JP2011252182A - Surface treated steel sheet and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treated steel sheet having fine appearance and excellent corrosion resistance, and to provide a manufacturing method thereof.SOLUTION: The steel sheet includes: a surface treated layer comprising a Zn-Ni alloy layer, an Sn-Zn-Ni alloy layer, an Sn layer, and an Sn-Zn alloy layer in this order from the steel sheet side; or a surface treated layer comprising the Zn-Ni alloy layer, the Sn-Zn-Ni alloy layer, and a mixed layer of an Sn and an Sn-Zn alloy in this order from the steel sheet side. In the surface treated layer of the surface treated steel sheet, the total amount of Zn is 7-20 g/m, and the mass ratio Zn/Ni between the total amount of Zn and the total amount of Ni is 4-10.

Description

  The present invention relates to a beautiful and corrosion-resistant surface-treated steel sheet used for home appliances and other applications, and a method for producing the same.

  It has been practiced for a long time to galvanize a steel sheet and improve the corrosion resistance of the steel sheet by the sacrificial anticorrosive action of zinc. However, since zinc is a very base metal compared to iron, it has the disadvantages of high dissolution rate and short life when exerting sacrificial anticorrosive action. Therefore, as a method for extending the life of the galvanized steel sheet, alloy plating of zinc and iron, nickel, etc. has been proposed in addition to the thickening of the galvanizing.

  Zn-Ni alloy-plated steel sheets have been put to practical use as rust-proof steel sheets for automobiles and the like because they are particularly excellent in unpainted corrosion resistance and also excellent in post-coating corrosion resistance and workability. In order to further improve the performance of the Zn—Ni alloy-plated steel sheet, various improvement methods such as multi-component alloying by adding a third component and composite plating have been disclosed.

For example, a Zn-Ni alloy plating containing Ti or a Ti compound (Patent Literature 1), an Al ₂ O ₃ containing material (Patent Literature 2) and the like can be mentioned. As for the production method, a method of adding SrSO ₄ to the plating bath (Patent Document 3) or the like is disclosed in order to prevent uneven surface gloss that is likely to occur in Zn—Ni alloy plating.

  However, the plated steel sheets disclosed in Patent Documents 1 and 2 have been developed with an emphasis on improving corrosion resistance, and the external appearance is not particularly considered, and the binary Zn-Ni is not considered. Like the alloy-plated steel sheet, it has a gray appearance with no metallic luster and is not beautiful.

  Therefore, in order to use it for applications in which appearance is important, it is necessary to apply a coating film having high concealment properties such as thick coating and having high design properties.

  The plated steel sheet obtained by the method disclosed in Patent Document 3 also does not have an appearance that can be said to be metallic luster.

In Patent Document 4, 0.05 to 10.0 g / m ² of Ni plating, 0.05 to 2.8 g / m ² of Sn plating, and 0.02 to 1.5 g / m in order from the steel plate side. ^After the Zn plating of ² is performed, at least a part of the plating layer is alloyed by heat treatment at 200 to 800 ° C., so that the Zn content is 5 to 80 mass% and the Ni content is 40 mass on the surface layer. %, And a total amount of 0.05 to 3.0 g / m ² of a Sn—Zn binary alloy layer or a Sn—Zn—Ni ternary alloy layer is formed. A manufacturing method is disclosed.

  According to this method, since the Sn—Zn alloy layer or the Sn—Zn—Ni alloy layer is formed on the outermost layer, a relatively beautiful appearance with white semi-gloss can be obtained. However, the white rust resistance surpasses that of the galvanized steel sheet, but the red rust resistance does not reach that of the galvanized steel sheet.

  Thus, with the conventionally proposed technology, a plated steel sheet satisfying a beautiful metallic luster appearance, white rust resistance and red rust resistance has not been obtained.

JP 58-104194 A JP-A 61-235600 Japanese Patent Publication No.58-39236 Japanese Patent Publication No. 6-53957

  An object of this invention is to provide the surface treatment steel plate which was beautiful and excellent in corrosion resistance, and its manufacturing method in view of the said situation.

