JPH0689472B2 - Thin Sn plated steel plate for can making and method for manufacturing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a surface-treated steel sheet for can making which is excellent in seam weldability and undercoat corrosion, and a method for producing the same.

[Conventional technology]

Conventional electrolytic Sn-plated steel sheet (hereinafter referred to as tin plate), electrolytic chromic acid treated steel sheet (hereinafter referred to as TFS-CT), or partially electrolytic Ni
Plated steel sheet (hereinafter referred to as TFS-NT) is known, and 3
Solder bonding, adhesive bonding,
Cans have been made by seam welding or the like.

Although tinplate has been most widely used as a material for conventional can manufacturing, tin plating has been thinned to reduce can manufacturing costs, and the can manufacturing method began to use seam welding instead of conventional soldering. When the Sn plating amount is 2000 mg / m ² or less per side, both coating corrosion resistance and seam weldability deteriorate, and TFS-NT (Ni plated steel sheet) used in some parts as a material for seam welding cans.
The seam welding performance is within the practical range, but it is not sufficient, and the coating corrosion resistance is insufficient for highly corrosive contents such as strongly acidic foods. Therefore, at low cost, the coating corrosion resistance and seam weldability are low. There is a demand for an excellent surface-treated steel sheet for can manufacturing.

[Problems to be Solved by the Invention]

On the other hand, the inventors of the present invention have disclosed a method in Japanese Patent Application Laid-Open No. 60-75586 in which a small amount of Ni plating is coated on a steel sheet, and then a Sn plating layer is overlaid, and in Japanese Patent Application No. 59-166989. We have already discovered and applied for a method to form a small amount of Ni plating coating after applying Sn plating coating. Further, in JP-A-57-169098, a surface-treated steel sheet for a seam welding can having a coating structure similar to the latter is already known. Compared with the conventional simple thin Sn-plated steel sheet, these are certainly effective in terms of seam weldability, coating corrosion resistance, etc., but at present the related consumers are demanding further improvement.

For this reason, the present inventors have a track record in food preservation performance from this point of view, and developed a surface-treated steel sheet excellent in low-cost, high-performance seam weldability and under-coat corrosion while utilizing effective Sn. As a result of earnest studies for the purpose, the present invention has been made.

[Means for Solving the Problems]

The gist of the present invention is as follows: (1) After a Sn plating coating of 1500 mg / m ² or less on one side of a steel plate is applied, a Sn plating layer is melted by heat treatment at a melting point of the Sn plating layer or higher, and water quenching is performed. In the thin Sn-plated steel sheet for can making obtained by performing the solidification treatment, the unalloyed β-Sn layer remaining after the melt solidification treatment has a maximum diameter of 30 μ or less, and,
A thin Sn-plated steel sheet for can manufacturing, which has coarse Sn grains having 100 or more convex portions per 0.1 mm ² .

(2) Ni or a Ni alloy layer containing at least one of Fe, P, Zn, Cu and Cr in Ni on a steel sheet is coated at 100 mg / m ² or less on one side in terms of Ni, and then either directly or by heat treatment. Part or all of the steel plate surface is diffused and then 1500 per side
After applying Sn plating coating to mg / m ² or less, melting treatment of the Sn plating layer by heat treatment above the melting point of the Sn plating layer, solidification treatment by quenching in water Unalloyed β-Sn layer remaining after the solidification treatment has a maximum diameter of 30μ or less, and has a thin Sn for can making, characterized in that it has coarse Sn particles having a convex portion consisting of 100 or more per 0.1 mm ^2. Plated steel plate.

(3) Thin Sn for can making, which is obtained by applying Sn plating coating of 1500 mg / m ² or less on one side of a steel plate, then melting the Sn plating layer by heat treatment above the melting point of the Sn plating layer, and solidifying by rapid cooling in water. In the method for producing a plated steel sheet, the heating temperature is set to
A method for producing a thin Sn-plated steel sheet for can making, which comprises setting the temperature to 240 to 300 ° C and the time from melting of the Sn plating layer to solidification by cooling in water to 0.2 to 1 sec.

