2,
In particular, it is suitable when both the inner and outer surfaces of the can are painted and used and food is filled as the contents of the can. Similarly, the adhesion amount of Sn plating adhesion amount of 20 to 200 mg / m ² and the metal Cr layer
The content of 80 to 200 mg / m ² is particularly suitable when the inner surface of the can is used without painting and is filled with an alkaline release agent or the like as the content. And the adhesion amount of Sn plating is
300 adhesion amount to 500 mg / m ² and the metal Cr layer is 100 to 200 mg / m
^{A value of 2} is particularly suitable when the inner surface of the can is mainly used without painting and is filled with an organic solvent or the like as the content.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, first, in order to secure excellent paint adhesion characteristic of electrolytic chromic acid-treated steel sheet, cathodic electrolysis in an aqueous solution mainly composed of chromic anhydride is carried out. It is necessary to form a surface film composed of a metal Cr layer and a Cr hydrated oxide layer (hereinafter referred to as electrolytic chromic acid-treated film) as the outermost layers on both surfaces of the steel sheet.

Next, under the electrolytic chromic acid treatment film,
It is necessary that at least one side of the steel sheet has an amount of Sn necessary for securing the weldability. The precipitation form of the Sn plating is not particularly limited, and may be continuous, discontinuous when viewed microscopically, or may be a granular or raised precipitation form. However, it is important that the Sn plating be heated and melted to just above the melting point of Sn, that is, provided without reflow. The reason is that, in the present invention, the amount of Sn plating is suppressed to the minimum necessary for ensuring the weldability, whereas when reflow is performed, 0.3 to
Since about 0.5 g / m ² of Sn is usually lost by alloying with the base steel, the loss of Sn due to reflow must be avoided.

However, if the reflow after the Sn plating is omitted, the adhesion between the Sn plating and the steel sheet deteriorates.
As described above. The inventors conducted various studies on ways to improve this point.By forming a Ni diffusion layer in advance on the steel sheet surface as a base for Sn plating,
It was newly found that the adhesion between the Sn plating and the base was significantly improved. The reason for this is not clear, but Sn and Ni interdiffuse at room temperature to form an alloy phase, so by providing a Ni diffusion layer on the surface of the steel sheet, It is presumed that a small amount of alloy phase is formed at the interface between Ni and Sn, and this may improve the adhesion.

Here, the Ni concentration on the surface of the Ni diffusion layer is
It is important to regulate to less than 20 wt%. Because Ni
This is because when the concentration exceeds 20 wt%, the corrosion resistance rapidly deteriorates. That is, the Fe-Ni binary system phase diagram (Binary Allo
y Phase Diagrams Second Edition, ASM Internationala
According to l), in thermal equilibrium below 200 ° C, Fe-2
0wt% Ni alloy is a solid solution of Ni in α-Fe and intermetallic compound F
eNi ₃ separated into two phases. Therefore, when the Ni concentration increases, the occupied area on the steel sheet surface by FeNi ₃ which is a different phase increases, and when exposed to a corrosive environment, the FeNi ₃ phase becomes a local cathode and becomes galvanic between the steel sheet serving as the anode. It is presumed that corrosion resistance deteriorates due to the increase in current.

The Ni concentration on the surface of the Ni diffusion layer is 1 wt%.
If it is less than 3, the formation of an alloy phase at the interface with Sn becomes insufficient and excellent adhesion cannot be obtained. Therefore, the Ni concentration on the surface of the Ni diffusion layer is 1 wt% or more, preferably 3 wt% or more. Is needed. It should be noted that the surface of the Ni diffusion layer is intended to have a depth that can be measured by Auger electron spectroscopy immediately after the Ni diffusion treatment, that is, a region of several nm. Then, as shown in FIG. 1, a typical example of a depth direction profile obtained when the Ni concentration in the region is measured by Auger electron spectroscopy from the surface of the steel sheet to the inside thereof is Sn and Sn in the profile. from the peak a ₁ of Ni appearing at the interface between the Fe a ₃
The integrated value A of the intensity up to and the integrated value B of the Fe intensity from a ₂ to a ₃ where Ni and Fe coexist are converted into a weight A /
Defined as (A + B).