  The inventors of the present invention diligently studied the above-mentioned problems, constructed a surface-treated steel sheet having a beautiful and excellent corrosion resistance and a method for producing the same, and arrived at the present invention.

  The gist of the present invention is as follows.

(1) In order from the steel plate side, a Zn—Ni alloy layer, a Sn—Zn—Ni alloy layer, a Sn layer, a surface treatment layer comprising a Sn—Zn alloy layer, or a Zn—Ni alloy layer, Sn in this order from the steel plate side A steel plate having a surface treatment layer comprising a Zn—Ni alloy layer, a mixed layer of Sn and Sn—Zn alloy, wherein the total Zn content in the surface treatment layer is 7 to 20 g / m ² , and A surface-treated steel sheet, wherein the mass ratio Zn / Ni between the total Zn content and the total Ni content is 4 to 10.

(2) The surface-treated steel sheet according to (1), wherein the total amount of Sn in the surface-treated layer is 0.5 to 5.6 g / m ² .

  (3) The surface-treated steel sheet according to (1) or (2), wherein the surface-treated steel sheet has a coating film mainly composed of an organic compound on the surface-treated layer.

  (4) After carrying out electric Zn-Ni alloy plating and then electric Sn plating on the steel plate, the steel plate after the plating is heated, and simultaneously with the melting treatment of the Sn plating layer, the Zn-Ni alloy plating layer and the Sn plating are performed. A layered structure that becomes a Zn—Ni alloy layer, a Sn—Zn—Ni alloy layer, a Sn layer, a Sn—Zn alloy layer, or a plating layer as a steel plate A method for producing a surface-treated steel sheet, comprising forming a laminated structure that sequentially becomes a Zn—Ni alloy layer, a Sn—Zn—Ni alloy layer, and a mixed layer of Sn and Sn—Zn alloy from the side.

  (5) The coating film is formed by applying and baking a coating agent mainly composed of an organic compound on the surface treatment layer obtained after the alloying treatment (4) A method for producing a surface-treated steel sheet according to claim 1.

  According to the present invention, it is possible to provide a surface-treated steel sheet having a beautiful appearance and good corrosion resistance and a method for producing the same.

  The steel plate subjected to the surface treatment of the present invention is not particularly limited, and a steel plate having an appropriate steel type, thickness, hardness, and surface roughness may be selected depending on the application.

  On the surface of the steel sheet, in order from the steel sheet side, a Zn—Ni alloy layer, a Sn—Zn—Ni alloy layer, a Sn layer, a surface treatment layer comprising a Sn—Zn alloy layer, or a Zn—Ni alloy in order from the steel sheet side. It is necessary to have a surface treatment layer composed of a layer, a Sn—Zn—Ni alloy layer, and a mixed layer of Sn and Sn—Zn alloy.

  Such a layer structure can be confirmed by analyzing the element distribution in the cross section of the plating layer by a known means such as EPMA, but it can also be easily confirmed by using glow discharge emission spectroscopy (GDS).

  The role which each layer plays in the surface-treated steel sheet of the present invention is as follows.

  The lowermost Zn—Ni alloy layer has a sacrificial anticorrosive action on the steel sheet and suppresses the occurrence of red rust over a long period of time. A preferable thickness range of the Zn—Ni alloy layer is 1.0 to 3.5 μm, and Ni is desirably 9 to 20 mass%.

  The Sn—Zn—Ni alloy layer relaxes the corrosion promotion of the Zn—Ni alloy layer. This is because when the Sn layer and the Zn—Ni alloy layer are in direct contact with each other, the potential difference is large and the corrosion of the relatively base Zn—Ni alloy layer is promoted. The Sn—Zn—Ni alloy layer having the following potential is covered with the Zn—Ni alloy layer, and an Sn layer is provided thereon to mitigate the promotion of corrosion of the Zn—Ni alloy layer.

