Surface-treated steel sheet

Abstract

A surface-treated steel sheet according to one embodiment of the present invention is provided with a base steel sheet, an Ni-containing layer disposed on the surface of the base steel sheet, and an Ni-W alloy layer disposed on the surface of the Ni-containing layer, the Ni-containing layer having an Fe-diffused alloy layer, and the number density of pinholes in the surface of the Ni-W alloy layer being 4.0 / cm2 or less. It is preferable that the average W concentration in the Ni-W alloy layer is 10-45 mass%. It is preferable that the adhesion amount of Ni contained in the Ni-containing layer and the Ni-W alloy layer is 1.8-35.6 g / m2.

Description

Technical Field

[0001] The present invention relates to a surface-treated steel plate.

[0002] This application claims priority based on Japanese Patent Application No. 2023-016704 filed in Japan on February 7, 2023, the contents of which are incorporated herein by reference. Background Art

[0003] Conventionally, nickel-plated steel sheets have been used as surface-treated steel sheets for battery cans. Due to the excellent chemical stability of nickel, nickel-plated steel sheets are used in various battery containers, such as alkaline manganese dry batteries, lithium-ion batteries, and nickel-metal hydride batteries.

[0004] In recent years, Ni-W alloy-plated steel sheets mainly composed of an alloy of Ni and W have also begun to be used as materials for battery cans, etc. Examples of Ni-W alloy-plated steel sheets are described in Patent Documents 1 to 4.

[0005] Patent Document 1 discloses a plated steel sheet for a battery container, characterized in that an iron-nickel alloy layer, a nickel layer, and a nickel-tungsten alloy layer are formed in this order from the bottom on the steel sheet on the side of the steel sheet that becomes the inner surface of the battery container.

[0006] Patent Document 2 discloses a surface-treated steel sheet, which is a Ni-containing surface-treated steel sheet for containers formed by press forming, comprising: a steel sheet having a first surface that becomes the outer side of the container after the press forming; 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 Above and 89g / m 2 the thickness of the Ni-W alloy plating layer is 0.02 μm or more and 2 μm or less; the W concentration in the Ni-W alloy plating layer is 10% or more and 65% or less by mass%.

[0007] Patent Document 3 discloses a steel plate for a non-aqueous electrolyte secondary battery case, comprising a steel plate and a Ni—W—Fe alloy plating layer formed on the surface of the steel plate. The Ni—W—Fe alloy plating layer contains a Ni—W—Fe alloy and serves as the inner surface of the non-aqueous electrolyte secondary battery case.

[0008] Patent document 4 discloses a steel plate for alkaline battery cans, which is used for battery cans of inside-out alkaline batteries. It is characterized in that a surface layer of one main surface of a substrate comprising a plate-shaped steel material has a plating layer selected from nickel-tungsten (Ni-W) and nickel-cobalt-tungsten (Ni-Co-W) alloys, and the above-mentioned plating layer has unevenness on the surface formed by the dissolution of the above-mentioned tungsten.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-51325

[0012] Patent Document 2: International Publication No. 2012 / 137823

[0013] Patent Document 3: International Publication No. 2017 / 006834

[0014] Patent Document 4: Japanese Patent Application Laid-Open No. 2020-155202 Summary of the Invention

[0015] Problems to be solved by the invention

[0016] Surface-treated steel sheets for battery cans are required to exhibit low contact resistance, high discharge characteristics, resistance to metal leaching, and good workability. Furthermore, the recent expansion of battery applications has necessitated corrosion resistance in these sheets. However, prior art has yet to fully investigate the corrosion resistance of surface-treated steel sheets primarily composed of Ni-W-Fe alloys.

[0017] Patent Document 1 aims to suppress contact resistance and improve discharge characteristics, but does not particularly investigate the corrosion resistance of the plated steel sheet.

[0018] Patent Document 2 addresses the issue of improving corrosion resistance after press forming. In the steel plate disclosed in Patent Document 2, an Fe-Ni diffusion alloy layer is used to prevent cracks generated during press forming from propagating to the base steel plate, thereby improving the corrosion resistance of the processed portion. However, Patent Document 2 does not specifically address the corrosion resistance of areas other than the processed portion of the plated steel plate.

[0019] Patent Document 3 aims to suppress degradation of battery performance and case corrosion caused by metal elution when the battery case potential rises. However, Patent Document 3 does not specifically examine corrosion resistance in corrosive environments, such as by evaluating red rust generation rates.

[0020] Patent Document 4 aims to improve the high-load discharge performance and long-term storage performance of steel sheets, but does not particularly investigate the corrosion resistance of the steel sheets.

[0021] In view of the above circumstances, an object of the present invention is to provide a surface-treated steel sheet having high corrosion resistance.

[0022] Means for solving problems

[0023] The gist of the present invention is as follows.

