JP2006233279A - Surface-treated steel sheet having excellent seam weldability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated steel sheet whose weldability is stable and satisfactory. <P>SOLUTION: Regarding the surface-treated steel sheet having excellent seam weldability, in a surface-treated steel sheet comprising insular tin in a metallic state, regarding the exposed parts in a substrate layer of the insular tin, the number of the parts whose linear length in the optional direction of the steel sheet surface is ≥20 μm is ≤20 pieces/mm<SP>2</SP>. Alternatively, in a surface-treated steel sheet comprising insular tin in a metallic state, the substrate layer of the insular tin is an Fe-Ni alloy layer or an Fe-Ni-Sn alloy layer of 2 to 100 mg/m<SP>2</SP>in terms of an Ni content. Further, the alloy layer comprises one or more selected from Mo, Mo compounds, W and W compounds, in total, by 1 to 20 mg/m<SP>2</SP>expressed in terms of metal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface-treated steel sheet for welding cans used for beverage cans, food cans and the like.

  Welding cans used for foods, beverages, etc. use tinplate or thin tin (Sn) plated steel plates (LTS, TNS), and welds known as “Sudronic”, where the can body is seam welded via copper wire. Canned by law. In order to obtain good wire seam weldability, it is said that a certain amount or more of metal Sn is necessary.

  The Sn-plated surface-treated steel sheet for welding cans usually has a metallic luster on the surface by performing a reflow treatment after Sn plating, but in a thin Sn-plated steel sheet (LTS, TNS) with a small amount of Sn adhesion, The ratio of alloying with the underlayer increases, and it becomes difficult to sufficiently leave the metal Sn necessary for ensuring weldability. Therefore, conventionally, as a Sn underlayer, a film having a high barrier property that suppresses alloying has been provided, or when Sn melts, it has been devised to suppress alloying by forming an island-shaped Sn. .

Japanese Patent Application Laid-Open No. 60-184688 (Patent Document 1) discloses a steel sheet having island-shaped Sn with a covering area ratio of 20 to 70% on a Sn—Fe—Ni ternary alloy layer. In Japanese Patent Application Laid-Open No. 60-208494 (Patent Document 2), a metal Sn layer having convex portions is formed such that each convex portion has an area of 1-800000 μm ² , an area percentage of 20-80%, and a thickness of 0.007-0. A steel sheet formed to be 7 μm is disclosed. In Japanese Patent Application Laid-Open No. Sho 62-103390 (Patent Document 3), by defining the diameter of island-shaped Sn as 30 μm and the number per 0.1 mm ² as 100 or more, alloying is suppressed by the effect of Sn thickness. Provides a way to do that.

Japanese Laid-Open Patent Publication No. 61-3886 (Patent Document 4) discloses a method of suppressing the formation of FeSn ₂ by using an Fe—P, Fe—Mo, or Fe—P—Mo alloy layer. Japanese Patent Application Laid-Open No. 61-264196 (Patent Document 5) discloses a method for obtaining island-shaped Sn by reflow treatment of Sn plating by anodizing a steel sheet with an aqueous solution having a pH of 10 or more before plating. JP-A-136993 (Patent Document 6) provides a method of suppressing alloying during reflow by forming a passive film by anodic electrolysis of a Ni-based base treatment coating layer in an oxidizing agent solution. Yes.

JP 60-184688 A JP 60-208494 A JP-A-62-103390 Japanese Patent Laid-Open No. 61-3886 JP-A 61-264196 Japanese Patent Laid-Open No. 1-136993

However, the island-shaped Sn on the surface of the steel sheet formed by the means described in the above-mentioned patent document is coarse or sparse and improves the weldability on average, but defects due to the generation of dust are sporadic. However, it is rare to obtain good weldability stably over the entire length and width of the coil. This is a factor that reduces the production efficiency in the can manufacturing line.
Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a surface-treated steel sheet having stable weldability and good quality.