(4) Ni or a Ni alloy layer containing one or more of Fe, P, Zn, Cu and Cr in Ni on a steel sheet, coated with 100 mg / m ² or less on one side in terms of Ni, and then either directly or by heat treatment. Part or all of the steel plate surface is diffused and then 1500 per side
After applying Sn plating coating to mg / m ² or less, melting treatment of the Sn plating layer by heat treatment of the Sn plating layer melting point or higher, in the method for producing a thin Sn-plated steel sheet for can making subjecting to solidification treatment by rapid cooling in water, The heating temperature is set to 240 to 300 ° C and the time from melting of the Sn plating layer to solidification by cooling in water is set.
It is a method for producing a thin Sn-plated steel sheet for can manufacturing, which is characterized in that the time is 0.2 to 1 sec.

The thin Sn-plated steel sheet for can manufacturing having such a form becomes coarse Sn particles in a convex shape and is distributed over the entire surface of the steel sheet, and this portion is 1500 mg / m ² per side and thin Sn plating. Nevertheless, since the Sn film thickness is larger than the average Sn film thickness, the free Sn layer remains during reflow and during coating air baking, and the coarse Sn particles have the effect of preventing the undercoat corrosion.

The present invention will be described in detail below.

As in the present invention, a surface-treated steel sheet having a thin plated coating layer for reducing can manufacturing cost is often used by coating a can-making coating, and the seam welded portion is coated by seam welding. It will be air-baked due to baking, at this time Sn
An alloy layer is formed by the progress of the solid phase diffusion reaction between the plating layer and the base Fe. Therefore, in a simple thin Sn-plated steel sheet, as is known in past academic societies, unalloyed free Sn, which is required to secure good seam weldability, decreases and the seam weldability becomes insufficient. Therefore, as described above, the inventors of the present invention, in JP-A-60-75586 and Japanese Patent Application No. 59-166989, respectively, a steel sheet coated with a small amount of Ni plating on the steel sheet and then a Sn plating coating in a multilayer coating, and We have already filed an application for a steel sheet with a plating coating configuration opposite to this. With these proposals, it is possible to secure free Sn after air burning,
We have found that the seam weldability is improved. However, the coating process for actual customers is complicated, and due to various reasons such as the trend toward high-speed, high-efficiency seam welding, and the increasing demands made by customers on the finish of seam welded cans, the seam weldability is further improved. It is desired to let them do.

Therefore, the present inventor has arrived at the present invention as a result of diligent research, the essential point is that the reflow treatment of the Sn plating coating layer is essential, and during the reflow treatment, the surface morphology of the free Sn layer remaining in the molten Sn It was found that the seam weldability and the undercoat corrosion were significantly changed due to the difference.

The Sn-plated layer of the Sn-plated steel sheet has a relatively uniform flat surface even at a thin coating with a coating amount of 1500 mg / m ² or less at the time of electrodeposition, but once the reflow that satisfies the conditions of the present invention method When processed, Sn dissolves once, so thin Sn
In the plating area, white island-shaped rough projections are observed on the surface due to insufficient interfacial tension and wettability of Sn. An example observed with a scanning electron microscope is shown in the sketch of a photograph (x1000). When EPMA analysis is performed on this convex portion, it is free of residue remaining in the reflow process.
It can be seen from FIG. 4 that it is a Sn layer.

As a result of various studies conducted by the present inventors on the properties of the island-shaped residual free Sn having this convex portion, a thin S of 1500 mg / m ² or less was obtained.
It has been found that, in an n-plated steel sheet, a thin Sn-plated steel sheet having a quality excellent in seam weldability and corrosiveness under a coating film can be obtained by forming a range of free Sn morphology. That is,
It was found that the grain size and distribution density of the free Sn layer were involved.

First, regarding the grain size of the free Sn layer, the grain size should be suppressed to 30 μm or less at the maximum. If it becomes a coarse grain of more than 30μ, the place will be a thin coating locally with a thin Sn plating coating of 1500 mg / m ² or less like flat electrodeposited grain, so there will be little residual free Sn layer,
In particular, seam weldability deteriorates. The lower limit of the grain size is not particularly limited, but is preferably at least 1 μm or less. Below this, the same behavior as in the case of having a substantially uniform Sn layer is exhibited, and the effect of the present invention cannot be expected. Distribution density of free Sn layer is 0.1m
More than 100 pieces should be distributed densely per m ² . If less than 100 particles per 0.1 mm ² remain coarsely, the grain spacing will be wide, and the residual free Sn layer will be small when viewed from the entire surface, and especially the undercoat corrosion will deteriorate.