[0024] (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 a surface of the Ni-containing layer, wherein the Ni-containing layer has an Fe diffusion alloy layer, and the number density of pinholes (also referred to as pores) in the surface of the Ni—W alloy layer is 4.0 pinholes / cm 2 the following.

[0025] (2) In the surface-treated steel sheet described in (1) above, it is preferred that the average W concentration in the Ni—W alloy layer is 10 to 45% by mass.

[0026] (3) Preferably, in the surface-treated steel sheet described in (1) or (2), 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 .

[0027] (4) In the surface-treated steel sheet according to any one of (1) to (3) above, preferably, the Fe diffusion alloy layer has a thickness of 0.1 to 3.0 μm.

[0028] (5) In the surface-treated steel sheet according to any one of (1) to (4), the Ni-containing layer preferably has a thickness of 0.2 to 4.0 μm.

[0029] (6) Preferably, in the surface-treated steel sheet described in any one of (1) to (5), the number density of the pinholes in the surface of the Ni-W alloy layer is 3.0 pinholes / cm 2 the following.

[0030] (7) In the surface-treated steel sheet according to any one of (1) to (6), preferably, only a portion of the Ni-containing layer is the Fe-diffused alloy layer.

[0031] (8) Preferably, in the surface-treated steel sheet described in any one of (1) to (6), the entire Ni-containing layer is the Fe-diffused alloy layer, and a portion of the Ni—W alloy layer is the Fe-diffused alloy layer.

[0032] Effects of the Invention

[0033] According to the present invention, a surface-treated steel sheet having high corrosion resistance can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic cross-sectional view of an example of a surface-treated steel sheet according to the present embodiment.

[0035] Figure 2This is a schematic cross-sectional view of another example of the surface-treated steel sheet according to the present embodiment.

[0036] Figure 3 This is a flowchart illustrating an example of a method for producing a surface-treated steel sheet according to the present embodiment. DETAILED DESCRIPTION

[0037] (1. Surface treated steel plate 1)

[0038] like Figure 1 or Figure 2 As shown, 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 the 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 includes an Fe diffusion alloy layer 14. The number density of pinholes P on the surface of the Ni-W alloy layer 13 is 4.0 pinholes / cm. 2 the following.

[0039] Hereinafter, the surface-treated steel sheet 1 of the present embodiment will be described in detail. In addition, the entire plating layer including the Ni-containing layer 12 and the Ni—W alloy layer 13 may be simply referred to as a “plating layer”.

[0040] (Base steel plate 11)

[0041] The surface-treated steel plate 1 includes a base steel plate 11. The base steel plate 11 is a steel plate serving as the base material of the surface-treated steel plate 1. The composition, thickness, and metal structure of the base steel plate 11 are not particularly limited and can be appropriately selected depending on the intended use of the surface-treated steel plate 1.

[0042] (Ni-containing layer 12)

[0043] The surface-treated steel sheet 1 includes 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 of the base steel sheet 11 or on both surfaces. The Ni-containing layer 12 has the effect of improving the corrosion resistance of the processed portion.

[0044] (Ni-W alloy layer 13)

[0045] The surface-treated steel sheet 1 further includes 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 composed primarily of Ni and further containing W. The Ni-W alloy plating is harder than Ni. By analyzing the compositional distribution of the plating layer using glow discharge emission spectroscopy, an analytical method capable of measuring the depth-wise distribution of chemical components, it is possible to distinguish between the Ni-W alloy layer 13, which has a high W concentration, and the Ni-containing layer 12, which has a low W concentration.

[0046] The Ni—W alloy layer 13 may be provided on only one surface or on both surfaces of the base steel plate 11. A surface treatment layer such as a coating film may be further provided on the surface of the Ni—W alloy layer 13.

[0047] (Fe diffusion alloy layer 14)

[0048] At least a portion of the Ni-containing layer 12 is an Fe-diffused alloy layer 14. That is, the Ni-containing layer 12 includes the Fe-diffused alloy layer 14. The Fe-diffused alloy layer 14 refers to an alloy layer 13 formed by diffusion of Fe from the base steel sheet 11 into the interior of the plated 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.

[0049] exist Figure 1 In the schematic cross-sectional view shown, only a portion of the Ni-containing layer 12 is the Fe diffusion alloy layer 14 in contact with the base steel plate 11. Figure 2 As shown in the example, the entire Ni-containing layer 12 may be formed as the Fe diffusion alloy layer 14. Figure 2 As shown in the example, the Fe diffusion alloy layer 14 may also reach the Ni-W alloy layer 13. That is, the Ni-W alloy layer 13 may also have an Fe diffusion alloy layer 14. Only a portion 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. Generally, 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 partially diffusion-plated steel sheets. In addition, a surface-treated steel sheet in which both the Ni-containing layer 12 and the Ni-W alloy layer 13 are entirely the Fe diffusion alloy layer 14 is referred to as a fully diffusion-plated steel sheet.