  The preferable thickness of the Sn—Zn—Ni alloy layer is 0.05 to 1.8 μm, and Sn: 20 to 40% by mass, Zn: 40 to 75% by mass, and Ni: 5 to 20% by mass are preferable.

  The Sn layer formed as the upper layer of the Sn—Zn—Ni alloy layer provides an excellent barrier effect, and exhibits corrosion resistance and a beautiful appearance due to the effect. The Sn layer has a white appearance with less gloss when electroplated from an acidic bath, but exhibits an excellent metallic luster appearance when the surface is smoothed by heating and melting treatment.

  The Sn—Zn alloy layer provided in the upper layer has a white semi-gloss appearance, and these two layers form a surface-treated steel sheet having a beautiful white gloss appearance.

  The thickness of the Sn layer is preferably 0.006 to 0.8 μm, and the thickness of the Sn—Zn alloy layer is preferably 0.03 to 0.1 μm. Zn in the Sn—Zn alloy layer is preferably 5 to 30% by mass. If the Sn—Zn alloy layer is too thick, it may cause poor gloss, but it is difficult to produce a thick layer as long as it is produced by the production method described later.

  The Sn—Zn alloy layer formed on the upper layer of the Sn layer has the sacrificial anticorrosive ability for the Sn layer, thereby improving the corrosion resistance of Sn and producing the effect of generating less white rust even in a chloride environment.

  Thus, it has beautiful and corrosion resistance by having the surface treatment layer which consists of a Zn-Ni alloy layer, a Sn-Zn-Ni alloy layer, a Sn layer, and a Sn-Zn alloy layer in order from the steel plate side on the surface of a steel plate. Excellent steel sheet.

  Further, when the surface treatment layer is composed of a Zn—Ni alloy layer, a Sn—Zn—Ni alloy layer, and a mixed layer of Sn and Sn—Zn alloy in this order from the steel plate side, the lowest Zn—Ni alloy layer is It has a sacrificial anticorrosive action on steel plates and suppresses the occurrence of red rust over a long period of time. The preferable thickness of the Zn—Ni alloy layer is 1.0 to 3.5 μm, and Ni is desirably 9 to 20% by mass.

  The Sn—Zn—Ni alloy layer relaxes the corrosion promotion of the Zn—Ni alloy layer. This is because, when the mixed layer of Sn and Sn—Zn alloy and the Zn—Ni alloy layer are in direct contact with each other, the corrosion of the relatively low potential Zn—Ni alloy layer is promoted. By covering the Zn-Ni alloy layer with a Sn-Zn-Ni alloy layer having an intermediate potential between the mixed layer of Zn and the Zn-Ni alloy layer, and providing a mixed layer of Sn and Sn-Zn alloy thereon, Zn -Mitigates corrosion promotion of Ni alloy layer.

  The preferable thickness of the Sn—Zn—Ni alloy layer is 0.05 to 1.8 μm, and Sn: 20 to 40% by mass, Zn: 40 to 75% by mass, and Ni: 5 to 20% by mass are preferable.

  The mixed layer of Sn and Sn—Zn alloy formed as the upper layer of the Sn—Zn—Ni alloy layer exhibits corrosion resistance due to an excellent barrier effect and a beautiful white gloss appearance.

  The thickness of the mixed layer of Sn and Sn—Zn alloy is preferably 0.04 to 0.9 μm. 2-15 mass% is preferable for Zn in the Sn-Zn alloy layer.

  The mixed layer of Sn and Sn—Zn alloy has the effect of generating less white rust even in a chloride environment as compared with Zn or Zn—Ni alloy.

  In this way, the surface of the steel sheet has, in order from the steel sheet side, a surface treatment layer composed of a Zn—Ni alloy layer, a Sn—Zn—Ni alloy layer, and a mixed layer of Sn and Sn—Zn alloy. It becomes a steel plate with excellent resistance.