The Ni diffusion layer is formed by subjecting a steel plate to Ni plating and then performing a heat treatment such as continuous annealing. Here, Ni plating performed before heat treatment is 5 mg / m
^If it is less than ² , the effect of improving the adhesion cannot be obtained, so that 5 mg / m
It is preferable to set it to ² or more. The upper limit of the amount of Ni plating should be determined in consideration of the heat treatment conditions so that the surface Ni concentration after the heat treatment is less than 20 wt% as described above. Plating amount 500mg /
If m ² is exceeded, the alloy phase of Sn and Ni increases, and the cohesive failure of this phase itself makes it impossible to secure the adhesion between the base steel and the Sn plating. Therefore, the content is preferably 500 mg / m ² or less.

Furthermore, the heat treatment conditions may be general continuous annealing conditions, and need not be particularly limited, and may be determined according to the steel type of the steel sheet material itself and the required mechanical properties. Next, after the heat treatment, the amount of Ni plating is desirably determined so that the Ni concentration on the surface of the Ni diffusion layer becomes a specified value. By the way, when the steel type is low carbon steel, 680
Usually, heat treatment is performed at about 700 ° C. for about 10 to 100 seconds, and when the steel type is extremely low carbon steel, heat treatment is performed at 760 ° C. for about 10 to 100 seconds.

As a film having a function similar to that of the Ni diffusion layer in the present invention, an Fe—Ni alloy plating or a trace amount of Ni plating may be considered. When a film of Ni alloy plating or a trace amount of Ni plating was provided, the effect of improving the adhesion was not obtained and the result was also inferior in corrosion resistance, unlike the case where thermal diffusion treatment was performed after Ni plating. I'm not sure why,
It is presumed to be due to the following differences.

That is, the Fe—Ni alloy plating is an alloy obtained by electrodeposition, and often has a phase constitution different from the thermal equilibrium state. It is presumed that the state is different from Ni in the Ni diffusion layer generated by the processing. In addition, the extremely small amount of Ni plating reduces the amount of plating as much as possible, so that the outermost Ni plating identified by surface analysis is
Concentrations can be apparently less than 20 wt%. However, in this case, the surface Ni should exist as a Ni phase to the last, and it is presumed that the structure is different from that of Ni present as a solid solution in the α-Fe phase of the steel sheet by the thermal diffusion treatment according to the present invention. Is done. Due to the above differences, Fe-Ni alloy plating film
When the Ni plating film is provided, unlike the case where the thermal diffusion treatment is performed after the Ni plating, the effect of improving the adhesion is not seen.
It is also considered that the corrosion resistance is poor.

In the present invention, the formation of the Sn plating on the Ni diffusion layer is as described above, and the amount of the Sn plating is in the range of ²⁰ to 500 mg / m ² . That is, if the amount of Sn deposited is less than 20 mg / m ² , the weldability becomes insufficient. On the other hand, if it exceeds 500 mg / m ² , the color tone of the electrolytic chromic acid-treated steel sheet cannot be obtained and the economy is impaired.

Further, as described above, the outermost layer on both surfaces of the steel sheet is provided with an electrolytic chromic acid-treated film. the range of 4mg / m ² ~18mg / m ² to obtain. That is, if the adhesion amount is less than 4 mg / m ² , the adhesion of the paint is insufficient, while if it exceeds 18 mg / m ² , the adhesion is hardly changed but the appearance is deteriorated.
² is the upper limit. On the other hand, the adhesion amount of the metal Cr layer in the electrolytic chromic acid-treated film is in the range of 30 mg / m ² to 200 mg / m ^{2 in} order to obtain excellent corrosion resistance after painting. That is, 30mg
/ m is less than ² is insufficient corrosion resistance after painting, whereas 200m
If it exceeds g / m ² , the corrosion resistance after coating hardly changes, but the appearance deteriorates.

When the electrolytic chromic acid-treated steel sheet having each of the above-mentioned coatings is used as a can body, both the inner and outer surfaces of the can can be used with or without painting. An alkaline release agent or an organic solvent can be filled.

In particular, when both the inner and outer surfaces of the can are painted and used, and food is filled as the contents of the can, the amount of Sn plating adhered is 50 to 300 mg / m ² and the metal Cr layer A steel sheet with a deposit of 30-120 mg / m ² is advantageously suitable. That is, if the adhesion amount of Sn plating is less than 50 mg / m ² , the weldability is insufficient, and if it exceeds 300 mg / m ² , the excellent paint adhesion characteristic of the electrolytic chromic acid-treated steel sheet is deteriorated. Further, adhesion of the metal Cr layer is insufficient in corrosion resistance after painting to be less than 30 mg / m ^2, whereas the corrosion resistance after coating and more than 120 mg / m ² is considering economical efficiency since almost unchanged 120 mg / m ² or less.

