Zn-Ni alloy plated steel sheet manufacturing method and manufacturing equipment

Abstract

To provide a method capable of producing a steel sheet of a uniform plating layer without decreasing the velocity of the steel sheet running through a plating solution even when a Zn-Ni plating layer is formed to have a large amount of the alloy in particular, upon carrying out Zn-Ni alloy plating.SOLUTION: The method of producing a Zn-Ni alloy plated steel sheet by carrying out Zn-Ni alloy electroplating, comprises feeding a plating solution through a gap between a continuously running steel sheet and an electrode plate opposingly disposed along the steel sheet, in the direction of the steel sheet, and concurrently feeding electricity by using the electrode plate as an anode and the steel sheet as a cathode, in which method, the discharge ratio of the plating solution, i.e., the ratio of the flow rate of the plating solution outflowing to the back side of the electrode plate not facing the steel sheet relative to the flow rate of the plating liquid being fed to the steel sheet, is kept 10% or lower.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a manufacturing method for efficiently manufacturing a Zn-Ni alloy plated steel sheet having excellent corrosion resistance, and to a manufacturing facility used in this manufacturing method. [Background technology]

[0002] Zn-Ni plated steel sheets are used as surface-treated steel sheets for automobiles. Zn-Ni plating is generally produced by electroplating. Compared to pure Zn plating, Zn-Ni plating is known to have superior corrosion resistance, and is used as steel sheet for hot pressing. In Zn-Ni plating, the Ni content in the film affects the corrosion resistance, so it is necessary to control the Ni content within an appropriate range. On the other hand, it is known that the electrodeposition of Zn-iron alloys, including Zn-Ni alloys, is an irregular codeposition in which Zn, a less noble metal, deposits preferentially over iron-group metals.

[0003] In addition, electroplated steel sheets are annealed in a continuous annealing line, and then produced in an electrogalvanizing line separate from the continuous annealing line. The coiled cold-rolled steel sheets are transported to the electrogalvanizing line, where they are subjected to a degreasing process to remove rust-preventive oil, a pickling process to remove the surface oxide film and activate the surface, and then an electroplating process to apply a coating of 5 to 80 g / m2 on one side. 2 The steel sheet is then shipped as electro-galvanized steel sheet after a chemical treatment process in which zinc or a zinc alloy is applied to the steel sheet and various chemical coatings are applied to improve corrosion resistance and paintability.

[0004] A horizontal flow cell system as shown in FIG. 1 is known as a general method for electroplating steel sheets. In this horizontal flow cell system electroplating apparatus, a passage 43 partitioned by electrode plates 42a and 42b is formed between two pairs of rolls, a conductor roll 40 and a backup roll 41. When a steel sheet P is passed through this passage 43, a plating solution 30 is supplied from a nozzle header 44 to a gap between the steel sheet P and the electrode plates 42a and 42b, and an electric current is applied between the front surface of the steel sheet P and the electrode plates 42a and 42b, with the electrode plates 42a and 42b as anodes and the steel sheet P as a cathode, thereby electroplating the steel sheet P with Fe. This system has the advantage that the front and back surfaces of the steel sheet can be plated simultaneously. The above electroplating apparatus usually has about 5 to 15 cells connected together, and performs continuous plating while passing the steel sheet through. The plating coverage per cell is 1 to 5 g / m 2 This is a plating method in which the thickness is thin and is layered. The current can be controlled according to the line speed and plate width, so the deposition weight distribution in the width and length directions is 0.5 to 1 g / m. 2 Another major feature is that it can achieve a uniform coating weight of within 20g / m2 and a beautiful appearance. 2 In the case of electrical galvanized steel sheets of this order, the plating section is not a bottleneck in production efficiency, but when the final coating weight is 60 g / m2 or more, higher corrosion resistance is required. 2 In the case of ultra-high-speed Zn-Ni plated steel sheets for automobiles, the plating section becomes a bottleneck in production efficiency because the desired plating weight cannot be achieved unless the sheet threading speed is reduced.

