Method for manufacturing hot-dip galvanized steel sheet and manufacturing facility for hot-dip galvanized steel sheet

Abstract

To provide a method capable of manufacturing a steel sheet including a beautiful plating layer and an easily oxidizable element, especially, a high tensile steel sheet without having quality defects such as non-plating and a pickup or the like due to, especially, a shape disorder of the steel sheet when subjecting the steel sheet to hot dip galvanizing and further to alloying.SOLUTION: A method for manufacture a hot-dip galvanized steel sheet comprises: an electroplating step of energizing a steel sheet continuously running using an electrode plate arranged to face along the steel sheet as an anode and the steel sheet as a cathode while supplying a ferrous plating solution toward the steel sheet in a gap between the steel sheet and the electrode plate and subjecting the steel sheet to electroplating to form a ferrous coating on the surface of the steel sheet; an annealing step of heating the steel sheet passing through the electroplating step; and a hot-dipping step of subjecting the steel sheet passing through the annealing step to hot dip galvanizing. In the electroplating step, a plating solution discharge ratio of a flow rate of the plating solution discharged on a rear side of the electrode plate without facing the steel sheet to that of the plating solution supplied to the steel sheet is less than 50%.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a hot-dip galvanized steel sheet, particularly a hot-dip galvanized steel sheet using a high-tensile steel sheet as a base material, and a manufacturing facility for the hot-dip galvanized steel sheet.

Background Art

[0002] In recent years, in fields such as automobiles, home appliances, and building materials, the demand for high-tensile steel sheets (high-tensile steel materials) that can be used for weight reduction of structures and the like has been increasing. As high-tensile steel materials, for example, steel sheets with good hole expansion properties by containing Si in the steel, and steel sheets with improved ductility by securing residual γ by containing Si, Al, and Mn are known.

[0003] However, when manufacturing a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet using a high-tensile steel sheet having a large amount of Si and Mn (particularly 0.2% by mass or more), for example, a tensile strength of 590 MPa or more as a base material, the following problems exist. That is, the hot-dip galvanized steel sheet is manufactured by heating and annealing the base steel sheet at a temperature of about 600 to 900 °C in a reducing atmosphere or a non-oxidizing atmosphere, and then performing a hot-dip galvanizing treatment on the steel sheet. Further, the alloyed hot-dip galvanized steel sheet is manufactured by heating and alloying the zinc plating after the above hot-dip galvanizing treatment. Here, Si and Mn in the steel are easily oxidizable elements, and are selectively oxidized even in a generally used reducing atmosphere or non-oxidizing atmosphere, concentrated on the surface of the steel sheet, and form oxides. This oxide reduces the wettability with molten zinc during the plating process, causing non-plating. Therefore, as the Si and Mn concentrations in the steel increase, the wettability rapidly decreases and non-plating frequently occurs. Also, even when non-plating does not occur, the problem is that the plating adhesion is poor. Further, when Si and Mn in the steel are selectively oxidized and concentrated on the surface of the steel sheet, a significant alloying delay occurs in the alloying process after hot-dip galvanizing, which significantly inhibits productivity.

[0004] Regarding such problems, for example, in Patent Document 1, 0.2 to 2 g / m is provided on the base steel sheet 2Apply Fe plating, and then adjust the heat treatment in a direct-fired furnace (DFF) and a radiant heating furnace (RTF) to predetermined conditions to cause surface diffusion of Si, Mn, or Al, which are difficult-to-plate elements contained in the steel, to suppress the formation of oxides, thereby preventing non-plating phenomena and ensuring excellent plating surface quality, plating adhesion, and high strength, and a method with low manufacturing cost is disclosed.

[0005] In addition, Patent Document 2 discloses a method for manufacturing a hot-dip galvanized steel sheet with excellent spot weldability by setting a predetermined grain boundary oxidation depth on the surface of a base steel sheet in a hot rolling process, then applying Fe plating of 3 g / m or more on the base steel sheet, and then performing an alloying hot-dip galvanizing treatment. 2 Apply Fe plating of 3 g / m or more, and then perform an alloying hot-dip galvanizing treatment to manufacture a hot-dip galvanized steel sheet with excellent spot weldability.

[0006] Furthermore, Patent Document 3 discloses a method for manufacturing an electroplated steel sheet at a high current density, in which a plating solution is injected between the steel sheet and the electrode from a plurality of through holes provided in the electrode, and the plating solution is discharged from the through holes of the electrode.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] Patent Document 1 does not describe the specific equipment configuration of the Fe plating process. However, when using a general horizontal electroplating cell or a vertical plating cell, for example, in the case of high-strength steel plates with a tensile strength of 590 MPa or more, the shape of the steel plate after cold rolling is poor. If the steel plate is directly passed through the electroplating process, contact troubles with the electrodes will occur. Also, even if contact does not occur, since the distance between the electrode and the steel plate fluctuates, the Fe plating thickness aimed at in the same Document 1: 0.2 - 2.0 g / m 2 varies greatly, and partial surface enrichment of Si and Mn occurs in the subsequent annealing process, resulting in non-plating defects and pickup defects, making it impossible to manufacture stably.