When the inner surface of the can is used without painting and is filled with an alkaline release agent or the like as the content, the anticorrosive effect of the coating film cannot be expected on the inner surface of the can. Corrosion resistance becomes important. For example, since a gallon can is used for a long time after being opened, the head space portion on the inner surface side of the can is particularly exposed to a severe corrosive environment. Therefore, for such applications,
A steel sheet having an Sn plating adhesion amount of 20 to 200 mg / m ² and a metal Cr layer having an adhesion amount of 80 to 200 mg / m ² per one side of the steel sheet is advantageously applied. That, Sn is an amphoteric metal, because it is corroded by the alkali, if the contents of such alkaline stripper was from where it is necessary to reduce the adhesion amount as much as possible, the upper limit is 200 mg / m ² . However, when the amount of Sn is 20
If it is less than mg / m ² , welding becomes difficult, so the lower limit is 20 mg / m ² . Further, in such a corrosive environment on the inner surface side of the can, the effect of improving corrosion resistance by the Ni diffusion layer formed on the surface of the steel sheet is great. Further, adhesion of the metal Cr layer, 80 mg / m less than ² when insufficient corrosion resistance, whereas 200 mg / m ² to more than the corrosion resistance since it hardly changes and economic considerations 200 g / m ² The following is assumed.

Furthermore, when the inner surface of the can is mainly used without painting and the content is filled with an organic solvent or the like, the anticorrosive effect of the coating film cannot be expected on the inner surface of the can. Becomes important. For example, since a gallon can is used for a long time after being opened, the head space portion on the inner surface side of the can is particularly exposed to a severe corrosive environment. Therefore, for such applications,
A steel sheet having an Sn plating adhesion amount of 300 to 500 mg / m ² and a metal Cr layer having an adhesion amount of 100 to 200 mg / m ² per one side of the steel plate is advantageously applicable. That is, the Sn plating adhesion amount is 500 mg /
If m ² is exceeded, the appearance becomes white, the color tone of the electrolytic chromic acid-treated steel sheet cannot be obtained, and the economic efficiency is impaired due to an increase in the amount of Sn, so the upper limit is 500 mg / m ² . On the other hand, the lower limit of the amount of Sn is 300 mg / m ^{2 in} order to secure corrosion resistance on the inner surface of the can.
And Further, adhesion of the metal Cr layer is insufficient corrosion resistance becomes less than 100 mg / m ^2, whereas the corrosion resistance is more than 200 mg / m ² is in consideration of economic efficiency since it almost unchanged 20
0 mg / m ² or less.

[0028]

[Example] An unannealed low carbon steel coil after cold rolling was led to a Ni plating facility installed on the entrance side of a continuous annealing line, and after degreasing and washing with a conventional method, the Ni plating conditions shown in Table 1 were obtained. A predetermined amount of Ni plating is performed, and immediately thereafter, the maximum temperature and the holding time at that temperature are 10 to 30 at 700 ° C.
Continuous annealing was performed under the condition of seconds to form a Ni diffusion layer on the surface of the steel sheet. Next, after passivation rolling to finish a plating base plate having a plate thickness of 0.32 mm and a hardness of T4CA, a predetermined amount of Sn plating was performed on the continuous plating line under the conditions shown in Table 2, and further under the conditions shown in Table 3. And subjected to electrolytic chromic acid treatment by a two-step method to finish a plated steel sheet. From the coil of the plated steel sheet thus obtained, a cut sheet having a sheet width of 1 m was cut out with a shear line, and further prepared into test pieces of an arbitrary size by a shearing machine, and then subjected to various quality evaluations described below. The amount of Ni deposited was measured by the X-ray fluorescence method, the surface Ni concentration after the Ni diffusion treatment was identified by Auger electron spectroscopy, the amount of Sn plated was determined by the electrolytic peeling method of JIS G3303, and the electrolytic chromic acid-treated film Of the metal Cr layer and the Cr hydrated oxide layer were measured by the fluorescent X-ray method of JISG3315. Each evaluation method is as follows.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

<Plating Adhesion Evaluation Method> A cell tape was stuck to the surface of the test material and then peeled off. The Sn count was measured on the adhesive surface of the cell tape by a fluorescent X-ray analyzer, and no Sn was detected on the cell tape. Is a material having good adhesion (symbol ◎), and a material having poor adhesion (symbol x) when Sn was detected on the cellophane tape.