[0005] In addition, if the steel sheet is warped in the width direction during threading, the distance between the steel sheet and the electrode will differ in the width direction, and the current distribution will change (more current will flow in the area where the steel sheet-electrode distance is close than in the area where the steel sheet-electrode distance is far), resulting in uneven coating weight. However, if the final coating weight is 60 g / m 2 In the case of ultra-high-speed Zn-Ni coated steel sheets for automobiles, excessive coating weight is produced in some areas in order to guarantee the minimum in-plane coating weight, which can cause problems during press working. Therefore, it is necessary to control the coating weight uniformly in the width direction.

[0006] The following technique is disclosed here as a high speed electroplating method. FIG. 3 of Patent Document 1 discloses a method for producing an electroplated steel sheet at a high current density, in which a nozzle header provided with a plurality of plating solution jetting ports is disposed on the back surface of an electrode at a distance from the electrode, and through holes are provided through the electrode at positions of the electrode corresponding to each of the plating solution jetting ports of the nozzle header for guiding the plating solution from the nozzle header to between the steel sheet and the electrode, and plating solution is jetted from the plurality of plating solution jetting ports of the nozzle header to impinge on the steel sheet in a direction substantially perpendicular to the steel sheet for plating.

[0007] Furthermore, as a plating method for making the plating amount uniform, FIG. 1 of Patent Document 2 discloses a method for correcting C-warp by providing ribs on both widthwise ends of a cushion-shaped nozzle electrode to increase static pressure. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2005-272999 A [Patent Document 2] Japanese Patent Application Publication No. 60-86296 Summary of the Invention [Problem to be solved by the invention]

[0009] According to the method described in Patent Document 1, high current density plating is possible with pure Zn plating. On the other hand, Zn-Ni alloy plating requires different appropriate electrode shape, plating solution spraying conditions, and current density conditions from those of pure Zn plating, so it is difficult to supply fresh plating solution to the steel sheet surface. Therefore, when carrying out Zn-Ni alloy plating, it is desirable to avoid unevenness in the coating weight in the width direction, Ni content in the plating film falling outside the desired range, and in-plane changes in the electrode-steel sheet distance due to large warping of the steel sheet in the plating cell.

[0010] The method of Patent Document 2 has the effect of flattening the steel sheet shape, but the plating solution tends to accumulate in the steel sheet, so the plating solution is not stable at 60A / dm 2 When the above-mentioned high current density plating is performed on Zn-Ni alloy plating, the Ni content in the plating film falls outside the desired range, and therefore it is not possible to increase the sheet running speed to produce a Zn-Ni alloy-plated steel sheet.

[0011] The present invention has been made in consideration of the above problems, and aims to propose a method for producing a steel sheet having a uniform plating layer without reducing the sheet passing speed, especially when forming a Zn-Ni alloy plating layer with a high adhesion weight. [Means for solving the problem]

[0012] The gist of the present invention for solving the above problems is as follows. 1. A method for producing a Zn-Ni alloy plated steel sheet, comprising the steps of: supplying a plating solution toward a steel sheet in a gap between a continuously traveling steel sheet and an electrode plate disposed opposite the steel sheet and passing an electric current through the electrode plate as an anode and the steel sheet as a cathode, thereby electroplating the steel sheet with a Zn-Ni alloy, A method for producing a Zn-Ni alloy plated steel sheet, in which a plating solution discharge rate, which is a ratio of a flow rate of the plating solution flowing out to a back side of the electrode plate not facing the steel sheet to a flow rate of the plating solution supplied to the steel sheet, is set to 10% or less.

[0013] 2. The method for producing a Zn-Ni alloy plated steel sheet according to 1 above, wherein the steel sheet has a chemical composition containing, by mass%, 0.3% or less of C, and 1.0 to 6.0% in total of at least one of Si and Mn.

