JPS62174397A - Thin sn plated steel sheet for container having excellent corrosion resistance and weldability - Google Patents

Abstract

PURPOSE:To develop a surface treated steel sheet for can making having excellent seam weldability and the corrosion resistance under a coated film by forming the chromate treatment layer of the steel sheet which has fine ruggedness on the surface and has an Fe-Sn alloy plating layer, Sn plating layer and chromate treatment layer to the thickness inversely proportional to the thickness of the Sn plating layer in said part. CONSTITUTION:The rugged Sn plating layer 2 which has the fine ruggedness of 1-30mum spacings in projecting parts and has <0.07mum plating thickness of recesses, >=0.20mum plating thickness of the projecting parts and <=0.17mum average plating thickness is formed on the steel sheet 4 coated with Ni or Ni alloy contg. 1 or >=2 kinds among Ni-Fe, Ni-P, Ni-Zn, Ni-Cu, and Ni-Cr alloys to form an Sn-Fe alloy layer 1 between the steel sheet and the plating layer by the inter-diffusion with the steel base. The chromate treatment film 3 is formed on such rugged Sn plating layer 2 in such a manner that the thickness thereof is inversely proportional to the thickness of the Sn plating layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a surface-treated steel sheet for can manufacturing that has excellent seam weldability and corrosion resistance under coating.

[Conventional technology]

Conventionally, electrolytic Sn-plated steel sheets (hereinafter referred to as tinplate), electrolytic chromic acid treated steel sheets (hereinafter referred to as TFS-CT), and some electrolytic Ni-plated steel sheets (hereinafter referred to as TFS-NT) are known. Cans have been made by soldering, adhesive bonding, seam containers, etc. as single can manufacturing methods.

Tinplate has traditionally been the most widely used material for can manufacturing, but in order to reduce can manufacturing costs, Sn has been made thinner, and 7-metal welding has begun to be adopted instead of the traditional hang method for can manufacturing. However, if the Sn plating amount is less than 0.20 μm per side, the corrosion resistance of the paint and the weldability will deteriorate.
Although the seam welding performance of Ni-plated steel sheets is within a practical range, it is not sufficient, and the paint corrosion resistance is also insufficient in the case of highly corrosive contents such as strong acid A non-defective products. There is a demand for surface-treated steel sheets for can making that have excellent seam weldability.

[Problem that the invention seeks to solve]

In contrast, the present inventors have proposed a method in Japanese Patent Laid-Open No. 60-75586 in which a thin Ni plating layer is applied to a steel plate and then a heavy Sn plating layer is applied.
A plated steel sheet for containers having a Sn plating coating similar to that of the present invention has also been proposed in No. Although these materials are certainly more effective than conventional simple thin Sn-plated steel sheets in terms of seam weldability, paint corrosion resistance, etc., the current situation is that related customers are demanding further improvements.

To this end, the present inventors will develop a low-cost, high-performance surface-treated steel sheet that is excellent in seam weldability and corrosion resistance under paint film, while utilizing Sn, which has a proven track record in food preservation performance and is effective. As a result of intensive research aimed at
This invention has been made.

[Means for solving problems]

The gist of the present invention is that the gap between the protrusions on the steel plate is 1.
An Sn plating layer with microscopic irregularities of ~30 μm, a plating thickness of 0.07 μm or less on the concave portions, a plating thickness of 0.20 μm or more on the convex portions, and an average plating thickness of 0.17 μm or less, and an optional layer on top of this. The point is that the chromate coating layer has a distribution in which the chromate coating thickness of a portion is inversely proportional to the Sn plating thickness of that portion, that is, the chromate coating thickness is thinner in the convex portions of the Sn plating layer and thinner in the concave portions of the Sn plating layer. and has a thick coating structure.

In the present invention, in order to obtain more crushed corrosion resistance, a steel sheet coated with N1 or an N1 alloy containing one or more of Ni K Fe, P, Zn, Cu, and Cr (hereinafter referred to as an Nl-based pretreated original sheet), or After coating these Ni5N1 alloys, a part or all of them may be subjected to diffusion treatment (hereinafter referred to as Ni-based diffusion treated original plate) by heat treatment.

