Ni-plated surface-treated steel sheet and battery container

Abstract

Provided is an Ni-plated surface-treated steel sheet comprising a steel sheet and an Fe-Ni-Cu-Cr layer formed on at least one surface of the steel sheet, wherein, when the Cu intensity is continuously measured in the depth direction from the front surface side of the Fe-Ni-Cu-Cr layer by radio-frequency glow discharge optical emission spectrometry (GDS), the ratio IRCu-0.1d of the Cu intensity InCu-0.1d at a position 0.1 μm in depth from the front surface side with respect to the Cu intensity InCu-steel in the steel sheet is at least 0.5 and less than 3.0.

Description

Ni-plated surface-treated steel sheet and battery container

[0001] The present invention relates to a Ni-plated surface-treated steel sheet and a battery container.

[0002] Conventionally, Ni-plated steel sheets containing Ni have been widely used as materials for battery containers. Patent Document 1 discloses a Ni-plated steel sheet for battery containers that has an Fe—Ni diffusion layer formed by forming a nickel plating layer on the steel sheet and then performing a thermal diffusion treatment to prevent the occurrence of pitting corrosion and liquid leakage, and in which the ratio of Ni to Fe in the outermost layer is controlled.

[0003] JP 2014-47359 A

[0004] However, with the trend toward higher battery capacities, battery containers using the Ni-plated steel sheet disclosed in Patent Document 1 have had the problem that, when an abnormality in the battery management system causes overdischarge, the potential of the Fe-Ni diffusion layer approaches the positive electrode potential, causing iron to leach from the Fe-Ni diffusion layer into the electrolyte, which can corrode the inner wall of the battery container. It is expected that the positive electrode potential will become even higher as battery capacities increase in the future, and Ni-plated steel sheets with even better electrolyte resistance during overdischarge will be required.

[0005] An object of the present invention is to provide a surface-treated Ni-plated steel sheet that has excellent electrolyte resistance during overdischarge.

[0006] As a result of intensive research into achieving the above object, the inventors have found that the above object can be achieved by forming an Fe—Ni—Cu—Cr layer on a Ni-plated surface-treated steel sheet, and have thus completed the present invention.

[0007] [1] According to a first aspect of the present invention, there is provided a steel sheet and an Fe—Ni—Cu—Cr layer formed on at least one surface of the steel sheet, wherein when Cu intensity is continuously measured from the surface side of the Fe—Ni—Cu—Cr layer in a depth direction by high-frequency glow discharge optical emission spectroscopy (GDS), the Cu intensity In Ｃｕ－ｓｔｅｅｌ Cu intensity In at a depth of 0.1 μm from the surface side Ｃｕ－０．１ｄ Ratio of IR Ｃｕ－０．１ｄis 0.5 or more and less than 3.0.

[0008] [2] According to the second aspect of the present invention, when the Cu intensity is continuously measured from the surface side of the Fe—Ni—Cu—Cr layer in the depth direction by high-frequency glow discharge optical emission spectroscopy (GDS), the Cu intensity In Ｃｕ－ｓｔｅｅｌ Cu intensity In at a depth of 0.5 μm from the surface side Ｃｕ－０．５ｄ Ratio of IR Ｃｕ－０．５ｄ is 0.5 or more and less than 3.0.

[0009] [3] According to the third aspect of the present invention, when the Cr intensity is continuously measured from the surface side of the Fe—Ni—Cu—Cr layer in the depth direction by high-frequency glow discharge optical emission spectroscopy (GDS), the Cr intensity In Ｃｒ－ｓｔｅｅｌ Cr intensity In at a depth of 0.5 μm from the surface side Ｃｒ－０．５ｄ Ratio of IR Ｃｒ－０．５ｄ is 0.2 or more and less than 2.0.

[0010] [4] According to the fourth aspect of the present invention, when the Cr intensity is continuously measured from the surface side of the Fe—Ni—Cu—Cr layer in the depth direction by high-frequency glow discharge optical emission spectroscopy (GDS), the Cr intensity In Ｃｒ－ｓｔｅｅｌ Cr intensity In at a depth of 0.1 μm from the surface side Ｃｒ－０．１ｄ Ratio of IR Ｃｒ－０．１ｄ The Ni-plated surface-treated steel sheet according to any one of Aspects 1 to 3 is provided, wherein the σ is 0.2 or more and less than 2.0.

[0011] [5] According to the fifth aspect of the present invention, when the Cu intensity is continuously measured from the surface side of the Fe—Ni—Cu—Cr layer in the depth direction by high-frequency glow discharge optical emission spectroscopy (GDS), the Cu intensity In Ｃｕ－ｓｔｅｅｌ The ratio IR of Cu intensity InCu-0.3d to 0.7d at a depth of 0.3 to 0.7 μm from the surface side Ｃｕ－０．３ｄ～０．７ｄ 5. The Ni-plated surface-treated steel sheet according to any one of Aspects 1 to 4, wherein is 0.5 or more and 3.0 or less.

[0012] [6] According to a sixth aspect of the present invention, there is provided the Ni-plated surface-treated steel sheet according to any one of the first to fifth aspects, wherein the Fe—Ni—Cu—Cr layer has a Cu-enriched region.

[0013] [7] According to the seventh aspect of the present invention, when the Cu intensity is continuously measured from the surface side of the Fe—Ni—Cu—Cr layer in the depth direction by high-frequency glow discharge optical emission spectroscopy (GDS), the maximum Cu intensity In is measured at a depth to the steel plate. ＭＡＸ The Cu strength In of the steel plate Ｃｕ－ｓｔｅｅｌ Ratio IR to Ｃｕ－ＭＡＸ 7. The Ni-plated surface-treated steel sheet according to any one of Aspects 1 to 6, wherein is more than 0.8 and not more than 3.0.

[0014] [8] According to an eighth aspect of the present invention, there is provided the Ni-plated surface-treated steel sheet according to any one of the first to seventh aspects, wherein the steel sheet is a low-carbon steel or an ultra-low-carbon steel.

[0015] [9] According to a ninth aspect of the present invention, there is provided the Ni-plated surface-treated steel sheet according to any one of the first to eighth aspects, wherein the steel sheet is a low-carbon steel, the Cu content in the steel sheet is 0.01 wt % to 1.0 wt %, and the Cr content in the steel sheet is 0.01 wt % to 1.0 wt %.

[0016]

[10] According to a tenth aspect of the present invention, there is provided a battery container made using the Ni-plated surface-treated steel sheet according to any one of the first to ninth aspects.

[0017] According to the present invention, it is possible to provide a Ni-plated surface-treated steel sheet that can suppress the elution of metals such as iron (Fe) into an electrolyte during overdischarge and has excellent electrolyte resistance.

[0018] FIG. 1 is a schematic cross-sectional view showing the configuration of a Ni-plated surface-treated steel sheet according to an embodiment of the present invention. FIG. 2 is an example of a temperature profile of a plated steel sheet illustrating a method for calculating the thermal history Y during thermal diffusion treatment. FIG. 3(a) is a chart obtained by radio-frequency glow discharge optical emission spectroscopy in Example 1, and FIG. 3(b) is an enlarged view of the chart obtained by radio-frequency glow discharge optical emission spectroscopy in Example 1. FIG. 4(a) is a chart obtained by radio-frequency glow discharge optical emission spectroscopy in Example 2, and FIG. 4(b) is an enlarged view of the chart obtained by radio-frequency glow discharge optical emission spectroscopy in Example 2. FIG. 5(a) is a chart obtained by radio-frequency glow discharge optical emission spectroscopy in Comparative Example 1, and FIG. 5(b) is an enlarged view of the chart obtained by radio-frequency glow discharge optical emission spectroscopy in Comparative Example 1. FIG. 6 is a schematic view of a measuring jig used to evaluate the electrolyte resistance of a Ni-plated surface-treated steel sheet by the LSV method.

[0019] Fig. 1 is a schematic cross-sectional view showing the configuration of a Ni-plated surface-treated steel sheet according to this embodiment. As shown in Fig. 1, the Ni-plated surface-treated steel sheet 1 according to this embodiment comprises a steel sheet 2 made of carbon steel and an Fe-Ni-Cu-Cr layer 3 formed on at least one surface of the steel sheet 2.

[0020] The steel sheet 2, which is the substrate of the Ni-plated surface-treated steel sheet 1, is made of carbon steel. The carbon steel used for the steel sheet 2 is not particularly limited as long as it has excellent formability, but examples that can be used include low-carbon steel (carbon content: 0.01 wt % to 0.15 wt %) such as low-carbon aluminum-killed steel in which the carbon content is controlled with aluminum during steel production, ultra-low carbon steel with a carbon content of less than 0.01 wt %, and non-aging ultra-low carbon steel obtained by adding Ti, Nb, or the like to ultra-low carbon steel.

[0021] Among these, a base plate made of carbon steel containing predetermined amounts of Cu and Cr can be preferably used as the steel plate 2, from the viewpoint of being able to diffuse Cu and Cr in the base plate used as the steel plate 2 into the Ni plating to form the Fe—Ni—Cu—Cr layer 3. The Cu content in the steel plate 2 is preferably 0.01 wt % to 1.0 wt %, and from the viewpoint of being able to increase the Cu amount in the Fe—Ni—Cu—Cr layer 3 and further enhance the suppression of metal elution, it is more preferably 0.05 wt % to 1.0 wt %, even more preferably 0.05 wt % to 0.5 wt %, and particularly preferably 0.1 wt % to 0.4 wt %. However, when the surface-treated steel plate 1 is used for cylindrical containers or the like that require deep drawing or the like in forming, the Cu content in the steel plate 2 is preferably 0.05 wt % to 0.4 wt %.

[0022] The Cr content in the steel plate 2 is preferably 0.01 wt % to 1.0 wt %, more preferably 0.03 wt % to 1.0 wt % from the viewpoint of further suppressing metal elution by increasing the Cr amount in the Fe—Ni—Cu—Cr layer 3, and even more preferably 0.03 wt % to 0.5 wt %, particularly preferably 0.03 wt % to 0.4 wt %, from the viewpoint of reducing a decrease in electrical conductivity and suppressing metal elution at the surface of the Fe—Ni—Cu—Cr layer 3. The method for adjusting the Cu and Cr contents in the steel plate 2 is not particularly limited, but examples include a method in which a steel material produced from raw materials including carbon steel scrap and iron scrap including SUS, Cu wire, etc. is used as the base plate for the steel plate 2.

[0023] In this embodiment, a hot-rolled carbon steel sheet may be pickled to remove surface scale (oxide film), cold-rolled, and then electrolytically cleaned by alkaline electrolytic degreasing or the like, followed by annealing and / or temper rolling, or a sheet that has been cold-rolled, electrolytically cleaned, and then not annealed or temper-rolled may be used as the base sheet for the steel sheet 2. From the viewpoint of productivity, it is preferable to use a continuous steel strip as the steel sheet 2. The hot-rolled sheet may be produced using a blast furnace or an electric furnace.