Next, the reason why the presence of the free Sn layer of the specific form of the present invention is advantageous for the seam weldability and the undercoat corrosion is described with reference to the conceptual diagram of the cross-section of plating after reflow in FIG.

FIG. 1A shows the form of the free Sn layer of the present invention. The Sn layer 2 electrodeposited on the base metal 1 is depicted in a wavy shape. Reference numeral 3 is an alloyed Sn layer formed by the reflow treatment, and 4 is a remaining thick free Sn layer. Fig. 1 (b) shows a comparative example in which the wave pitch is larger and the residual free Sn layer is thinner and smaller in quantity than (a). Fig. 1 (c) shows a comparative example in which the density of the convex portions of the residual free Sn layer is small. Indicates. Incidentally, in these figures, the chromate coating layer existing on the outermost surface is omitted. First, in the case of the form in which the island-shaped convex portions are densely distributed as in the present invention (a), since the electrodeposited Sn2 is locally electrodeposited more than the average adhered Sn amount in the convex portions, naturally this portion is It remains as a free Sn layer 4 during the reflow process.

This part is free even during air baking during the later can manufacturing process.
Remains as Sn. Also, since the convex parts are densely distributed,
Even with thin Sn plating of 1500 mg / m ² or less over the entire surface of the steel sheet, free Sn that is effective for seam weldability is scattered over the entire steel sheet, and deterioration of seam weldability due to thin Sn plating can be prevented. .

On the other hand, in the comparative example (b), since the reflow treatment was performed so as to obtain a uniform surface, the free Sn layer 4 remaining after the reflow treatment due to thin Sn plating is thin and small in quantity. Therefore, the residual free Sn layer 4 disappears during can baking and the deterioration of seam weldability is unavoidable, and the Sn plating amount must be increased inevitably. Further, in Comparative Example (C), the amount of Sn electrodeposited on the pole portion is larger than that of the invention Example (A), but since the distribution density of the convex portions is small, for example, when the can is air-baked in the can, it remains on the pole portion. Even if the free Sn layer remains, the total amount of the residual free Sn layer is small and the seam weldability deterioration cannot be avoided.

Further, the drawback of the thin Sn-plated steel sheet as in the present invention is that there is a problem of seam weldability and insufficient undercoat corrosion such as rust under coating during can storage. As a result of the inventors' studying the improvement, it has been found that the corrosion resistance can be improved by forming a residual free Sn layer after the reflow treatment in the specific region as described above. Therefore, the surface-treated steel sheet produced according to the present invention has excellent seam weldability and corrosion resistance.

Further, as shown in FIG. 1 (a), in the present invention, the alloyed Sn layer formed by the reflow treatment also has irregularities corresponding to the irregularities of the electrodeposited Sn layer 2, that is, the local Sn content and alloy Sn content. One of the features is that they are manufactured to have a proportional relationship.

As described above, the reason why the rust corrosion resistance under the coating film is improved is that, as described above, even though a thin Sn plating is left, a large amount of the free Sn layer remains, and the free Sn layer excellent in corrosion resistance uniformly covers the steel sheet. In addition, it is thought that the electrochemical properties of the plating layer such as cathode polarization resistance are improved due to the change in crystal structure in which the free Sn layer once melted and solidified by the reflow process is discontinuously and densely distributed in an island shape. To be

As described above, the desirable form in the thin Sn plating of 1500 mg / m ² or less, which is the characteristic point of the present invention, is explained as another embodiment, in the lower layer of the Sn plating layer Ni or Ni in Fe, P, Zn, Cu, a kind of Cr. Ni alloy plated coating containing the above is 100 mg / Ni equivalent
By interposing a small amount of m ^{2, a} larger amount of free Sn layer can be left during reflow processing or air baking during can making, as compared with the case where only Sn is coated. In addition, if more than 100 mg / m ² Ni layer is interposed, not only the free Sn layer residual effect due to heat treatment is saturated, but also a large amount of metallic Ni remains in the Sn plating layer due to heat treatment, which may adversely affect the corrosion resistance. become.

