Surface-treated steel sheet

Abstract

A surface-treated steel sheet according to one embodiment of the present invention comprises a base steel sheet, a Ni-containing layer disposed on a surface of the base steel sheet, and a Ni-W alloy layer disposed on the surface of the Ni-containing layer, the Ni-containing layer having an Fe-diffused alloy layer, and a pinhole density on the surface of the Ni-W alloy layer of 4.0 pinholes / cm 2 Preferably, the average W concentration in the Ni-W alloy layer is 10 to 45 mass %. Preferably, the Ni-containing layer and the Ni-W alloy layer have a Ni coating weight of 1.8 to 35.6 g / m 2 It is.

Description

[Technical field]

[0001] The present invention relates to a surface-treated steel sheet. This application claims priority based on Japanese Patent Application No. 2023-016704, filed on February 7, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Ni-plated steel sheets have been used as surface-treated steel sheets for battery cans. Due to the excellent chemical stability of Ni, Ni-plated steel sheets are used for various battery containers, such as battery cans for alkaline manganese dry batteries, lithium ion batteries, and nickel-metal hydride batteries.

[0003] In recent years, Ni-W alloy plated steel sheets containing an alloy of Ni and W as the main components have also begun to be used as materials for battery cans, etc. Examples of Ni-W alloy plated steel sheets are the steel sheets described in Patent Documents 1-4.

[0004] Patent Document 1 discloses a plated steel sheet for battery containers, characterized in that an iron-nickel alloy layer, a nickel layer, and a nickel-tungsten alloy layer are formed, in that order from the bottom, on the side of the steel sheet that will become the inner surface of the battery container.

[0005] Patent Document 2 discloses a Ni-containing surface-treated steel sheet for containers formed by press molding, which includes a steel sheet having a first surface that will become the outside of the container after the press molding, a Ni-containing layer disposed on the first surface of the steel sheet, and a Ni-W alloy plating layer disposed on the Ni-containing layer. The Ni-containing layer has an Fe-Ni diffusion alloy layer, and the amount of Ni contained in the Ni-containing layer is 5 g / m 2 More than 89g / m 2 the thickness of the Ni-W alloy plating layer is 0.02 μm or more and 2 μm or less; and the W concentration in the Ni-W alloy plating layer is, in mass %, 10% or more and 65% or less.

[0006] Patent Document 3 discloses a steel sheet for a non-aqueous electrolyte secondary battery case, comprising: a steel sheet; and a Ni-W-Fe alloy plating layer formed on the surface of the steel sheet, containing a Ni-W-Fe alloy, and serving as the inner surface of the non-aqueous electrolyte secondary battery case.

[0007] Patent Document 4 discloses a steel sheet for use in battery cans of inside-out type alkaline batteries, characterized in that the steel sheet has a plating layer selected from nickel-tungsten (Ni-W) and nickel-cobalt-tungsten (Ni-Co-W) alloys on the surface of one main surface of a base material made of a plate-shaped steel material, and the plating layer has irregularities on the surface formed by dissolution of the tungsten. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2007-51325 A [Patent Document 2] International Publication No. 2012 / 137823 [Patent Document 3] International Publication No. 2017 / 006834 [Patent Document 4] JP 2020-155202 A Summary of the Invention [Problem to be solved by the invention]

[0009] Surface-treated steel sheets for battery cans are required to have low contact resistance, high discharge characteristics, resistance to metal elution, and workability. Furthermore, in recent years, as the applications of batteries have expanded, surface-treated steel sheets for battery cans are also required to have corrosion resistance. However, the corrosion resistance of surface-treated steel sheets mainly composed of Ni-W-Fe alloy has not been fully investigated in the prior art.

[0010] Patent Document 1 aims to suppress contact resistance and improve discharge characteristics, but does not particularly consider the corrosion resistance of plated steel sheets.

[0011] Patent Document 2 aims to improve corrosion resistance after press forming. In the steel sheet of Patent Document 2, an Fe-Ni diffusion alloy layer is used to prevent cracks generated during press forming from reaching the base steel sheet, thereby improving the corrosion resistance of the processed portion. However, Patent Document 2 does not particularly consider the corrosion resistance of regions other than the processed portion of the plated steel sheet.

[0012] The problem of Patent Document 3 is to suppress deterioration of battery performance and corrosion of the case due to metal elution when the potential of the battery case increases. However, Patent Document 3 does not particularly consider corrosion resistance in a corrosive environment, such as that evaluated by the rate of red rust formation.

[0013] Patent Document 4 aims to improve the high-load discharge performance and long-term storage performance of a steel sheet, but does not particularly consider the corrosion resistance of the steel sheet.

[0014] In view of the above circumstances, an object of the present invention is to provide a surface-treated steel sheet having high corrosion resistance. [Means for solving the problem]

[0015] The gist of the present invention is as follows.