[0024] In this embodiment, since Fe, Cu, and Cr diffuse on the surface of the original steel sheet 2 in the thermal diffusion treatment step described below, the Cu and Cr contents decrease near the boundary between the Fe-Ni-Cu-Cr layer 3 and the steel sheet 2, but the area where the Cu and Cr contents decrease is only a small part of the overall thickness of the steel sheet 2, and there is almost no effect on the component ratios of the entire steel sheet 2. Therefore, there is no problem in recognizing that the Cu and Cr contents in the steel sheet 2 are the same as the Cu and Cr contents in the original steel sheet. Similarly, for components other than Cu and Cr, the component ratios of the original steel sheet 2 and the steel sheet 2 before and after the thermal diffusion treatment step can be recognized as being approximately the same. That is, like the steel plate 2, the base plate for the steel plate 2 is not particularly limited as long as it is a carbon steel that has excellent formability. For example, low-carbon steel (carbon content: 0.01% to 0.15% by weight) such as low-carbon aluminum-killed steel in which the carbon content is controlled with aluminum during steel production, ultra-low carbon steel with a carbon content of less than 0.01% by weight, or non-aging ultra-low carbon steel obtained by adding Ti, Nb, or the like to ultra-low carbon steel can be used. From the viewpoint of being able to diffuse Cu and Cr in the base plate into the Ni plating to form the Fe—Ni—Cu—Cr layer 3, a base plate made of carbon steel containing predetermined amounts of Cu and Cr can be preferably used.

[0025] The thickness of the steel sheet 2 is not particularly limited and may be appropriately selected depending on the application of the Ni-plated surface-treated steel sheet 1, but from the viewpoint of reducing production costs, it is preferably 1.5 mm or less, more preferably 1.25 mm or less, and even more preferably 0.9 mm or less. Furthermore, from the viewpoint of improving the mechanical properties of the Ni-plated surface-treated steel sheet 1, the thickness of the steel sheet 2 is preferably 0.03 mm or more, more preferably 0.1 mm or more, even more preferably 0.15 mm or more, and particularly preferably 0.2 mm or more.

[0026] The Ni-plated surface-treated steel sheet 1 of this embodiment includes an Fe—Ni—Cu—Cr layer 3 on a steel sheet 2. The Fe—Ni—Cu—Cr layer 3 is formed by forming a Ni-plated layer on the steel sheet 2 and then performing a thermal diffusion treatment on the steel sheet 2 with the Ni-plated layer, thereby thermally diffusing iron (Fe), copper (Cu), and chromium (Cr) constituting the steel sheet 2 and nickel (Ni) constituting the Ni-plated layer. The Fe—Ni—Cu—Cr layer 3 may be formed on at least one surface of the steel sheet 2, or may be formed on both surfaces of the steel sheet 2. The Ni-plated surface-treated steel sheet 1 of this embodiment includes the Fe—Ni—Cu—Cr layer 3, and therefore has excellent electrolyte resistance during overdischarge.

[0027] The presence of the Fe—Ni—Cu—Cr layer 3 in the Ni-plated surface-treated steel sheet 1 can be confirmed by performing elemental analysis on the surface of the Ni-plated surface-treated steel sheet 1. Specifically, this can be confirmed by performing a composition analysis of the surface using techniques such as high-frequency glow discharge optical emission spectroscopy (GDS), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). For example, high-frequency glow discharge optical emission spectroscopy is performed on a standard sample of low-carbon steel with a Ni-plated layer formed thereon and on the Ni-plated surface-treated steel sheet 1 in the depth direction from the surface toward the steel sheet 2, and the changes in Fe intensity, Ni intensity, Cu intensity, and Cr intensity with respect to the measurement time are continuously measured. When the intensities of the standard sample and the Ni-plated surface-treated steel sheet 1 are compared in the obtained data, it can be determined that Fe is present in the Ni-plated surface-treated steel sheet 1 in a range where the Fe intensity is 10% or more of the maximum Fe intensity of the standard sample. Similarly, it can be determined that Ni is present in the Ni-plated surface-treated steel sheet 1 when the Ni intensity is 10% or more of the maximum Ni intensity of the standard sample. Furthermore, if the Cu intensity at a given depth in the Ni-plated surface-treated steel sheet 1 is higher than the Cu intensity at the same depth in the Ni-plated layer of the standard sample, it can be determined that Cu is present at that depth. Similarly, if the Cr intensity at a given depth in the Ni-plated surface-treated steel sheet 1 is higher than the Cr intensity at the same depth in the Ni-plated layer of the standard sample, it can be determined that Cr is present at that depth. If there is a position where it can be determined that all of Fe, Ni, Cu, and Cr are present, it can be determined that an Fe—Ni—Cu—Cr layer 3 has been formed at that location. The standard sample will be described in detail later.

[0028] Note that Cu and Cr in the Fe—Ni—Cu—Cr layer 3 are diffused from the original sheet used as the steel sheet 2, and therefore the proportions of Cu and Cr present in the Fe—Ni—Cu—Cr layer 3 are very small compared to the proportions of Fe and Ni. That is, the proportions of Fe and Ni are dominant in the metal composition of the Fe—Ni—Cu—Cr layer 3. Specifically, the contents of Cu and Cr in the Fe—Ni—Cu—Cr layer 3 are approximately the same as or less than the respective contents of Cu and Cr in the steel sheet 2, and therefore the total amount of Cu and Cr is 2 wt % or less, and the total amount of iron and nickel is 98 wt % or more.

[0029] The Ni-plated surface-treated steel sheet 1 may have an Fe—Ni—Cu—Cr layer 3, but the Cu intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy Ｃｕ－ｓｔｅｅｌ Cu intensity In at a depth of 0.5 μm from the surface side Ｃｕ－０．５ｄ Ratio of IR Ｃｕ－０．５ｄ (=In Ｃｕ－０．５ｄ / In Ｃｕ－Ｓｔｅｅｌ ) is preferably 0.50 or more and less than 3.0. Ｃｕ－０．５ｄ By ensuring that the Cu content is within the above range, the Ni-plated surface-treated steel sheet 1 can have better electrolyte resistance during overdischarge. Although the reason for this is unclear, it is believed that a mixed potential can be achieved in the surface layer of the Fe—Ni—Cu—Cr layer 3, thereby suppressing local dissolution when the layer comes into contact with an electrolyte. If the amount of Cu near the surface layer is too small, the number of crystal grains containing Cu in the surface layer of the Fe—Ni—Cu—Cr layer 3 will be reduced, or the area where Cu is present will be small, which may prevent a sufficient mixed potential from being achieved. Furthermore, if the amount of Cu near the surface layer is too large, localized areas of the Fe—Ni—Cu—Cr layer 3 will have a noble potential, widening the potential difference with Fe and potentially increasing the elution of metals such as iron. From the viewpoint of further suppressing the elution of metals such as iron during overdischarge, the intensity ratio IR Ｃｕ－０．５ｄ The lower limit of the intensity ratio IR is more preferably 0.7 or more, and even more preferably 0.8 or more. Ｃｕ－０．５ｄThe upper limit of is more preferably 2.5 or less, further preferably 2.0 or less, and particularly preferably 1.8 or less. Ｃｕ－ｓｔｅｅｌ The method for determining the intensity ratio IR will be described in detail later. In particular, when the amount of Ni attached is relatively small, Ｃｕ－０．５ｄ It is important to set the value within the above range in order to improve the electrolyte resistance during overdischarge.

[0030] The intensity of each element at each depth position in radio frequency glow discharge optical emission spectroscopy can be determined by calculating the depth from the sample surface using the measurement time (etching time) and the etching rate (unit: μm / sec) by sputtering, and then reading the intensity at that position. In this embodiment, the measurement time is converted to the measurement depth using the etching rate of Ni. The method for converting the measurement time to the measurement depth is specifically as follows.

[0031] First, the Ni etching rate is determined. To determine the Ni etching rate, a standard sample is prepared from a Ni-plated steel sheet that has not been subjected to heat treatment and whose plating layer thickness (or deposition amount) is known. For example, a standard Ni-plated steel sheet is prepared by applying a 1.1 μm thick matte Ni plating to a 0.3 mm thick low-carbon steel sheet. The plating process for applying the matte Ni plating to the standard Ni-plated steel sheet is not particularly limited, but can be carried out using, for example, the following Watts bath. <Ni plating conditions> Bath composition: nickel sulfate hexahydrate 250 g / L, nickel chloride hexahydrate 45 g / L, boric acid 30 g / L pH: 4.0 to 5.0 Bath temperature: 60°C Current density: 10 A / dm ２The Ni plating thickness of a standard Ni-plated steel sheet can be determined by measuring the thickness through cross-sectional observation of the Ni-plated steel sheet using an SEM, or by converting the Ni coating weight determined by X-ray fluorescence analysis into a thickness using the specific gravity of Ni. For this standard sample, the Fe and Ni intensities in the standard Ni-plated steel sheet are measured from the Ni-plated side using a high-frequency glow discharge optical emission spectrometer until the Fe intensity reaches saturation, and a chart is obtained. The resulting chart is used to determine the time during which the Ni plating layer was etched. Specifically, the Ni etching time is defined as the time from the start of measurement until the Fe intensity reaches 10% of its saturation value. The Ni etching rate can be calculated from the Ni etching time and the thickness of the Ni plating layer. The saturated value of the Fe intensity is determined from the time rate of change of the Fe intensity (Fe intensity change / second). The time rate of change of the Fe intensity increases rapidly when Fe is detected after the start of measurement, then decreases after passing the maximum value and stabilizes at approximately zero. The value of the Fe intensity when the time rate of change stabilizes at approximately zero is the saturated value of the Fe intensity. Specifically, when the time rate of change of the Fe intensity becomes 0.02 (Fe intensity / second) or less, the Fe intensity can be considered to be saturated.

[0032] The Ni etching rate determined as described above is a parameter indicating the relationship between the depth time (measurement time using a radio-frequency glow discharge optical emission spectrometer) and the actual thickness of a steel sheet having a Ni-plated layer that has not been subjected to thermal diffusion treatment and whose Ni plating thickness is known. Therefore, the Ni etching rate determined as described above can be used to convert the measurement time of radio-frequency glow discharge optical emission spectrometer analysis of the Ni-plated surface-treated steel sheet 1 into etching depth (thickness). It is known that the etching rates of iron and nickel are similar in measurements using a radio-frequency glow discharge optical emission spectrometer. Furthermore, because the copper and chromium contained in the Fe-Ni-Cu-Cr layer 3 are diffused from the carbon steel base sheet, the amounts of copper and chromium contained in the Fe-Ni-Cu-Cr layer 3 are very small, and copper and chromium have almost no effect on the etching rate. Therefore, the etching rate of the Fe-Ni-Cu-Cr layer 3 is dominated by iron and nickel, and the etching rate of Ni determined using a pure Ni plating layer can be used as the etching rate of the Fe-Ni-Cu-Cr layer 3 and the steel plate 2.