In a 48n plated steel sheet for can manufacturing having such a configuration, convex coarse Sn grains are scattered and distributed over the entire surface of the A plate, and sometimes the plating thickness is 0.17 μm or less per side in this area. Even when plated, the average Sn film thickness is the same.
Because of its large size, it can also be used for temporary reflow and paint dry baking.
The 8n layer remains, and the chromate coating layer is thinner at the convex parts of the Sn plating layer and thicker at the concave parts, so the chromate coating layer, which is an insulating coating, is thin at the convex parts of the Sn plating layer, which is the starting point of current conduction during welding. As a result, the weldability of the 7-metal is improved, and since the cucomate coating becomes thick in the concave portions where the Sn layer is thin and the corrosion resistance decreases, the decrease in corrosion resistance can be suppressed by the anticorrosion effect of the chromate coating. That is, by adopting the plating film structure shown in the present invention, it is possible to improve seam weldability and corrosion resistance, which have been considered drawbacks of conventional thin Sn-plated steel sheets, in a well-balanced manner.

Next, the present invention will be explained in more detail.

Surface-treated steel sheets with a thinner plating coating layer as in the present invention to reduce can manufacturing costs are often used after being coated with can manufacturing paint, and the seam welding area is coated with a coating by the time of seam welding. The S
As is known from past academic conferences, the alloy layer is formed due to the progress of a solid phase wave number reaction between the n-plated coating layer and the base material Fe, which is necessary to ensure good seam weldability.
n decreases and seam weldability becomes insufficient. For this reason, as mentioned above, the present inventors have proposed a steel plate in which a trace amount of N1 plating is applied to a steel plate and then a multilayer Sn plating coating is applied to the steel plate in Japanese Patent Application Laid-Open No. 60-75586 and Japanese Patent Application No. 59-166989. Patent Application No. 60-242749 has already disclosed an @Sn-plated steel plate having local irregularities similar to the invention. These suggestions will certainly improve the image quality after dry firing.
Although we have found that it is possible to secure J-Sn and improve seam weldability, the demands from customers are becoming increasingly strict, and it is necessary to further improve seam weldability and corrosion resistance. was desired.

Therefore, the inventors conducted further intensive studies and solved the problem by not only making the Sn plating layer have local irregularities, but also depositing the chromate coating so that it had a distribution opposite to that of the Sn plating layer. It is. That is, since the chromate coating layer is a type of insulating coating, it obstructs stable current flow during seam welding, and also has the effect of improving the resistance of the thin Sn-plated steel sheet, such as seam welding adhesion and corrosion under coating. Therefore, if the amount of chromate coating is reduced to improve the seam weldability of a thin Sn-plated steel sheet, the corrosion resistance will deteriorate, and if the amount of chromate coating is increased to improve the corrosion resistance, the seven-layer weldability will deteriorate. A chromate coating with a uniform coating thickness was able to ensure a good balance between seam weldability and corrosion resistance of thin Sn-plated steel sheets. Therefore, as mentioned above, the present inventors made the chromate coating distribution non-uniform and made the chromate coating thinner at the part where the current flow starts during seam bath contact to stabilize the current conduction state.
The present invention was achieved by realizing the idea of improving chromate weldability and ensuring corrosion resistance locally in areas where the chromate coating is thick.

Next, the plating layer structure according to the present invention is shown in FIGS. 1 and 12.3, respectively, in comparison with the conventional one. In addition, each figure Sn
It is an image diagram when the plating thickness is 0.11 μm. Figure 1 shows an example of the present invention, Figure 2 shows a uniform Sn plating layer,
Comparative Example with Chromate Coating, FIG. 3 shows a Comparative Example with a Sn plating layer with local irregularities but with a uniform chromate coating. In each figure, 1 indicates the alloy Sn, 2 indicates the metal Sn layer, 3 indicates the chromate coating layer, and 4 indicates the base steel. In the case of Figures 1 and 3, the current conduction during welding is thought to occur at the tip of the Sn part that has a convex shape, but in the example shown in Figure 2, there is no part that should be the starting point of current conduction, and for some reason the chromate It is thought that the coating is destroyed and the welding current tends to flow concentrated in the next part, so it can be assumed that welding defects such as splash are more likely to occur. Therefore, the plating layer structure shown in FIGS. 1 and 3 is advantageous in terms of seam weldability, but as shown in FIG.
The chromate coating is thinner in the convex parts of the plating layer, and the chromate coating is thicker in the concave parts of the Sn plating layer, which is a weak point in terms of corrosion resistance.For the reasons mentioned above, Fig. 3 is advantageous in terms of seam weldability and corrosion resistance compared to the conventional example. It is easy to understand that.