[0050] (Number density of pinholes P)

[0051] Pinholes P may form in the plating layer. Pinholes P are tiny holes that penetrate from the surface of the plating layer to the base steel plate 11. Pinholes P expose the base steel plate 11 to a corrosive environment, accelerating corrosion of the base steel plate 11. While pits, which are holes that do not penetrate the plating layer, may form on the surface of the plating layer, in the surface-treated steel sheet 1 of this embodiment, pits and pinholes P are distinguished.

[0052] The number density of pinholes P can be determined by a porosity test (ferroxyl test) performed under specific conditions. In the porosity test, first, a filter paper infiltrated with a test solution for corroding the base steel plate 11 is attached to the surface of the coating for a predetermined time. Next, the number of spots of iron complex ions attached to the filter paper is counted. In areas where spots are generated, pinholes P are considered to exist, and the number of spots is considered to be the number of pinholes P. In addition, the porosity test does not detect pits. The detailed conditions of the porosity test will be described later.

[0053] In the surface-treated steel sheet 1 of the present embodiment, the number density of pinholes P on the surface of the Ni—W alloy layer 13 is 4.0 pinholes / cm 2 The number of pinholes P can be 3.8 / cm 2 Below, 3.5 pieces / mm 2 Less than or 3.0 / cm 2 The smaller the number of pinholes P, the better. Therefore, the number density of pinholes P can be 0 / cm 2 However, the number density of pinholes P can also exceed 0 / cm 2 , 1.0 / cm 2 Above, 1.5 / cm 2 Above or 2.0 / cm 2 above.

[0054] (Effect: Improves corrosion resistance by suppressing pinholes P)

[0055] The present inventors have discovered that the heat treatment, or alloying treatment, to form the Fe diffusion alloy layer 14 reduces the corrosion resistance of areas other than the processed portion. The present inventors have discovered that alloying treatment increases the number density of pinholes P, and that there is a close correlation between the number density of pinholes P and corrosion resistance. The higher the number density of pinholes P, the more the corrosion resistance deteriorates. Pinholes P have the effect of exposing the base steel plate 11 to a corrosive environment.

[0056] However, the present inventors were able to reduce the number density of pinholes P to 4.0 pinholes / cm by optimizing the manufacturing conditions, specifically optimizing the plating conditions before annealing. 2 By making the number density of pinholes P 4.0 / cm 2 Next, the corrosion resistance of the non-bending region of the surface-treated steel sheet 1 can be improved to a level close to that of the surface-treated steel sheet 1 before the alloying treatment.

[0057] As described above, in the surface-treated steel sheet 1 of this embodiment, the Ni-containing layer 12 is used to improve the corrosion resistance of the processed portion. Furthermore, in the surface-treated steel sheet 1 of this embodiment, the number density of pinholes P is reduced, thereby suppressing the reduction in corrosion resistance of the flat portion caused by the alloying treatment. As a result, the surface-treated steel sheet 1 of this embodiment has extremely excellent corrosion resistance.

[0058] The most basic embodiment of the surface-treated steel sheet 1 according to the present embodiment has been described above. Next, a more preferred embodiment of the surface-treated steel sheet 1 according to the present embodiment will be described.

[0059] (Average W Concentration in Ni—W Alloy Layer 13)

[0060] The Ni-W alloy layer 13 contains Ni as a main component and further contains W. "Containing Ni as a main component" means that the Ni concentration is 50 mass % or higher. The average W concentration in the Ni-W alloy layer 13 is not particularly limited and can be, for example, within a range of 10 to 45 mass %.

[0061] W has the effect of suppressing the formation 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 set to 15% by mass or greater, 20% by mass or greater, 25% by mass or greater, or 30% by mass or greater. The average W concentration in the Ni-W alloy layer 13 may also be set to 43% by mass or less, 42% by mass or less, 41% by mass or less, or 40% by mass or less. The Ni-W alloy layer 13 may contain, for example, Cr and Mo.

[0062] (Ni adhesion amount)

[0063] 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, and can be, for example, 1.8 to 35.6 g / m 2 By making the Ni adhesion amount 1.8g / m 2 As described above, the corrosion resistance of the surface treated steel sheet 1 can be further improved. By setting the Ni deposition amount to 35.6 g / m 2 The following can reduce the manufacturing cost of the surface-treated steel sheet 1. The Ni deposition amount can be 4.5 g / m 2 Above, 6.2g / m 2 Above or 8.9g / m 2 The Ni adhesion amount can be 26.7g / m 2 Below, 17.8g / m 2 Below or 13.4g / m 2 the following.

[0064] The thickness of the plating layer (ie, 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 a range of 0.2 μm to 4.0 μm.