[0014] 3. A manufacturing facility for Zn-Ni alloy plated steel sheet, comprising electrode plates arranged opposite to each other along a running line of a steel sheet, and a spray nozzle for supplying a plating solution from the electrode plate side toward the running line, wherein the electrode plates are the anode and the steel sheet is the cathode, and the plating solution discharge rate, which is the ratio of the flow rate of plating solution flowing out to the back side of the electrode plates not facing the steel sheet to the flow rate of plating solution supplied from the spray nozzle, is 10% or less.

[0015] 4. The manufacturing equipment for Zn-Ni alloy plated steel sheet according to 3, wherein the electrode plate has at least one through hole extending in a direction intersecting with the traveling line and penetrating the electrode plate, and the injection nozzle is disposed in at least one of the through holes.

[0016] 5. A manufacturing facility for Zn-Ni alloy plated steel sheet as described in 3 or 4 above, comprising, on the back side of the electrode plate, a back plate and a jet header in that order from the traveling line side, a plurality of the jet nozzles extending through the back plate and the electrode plate being connected to the jet header, the back plate being connected to the back side of the electrode plate via an electrode connection part, and an insulator being placed in the space between the back plate and the electrode plate by the electrode connection part.

[0017] 6. The manufacturing equipment for Zn-Ni alloy plated steel sheet according to 5 above, comprising one or more plating cells in which a plurality of the electrode plates are assembled together without any gaps onto one of the back plates.

[0018] 7. The manufacturing equipment for Zn-Ni alloy plated steel sheet according to 6, wherein in each of the plating cells, the jet header is divided into a plurality of parts at positions that do not interfere with the electrode connection portion.

[0019] 8. The manufacturing equipment for Zn-Ni alloy plated steel sheet according to 5 above, wherein the jet header has plating solution piping for supplying plating solution into the jet header, and a ratio Ak / An of a cross-sectional area Ak of ​​the plating solution piping to a total cross-sectional area An of the injection ports of the injection nozzles connected to the jet header is 2.5 or more. Here, the manufacturing facility of the above item 8 is preferably the manufacturing facility of the Zn-Ni alloy plated steel sheet according to any one of items 5 to 7 above. Effect of the Invention

[0020] According to the method for producing an electroplated steel sheet of the present invention, it is possible to efficiently produce a Zn-Ni alloy plated steel sheet having a uniform plating layer. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram of a conventional horizontal flow cell setup. [Diagram 2] 1 is a schematic cross-sectional side view of an electroplating cell of the present invention; [Diagram 3] FIG. 2 is an enlarged view of the periphery of a circular tube nozzle of the electroplating cell of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, the method for producing a Zn-Ni alloy plated steel sheet of the present invention will be specifically described with reference to the drawings. The method for producing a Zn-Ni alloy plated steel sheet of the present invention is characterized in that, when Zn-Ni alloy electroplating is performed in a gap between a continuously running steel sheet and an electrode plate arranged opposite to the steel sheet, a plating solution is supplied toward the steel sheet while an electric current is passed through the electrode plate as an anode and the steel sheet as a cathode, and a plating solution discharge rate, which is the ratio of the flow rate of plating solution flowing out to the back side of the electrode plate not facing the steel sheet to the flow rate of plating solution supplied to the steel sheet, is set to 10% or less.

[0023] First, an embodiment of a hot-dip galvanizing production facility used in the method for producing a hot-dip galvanized steel sheet of the present invention will be described with reference to Fig. 2. In the embodiment shown in Fig. 2, a steel sheet P is made to travel on a traveling line in a horizontal direction, and a pair of electrode plates 10 are arranged opposite to the continuously traveling steel sheet P. The electrode plates 10 are preferably insoluble. Furthermore, a conductor roll 20 and a backup roll 21 for passing a current through the steel sheet P are arranged upstream and downstream of the electrode plate 10 in the traveling direction of the steel sheet P, respectively.