The total Zn amount in the surface treatment layer is 7 to 20 g / m ² , and the mass ratio Zn / Ni between the total Zn amount and the total Ni amount needs to be 4 to 10.

If the total Zn content is less than 7 g / m ² , the sacrificial anticorrosive action on the steel sheet is insufficient, and depending on the corrosive environment, red rust will occur in a short period of time. On the other hand, the total Zn amount exceeding 20 g / m ² is excessive for ensuring corrosion resistance in a conceivable use environment, and excessive Zn causes deterioration in appearance.

  It is difficult to obtain a Zn-Ni alloy-plated steel sheet having a mass ratio Zn / Ni of less than 4 of the total Zn content and the total Ni content. Therefore, even if a Sn layer and a Sn—Zn alloy layer are present in the upper layer, it is difficult to obtain a glossy appearance.

  On the other hand, when the mass ratio Zn / Ni between the total Zn amount and the total Ni amount exceeds 10, this layer exhibits substantially the same behavior as the Zn layer, and is rapidly dissolved in the acidic Sn plating bath. Since it is large, a surface-treated steel sheet having a predetermined adhesion amount and a good appearance cannot be obtained.

The total amount of Sn in the surface treatment layer is preferably 0.5 to 5.6 g / m ² . When it is less than 0.5 g / m ^2, it is difficult to obtain a beautiful gloss appearance peculiar to Sn and Sn—Zn. On the other hand, when the total Sn amount exceeds 5.6 g / m ² , the production cost is increased, and the appearance is not improved, but the Sn—Zn alloy layer may be too thick. In that case, a white appearance with insufficient gloss is obtained.

  The surface of the surface-treated steel sheet may have a film made of at least one of an inorganic compound and an organic compound. What is necessary is just to provide the processing layer suitable for the required characteristics, such as paint adhesiveness and electroconductivity.

  If the plated steel plate of this invention satisfies the essential requirements mentioned above, it is not necessary to limit the manufacturing method. For example, a method of laminating a plating layer which becomes a predetermined component by means such as vapor deposition plating, or a method of laminating a plating layer which becomes a predetermined component by combining known plating methods such as vapor deposition plating and electroplating It is possible to manufacture with.

  However, these methods require large-scale capital investment, and are not practical considering productivity, cost, etc. in addition to manufacturing equipment. According to the method proposed in the present invention, it is not necessary to make a large capital investment, and it is possible to manufacture the device easily and at low cost.

  Next, a method for producing a surface-treated steel sheet having excellent appearance and corrosion resistance according to the present invention will be described.

  First, an electrical Zn—Ni alloy plating and then an electrical Sn plating are applied to the steel plate. Thereafter, the steel plate is heated to melt Sn. At this time, alloying proceeds simultaneously, an Sn—Zn layer is formed on the outermost surface, and an Sn—Zn—Ni alloy layer is formed below the Sn layer. Alternatively, a mixed layer of Sn and Sn—Zn is formed on the outermost surface, and a Sn—Zn—Ni alloy layer is formed in the lower layer.

  The electric Zn—Ni alloy plating is obtained by a method of electrolysis from a sulfuric acid acidic plating bath containing Zn (II) ions, Ni (II) ions, and sulfuric acid as main components. Sodium sulfate or the like may be added to increase the conductivity of the liquid. Zn (II) 0.1-0.5 mol / L, Ni (II) 0.3-1.0 mol / L, sulfuric acid 0.15-0.4 mol / L provide good electrical Zn-Ni alloy plating Easy concentration range. The plating solution temperature is preferably 40 to 65 ° C.

A preferable Zn—Ni plating can be obtained at a cathode current density of 100 to 300 A / dm ² in a circulation cell using the above plating solution. The amount of plating can be adjusted by changing the electrolysis time. The Zn amount in the Zn—Ni plating is 7 to 20 g / m ² , and Ni is 9 to 20% by mass. The amount of Ni is preferably 7 to ²⁰ g / m2.