[0016] (1) A surface-treated steel sheet according to one embodiment of the present invention comprises a base steel sheet, a Ni-containing layer disposed on a surface of the base steel sheet, and a Ni-W alloy layer disposed on the surface of the Ni-containing layer, the Ni-containing layer having an Fe-diffused alloy layer, and a pinhole density on the surface of the Ni-W alloy layer of 4.0 pinholes / cm. 2 The following is the result. (2) In the surface-treated steel sheet according to the above (1), the Ni—W alloy layer preferably has an average W concentration of 10 to 45 mass %. (3) In the surface-treated steel sheet according to the above (1) or (2), preferably, the Ni-containing layer and the Ni-W alloy layer have a coating weight of Ni of 1.8 to 35.6 g / m 2 It is. (4) In the surface-treated steel sheet according to any one of the above (1) to (3), the Fe-diffused alloy layer preferably has a thickness of 0.1 to 3.0 μm. (5) In the surface-treated steel sheet according to any one of the above (1) to (4), the Ni-containing layer preferably has a thickness of 0.2 to 4.0 μm. (6) In the surface-treated steel sheet according to any one of the above (1) to (5), preferably, the number density of the pinholes on the surface of the Ni-W alloy layer is 3.0 pinholes / cm 2 The following is the result. (7) In the surface-treated steel sheet according to any one of the above (1) to (6), preferably, only a part of the Ni-containing layer is the Fe-diffused alloy layer. (8) In the surface-treated steel sheet according to any one of the above (1) to (6), preferably, the entire Ni-containing layer is the Fe-diffusion alloy layer, and a portion of the Ni-W alloy layer is the Fe-diffusion alloy layer. Effect of the Invention

[0017] According to the present invention, a surface-treated steel sheet having high corrosion resistance can be provided. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional view of an example of a surface-treated steel sheet according to an embodiment of the present invention. FIG. [Diagram 2] FIG. 2 is a schematic cross-sectional view of another example of the surface-treated steel sheet according to the present embodiment. [Diagram 3] 2 is a flowchart illustrating an example of a method for manufacturing a surface-treated steel sheet according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (1. Surface-treated steel sheet 1) As shown in FIG. 1 or FIG. 2 , a surface-treated steel sheet 1 according to one embodiment of the present invention comprises a base steel sheet 11, a Ni-containing layer 12 disposed on a surface of the base steel sheet 11, and a Ni-W alloy layer 13 disposed on the surface of the Ni-containing layer 12, the Ni-containing layer 12 having an Fe-diffused alloy layer 14, and the number density of pinholes P on the surface of the Ni-W alloy layer 13 is 4.0 pcs / cm 2 The following is the result.

[0020] The surface-treated steel sheet 1 according to this embodiment will be described in detail below. The entire plating layer including the Ni-containing layer 12 and the Ni-W alloy layer 13 may be simply referred to as the "plating layer".

[0021] (Base material steel plate 11) The surface-treated steel sheet 1 has a base steel sheet 11. The base steel sheet 11 is a steel sheet that serves as a substrate for the surface-treated steel sheet 1. The components, sheet thickness, metal structure, and the like of the base steel sheet 11 are not particularly limited and can be appropriately selected depending on the application of the surface-treated steel sheet 1.

[0022] (Ni-containing layer 12) The surface-treated steel sheet 1 has a Ni-containing layer 12 disposed on the surface of a base steel sheet 11. The Ni-containing layer 12 is a layer containing Ni provided on the surface of the base steel sheet 11. The Ni-containing layer 12 may be provided on only one surface or both surfaces of the base steel sheet 11. The Ni-containing layer 12 has the effect of improving the corrosion resistance of the processed portion.

[0023] (Ni-W alloy layer 13) The surface-treated steel sheet 1 further has a Ni-W alloy layer 13 disposed on the surface of the Ni-containing layer 12. The Ni-W alloy layer 13 is an alloy plating layer containing Ni as a main component and further containing W. The Ni-W alloy plating is harder than Ni. By analyzing the component distribution of the plating layer using glow discharge optical emission spectrometry, which is an analytical method capable of measuring the depth distribution of chemical components, it is possible to distinguish between the Ni-W alloy layer 13 having a high W concentration and the Ni-containing layer 12 having a low W concentration.

[0024] The Ni-W alloy layer 13 may be provided on only one surface or both surfaces of the base steel sheet 11. A surface treatment layer such as a coating film may be further provided on the surface of the Ni-W alloy layer 13.

[0025] (Fe diffusion alloy layer 14) At least a portion of the Ni-containing layer 12 is an Fe-diffused alloy layer 14. That is, the Ni-containing layer 12 has an Fe-diffused alloy layer 14. The Fe-diffused alloy layer 14 is an alloy layer 13 formed by diffusing Fe of the base steel sheet 11 into the inside of the plating layer. The Fe-diffused alloy layer 14 is obtained, for example, by plating the surface of the base steel sheet 11 and then performing an alloying treatment such as annealing.

[0026] In the cross-sectional schematic diagram illustrated in FIG. 1, only a part of the Ni-containing layer 12 is the Fe diffusion alloy layer 14 in contact with the base steel plate 11. On the other hand, as illustrated in FIG. 2, the entire Ni-containing layer 12 may be the Fe diffusion alloy layer 14. Also, as illustrated in FIG. 2, the Fe diffusion alloy layer 14 may extend to the Ni-W alloy layer 13. That is, the Ni-W alloy layer 13 may have the Fe diffusion alloy layer 14. Only a part of the Ni-W alloy layer 13 may be the Fe diffusion alloy layer 14, or the entire Ni-W alloy layer 13 may be the Fe diffusion alloy layer 14. The Fe diffusion alloy layer 14 formed in the Ni-containing layer 12 may be referred to as a Ni-Fe alloy layer, and the Fe diffusion alloy layer 14 formed in the Ni-W alloy layer 13 may be referred to as a Ni-W-Fe alloy layer. In general, a surface-treated steel sheet in which only a portion of the Ni-containing layer 12 is the Fe diffusion alloy layer 14 and a surface-treated steel sheet in which the entire Ni-containing layer 12 is the Fe diffusion alloy layer 14 and only a portion of the Ni-W alloy layer 13 is the Fe diffusion alloy layer 14 are referred to as a partial diffusion-plated steel sheet. Also, a surface-treated steel sheet in which the entire Ni-containing layer 12 and the entire Ni-W alloy layer 13 are the Fe diffusion alloy layer 14 are referred to as a fully diffusion-plated steel sheet.