[0009] The same is true for the method described in Patent Document 2. When attempting to apply Fe plating to such an extent that partial surface enrichment of Si and Mn does not occur in the annealing process, a coating weight of: 10 g / m 2 exceeding this is required, the equipment length becomes long, and a significant cost increase becomes a problem. It should be noted that it is also conceivable to pass through a separate straightening process or a pre-annealing process to improve the shape of the steel plate, but still, a significant cost increase is a problem.

[0010] In the plating electrode corresponding to a high current density described in Patent Document 3, in order to avoid a decrease in electrolysis efficiency due to the generation of a large amount of electrolytic gas at high current density, a device is made to remove bubbles (electrolytic gas) through both the gap between the hole 9 and the nozzle 8a and the plating solution discharge port 11, improving the removal of bubbles (electrolytic gas), that is, the gas exhaust property. On the other hand, improving the gas exhaust property also means that the jet pressure of the plating solution is less likely to accumulate between the electrode and the steel plate. Especially for steel plates with a distorted shape, it is difficult to make the plating adhesion amount uniform, and improvement is required.

[0011] The present invention has been made in view of the above problems, and when performing hot-dip galvanizing on a steel sheet containing easily oxidizable elements such as Si and Mn, or even when performing an alloying treatment, especially when there are no quality defects such as non-plating and pickup caused by shape distortion of the steel sheet, and an object of the present invention is to propose a method capable of manufacturing a steel sheet having a beautiful plating layer.

Means for Solving the Problems

[0012] The gist of the present invention for solving the above problems is as follows. 1. An electroplating step of forming an iron-based film on the surface of the steel sheet by electroplating, in which an iron-based plating solution is supplied toward the steel sheet while energizing with the electrode plate as an anode and the steel sheet as a cathode in a gap between the continuously running steel sheet and the electrode plate arranged opposite along the steel sheet, An annealing step of heat-treating the steel sheet that has undergone the electroplating step, A method for manufacturing a hot-dip galvanized steel sheet through a hot-dip plating step of performing hot-dip galvanizing on the steel sheet that has undergone the annealing step, wherein In the electroplating step, the plating solution discharge rate, which is the ratio of the flow rate of the plating solution flowing out to the back side of the electrode plate not facing the steel sheet to the flow rate of the plating solution supplied to the steel sheet, is less than 50%. A method for manufacturing a hot-dip galvanized steel sheet.

[0013] 2. The method for manufacturing a hot-dip galvanized steel sheet according to 1 above, wherein the adhesion amount of the iron-based film is 2.0 g / m 2 or more.

[0014] 3. The method for manufacturing a hot-dip galvanized steel sheet according to 1 or 2 above, wherein the plating solution discharge rate is 10% or less.

[0015] 4. The method for manufacturing a hot-dip galvanized steel sheet according to 1 above, wherein the plating solution flow rate Q (m 3 / min) per side of the electrode plate satisfies the following formula (1). Q ≧ 60WLH ····(1) Here, W is the width of the steel sheet (m), L is the length of the electrode in the longitudinal direction (m), and H is the distance between the electrode and the steel sheet (m). Here, the method of item 4 is preferably the method for manufacturing a hot-dip galvanized steel sheet described in any one of items 1 to 3 above.

[0016] 5. The method for manufacturing a hot-dip galvanized steel sheet according to item 1 above, wherein the steel sheet has a component composition containing, by mass%, 0.3% or less of C and 1.0 to 6.0% in total of one or more of Si and Mn. Here, the method of item 5 is preferably the method for manufacturing a hot-dip galvanized steel sheet described in any one of items 1 to 4 above.

[0017] 6. An electroplating apparatus for forming an iron-based film on a steel sheet continuously running on a running line, An annealing apparatus for heat-treating the steel sheet that has passed through the electroplating apparatus, A hot-dip plating apparatus for subjecting the steel sheet that has passed through the annealing apparatus to a hot-dip galvanizing treatment, and the manufacturing equipment for a hot-dip galvanized steel sheet, wherein the electroplating apparatus has electrode plates arranged opposite to each other along the running line of the steel sheet and injection nozzles for supplying an iron-based plating solution from the side of the electrode plates toward the running line, the electrode plates are anodes and the steel sheet is a cathode, and the plating solution discharge rate, which is the ratio of the flow rate of the plating solution flowing out to the back side of the electrode plates not facing the steel sheet to the flow rate of the plating solution supplied from the injection nozzles, is less than 50%.

[0018] 7. The manufacturing equipment for a hot-dip galvanized steel sheet according to item 6 above, wherein the electrode plates have at least one through-hole extending in a direction intersecting the running line and penetrating the electrode plates, and the injection nozzles are arranged in at least one of the through-holes.

[0019] ​8. On the back side of the electrode plate, in order from the side of the running line, there are a back plate and a jet header, and a plurality of the injection nozzles that penetrate through the back plate and the electrode plate are connected to the jet header. The back plate is connected to the back surface of the electrode plate via an electrode connection part, and an insulator is disposed in the space between the back plate and the electrode plate due to the presence of the electrode connection part. The manufacturing equipment for the hot-dip galvanized steel sheet according to item 6 or 7 above.

[0020] 9. The manufacturing equipment for the hot-dip galvanized steel sheet according to item 8 above, comprising one or more plating cells formed by combining the electrode plates as an aggregate of a plurality of sheets without a gap with one back plate.