  The electric Sn plating is preferably performed in an acid bath typified by a sulfuric acid bath or a phenolsulfonic acid bath in order to obtain a good Sn plating layer. For example, it is obtained by a method by electrolysis from an acidic plating bath containing Sn (II) 0.17 mol / L, phenolsulfonic acid 0.35 mol / L, and an organic additive.

  However, when a steel sheet plated with Zn—Ni alloy is immersed in an acidic Sn plating bath, the Zn—Ni alloy layer dissolves quickly. It is good to arrange | position to a plating tank entrance side.

The Sn plating adhesion amount is preferably 0.5 to 5.6 g / m ^{2 and} may be controlled by the energization amount. If it is less than 0.5 g / m < ² >, there exists a tendency for glossiness and a color tone to become excellent with the fall of the amount of plating. Moreover, even if it exceeds 5.6 g / m ² , there is no particularly improved performance, and it is better to avoid it for economic reasons.

  The heating and melting of Sn can be performed by any method such as electric heating, induction heating, infrared heating, hot air heating, or a combination thereof. As for the ultimate temperature of a steel plate, 240-260 degreeC is preferable. This temperature range gives the best results.

  Immediately after Sn is melted by heating, the steel sheet is water-cooled, but the surface layer structure varies depending on the molten state of tin immediately before water-cooling. That is, when water is cooled in the molten state, a surface treatment layer composed of a Zn—Ni alloy layer, a Sn—Zn—Ni alloy layer, a Sn layer, and a Sn—Zn alloy layer is formed in this order from the steel plate side. When water-cooled in a solidified state, a Zn—Ni alloy layer, a Sn—Zn—Ni alloy layer, and a mixed layer of Sn and Sn—Zn alloy are formed in this order from the steel plate side.

  After applying the above-mentioned plating and heat treatment, if coating film is formed by applying and baking a coating agent mainly composed of organic compounds, corrosion of steel sheet can be better prevented from aqueous corrosive liquid such as salt water. it can. As an example, a water-based polyurethane resin, a crosslinking agent, and an inorganic rust preventive agent are blended, and a coating agent prepared by stirring using a paint disperser is applied with a roll coater and dried with hot air to meet the purpose. A coating film can be obtained.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  A cold-rolled steel strip (SPCC) having a thickness of 0.8 mm was subjected to immersion alkali degreasing and dilute sulfuric acid pickling in the usual manner, and then subjected to the following surface treatment.

Zn—Ni alloy plating: 60 ° C. sulfuric acid acid plating containing 0.1 to 0.5 mol / L of Zn ²⁺ , 0.3 to 1.0 mol / L of Ni ²⁺ and 1.4 mol / L of Na ⁺ Using a bath, the electrolytic treatment was performed at a cathode current density of 100 to 300 A / dm ² at a relative flow rate of the steel strip and the plating solution of 200 m / min in a horizontal electrolytic cell. As the anode, platinum-plated titanium was used.

Sn plating: Sn ²⁺ 0.17 mol / L, phenol sulfonate ion 0.35 mol / L, and using a ferrostan bath at 43 ° C. containing an appropriate amount of surfactant at a cathode current density of 20 A / dm ² Cathodic electrolysis. As the anode, platinum-plated titanium was used. The adhesion amount of Sn plating was adjusted by electrolysis time.

  After Sn plating, it is immersed in water or a solution obtained by diluting the Sn plating solution 10 times, drained with a rubber roll, dried with cold air, heated to 250 ° C. for 6 seconds by electric heating, Sn was melted and quenched with water at 80 ° C. after 1 second or 0.2 second after stopping energization.

  Some samples were subjected to an evaluation test after being coated with the coating film described below.

  The coating agent for forming the surface-treated coating layer was prepared by reacting polyester diol obtained from bisphenol A-type diol, neopentyl glycol and isophthalic acid, 2,2 dimethylolpropionic acid and isophorone diisocyanate, and then adding it with triethylamine. 74% by mass of an aqueous polyurethane resin prepared by mixing and dispersing in water, 5% by mass of dibutoxybis (triethanolaminato) titanium as a crosslinking agent, and colloidal silica (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) as an inorganic rust inhibitor It was prepared by blending 20% by mass and 1% by mass of diammonium hydrogen phosphate and stirring the mixture using a paint disperser.