[0065] (Thickness of Fe Diffusion Alloy Layer 14)

[0066] The thickness of the Fe diffusion alloy layer 14 is not particularly limited. Even with a small thickness, the Fe diffusion alloy layer 14 can improve the processability of the surface-treated steel plate 1 and improve the corrosion resistance of the processed portion. On the other hand, the thickness of the Fe diffusion alloy layer 14 can also be set to, for example, 0.1 μm or more. In this way, the processability of the surface-treated steel plate 1 can be further improved. The thickness of the Fe diffusion alloy layer 14 can be greater than 0.2 μm, greater than 0.3 μm or greater than 0.5 μm. The upper limit of the thickness of the Fe diffusion alloy layer 14 is not particularly specified. For example, the entire plating layer can be the Fe diffusion alloy layer 14. On the other hand, the Fe diffusion alloy layer 14 can also be less than 3.0 μm, less than 2.5 μm or less than 2.0 μm.

[0067] (Thickness of Ni-Containing Layer 12)

[0068] The thickness of the Ni-containing layer 12 is not particularly limited. Even with a small thickness, the Ni-containing layer 12 can improve the processability of the surface-treated steel plate 1 and improve the corrosion resistance of the processed portion. On the other hand, the thickness of the Ni-containing layer 12 can be set to, for example, 0.2 μm or more. In this way, the processability of the surface-treated steel plate 1 can be further improved. The thickness of the Ni-containing layer 12 can be greater than 0.5 μm, greater than 1.0 μm, or greater than 1.5 μm. The upper limit of the thickness of the Ni-containing layer 12 is not particularly specified. For example, the thickness of the Ni-containing layer 12 can be less than 4.0 μm, less than 3.5 μm, or less than 3.0 μm.

[0069] (Composition of Ni-Containing Layer 12)

[0070] The Ni-containing layer 12 is a layer mainly composed of Ni and Fe diffused from the parent steel plate 11. For example, the total content of Ni and Fe in the Ni-containing layer 12 can be 98.0% by mass or more, 98.5% by mass or more, or 99.0% by mass or more. The total content of Ni and Fe in the Ni-containing layer 12 can be 100% by mass or less, 99.5% by mass or less, or 99.0% by mass or less. It should be noted that the ratio of Ni and Fe in the Ni-containing layer 12 is different in the thickness direction of the Ni-containing layer 12 (the thickness direction of the surface-treated steel plate 1). This is because, as mentioned above, part or all of the Ni-containing layer 12 is the Fe diffusion alloy layer 14, and in the Fe diffusion alloy layer 14, the diffusion amount of Fe from the parent steel plate 11 is different in the thickness direction of the Fe diffusion alloy layer 14. In the Fe diffusion alloy layer 14, the closer to the parent steel plate 11, the greater the Fe content. In addition, the thickness of the Fe diffusion alloy layer 14 can be appropriately selected.

[0071] The Ni-containing layer 12 may also contain elements other than Ni and Fe. The Ni-containing layer 12 may also contain, for example, Cr and Mo. It is also possible that, for example, the Ni-containing layer 12 contains one or both of Cr and Mo, and the total content of Cr and Mo exceeds 0 mass% and is 0.1 mass% or less. In addition, the various alloying elements contained in the base steel plate 11 sometimes diffuse and invade into the Ni-containing layer 12 during the alloying treatment. Therefore, the Ni-containing layer 12 may contain various impurity elements. In addition, W sometimes diffuses and invades from the Ni-W alloy layer 13 into the Ni-containing layer 12. However, the W content of the Ni-containing layer 12 is generally less than 1.0%.

[0072] (Composition and Thickness of Ni-W Alloy Layer 13)

[0073] As described above, the Ni-W alloy layer 13 contains Ni as a main component and also contains W. Figure 2As illustrated, when a portion or all of the Ni-W alloy layer 13 is an Fe diffusion alloy layer 14, the Ni-W alloy layer 13 may further contain Fe. When the Ni-W alloy layer 13 does not include 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 include 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 includes 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 includes the Fe diffusion 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.

[0074] Similar to the Ni-containing layer 12, the Ni-W alloy layer 13 may also contain elements other than Ni and W. The Ni-W alloy layer 13 may contain, for example, Cr and Mo. For example, the Ni-W alloy layer 13 may contain one or both of Co and Mo, with the combined content of Co and Mo exceeding 0% by mass and not exceeding 5% by mass. Furthermore, the Ni-W alloy layer 13 may contain the aforementioned Fe and various other impurity elements.

[0075] The thickness of the Ni-W alloy layer 13 is not particularly limited. Even with a small thickness, the Ni-W alloy layer 13 improves the corrosion resistance of the surface-treated steel plate 1. In addition, from the perspective of further improving the processability of the Ni-W alloy layer 13, a smaller thickness of the Ni-W alloy layer 13 is advantageous. On the other hand, from the perspective of further improving the corrosion resistance of the Ni-W alloy layer 13, a larger thickness of the Ni-W alloy layer 13 is advantageous. Therefore, the thickness of the Ni-W alloy layer 13 can be, for example, 0.01 μm or more. In this way, the corrosion resistance of the surface-treated steel plate 1 can be further improved. The thickness of the Ni-W alloy layer 13 can 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 can be 2.0 μm or less, 1.5 μm or less, or 1.0 μm or less.