[0021] 10. The manufacturing equipment for the hot-dip galvanized steel sheet according to item 9 above, 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 part.

[0022] 11. The jet header has a plating solution pipe for supplying a plating solution into the jet header, and the ratio Ak / An of the cross-sectional area Ak of the plating solution pipe to the total cross-sectional area An of the injection ports of the injection nozzles connected to the jet header is 2.5 or more. The manufacturing equipment for the hot-dip galvanized steel sheet according to item 8 above. Here, the manufacturing equipment of item 11 is preferably the manufacturing equipment for the hot-dip galvanized steel sheet according to any one of items 8 to 10 above.

[0023] 12. The electroplating device and the annealing device are on the same line. The manufacturing equipment for the hot-dip galvanized steel sheet according to item 6 above. Here, the manufacturing equipment of item 12 is preferably the manufacturing equipment for the hot-dip galvanized steel sheet according to any one of items 6 to 11 above.

[0024] 13. The electroplating device and the annealing device are on separate lines. The manufacturing equipment for the hot-dip galvanized steel sheet according to item 6 above. Here, the manufacturing equipment of item 13 is preferably the manufacturing equipment for the hot-dip galvanized steel sheet according to any one of items 6 to 11 above.

Advantages of the Invention

[0025] According to the method for manufacturing a hot-dip galvanized steel sheet of the present invention, even when hot-dip galvanizing is applied to a high-tensile steel sheet that is likely to generate shape distortion, for example, it is possible to manufacture a steel sheet having a beautiful hot-dip plating layer without quality defects such as non-plating and pick-up.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0027] Hereinafter, with reference to the drawings, the method for manufacturing a hot-dip galvanized steel sheet of the present invention will be specifically described. The method for manufacturing a hot-dip galvanized steel sheet according to the present invention is a method for manufacturing a hot-dip galvanized steel sheet through an electroplating step of forming an iron-based film on the surface of the steel sheet by electroplating, an annealing step of heat-treating the steel sheet that has undergone the electroplating step, and a hot-dip plating step of performing hot-dip galvanizing on the steel sheet that has undergone the annealing step. In the electroplating step, the plating solution discharge rate, which is the ratio of the flow rate of the plating solution flowing out to the back side of the electrode plate not facing the steel sheet to the flow rate of the plating solution supplied to the steel sheet, is less than 50%.

[0028] First, an embodiment of the manufacturing equipment for hot-dip galvanizing used in the method for manufacturing a hot-dip galvanized steel sheet according to the present invention will be described with reference to FIG. 1. The embodiment shown in FIG. 1 is a continuous hot-dip galvanizing manufacturing facility having an electroplating apparatus responsible for the electroplating step in-line. For example, in order from the upstream side of the running line of the steel sheet P, which is a high-tensile steel strip, there are a pay-off reel 51, a coil joining device 52, an in-side looper 53, a degreasing device 54, a pickling device 55, an electroplating device 56, a water washing device 57, an annealing device 58, a hot-dip galvanizing device 59, an alloying treatment device 60 (used when manufacturing an alloyed hot-dip galvanized steel sheet), a temper rolling device 61, a post-treatment device 62, an out-side looper 63, and an inspection device 64.

[0029] Further, FIG. 2 shows another embodiment in which the electroplating apparatus is on a separate line from the hot-dip galvanizing apparatus. That is, Fe plating is performed in a series of apparatuses having a pay-off reel 51, a coil joining device 52, an in-side looper 53, a degreasing device 54, a pickling device 55, an electroplating device 56, a water washing device 57, an out-side looper 63, and an inspection device 64. Then, a zinc plating treatment is performed on a normal continuous hot-dip galvanizing line having a pay-off reel 51, a coil joining device 52, an in-side looper 53, a degreasing device 54, an annealing device 58, a hot-dip galvanizing device 59, an alloying treatment device 60, a temper rolling device 61, a post-treatment device 62, an out-side looper 63, and an inspection device 64.

[0030] In the annealing devices in the former continuous hot-dip galvanizing production facility (Figure 1) and the latter continuous hot-dip galvanizing production facility (Figure 2), the heating zones can be in any of the forms of a direct-fired furnace (DFF) + a radiant furnace (RTF), an induction heating furnace (IHF) + a radiant furnace, or a full-area radiant furnace.

[0031] The former is characterized by extremely high production efficiency because it can complete the hot-dip galvanizing process in one line. On the other hand, the latter is produced in two lines, so although its production efficiency is slightly lower than that of the former, an Fe electroplating device can be used for multiple hot-dip galvanizing lines that do not have a normal Fe plating device. Therefore, as a single Fe plating device, it has the advantages of high production efficiency and minimal initial investment.

[0032] The amount of Fe plating formed by the electroplating device 56 described above is desirably 2.0 g / m or more according to the added elements in the steel and the length of the annealing device. If it is less than 2.0 g / m, it is impossible to avoid the surface enrichment of Si and Mn during annealing in a general annealing device, and non-plating defects and pickup defects will occur. Although the upper limit of the Fe plating amount is not particularly defined, if it exceeds 8.0 g / m, the running cost will be excessively high. Therefore, it is preferably 8.0 g / m or less. 2 above. 2 below, it is impossible to avoid the surface enrichment of Si and Mn during annealing in a general annealing device, and non-plating defects and pickup defects will occur. Although the upper limit of the Fe plating amount is not particularly defined, if it exceeds 8.0 g / m, the running cost will be excessively high. Therefore, it is preferably 8.0 g / m or less. 2 exceeding, the running cost will be excessively high. Therefore, it is preferably 8.0 g / m or less. 2 or less.