[0033] For example, the Cu intensity In at a position 0.5 μm deep from the surface side Ｃｕ－０．５ｄ When calculating Cu intensity, the Cu intensity can be read when the Ni etching rate is multiplied by the measurement time to obtain a depth of 0.5 μm. Depending on the etching rate, it may not always be possible to obtain an intensity at a depth that matches each target value, so it is sufficient to read the intensity within a range of ±0.03 μm from the target value. For example, an intensity within a range of 0.5 μm ±0.03 μm can be treated as the intensity at a depth of 0.5 μm. The Cu intensity at depths other than 0.5 μm, as described below, can also be read in a similar manner.

[0034] In radio-frequency glow discharge optical emission spectroscopy, measurements are continuously taken from the surface of the sample toward the depth direction. Therefore, when radio-frequency glow discharge optical emission spectroscopy is performed on the Ni-plated surface-treated steel sheet 1 of this embodiment, as shown in FIG. 3( a), data is obtained in which the Fe intensity, Ni intensity, Cu intensity, and Cr intensity fluctuate. Then, as shown in FIG. 3( a), the depth change (time change) of each of the Fe intensity, Ni intensity, Cu intensity, and Cr intensity approaches zero, and data is obtained in which the Fe intensity, in particular, is nearly saturated. Furthermore, the Ni-plated surface-treated steel sheet 1 has a structure in which the Fe—Ni—Cu—Cr layer 3 and the steel sheet 2 are laminated, and in the steel sheet 2, the concentration of each metal is usually constant in the depth direction. Therefore, the intensity data at points where the depth change approaches zero indicate the intensity data of each metal in the steel sheet 2. Furthermore, when the results of high-frequency glow discharge optical emission spectroscopy for the Ni-plated surface-treated steel sheet 1 in this embodiment and the standard sample are compared, the measurement results for the Ni-plated surface-treated steel sheet 1 show that the Ni intensity of the Ni-plated surface-treated steel sheet 1 is 2% of the maximum Ni intensity of the standard sample at a depth (hereinafter referred to as D Ｎｉ２％ In the case of the Ni-plated surface-treated steel sheet 1, the depth change amount of the intensity data of each metal is close to 0. Therefore, in this embodiment, the depth D Ｎｉ２％ The strength of each metal in the steel sheet 2 is used as the strength data of each metal in the steel sheet 2. That is, the Cu strength In Ｃｕ－ｓｔｅｅｌ is the depth D Ｎｉ２％ Similarly, for chromium, the Cr intensity can be calculated as In Ｃｒ－ｓｔｅｅｌ is the depth D Ｎｉ２％ 3A is a chart obtained by high frequency glow discharge optical emission spectroscopy in Example 1 described later.

[0035] In this embodiment, the boundary position between the Fe—Ni—Cu—Cr layer 3 and the steel sheet 2 serving as the substrate is defined as the point where the Ni intensity measured on the Ni-plated surface-treated steel sheet 1 is 10% of the maximum Ni intensity of a standard sample measured under the same conditions, and the depth at this point is defined as the thickness of the Fe—Ni—Cu—Cr layer 3. The thickness of the Fe—Ni—Cu—Cr layer 3 is preferably 0.5 to 3.5 μm, and more preferably 0.7 to 3.0 μm.

[0036] The Cu strength In Ｃｕ－ｓｔｅｅｌ Cu intensity In at a depth of 0.5 μm from the surface side Ｃｕ－０．５ｄ Ratio of (IR Ｃｕ－０．５ｄ = In Ｃｕ－０．５ｄ / In Ｃｕ－Ｓｔｅｅｌ ) represents the ratio of the Cu intensity near the surface of the Fe—Ni—Cu—Cr layer 3 to the Cu intensity in the steel plate 2, and is an index showing to what extent Cu in the steel plate 2 has diffused to the surface.

[0037] In the Ni-plated surface-treated steel sheet 1, the Cu intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy (GDS) Ｃｕ－ｓｔｅｅｌ Cu intensity In at a depth of 0.1 μm from the surface side Ｃｕ－０．１ｄ Ratio of IR Ｃｕ－０．１ｄ (=In Ｃｕ－０．１ｄ / In Ｃｕ－ｓｔｅｅｌ ) is 0.50 or more and less than 3.0. Ｃｕ－０．１ｄ represents the ratio of the Cu intensity near the outermost surface of the Fe—Ni—Cu—Cr layer 3 to the Cu intensity in the steel sheet 2, and is an index showing the extent to which Cu in the steel sheet 2 has diffused to the outermost surface. If there is too little Cu near the outermost surface, the number of crystal grains containing Cu at the outermost surface of the Fe—Ni—Cu—Cr layer 3 will be reduced, or the area where Cu is present will be smaller, which may prevent a sufficient mixed potential state from being achieved. Furthermore, if there is too much Cu near the outermost surface, there is a possibility that metal elution will increase. From the viewpoint of further suppressing metal elution during overdischarge, the intensity ratio IR Ｃｕ－０．１ｄ The lower limit of the intensity ratio IR is more preferably 0.6 or more, further preferably 0.7 or more, and particularly preferably 0.8 or more.Ｃｕ－０．１ｄ The upper limit of Cu intensity ratio IR is more preferably 2.0 or less, further preferably 1.5 or less, and particularly preferably less than 1.0. Ｃｕ－０．１ｄ When the intensity ratio IR is within the above range, the Ni-plated surface-treated steel sheet 1 can have excellent electrolyte resistance during over-discharge. Ｃｕ－０．１ｄ By setting the value of the surface-treated Ni-plated steel sheet 1 within the above range, even if the Ni deposition amount is relatively small, the Ni-plated steel sheet 1 can have excellent electrolyte resistance during overdischarge.

[0038] In the Ni-plated surface-treated steel sheet 1, the Cu intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy Ｃｕ－ｓｔｅｅｌ Cu intensity In at a depth of 0.3 μm from the surface side Ｃｕ－０．３ｄ Ratio of IR Ｃｕ－０．３ｄ (=In Ｃｕ－０．３ｄ / In Ｃｕ－ｓｔｅｅｌ From the viewpoint of further suppressing metal elution during overdischarge, it is preferable that the intensity ratio IR Ｃｕ－０．３ｄ The lower limit of the intensity ratio IR is more preferably 0.7 or more, further preferably 0.8 or more, and particularly preferably 0.9 or more. Ｃｕ－０．３ｄ The upper limit of Cu intensity ratio IR is more preferably 2.5 or less, further preferably 2.0 or less, and particularly preferably 1.8 or less. Ｃｕ－０．３ｄ When the intensity ratio IR is within the above range, the Ni-plated surface-treated steel sheet 1 can have excellent electrolyte resistance during over-discharge. Ｃｕ－０．３ｄ By setting the value of the surface-treated Ni-plated steel sheet 1 within the above range, even if the Ni deposition amount is relatively small, the Ni-plated steel sheet 1 can have excellent electrolyte resistance during overdischarge.

[0039] In the Ni-plated surface-treated steel sheet 1, the Cu intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy Ｃｕ－ｓｔｅｅｌ Cu intensity In at a depth of 0.7 μm from the surface side Ｃｕ－０．７ｄ Ratio of IR Ｃｕ－０．７ｄ (=In Ｃｕ－０．７ｄ / In Ｃｕ－ｓｔｅｅｌFrom the viewpoint of further suppressing metal elution during overdischarge, it is preferable that the intensity ratio IR Ｃｕ－０．７ｄ The lower limit of the intensity ratio IR is more preferably 0.7 or more, further preferably 0.8 or more, and particularly preferably 0.9 or more. Ｃｕ－０．７ｄ The upper limit of Cu intensity ratio IR is more preferably 2.5 or less, further preferably 2.0 or less, and particularly preferably 1.8 or less. Ｃｕ－０．７ｄ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0040] In the Ni-plated surface-treated steel sheet 1, the Cu intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy Ｃｕ－ｓｔｅｅｌ Cu intensity In at a depth of 0.9 μm from the surface side Ｃｕ－０．９ｄ Ratio of IR Ｃｕ－０．９ｄ (=In Ｃｕ－０．９ｄ / In Ｃｕ－ｓｔｅｅｌ From the viewpoint of further suppressing metal elution during overdischarge, it is preferable that the intensity ratio IR Ｃｕ－０．９ｄ The lower limit of the intensity ratio IR is more preferably 0.7 or more, further preferably 0.8 or more, and particularly preferably 0.9 or more. Ｃｕ－０．９ｄ The upper limit of Cu intensity ratio IR is more preferably 2.5 or less, further preferably 2.0 or less, and particularly preferably 1.8 or less. Ｃｕ－０．９ｄ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0041] In the Ni-plated surface-treated steel sheet 1, the Cu intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy Ｃｕ―ｓｔｅｅｌ The maximum value In of Cu intensity in the region from the surface to the boundary between the Fe-Ni-Cu-Cr layer 3 and the steel plate 2 Ｃｕ―ＭＡＸ Ratio of IR Ｃｕ－ＭＡＸ (=In Ｃｕ―ＭＡＸ / In Ｃｕ―ｓｔｅｅｌ From the viewpoint of further suppressing metal elution during overdischarge, it is preferable that IR Ｃｕ－ＭＡＸis more preferably 0.9 or more and 2.5 or less, further preferably 0.9 or more and 2.0 or less, and particularly preferably 1.0 or more and 1.8 or less. Ｃｕ－ＭＡＸ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0042] In addition, in the Ni-plated surface-treated steel sheet 1, the Cu intensity In Ｃｕ－ｓｔｅｅｌ The ratio IR of the Cu intensity InCu-0.3d to 0.7d in the region 0.3 μm to 0.7 μm deep from the surface (i.e., the Cu intensity measured at an arbitrary depth position in the region 0.3 μm to 0.7 μm deep from the surface) Ｃｕ－０．３ｄ～０．７ｄ (=InCu-0.3d~0.7d / In Ｃｕ－ｓｔｅｅｌ ) is preferably 0.5 or more and 3.0 or less. Ｃｕ－０．３ｄ～０．７ｄ By making the intensity ratio IR Ｃｕ－０．３ｄ～０．７ｄ The lower limit of the intensity ratio IR is more preferably 0.7 or more, further preferably 0.8 or more, and particularly preferably 0.9 or more. Ｃｕ－０．３ｄ～０．７ｄ The upper limit of Cu intensity ratio IR is more preferably 2.5 or less, further preferably 2.0 or less, and particularly preferably 1.8 or less. Ｃｕ－０．３ｄ～０．７ｄ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0043] The Fe-Ni-Cu-Cr layer 3 preferably has a Cu-enriched region formed in an intermediate region (i.e., a region deeper than the outermost surface of the Ni-plated surface-treated steel sheet 1 and shallower than the boundary between the Fe-Ni-Cu-Cr layer 3 and the steel sheet 2). The fact that the Fe-Ni-Cu-Cr layer 3 has a Cu-enriched region means, for example, that the Cu intensity InCu-boundary at the boundary position between the Fe-Ni-Cu-Cr layer 3 and the steel sheet 2 serving as the base material, and the Cu intensity InCu-boundary in the steel sheet 2 Ｃｕ－ｓｔｅｅｌ Intensity ratio IR Ｃｕ－ｂｏｕｎｄａｒｙ (=InCu-boundary / In Ｃｕ－ｓｔｅｅｌ ) can be confirmed by the following formulas (1) and (2). When the following formulas (1) and (2) are satisfied, it can be determined that the Fe—Ni—Cu—Cr layer 3 has a Cu-enriched region in the intermediate region. In this case, the position where the Cu intensity is maximum is preferably between a position 0.3 μm deep from the surface and a position 0.1 μm shallower than the boundary between the Fe—Ni—Cu—Cr layer 3 and the steel sheet 2 serving as the substrate. Furthermore, the position where the Cu intensity is maximum is preferably a position whose depth from the surface is 60% or less of the thickness of the Fe—Ni—Cu—Cr layer 3. By forming a Cu-enriched region in the intermediate region of the Fe—Ni—Cu—Cr layer 3, the Ni-plated surface-treated steel sheet 1 can be made to have superior electrolyte resistance during overdischarge. IR Ｃｕ－ＭＡＸ -IR Ｃｕ－０．１ｄ >0.05 (1) IR Ｃｕ－ＭＡＸ -IR Ｃｕ－ｂｏｕｎｄａｒｙ >0.05 (2)