  This was applied by a roll coater, heated and dried so that the ultimate plate temperature was 150 ° C., immediately cooled with water, and then dried by blowing warm air. The coating thickness after drying was adjusted to 1.0 μm.

  The surface-treated steel sheet produced by the above method was subjected to the following evaluation tests (A), (B), and (C), and the characteristics were compared.

(A) Structure of surface treatment layer The adhesion amounts of Zn, Ni, and Sn were calculated from the fluorescent X-ray intensity using a calibration curve prepared in advance. The layer structure of the plating layer was confirmed by glow discharge emission spectroscopy (GDS). In the GDS chart, the Sn-Zn layer is the surface layer where Sn and Zn appear on the outermost surface, the Sn layer is the layer where only Sn appears, and the Sn-Zn-layer is the layer where Sn, Zn and Ni appear next. The Ni layer and the layer in which Sn disappears and only Zn and Ni appear are Zn-Ni layers.

  The thickness of each layer was determined as follows. The depth of the etched portion is measured with a stylus type roughness meter by GDS measurement, and the relationship between time and depth is obtained in advance from this and the measurement time. Converted into Moreover, the thickness of the coating film mainly composed of an organic compound was calculated from the fluorescent X-ray intensity of Si using a calibration curve prepared in advance.

(B) Appearance The appearance of the surface-treated steel sheet before and after the coating coating treatment was evaluated by the following method.

(B) -1 (Glossy)
The 60 ° specular gloss (Gs60 °) in the longitudinal direction of the steel strip was measured. As for Gs60 °, 300 or more was evaluated as ◎, 150 or more and less than 300 as ◯, 100 or more and less than 150 as Δ, and less than 100 as ×.

(B) -2 (color tone)
Using a spectrocolorimeter, the color tone of the test material represented by the L ^* a ^* b ^* color system was measured. C ^* = ((a ^* ) ² + (b ^* ) ² ) ^1/2 where the saturation C ^* is 2.0 or less, and the lightness L ^* is 55 or more, ○, the saturation C ^* , A case where only one of the lightness L ^{* s} deviates from the above-mentioned standard is indicated by Δ, and a case where both the chroma C ^* and the lightness L ^* deviate from the above-mentioned standard are indicated by x.

Furthermore, the case where the chroma C ^* is 1.5 or less and the lightness L ^* is 60 or more and exhibits a particularly excellent appearance is marked as ◎.

(C) Corrosion resistance The surface-treated steel sheet before and after the coating coating treatment was cut into a size of 50 mm × 100 mm and subjected to 7 mm overhanging with an Erichsen tester. The back surface and the end surface were tape-sealed, and a salt spray test (JIS-Z-2371) was performed. The salt spray test visually evaluated the rusting state after spraying a 5 mass% sodium chloride aqueous solution at 35 ° C. for 120 hours.

  Evaluation criteria are: ◎: no red rust, no white rust, ○: minimal red rust or little white rust, △: little red rust or slightly large white rust, ×: red rust occurring or slightly large white rust, xx: red rust Occurrence was large.

  The above performance evaluation results are shown in Tables 1-4.

  In the performance evaluation results shown in Tables 1 to 4, the overall evaluation is classified into four stages: ◎ (very good), ○ (good), △ (slightly bad), and × (bad). It was.

  Each of Examples 1 to 42 of the present invention had an overall evaluation ◎ or ◯, and had excellent appearance and corrosion resistance.

  Comparative Examples 1 and 32 were examples in which the amount of Zn deposited was small, and the corrosion resistance was poor. Comparative Examples 2-5 and 33-36 are examples in which the amount of deposited Zn is small and Zn / Ni is low. Both gloss and color tone were insufficient, and corrosion resistance was inferior.