[0024] Here, the conductor roll 20 may be one having a hard chrome plating structure using copper plating or nickel plating with good conductivity as a base. The material and thickness of the electrode plate 10 are not particularly limited, but the material is preferably titanium coated with iridium oxide, and the thickness is preferably 5 to 100 mm. The distance between the steel plate P and the electrode plate 10 is also not particularly limited, but is preferably in the range of 2 to 20 mm.

[0025] A back plate 12 is disposed on the back surface of each electrode plate 10 (the side of the electrode plate opposite the steel plate P) via an electrode connection portion 11, and current output from a rectifier (not shown) is input to the back plate 12 through a current-carrying rod 16. A nozzle header 14 for supplying plating solution 30 is disposed on the back surface of the back plate 12. To ensure uniform current distribution, the back plate 12 is preferably formed as an integral part within one cell. On the other hand, the electrode plate 10 facing the steel plate is preferably appropriately divided in the width direction and length direction in consideration of replacement work and the like.

[0026] The nozzle header 14 has a plurality of circular tube nozzles 15 made of an insulating material, which extend from the back plate 12 side to the electrode plate 10 side through a plurality of through holes 10a and 12a provided in the electrode plate 10 and the back plate 12, respectively, and stay within the through holes 10a of the electrode plate 10. Here, the reason why it is preferable to form the circular tube nozzles 15 from an insulating material is that by making the entire plating solution supply system out of an insulating material, unintended electrodeposition in the plating solution flow path can be avoided, and damage to components due to sparks between the circular tube nozzles 15 and the electrode plate 10 can be avoided.

[0027] The cylindrical nozzle 15 is preferably disposed so that its axis is perpendicular to the surface of the steel sheet P. The plating solution 30 is supplied from the nozzle header 14 to the cylindrical nozzle 15, and sprayed toward the steel sheet P from the nozzle outlet at the tip of the cylindrical nozzle 15.

[0028] In this manner, while the steel sheet P is traveling horizontally, a plating solution 30 is supplied to the gap between the steel sheet P and the electrode plate 10, and with the electrode plate 10 serving as the anode and the steel sheet P serving as the cathode, a current is passed between the plating surface of the steel sheet P and the electrode plate 10 to electroplate the steel sheet.

[0029] 3 shows an enlarged view of one nozzle header 14 and its periphery in the electroplating apparatus 56 described above. The tip of the circular pipe nozzle 15 is long enough to remain within the through hole 10a so as not to protrude beyond the surface of the electrode plate 10 on the steel sheet P side toward the steel sheet P. Furthermore, in order to prevent the plating solution 30 from flowing out from the through hole 10a to the back side of the electrode plate 10, the space formed between the electrode plate 10 and the back plate 12 by the electrode connection part 11 (including any gap between the inner wall of the through hole 10a and the circular pipe nozzle 15) needs to be blocked by an insulator 13 made of, for example, resin.

[0030] That is, at least the space formed between the electrode plate 10 and the back plate 12 needs to be filled with the insulator 13 so that the plating solution does not flow out from the steel sheet P side to between the electrode plate 10 and the back plate 12. If there is a gap between the inner wall of the through hole 10a of the electrode plate 10 and the outer circumferential surface of the circular tube nozzle 15, it is preferable to fill it with the insulator 13. Here, if the above-mentioned gap in the through hole 10a can be completely filled so that there is no liquid leakage, there is no need to fill the gap between the electrode plate 10 and the back plate 12 with the insulator 13. However, considering that it is technically or cost-wise difficult to completely block the above-mentioned gaps in all of the many through holes of the electrode plate 10 with the insulator, it is effective to block the space formed between the electrode plate 10 and the back plate 12 with the insulator 13 more simply.

[0031] In order to pass current uniformly from the back plate 12 to the multiple electrode plates 10, it is preferable to machine the connection surface between the back plate 12 and the electrode connection portion 11 smoothly and then fasten them with bolts (not shown). This structure is extremely effective in assembling this device. That is, it is structurally possible to fasten the back plate 12 and the electrode plate 10 without providing the electrode connection portion 11, but if the back plate 12 and the electrode plate 10 are in close contact only around the fastening bolt and a small gap occurs at a position slightly away from the fastening bolt, a spark will occur at the position of the gap when electricity is applied, damaging the back plate 12 and the electrode plate 10, so such a structure is not desirable.