[0027] (Number density of pinholes P) Pinholes P may be formed in the plating layer. The pinholes P are minute holes that penetrate from the surface of the plating layer to the base steel sheet 11. The pinholes P expose the base steel sheet 11 to a corrosive environment, promoting corrosion of the base steel sheet 11. Note that pits, which are holes that do not penetrate the plating layer, may be formed on the surface of the plating layer, but in the surface-treated steel sheet 1 according to this embodiment, a distinction is made between the pits and the pinholes P.

[0028] The density of the pinholes P can be determined by a ferroxyl test performed under specific conditions. In the ferroxyl test, first, filter paper soaked in a test liquid that corrodes the base steel sheet 11 is attached to the surface of the plating layer for a specified period of time. Next, the number of spots of iron complex ions attached to the filter paper is counted. The locations where spots have appeared are deemed to have pinholes P, and the number of spots is regarded as the number of pinholes P. Note that the ferroxyl test does not detect pits. Detailed conditions for the ferroxyl test will be described later.

[0029] In the surface-treated steel sheet 1 according to this embodiment, the density of pinholes P on the surface of the Ni-W alloy layer 13 is 4.0 pcs / cm 2 The number of pinholes P is 3.8 / cm 2 Below, 3.5 pieces / mm 2 Less than or equal to 3.0 pieces / cm 2 The smaller the number of pinholes P, the better, so the density of pinholes P is 0 pcs / cm 2 However, the density of the pinholes P may be 0 / cm 2 Super, 1.0 pieces / cm 2 More than 1.5 pieces / cm 2 or more than 2.0 pieces / cm 2 It may be more than that.

[0030] (Effect: Improved corrosion resistance through suppression of pinhole P) The present inventors have found that the heat treatment for forming the Fe-diffused alloy layer 14, i.e., the alloying treatment, reduces the corrosion resistance of regions other than the processed portion. The present inventors have found that the alloying treatment increases the number density of the pinholes P, and that there is a close correlation between the number density of the pinholes P and the corrosion resistance. The greater the number density of the pinholes P, the more the corrosion resistance is impaired. The pinholes P have the function of exposing the base steel plate 11 to a corrosive environment.

[0031] However, the inventors have optimized the manufacturing conditions, specifically the plating conditions before annealing, to reduce the number density of pinholes P to 4.0 pcs / cm 2 The density of pinholes P was reduced to 4.0 / cm 2 By doing as described below, it was possible to increase the corrosion resistance of the non-bending region of the surface-treated steel sheet 1 to a level close to that of the surface-treated steel sheet 1 before the alloying treatment.

[0032] As described above, in the surface-treated steel sheet 1 according to this embodiment, the corrosion resistance of the processed portion is improved by using the Ni-containing layer 12. Furthermore, in the surface-treated steel sheet 1 according to this embodiment, the number density of the pinholes P is reduced, thereby suppressing the decrease in corrosion resistance of the flat portion due to the alloying treatment. As a result, the surface-treated steel sheet 1 according to this embodiment has extremely excellent corrosion resistance.

[0033] The above describes the most basic aspect of the surface-treated steel sheet 1 according to this embodiment. Next, a more preferred aspect of the surface-treated steel sheet 1 according to this embodiment will be described.

[0034] (Average W concentration in Ni-W alloy layer 13) The Ni-W alloy layer 13 contains Ni as a main component and further contains W. "Contains Ni as a main component" means that the Ni concentration is 50 mass % or more. The average W concentration in the Ni-W alloy layer 13 is not particularly limited, but can be within the range of 10 to 45 mass %, for example.

[0035] W has the function of suppressing the generation of pinholes P. By setting the average W concentration within the above range, the number density of pinholes P can be further suppressed. The average W concentration in the Ni-W alloy layer 13 may be 15 mass% or more, 20 mass% or more, 25 mass% or more, or 30 mass% or more. The average W concentration in the Ni-W alloy layer 13 may be 43 mass% or less, 42 mass% or less, 41 mass% or less, or 40 mass% or less. For example, the Ni-W alloy layer 13 may contain Cr, Mo, etc.

[0036] (Ni deposition amount) The amount of Ni contained in the plating layer (i.e., the Ni-containing layer 12 and the Ni-W alloy layer 13) is not particularly limited, but may be, for example, 1.8 to 35.6 g / m 2 The Ni coating weight may be within the range of 1.8 g / m 2 By setting the amount of Ni to 35.6 g / m or more, the corrosion resistance of the surface-treated steel sheet 1 can be further improved. 2 By setting the Ni coating amount to 4.5 g / m or less, the manufacturing cost of the surface-treated steel sheet 1 can be reduced. 2 More than 6.2g / m 2 or more than 8.9 g / m 2 The Ni coating weight may be 26.7 g / m or more. 2 Below, 17.8g / m 2 or less than 13.4 g / m 2 It may be the following.

[0037] The thickness of the plating layer (that is, the total thickness of the Ni-containing layer 12 and the Ni-W alloy layer 13) is not particularly limited. For example, the thickness of the plating layer may be within the range of 0.2 μm to 4.0 μm.