[0044] In the Ni-plated surface-treated steel sheet 1, the Cu intensity InCu-0.5d-ref at a depth of 0.5 μm measured by high-frequency glow discharge optical emission spectroscopy of a standard sample is compared with the Cu intensity InCu-0.5d-ref at an arbitrary depth position from the surface measured by high-frequency glow discharge optical emission spectroscopy. Ｃｕ－ｄ Ratio of IR Ｃｕ－ｄ－ｖｒｅｆ (=In Ｃｕ－ｄ / InCu-0.5d-ref) is preferably within a predetermined range. Ｃｕ－ｄ－ｖｒｅｆis preferably 2.0 or more and 20 or less in the range of 0.1 μm to 0.5 μm in depth from the surface. If the absolute amount of Cu from the vicinity of the outermost surface to the vicinity of the surface layer is too small, the number of crystal grains containing Cu in the Fe—Ni—Cu—Cr layer 3 will be reduced, or the area where Cu exists will be small, which may prevent a sufficient mixed potential state from being achieved. Furthermore, if the absolute amount of Cu from the vicinity of the outermost surface to the vicinity of the surface layer is too large, there is a possibility that metal elution will increase. From the viewpoint of further suppressing metal elution during overdischarge, in the range of 0.1 μm to 0.5 μm in depth from the surface (over the entire range of 0.1 μm to 0.5 μm in depth from the surface), IR Ｃｕ－ｄ－ｖｒｅｆ is more preferably 2.3 or more and 10 or less, and further preferably 3.0 or more and 10 or less. Ｃｕ－ｄ－ｖｒｅｆ When the depth from the surface is in the range of more than 0.5 μm and not more than 0.9 μm, the value is preferably 2.0 or more and 20 or less, more preferably 2.5 or more and 15 or less, and even more preferably 3.0 or more and 15 or less.

[0045] In the Ni-plated surface-treated steel sheet 1, the relative IR Ｃｕ－ＭＡＸ (=In Ｃｕ―ＭＡＸ / In Ｃｕ―ｓｔｅｅｌ ) and the relative IR Ｃｕ－０．１ｄ (=In Ｃｕ－０．１ｄ / In Ｃｕ－ｓｔｅｅｌ ) difference IR Ｃｕ－ＭＡＸ -IR Ｃｕ－０．１ｄ is preferably 1.0 or less, more preferably 0.6 or less, even more preferably 0.5 or less, and particularly preferably 0.3 or less. Ｃｕ－ＭＡＸ -IR Ｃｕ－０．１ｄ The smaller the value of IR, the more Cu is diffused to the vicinity of the outermost surface in the Fe—Ni—Cu—Cr layer 3 with less variation in the Cu intensity distribution. Ｃｕ－ＭＡＸ -IR Ｃｕ－０．１ｄ By setting the value of the surface-treated Ni-plated steel sheet 1 within the above range, the Ni-plated steel sheet 1 can have excellent electrolyte resistance during overdischarge, especially when the Ni deposition amount is relatively small.

[0046] In the Ni-plated surface-treated steel sheet 1, the Cr intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy (GDS) Ｃｒ－ｓｔｅｅｌ Cr intensity In at a depth of 0.1 μm from the surface side Ｃｒ－０．１ｄ Ratio of IR Ｃｒ－０．１ｄ (=In Ｃｒ－０．１ｄ / In Ｃｒ－ｓｔｅｅｌ ) is preferably 0.2 or more and less than 2.0, more preferably 0.2 or more and less than 1.0, and even more preferably 0.2 or more and less than 0.95, from the viewpoint of suppressing metal elution due to the formation of a mixed potential. Ｃｒ－０．１ｄ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0047] In the Ni-plated surface-treated steel sheet 1, the Cr intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy (GDS) Ｃｒ－ｓｔｅｅｌ Cr intensity In at a depth of 0.3 μm from the surface side Ｃｒ－０．３ｄ Ratio of IR Ｃｒ－０．３ｄ (=In Ｃｒ－０．３ｄ / In Ｃｒ－ｓｔｅｅｌ ) is preferably 0.2 or more and less than 2.0, more preferably 0.2 or more and less than 0.95, and even more preferably 0.2 or more and less than 0.7. Ｃｒ－０．３ｄ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0048] In the Ni-plated surface-treated steel sheet 1, the Cr intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy (GDS) Ｃｒ－ｓｔｅｅｌ Cr intensity In at a depth of 0.5 μm from the surface side Ｃｒ－０．５ｄ Ratio of IR Ｃｒ－０．５ｄ (=In Ｃｒ－０．５ｄ / In Ｃｒ－ｓｔｅｅｌ) is preferably 0.2 or more and less than 2.0 from the viewpoint of diffusing Cr to the vicinity of the surface layer and achieving a stable and sufficient mixed potential state. If the amount of Cr near the surface layer is too small, the number of crystal grains containing Cr in the surface layer of the Fe—Ni—Cu—Cr layer 3 may decrease, or the area where Cr exists may become smaller. Furthermore, if the amount of Cr near the surface layer is too much, there may be areas where the potential difference with Fe widens locally. From the viewpoint of stably improving the electrolyte resistance during overdischarge, it is more preferably 0.2 or more and less than 0.95, and even more preferably 0.2 or more and less than 0.8. Cr intensity ratio IR Ｃｒ－０．５ｄ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0049] In the Ni-plated surface-treated steel sheet 1, the Cr intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy (GDS) Ｃｒ－ｓｔｅｅｌ Cr intensity In at a depth of 0.7 μm from the surface side Ｃｒ－０．７ｄ Ratio of IR Ｃｒ－０．７ｄ (=In Ｃｒ－０．７ｄ / In Ｃｒ－ｓｔｅｅｌ ) is preferably 0.2 or more and less than 2.0, more preferably 0.2 or more and less than 0.95, and even more preferably 0.2 or more and less than 0.8. Ｃｒ－０．７ｄ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0050] In the Ni-plated surface-treated steel sheet 1, the Cr intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy (GDS) Ｃｒ－ｓｔｅｅｌ Cr intensity In at a depth of 0.9 μm from the surface side Ｃｒ－０．９ｄ Ratio of IR Ｃｒ－０．９ｄ (=In Ｃｒ－０．１ｄ / In Ｃｒ－ｓｔｅｅｌ ) is preferably 0.2 or more and less than 2.0, more preferably 0.2 or more and less than 1.0, and even more preferably 0.2 or more and 0.95 or less. Ｃｒ－０．９ｄWhen the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0051] In the Ni-plated surface-treated steel sheet 1, the Cr intensity In in the steel sheet 2 measured by high-frequency glow discharge optical emission spectroscopy Ｃｒ―ｓｔｅｅｌ The maximum value In of the Cr strength in the region from the surface to the boundary between the Fe-Ni-Cu-Cr layer 3 and the steel plate 2 Ｃｒ―ＭＡＸ Ratio of IR Ｃｒ－ＭＡＸ (=In Ｃｒ―ＭＡＸ / In Ｃｒ―ｓｔｅｅｌ ) is preferably 0.3 or more and 2.0 or less, and more preferably 0.3 or more and 0.95 or less. Ｃｒ－ｍａｘ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0052] In addition, in the Ni-plated surface-treated steel sheet 1, the Cr intensity In Ｃｒ－ｓｔｅｅｌ The ratio IR of the Cr intensity InCu-0.3d to 0.7d in the region 0.3 μm to 0.7 μm deep from the surface (i.e., the Cr intensity measured at an arbitrary depth position in the region 0.3 μm to 0.7 μm deep from the surface) Ｃｒ－０．３ｄ～０．７ｄ (=InCr-0.3d~0.7d / In Ｃｒ－ｓｔｅｅｌ ) is preferably 0.2 or more and 2.0 or less, and more preferably 0.2 or more and less than 0.95. Ｃｒ－０．３ｄ～０．７ｄ When the value of the surface-treated Ni-plated steel sheet 1 is within the above range, the Ni-plated steel sheet 1 can have better resistance to an electrolyte during overdischarge.

[0053] In the Ni-plated surface-treated steel sheet 1, the Cr intensity InCr-0.5d-ref at a depth of 0.5 μm measured by high-frequency glow discharge optical emission spectroscopy of a standard sample is compared with the Cr intensity InCr-0.5d-ref at an arbitrary depth position from the surface measured by high-frequency glow discharge optical emission spectroscopy. Ｃｒ－ｄ Ratio of IR Ｃｒ－ｄ－ｖｒｅｆ = (In Ｃｒ－ｄ / InCr-0.5d-ref) is preferably within a predetermined range. Ｃｒ－ｄ－ｖｒｅｆis preferably 2.0 or more and 30 or less in the range of 0.1 μm to 0.5 μm in depth from the surface. If the amount of Cr from the vicinity of the outermost surface to the vicinity of the surface layer is too small, the number of crystal grains containing Cr at the outermost surface of the Fe—Ni—Cu—Cr layer 3 will be small, or the area where Cr exists will be small, and therefore, there is a possibility that a sufficient mixed potential state cannot be achieved. Furthermore, if there is too much Cr from the vicinity of the outermost surface to the vicinity of the surface layer, there is a possibility that the electrical resistance value of the surface will be too high. In the range of 0.1 μm to 0.5 μm in depth from the surface, IR Ｃｒ－ｄ－ｖｒｅｆ is more preferably 2.5 or more and 30 or less, further preferably 5.5 or more and 30 or less, and particularly preferably 7.0 or more and 20 or less. Ｃｒ－ｄ－ｖｒｅｆ When the depth from the surface is in the range of more than 0.5 μm and 0.9 μm or less, the value is preferably 2.0 or more and 50 or less, and more preferably 5.5 or more and 40 or less.