Regarding the means of intervening a trace amount of Ni layer and the effect,
The present applicant has already filed JP-A-60-56074 and JP-A-60-75586.
It is disclosed in Japanese Patent Publication.

Next, a method for manufacturing the surface-treated steel sheet according to the present invention will be described.

The present invention, the steel sheet surface cleaned by a conventional method, preferably Ni plating coating, or Ni Fe, P, Ze, is applied Ni alloy plating coating containing one or more of Cr, for this coating method A known method can be applied without particularly setting the limiting condition. The coating amount is preferably 100 mg / m ² or less, and the reason for limitation is as described above. And Ni or
The Ni alloy plating coating may be left as it is, or these Ni plating coating and Ni alloy plating coating may be subjected to a diffusion reaction with the surface of the steel sheet by an appropriate heat treatment.

When using the heat treatment means, the heating means is not particularly limited, but it is rational to use the annealing process of the steel sheet, and even if all of Ni or Ni alloy is diffused with the steel sheet, some of them remain unalloyed. Is also good. The elements Fe, Zn, Co, Cr, and P of the Ni alloy all have the effect of alloying with Ni and leaving free Sn after heating.

Next, Sn plating is applied. An electroplating method is rational as a Sn plating coating means, but the Sn plating coating means is not particularly limited thereto. Further, the coating amount was 1500 mg / m ² or less per one side, but this is because the optimum Sn plating coating amount which enjoys the effect of the present invention becomes remarkable at 1500 mg / m ² or less, and particularly 1000 mg / m per one side. ^The method of the present invention is effective when the Sn plating coverage is ² or less. In the present invention, it is also possible to perform differential thickness plating by changing the Sn plating coating amount on the front and back of the steel sheet, and in particular, it is advantageous that the Sn plating coating amount on the inner surface of the can after the can is made larger than the outer surface of the can. Is. The Sn plating condition may be an operation within a normal gloss range, but for example, low current density electrolysis outside the gloss range may be performed.

Next, the Sn plating coating form that is a feature of the present invention, that is, the free Sn thickness remaining after reflow has a maximum diameter of 30 μ or less and 0.1 m
Describe the conditions for 100 or more per m ² , Sn
After plating, the present invention is subjected to a reflow treatment, which is a feature of the present invention. Generally, a flux treatment is performed before reflow to improve Sn fluidity during reflow. As the flux treatment, stannous sulfate, so-called ferrostane tin plating bath mainly composed of phenol sulfonic acid is immersed in a flux bath mainly composed of phenol sulfonic acid,
It is carried out by drying, and in a so-called halogen tin plating bath mainly containing stannous chloride, sodium chloride, etc., it is similarly carried out in a flux bath mainly containing chloride such as ammonium chloride. It is preferable to adjust the flux treatment as described below in order to obtain the Sn plating coating form as described above.

In other words, the flux bath concentration, which is generally applied to conventional thick plating tinplate as flux treatment, is 2/3 to 1/3.
It is preferable to carry out after diluting below, or to carry out no flux treatment at all, and to perform reflow after washing with water after Sn plating. However, since the latter is not subjected to flux treatment at all, variations in the gloss of the Sn plating layer after reflow may occur, so it is necessary to perform sufficient manufacturing control. In order to obtain the Sn plating coating form of the present invention, the influence of the reflow treatment conditions described below is great, and it is possible to achieve it only by the reflow treatment conditions, and it is not always necessary to adjust the flux treatment conditions as described above.

Subsequently, this Sn-plated steel sheet is heated to a melting point of Sn (232 ° C.) or higher and subjected to reflow treatment. However, in order to obtain the Sn-plated coating form of the present invention, it is necessary to appropriately adjust the reflow treatment conditions.