[0038] (Thickness of Fe diffusion alloy layer 14) The thickness of the Fe diffusion alloy layer 14 is not particularly limited. Even if the thickness is small, the Fe diffusion alloy layer 14 can improve the workability of the surface-treated steel sheet 1 and the corrosion resistance of the processed portion. On the other hand, the thickness of the Fe diffusion alloy layer 14 may be, for example, 0.1 μm or more. This further improves the workability of the surface-treated steel sheet 1. The thickness of the Fe diffusion alloy layer 14 may be 0.2 μm or more, 0.3 μm or more, or 0.5 μm or more. The upper limit of the thickness of the Fe diffusion alloy layer 14 is not particularly specified. For example, the entire plating layer may be the Fe diffusion alloy layer 14. On the other hand, the Fe diffusion alloy layer 14 may be 3.0 μm or less, 2.5 μm or less, or 2.0 μm or less.

[0039] (Thickness of Ni-containing layer 12) The thickness of the Ni-containing layer 12 is not particularly limited. Even if the Ni-containing layer 12 has a small thickness, it can improve the workability of the surface-treated steel sheet 1 and the corrosion resistance of the processed portion. On the other hand, the thickness of the Ni-containing layer 12 may be, for example, 0.2 μm or more. This can further improve the workability of the surface-treated steel sheet 1. The thickness of the Ni-containing layer 12 may be 0.5 μm or more, 1.0 μm or more, or 1.5 μm or more. The upper limit of the thickness of the Ni-containing layer 12 is not particularly specified, but the thickness of the Ni-containing layer 12 may be, for example, 4.0 μm or less, 3.5 μm or less, or 3.0 μm or less.

[0040] (Components of Ni-containing layer 12) The Ni-containing layer 12 is a layer mainly composed of Ni and Fe diffused from the base steel sheet 11. For example, the total content of Ni and Fe in the Ni-containing layer 12 may be 98.0 mass% or more, 98.5 mass% or more, or 99.0 mass% or more. The total content of Ni and Fe in the Ni-containing layer 12 may be 100 mass% or less, 99.5 mass% or less, or 99.0 mass% or less. The ratio of Ni and Fe in the Ni-containing layer 12 is not uniform in the thickness direction of the Ni-containing layer 12 (thickness direction of the surface-treated steel sheet 1). This is because, as described above, a part or the whole of the Ni-containing layer 12 is made into the Fe diffusion alloy layer 14, and the amount of Fe diffused from the base steel sheet 11 in the Fe diffusion alloy layer 14 differs in the thickness direction of the Fe diffusion alloy layer 14. In the Fe diffusion alloy layer 14, the Fe content increases closer to the base steel sheet 11. The thickness of the Fe diffusion alloy layer 14 can be appropriately selected.

[0041] The Ni-containing layer 12 may contain elements other than Ni and Fe. For example, the Ni-containing layer 12 may contain Cr and Mo. For example, the Ni-containing layer 12 may contain one or both of Cr and Mo, and the total content of Cr and Mo may be more than 0 mass% and 0.1 mass% or less. In addition, various alloy elements contained in the base steel plate 11 may diffuse into the Ni-containing layer 12 during the alloying treatment. Therefore, the Ni-containing layer 12 may contain various impurity elements. In addition, W may diffuse into the Ni-containing layer 12 from the Ni-W alloy layer 13. However, the W content of the Ni-containing layer 12 is usually less than 1.0%.

[0042] (Components and thickness of Ni-W alloy layer 13) As described above, the Ni-W alloy layer 13 contains Ni as a main component and further contains W. As illustrated in FIG. 2, when a part or all of the Ni-W alloy layer 13 is the Fe diffusion alloy layer 14, the Ni-W alloy layer 13 may further contain Fe. When the Ni-W alloy layer 13 does not have the Fe diffusion alloy layer 14, the total content of Ni and W in the Ni-W alloy layer 13 may be 95.0 mass% or more, 96.0 mass% or more, or 97.0 mass% or more. When the Ni-W alloy layer 13 does not have the Fe diffusion alloy layer 14, the total content of Ni and W in the Ni-W alloy layer 13 may be 100 mass% or less, 99.0 mass% or less, or 98.0 mass% or less. When the Ni-W alloy layer 13 has the Fe diffusion alloy layer 14, the total content of Ni, W, and Fe in the Ni-W alloy layer 13 may be 95.0 mass% or more, 96.0 mass% or more, or 97.0 mass% or more. When the Ni--W alloy layer 13 has the Fe-diffused alloy layer 14, the total content of Ni, W, and Fe in the Ni--W alloy layer 13 may be 100 mass % or less, 99.0 mass % or less, or 98.0 mass % or less.

[0043] Like the Ni-containing layer 12, the Ni-W alloy layer 13 may contain elements other than Ni and W. For example, the Ni-W alloy layer 13 may contain Cr and Mo. For example, the Ni-W alloy layer 13 may contain one or both of Co and Mo, and the total content of Co and Mo may be more than 0 mass % and 5 mass % or less. The Ni-W alloy layer 13 may also contain the above-mentioned Fe and various other impurity elements.

[0044] The thickness of the Ni-W alloy layer 13 is not particularly limited. Even if the thickness is small, the Ni-W alloy layer 13 enhances the corrosion resistance of the surface-treated steel sheet 1. In addition, from the viewpoint of further enhancing the workability of the Ni-W alloy layer 13, it is advantageous for the Ni-W alloy layer 13 to have a small thickness. On the other hand, from the viewpoint of further enhancing the corrosion resistance of the Ni-W alloy layer 13, it is advantageous for the Ni-W alloy layer 13 to have a large thickness. Therefore, the thickness of the Ni-W alloy layer 13 may be, for example, 0.01 μm or more. This can further enhance the corrosion resistance of the surface-treated steel sheet 1. The thickness of the Ni-W alloy layer 13 may be 0.05 μm or more, 0.08 μm or more, or 0.10 μm or more. The upper limit of the thickness of the Ni-W alloy layer 13 is not particularly specified. For example, the Ni-W alloy layer 13 may be 2.0 μm or less, 1.5 μm or less, or 1.0 μm or less.