[0032] Furthermore, as described above, by filling the gap between the back plate 12 and the electrode plate 10 with the insulator 13, it is possible to prevent uneven current flow between the back plate 12 and the electrode plate 10. If the material filling the gap between the back plate 12 and the electrode plate 10 is not an insulator, current will flow in places other than the electrode connection parts 11, resulting in uneven current distribution when the electrode plate is viewed from the steel plate.

[0033] With the above structure, the plating solution does not flow out from the through holes to the back side of the electrode plates 10, so the jet of plating solution from the circular pipe nozzle 15 is concentrated in the gap between the electrode plates 10, and the jet pressure of the plating solution can be applied to the steel sheet P passing through the gap without any waste. As a result, a straightening force acts on both the top and bottom of the steel sheet P, making it possible to pass and pass a current through the steel sheet P while flattening the poorly shaped steel sheet.

[0034] Here, in one section of electroplating (3 cells: electrode size of one cell: width 1.5 m × length in the sheet passing direction 1 m) shown in Fig. 2, the pressing force of the plating solution jet from the circular tube nozzle onto the steel sheet P was investigated for the case where an electrode plate with discharge holes as described in the above-mentioned Patent Document 1 was used, and the case where an electrode plate according to the present invention as shown in Fig. 3 was used. That is, in one section of electroplating shown in Fig. 2, a total of 120 circular tube nozzles with an inner diameter of φ8 mm were arranged on one side of the pair of electrode plates, with 10 nozzles in the electrode width direction × 12 rows in the sheet passing direction, and the total plating solution flow rate was set at 2.5 m 3 The pressing force applied to the steel sheet when the plating solution jet was sprayed at 10000 / min was measured. As a result, in the electrode provided with the discharge holes described in Patent Document 1, the steel sheet pressing force was applied only to the collision position of the plating solution jet from the nozzle, and the pressing force acting on one side of the steel sheet was 290 N in total (1.53 N per nozzle). In contrast, in the electrode of the present invention shown in Fig. 3, the plating solution is discharged only from the inlet side and outlet side of the steel sheet P of the electrode plate, so that the pressure corresponding to the pressure loss of the plating solution flowing between the nozzle and the steel sheet is applied to the entire electrode surface (the effective area on which the steel sheet pressing force actually acts is about 50% of the electrode plate area), resulting in a form in which the steel sheet is pressed, and the steel sheet pressing force reached 3500 N, more than 12 times as much. In this way, according to the present invention, straightening forces act from above and below the steel sheet in the plating cell, making it possible to flatten a steel sheet with a poor shape while passing it through and passing a current through it.

[0035] In order to obtain the above-mentioned effects, it is essential to keep the above-mentioned plating solution drainage rate during electroplating at 10% or less. In other words, if the plating solution drainage rate exceeds 10%, the flow rate of the plating solution flowing between the electrode plate and the steel sheet decreases, and the pressing force against the steel sheet decreases.

[0036] 3, in one divided jet header 14, the ratio Ak / An of the cross-sectional area Ak of ​​the plating solution pipe 14a supplying the plating solution 30 to the jet header 14 and the total cross-sectional area An of the nozzles of the circular pipe nozzles 15 provided in the jet header 14 is preferably 2.5 or more. That is, when Ak / An is less than 2.5, the pressure distribution in the jet header is likely to become non-uniform, and the variation in the jet speed from the circular pipe nozzle 15 may increase, which may cause problems such as uneven adhesion. When Ak / An exceeds 12, a sudden contraction pipe state occurs in which the change in the flow path cross-sectional area from the jet header to the circular pipe nozzle is large, which increases the pressure loss and requires an excessive capacity of the plating solution delivery pump. Therefore, from the viewpoint of economy, it is preferable to set the ratio to 12 or less.