[0054] In the Ni-plated surface-treated steel sheet 1, from the viewpoint of being able to provide better electrolyte resistance during overdischarge and to improve battery characteristics, the Cu strength In Ｃｕ－ｓｔｅｅｌ The Cu intensity In at a depth of 0.5 μm from the surface side in the Fe—Ni—Cu—Cr layer 3 relative to Ｃｕ－０．５ｄ Ratio of IR Ｃｕ－０．５ｄ (=In Ｃｕ－０．５ｄ / In Ｃｕ－Ｓｔｅｅｌ ) is 0.50 or more and less than 3.0, and the Cr strength In Ｃｒ－ｓｔｅｅｌ Cr intensity In Ｃｒ－０．５ｄ Ratio of IR Ｃｒ－０．５ｄ (=In Ｃｒ－０．５ｄ / In Ｃｒ－ｓｔｅｅｌ ) is preferably 0.2 or more and less than 2.0. It is believed that by controlling both the Cu intensity ratio and the Cr intensity ratio so as to be within the above range, it is possible to stabilize the mixed potential state due to the inclusion of Cu and Cr near the surface layer of the Fe—Ni—Cu—Cr layer 3. Furthermore, even if Cr is present particularly near the outermost surface or near the surface layer, the inclusion of Cu in the Fe—Ni—Cu—Cr layer 3 makes it possible to suppress an increase in contact resistance, thereby suppressing metal elution and achieving better battery characteristics.

[0055] In the Ni-plated surface-treated steel sheet 1, the Fe intensity InFe-MAX-ref at a depth of 0.1 μm from the surface side is measured by high-frequency glow discharge optical emission spectroscopy on a standard sample (Ni-plated steel sheet) from the surface toward the steel sheet. Ｆｅ－０．１ｄ Ratio of IR Ｆｅ－０．１ｄ (=In Ｆｅ－０．１ｄ / (0.1×InFe-MAX-ref)) is 1.0 or more, and preferably 2.0 or more and less than 7.0. Ｆｅ－０．１ｄ Within the above range, an Fe—Ni—Cu—Cr layer can be formed over the entire surface of the surface-treated steel sheet 1 even if the steel sheet 1 has a large width or area, and the electrolyte resistance can be stably improved.

[0056] In the Ni-plated surface-treated steel sheet 1, the lower limit of the Ni coating mass on the surface on which the Fe-Ni-Cu-Cr layer 3 is formed as the outermost layer is set to 0.45 g / m from the viewpoint of appropriately forming the Fe-Ni-Cu-Cr layer 3 and controlling the Cu intensity ratio and Cr intensity ratio between the steel sheet 2 and the Fe-Ni-Cu-Cr layer 3 within an appropriate range. ２ More than 0.8 g / m ２ More preferably, 2.5 g / m or more ２ More preferably, 3.0 g / m or more ２ In the Ni-plated surface-treated steel sheet 1, the upper limit of the Ni coating amount on the surface on which the Fe—Ni—Cu—Cr layer 3 is formed as the outermost layer is 10.7 g / m, because it is difficult for Fe to diffuse to the outermost surface and it becomes necessary to increase the heat treatment temperature or lengthen the heat treatment time in order to sufficiently diffuse Fe. ２ Preferably, 8.9 g / m or less ２ More preferably, less than 8.0 g / m ２ More preferably, 7.2 g / m or less ２ The following is particularly preferred. The Ni deposition amount can be determined by X-ray fluorescence measurement. In X-ray fluorescence measurement, quantification using a calibration curve method is possible. X-ray fluorescence measurement may be performed on the Ni-plated surface-treated steel sheet 1 on which the Fe—Ni—Cu—Cr layer 3 has been formed by thermal diffusion treatment, or on the steel sheet 2 on which the Ni-plated layer has been formed before thermal diffusion treatment.

[0057] In this embodiment, as shown in FIG. 1 , the Fe—Ni—Cu—Cr layer 3 is formed only on one surface of the steel sheet 2, but the configuration of the Ni-plated surface-treated steel sheet 1 is not particularly limited to this, and it is sufficient that the Fe—Ni—Cu—Cr layer 3 is formed on at least one outermost surface of the steel sheet 2, or it may be formed on both outermost surfaces of the steel sheet 2.

[0058] The Ni-plated surface-treated steel sheet 1 in this embodiment can be produced as follows.

[0059] First, a Ni plating layer is formed on the base steel sheet 2. As described above, carbon steel containing Cu and Cr in a predetermined ratio can be suitably used as the base steel sheet 2. The Cu content of the carbon steel used here is preferably 0.05 to 1.0 wt%, and more preferably 0.05 to 0.5 wt%. The Cr content of the carbon steel is more preferably 0.03 to 1.0 wt%, more preferably 0.03 to 0.5 wt%, and particularly preferably 0.03 to 0.4 wt%. The Ni plating bath used to form the Ni plating layer can be a commonly used plating bath, such as a Watts bath, sulfamic acid bath, boron fluoride bath, or chloride bath. For example, the Ni plating layer is formed using a Watts bath with a bath composition of 200 g / L to 350 g / L of nickel sulfate hexahydrate, 20 g / L to 60 g / L of nickel chloride hexahydrate, and 10 g / L to 50 g / L of boric acid, at a pH of 3.0 to 5.0, a bath temperature of 40°C to 70°C, and a current density of 5 A / dm ２ ~40 A / dm ２ The Ni plating layer may be formed on at least one side of the base sheet of the steel sheet 2, but is preferably formed on both sides.

[0060] In this embodiment, from the viewpoint of facilitating the diffusion of Cu and Cr contained in the base steel sheet 2 in the thermal diffusion treatment step described below, thereby forming the Fe—Ni—Cu—Cr layer 3, it is preferable to add a small amount of a semi-brightener composed of a sulfur-free compound, such as an aliphatic unsaturated alcohol (e.g., a polyoxyethylene adduct of an unsaturated alcohol), an unsaturated carboxylic acid, formaldehyde, or coumarin, to the Ni plating bath. Specifically, the amount of semi-brightener added is preferably such that the total amount of semi-brightener in the plating bath is 0.6 mL / L to 6.0 mL / L, more preferably 0.8 mL / L to 5.0 mL / L, and even more preferably 1.2 mL / L to 5.5 mL / L. One type of semi-brightener may be used, or multiple types may be used in combination. When multiple types are combined, the total amount of the multiple semi-brighteners is preferably within the above range.

[0061] The amount W of Ni deposited on the base sheet of the steel sheet 2 by forming the Ni plating layer is not particularly limited as long as the Fe-Ni-Cu-Cr layer 3 can be formed as the outermost surface of the Ni-plated surface-treated steel sheet 1 and its configuration can be controlled. However, if the amount of deposition is too large, it becomes difficult to diffuse Fe, Cu, and Cr to the outermost surface, and it becomes necessary to increase the heat treatment temperature or lengthen the heat treatment time in order to sufficiently diffuse Fe, Cu, and Cr, which may make it difficult to properly form the Fe-Ni-Cu-Cr layer 3. Therefore, the amount W of Ni deposited on the base sheet of the steel sheet 2 is set to 10.7 g / m. ２ Preferably, 8.9 g / m or less ２ More preferably, 8.0 g / m or less ２ More preferably, 7.2 g / m or less ２ On the other hand, if the Ni deposition amount W is too small, it is difficult to properly form the Fe—Ni—Cu—Cr layer 3, and there is a risk that the electrolyte resistance during overdischarge may decrease. Therefore, the Ni deposition amount W is set to 0.45 g / m or less. ２ More than 0.8 g / m ２ More preferably, 2.5 g / m or more ２ More preferably, 3.0 g / m or more ２The above is particularly preferable. When the Fe—Ni—Cu—Cr layer 3 is formed on the outermost surface of both sides of the steel sheet 2, it is preferable that the Ni coating weight W on each surface is set within the above range. Furthermore, when the Ni-plated surface-treated steel sheet 1 of this embodiment is used for a can-shaped battery container, it is preferable to form the Fe—Ni—Cu—Cr layer 3 on the outermost surface of the surface that will become the inner surface of the battery container, while forming an Fe—Ni diffusion layer on the surface that will become the outer surface of the battery container, and then forming a Ni layer on the Fe—Ni diffusion layer. In order to configure the outer surface of the battery container in this way, the Ni coating weight on the surface that will become the outer surface of the battery container is 9.0 g / m ２ ~90g / m ２ is preferred.

[0062] Next, the steel sheet 2 having the Ni plating layer formed on the surface thereof (hereinafter referred to as the plated steel sheet) is subjected to a thermal diffusion treatment to form an Fe—Ni—Cu—Cr layer 3. By appropriately controlling the conditions of the thermal diffusion treatment, the Fe—Ni—Cu—Cr layer 3 can be formed on the steel sheet.

[0063] The thermal diffusion treatment may be either a continuous annealing method or a box annealing method, and is not particularly limited. The heat treatment atmosphere is preferably a non-oxidizing atmosphere or a reducing protective gas atmosphere. When a reducing protective gas atmosphere is used, for example, H 2 O 3 , also known as HNX gas, is used. ２ and N ２ In this embodiment, the thermal diffusion treatment includes an initial heating step, a final heating step, and a cooling step.

[0064] The initial heating step is a step of heating the plated steel sheet from room temperature to the starting temperature of the final heating step (final heating starting temperature) described below. The temperature rise rate in the initial heating step (hereinafter also referred to as the initial heating rate) is a rate determined by calculating the slope of the temperature profile of the plated steel sheet in the initial heating step. In other words, it can be calculated by dividing the temperature difference from the starting temperature of the initial heating step to the starting temperature of the final heating step by the required time. The initial heating rate is preferably greater than the temperature rise rate in the final heating step described below. Specifically, the initial heating rate is preferably greater than 4°C / s and not greater than 14°C / s.

[0065] The maximum temperature rise rate in the initial heating step (hereinafter also referred to as the maximum temperature rise rate) is a rate determined by calculating the maximum slope of the temperature profile of the plated steel sheet in the initial heating step, i.e., the temperature profile from room temperature to the starting temperature of the final heating step, and is preferably 4°C / sec or more. Furthermore, from the viewpoint of properly forming the Fe—Ni—Cu—Cr layer 3 and controlling the Cu intensity ratio and Cr intensity ratio between the steel sheet 2 and the Fe—Ni—Cu—Cr layer 3 within appropriate ranges, the maximum temperature rise rate in the initial heating step is preferably 14°C / sec or less, more preferably 12°C / sec or less, and even more preferably 10°C / sec or less. In particular, from the viewpoint of suppressing diffusion of Fe to the outermost surface, the maximum temperature rise rate in the temperature profile of 450°C or more in the initial heating step is preferably 14°C / sec or less, more preferably 12°C / sec or less, and even more preferably 10°C / sec or less.

[0066] The final heating step is a step of heating from the final heating start temperature to the maximum temperature in the thermal diffusion treatment (hereinafter referred to as the final temperature). The final heating start temperature is preferably 600°C or higher, at which point Ni in the Ni-plated layer and Fe in the steel sheet 2 begin to diffuse actively, and more preferably 650°C or higher, at which point they begin to interdiffuse more actively. From the viewpoint of easily promoting the active diffusion of Cu and Cr in the final heating step, the final heating start temperature is even more preferably 680°C or higher, and particularly preferably 710°C or higher. The final heating start temperature is preferably less than 900°C, more preferably less than 850°C. From the viewpoint of appropriately forming the Fe—Ni—Cu—Cr layer 3, the final temperature is preferably less than 930°C, more preferably less than 900°C, and even more preferably less than 870°C. Note that the final heating temperature can be set based on the final heating start temperature so that the temperature difference from the final heating start temperature is a predetermined temperature difference, as described below.