Next, a desirable plating layer structure in the present invention, particularly a desirable chromate coating distribution, will be explained.

In the present invention, it is essential that the chromate coating thickness at a given position has an inversely proportional relationship with the Sn plating thickness at that part, but the Sn plating thickness and chromate thickness in such a minute area can be determined by fluorescent X-ray analysis, etc. Since it is not possible to quantify with
It is necessary to quantify it using a method such as EPMA (electron f-rope microanalysis method). In this case S
Although it is necessary to correct all the influences of Cr contained in the Cr pack ground and base steel on Sn and Fe, an example of the correspondence relationship between Sn and Cr in the present invention is shown in FIG. In this case, the vertical and horizontal axes are the E of Sn and Cr after the above correction.
Regarding the PMA K eJ strength, the Sn plating shown in the figure; Cr+iH of one convex part is about half of Cri of the concave part. In order to quantify this relationship, we use statistical regression calculation to express the Sn amount Cr'H in an arbitrary part as X + y, assuming that the Sn content, Cr, and l of the convex part where the Sn plating layer is very thick are the base values of 1. has the relationship y = -ax + b, where a and b are positive constants, but in the present invention it is preferable that a be in the range 15≦a≦-0,1; The intercept is necessarily 1.1≦b≦5
has a range of For example, if Figure 4 is rewritten using this method, it will become like Figure 2g5, and the slope a is a=-0,82
becomes.

When expressed in this way, if a is -0.1 or more, the present invention has almost no effect, and if a is -5 or less, Sn
The thickness of the chromate coating in the concave portions of the plating layer increases too much, resulting in poor weldability.

The desirable plating form of the thin Sn-plated steel sheet, which is a feature of the present invention, has been explained above. The plate A used to obtain the plated steel sheet of the present invention is subjected to the Ni-based pretreatment original plate or the Nl-based diffusion treatment described above. If the original plate is used, finely deposited N1 will infiltrate into the Sn alloy layer generated during the S70 process and FFR burning process, which will make the alloy S1 denser and further improve its corrosion resistance. Alloying is also suppressed, so more free Snl! can be caused to remain.

Next, reason 7 for limiting the thin Sn-plated steel sheet for containers of the present invention! ! I will explain how to send it.

The present invention is applied to a steel plate whose surface has been cleaned by a conventional method, preferably coated with N1 agate or Ni K Fe, P, or Zn.

A coating of N1 alloy plating containing at least one of Cu and Cr is applied once, but there are no particular limitations on this coating method, and any known method can be applied.

The Ni or Ni alloy plated coating may be left as it is, or the Ni plating coating or the N1 alloy plating coating may be subjected to an appropriate heat treatment to cause a diffusion reaction with the steel sheet surface.

When using heat treatment means, the heating means is not particularly limited, but it is reasonable to use a steel plate annealing process, N1 or N
All of one alloy may be diffused into the steel sheet, or a portion may remain unalloyed. Note that the elements Fe, Zn, and C of the Ni alloy
O, Cr, and P are all alloyed with N1 and then heated to form an IJ
This has the effect of causing -8n to remain.

Next, Sn plating is applied. Electroplating is a reasonable method for Sn plating, but it is not particularly limited to this method. In the present invention, the Sn plating layer is 1~
It has microscopic irregularities with a gap of 30 μm between the convex portions, the plating thickness of the concave portions is 0.07 μm or less, and the plating thickness of the convex portions is 0.07 μm or less.
The reason for specifying that the average Sn plating thickness is 20 μm or more and 0.17 μm or less is that the effect of the present invention becomes remarkable when the average Sn plating thickness is 0.17 μm or less as determined by fluorescent X-ray analysis, etc. The present invention is very effective when the plating thickness is 0.12 μm or less.