The present inventors diligently studied the above problems, and the weldability of the Sn-plated steel sheet is not controlled only by the amount of metal Sn, the area ratio of island-shaped Sn, or the number per area, but island-shaped Sn. It has been found that the influence of the denseness and uniformity of the distribution is large. Furthermore, it has been found that a good distribution of island-shaped Sn can be realized by applying appropriate plating to the base, and the present invention has been achieved.
That is, the main point of the present invention is that
(1) A surface-treated steel sheet having island-shaped tin in a metallic state, wherein the exposed portion of the underlayer of island-shaped tin is 20 pieces / mm where the linear length in any direction on the steel sheet surface is 20 μm or more. A surface-treated steel sheet excellent in seam weldability, characterized by being ² or less.

(2) A surface-treated steel sheet having metal-like island-shaped tin, wherein the underlayer of island-shaped tin is an Fe—Ni alloy layer or Fe—Ni—Sn alloy layer having a Ni content of ^{2 to} 100 mg / m ^2. The alloy layer further contains one or two or more selected from Mo, Mo compound, W, and W compound in terms of metal in total of 1 to 20 mg / m ^2, and the seam weldability Excellent surface-treated steel sheet.

(3) The above-mentioned (2), wherein the exposed portion of the underlayer of island-shaped tin is 20 pieces / mm ² or less where the linear length measured in an arbitrary direction on the surface of the steel sheet is 20 μm or more. Surface-treated steel sheet with excellent seam weldability,
(4) The surface-treated steel sheet having excellent seam weldability according to any one of (1) to (3), wherein the coverage area ratio with island-shaped tin is 60 to 90%,
(5) The surface-treated steel sheet excellent in seam weldability according to any one of (1) to (4), wherein the total Sn adhesion amount is 300 to 1500 mg / m ² in terms of metallic tin.

(6) A surface-treated steel sheet having excellent seam weldability according to any one of (1) to (5), which has a chemical conversion coating on the outermost layer,
(7) The seam welding according to (6) above, wherein the chemical conversion coating is one or both of Cr (III) hydrated oxide or metal Cr layer of ² to 40 mg / m ^{2 in} terms of metal Cr. It is a surface-treated steel sheet with excellent properties.

  By using the surface-treated steel sheet according to the present invention, compared with the conventional thin Sn-plated steel sheet, the welding current range in wire seam welding is widened, and the variation between manufacturing chances and individual unit variations are reduced. This contributes to minimizing the decrease in production efficiency due to welding troubles.

The present invention is described in detail below.
The material of the steel plate used in the present invention need not be particularly limited. Component steel plates such as aluminum killed steel and low carbon steel conventionally used for steel plates for cans may be used. The thickness and hardness of the steel sheet are specified by the user according to the purpose of use, and may be followed. In recent years, steel plates for beverage cans generally tend to be thin, and welding cans having a thickness of about 0.18 mm are often used. Further, along with thinning, hard materials such as tempering degree T-5CA, DR-8 and DR-9 are becoming common.

As a result of the study by the present inventors, fine island-shaped Sn is densely distributed on the surface of the steel sheet, and the smaller the exposed portion of the surface of the underlayer of 20 μm or more in a straight line length in any direction of the steel sheet surface, the better Wire seam weldability was found to be obtained. The number of exposed portions of the base layer having a linear length of 20 μm or more is required to be 0 to 20 per 1 mm ² , more preferably 0 to 10 and even more preferably 0 to 5. If the number exceeds 20, scattering of molten metal called dust will frequently occur during welding.

  Here, island-like Sn means metal Sn taking the form of discontinuous islands, and it can be confirmed as a rounded bright part by an image by SEM (scanning electron microscope). Easy. For example, with a SEM having an acceleration voltage of 10 kV and a magnification of 1000, the surface of the steel plate may be selected and observed at random for 100 views per sample, and the number of exposed ground portions having a linear length of 20 μm or more may be counted.

  As described above, it has been found that when the exposed portion of the base layer having a linear length of 20 μm or more increases, dust is likely to be generated during welding. The reason is considered as follows. When wire seam welding of a can body is performed, a very early welding current flows through the metal Sn, but since it is soft, it can be deformed by pressurization with an electrode ring and a sufficient current path can be secured. As the temperature rises, the metal Sn melts and is pressurized to remove most of the welded portion, thereby forming a joint between the steel plate and the steel plate. However, if the exposed portion of the steel plate surface or the base plating surface, which is the base layer not covered with Sn, is long, the initial welding current flows through that portion.