[0037] The above-mentioned cross-sectional areas are the minimum areas of the inner cross sections perpendicular to the axial direction of each tube. In addition, when each jet header 14 has a plurality of plating solution pipes and circular pipe nozzles, the total cross-sectional areas of each tube are Ak and An, respectively. Therefore, in the jet header 14 shown in FIG. 4, Ak is the cross-sectional area of ​​the plating solution pipe 14a, and An is the total cross-sectional area of ​​the three jet nozzles of the circular pipe nozzle 15.

[0038] By the way, in order to stably obtain a Ni content of 10-15% in the Zn-Ni plating film in a commonly used electroplating device, the current density should be 5-20A / dm 2 On the other hand, the electroplating equipment of the present invention has a current of 30 to 250 A / dm 2 This allows production at 250A / dm for horizontal electroplating equipment. 2 At the above speeds, power losses due to the electrical resistance of the plating solution and Joule heat in the steel sheet and electrical circuits are large, and power consumption becomes excessive relative to productivity improvements achieved by increasing the sheet threading speed, making economical production impossible.

[0039] The above-mentioned plating target is not particularly limited, and may be any steel plate. Examples of plating targets include ordinary steel, stainless steel, and aluminum plates. The present invention is effective when applied to steel plates, and is particularly advantageous when applied to high-tensile steel plates. As high-tensile steel plates, steel plates having the following composition are suitable. In the following composition, "%" refers to mass % unless otherwise specified.

[0040] C: 0.025~0.300% C is preferably contained in an amount of 0.025% or more because it forms a retained austenite layer, a martensite phase, etc. in the steel structure, which facilitates improving workability. On the other hand, if it exceeds 0.300%, weldability deteriorates, so the C content is preferably 0.300% or less.

[0041] Silicon: 0.2 to 2.5% Since Si is an effective element for strengthening steel and obtaining good material properties, 0.2% or more is added to high-tensile steel sheets. If the Si content is less than 0.2%, expensive alloying elements are required to obtain high strength. On the other hand, if the Si content exceeds 2.5%, the formation of an oxide film during oxidation treatment is suppressed. In addition, the alloying temperature also becomes high, making it difficult to obtain the desired mechanical properties. Therefore, it is preferable that the Si content be 2.5% or less.

[0042] Mn: 1.5-3.5% Mn is an element that is effective in increasing the strength of steel. In order to ensure a tensile strength of 590 MPa or more, it is preferable to include 0.5% or more. On the other hand, if it exceeds 3.0%, it may become difficult to ensure the weldability, plating adhesion, and strength-ductility balance. Therefore, the Mn content is preferably 1.5 to 3.5%.

[0043] In addition to the above components, the following elements may also be contained. Al: 0.001 to 1.000% Al is added for the purpose of deoxidizing molten steel, but if its content is less than 0.001%, this purpose is not achieved. On the other hand, if its content exceeds 1.000%, Al forms oxides on the surface, which deteriorates the plating appearance (surface appearance). Therefore, the Al content may be 0.001% or more and 1.000% or less.

[0044] P:0.10% or less P is one of the elements that is inevitably contained, and since there is a concern that costs will increase if the content is less than 0.005%, it is desirable to have a content of 0.005% or more. On the other hand, as the content of P increases, the manufacturability of slabs deteriorates. Furthermore, the inclusion of P inhibits the alloying reaction and causes uneven plating. In order to inhibit these, it is necessary to keep the content at 0.10% or less. Therefore, the amount of P may be 0.10% or less, and is preferably 0.05% or less.

[0045] S: 0.01% or less S is an element that is inevitably contained during the steelmaking process. However, if it is contained in a large amount, it deteriorates weldability. Therefore, S content may be limited to 0.01% or less. When the above components are contained, the balance is Fe and unavoidable impurities.