[0033] For electroplated Fe, there are no special restrictions on its component system as long as it is an iron-based plating. For example, it may be any of the systems of pure Fe, Fe-B, Fe-C, Fe-P, Fe-N, or Fe-O, but a pure Fe system is particularly preferred. Examples of the plating bath composition of the pure Fe system include 55 - 65 g / L of pure Fe (iron component) and 5 - 7 g / L of sodium, with a pH of 2.0 - 2.2.

[0034] The electroplating bath for electroplating Fe can contain Fe ions and at least one element selected from the group consisting of B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co. The total content of these elements in the electroplating bath for electroplating Fe is preferably such that the total content of these elements in the electroplated Fe layer is 10% by mass or less.

[0035] Next, with reference to FIGS. 3 and 4, the Fe electroplating apparatus 56 of the present invention will be specifically described. FIG. 3 shows a horizontal electroplating apparatus used in one embodiment of the present invention. In this electroplating apparatus, a steel sheet P is run on a running line in the horizontal direction, and a pair of electrode plates 10 are arranged opposite to each other along the continuously running steel sheet P. The electrode plate 10 is preferably insoluble. Further, a conductor roll 20 and a backup roll 21 for energizing the steel sheet P are arranged on the upstream side and the downstream side of the electrode plate 10 in the running direction of the steel sheet P, respectively.

[0036] Here, as the conductor roll 20, one having a structure of hard chromium plating using copper plating or nickel plating with good conductivity as a base can be used. The material and thickness of the electrode plate 10 are not particularly limited, but as the material, titanium coated with iridium oxide is preferable, and the thickness is preferably 5 to 100 mm. The distance between the steel sheet P and the electrode plate 10 is not particularly limited, but is preferably in the range of 2 to 20 mm.

[0037] On the back surface (the side opposite to the steel sheet P of the electrode plate) of each electrode plate 10, a back plate 12 is arranged via an electrode connection portion 11, and the current output from a rectifier (not shown) is input to the back plate 12 through a current-carrying bar 16. A nozzle header 14 for supplying the plating solution 30 is arranged on the back surface of the back plate 12. The back plate 12 is preferably formed as an integral body within one cell for uniformizing the current distribution. On the other hand, the electrode plate 10 facing the steel sheet is preferably appropriately divided in the width direction and the longitudinal direction in consideration of replacement work and the like.

[0038] The nozzle header 14 has a plurality of circular tube nozzles 15 made of an insulating material that extend from the back plate 12 side to the electrode plate 10 side through a plurality of through holes 10a 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, it is preferable to form the circular tube nozzles 15 from an insulating material because it is effective to avoid unintended electrolysis in the plating solution flow path by making the entire plating solution supply system an insulating material, and to avoid member damage due to sparks between the circular tube nozzles 15 and the electrode plate 10.

[0039] The circular tube nozzles 15 are preferably arranged such that their axes are perpendicular to the surface of the steel plate P. The plating solution 30 is supplied from the nozzle header 14 to the circular tube nozzles 15 and is jetted from the ejection ports at the tips of the circular tube nozzles 15 toward the steel plate P.

[0040] In this way, while the steel plate P is running in the horizontal direction, the plating solution 30 is supplied to the gap (gap) between the steel plate P and the electrode plate 10, and the electrode plate 10 is used as the anode and the steel plate P is used as the cathode, and electric current is passed between the plating surface of the steel plate P and the electrode plate 10 to electroplate the steel plate.

[0041] FIG. 4 shows an enlarged view of one nozzle header 14 and its surroundings in the above-described electroplating apparatus 56. The tip of the circular tube nozzle 15 is set to a length that stays within the through hole 10a so as not to protrude toward the steel plate P side beyond the surface of the electrode plate 10 on the steel plate P side. Further, in order to prevent the plating solution 30 from flowing out to the back side of the electrode plate 10 from the through hole 10a, it is necessary to block the space formed between the electrode plate 10 and the back plate 12 by the intervention of the electrode connection portion 11 with an insulator 13 made of, for example, resin.

[0042] That is, in order to prevent the plating solution from flowing out between the electrode plate 10 and the back plate 12 from the side of the steel plate P, at least the space formed between the electrode plate 10 and the back plate 12 needs to be filled with the insulator 13. In addition, if there is a gap between the inner wall of the through-hole 10a of the electrode plate 10 and the outer peripheral surface of the circular tube nozzle 15, it is preferable to fill it with the insulator 13. Here, if the gap in the through-hole 10a can be completely filled so that there is no liquid leakage, it is not necessary to fill the gap between the electrode plate 10 and the back plate 12 with the insulator 13. However, considering that it is difficult technically or in terms of cost to completely block the gap with an insulator in all of the numerous through-holes of the electrode plate 10, it is effective to more simply block the space formed between the electrode plate 10 and the back plate 12 with the insulator 13. In order to uniformly flow the current from the back plate 12 to the numerous electrode plates 10, it is preferable to smoothly process the connection surface between the back plate 12 and the electrode connection portion 11 and then fasten them with bolts (not shown). This structure is extremely effective in assembling this device. That is, although it is structurally possible to fasten the back plate 12 and the electrode plate 10 without providing the electrode connection portion 11, if only the periphery of the fastening bolt has the back plate 12 and the electrode plate 10 in close contact and a slight gap is generated at a position slightly away from the fastening bolt, a spark will occur at the position of the gap during energization, damaging the back plate 12 and the electrode plate 10. Therefore, such a structure is not desirable. Furthermore, as described above, by filling the gap between the back plate 12 and the electrode plate 10 with the insulator 13, non-uniform energization between the back plate 12 and the electrode plate 10 can be avoided. When the member filling the gap between the back plate 12 and the electrode plate 10 is not an insulator, energization locations other than the electrode connection portion 11 will be formed, resulting in a non-uniform current distribution when looking at the electrode plate from the steel plate.