The plating thickness of the concave portions of the Sn plating layer was specified to be 0.07 μm or less, and the plating thickness of the convex portions was 0.20 μm or more, because if there were no more unevenness in the Sn plating layer, the S
Not only does the significance of providing unevenness in the n-plated layer disappear, and its properties are virtually the same as those with the smooth Sn plating distribution shown in Figure 2, but also the characteristics of the romate coating, which is the key point of the present invention, are eliminated. This is because it becomes difficult to achieve distribution. Note that the average Sn plating thickness in the present invention is 0.0
The thickness is desirably 3 μm or more, because if it is less than 3 μm, the plating thickness cannot be ensured, especially on the convex portions. In the present invention, naturally, in the concave portion of the Sn plating layer, if the Sn alloy layer is exposed because the Sn layer is actually O and the Sn alloy layer is exposed locally, this also occurs. And this more Sn
Means for achieving the plating layer distribution are not particularly limited in the present invention, and may include adjusting the electrolytic conditions during Sn plating, such as adjusting the current density, changing the Sn plating bath composition, such as adjusting the addition of brightness additives, and Patent application 1986-242749
As disclosed by the inventors in the above issue, it is possible to appropriately adjust the reflow treatment conditions after the Sn plating process, but considering actual production, it is necessary to adjust the flow treatment conditions in terms of workability and stability, such as reflow treatment. It is preferable to carry out this by adjusting the previous 7 lux conditions, heating conditions and cooling conditions during reflow.

In addition, the gap between the convex parts of the Sn plating layer with concavities and convexities is set to 1 to 30
The reason for limiting the length to 41 m is that when the protrusion gap is less than 1 μm and the protrusions are close to each other, the plating layer is virtually continuous and the distribution of the chromate coating layer, which is a feature of the present invention, covers the Sn plating layer all over.
Impairs seam weldability. - 10,000, the gap between the convex parts is 30μm
If the IJ-8n layer is scattered far apart in the swamp, even if the residual IJ-8n layer remains in some areas during the complete burning of the can, the residual IJ-8n layer will remain as a whole.
Since the number of layers is small, deterioration in 7-m weldability is unavoidable.

In addition, in the present invention, it is also possible to perform differential thickness plating by changing the amount of Sn plating on the front and back sides of the steel sheet, and as the I770 treatment method, general resistance heating method and high frequency induction heating method can be used.
Non-oxidizing reflow may be performed in an inert gas atmosphere.

Next, a chromate treatment is performed as a passivation treatment on the outermost surface, but before the chromate treatment, a cathodic reduction treatment in, for example, soda carbonate is performed, and the S of the Sn plating coated surface is
The nd film may be removed in advance.

Although the chromate treatment method is important in order to obtain the chromate coating distribution which is the key point of the present invention, the method is not particularly limited in the present invention. However, the most preferable treatment is to perform cathodic electrolysis treatment in a treatment bath in which sulfuric acid, hydrochloric acid, or a fluoride such as sodium silicate or ammonium fluoride is added to chromic anhydride. What is necessary is to appropriately adjust the amount of anions to be added and further appropriately select the cathode current density. Specifically, chromic anhydride 4 degree is 10 to 1
009/L, total added anion brushing 0.2-3g/
The cathode %LR and density are preferably about 5 to 80 persons/dm', and the time for immersion in the reading treatment bath after completion of the cathode electrolytic treatment may be appropriately adjusted. Regarding the amount of chromate covered, the local amount of coverage can be measured using EPMA, etc., but the average amount of chromate covered by fluorescent X-rays etc. is 5 to 30 m9/m in terms of metallic chromium in the present invention. ' is preferable. If the thickness is less than 5 m97 m', corrosion resistance will be insufficient even if the present invention is applied.

Moreover, if it exceeds 301Q/m2, weldability will deteriorate. Conventionally, when the amount of chromate coating was about 25 to 30m97m, it was difficult to apply because the current flow during seam welding was obstructed and the seam weldability deteriorated. This method is applicable because the thickness of the chromate coating on the convex parts of the Sn plating layer, which is the point of conduction, is thinner.
Since restrictions on seam weldability regarding the thickness of the chromate coating are relaxed, it is further advantageous for improving corrosion resistance. As is well known, the chromate coating layer of the present invention is formed of a hot alkali-insoluble chromium layer and a hot alkali-soluble chromium layer, and although the content ratio of both is not particularly limited, it is preferable that the chromate coating layer is formed of a hot alkali-insoluble chromium layer and a hot alkali-soluble chromium layer. The higher the ratio of the insoluble chromium layer, the better.