[0045] (11 types of base steel plate, etc.) There are no particular limitations on the components and metal structure of the base steel sheet 11. The components and metal structure of the base steel sheet 11 can be appropriately selected depending on the application of the surface-treated steel sheet 1. For example, the chemical components of the base steel sheet 11 may be C: 0.0001-0.08, Si: 0.001-0.03, Mn: 0.01-0.4, P: 0.001-0.03, and S: 0.000-0.03.

[0046] When the surface-treated steel sheet 1 is used as a material for a battery container, for example, the base steel sheet 11 is preferably low carbon aluminum-killed steel, IF steel (Interstitial Free Steel / ultra-low carbon steel), etc. Specific examples of the chemical composition (unit: mass%) of the base steel sheet 11 are as follows:

[0047] (Example 1) Low carbon aluminum killed steel C: 0.057, Si: 0.004, Mn: 0.29, P: 0.014, S: 0.007, Al: 0.050, Cu: 0.034, Ni: 0.021, balance: Fe and impurities

[0048] (Example 2) IF steel C: 0.004, Si: 0.01, Mn: 0.16, P: 0.013, S: 0.006, Al: 0.029, Cu: 0.027, Ni: 0.022, Ti: 0.013, balance: iron and impurities

[0049] (Example 3) IF steel C: 0.0012, Si: less than 0.01, Mn: 0.16, P: 0.013, S: 0.006, Al: 0.029, Cu: 0.027, Ni: 0.022, Ti: 0.020, balance: iron and impurities

[0050] There is also no particular limitation on the thickness of the base steel sheet 11. When the surface-treated steel sheet 1 is used, for example, as a material for a battery container, the thickness of the base steel sheet 11 is preferably, for example, 0.15 to 2.00 mm.

[0051] (Measurement method) The method for measuring the number density of pinholes P includes the steps of taking a test piece from the surface-treated steel sheet 1, attaching filter paper impregnated with a test liquid to the test surface of the test piece, peeling the filter paper from the test surface and rinsing it with water, and counting the number of spots attached to the filter paper. The test liquid is 10 g / L of potassium hexacyanoferrate (II) trihydrate (potassium ferrocyanide), 10 g / L of potassium hexacyanoferrate (III) (potassium ferricyanide), and 60 g / L of sodium chloride dissolved in pure water. This measurement method complies with Annex 3 (regulation) "Ferroxyl test method" of JIS H 8617:1999.

[0052] The method for measuring the average W concentration in the Ni-W alloy layer 13 is as follows. Measurement is performed using XPS (X-ray Photoelectron Spectroscopy). First, the surface of the surface-treated steel sheet 1 is sputtered using argon and / or xenon. Next, the components of the Ni-W alloy layer 13 of the surface-treated steel sheet 1 are measured from the surface toward the inside. After the measurement is completed, the cycle of sputtering again and then measuring is repeated. The analysis results of the W concentration along the depth direction are plotted on a graph with the horizontal axis being the depth and the vertical axis being the W concentration. The value obtained by integrating the graph of the W concentration is then divided by the width of the interval (i.e., the thickness of the Ni-W alloy layer 13) and regarded as the average W concentration. The above-mentioned calculation performed on the W concentration is also applied to the Ni and Fe analysis results, so that the average Ni concentration and the average Fe concentration in the Ni-W alloy layer 13 can be obtained. The component measurement of the plating layer using XPS is performed using a Mg radiation source. In the analysis using the Mg radiation source, there were no Auger peaks overlapping with the photoelectron peaks of Ni, W, or Fe. Peaks of 2p orbitals of Fe, 2p orbitals of Ni, and 4f orbitals of W were observed.

[0053] The amount of Ni attached is measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). First, a specified area of ​​the plating layer is dissolved in acid. Next, the total amount of Ni contained in the solution is quantitatively analyzed by ICP-OES. The total amount of Ni quantified by ICP-OES is divided by the specified area mentioned above to obtain the amount of Ni attached per unit area.

[0054] The thickness of the Ni-containing layer 12, the Ni-W alloy layer 13, and the Fe-diffused alloy layer 14 are measured by GDS (Glow Discharge Optical Emission Spectrometry). By using GDS to measure the distribution of element concentration in the depth direction, an element concentration curve can be obtained.

[0055] The measurement is performed using a high-frequency glow discharge optical emission surface analyzer (manufactured by Horiba, Ltd., model number: GD-Profiler2). The GDS measurement conditions are as follows: Anode diameter: φ4mm Gas: Ar Gas pressure: 600Pa Output: 35W

[0056] In the surface-treated steel sheet 1 according to this embodiment, a region in the plating layer containing an Fe concentration of 5.0 mass % or more is regarded as an Fe-diffused alloy layer 14. When a component analysis is performed continuously from the surface of the plating layer in the depth direction, the Fe concentration increases closer to the base steel sheet 11. A location with an Fe concentration of 5.0 mass %, identified by a component analysis performed continuously from the surface of the plating layer in the depth direction, is regarded as an interface between the Fe-diffused alloy layer 14 and a plating layer that is not the Fe-diffused alloy layer 14.