[0067] In this embodiment, from the viewpoint of improving the electrolyte resistance of the Ni-plated surface-treated steel sheet 1 during overdischarge as described below, the temperature rise rate in the final heating step (hereinafter also referred to as the final temperature rise rate) is preferably 4° C. / sec or less, more preferably 3° C. / sec or less, and even more preferably 1° C. / sec or less. The temperature rise rate in the final heating step is preferably 0.1° C. / sec or more, and more preferably 0.2° C. / sec or more.

[0068] The temperature difference between the ultimate temperature and the final heating start temperature should be 10°C or more, preferably 30°C or more, and more preferably 40°C or more. If the temperature difference is too small, the heating time in the final heating step (final heating time) may be insufficient, and the desired alloy state of the Fe-Ni-Cu-Cr layer 3 may not be obtained. In particular, when the Ni deposition weight is 2.5 g / m ２ When the temperature difference is higher than this, it is preferably 30°C or higher, more preferably 40°C or higher, and even more preferably 60°C or higher. By making the temperature difference 60°C or higher, the desired surface alloy state can be obtained, and a Ni-plated surface-treated steel sheet 1 with higher electrolyte resistance during overdischarge can be stably obtained. The upper limit of the temperature difference is preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower. In this embodiment, it is preferable to set the final heating rate to 4°C / second or lower, and therefore if the temperature difference is too large, the time in the high temperature range will be too long, and the desired surface alloy state may not be obtained.

[0069] In the cooling step, the plated steel sheet heated to the ultimate temperature is cooled to 120° C. or less. There are no particular restrictions on the cooling rate, but from the viewpoint of preventing defects in shape and the occurrence of wrinkles, the cooling rate is preferably 1° C. / sec to 20° C. / sec, and more preferably 1° C. / sec to 10° C. / sec.

[0070] FIG. 2 shows an example of a temperature profile of a plated steel sheet, illustrating a method for calculating the thermal history Y in a thermal diffusion treatment.

[0071] From the viewpoint of improving the electrolyte resistance of the Ni-plated surface-treated steel sheet 1 during overdischarge, the thermal history Y applied to the plated steel sheet through the initial heating step, final heating step, and cooling step in the thermal diffusion treatment is preferably 150,000°C·sec or less, more preferably 120,000°C·sec or less, and even more preferably 100,000°C·sec or less. Furthermore, from the viewpoint of sufficiently thermally diffusing Fe and Ni to obtain the desired alloy state, the thermal history Y is preferably 15,000°C·sec or more, more preferably 35,000°C·sec or more, and even more preferably 45,000°C·sec or more. The thermal history Y can be calculated by integrating the changes in heating temperature and cooling temperature over time at temperatures above 450°C. That is, the area of ​​the shaded portion in Figure 2 corresponds to the thermal history Y in the thermal diffusion treatment. In order to set the thermal history Y of the plated steel sheet within the above range, the heating rate (including the maximum heating rate) at 450°C or higher in the initial heating step and the final heating step, the heating start temperature, the ultimate temperature, and the cooling rate in the cooling step may be appropriately adjusted.

[0072] If the thermal history Y in the thermal diffusion treatment is too large or too small, the desired alloy state cannot be obtained, and the electrolyte resistance during overdischarge tends to decrease.

[0073] Ni adhesion amount W (g / m ２ ) and the thermal history Y, W / Y × 10 ５ is preferably 1.0 or more. ５ If the Ni deposition amount W (g / m) is less than 1.0, the desired surface alloy state cannot be obtained, and the electrolyte resistance during overdischarge may be deteriorated. ２ ) and the thermal history Y, W / Y × 10 ５ is preferably 20.0 or less, more preferably 10.0 or less, and even more preferably 7.0 or less. ５ If the value exceeds 20.0, the metal may not be sufficiently diffused, and the desired alloy state may not be obtained.

[0074] As described above, the inventors have found that by controlling the Ni deposition weight W on the steel sheet within the above range and performing thermal diffusion treatment of the Ni-plated steel sheet under the above conditions, the Ni in the Ni plating layer and the Fe, Cu, and Cr in the steel sheet 2 can be interdiffused to form an Fe—Ni—Cu—Cr layer 3 on the steel sheet 2. The Ni-plated surface-treated steel sheet 1 produced by the above method has excellent electrolyte resistance during overdischarge due to the presence of the Fe—Ni—Cu—Cr layer 3.

[0075] In a conventional method for improving the electrolyte resistance of a Ni-plated steel sheet, a steel sheet having a Ni-plated layer formed thereon is subjected to a thermal diffusion treatment to form an Fe—Ni diffusion layer. However, the present inventors have discovered that the electrolyte resistance of a Ni-plated surface-treated steel sheet 1 can be made even better by diffusing not only Fe but also Cu and Cr contained in the steel sheet 2 to form an Fe—Ni—Cu—Cr layer 3 on the steel sheet 2.

[0076] The reasons why the above thermal diffusion treatment method can form the Fe—Ni—Cu—Cr layer 3 are unclear, but the following is thought to be possible. First, the diffusion coefficients of nickel and chromium in iron are similar, and the diffusion coefficient of copper is slightly higher but nearly similar. Chromium actively diffuses above 700°C and its diffusion rate drops significantly below 700°C. Copper also begins to actively diffuse above 700°C. Therefore, in the above thermal diffusion treatment method, by gradually increasing the temperature in the initial heating step, the diffusion of copper and chromium can be suppressed and a copper and chromium deficiency near the interface can be prevented. Furthermore, in the above thermal diffusion treatment method, heating to 700°C or higher in the final heating step can promote the migration of copper and chromium from the interface toward the surface. It is believed that this copper and chromium diffusion mechanism enables the formation of an Fe—Ni—Cu—Cr layer 3 containing not only iron but also copper and chromium. Furthermore, by continuing to increase the temperature in the final heating step, it is believed that a rapid change from the nickel crystal structure to the iron-nickel alloy crystal structure is suppressed, thereby preventing the diffusion routes of copper and chromium from being obstructed, and making it possible to obtain an Fe—Ni—Cu—Cr layer 3 containing sufficient but trace amounts of copper and chromium on the surface.

[0077] Furthermore, a more preferable Fe—Ni—Cu—Cr layer 3 can be obtained by forming the Ni plating layer before thermal diffusion using a Ni plating bath containing a trace amount of semi-brightener. A Ni plating layer formed using a nickel plating bath containing a trace amount of semi-brightener contains more plating strain than a Ni plating layer formed using a matte Ni plating bath. This increases the driving force of atoms associated with changes in the crystal structure when the plating strain is released during thermal diffusion treatment. As a result, not only iron but also copper and chromium are more likely to diffuse from the steel sheet into the Ni plating layer, particularly during the final heating step, resulting in a more preferable Fe—Ni—Cu—Cr layer 3. On the other hand, adding too much semi-brightener to the Ni plating bath can reduce the crystal grain size of the Ni plating layer, and the addition of copper and chromium can potentially make the Fe—Ni—Cu—Cr layer 3 too hard. Therefore, the amount of semi-brightener added is preferably 6.0 mL / L or less.

[0078] In this manner, the Ni-plated surface-treated steel sheet 1 of this embodiment is manufactured.

[0079] After the thermal diffusion treatment, the Ni-plated surface-treated steel sheet may be subjected to temper rolling, if necessary. By performing temper rolling, it is possible to control mechanical properties, correct the shape, and impart surface roughness.

[0080] <Battery Container> The battery container in this embodiment is obtained by forming the Ni-plated surface-treated steel sheet 1 so that the surface of the Ni-plated surface-treated steel sheet 1 on which the Fe—Ni—Cu—Cr layer 3 is formed faces the inside of the battery container. Specifically, the battery container can be obtained by forming the Ni-plated surface-treated steel sheet 1 into the shape of a battery container by press forming such as drawing, ironing, DI (Drawing and Ironing), or DTR (Draw and Thin Redraw). The shape of the battery container can be cylindrical, prismatic, pouch-shaped, or cup-shaped, as well as plate-shaped shapes with irregularities or holes in part, such as the lid, current collector, or terminal.

[0081] The battery container obtained by molding the Ni-plated surface-treated steel sheet 1 in this embodiment has an Fe-Ni-Cu-Cr layer 3 formed on the inner surface, which provides high electrolyte resistance during overdischarge and can suppress corrosion due to the elution of Fe.

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for evaluating each property are as follows.

[0083] <Thickness of Ni plating layer> In each example and comparative example, the Ni coating weight per one side of the Ni-plated steel sheet was determined by measuring the Ni coating layer formed on the plated steel sheet using a fluorescent X-ray analyzer. A ZSX100e (manufactured by Rigaku Corporation) was used as the fluorescent X-ray analyzer, and measurements were made using a calibration curve method. The Ni coating weight was calculated based on the density of Ni (8.9 g / cm ３ ) was converted into thickness to determine the thickness of the Ni plating layer.

[0084] <Intensity, Intensity Ratio, and Fe—Ni—Cu—Cr Layer Thickness of Each Metal by GDS> Using a high-frequency glow discharge optical emission spectrometer (manufactured by HORIBA, Ltd., model number: GD-PROFILER2), the Ni etching rate was first determined to be 0.035 μm / sec using a standard Ni-plated steel sheet (standard sample) prepared by applying a 1.1 μm-thick matte Ni plating to a 0.3 mm-thick low-carbon steel sheet using the method described above. Furthermore, the maximum Ni intensity in the standard Ni-plated steel sheet, as well as the Cu intensity and Cr intensity at depths of 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, and 0.9 μm, were determined. Next, measurements were performed on the Ni-plated surface-treated steel sheet 1, and the changes in Fe intensity, Ni intensity, Cu intensity, and Cr intensity with respect to the measurement time (etching time) were measured. Based on the Ni etching rate, the measurement time (etching time) of the Ni-plated surface-treated steel sheet 1 in radio-frequency glow discharge optical emission spectroscopy was converted into depth. The resulting charts are shown in FIGS. 3( a) to 5(b). FIG. 3(a) is a chart obtained by radio-frequency glow discharge optical emission spectroscopy in Example 1, and FIG. 3(b) is an enlarged view of FIG. 3(a). FIG. 4(a) is a chart obtained by radio-frequency glow discharge optical emission spectroscopy in Example 2, and FIG. 4(b) is an enlarged view of FIG. 4(a). FIG. 5(a) is a chart obtained by radio-frequency glow discharge optical emission spectroscopy in Comparative Example 1, and FIG. 5(b) is an enlarged view of FIG. 5(a).