<Weldability evaluation method> The welding resistance was evaluated by a dynamic resistance measuring device using a spot welding machine as shown in FIG. That is, as shown in the figure, two test materials 3a and 3b are arranged in a superposed manner between the spot welding electrode tips 1 and 2, and a welding current of a rectangular wave shown in FIG. And
At that time, a resistance value between the superposed test materials 3a and 3b was monitored in a time zone showing a constant current value.

The resistance during spot welding thus measured is called dynamic resistance. As shown in FIG. 4, a measurement example of the dynamic resistance value generally shows that a plated steel sheet having good weldability such as tinplate has a low initial resistance value and rises with time as shown by a solid line in FIG. It shows a behavior in which the resistance value increases. This is because the resistance of the steel sheet bulk increases when the steel sheet is electrically heated. On the other hand, a material having poor weldability, such as a normal electrolytic chromic acid-treated steel sheet, shows a remarkably high resistance value at the beginning as shown by a dotted line in FIG. This is because the contact resistance on the surface of the steel sheet is large, which causes local heat generation, which easily generates dust on the molten steel sheet. That is, the weldability in an actual can-making line can be estimated from the waveform of the dynamic resistance value with time and the initial resistance value. The fact that such dynamic resistance behavior at the time of spot welding has a correlation with the weldability in the actual can making line,
For example, Toshihiro Kikuchi, Kazuo Mochizuki, Hideo Kugaminato, surface technology,
vol.47 (1996), p.62-66. Therefore, the weldability was evaluated by measuring the dynamic resistance value. Table 4 shows the welding experimental conditions.
Table 5 shows the criteria for determining weldability.

[0035]

[Table 4]

[0036]

[Table 5]

<Evaluation Method of Coating Adhesion> An epoxyphenol-based coating was applied on one side of the test material at a dry weight of 50 mg / m ² .
The painted surfaces are crimped with nylon film and 5mm x 100m
Using a test piece cut out to a length of m, a T-peel peel test was performed at a tensile speed of 100 mm / min according to the conditions shown in FIG. The criteria are shown in Table 6.

[0038]

[Table 6]

<Evaluation method of corrosion resistance after coating> One surface of the test material was coated with an epoxyphenol-based paint at a dry weight of 50 mg / m ² , cut out into a sheet thickness × 50 mm × 100 mm, and the end face was sealed. Further, a crosscut reaching the base steel from the top of the coating film was put with a cutter knife, immersed in a corrosive solution at 50 ° C. for 4 days, dried, and the paint at the crosscut portion was peeled off with cellophane tape. The judgment was made based on the peel width. The composition of the etchant is shown in Table 7 and the criteria are shown in Table 8.

[0040]

[Table 7]

[0041]

[Table 8]

<Natural corrosion resistance evaluation method>
× 100mm, cut into a glass bottle so that half of the test piece is immersed in the corrosive liquid, sealed and conducted a corrosion promotion test at 50 ° C for 30 days.After the test, the gas-liquid interface and the corrosion of the head space Was determined from the appearance. As the etchant, a commercially available release agent and a regenerated thinner were used. The criteria are shown in Table 9.

[0043]

[Table 9]

<Appearance Evaluation Method> A visual evaluation was performed to judge whether or not it felt equivalent to a normal electrolytic chromic acid-treated steel sheet. The evaluation was equivalent (同等) and clearly different (x).

<Plating conditions of comparative material> A comparative material was prepared in the same procedure as the test material of the example, and was replaced with a Ni diffusion treatment.
In the case of Fe-Ni alloy plating and trace Ni plating, Ni plating prior to continuous annealing was not performed, and Fe-Ni alloy plating or trace Ni coating was performed immediately before Sn plating under the conditions shown in Table 10. went.