Next, the present invention will be explained by examples.

〔Example〕

Example-1 Flux treatment in which Sn is electroplated to an average thickness of 0.07 to 0.14 μm per side under the conditions shown in 1 on both sides of a steel plate whose surface has been surface-cleaned by a normal method, and after washing with water, it is immersed in various fluxes and dried. , or after omitting the flux treatment, the Sn plating J- was subsequently subjected to reflow treatment using a resistance heating method under various conditions. Then, cathode peeping treatment was carried out under various conditions in the chromate treatment bath shown in H to form a chromate coating layer with an average coverage of f12 to 25 m97 m' per side in terms of metal chromium, and this was used as a sample.

This chromate coating layer consists of chromium that dissolves when the steel plate is immersed in NaOH at a concentration of 20 to 80 g/l and a temperature of 90'0 or higher (thermal alkali soluble chromium), and chromium that does not dissolve under these conditions (thermal alkali insoluble chromium). ), and the average coating amount is 7 to 19, respectively, in terms of metallic chromium.
'I'9/rn', 3-15 '17/m'.

Bath temperature: 40-50"C Cathode" ILm density: 2-30 people/d1rL bath temperature: 40
~60℃ Cathode 4 flow density: 5 to 90 people/dmQ Example-2 In Example 1, Sn plating was carried out under the conditions shown in ■,
Also, this is an example in which the 7-lux treatment was not performed, and only water washing, drying, and rinsing were performed, and the other items were the same as in Example 1.

Bath temperature 65°C Cathode current density: 48 A/dm' Example-3 Both sides of the steel plate whose surface was cleaned in Example 1 were air-plated with Ni at 15 m9/7rL'1M per side under the conditions shown in ff, and then Sn plated. This is an example, and other conditions are the same as in Example 1.

Bath temperature: 50゛C Cathode current density: 5 people/d□1 Example-4 In place of the Ni plating shown at 1V in Example 3, Ni-Fe alloy plating was applied under the conditions shown in V (alloy plating The other items are the same as Example 3.

Bath temperature: 50°C Cathode DC density: 10 A/dze Example-5 N was applied to both surfaces of the surface-cleaned copper plate under the conditions shown in Example 30■.
After electroplating 50 m97 m' per side, NH
720'Q in X gas (5%H2-95CHN2) atmosphere
, 15 seconds to diffuse the V type layer into the base steel sheet. Thereafter, two rounds of temper rolling were carried out, followed by degreasing and side washing in the usual process.

Subsequently, Sn plating coating, 7lux treatment, reflow treatment, electrolytic chromate treatment, and oiling were performed, but all of these steps were carried out in the same manner as in Example 3.

Example 6 This is an example in which the 5n41 film formed during reflow was reduced and removed under the conditions shown in (2) after the reflow treatment in Example 1, and then chromate treatment was performed, and the other items were the same as in Example 1.

Bath temperature: 35℃, hardening current density: 2゜5 people/dm' And in addition to the above, as a conventional example, using a #25 bushing with a single-sided Sn plating coating thickness of 0.38μm, the following (A) is used.
The evaluation tests of ~(D) were conducted and the results are shown in Table 1.

(A) Microscopic observation The surface condition of the obtained plated steel plate was observed using a scanning electron microscope (hereinafter referred to as SEM). SEM observation is mainly 1000
Observation was carried out at 5x magnification and at least 5 fields of view were observed at different positions, but if clear unevenness was observed in the Sn plating layer, the gap between the projections was measured at 3 or more points in 1 field of view, and the average value of these is shown. Just in case. In addition, when no clear unevenness was observed, it was indicated as "No unevenness observed."

(B) EPMA measurement After investigating the distribution of the Sn plating layer using the method shown in section (A), the amount of chromate covered on the Sn plating layer was measured using EPMA (electron globe microanalysis method) with a beam diameter of 1μ. We investigated. If clear unevenness is observed in the Sn plating layer by the observation in item (A), characteristic X-rays of Sn and Cr should be taken using 3-point APM on a 3-point plate for both concave and convex areas in a 2000x field of view at any location. Measure the intensity (cps), and if no clear unevenness is observed in the observation in item (A), measure any 6 points in the 2000x field of view.
Measurements were made in the same manner above the point. Then, this measurement was carried out in at least 5 fields of view at different positions, and the above-mentioned Fig. 4,
The 1 series number a was determined using the method shown in the example of FIG.