  Unlike the metal Sn, this underlayer is a hard alloy layer, so it is difficult to be deformed and has a high electric resistance, so that a sufficient current path cannot be secured, and a welding current flows in a narrow area, resulting in local Abnormally fever. This is thought to be the cause of dust. This phenomenon occurs when the exposed portion of the surface of the underlayer is 20 μm or more in a linear length in an arbitrary direction of the steel plate surface, and no dust is generated from the exposed portion of less than 20 μm.

When the exposed portion of the underlayer surface measured in an arbitrary direction on the steel sheet surface is 1 piece / mm ^{2 in} terms of a linear length of 50 μm or more, the weldability deteriorates remarkably. Island-shaped Sn can also be defined using EPMA (electron probe microanalysis). Sn on the surface of the steel plate is mapped with an acceleration voltage of 15 kV, and a rounded portion having a Sn concentration of 30% or more is defined as island-shaped Sn. The portion where the Sn concentration exceeds 0% and is less than 30% is determined not to be thick metallic Sn, but mostly Sn alloyed with the underlayer.

It is necessary to have an Fe—Ni alloy layer or an Fe—Ni—Sn alloy layer having a Ni amount of ² to 100 mg / m ² as an underlayer of the metal Sn layer. If island-shaped Sn is formed on the surface of the steel sheet without providing an alloy layer, the island-shaped Sn takes various shapes, and it is difficult to obtain the distribution of island-shaped Sn having the above characteristics. In addition, when the base layer before the reflow process is not an alloy layer but a metal Ni layer, Ni—Sn alloying remarkably proceeds during the reflow process, and the amount of the metal Sn may remain under normal reflow process conditions. Have difficulty.

The reason why the amount of the alloy layer is limited to ² to 100 mg / m ^{2 in} terms of Ni is that if it is less than 2 mg / m ² , the effect on the shape of the island-shaped Sn formed by Sn reflow is not observed, whereas 100 mg This is because, even if exceeding / m ² , the effect on the shape and distribution of the island-shaped Sn is saturated and the cost is disadvantageous. The Fe—Ni alloy layer or the Fe—Ni—Sn alloy layer must contain a total of 1 to 20 mg / m ² of one or more of Mo, Mo compound, W, and W compound in terms of metal. . Examples of the Mo compound include molybdenum (VI) oxide and nickel molybdenum (VI) acid, and examples of the W compound include tungsten oxide (VI) and tungstic acid (VI) nickel.

The Fe—Ni alloy layer containing one or more of these Mo, Mo compound, W, and W compound is subjected to electrolytic treatment at a current density of 1 to 5 A / dm ² or less in an electrolyte solution described later. In this range, in order of increasing current density, in the case of molybdenum, the content of metal Mo, molybdenum oxide (VI), nickel molybdenum (VI) nickel is high, and in the case of tungsten, metal W, tungsten oxide ( VI), the content of nickel tungsten (VI) acid is increased.

The base layer obtained in this manner is appropriately repelled and aggregated during reflow to form fine island-shaped Sn, and the distribution of island-shaped Sn is uniform, and the linear length is 20 μm or more. The exposed part is less likely to occur. However, when the content of one or more of Mo, Mo compound, W, and W compound is less than 1 mg / m ² , the effect of these additions on the form and distribution of island-shaped Sn does not appear clearly. On the other hand, when the content of one or more of Mo, Mo compound, W, and W compound exceeds 20 mg / m ² , Sn is hardly formed into an island shape by reflow treatment and spreads with insufficient adhesion. End up. Note that the Fe—Ni—Sn alloy layer containing one or more of Mo, Mo compound, W, and W compound is a layer formed by alloying Sn and the underlayer by reflow treatment.

  The Fe—Ni alloy layer or Fe—Ni—Sn alloy layer containing one or more of Mo, Mo compound, W, W compound makes Sn fine islands, and the distribution of island Sn is uniform. Although the details of the reason for this are unknown, it is presumed that the wettability of Mo, Mo compound, W, W compound and Sn is low. The method of forming the Fe—Ni alloy layer containing one or more of Mo, Mo compound, W, and W compound on the steel sheet surface is not limited, but simplicity, economy, and the existing production line In view of structure, it is preferable to adopt a method by electroplating, and the following examples can be given.