[0043] With the above structure, since the plating solution does not flow out from the through holes to the back side of the electrode plate 10, the jet flow of the plating solution from the circular tube nozzle 15 concentrates in the gap between the electrode plates 10, and the jet pressure of the plating solution can be imparted to the steel plate P passing through the gap without any excess. As a result, correction forces act on the steel plate P from both the upper and lower surfaces, enabling the steel plate with a poor shape to be flattened while passing through the plate and energized. Therefore, even if the cold-rolled material is passed through the plate without pre-correction, since it is not affected by shape distortion during plating as described above, a uniform plating adhesion amount can be realized over the entire width, and it is possible to suppress the surface enrichment of Si and Mn with a minimum Fe plating adhesion amount.

[0044] Here, in one section of the electroplating shown in FIG. 3 (3 cells: electrode size of 1 cell: width 1.5 m × length in the plate passing direction 1 m), regarding the case of using the electrode plate provided with the discharge holes described in Patent Document 3 above and the case of using the electrode plate shown in FIG. 4 according to the present invention, the pressing force on the steel plate P by the jet flow of the plating solution from the circular tube nozzle was investigated. That is, in one section of the electroplating shown in FIG. 3, 120 circular tube nozzles with an inner diameter of 8 mmφ were arranged in 10 rows in the electrode width direction and 12 columns in the plate passing direction on one side of the pair of electrode plates, and the total plating solution flow rate was 2.5 m 3 / min was injected, and the pressing force applied to the steel plate was measured. As a result, in the electrode provided with the discharge holes described in Patent Document 3, only the position where the jet flow of the plating solution from the nozzle collides becomes the point where the steel plate pressing force acts, and the total pressing force acting on one side of the steel plate was 290 N (1.53 N per nozzle). On the other hand, in the electrode of FIG. 4 of the present invention, since the plating solution is discharged only from the inlet side and the outlet side of the steel plate P of the electrode plate, the pressure corresponding to the pressure loss of the plating solution flowing between the electrode plate and the steel plate is added to the entire electrode surface (the effective area where the steel plate pressing force substantially acts is about 50% of the electrode plate area). As a result, a form of pressing the steel plate is realized, and it was found that the steel plate pressing force reached 3500 N, more than 12 times. By following the present invention in this way, correction forces act on the steel plate from above and below in the plating cell, enabling the steel plate with a poor shape to be flattened while passing through the plate and energized.

[0045] In order to obtain the above-described effects, it is essential that the plating solution discharge rate during electroplating be less than 50%. That is, when the plating solution discharge rate becomes 50% or more, the flow rate of the plating solution flowing between the electrode plate and the steel plate decreases, so the pressing force of the steel plate decreases. Preferably, it is 10% or less.

[0046] On the other hand, regarding the bubbles (electrolysis gas) generated during plating, it is preferable to set the flow rate Q (m 3 / min) of the plating solution per one-sided area of the electrode to satisfy the following formula (1). By satisfying this formula (1), it has been found that the bubbles are sufficiently discharged. Q ≧ 60WLH ····(1) Here, W is the width of the steel plate (m), L is the length in the longitudinal direction of the electrode (m), and H is the distance between the electrode and the steel plate (m). The distance between the electrode and the steel plate is the shortest distance between the electrode and the steel plate in the direction orthogonal to the traveling direction of the steel plate. That is, 60WLH represents a volume 60 times the volume of the space between the steel plate and the electrode. If the plating solution flow rate Q is 60WLH or more, the plating solution existing between the steel plate and the electrode can be replaced within 1 second, so it is possible to avoid a decrease in electrical conductivity due to electrolysis gas.

[0047] Also, in one divided jet header 14 as shown in FIG. 4, the ratio Ak / An of the cross-sectional area Ak of the plating solution pipe 14a that supplies the plating solution 30 to the jet header 14 and the total cross-sectional area An of the injection ports 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 tends to be non-uniform, and the variation in the injection speed from the circular pipe nozzles 15 may increase, and problems such as uneven deposition amount may occur. When Ak / An exceeds 12, it becomes a sudden contraction small tube state with a large change in the flow path cross-sectional area from the jet header to the circular pipe nozzle, and the pressure loss increases, requiring excessive capacity for the plating solution feed pump. Therefore, from the viewpoint of economy, it is preferably 12 or less.