[0046] Furthermore, one or more elements selected from B: 0.001-0.005%, Nb: 0.005-0.050%, Ti: 0.005-0.080%, Cr: 0.001-1.000%, Mo: 0.05-1.00%, Cu: 0.05-1.00%, Ni: 0.05-1.00%, and Sb: 0.001-0.200% may be contained as necessary. When these elements are added, the appropriate contents and the reasons for limiting the contents are as follows:

[0047] B: 0.001 to 0.005% At 0.001% or more, B has a hardening-promoting effect. On the other hand, at more than 0.005%, phosphatability deteriorates. Therefore, if B is contained, the B content may be 0.001% or more and 0.005% or less.

[0048] Nb: 0.005 to 0.050% Nb has the effect of adjusting (improving) strength when it is 0.005% or more. On the other hand, if it exceeds 0.05%, it will lead to an increase in costs. Therefore, if Nb is contained, the Nb content may be 0.005% or more and 0.05% or less.

[0049] Ti: 0.005 to 0.080% At 0.005% or more, Ti has the effect of adjusting (improving) strength. On the other hand, at more than 0.080%, it causes deterioration of chemical conversion treatability. Therefore, when Ti is contained, the Ti content may be 0.005% or more and 0.080% or less.

[0050] Cr: 0.001~1.000% At 0.001% or more, Cr has a hardenability effect. On the other hand, at more than 1.000%, Cr is concentrated on the surface, which deteriorates weldability. Therefore, if Cr is contained, the Cr content should be 0.001% or more and 1.000% or less.

[0051] Mo: 0.05 to 1.00% Mo has the effect of adjusting strength (strength improvement) when it is 0.05% or more. On the other hand, if it exceeds 1.00%, it will lead to an increase in costs. Therefore, if Mo is contained, the Mo content may be 0.05% or more and 1.00% or less.

[0052] Cu: 0.05-1.00% Cu has an effect of promoting the formation of the residual γ phase when it is 0.05% or more. On the other hand, if it exceeds 1.00%, it will lead to an increase in costs. Therefore, if Cu is contained, the Cu content may be 0.05% or more and 1.00% or less.

[0053] Ni: 0.05 to 1.00% Ni content of 0.05% or more has the effect of promoting the formation of the residual γ phase. On the other hand, Ni content exceeding 1.00% leads to an increase in costs. Therefore, when Ni is contained, the Ni content may be 0.05% or more and 1.00% or less.

[0054] Sb: 0.001 to 0.200% Sb can be contained from the viewpoint of suppressing nitridation and oxidation of the steel sheet surface, or decarburization of the steel sheet surface in an area of ​​several tens of microns caused by oxidation. Suppressing nitridation and oxidation prevents a decrease in the amount of martensite formed on the steel sheet surface, improving fatigue properties and surface quality. Such effects can be obtained at 0.001% or more. On the other hand, if it exceeds 0.200%, toughness deteriorates. Therefore, if Sb is contained, the amount of Sb may be 0.001% or more and 0.200% or less.

[0055] In addition, examples of trace elements permitted in the plating solution include Pb (1.0 ppm or less), Cr (200 ppm or less), Hg (200 ppm or less), Cu (2.0 ppm or less), Cd (6.0 ppm or less), Sr (30 ppm or less), and sludge (solid content 100 ppm or less). EXAMPLES

[0056] The following describes examples of the present invention, but the technical scope of the present invention is not limited to the following examples. An example of the present invention uses an electroplating apparatus (one cell) with the configuration shown in Figures 2 and 3. That is, the plating cell that constitutes the electroplating apparatus has an electrode length in the longitudinal direction of 2 m in each cell, and 15 cells are connected. The electrode plate is made of titanium, and the current-carrying surface is coated with an iridium oxide film, and has a width that almost covers the strip. As comparative examples, a general horizontal flow cell (FIG. 1) and a horizontal multi-hole plating cell having plating solution discharge holes (based on the description in FIG. 1 of Patent Document 1) were used.