[0076] (Type of base steel plate 11, etc.)

[0077] The composition and metal structure of the base steel plate 11 are not particularly limited. The composition and metal structure of the base steel plate 11 can be appropriately selected according to the intended use of the surface-treated steel plate 1. For example, the chemical composition of the base steel plate 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.

[0078] When the surface treated steel sheet 1 is used as a material for a battery container, the base steel sheet 11 is preferably low carbon aluminum killed steel or IF steel (Interstitial Free Steel). Specific examples of the chemical composition (unit: mass %) of the base steel sheet 11 are as follows.

[0079] (Example 1) Low carbon aluminum killed steel:

[0080] 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: includes iron and impurities.

[0081] (Example 2) IF steel:

[0082] 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: includes iron and impurities.

[0083] (Example 3) IF steel:

[0084] 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, and the remainder includes iron and impurities.

[0085] There is no particular limitation on the thickness of the base steel plate 11. When the surface-treated steel plate 1 is used as a material for a battery container, for example, the thickness of the base steel plate 11 is preferably 0.15 to 2.00 mm, for example.

[0086] (Measurement method)

[0087] The method for measuring the number density of pinholes P includes the following steps: collecting a test piece from the surface-treated steel plate 1; attaching filter paper soaked in a test solution to the test surface of the test piece; peeling the filter paper from the test surface and washing it with water; and counting the number of spots attached to the filter paper. The test solution is prepared by dissolving 10 g / L of potassium hexacyanoferrate(II) trihydrate (potassium ferrocyanide), 10 g / L of potassium hexacyanoferrate(III) (potassium ferrocyanide), and 60 g / L of sodium chloride in pure water. This measurement method complies with Appendix 3 (Regulations) "Porosity Test Methods" of JIS H 8617:1999.

[0088] The method for determining the average W concentration in the Ni-W alloy layer 13 is as follows. The measurement is performed using XPS (X-ray Photoelectron Spectroscopy). First, the surface of the surface-treated steel plate 1 is sputtered using argon and / or xenon. Next, the composition of the Ni-W alloy layer 13 is measured from the surface of the Ni-W alloy layer 13 of the surface-treated steel plate 1 to the inside. After the measurement is completed, sputtering is performed again, and then measurement is performed, and this cycle is repeated. In a graph with depth as the horizontal axis and W concentration as the vertical axis, the analysis results of W concentration along the depth direction are plotted. Then, the value obtained by integrating the W concentration graph is divided by the width of the interval (i.e., the thickness of the Ni-W alloy layer 13) to obtain the average W concentration. By also applying the above-mentioned calculations performed on the W concentration to the Ni and Fe analysis results, the average Ni concentration and the average Fe concentration in the Ni-W alloy layer 13 can be calculated. It should be noted that the composition determination of the coating using XPS is implemented by using a Mg ray source. In the analysis using the Mg radiation source, there are no Auger peaks that overlap with the photoelectron peaks of Ni, W, and Fe. Peaks corresponding to the 2p orbital of Fe, the 2p orbital of Ni, and the 4f orbital of W are observed.

[0089] The amount of Ni deposited is determined by ICP optical emission spectrometry (ICP-OES). First, a predetermined area of the coating is dissolved with acid. Next, the total Ni content in the solution is quantitatively analyzed using ICP-OES. The total Ni content determined by ICP-OES is divided by the predetermined area to determine the amount of Ni deposited per unit area.

[0090] 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 measuring the depth distribution of element concentration using GDS, an element concentration profile can be obtained.

[0091] A high-frequency glow discharge emission surface analyzer (manufactured by Horiba, Ltd., model: GD-Profiler 2) was used for the measurement. The GDS measurement conditions are as follows.

[0092] Anode diameter: φ4mm

[0093] Gas: Ar

[0094] Gas pressure: 600Pa

[0095] Output: 35W

[0096] In the surface-treated steel sheet 1 of this embodiment, a region containing an Fe concentration of 5.0 mass% or greater in the coating layer is considered to be the Fe diffusion alloy layer 14. When component analysis is performed continuously along the depth direction from the surface of the coating layer, the Fe concentration increases as it approaches the base steel sheet 11. A region having an Fe concentration of 5.0 mass%, as determined by continuous component analysis along the depth direction from the surface of the coating layer, is considered to be the interface between the Fe diffusion alloy layer 14 and the coating layer other than the Fe diffusion alloy layer 14.

[0097] In the surface-treated steel sheet 1 of this embodiment, the region having a Ni concentration of 1.0% by mass or greater is considered the plating layer, and the remaining region is considered the base steel sheet 11. In the plating layer of the surface-treated steel sheet 1 manufactured by alloying, the Ni concentration decreases as it approaches the base steel sheet 11. The region where the Ni concentration reaches 1.0% by mass, as determined by continuous component analysis from the surface of the plating layer in the depth direction, is considered 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).