Ni ion 5-50 g / L, iron (II) ion 2-20 g / L, molybdenum (VI) acid ion 0.05-4 g / L, citrate ion 20-100 g / L, sulfuric acid as supporting electrolyte An aqueous solution having a pH of 4 to 6 containing 20 to 150 g / L of sodium is kept at 20 to 60 ° C., and a degreased and acidified steel plate is immersed in this bath and subjected to cathodic electrolytic treatment at a current density of 1 to 5 A / dm ² .

By this method, an Fe—Ni alloy layer containing one or both of Mo and Mo compound is formed. Similarly, 5 to 50 g / L of Ni ions, 2 to 20 g / L of iron (II) ions, 0.05 to 4 g / L of tungsten (VI) ion, and 20 to 100 g / L of citrate ion are supported. Cathodic electrolysis at a current density of 1 to 5 A / dm ² is performed by keeping an aqueous solution of pH 4 to 6 containing 20 to 150 g / L of sodium sulfate as an electrolyte at 20 to 60 ° C. and immersing the degreased and pickled steel plate in this bath. Process. By this method, an Fe—Ni alloy layer containing one or both of W and W compounds is formed. Furthermore, an Fe—Ni—Sn alloy layer containing one or more of Mo, Mo compound, W, and W compound is also formed by performing reflow treatment after Sn plating on the upper layer.

  In the Fe—Ni—Sn alloy layer containing one or more of Mo, Mo compound, W, W compound, trace amounts of calcium, magnesium, sodium, potassium, zinc, copper, manganese, cobalt, etc. as impurities Or a metal salt, sulfate, phosphate, nitrate, chloride, silica or the like. The coverage area ratio by island-shaped Sn is desirably 60 to 90%. If it is less than 60%, the exposed portion of the underlying layer increases, and it is difficult to eliminate the exposed portion having a linear length of 20 μm or more. On the other hand, if it exceeds 90%, it may cause poor adhesion of organic films such as paints and resin films. This is because, as is well known, the Sn oxide layer is likely to cohesively break, so that it is necessary to ensure the adhesiveness of the underlayer.

The steel sheet surface preferably has 300 to 1500 mg / m ² of Sn as the total Sn adhesion amount. If it is less than 300 mg / m ^{2, the} initial welding current will not be sufficiently stable regardless of the form of Sn, and splash will easily occur, and the desired high-speed wire seam weldability will not be obtained. On the other hand, even if it exceeds 1500 mg / m ² , not only the weldability is almost improved, but also the steel plate surface is almost covered with Sn, which causes poor adhesion of the paint and the resin film. High adhesion amounts of Sn plating without performance merit should be avoided for economic reasons.

It is preferable to have a chemical conversion treatment film on the outermost layer on the exposed base Fe—Ni alloy layer or island-like Sn layer. Without a chemical conversion coating, it is difficult to ensure the adhesion of organic compound layers such as paints and resin films.
As the chemical conversion film, one or both of ² to 40 mg / m ² of Cr (III) hydrated oxide or metal Cr layer in terms of metal Cr is suitable. Is less than 2 mg / m ^2, not seen the effect of coating adhesion improvement by chemical treatment applied. On the other hand, even if it exceeds 40 mg / m ² , the coating film adhesion improving effect is not only saturated, but also the contact electrical resistance is increased and the seam weldability is lowered.

The method of laminating the chemical conversion film is not limited, but as an example, chromic anhydride 50 to 150 g / L, sulfate ion 0.01 to 0.2 g / L, sodium silicofluoride 1 to 5 g / L, ammonium fluoride 0. Contains 1-2 g / L. Cathodic electrolysis may be performed at a current density of 30 to 60 A / dm ² in a 40 to 60 ° C. bath. The island-shaped Sn is formed by performing a reflow process after Sn plating. In addition, Sn can be distributed in islands by sufficiently washing the organic compound component of the Sn plating bath having a flux effect and then performing a reflow treatment.