[0048] Incidentally, the above cross-sectional area is the minimum area of the inner cross-section orthogonal to the axial direction of each type of pipe. Further, in each jet header 14, when there are a plurality of plating liquid pipes and circular pipes nozzles, the total cross-sectional area of each pipe becomes Ak and An, respectively. Therefore, in the jet header 14 shown in FIG. 4, Ak is the cross-sectional area of the plating liquid pipe 14a, and An is the total cross-sectional area of three times the cross-sectional area of the injection port of the circular pipe nozzle 15.

[0049] Incidentally, the objects of the above-described electroplating Fe plating and zinc plating are not particularly limited, and any steel plate may be used. Examples of the plating object include steel plates such as ordinary steel and stainless steel, as well as aluminum plates and the like. The present invention is effective when applied to steel plates, and is particularly advantageous when targeting high-tensile steel plates. Incidentally, as the high-tensile steel plate, a steel plate having the following component composition is suitable. In the following component composition, the “%” indication means mass % unless otherwise specified.

[0050] C: 0.025 to 0.300% C is preferably contained in an amount of 0.025% or more in order to easily improve workability by forming a retained austenite layer, a martensite phase, etc. as a steel structure. On the other hand, if it exceeds 0.300%, the weldability deteriorates, so the amount of C is preferably 0.300% or less.

[0051] Si: 0.2 to 2.5% Si is an element effective for strengthening steel to obtain good material properties, so 0.2% or more is added to the high-tensile steel plate. If Si is less than 0.2%, expensive alloying elements are required to obtain high strength. On the other hand, if it exceeds 2.5%, the formation of an oxide film in the oxidation treatment is suppressed. Further, since the alloying temperature also becomes high, it becomes difficult to obtain desired mechanical properties. Therefore, the amount of Si is preferably 2.5% or less.

[0052] Mn: 1.5 to 3.5% Mn is an element effective for strengthening steel. To ensure a tensile strength of 590 MPa or more, it is preferably contained at 0.5% or more. On the other hand, if it exceeds 3.0%, it may become difficult to ensure weldability, plating adhesion, and the balance between strength and ductility. Therefore, the Mn content is preferably 1.5 - 3.5%.

[0053] In addition to the above components, it is possible to contain the following elements. Al: 0.001 - 1.000% Al is added for the purpose of deoxidizing molten steel. However, if its content is less than 0.001%, that purpose cannot be achieved. On the other hand, if it exceeds 1.000%, Al forms oxides on the surface, deteriorating the plating appearance (surface appearance). Therefore, the Al content may be 0.001% or more and 1.000% or less.

[0054] P: 0.10% or less P is one of the unavoidably contained elements. To reduce it to less than 0.005%, an increase in cost is a concern, so 0.005% or more is desirable. On the other hand, as P increases, slab manufacturability deteriorates. Furthermore, the inclusion of P suppresses the alloying reaction and causes plating unevenness. To suppress these, it is necessary to make the content 0.10% or less. Therefore, the P content may be 0.10% or less. Preferably it is 0.05% or less.

[0055] S: 0.01% or less S is an element unavoidably contained in the steelmaking process. However, if it is contained in a large amount, weldability deteriorates. Therefore, S may be 0.01% or less. When containing the above components, the balance is Fe and unavoidable impurities.

[0056] 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%, Sb: 0.001 - 0.200% may be contained as necessary. The appropriate content and the reasons for its limitation when adding these elements are as follows.

[0057] B: 0.001 - 0.005% When B is 0.001% or more, the quenching acceleration effect can be obtained. On the other hand, when it exceeds 0.005%, the chemical conversion treatment property deteriorates. Therefore, when contained, the amount of B may be 0.001% or more and 0.005% or less.

[0058] Nb: 0.005 - 0.050% When Nb is 0.005% or more, the effect of strength adjustment (strength improvement) can be obtained. On the other hand, when it exceeds 0.05%, it causes a cost increase. Therefore, when contained, the amount of Nb may be 0.005% or more and 0.05% or less.

[0059] Ti: 0.005 - 0.080% When Ti is 0.005% or more, the effect of strength adjustment (strength improvement) can be obtained. On the other hand, when it exceeds 0.080%, it causes deterioration of the chemical conversion treatment property. Therefore, when contained, the amount of Ti may be 0.005% or more and 0.080% or less.

[0060] Cr: 0.001 - 1.000% When Cr is 0.001% or more, the hardenability effect can be obtained. On the other hand, when it exceeds 1.000%, Cr surface-enriches, resulting in deteriorated weldability. Therefore, when contained, the amount of Cr may be 0.001% or more and 1.000% or less.

[0061] Mo: 0.05 - 1.00% When Mo is 0.05% or more, the effect of strength adjustment (strength improvement) can be obtained. On the other hand, when it exceeds 1.00%, it causes a cost increase. Therefore, when contained, the amount of Mo may be 0.05% or more and 1.00% or less.

[0062] Cu: 0.05 - 1.00% When Cu is 0.05% or more, the effect of promoting the formation of the residual γ phase can be obtained. On the other hand, when it exceeds 1.00%, it causes a cost increase. Therefore, when contained, the amount of Cu may be 0.05% or more and 1.00% or less.