[0098] The distance between these interfaces is regarded as the thickness of the Fe diffusion alloy layer 14 in the sample obtained by the above steps. This measurement is performed on 5 samples, and the average value is calculated. This average value is regarded as the thickness of the Fe diffusion alloy layer 14 of the surface-treated steel sheet 1.

[0099] In the surface-treated steel sheet 1 of the present 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 portion where the W concentration is 1.0 mass %, as determined by continuous component analysis along the depth direction from the surface of the plating layer, is regarded as the interface between the Ni—W alloy layer 13 and the Ni-containing layer 12.

[0100] The distance from the interface between the Ni-W alloy layer 13 and the Ni-containing layer 12 to the interface between the coating and the base steel plate 11 is regarded as the thickness of the Ni-containing layer 12 in the sample obtained by the above steps. This measurement is performed on 5 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 plate 1. In addition, the distance from the surface of the coating 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 steps. This measurement is performed on 5 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 plate 1.

[0101] (2. Method for manufacturing surface-treated steel sheet)

[0102] Next, a method for producing a surface-treated steel sheet according to the present embodiment will be described. For example, the production method according to the present embodiment can appropriately produce the surface-treated steel sheet 1 having the above-mentioned components.

[0103] like Figure 3 As illustrated, the method for producing a surface-treated steel sheet according to another embodiment of the present invention includes the following steps:

[0104] (S1) a step of electroplating the base steel plate 11 with Ni;

[0105] (S2) a step of electroplating the base steel plate 11 with a Ni-W alloy; and

[0106] (S3) a step of annealing the base steel plate 11 having the Ni plating layer and the Ni-W alloy layer 13 disposed thereon,

[0107] The current condition during Ni electroplating was set to 1.0 to 5.0 A / dm 2 , the current condition in the Ni-W alloy electroplating is set to 1.0~5.0A / dm 2 .

[0108] (S1 Ni plating)

[0109] First, the base steel plate 11 is electroplated with Ni. The plated base material is the same as the base steel plate 11 of the surface treated steel plate 1 of the present embodiment described above. Figure 3 As shown, a Ni-containing layer 12 is provided on the surface of a base steel plate 11. Hereinafter, a steel plate obtained by Ni electroplating is referred to as a Ni-plated steel plate.

[0110] (S2 electroplating Ni-W alloy)

[0111] Next, the Ni-plated steel sheet is electroplated with Ni-W alloy. Figure 3As shown, a Ni-W alloy layer 13 is provided on the surface of the Ni-plated steel sheet. Hereinafter, a plated steel sheet obtained by electroplating Ni-W alloy is referred to as a multilayer plated steel sheet.

[0112] (S3 annealing)

[0113] Next, the multi-layer plated steel sheet (i.e., the base steel sheet 11 having the Ni plated layer and the Ni-W alloy layer 13 disposed thereon) is annealed. Figure 3 As shown, Fe in the base steel sheet 11 is diffused into a portion of the plating layer to form an Fe diffusion alloy layer 14. Thus, a surface-treated steel sheet 1 is obtained, comprising: a base steel sheet 11; a Ni-containing layer 12 disposed on the surface of the base steel sheet 11; and a Ni—W alloy layer 13 disposed on the surface of the Ni-containing layer 12, wherein the Ni-containing layer 12 has the Fe diffusion alloy layer 14.

[0114] In the Ni electroplating of (S1), the current density needs to be within a range lower than usual. It is generally believed that the current density in the Ni electroplating does not affect the characteristics of the Ni plating layer much. Therefore, unless there are special circumstances, the current density in the Ni electroplating or multilayer plating including Ni electroplating is usually set to a current density lower than 5.0 A / dm 2 A high value is obtained, thereby improving manufacturing efficiency. For example, in "Electrochemistry for Surface Technicians" by Shiro Haruyama, 2nd edition, Maruzen Publishing, Japan, 2005, p173, there is a description that the current density of the plating is preferably as large as possible. The document explains that: the higher the current density of the plating, (1) the shorter the plating time, (2) the base metal can be plated with a high current efficiency due to the increase in hydrogen overvoltage, and (3) a dense, high-strength plating film is obtained by the miniaturization of the grains accompanying the increase in overvoltage. However, in the method for manufacturing the surface-treated steel sheet of this embodiment, it is necessary to set the power-on condition in the electroplating Ni to 1.0 to 5.0 A / dm 2 .

[0115] Furthermore, in the Ni-W alloy electroplating of (S2), the current density must also be within a predetermined range. Specifically, the current flow conditions in the Ni-W alloy electroplating are set to 1.0 to 5.0 A / dm 2 .