  The method for the reflow treatment is not particularly limited, but it is preferable to carry out by electrical resistance heating, high-frequency induction heating, or a combination thereof from the viewpoint of the stability of the heating rate and the ultimate plate temperature, and economical efficiency. The steel sheet is heated to a melting point of Sn of 232 ° C. or higher by these methods and then quenched with water. The temperature of water is easy to handle from room temperature to about 80 ° C. Without quenching, tin alloying proceeds, the Fe—Sn alloy layer or the Fe—Ni—Sn alloy layer becomes thicker, resulting in a brittle film, and ensuring seam weldability. It becomes difficult to leave the necessary metal Sn. Moreover, when the melted Sn comes into contact with the roll and builds up on the roll, or the appearance of the product is impaired, an undesirable situation occurs.

Hereinafter, the present invention will be described in more detail by way of examples.
A steel strip having a sheet thickness of 0.18 mm and a tempering degree of T-5CA obtained by continuous annealing and then temper rolling of a low carbon cold rolled steel strip was used. As a pretreatment for plating, electrolytic degreasing was carried out in a 5 mass% sodium hydroxide solution, followed by pickling in dilute sulfuric acid. The pretreated steel strip was subjected to cathodic electrolytic treatment in an Fe—Ni—Mo alloy plating bath having the following composition. The bath temperature was set to 40 ° C., and electrolysis was performed at a current density of 3 A / dm ² while varying the electrolysis time to obtain an Fe—Ni alloy plating layer containing Mo and molybdenum oxide (VI).

Fe-Ni-Mo alloy plating bath composition Nickel sulfate hexahydrate: 50 g / L
Iron (II) sulfate heptahydrate: 20g / L
Trisodium citrate: 75 g / L
Sodium molybdate dihydrate: 0 to 2 g / L
Sodium sulfate: 70 g / L
pH 5

Similarly, the pretreated steel strip was subjected to cathodic electrolytic treatment in an Fe—Ni—W alloy plating bath having the following composition. The bath temperature was set to 40 ° C., and electrolysis was performed at a current density of 3 A / dm ² while varying the electrolysis time to obtain an Fe—Ni alloy plating layer containing W and tungsten oxide (VI).
Fe-Ni-W alloy plating bath composition Nickel sulfate hexahydrate: 50 g / L
Iron (II) sulfate heptahydrate: 20g / L
Trisodium citrate: 75 g / L
Sodium tungstate dihydrate: 0 to 2 g / L
Sodium sulfate: 70 g / L
pH 5

Similarly, the pretreated steel strip was subjected to cathodic electrolytic treatment in a Fe—Ni—Mo—W alloy plating bath having the following composition. The bath temperature was set to 40 ° C., and the electrolysis was performed at a current density of 3 A / dm ² while varying the electrolysis time to obtain an Fe—Ni alloy plating layer containing Mo, molybdenum oxide (VI), W, and tungsten oxide (VI). .
Fe-Ni-Mo-W alloy plating bath composition Nickel sulfate hexahydrate: 50 g / L
Iron (II) sulfate heptahydrate: 20g / L
Trisodium citrate: 75 g / L
Sodium molybdate dihydrate: 0.3 to 1.5 g / L
Sodium tungstate dihydrate: 0.3 to 1.5 g / L
Sodium sulfate: 70 g / L
pH 5

Subsequently, electro Sn plating was performed using a ferrostan bath. The plating bath composition was Sn ion: 20 g / L, phenol sulfonate ion: 75 g / L, surfactant: 5 g / L, bath temperature was 43 ° C., and electrolysis was performed at a current density of 20 A / dm ² . The electrolysis time was adjusted so that a predetermined Sn plating amount was obtained. After Sn plating, the plate was washed with water, drained with a roller, dried with cold air, heated to 250 ° C. in 10 seconds by electric heating, and immediately cooled with water. By this treatment, Sn melts and aggregates to form island-shaped Sn, and a part of Sn is alloyed with the underlayer, and an Fe—Ni—Sn layer containing Mo, Mo compound or W, W compound Formed. After the reflow treatment, chromic acid treatment was performed as a chemical conversion treatment. Bath composition is chromic anhydride: 80 g / L, sulfate ion: 0.05 g / L, sodium silicofluoride: 2.5 g / L, ammonium fluoride: 0.5 g / L, bath temperature is 50 ° C., current density is 30 A Cathodic electrolysis at / dm ² .