[0063] Ni: 0.05 to 1.00% When Ni is 0.05% or more, the effect of promoting the formation of the retained γ-phase can be obtained. On the other hand, when it exceeds 1.00%, the cost increases. Therefore, when contained, the amount of Ni may be 0.05% or more and 1.00% or less.

[0064] Sb: 0.001 to 0.200% Sb can be contained from the viewpoint of suppressing nitridation, oxidation, or decarburization in the several tens of micron region on the surface of the steel sheet caused by oxidation. By suppressing nitridation and oxidation, a decrease in the amount of martensite formed on the surface of the steel sheet is prevented, and the fatigue characteristics and surface quality are improved. Such an effect can be obtained when it is 0.001% or more. On the other hand, when it exceeds 0.200%, the toughness deteriorates. Therefore, when contained, the amount of Sb may be 0.001% or more and 0.200% or less.

Examples

[0065] Examples of the present invention will be described below. Note that the technical scope of the present invention is not limited to the following examples. The case where a hot-dip galvanized coating production facility having the configuration shown in FIG. 1 or 2 is used, and the electroplating apparatus (1 cell) shown in FIG. 3 is used for these production facilities is taken as an example of the present invention. That is, in the plating cell constituting the electroplating apparatus, the electrode length in the longitudinal direction within 1 cell is 2 m, and 2 cells of this cell are connected. Further, as comparative examples, a form that does not use Fe plating, a form of a general horizontal flow cell (FIG. 5), and a form of a horizontal porous plating cell having a plating solution discharge hole (conforming to the description of FIG. 1 of Patent Document 3) were used.

[0066] Here, the horizontal flow cell type electroplating Fe apparatus shown in Fig. 5 forms a passage 43 partitioned by electrode plates 42a and 42b between two pairs of roll pairs of a conductor roll 40 and a backup roll 41. When passing a steel plate P through this passage 43, plating solution 30 is supplied from a nozzle header 44 to the gap between the steel plate P and the electrode plates 42a and 42b. With the electrode plates 42a and 42b as anodes and the steel plate P as a cathode, by energizing between the surface of the steel plate P and the electrode plates 42a and 42b, it is an apparatus for performing electroplating Fe on the steel plate P.

[0067] The shape of the steel plate before passing through the electroplating apparatus was measured using a laser type shape measuring instrument installed upstream of the first plating cell of the electroplating apparatus and quantified as the amount of warp based on the definition in Fig. 6. Specifically, as shown in Fig. 6 when looking directly at the steel plate P from the running direction, when warp occurs in the steel plate P, when the steel plate P is placed on a flat plate, a portion Pb with a higher height than the placement portion Pa is formed in the width direction of the steel plate P. In the steel plate P before electroplating Fe, the height difference between the highest portion Pb and the lowest placement portion Pa was measured as the amount of warp.

[0068] Using each of the above cases of the hot dip galvanizing manufacturing equipment, a steel plate with a thickness of 1.4 mm × width of 1200 mm was run at a passing speed of 1.5 m / s, and Fe electroplating and hot dip galvanizing treatments were performed. The component composition of the steel plate is as shown in Table 1.

[0069]

Table 1

[0070] The Fe plating bath was a sulfuric acid bath, and its components were 55 - 65 g / L of iron component and 5 - 7 g / L of sodium, and the pH was adjusted to 2.0 - 2.2. Other plating conditions are as shown in Table 1. In the steel plate after the Fe electroplating treatment, the amount of iron plating adhesion was measured. The amount of iron plating adhesion was continuously measured at five points in the width direction of the steel plate by on-line fluorescent X-ray based on a calibration curve created in advance, and the variation in the adhesion amount was evaluated.

[0071] The above hot-dip galvanization was carried out by a common method. In the case of the GA bath, the Al concentration was 0.13%, and in the case of the GI bath, the Al concentration was 0.20% (the balance was zinc in both cases). For the steel sheet after hot-dip galvanization, the amount of zinc coating adhered was measured. In addition, based on the calibration curve prepared in advance, the zinc coating adhered amount was measured at three points in the width direction of the steel sheet by on-line fluorescence X-ray, and the average value was taken.

[0072] Furthermore, the plating appearance after hot-dip galvanization was also evaluated. The plating appearance score was evaluated as 1 point if non-plating, severe color unevenness, and ripple defects always occurred; 2 points if there were non-plating, color unevenness, and ripple defects and most of them needed to be removed; 3 points if partial removal was needed due to color unevenness or ripple defects; 4 points if removal was not necessary but there were very slight color unevenness or appearance defects; and 5 points if it was in a good condition where non-plating, alloying unevenness, and ripple defects were not recognized.

[0073] Also, the plating solution discharge rate to the back surface of the electrode plate was obtained from the discharge flow rate of the plating solution from the plating solution discharge ports 19 (see Fig. 3) provided at both ends in the longitudinal direction of the upper surface side electrode plate and the total flow rate of the plating solution supplied to the gap between the upper surface side electrode plate and the steel sheet P. The results of the above measurements and evaluations are shown in Table 2 together with the electroplating conditions.

[0074]

Table 2

[0075] As shown in Table 2, in the hot-dip galvanized steel sheet obtained according to the present invention, a sound zinc coating layer is obtained despite the shape distortion before electroplating. That is, by following the present invention, plating that is not affected by the shape distortion of the steel sheet before plating is realized. In other words, from the results shown in Table 2, it can be seen that the correction of the steel sheet shape during electroplating according to the present invention is sufficiently achieved.