[0057] Moreover, in the surface-treated steel sheet 1 according to this embodiment, the region where the Ni concentration is 1.0 mass % or more is regarded as the plating layer, and the other region is regarded as the base steel sheet 11. In the plating layer of the surface-treated steel sheet 1 manufactured by alloying treatment, the Ni concentration decreases toward the base steel sheet 11. A location where the Ni concentration is 1.0 mass %, which is identified by continuously performing component analysis from the surface of the plating layer in the depth direction, is regarded as the interface between the plating layer and the base steel sheet 11 (i.e., the interface between the Fe-diffused alloy layer 14 and the base steel sheet 11).

[0058] The distance between these interfaces is regarded as the thickness of the Fe-diffused alloy layer 14 in the sample obtained by the above-mentioned procedure. This measurement is performed on five samples, and the average value is calculated. This average value is regarded as the thickness of the Fe-diffused alloy layer 14 of the surface-treated steel sheet 1.

[0059] Furthermore, in the surface-treated steel sheet 1 according to this embodiment, a region in the plating layer where the W concentration is 1.0 mass% or more is regarded as the Ni-W alloy layer 13, and a region where the W concentration is less than 1.0 mass% is regarded as the Ni-containing layer 12. A location where the W concentration is 1.0 mass%, which is identified by continuously performing a component analysis from the surface of the plating layer in the depth direction, is regarded as the interface between the Ni-W alloy layer 13 and the Ni-containing layer 12.

[0060] The distance from the interface between the Ni-W alloy layer 13 and the Ni-containing layer 12 to the interface between the plating layer and the base steel sheet 11 is regarded as the thickness of the Ni-containing layer 12 in the sample obtained by the above-mentioned procedure. This measurement is performed on five samples, and the average value is calculated. This average value is regarded as the thickness of the Ni-containing layer 12 of the surface-treated steel sheet 1. In addition, the distance from the surface of the plating layer to the interface between the Ni-W alloy layer 13 and the Ni-containing layer 12 is regarded as the thickness of the Ni-W alloy layer 13 in the sample obtained by the above-mentioned procedure. This measurement is performed on five samples, and the average value is calculated. This average value is regarded as the thickness of the Ni-W alloy layer 13 of the surface-treated steel sheet 1.

[0061] (2. Manufacturing method of surface-treated steel sheet) Next, a method for producing a surface-treated steel sheet according to the present embodiment will be described. For example, the method for producing a surface-treated steel sheet 1 having the above-mentioned components can be suitably obtained by the method according to the present embodiment.

[0062] As illustrated in FIG. 3, a method for producing a surface-treated steel sheet according to another embodiment of the present invention includes the steps of: (S1) a step of electrolytically plating a base steel sheet 11 with Ni; (S2) A process of electroplating the base steel sheet 11 with a Ni-W alloy; (S3) a step of annealing the base steel sheet 11 having the Ni plating layer and the Ni-W alloy layer 13 disposed thereon; The current conditions for electric Ni plating are 1.0 to 5.0 A / dm 2 The current conditions for electric Ni-W alloy plating were 1.0 to 5.0 A / dm 2 Let us assume that.

[0063] (S1 Electroplating) First, a base steel sheet 11 is electroplated with Ni. The plating base material is the same as the base steel sheet 11 of the surface-treated steel sheet 1 according to the present embodiment described above. As a result, a Ni-containing layer 12 is provided on the surface of the base steel sheet 11, as shown in Fig. 3. The plated steel sheet obtained by electroplating with Ni is hereinafter referred to as a Ni-plated steel sheet.

[0064] (S2 Electric Ni-W alloy plating) Next, the Ni-plated steel sheet is subjected to electric Ni-W alloy plating. As a result, a Ni-W alloy layer 13 is provided on the surface of the Ni-plated steel sheet as shown in Fig. 3. The plated steel sheet obtained by electric Ni-W alloy plating is hereinafter referred to as a multi-layer plated steel sheet.

[0065] (S3 annealing) Next, the multi-layer plated steel sheet (i.e., the base steel sheet 11 having the Ni plating layer and the Ni-W alloy layer 13 disposed thereon) is annealed. As a result, as shown in Fig. 3, Fe of the base steel sheet 11 is diffused into a part of the plating layer to form an Fe diffused alloy layer 14. In this way, a surface-treated steel sheet 1 can be obtained which includes the base steel sheet 11, the Ni-containing layer 12 disposed on the surface of the base steel sheet 11, and the Ni-W alloy layer 13 disposed on the surface of the Ni-containing layer 12, and in which the Ni-containing layer 12 has the Fe diffused alloy layer 14.

[0066] In the case of (S1) Ni electroplating, the current density must be set to a lower range than usual. In general, it is believed that the current density in Ni electroplating does not affect the properties of Ni plating very much. Therefore, unless there are special circumstances, the current density in Ni electroplating or multi-layer plating including Ni electroplating should be set to 5.0A / dm 2It is common to set the current density higher than 1.0A / dm to improve production efficiency. For example, Shiro Haruyama, "Electrochemistry for Surface Engineers," 2nd Edition, Maruzen Publishing, Japan, 2005, p. 173, explains that it is desirable to have as high a current density for plating as possible. This document explains that the higher the current density for plating, the better: (1) the plating time can be shortened, (2) less noble metals can be plated with high current efficiency due to an increase in hydrogen overvoltage, and (3) a denser, stronger plating film can be obtained due to the refinement of crystal grains accompanying the increase in overvoltage. However, in the manufacturing method for surface-treated steel sheet according to this embodiment, the current flow conditions for electric Ni plating are set to 1.0 to 5.0A / dm 2 It is necessary to do so.