[0057] Using each of the above plating manufacturing equipment examples, a steel plate with a thickness of 0.7 mm and a width of 1200 mm was run at a sheet speed of 0.7 to 3.5 m / s, and the coating weight was 65 g / m on one side at a plating efficiency of 70%. 2 The current density was set so that Zn-Ni alloy plating was performed. Specific conditions of the sheet passing speed and current density are as shown in Table 1. The plating bath was a sulfuric acid bath, the components of which were zinc 24-40g / L and nickel 45-70g / L, and the pH was adjusted to 1.5-1.7.

[0058] The electroplated steel sheets thus obtained were subjected to measurement of the coating weight and Ni content in the coating. The coating weight and Ni content were calculated as the average values ​​of 10 measurements taken in the longitudinal direction at 16 points in the width direction. The coating weight distribution in the width direction was calculated as the coating weight change rate (%) at both ends in the width direction (positions 30 mm from the steel sheet edge) relative to the coating weight at three points in the width direction center, with a value of 5% or less being considered good. The results of the above measurements and evaluations are shown in Table 1 together with the electroplating conditions.

[0059] [Table 1] [Explanation of symbols]

[0060] P steel plate 10 Electrode plate 11 Electrode connection part 12 Backplate 13 Insulators 14 Jet Header 15 Circular Tube Nozzle 16 Electrifying rod 20 Conductor Roll 21 Backup Role

Claims

1. A method for producing a Zn-Ni alloy-plated steel sheet, comprising the steps of: supplying a plating solution from a spray nozzle on the electrode plate in a direction perpendicular to a surface of the steel sheet in a gap between the continuously traveling steel sheet and an electrode plate disposed opposite the steel sheet along the steel sheet; and applying an electric current to the electrode plate as an anode and the steel sheet as a cathode, thereby electroplating the steel sheet with a Zn-Ni alloy, A method for producing a Zn-Ni alloy-plated steel sheet, in which a plating solution discharge rate, which is a ratio of a flow rate of the plating solution flowing out to a back side of the electrode plate not facing the steel sheet to a flow rate of the plating solution supplied from the spray nozzle to the steel sheet, is set to 10% or less.

2. The method for producing a Zn-Ni alloy plated steel sheet according to claim 1, wherein the steel sheet has a composition containing, in mass%, 0.3% or less of C, and 1.0 to 6.0% in total of one or more of Si and Mn.

3. a back plate and a jet header on a back side of the electrode plate, in that order from the traveling line side, and a plurality of the jet nozzles extending through the back plate and the electrode plate are connected to the jet header, the back plate is connected to a back side of the electrode plate via an electrode connection part, and an insulator is disposed in a space between the back plate and the electrode plate, the space being defined by the electrode connection part; and a plating solution discharge rate, which is a ratio of a flow rate of plating solution flowing out to a back side of the electrode plate not facing the steel sheet to a flow rate of plating solution supplied from the jet nozzle, is 10% or less.

4. The manufacturing equipment for a Zn-Ni alloy plated steel sheet according to claim 3, wherein the electrode plate has at least one through hole extending in a direction intersecting with the traveling line and penetrating the electrode plate, and the injection nozzle is disposed in at least one of the through holes.

5. The manufacturing equipment for the Zn-Ni alloy plated steel sheet according to claim 3 or 4, comprising one or more plating cells in which a plurality of the electrode plates are combined with one of the back plates without any gaps as an assembly.

6. 6. The equipment for producing a Zn-Ni alloy plated steel sheet according to claim 5, wherein in each of the plating cells, the jet header is divided into a plurality of parts at positions not interfering with the electrode connection portion.

7. 5. The production facility for Zn-Ni alloy plated steel sheet according to claim 3 or 4, wherein the jet header has a plating solution piping for supplying a plating solution into the jet header, and a ratio Ak / An of a cross-sectional area Ak of ​​the plating solution piping to a total cross-sectional area An of the injection ports of the injection nozzles connected to the jet header is 2.5 or more.

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