Explanation of Reference Signs

[0076] P steel plate 10 Electrode plate 11 Electrode connection part 12 Back plate 13 Insulator 14 Jet header 15 Circular tube nozzle 16 Energizing rod 20 Conductor roll 21 Backup roll 51 Payoff reel 52 Joining device 53 Inlet side looper 54 Degreasing device 55 Pickling device 56 Fe electroplating device 57 Water washing device 58 Annealing device 59 Hot dip galvanizing device 60 Alloying treatment device 61 Temper rolling device 62 Post-treatment device 63 Outlet side looper 64 Inspection device 63 Tension reel

Claims

1. In the gap between a continuously running steel plate and electrode plates disposed opposite along the steel plate, while supplying an iron-based plating solution toward the steel plate, the electrode plates are used as anodes and the steel plate is used as a cathode and energized to perform electroplating to form an iron-based film on the surface of the steel plate; an electroplating step; An annealing step of heat-treating the steel plate that has undergone the electroplating step; A method for manufacturing a hot-dip galvanized steel plate through a hot-dip plating step of performing hot-dip galvanizing on the steel plate that has undergone the annealing step, wherein: In the electroplating step, it has electrode plates disposed opposite along the running line of the steel plate and injection nozzles for supplying an iron-based plating solution from the side of the electrode plates toward the running line, the electrode plates are anodes and the steel plate is a cathode, on the back side of the electrode plates, in order from the running line side, there are a back plate and a jet header, a plurality of the injection nozzles extending through the back plate and the electrode plates are connected to the jet header, the back plate is connected to the back of the electrode plate through an electrode connection part, and an insulator is disposed in the space between the back plate and the electrode plate due to the interposition of the electrode connection part. Using an electroplating apparatus, a method for manufacturing a hot-dip galvanized steel plate, wherein the plating solution discharge rate, which is the ratio of the flow rate of the plating solution flowing out to the back side of the electrode plate not facing the steel plate to the flow rate of the plating solution supplied to the steel plate, is less than 50%.

2. The method for manufacturing a hot-dip galvanized steel plate according to Claim 1, wherein the adhesion amount of the iron-based film is 2.0 g / m ２ or more.

3. The method for manufacturing a hot-dip galvanized steel plate according to Claim 1 or 2, wherein the plating solution discharge rate is 10% or less.

4. The method for manufacturing a hot-dip galvanized steel plate according to Claim 1, wherein the plating solution flow rate Q (m ３ / min) per side of the electrode plate satisfies the following formula (1). Q ≧ 60WLH... (1) Here, W is the width of the steel sheet (m), L is the longitudinal length of the electrode (m), and H is the distance between the electrode and the steel sheet (m).

5. The method for manufacturing a hot-dip galvanized steel sheet according to claim 1, wherein the steel sheet has a component 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.

6. An electroplating apparatus for forming an iron-based film on a steel sheet continuously running on a running line, An annealing apparatus for heat-treating the steel sheet that has passed through the electroplating apparatus, A hot-dip plating apparatus for subjecting the steel sheet that has passed through the annealing apparatus to a hot-dip galvanizing treatment, comprising: The electroplating apparatus has electrode plates arranged to face each other along the running line of the steel sheet and injection nozzles for supplying an iron-based plating solution from the side of the electrode plates toward the running line. The electrode plates are anodes and the steel sheet is a cathode. On the back side of the electrode plates, in order from the running line side, there are a back plate and a jet header. A plurality of the injection nozzles extending through the back plate and the electrode plates are connected to the jet header. The back plate is connected to the back of the electrode plate via an electrode connection part, and an insulator is arranged in the space between the back plate and the electrode plate due to the interposition of the electrode connection part. The plating solution discharge rate, which is the ratio of the flow rate of the plating solution flowing out to the back side of the electrode plate that does not face the steel sheet to the flow rate of the plating solution supplied from the injection nozzles, is less than 50%. Manufacturing equipment for hot-dip galvanized steel sheets.

7. The manufacturing equipment for hot-dip galvanized steel sheets according to claim 6, wherein the electrode plate has at least one through hole extending in a direction intersecting the running line and passing through the electrode plate, and the injection nozzle is arranged in at least one of the through holes.

8. The manufacturing equipment for hot-dip galvanized steel sheets according to claim 6, comprising one or more plating cells in which the electrode plates are combined without gaps as an aggregate on one of the back plates.

9. The manufacturing equipment for hot-dip galvanized steel sheets according to claim 8, wherein in each of the plating cells, a plurality of jet headers are divided at positions that do not interfere with the electrode connection parts.

10. The jet header has a plating solution pipe for supplying a plating solution into the jet header, and the ratio Ak / An of the cross-sectional area Ak of the plating solution pipe to the total cross-sectional area An of the injection ports of the injection nozzles connected to the jet header is 2.5 or more. The manufacturing equipment for hot-dip galvanized steel sheets according to claim 6.

11. The electroplating apparatus and the annealing apparatus are on the same line. The manufacturing equipment for hot-dip galvanized steel sheets according to claim 6.

12. The electroplating apparatus and the annealing apparatus are on separate lines. The manufacturing equipment for hot-dip galvanized steel sheets according to claim 6.

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