  Comparative Examples 6, 10, 13, 14, 17, 18, 37, 41, 44, 45, 48, and 49 are examples in which Zn / Ni is high. There was much dissolution of the Zn-Ni layer by the Sn plating solution, and both gloss and color tone deteriorated.

  Comparative Examples 7, 8, 9, 11, 12, 15, 16, 19, 20, 38, 39, 40, 42, 43, 46, 47, 50, and 51 are examples in which Zn / Ni is low, The gloss was insufficient. Some colors were inferior.

  Comparative Examples 21, 22, 52, and 53 are examples in which the Zn deposition amount is large and Zn / Ni is high. Both gloss and color tone deteriorated due to poor gloss due to excessive Zn deposition and dissolution of the Zn-Ni layer surface with Sn plating solution.

  Comparative Examples 23 to 25 and 54 to 56 are examples in which the amount of Zn deposited is large, and the gloss was inferior. Comparative Examples 26 and 57 are examples in which the Zn deposition amount is large and Zn / Ni is low. The gloss and color were insufficient.

  Comparative Examples 27 and 58 are examples in which the amount of deposited Zn is small and Zn / Ni is low. Both gloss and color tone were inferior, and even when a coating film was applied, the corrosion resistance was insufficient. Comparative Examples 28 and 59 are examples in which Zn / Ni is high, and the Zn—Ni layer was frequently dissolved by the Sn plating solution, and both gloss and color tone were deteriorated.

  Comparative Examples 29 and 60 were examples in which the amount of Zn deposited was large and the gloss was inferior. Comparative Examples 30 and 31 are examples in which Sn plating is not performed, and thus there is no Sn—Zn—Ni alloy layer, Sn layer, or Sn—Zn alloy layer. It had a blackish, low gloss appearance and insufficient corrosion resistance.

  As described above, according to the present invention, it is possible to provide a surface-treated steel sheet having a beautiful appearance and good corrosion resistance and a method for producing the same. Therefore, the present invention has great applicability in the production and use industries of surface-treated steel sheets.

Claims (5)

In order from the steel plate side, Zn—Ni alloy layer, Sn—Zn—Ni alloy layer, Sn layer, surface treatment layer comprising Sn—Zn alloy layer, or in order from the steel plate side, Zn—Ni alloy layer, Sn—Zn— A steel plate having a surface treatment layer comprising a Ni alloy layer, a mixed layer of Sn and Sn—Zn alloy, wherein the total Zn amount in the surface treatment layer is 7 to 20 g / m ² , and the total Zn amount A surface-treated steel sheet, wherein the mass ratio Zn / Ni of the total Ni amount is 4 to 10. ^2. The surface-treated steel sheet according to claim 1, wherein the total amount of Sn in the surface-treated layer is 0.5 to 5.6 g / m ² .   The surface-treated steel sheet according to claim 1 or 2, further comprising a coating film mainly composed of an organic compound on the surface-treated layer.   The steel plate is subjected to electric Zn—Ni alloy plating and then electric Sn plating, and then the plated steel plate is heated, and simultaneously with the melting treatment of the Sn plating layer, the Zn—Ni alloy plating layer and the Sn plating layer are formed. Alloying treatment is performed, and the plating layer is sequentially formed from the steel plate side, the Zn-Ni alloy layer, the Sn-Zn-Ni alloy layer, the Sn layer, the laminated structure that becomes the Sn-Zn alloy layer, or the plating layer is sequentially formed from the steel plate side. A method for producing a surface-treated steel sheet, comprising forming a laminated structure to be a Zn—Ni alloy layer, a Sn—Zn—Ni alloy layer, and a mixed layer of Sn and Sn—Zn alloy.   5. The surface according to claim 4, wherein after the alloying treatment, a coating agent comprising an organic compound as a main component is applied and baked on the obtained surface treatment layer to form a coating film. A method for producing a treated steel sheet.