About the said processing material, the evaluation test was implemented about each item of (A)-(D) shown below.
(A) Island-like Sn distribution: SEM observation of the steel sheet surface was performed at an acceleration voltage of 10 kV and a magnification of 1000 times. For each sample, 100 randomly selected visual fields were observed, and the number of ground exposed portions having a linear length of 20 μm or more was counted. The size of one visual field is 87 μm × 115 μm (10000 μm ² ), and 100 visual fields correspond to 1 mm ² . The coverage of the surface with island-shaped Sn was obtained by image analysis with a computer using five of the SEM images. In other words, the image was binarized by brightness, and the area ratio was calculated with the white part excluding the part where the brightness was high due to the protrusions such as wrinkles and roughness on the steel sheet surface as the part covered with tin .

(B) Wire seam weldability: The following welding was performed on an evaluation material (n = 10) obtained by applying 50 mg / m ^{2 of} an epoxy / phenol paint in a dry mass and baking at 280 ° C. for 15 seconds except for a portion to be welded. Wire seam welding was performed under the conditions and evaluated. Wide appropriate current range (ACR) consisting of a minimum current value at which sufficient welding strength can be obtained and a maximum current value at which welding defects such as dust start to stand out, with a lapping margin of 0.4 mm and welding wire speed of 80 m / min. Was evaluated. In addition, the welding current was set to the median value of the appropriate current range obtained in this way, 1000 cans were welded, and the cans that produced poor welding (occurrence of dust) were counted. The number of defective cans is most preferably 0, but less than 5 cans are considered acceptable levels.

(C) Film adhesion: After laminating a PET (polyethylene terephthalate) film having a thickness of 15 μm, to which an epoxy adhesive has been applied in advance to 2 μm, at 230 ° C., a cross-cut is made until the base iron is reached. The film was heated to 240 ° C., and 5 kg / cm ² of air gas was blown vertically to the center of the crosscut to evaluate the peeling state of the film. ◎ (very good) where no peeling was observed, ○ (good) where peeling of 0.5 mm or less from the cut part was recognized, and peeling exceeding 0.5 mm from the cut part X (defect). In addition, (circle) or more was judged as the pass level of film adhesiveness.

(D) Corrosion resistance: In order to evaluate the corrosion resistance of the surface corresponding to the inner surface of the can of the evaluation material, a UCC (under cutting corrosion) test was conducted. After laminating a PET (polyethylene terephthalate) film with a thickness of 15 μm on the surface corresponding to the inner surface of the can and making a crosscut until it reaches the ground iron, it consists of 1.5% citric acid and 1.5% sodium chloride. The sample was immersed in a test solution at 55 ° C. for 96 hours under the atmosphere. After washing with water and drying, the scratched part and the flat part were quickly peeled off with a tape, and the corrosion state in the vicinity of the scratch part, the pitting corrosion of the scratch part and the film peeling state of the flat part were observed to evaluate the corrosion resistance. ◎ (very good) where no tape peeling or corrosion is observed, ○ (good) where one or both of tape peeling less than 0.4 mm from scratch or slight corrosion not visually recognized is observed The case where one or both of tape peeling of 0.4 mm or more and 1 mm or less from the scratch part or small corrosion visually observed was recognized as Δ (somewhat poor).
From the above performance evaluation results, the overall evaluation was classified into four stages: ◎ (very good), ◯ (good), △ (slightly bad), and x (bad), and ◎ and ◯ were regarded as acceptable levels. The evaluation results are shown in Table 1.

Invention Example No. 1 shown in Table 1. Nos. 1 to 20 satisfied the evaluation items (A) to (D) above, and good performance was stably obtained.
Comparative Example No. No. 21 does not contain any of Mo and W in the Fe-Ni alloy plating layer of the Sn plating base, and the distribution of island-like Sn is sparse, and the base exposed portion having a linear length of 20 μm or more is very large. It is. In the 1000-can welding test at the median ACR obtained from the welding evaluation of 10 cans, the occurrence frequency of dust was high.

  Comparative Example No. No. 22 is an example in which neither Fe nor Ni is contained in the Fe—Ni alloy plating layer of the Sn plating base, the amount of Ni is small, and island Sn is not substantially formed. Although the coverage area ratio by Sn was high, the linear length of the exposed portion of the base layer was often long. Although the ACR is 400A, the occurrence frequency of dust was high in the 1000-can welding test at the median ACR. Moreover, the coverage area ratio by Sn was high, and sufficient film adhesiveness was not obtained.