[0116] By setting the current density in the Ni electroplating and Ni-W alloy electroplating within the above range, the number density of pinholes P on the surface of the Ni-W alloy layer 13 can be set to 4.0 pinholes / cm 2 the following.

[0117] The present inventors speculate as to why the number density of pinholes P can be reduced by keeping the electroplating conditions within the above range. During electroplating, the metal ions contained in the plating bath are deposited on the surface of the substrate, and the hydrogen ions contained in the plating bath are converted into hydrogen gas on the surface of the substrate. As a result, hydrogen gas is taken into the plating layer. This hydrogen gas forms pinholes P during annealing. It is believed that the greater the current density, the greater the amount of hydrogen gas taken in. Therefore, if the current density in the electroplating of Ni or the electroplating of Ni-W alloy is higher than 5.0A / dm 2 , the amount of hydrogen taken into the electroplating layer is excessive, and the number density of pinholes P cannot be reduced to 4.0 / cm 2 However, if the current density in Ni electroplating or Ni-W alloy electroplating is set to 5.0A / dm 2 Below, the amount of hydrogen 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 pinholes / cm 2 the following.

[0118] According to the experimental results of the present inventors, the lower the current density in the Ni electroplating and Ni-W alloy electroplating, the smaller the number density of pinholes P. For example, by setting the current density in the Ni electroplating to 2.0 A / dm 2 Hereinafter, the current density in the Ni-W alloy electroplating is set to 2.0 A / dm 2 Below, the number density of pinholes P is 3.0 / cm 2 The following surface treated steel plates.

[0119] In addition, it is believed that if the amount of current in the Ni electroplating or Ni-W alloy electroplating is insufficient, the productivity will deteriorate. Therefore, the current density in the Ni electroplating or Ni-W alloy electroplating is 1.0 A / dm 2 above.

[0120] 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.

[0121] (bath ingredients)

[0122] The Ni plating bath used in Ni electroplating contains Ni as its main component. For example, the proportion of Ni contained in the plating bath to the total metal elements contained in the plating bath can be 95% by mass or more, 96% by mass or more, or 97% by mass or more. In addition to Ni, the Ni plating bath may also contain Cr, Mo, etc.

[0123] The Ni-W plating bath used in Ni-W alloy electroplating contains Ni and W as its main components. For example, the proportion of W contained in the plating bath to the total metal elements contained in the plating bath can be in the range of 10-90 mass%. Furthermore, for example, the total proportion of Ni and W contained in the plating bath to the total metal elements contained in the plating bath can 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 also contain Cr and Mo.

[0124] (Adhesion amount)

[0125] In the case of Ni electroplating and Ni-W alloy electroplating, the amount of Ni deposited is not particularly limited, and may be, 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 can be adjusted to 1.8 to 35.6 g / m 2 The more preferable Ni deposition amount may be the same as the more preferable Ni deposition amount in the surface-treated steel sheet 1 of the present embodiment described above. The Ni deposition amount can be controlled by the composition of the plating bath and the amount of current flow.

[0126] (Annealing conditions)

[0127] The annealing conditions are not particularly limited. For example, the annealing temperature during annealing can be set to 630 to 860°C, and the annealing time can be set to 10 to 180 seconds. The higher the annealing temperature, the thicker the Fe diffusion alloy layer 14. In addition, the longer the annealing time, the thicker the Fe diffusion alloy layer 14. As described above, at least a portion of the Ni-containing layer 12 can be set as the Fe diffusion alloy layer 14. The entire Ni-containing layer 12 can be set as the Fe diffusion alloy layer 14, and further, a portion or the entire Ni-W alloy layer 13 can be set as the Fe diffusion alloy layer 14. The annealing time and annealing temperature can be appropriately adjusted according to the use of the surface-treated steel sheet 1.

[0128] The thickness ratio between the Ni-containing layer 12 and the Ni-W alloy layer 13 before annealing is not particularly limited. A thicker Ni-containing layer 12 is more advantageous from the perspective of further improving workability. On the other hand, a thicker Ni-W alloy layer 13 is more advantageous for further reducing the number density of pinholes P. The thickness ratio can be appropriately selected depending on the application of the surface-treated steel sheet 1.

[0129] Furthermore, the various embodiments described with respect to the surface-treated steel sheet 1 of this embodiment can be applied to the method for manufacturing the surface-treated steel sheet of this embodiment. For example, the preferred embodiment of the base steel sheet 11 in the surface-treated steel sheet 1 of this embodiment can naturally be applied to the method for manufacturing the surface-treated steel sheet of this embodiment.

[0130] Example

[0131] The effects of one embodiment of the present invention will be described in more detail using examples. However, the conditions in the examples are merely examples of conditions employed to confirm the feasibility and effects of the present invention. The present invention is not limited to this single example of conditions. Various conditions can be employed in the present invention as long as they achieve the objectives of the present invention without departing from the main purpose of the present invention.