Further, the Sn plating thickness of the concave and convex portions of the Sn plating layer was determined by comparing the Sn characteristics X and 'fa intensity measured here with a calibration curve determined from a standard sample.

(C) Seam weldability test After each specimen was formed into a can body, a seam welding machine for can manufacturing was used to determine the lap width Q, 4 + 11 of the can body joint.

Under the conditions of pressurizing force of 4 sktit and M double speed of 45 mpm,
The investigation was conducted by changing the welding secondary current.

The evaluation was expressed in the welding secondary current range that allowed good welding.

The lower limit value of the appropriate secondary welding current was determined by the lower limit of the strength of the welded part, and the upper limit value was determined by the upper limit of slushy generation. The appearance of the seam weld was determined by visual inspection based on the presence or absence of looseness. All of the specimens used in the seam weldability test were completely burnt at 210° C. for 20 minutes in a sleepy air oven.

CD) Paint resistance subcontractability test Each specimen was coated with epoxy-phenol paint for can manufacturing on one side.
55 m9/dm'' roll coating, baking at 205'O for 10 minutes, and additionally baking at 190''O for 10 minutes. Then, a scratch was made on the coating film using a cutter knife, and Efsen processing of 5111 m was performed using an Efsen testing machine to prepare a test sample. The test sample is 5% NaC
After performing one hour of salt water spraying using No. 1, it was kept in a constant temperature and humidity tester at 25°C and relative humidity of 85°C for 14 days, and the state of rust was visually evaluated from the scratched area. The evaluation was as follows: ◎ No thread rust occurred, 0 small occurrence, Δ slightly large, and X large.

The above test results are summarized in Table 1. All of the test results that satisfied the scope of the present invention had good seam weldability and coating resistance, and in particular, Sn-mets-? The materials subjected to KNj-based pretreatment are good, whereas the comparative examples outside the scope of the present invention are all poor.

〔Effect of the invention〕

In the present invention, the chromate coating layer has irregularities, and the lower layer Sn
Because it has an inversely proportional relationship with the plating layer, it becomes a container material with excellent corrosion resistance and seam weldability, which compensates for the conventional drawbacks of the thin Sn plating layer.

[Brief explanation of drawings]

Figures 1, 2, and 3 show S formed on the surface of the steel plate, respectively.
FIG. 1 is a conceptual diagram showing the cross-sectional structure of the n-plated layer and the chromate coating layer, and FIG. 1 is an example of the present invention, and FIGS. 2 and 3 are comparative examples. FIGS. 4 and 5 are characteristic diagrams illustrating the relationship between the Sn plating layer and the chromate coating layer of the present invention. 1... Alloy Sn layer 2... Metal Sn layer 3...
・Chromate coating layer 4...Substrate 1 Figure 4 Figure 5 Figure 5n Amount of precipitation: y- Procedural amendment dated March 7, 1939, by the Commissioner of the Japan Patent Office. 1. Indication of the case Relationship with Patent Application No. 1 Otsu 4-q1 115 filed in 1986 Applicant 4: Amendment by Agent We will amend the following statements in the specification of the present application. Note 1, page 24, “Table 1” is corrected as follows. Procedural amendment 1933 ← Month/

Claims (1)

[Claims] 1. In order from the steel plate surface, the alloy Sn layer, the gap between the convex parts is 1 to 3
0 μm, the plating thickness on the concave parts is 0.07 μm or less, the plating thickness on the convex parts is 0.20 μm or more, and the average thickness is 0.17 μm.
In a plated steel sheet consisting of a Sn plating layer with irregularities of less than m and a chromate coating layer, corrosion resistance and welding are achieved with a chromate coating distribution in which the chromate coating thickness is inversely proportional to the Sn plating thickness in that part. Thin Sn-plated steel sheet for containers with excellent properties. 2. As a steel plate, Ni or Ni is coated with Fe, P, Zn,
Claim No. 1, characterized in that a steel plate is used, which is coated with a Ni alloy containing one or more of Cu and Cr, either as it is, or whose surface is partially or completely diffused by thermal diffusion treatment. The thin Sn-plated steel sheet for containers having excellent corrosion resistance and weldability as described in item 1.