[0046]

[Table 10]

Tables 11 and 12 show the results of each quality evaluation and the structure of the film. From the table, it can be seen that all of Examples 1 to 18 according to the present invention satisfy the requirements of Claim 1, and therefore have excellent plating adhesion and corrosion resistance after coating. That is, in Example 1, although the amount of Sn deposited was small and did not satisfy the requirement of Claim 4, bare corrosion resistance in thinner was slightly inferior. However, since the requirements of Claims 2 and 3 were satisfied, the other qualities were not satisfied. The second and third embodiments are similar to the first embodiment without any problem. Example 3 is an example in which a Ni diffusion layer and Sn plating are provided only on one side of a steel sheet.

[0048]

[Table 11]

[0049]

[Table 12]

In Example 4, since the amount of Sn deposited exceeds the upper limit of claim 3, the bare corrosion resistance in the release agent is slightly inferior, but there is no problem in other characteristics. Examples 5 and 6
Is inferior in paint adhesion, especially naked corrosion resistance in a release agent due to a large amount of Sn, but is sufficiently used as an unpainted can holding a thinner as a content to satisfy the requirements of claim 4. It is possible. Example 6 is an example having a Ni diffusion layer and Sn plating only on one side of a steel sheet.

Next, Example 7 is an example in which the weldability is slightly inferior due to the small amount of Sn, and the bare corrosion resistance to thinner is insufficient. However, the requirement of claim 3 is satisfied. In Examples 8 and 9, the amount of metal Cr is as defined in claims 3 and 4.
This is an example in which the corrosion resistance at the time of bare use is insufficient because the value is less than the lower limit in the above. However, in order to satisfy the requirements of claim 2,
Since the weldability, paint adhesion, and corrosion resistance after painting are sufficient,
It has sufficient quality for applications where the inner surface of the can is painted and used.

In Examples 10, 11 and 12, the corrosion resistance when barely used in a thinner is inferior because the Sn adhesion amount is less than the range in claim 4, but the requirements in claims 2 and 3 are satisfied. Demonstrate sufficient quality when used in other environments. Examples 10 and 11 are examples having the Ni diffusion layer and the Sn plating only on one side of the steel sheet.

In Example 13, since the amount of Sn was larger than the range of Claims 2 and 3, the paint adhesion and the bare corrosion resistance in the release agent were deteriorated. This is an example that can be used satisfactorily as an unpainted can holding a thinner as a content. On the other hand, in Example 14, since the amount of Sn was smaller than the range in claims 2 and 4, the weldability was slightly inferior, and the bare corrosion resistance in thinner was deteriorated. Since it is satisfied, it is an example which can be used sufficiently as an uncoated can holding an alkaline solution as a content.

Example 15 is an example that satisfies the requirement of claim 2, and the bare corrosion resistance is deteriorated because the amount of metal Cr is smaller than the required level of claims 3 and 4. 2
This is an example that can be sufficiently used as a painted can because the requirements are satisfied. In Example 15, the Ni diffusion layer and the Sn
This is an example in which plating is provided only on one side of a steel sheet.

Example 16 is an example that satisfies Claims 1 and 3, in which the amount of Sn is smaller than the required level in Claims 2 and 4, so that the bare corrosion resistance in thinner is deteriorated. Further, since the amount of Sn is the upper limit of the third aspect, an uncoated can that holds an alkaline solution as the content can be used although the corrosion resistance is slightly inferior. Example 16
Is an example having a Ni diffusion layer and Sn plating only on one side of a steel sheet.

Example 17 is an example in which the corrosion resistance at the time of bare use is insufficient because the amount of metal Cr is smaller than the range of claim 3 and the amount of Sn adhesion is larger than the range of claim 3. However, in order to satisfy the requirements of claim 2, weldability, paint adhesion,
The corrosion resistance after painting is sufficient, and the quality is sufficient for applications where the inner surface of the can is painted and used.

In Example 18, the amount of Sn deposited was larger than the upper limit in claim 3 and smaller than the lower limit in claim 4,
When used naked, both in alkaline solution and in thinner, it is insufficient in any case, and there is a problem that the amount of metal Cr is larger than the upper limit of claim 2 and is slightly over-specified. The corrosion resistance is excellent when used. Example 18 is an example in which a Ni diffusion layer and Sn plating are provided only on one side of a steel sheet.

Next, Comparative Examples 1 and 2 are examples in which the corrosion resistance deteriorates because the Ni concentration of the Ni diffusion layer is 20 wt% or more. From this result, it is well understood that controlling the Ni concentration of the Ni diffusion layer is a very important requirement.