During the reflow treatment, the morphology change, that is, spheroidization, progresses so that the surface energy of the molten Sn is minimized as the molten Sn flows along the plate surface. Therefore, if the time from melting of the Sn plating layer to solidification by rapid cooling in water is regulated, spheroidized Sn appears in the state of being left as it is during the flow process. The Sn plating coating form of the present invention thus regulates the time from melting to solidification of the Sn layer.
Although it depends on the plating amount, it is necessary to set the range to 0.2 to 1 sec for materials with Sn plating amount of 1500 mg / m ² or less. This phenomenon is also related to the temperature of molten Sn, and if the heating temperature is 240 ° C or less, the Sn plating coating form of the present invention cannot be obtained, and
On the contrary, conversely, the alloying reaction between molten Sn and the base steel proceeds in a short time, and it becomes impossible to secure free Sn. Therefore, the heating temperature during reflow needs to be in the range of 240 to 300 ° C. Preferably, the temperature may be controlled to 250 ° C to 270 ° C.

Further, in the present invention, alloying formed during reflow
The reflow conditions must be sufficiently controlled so that the Sn layer distribution has an unevenness distribution corresponding to the unevenness of the electrodeposited Sn layer as described in FIG. 1 (a).

A general resistance heating method or a high-frequency induction heating method can be used as the reflow treatment method, and the atmosphere thereof may be non-oxidative reflow in an inert gas.

Next, a chromate treatment or the like is performed as the passivation treatment of the outermost surface, but before performing the chromate treatment, a cathodic reduction treatment in, for example, sodium carbonate or the like is performed to remove the Sn oxide film on the Sn plating coated surface in advance. Good. The chromate treatment method is also not particularly limited, and it is conventionally used as a dipping treatment in a sodium dichromate aqueous solution that has been applied to tinplate, or negative / positive electrolytic treatment, and conventionally used as a TFS-CT plating bath. Cathodic electrolysis treatment in a bath in which an anion aid such as sulfuric acid or sodium fluorosilicate is added to chromic acid can be applied. Further, as a non-chromate treatment, dipping in a sodium phosphate bath or the like, and cathodic electrolysis treatment can also be applied.

The present invention will be described below with reference to specific examples in which a product is formed after forming an oil layer such as dioctyl sebacate and is used.

[Example] <Example 1> 800 mg / m ² of Sn was electroplated on one side of each steel plate under the conditions shown in (1) on both surfaces of a steel sheet whose surface had been cleaned by a conventional method, and after washing with water (2)
It was dipped in the flux shown in and dried. Subsequently, the Sn plating coating layer is reflow-treated by resistance heating method. In the reflow treatment, the time from melting of the Sn layer to solidification (hereinafter reflow treatment time) is 0.5 sec, and the heating temperature is the temperature at which the molten Sn reaches (hereinafter reflow treatment). ) Was 260 ° C.
The amount of Sn in the alloy layer formed during reflow (hereinafter referred to as the amount of reflow alloy) was 300 mg / m ² per side. And (3)
Electrolytic chromate treatment is applied to both sides of the steel plate under the conditions shown in
After forming a chromate coating layer of 15 mg / m ^{2 on} one side in terms of metallic chromium, DOS was applied at 4 mg / m ² on one side by the usual method to obtain a test material.

<Example 2> This is an example in which Sn plating was carried out under the conditions shown in (4) in Example 1, and no flux treatment was carried out, only washing and drying were carried out, and other items are the same as in Example 1. .

<Example 3> This is an example in which Ni was electroplated on both surfaces of the surface-cleaned steel sheet in Example 1 under the conditions shown in (5) to 15 mg / m ² on one side and then Sn plating, and the reflow treatment was performed by a resistance heating method. The reflow time was 0.4 sec and the reflow temperature was 260 ° C. The amount of reflow alloy was 250 mg / m ² per side. Other conditions are the same as in Example 1.

<Example 4> can outer surface and the forming surface after canning Sn plating coverage In Example 3 600 mg / m ^2, the can inner surface and the plane formed is an embodiment in which a different thickness plating of 900 mg / m ² The other items are the same as in Example 3.

<Example 5> In Example 1, the high-frequency induction heating method was adopted instead of the resistance heating method as the reflow processing method in Example 1, and the atmosphere during the reflow was N ₂ . Other items are the same as in Example 1.