Comparative Example No. No. 23 is an example in which Mo is contained in the base alloy plating layer and fine island-shaped Sn is obtained, but the Mo content is not appropriate, and the base exposed portion having a linear length of 20 μm or more is scattered. . In the 1000-can welding test at the median value of ACR, generation of dust occurred sporadically.
Comparative Example No. No. 24 is an example in which the amount of Mo contained in the base alloy plating layer is excessive, and Sn spreads with insufficient adhesion to the base layer at the time of reflow and does not become a fine island. ACR was narrow, and film adhesion and corrosion resistance were inferior.

Comparative Example No. No. 25 is an example in which the Mo amount is excessive, the Sn adhesion amount is small, and the base exposed portion having a linear length of 20 μm or more is large. Due to the lack of ACR, generation of dust occurred sporadically in the 1000-can welding test at the median value of ACR. Corrosion resistance was also poor.
Comparative Example No. No. 26 contains Mo and W in the base alloy plating layer, but the amount is excessive, and Sn spreads with insufficient adhesion to the base layer at the time of reflow, and does not become a fine island shape It is. ACR was narrow, and film adhesion and corrosion resistance were inferior.

Comparative Example No. No. 27 is an example in which W is contained in the base alloy plating layer and fine island-shaped Sn is obtained, but the W content is not appropriate, and the base exposed portion having a linear length of 20 μm or more is scattered. . In the 1000-can welding test at the median value of ACR, generation of dust occurred sporadically.
Comparative Example No. No. 28 is an example in which the amount of W contained in the base alloy plating layer is excessive, and Sn spreads with insufficient adhesion to the base layer at the time of reflow and does not become a fine island shape. ACR was narrow, and film adhesion and corrosion resistance were inferior.

Comparative Example No. No. 29 is an example in which the amount of W is excessive, the amount of deposited Sn is small, and there are many ground exposed portions having a linear length of 20 μm or more. Due to the lack of ACR, generation of dust occurred sporadically in the 1000-can welding test at the median value of ACR. Corrosion resistance was also poor.
In addition, this invention example No. None of the samples 1 to 20 were found to have a portion where the exposed portion of the surface of the base layer measured in an arbitrary direction on the steel plate surface was 50 μm or more in linear length. However, Comparative Example No. In the samples 21, 22, 25, 26, and 29, there were some portions where the linear length was 50 μm or more.


Patent applicant: Nippon Steel Corporation
Attorney Attorney Shiina and others 1

Claims (7)

A surface-treated steel sheet having island-shaped tin in a metal state, wherein the exposed portion of the underlayer of island-shaped tin is 20 pieces / mm ² or less where the linear length in an arbitrary direction on the steel sheet surface is 20 μm or more. A surface-treated steel sheet with excellent seam weldability. A surface-treated steel sheet having island-shaped tin in a metal state, wherein the underlayer of island-shaped tin is an Fe-Ni alloy layer or Fe-Ni-Sn alloy layer having a Ni amount of ^{2 to} 100 mg / m2, The alloy layer further contains one or two or more selected from Mo, Mo compound, W, and W compound in terms of metal, and has excellent seam weldability, characterized in that it contains 1 to ²⁰ mg / m ² in total. Surface treated steel sheet. 3. The seam welding according to claim 2, wherein the exposed portion of the underlayer of the island-shaped tin is 20 pieces / mm < ² > or less where the linear length measured in an arbitrary direction on the steel sheet surface is 20 [mu] m or more. Surface treated steel plate with excellent properties. The surface-treated steel sheet excellent in seam weldability according to any one of claims 1 to 3, wherein a covering area ratio of island-shaped tin is 60 to 90%. The surface-treated steel sheet excellent in seam weldability according to any one of claims 1 to 4, wherein the total tin adhesion amount is 300 to 1500 mg / m ² in terms of metallic tin. The surface-treated steel sheet excellent in seam weldability according to any one of claims 1 to 5, which has a chemical conversion coating on the outermost layer. 7. The seam weldability according to claim 6, wherein the chemical conversion treatment film is one or both of Cr (III) hydrated oxide or metal Cr layer of ² to 40 mg / m ^{2 in} terms of metal Cr. Surface treated steel sheet.