[0132] The base steel sheets were subjected to Ni electroplating, Ni-W alloy electroplating, and annealing to produce various surface-treated steel sheets. The composition of the base steel sheets is shown in Table 1. The composition of the Ni-W alloy electroplating bath is shown in Table 2. The manufacturing conditions for the surface-treated steel sheets are shown in Table 3. The evaluation results of the surface-treated steel sheets are shown in Table 4. Conditions not listed in the tables are the same for all examples and are described below.

[0133] The composition of the Ni electroplating bath was 240 g / L NiSO₄·6H₂O, 70 g / L NiCl₂·6H₂O, and 45 g / L H₃BO₃. The pH of the Ni electroplating bath was set to 4, and the temperature was set to 50°C. The amount of plating deposited during Ni electroplating was controlled by the duration of the current flow.

[0134] In the electroplating of Ni-W alloy, the Ni ion source is set to NiSO4·6H2O, and the W ion source is set to Na2WO4·2H2O. The composition of the Ni-W alloy plating layer (W content) is adjusted by changing the ratio of the Ni ion concentration to the W ion concentration. In addition, in order to stabilize the W ions in the bath, 0.5 mol / L of citric acid is added to the plating bath for electroplating Ni-W alloy. The pH of the plating bath for electroplating Ni-W alloy is set to 6 and the temperature is set to 50°C. The plating adhesion in the electroplating Ni-W alloy is controlled by the power-on time.

[0135] The number density of pinholes was measured by the porosity test method described above. The measurement results are shown in Table 5.

[0136] The average W concentration in the Ni—W alloy layer was measured by the above-mentioned XPS method. The measurement results are shown in Table 5.

[0137] The total amount of Ni deposited was measured by the above-mentioned ICP emission spectrometry. The measurement results are shown in Table 5.

[0138] The thickness of the Ni-containing layer and the thickness of the Fe-diffusion alloy layer were measured by the above-mentioned GDS method. The measurement results are shown in Table 5.

[0139] Corrosion resistance was evaluated using the salt spray test (SST) in accordance with JIS Z 2371:2015. Test specimens were 50 x 100 mm, and the ends were sealed with polyester tape. The temperature within the test chamber was maintained at 35 ± 1°C, and the spray was conducted using salt water, prepared by dissolving sodium chloride in deionized water to a concentration of 50 g / L. Four hours after the start of the test, the area percentage of red rust on each specimen was measured and evaluated according to the following criteria.

[0140] Test pieces with a red rust area ratio of 10% or more: 3

[0141] Test pieces with a red rust area ratio of 5% or more and less than 10%: 2

[0142] Test piece with red rust area ratio less than 5%: 1

[0143] Table 1

[0144]

[0145] Table 2

[0146]

[0147] Table 3

[0148]

[0149] Table 4

[0150]

[0151] The number density of pinholes in the test pieces of Examples 2 and 3 was excessive. The corrosion resistance of these test pieces was "3," indicating poor corrosion resistance. It should be noted that in the production of Example 2, the amount of current applied to the Ni plating was excessive. In the production of Example 3, the amount of current applied to the Ni-W plating was excessive. In other words, in Examples 2 and 3, due to inappropriate manufacturing conditions, it is presumed that numerous pinholes formed in the plating layer.

[0152] On the other hand, in the test pieces obtained by the appropriate manufacturing method, the generation of pinholes was suppressed. These test pieces had good corrosion resistance. In addition, when the current density in the Ni electroplating was set to 2.0 A / dm 2 Below, and the current density in the Ni-W alloy electroplating is set to 2.0A / dm 2 In the following examples 1, 5, 6, 8 to 15, the pinhole density is 3.0 pinholes / cm 2 The corrosion resistance and pinhole density of Examples 1, 5, 6, 8 to 15 are more than 3.0 / cm 2 The example is better than the one above.

[0153] Description of Reference Numerals

[0154] 1: Surface treated steel plate

[0155] 11: Base steel plate

[0156] 12: Ni-containing layer

[0157] 13: Ni-W alloy layer

[0158] 14: Fe diffusion alloy layer

[0159] P: Pinhole

Claims

1. A surface-treated steel plate comprising: Base steel plate, a Ni-containing layer disposed on the surface of the base steel plate, and a Ni-W alloy layer disposed on the surface of the Ni-containing layer, in, The Ni-containing layer has an Fe diffusion alloy layer, The number density of pinholes in the surface of the Ni-W alloy layer is 4.0 pinholes / cm 2 the following.

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

3. The surface-treated steel sheet according to claim 1 or 2, characterized in that: The Ni-containing layer and the Ni-W alloy layer contain Ni in an amount of 1.8 to 35.6 g / m 2 .

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

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

6. The surface-treated steel sheet according to claim 1 or 2, characterized in that: The number density of the pinholes in the surface of the Ni-W alloy layer is 3.0 pinholes / cm 2 the following.

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

8. The surface-treated steel sheet according to claim 1 or 2, characterized in that: 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.

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