[0085] In the obtained chart, the formation of the Fe—Ni—Cu—Cr layer 3 was confirmed by comparing it with a standard Ni-plated steel sheet using the above-mentioned method. The Cu intensity and Cr intensity were also determined at depths of 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, and 0.9 μm. The depth D at which the Ni intensity was 2% of the maximum Ni intensity of the standard sample was also determined. Ｎｉ２％ The Cu strength and Cr strength in steel plate 2 are Ｃｕ－ｓｔｅｅｌ and Cr intensity In Ｃｒ－ｓｔｅｅｌ The maximum value In of Cu intensity in each Ni-plated surface-treated steel sheet 1 was calculated as follows. Ｃｕ－ＭＡＸ and the maximum value of Cr intensity In Ｃｒ－ＭＡＸThe depth at which the maximum value was reached was also determined. In addition, the Cu intensity was measured at a depth where the Ni intensity was 10%, which is the boundary point between the Fe-Ni-Cu-Cr layer 3 and the steel plate 2, and the thickness of the Fe-Ni-Cu-Cr layer 3 was determined from that depth. Furthermore, the Fe intensity InFe-MAX-ref at a position 0.1 μm deep from the surface side relative to 10% of the maximum Fe intensity InFe-MAX-ref of the standard sample was calculated. Ｆｅ－０．１ｄ Ratio of IR Ｆｅ－０．１ｄ asked for.

[0086] Cu intensity In at a depth of 0.1 μm from the surface Ｃｕ－０．１ｄ and Cu strength In in steel plate 2 Ｃｕ－ｓｔｅｅｌ Relative to IR Ｃｕ－０．１ｄ Similarly, the Cu intensity ratio IR at depths of 0.3 μm, 0.5 μm, 0.7 μm, and 0.9 μm was calculated. Ｃｕ－０．３ｄ , I.R. Ｃｕ－０．５ｄ , I.R. Ｃｕ－０．７ｄ , and I.R. Ｃｕ－０．９ｄ Similarly, the Cr intensity ratios IR at depths of 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, and 0.9 μm were calculated. Ｃｒ－０．３ｄ , I.R. Ｃｒ－０．５ｄ , I.R. Ｃｒ－０．７ｄ , and I.R. Ｃｒ－０．９ｄ The maximum value of Cu intensity In Ｃｕ－ＭＡＸ and the maximum value of Cr intensity In Ｃｒ－ＭＡＸ , and the Cu strength In in steel plate 2 Ｃｕ－ｓｔｅｅｌ The ratio of these to IR Ｃｕ－ＭＡＸ and I.R. Ｃｒ－ＭＡＸ Furthermore, the Cu intensity ratio IR at each depth position relative to the Cu intensity InCu-0.5d-ref at a depth of 0.5 μm of the standard sample was calculated. Ｃｕ－ｄ－ｖｒｅｆ , and the Cr intensity ratio IR at each depth position to the Cr intensity InCr-0.5d-ref at a depth of 0.5 μm of the standard sample Ｃｒ－ｄ－ｖｒｅｆThe specific measurement conditions for the high frequency glow discharge optical emission spectrometer were as follows: Measurement mode: HDD mode Excitation mode: RF (normal) Output: 35 W Pressure: 600 Pa Module: 7 V Fuse: 5 V Anode diameter: 4 mm Gas replacement time: 30 seconds Pre-sputtering time: 30 seconds Background measurement time: 5 seconds Measurement time: 100 seconds Capture interval: 0.1 seconds

[0087] <Evaluation of Electrolyte Resistance During Over-Discharge> The Ni-plated surface-treated steel sheet 1 was evaluated for electrolyte resistance during over-discharge by the LSV (Linear Sweep Voltammetry) method using a multi-electrochemical measurement system HZ-Pro (Model: HAG-PROM12, manufactured by Hokuto Denko Corporation). For the measurement, a measurement jig shown in FIG. 6 was used. FIG. 6 is a schematic diagram of the measurement jig used for evaluating the electrolyte resistance of the Ni-plated surface-treated steel sheet 1 by the LSV method. As shown in FIG. 6, the Ni-plated surface-treated steel sheet 1 was attached to the bottom of the measurement jig, and an electrolyte (1 mol / L LiPF ６ , EC:DEC (1:1 v / v%), manufactured by Kishida Chemical Co., Ltd.) was added, and metallic lithium (manufactured by Honjo Metals Co., Ltd.) was attached to the upper electrode of the jig as a counter electrode and a reference electrode. The surface area of ​​the measurement surface was 1.04 cm ２ The surface area of ​​the counter electrode and the reference electrode is 1.2 cm ２ The distance between the reference electrode and the working electrode was 2 mm, the distance between the counter electrode and the working electrode was 2 mm, and the distance between the counter electrode and the reference electrode was 12 mm. The measurement was carried out in a dry room with a dew point of -40°C or less and a room temperature of 23°C. The voltage was measured at a scanning rate of 2 mV / sec from the natural potential to +4.1 V (vs. Li / Li), which corresponds to overdischarge. ＋ ) and the current value (μA / cm ２ ) was measured to evaluate the electrolyte resistance during overdischarge of the Ni-plated surface-treated steel sheet 1. A smaller current value indicates less elution of metals such as Fe, and more excellent electrolyte resistance during overdischarge.

[0088] <Contact Resistance Value> A 25 mm square test piece was prepared by cutting the Ni-plated surface-treated steel sheet 1. Next, one of the prepared test pieces was measured for contact resistance value [mΩ] using an electrical contact simulator (manufactured by Yamazaki Precision Laboratory Co., Ltd., model number: CRS-1) under a contact load of 150 gf. A smaller contact resistance value indicates better battery characteristics when the Ni-plated surface-treated steel sheet 1 is used as a battery container.

[0089] <<Example 1>> As the base sheet for steel sheet 2, a cold-rolled steel sheet (low-carbon steel A) having a thickness of 0.5 mm and made of low-carbon aluminum-killed steel having a Cu content of 0.2 wt % or more and 0.4 wt % or less and a Cr content of 0.1 wt % or more and less than 0.3 wt % was prepared.

[0090] The prepared cold-rolled steel sheet was subjected to alkaline electrolytic degreasing and pickling by immersion in sulfuric acid, and then electroplated (Ni plating) under the following conditions using a Ni plating bath having the following bath composition, to obtain a Ni coating weight W of 4.45 g / m on the surface of the cold-rolled steel sheet. ２ A Ni plating layer of 1000 ppm was formed on the surface of the steel sheet, and a plated steel sheet was obtained. <Ni plating conditions> Bath composition: nickel sulfate hexahydrate 250 g / L, nickel chloride hexahydrate 45 g / L, boric acid 30 g / L, semi-brightener (unsaturated alcohol polyoxyethylene adduct, unsaturated carboxylic acid, formaldehyde) 3.0 mL / L, pH: 4.0 to 5.0, bath temperature: 60°C, current density: 10 A / dm ２

[0091] Next, the steel sheet (plated steel sheet) on which the Ni plating layer was formed was subjected to thermal diffusion treatment by continuous annealing in a reducing protective gas atmosphere to form an Fe—Ni—Cu—Cr layer 3. After the thermal diffusion treatment, the steel sheet was further subjected to temper rolling at a rolling reduction of 3% or less to obtain a Ni-plated surface-treated steel sheet 1 including a steel sheet 2 and an Fe—Ni—Cu—Cr layer 3 formed on one side of the steel sheet 2. In the continuous annealing, in the initial heating step, the plated steel sheet was heated from room temperature to a final heating start temperature. The final heating start temperature was set within a temperature range of 660 to 694°C. The maximum heating rate (maximum heating rate) in the initial heating step was 4.96°C / sec. Next, in the final heating step, the final temperature was set within a temperature range of 695 to 729°C so that the difference between the final heating start temperature and the final heating temperature (temperature difference in the final heating step) was 40°C, and the plated steel sheet was heated at a heating rate of 0.37°C / sec. Next, in the cooling step, a cooling gas such as HNX gas was sprayed onto the plated steel sheet, thereby cooling it until the temperature reached 120° C. or less. The thermal history Y applied to the Ni-plated steel sheet through the initial heating step, final heating step, and cooling step was 57,920° C. seconds.

[0092] The obtained Ni-plated surface-treated steel sheet 1 was subjected to various evaluations according to the above-mentioned methods. The results are shown in Table 1. In Table 1, the Cu intensity and Cr intensity at each depth position are collectively referred to as In Ｃｕ－ｄ , and In Ｃｒ―ｄ The ratio of the Cu intensity at each depth position to the Cu intensity in the steel plate 2 is collectively referred to as IR Ｃｕ－ｄ The ratio of the Cr intensity at each depth position to the Cr intensity in the steel plate 2 is collectively referred to as IR Ｃｒ－ｄ It was written as follows.

[0093] Example 2 A Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 1, except that the base sheet of steel sheet 2 was changed to a cold-rolled steel sheet having a thickness of 0.5 mm and made of low-carbon aluminum-killed steel (low-carbon steel B) having a Cu and Cr content of 0.01 wt % or more and less than 0.05 wt %, and evaluation was performed in the same manner. The results are shown in Table 1.

[0094] <<Example 3>> A Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 1, except that the base sheet of the steel sheet 2 was changed to a cold-rolled steel sheet (low-carbon steel C) with a thickness of 0.5 mm and made of low-carbon aluminum-killed steel having a Cu content of 0.1 wt % or more and less than 0.2 wt % and a Cr content of 0.03 wt % or more and less than 0.05 wt %, and that thermal diffusion treatment was carried out under the conditions shown in Table 5. The Ni-plated surface-treated steel sheet 1 was then evaluated in the same manner as in Example 1.

[0095] <<Examples 4-5>> Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 3, except that the thermal diffusion treatment was carried out under the conditions shown in Table 5, and was evaluated in the same manner.

[0096] <<Example 6>> Ni plating deposition amount: 0.89 g / m ２ and the thermal diffusion treatment was carried out under the conditions shown in Table 5, the same procedure as in Example 3 was repeated to obtain Ni-plated surface-treated steel sheet 1, which was then evaluated in the same manner.

[0097] <<Examples 7-8>> Ni plating deposition weight: 2.67 g / m ２ and the thermal diffusion treatment was carried out under the conditions shown in Table 5, the same procedure as in Example 3 was repeated to obtain Ni-plated surface-treated steel sheet 1, which was then evaluated in the same manner.

[0098] Example 9 A Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 1, except that the base sheet of steel sheet 2 was changed to a 0.5 mm thick cold-rolled steel sheet (low-carbon steel D) of low-carbon aluminum-killed steel having a Cu content of 0.05 wt % or more and less than 0.1 wt % and a Cr content of 0.03 wt % or more and less than 0.05 wt %, and that thermal diffusion treatment was carried out under the conditions shown in Table 5, and then evaluation was similarly carried out.

[0099] <<Example 10>> Ni plating deposition amount: 6.68 g / m ２ and the thermal diffusion treatment was carried out under the conditions shown in Table 5, the same procedure as in Example 3 was repeated to obtain Ni-plated surface-treated steel sheet 1, which was then evaluated in the same manner.

[0100] <<Example 11>> A Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 10, except that the base sheet of steel sheet 2 was changed to low-carbon steel D, and was evaluated in the same manner.

[0101] <<Example 12>> A Ni-plated surface-treated steel sheet 1 was obtained in the same manner as in Example 11, except that the base sheet of steel sheet 2 was changed to low-carbon steel B, and was evaluated in the same manner.