[0067] In addition, in the electric Ni-W alloy plating of (S2), the current density must be within a predetermined range. Specifically, the current density in the electric Ni-W alloy plating is set to 1.0 to 5.0 A / dm 2 Let us assume that.

[0068] By setting the current density in the electric Ni plating and electric Ni-W alloy plating within the above-mentioned range, the number density of pinholes P on the surface of the Ni-W alloy layer 13 is set to 4.0 pieces / cm 2 It can be as follows:

[0069] The inventors presume that the reason why the number density of pinholes P can be reduced by setting the electroplating conditions within the above-mentioned ranges is as follows. During electroplating, metal ions contained in the plating bath are electrodeposited on the surface of the substrate, and at the same time, hydrogen ions contained in the plating bath become hydrogen gas on the surface of the substrate. This causes hydrogen gas to be taken into the plating layer. This hydrogen gas forms pinholes P during annealing. It is believed that the larger the current density, the greater the amount of hydrogen gas taken in. Therefore, when the current density in Ni electroplating or Ni-W alloy electroplating is 5.0 A / dm 2 If the temperature is higher than 4.0, the amount of hydrogen gas absorbed into the plating layer becomes excessive, and the density of pinholes P becomes 4.0 / cm 2However, the current density in electric Ni plating or electric Ni-W alloy plating cannot be set below 5.0A / dm 2 or less, the amount of hydrogen gas contained in the Ni-containing layer 12 and the Ni-W alloy layer 13 before annealing can be reduced, and the number density of pinholes P can be reduced to 4.0 pcs / cm 2 You can do the following:

[0070] According to the results of experiments by the present inventors, the lower the current density in Ni electroplating and Ni-W alloy electroplating, the smaller the density of the number of pinholes P. For example, when the current density in Ni electroplating is 2.0 A / dm 2 The current density in the electric Ni-W alloy plating is 2.0 A / dm 2 By setting the number of pinholes P to 3.0 / cm or less, the number density of pinholes P is 3.0 / cm 2 The following surface-treated steel sheet is obtained:

[0071] In addition, it is believed that insufficient current flow in Ni electroplating or Ni-W alloy electroplating will deteriorate productivity. Therefore, the current density in Ni electroplating or Ni-W alloy electroplating is set to 1.0 A / dm 2 That's all.

[0072] The most basic aspect of the method for producing a surface-treated steel sheet according to the present embodiment has been described above. Next, a more preferred aspect of the method for producing a surface-treated steel sheet according to the present embodiment will be described.

[0073] (Bath ingredients) The Ni plating bath used in the electric Ni plating contains Ni as a main component. For example, the proportion of Ni element contained in the plating bath to all metal elements contained in the plating bath may be 95 mass% or more, 96 mass% or more, or 97 mass% or more. In addition to Ni, the Ni plating bath may contain Cr, Mo, etc. The Ni-W plating bath used in the electric Ni-W alloy plating contains Ni and W as main components. For example, the ratio of the W element contained in the plating bath to all metal elements contained in the plating bath may be within the range of 10 to 90 mass%. Also, for example, the ratio of the total of the Ni element and the W element contained in the plating bath to all metal elements contained in the plating bath may be 95 mass% or more, 96 mass% or more, or 97 mass% or more. In addition to Ni and W, the Ni-W plating bath may contain Cr and Mo.

[0074] (Amount of adhesion) In the Ni electroplating and Ni-W alloy electroplating, the Ni coating weight is not particularly limited, but is, for example, 1.8 to 35.6 g / m 2 As a result, the amount of Ni contained in the Ni-containing layer 12 and the Ni-W alloy layer 13 may be set to 1.8 to 35.6 g / m 2 The more preferable Ni coating weight may be the same as the more preferable Ni coating weight in the surface-treated steel sheet 1 according to the present embodiment described above. The Ni coating weight can be controlled via the components of the plating bath and the amount of current.

[0075] (Annealing conditions) The annealing conditions are not particularly limited, but for example, the annealing temperature in the annealing may be 630 to 860°C, and the annealing time may be 10 to 180 s. The higher the annealing temperature, the thicker the Fe diffusion alloy layer 14. Furthermore, the longer the annealing time, the thicker the Fe diffusion alloy layer 14. As described above, at least a part of the Ni-containing layer 12 may be the Fe diffusion alloy layer 14. The entire Ni-containing layer 12 may be the Fe diffusion alloy layer 14, and further, a part or the entire Ni-W alloy layer 13 may be the Fe diffusion alloy layer 14. The annealing time and the annealing temperature can be appropriately adjusted depending on the application of the surface-treated steel sheet 1.

[0076] The thickness ratio between the Ni-containing layer 12 and the Ni-W alloy layer 13 before annealing is not particularly limited. The thicker the Ni-containing layer 12, the more advantageous it is in terms of further improving the workability. On the other hand, the thicker the Ni-W alloy layer 13, the more advantageous it is in terms of further reducing the number density of the pinholes P. The thickness ratio can be appropriately selected depending on the application of the surface-treated steel sheet 1.