Comparative Example 3 is an example in which the amount of Sn is larger than the range of the present invention, and the paint adhesion and the bare corrosion resistance in a release agent are deteriorated, and the appearance is different from that of a normal electrolytic chromic acid-treated steel sheet. This is an example that is unacceptable to users. Comparative Example 4 is an example in which weldability is insufficient because there is no Sn plating on the surface.

Comparative Example 5 is an example in which the amount of adhering metal Cr is small and the paint adhesion and the corrosion resistance are poor. In Comparative Example 6, since the amount of metallic Cr exceeded the upper limit of Claim 1, the appearance was poor and unacceptable to the user. In addition, since the amount of Sn deposited is larger than the upper limit of claim 3 and smaller than the lower limit of claim 4, when used naked, it is insufficient in both alkaline solutions and thinners.

Comparative Example 7 is an example in which the amount of Cr hydrated oxide adhered was small and paint adhesion and corrosion resistance were poor. Comparative Example 8
Is an example of reflowing Sn plating, which has poor weldability and cannot be used as a steel plate for cans. Comparative Example 9
Since the amount of the Cr hydrated oxide layer is too large, the appearance is poor and the product is not obtained. Comparative Example 10 is an example in which no Ni-diffusion layer is present on the surface of the base steel sheet, so that the adhesion of the no-reflow Sn plating is poor, and it cannot be used at all. In addition, evaluation other than plating adhesion was not performed.

In Comparative Example 11, instead of the Ni diffusion treatment, an Fe—Ni alloy plating was performed by electroplating just before Sn plating to reduce the Ni content in the Fe—Ni alloy to 40 mg / m ² and the Ni This is an example in which the film configuration is the same as that in Example 2 except that the concentration is 10 wt%. As described above, in such a case, plating adhesion and corrosion resistance are insufficient. In Comparative Example 12, instead of Ni diffusion treatment, a slight amount of Ni alloy plating was performed by electroplating immediately before Sn plating, and the Ni concentration on the surface was apparently 18
This example is an example in which the coating composition is the same as that of the second embodiment except that wt% is used. As described above, in such a case, plating adhesion and corrosion resistance are insufficient.

[0063]

According to the present invention, the weldability of the electrolytic chromic acid-treated steel sheet is remarkably improved, the adhesion of plating is excellent, and the paint adhesion, post-coat corrosion resistance, bare corrosion resistance and appearance are excellent. Material is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a typical example of a depth direction profile obtained when measurement is performed by Auger electron spectroscopy.

FIG. 2 is a schematic diagram showing a dynamic resistance measuring device.

FIG. 3 is a diagram showing a welding current waveform during dynamic resistance measurement.

FIG. 4 is a diagram showing a measurement example of dynamic resistance.

FIG. 5 is a diagram showing a tension method in a T-peel peel test.

[Explanation of symbols]

 1, 2 Spot welding electrode tips 3a, 3b Test material

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kenichiro Akao 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel Co., Ltd. (72) Inventor: Toshiyuki Kato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Pref.

Claims (4)

[Claims] An Ni diffusion layer having a Ni concentration of 1 wt% or more and less than 20 wt% on at least one side of a steel sheet, and an adhesion amount per side of the steel sheet formed on the Ni diffusion layer without reflow of 20 to 20% by weight. 500 mg / m ² of having a Sn plating, further the outermost layer of the steel sheet both sides, coating weight of 30 to 200 mg / m ² per steel sided
Non-grinding with excellent plating adhesion and corrosion resistance, characterized by being covered with a surface coating of a chromium hydrated oxide layer with a metal Cr layer of 4 to 18 mg / m ^{2 in} equivalent Cr as Cr Electrolytic chromic acid treated steel sheet. 2. The electrolytic chromic acid-treated steel sheet according to claim 1, wherein the adhesion amount of the Sn plating is 50 to 300 mg / m ² and the adhesion amount of the metal Cr layer is 30 to 120 mg / m ² . 3. The electrolytic chromic acid-treated steel sheet according to claim 1, wherein the adhesion amount of the Sn plating is 20 to 200 mg / m ² and the adhesion amount of the metal Cr layer is 80 to 200 mg / m ² . 4. The electrolytic chromic acid-treated steel sheet according to claim 1, wherein the adhesion amount of the Sn plating is 300 to 500 mg / m ² and the adhesion amount of the metal Cr layer is 100 to 200 mg / m ² .