[0102] <<Comparative Example 1>> Ni deposition amount: 8.9 g / m ２ Ni-plated steel sheets were obtained in the same manner as in Example 2, except that the temperature was changed to 0.15°C and the thermal diffusion treatment was not performed, and evaluations were performed in the same manner. The results are shown in Table 1. In Comparative Example 1, the intensities of each element in high-frequency glow discharge optical emission spectroscopy were similar to those of the standard Ni-plated steel sheet, so it was determined that the Fe-Ni-Cu-Cr layer 3 was not formed. It was also confirmed that the Cu intensity ratio and Cr intensity ratio at each depth position of the Ni-plated layer to the steel sheet 2 in Comparative Example 1 were less than 0.5 and less than 0.2, respectively.

[0103] <<Comparative Example 2>> Ni-plated steel sheets were obtained in the same manner as in Example 10, except that the thermal diffusion treatment was carried out under the conditions shown in Table 5, and were evaluated in the same manner.

[0104] <<Comparative Example 3>> Ni plating deposition amount: 8.9 g / m ２ Ni-plated steel sheets were obtained in the same manner as in Example 10, except that the temperature was changed to

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] As shown in Tables 1 to 3, in Examples 1 to 12, when the strengths of the standard nickel-plated steel sheet measured by radio-frequency glow discharge optical emission spectroscopy were compared with those of the Ni-plated surface-treated steel sheet 1, alloy regions were found in which the Fe and Ni intensities were 10% or more of the maximum strengths of the standard Ni-plated steel sheet, and the Cu and Cr intensities were higher than the respective intensities in the Ni plating layer of the standard Ni-plated steel sheet. This confirmed the formation of alloy regions in which it was determined that Fe, Ni, Cu, and Cr were all present, i.e., the Fe-Ni-Cu-Cr layer 3. Specifically, the presence of the alloy regions was evident at least at depths of 0.1 μm, 0.3 μm, and 0.5 μm. It was confirmed that the intensity ratios of both Cu and Cr at each position relative to the standard Ni-plated steel sheet were 2.0 or more, i.e., more than twice the intensity ratio. Furthermore, in Examples 1 to 12, the intensity ratio IR between the 0.1 μm depth and the steel sheet 2 was 1.0 or more. Ｃｕ－０．１ｄ It was confirmed that the intensity ratio IR between the depth position of 0.5 μm and the steel plate 2 was 0.5 or more and 3.0 or less. Ｃｕ－０．５ｄ is 0.5 or more, and IR Ｃｒ－０．５ｄ It was confirmed that the value was 0.20 or more.

[0111] As shown in Tables 1 to 3, the Ni-plated surface-treated steel sheet 1 having the Fe-Ni-Cu-Cr layer 3 had a small current value caused by the elution of metals such as Fe at 4.1 V, which corresponds to overdischarge, and had excellent electrolyte resistance during overdischarge (Examples 1 to 12). In particular, Example 1 had a current value that was approximately 60% smaller than that of Comparative Example 1 shown in Table 4, and was particularly excellent in electrolyte resistance. Furthermore, the Ni-plated surface-treated steel sheet 1 of Example 1 had a smaller Cr intensity ratio IR at each depth position to the Cr intensity InCr-0.5d-ref at a depth of 0.5 μm of the standard sample than the Ni-plated surface-treated steel sheet 2 of Example 2. Ｃｒ－ｄ－ｖｒｅｆ This is thought to be because Example 1 contains a large amount of Cr, but also contains a sufficient amount of Cu diffused from the steel plate 2 into the Fe—Ni—Cu—Cr layer 3.

[0112] Furthermore, in Example 1, the intensity ratio IR between the depth position of 0.5 μm and the steel plate 2 Ｃｕ－０．５ｄIt was confirmed that the difference in Cu intensity ratio IR Ｃｕ－ＭＡＸ -IR Ｃｕ－０．１ｄ is more than 0.05, and satisfies the above formula (1), and the difference in Cu intensity ratio IR Ｃｕ－ＭＡＸ -IR Ｃｕ－ｂｏｕｎｄａｒｙ was greater than 0.05, satisfying the above formula (2). That is, in Example 1, it was confirmed that a region where copper was concentrated existed in the intermediate region of the Fe—Ni—Cu—Cr layer 3. This can also be confirmed from the fact that the depth at which the maximum Cu intensity in Example 1 was reached was 0.59 μm, which is shallower than the boundary point with the steel sheet 2, and from the fact that, unlike Example 2 and Comparative Example 1, in the chart of Example 1, the Cu intensity decreased toward the boundary point with the steel sheet 2 after reaching a maximum, as shown in FIG. 3( b). Furthermore, in Example 1, the Cu intensity ratio IR Ｃｕ－ｄ－ｖｒｅｆ was 2.3 or more and 10 or less, which was larger than that of Example 2. From this, it can be said that Example 1 had a larger absolute amount of Cu near the surface layer than Example 2. Example 1 had a smaller current value caused by the elution of metals such as Fe at 4.1 V, which corresponds to overdischarge, than Example 2, and was particularly excellent in electrolyte resistance during overdischarge. It is thought that these results were obtained in Example 1 by using carbon steel with a particularly high Cu content compared to Example 2.

[0113] As shown in Example 3-5, even when carbon steel C having a Cu content of 0.1 wt % or more and less than 0.2 wt % and a Cr content of 0.03 wt % or more and less than 0.05 wt % was used, a Ni-plated surface-treated steel sheet 1 having excellent electrolyte resistance was obtained.

[0114] As shown in Table 2, even when the amount of Ni plating applied is relatively small, the Fe-Ni-Cu-Cr layer 3 is formed using carbon steel containing a predetermined amount of Cu and Cr as the base plate, and the intensity ratio IR between the depth position of 0.1 μm and the steel plate 2 is Ｃｕ－０．１ｄ By adjusting the value to 0.5 or more and 3.0 or less, the Ni-plated surface-treated steel sheet 1 had excellent electrolyte resistance (Examples 6 to 9).

[0115] As shown in Table 3, when the amount of Ni plating applied was relatively large, the Cu intensity ratio IR Ｃｕ－ｄ Cu intensity ratio IR with standard sample Ｃｕ－ｄ－ｖｒｅｆ However, as can be seen from the comparison with Comparative Example 2 shown in Table 4, even when the Ni plating coating weight was relatively large, the Fe-Ni-Cu-Cr layer 3 was formed, and the intensity ratio IR between the depth position of 0.1 μm and the steel sheet 2 was Ｃｕ－０．１ｄ By adjusting the value of the saturation coefficient to 0.5 or more and 3.0 or less, the electrolyte resistance could be improved.

[0116] On the other hand, the Ni-plated steel sheet in which the formation of the Fe-Ni-Cu-Cr layer was not observed showed a large current value due to the dissolution of Fe at 4.1 V, which corresponds to overdischarge, and had poor electrolyte resistance (Comparative Example 1).

[0117] In addition, even when the Fe—Ni—Cu—Cr layer 3 is formed, the intensity ratio IR Ｃｕ－０．１ｄ When the diffusion coefficient was less than 0.5 and Cu was not sufficiently diffused near the surface, the electrolyte resistance was poor (Comparative Example 2-3).

[0118] 1...Ni-plated surface-treated steel sheet 2...Steel sheet 3...Fe-Ni-Cu-Cr layer

Claims

1. A Ni-plated surface-treated steel sheet comprising a steel sheet made of carbon steel and an Fe-Ni-Cu-Cr layer formed on at least one surface of the steel sheet, wherein when the Cu intensity is continuously measured in the depth direction from the surface side of the Fe-Ni-Cu-Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the Cu intensity In Ｃｕ－ｓｔｅｅｌ at a position 0.1 μm deep from the surface side with respect to the Cu intensity In Ｃｕ－０．１ｄ in the steel sheet has a ratio IR Ｃｕ－０．１ｄ of 0.5 or more and less than 3.

0.

2. When continuously measuring the Cu intensity in the depth direction from the surface side of the Fe—Ni—Cu—Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the Cu intensity In Ｃｕ－ｓｔｅｅｌ at a depth of 0.5 μm from the surface side with respect to the Cu intensity In Ｃｕ－０．５ｄ at the position of is a ratio IR Ｃｕ－０．５ｄ of 0.5 or more and less than 3.0, the Ni-plated surface-treated steel sheet according to claim 1.

3. When continuously measuring the Cr intensity in the depth direction from the surface side of the Fe—Ni—Cu—Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the Cr intensity In in the steel sheet Ｃｒ－ｓｔｅｅｌ at a position with a depth of 0.5 μm from the surface side with respect to the Cr intensity In Ｃｒ－０．５ｄ has a ratio IR Ｃｒ－０．５ｄ of 0.2 or more and less than 2.0, and the Ni-plated surface-treated steel sheet according to claim 1 or 2.

4. When continuously measuring the Cr intensity in the depth direction from the surface side of the Fe—Ni—Cu—Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the Cr intensity In Ｃｒ－ｓｔｅｅｌ at the position with a depth of 0.1 μm from the surface side with respect to the Cr intensity In Ｃｒ－０．１ｄ of the ratio IR Ｃｒ－０．１ｄ is 0.2 or more and less than 2.0, and the Ni-plated surface-treated steel sheet according to any one of claims 1 to 3.

5. When continuously measuring the Cu intensity in the depth direction from the surface side of the Fe—Ni—Cu—Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the Cu intensity In Ｃｕ－ｓｔｅｅｌ in the steel sheet at a depth of 0.3 to 0.7 μm from the surface side with respect to the Cu intensity In, the ratio IR Ｃｕ－０．３ｄ～０．７ｄ of the Cu intensity InCu-0.3d to 0.7d at a depth of 0.3 to 0.7 μm from the surface side is 0.5 or more and 3.0 or less. The Ni-plated surface-treated steel sheet according to any one of claims 1 to 4.

6. The Ni-plated surface-treated steel sheet according to any one of claims 1 to 5, wherein the Fe-Ni-Cu-Cr layer has a Cu-enriched region.

7. When continuously measuring the Cu intensity in the depth direction from the surface side of the Fe—Ni—Cu—Cr layer by high-frequency glow discharge optical emission spectroscopy (GDS), the Cu intensity In in the steel sheet Ｃｕ－ｓｔｅｅｌ at the depth up to the steel sheet with respect to the maximum Cu intensity In ＭＡＸ of the ratio IR Ｃｕ－ＭＡＸ is more than 0.8 and 3.0 or less, the Ni-plated surface-treated steel sheet according to any one of claims 1 to 6.

8. The Ni-plated surface-treated steel sheet according to any one of claims 1 to 7, wherein the steel sheet is a low-carbon steel or an extra-low-carbon steel.

9. The Ni-plated surface-treated steel sheet according to any one of claims 1 to 8, wherein the steel sheet is a low-carbon steel, the content of Cu in the steel sheet is 0.01% by weight to 1.0% by weight, and the content of Cr in the steel sheet is 0.01% by weight to 1.0% by weight.

10. A battery container made using the Ni-plated surface-treated steel sheet according to any one of claims 1 to 9.

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