<Example 6> In Example 3, both sides of the Sn plating amount were 600 m on each side.
an embodiment in which the g / m ^2, the reflow process is carried out in the conditions of the reflow process 0.3 sec, the reflow temperature 260 ° C. by the resistance heating method, the amount of reflow alloy was per side 180 mg / m ^2. Other items are the same as in Example 3.

<Example 7> In Example 3, instead of the Ni plating coating shown in (5), a Ni-Fe alloy plating coating (Fe content ratio in the alloy plating: 80 wt%) was used as Ni under the conditions shown in (6). The other items in the example in which the amount was 30 mg / m ² per side were the same as in example 3.

<Embodiment 8> On both surfaces of the surface-cleaned steel sheet, Ni was electroplated at 50 mg / m ² per one surface under the conditions shown in (5) of Embodiment 3, and then NHX gas (5
% H ₂ -95% N ₂ ) in an atmosphere of 720 ° C. for 1 _second to diffuse the coating layer into the base steel sheet. After that, 2% temper rolling was performed, and then degreasing and pickling treatment were performed in the usual steps. Subsequently, Sn plating coating, flux treatment, reflow treatment, and electrolytic chromate treatment were applied, and all of these steps were performed in the same manner as in Example 3.

<Comparative Example 1> This is a comparative example in which the method of immersing in the treatment bath shown in (7) and drying is performed as the flux treatment in Example 1, and the reflow treatment is a resistance heating method for a reflow time of 1.2 sec and a reflow temperature of 270. The reflow alloy amount was 350 mg / m ² per side. Other items are the same as in Example 1.

<Comparative Example 2> In Example 2, the reflow time was 0.3 sec and the reflow temperature was 23.
In the comparative example in which the temperature was 5 ° C., the amount of reflow alloy was 90 mg / m ² per side. Other items are the same as in Example 2.

<Comparative Example 3> In Example 3, the reflow time was 1.4 sec and the reflow temperature was 29.
Carry out at 0 ℃, reflow alloy amount is 500mg / m per side
^The comparative example is set to ² and the other items are the same as in Example 3.

And the present invention examples and comparative examples as well as the conventional example Sn plating coating amount per one surface 2800mg / m ² (reflow alloy 800
The following evaluation tests (A) to (C) were carried out using # 25 tinplate of mg / m ² ).

(A) Scanning Electron Microscope, Optical Microscope Observation The grain size Sn grains having a convex portion, which is the point of the present invention, are observed using a scanning electron microscope (hereinafter SEM) and an optical microscope (hereinafter optical microscope), and their size. And the distribution situation was investigated. The size (maximum diameter) was obtained mainly by SEM observation at 2000 times, and the distribution condition (number of distributions per 0.1 mm ² ) was obtained from SEM observation at 1000 times and light microscope observation at 180 times. The size (maximum diameter) was measured as shown in FIG. 2 for a simple granular shape, and as shown in FIG. 3 for a shape in which several coarse granular Sn particles were merged. Then, these measurements were performed by SEM observation at a magnification of 2000 at different positions for at least 10 visual fields, and the average of the measured values for each visual field was displayed. Moreover, the distribution situation is 1000 times SEM.
In the observation, it was similarly displayed as a total average value.

(B) Seam weldability test After forming each test piece into a can body, using a seam welding machine for can body making, wrap width of can body joint part 0.3mm, pressurizing force 45kgf, can making speed 45mpm , Welding secondary current was investigated by changing. And the evaluation is welding 2 which enables good welding.
Displayed in the next current range.

The lower limit of the proper welding secondary current is determined by the lower limit of the strength of the welded part, and the upper limit is determined by the upper limit of the occurrence of splash. It was judged by a pulling test, and the appearance of the seam welded part was visually judged by the presence or absence of scattering. All the samples used in the seam weldability test were air-baked at 210 ° C for 20 minutes in an electric air oven.