[0077] Additionally, the various aspects described with respect to the surface-treated steel sheet 1 according to the present embodiment can be applied to the manufacturing method of the surface-treated steel sheet according to the present embodiment. For example, it goes without saying that the preferred aspects of the base steel sheet 11 in the surface-treated steel sheet 1 according to the present embodiment can be applied to the manufacturing method of the surface-treated steel sheet according to the present embodiment. EXAMPLES

[0078] The effects of one embodiment of the present invention will be explained more specifically with reference to an example. However, the conditions in the example are merely an example of conditions adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to this example of conditions. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0079] Various surface-treated steel sheets were produced by electroplating Ni, electroplating Ni-W alloy, and annealing the base steel sheet. The composition of the base steel sheet is shown in Table 1. The composition of the Ni-W alloy electric plating bath is shown in Table 2. The manufacturing conditions of the surface-treated steel sheets are shown in Table 3. The evaluation results of the surface-treated steel sheets are shown in Table 4. Note that conditions not listed in the table were the same for all examples, and their details are as follows:

[0080] The composition of the plating bath for Ni electroplating was NiSO4·6H2O: 240g / L, NiCl2·6H2O: 70g / L, and H3BO3: 45g / L. The pH of the plating bath for Ni electroplating was 4, and the temperature was 50°C. The plating weight in Ni electroplating was controlled by changing the current flow time.

[0081] In the electric Ni-W alloy plating, the Ni ion source was NiSO4·6H2O and the W ion source was Na2WO4·2H2O. The composition (W content) of the Ni-W alloy plating was adjusted by changing the ratio of Ni ion concentration and W ion concentration. In addition, 0.5 mol / L of citric acid was added to the plating bath for electric Ni-W alloy plating to stabilize the W ions in the bath. The pH of the plating bath for electric Ni-W alloy plating was set to 6, and the temperature was set to 50°C. The plating weight in electric Ni-W alloy plating was controlled via the current flow time.

[0082] The pinhole density was measured by the Ferroxyl test method described above, and the results are shown in Table 5.

[0083] The average W concentration in the Ni-W alloy layer was measured by the above-mentioned method using XPS. The measurement results are shown in Table 5.

[0084] The total amount of Ni attached was measured by the above-mentioned ICP atomic emission spectrometry, and the measurement results are shown in Table 5.

[0085] The thickness of the Ni-containing layer and the Fe-diffused alloy layer were measured by the above-mentioned method using GDS. The measurement results are shown in Table 5.

[0086] Corrosion resistance was evaluated by a salt spray test (SST) in accordance with JIS Z 2371:2015. The test pieces were 50 x 100 mm, and the edges were sealed with polyester tape. The temperature inside the test tank was 35±1°C, and the salt water used for spraying was adjusted to 50g / L by dissolving sodium chloride in deionized water. The area ratio of red rust on each test piece was measured 4 hours after the start of the test, and was evaluated according to the following criteria. Test piece with red rust occurrence rate of 10% or more: 3 Test piece with red rust occurrence area rate of 5% or more and less than 10%: 2 Test piece with red rust occurrence rate of less than 5%: 1

[0087] [Table 1]

[0088] [Table 2]

[0089] [Table 3]

[0090] [Table 4]

[0091] The test pieces of Examples 2 and 3 had excessive pinhole density. The corrosion resistance of these test pieces was rated "3", i.e., inferior. In the production of Example 2, the amount of current passed in the Ni plating was excessive. In the production of Example 3, the amount of current passed in the Ni-W plating was excessive. That is, it is presumed that in Examples 2 and 3, the production conditions were inappropriate, causing a large number of pinholes to form in the plating layer.

[0092] On the other hand, the test pieces obtained by the appropriate manufacturing method had suppressed the occurrence of pinholes. The corrosion resistance of these test pieces was good. In addition, the current density in the Ni electroplating was set at 2.0 A / dm 2 and the current density in the electric Ni-W alloy plating is 2.0A / dm 2 In the following Examples 1, 5, 6, 8 to 15, the pinhole density was 3.0 pcs / cm 2 The corrosion resistance of Examples 1, 5, 6, and 8 to 15 was such that the pinhole density was 3.0 / cm 2 It was even better than the super example. [Explanation of symbols]

[0093] 1. Surface-treated steel sheets 11 Base steel plate 12 Ni-containing layer 13 Ni-W alloy layer 14 Fe diffusion alloy layer P Pinhole

Claims

1. A base steel plate; A Ni-containing layer disposed on a surface of the base steel sheet; A Ni-W alloy layer disposed on a surface of the Ni-containing layer; Equipped with The Ni-containing layer has an Fe diffusion alloy layer, The density of pinholes on the surface of the Ni-W alloy layer is 4.0 pinholes / cm ２ is less than or equal to Surface treated steel sheet.

2. The average W concentration in the Ni--W alloy layer is 10 to 45 mass %. The surface-treated steel sheet according to claim 1 .

3. The amount of Ni contained in the Ni-containing layer and the Ni-W alloy layer is 1.8 to 35.6 g / m ２ is The surface-treated steel sheet according to claim 1 or 2.

4. The thickness of the Fe diffusion alloy layer is 0.1 to 3.0 μm. The surface-treated steel sheet according to claim 1 or 2.

5. The thickness of the Ni-containing layer is 0.2 to 4.0 μm. The surface-treated steel sheet according to claim 1 or 2.

6. The number density of the pinholes on the surface of the Ni—W alloy layer is 3.0 pinholes / cm ２ is less than or equal to The surface-treated steel sheet according to claim 1 or 2.

7. Only a portion of the Ni-containing layer is the Fe diffusion alloy layer. The surface-treated steel sheet according to claim 1 or 2.

8. The entire Ni-containing layer is the Fe diffusion alloy layer, and a part of the Ni-W alloy layer is the Fe diffusion alloy layer. The surface-treated steel sheet according to claim 1 or 2.

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