(C) Rust resistance test under coating film Each surface of each test piece was coated with epoxy-phenolic paint for can manufacturing 55
mg / dm ² roll coating, baking at 205 ° C for 10 minutes, then 1
It was additionally burnt at 90 ° C for 10 minutes. Then, a scratch was put on the coating film using a cutter knife, and 5 mm execut processing was performed by an exe tester to obtain a test sample. The test sample was sprayed with salt water using 5% NaCl for 1 hour and then held in a constant temperature / humidity tester at 25 ° C. and a relative humidity of 85% for 14 days, and the rusting state was visually evaluated from the scratch portion. The judgment was ◎ no thread rust, ○ small, △ slightly large, × large.

The above test results are summarized in Table 1. In all the examples of the present invention, the seam weldability and the rust resistance under the coating film are good.
The material pretreated with Ni before plating is good, but the comparative examples are all inferior.

(Effects of the invention) The present invention has a Sn coating amount per one surface of 1500 mg / m ² or less in a thin Sn-plated steel sheet, which is obtained by appropriately performing the Sn plating layer reflow treatment, and a residual unalloyed β-Sn layer. The morphological distribution situation is regulated within a specific range. As a result, it is possible to obtain a thin Sn-plated steel sheet with good seam weldability and rust resistance under the coating film, and it is possible to supply a low-cost, high-performance material that replaces # 25 tinplate.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a cross section of a plating layer according to the present invention and a conventional method.
2 and 3 are conceptual diagrams of particle size measurement of grain-sized Sn grains having a convex portion, which is the point of the present invention, and FIG. 4 is a SPMA line analysis result of Sn corresponding to the photograph sketched in FIG. FIG. 5 is a sketch of an SEM observation photograph of the surface of the Sn plating layer in the example of the present invention.

Claims (4)

[Claims] Claims: 1. Obtained by applying Sn plating coating of 1500 mg / m ² or less on one side to a steel plate, and then subjecting the Sn plating layer to melting treatment by heat treatment above the melting point of the Sn plating layer and solidification treatment by rapid cooling in water. In thin Sn-plated steel sheet for can manufacturing, the unalloyed β-Sn layer remaining after the melting and solidifying treatment has a maximum diameter of 30 μm or less,
In addition, coarse S with 100 or more protrusions per 0.1 mm ²
A thin Sn-plated steel sheet for can manufacturing, which has n grains. 2. A Ni alloy layer containing Ni or at least one of Fe, P, Zn, Cu and Cr on a steel sheet, calculated as Ni, is 100 mg / m ² per side.
After coating below, as it is, or partially or entirely diffused on the surface of the steel sheet by heat treatment, and subsequently subjected to Sn plating coating at 1500 mg / m ² or less per one side, Sn by heat treatment above the Sn plating layer melting point In the thin Sn-plated steel sheet for can making obtained by subjecting the plating layer to melting treatment and solidifying treatment by rapid cooling in water, unalloyed β-
A thin Sn-plated steel sheet for can manufacturing, wherein the Sn layer has a maximum diameter of 30 μm or less and has coarse Sn grains having 100 or more protrusions per 0.1 mm ² . 3. A can for which a Sn plating coating of 1500 mg / m ² or less on one side of a steel plate is applied, and then the Sn plating layer is melted by heating at a melting point of the Sn plating layer or higher, and solidified by rapid cooling in water. In the method for producing a thin Sn-plated steel sheet, the heating temperature is set to 240 to 300 ° C., and the time from the Sn plating layer melting to the solidification by cooling in water is set to 0.2 to 1 sec. Manufacturing method of plated steel sheet. 4. A Ni alloy layer containing Ni or at least one of Fe, P, Zn, Cu and Cr on a steel sheet, calculated as Ni, is 100 mg / m ² per side.
After coating below, as it is, or partially or entirely diffused on the surface of the steel sheet by heat treatment, and subsequently subjected to Sn plating coating of 1500 mg / m ² or less per one surface, Sn by heat treatment above the Sn plating layer melting point Melting treatment of the plating layer, in the method of manufacturing a thin Sn-plated steel sheet for can making subject to solidification treatment by rapid cooling in water, the heating temperature is 240 ~ 300 ° C. and the time from Sn plating layer melting to solidification by cooling in water Of 0.2 to 1 sec, a method for producing a thin Sn-plated steel sheet for can manufacturing.