Titanium plate manufacturing method and titanium plate

Abstract

To provide a method of producing a titanium plate material having both corrosion resistance and processability at a high level.SOLUTION: The method of producing a titanium plate material pertaining to one embodiment of the present invention is a method of producing a titanium plate material including a platy titanium substrate layer, a first surface layer formed on one surface of the titanium substrate layer, and a second surface layer formed on the other surface of the titanium substrate layer, where the first surface layer and the second surface layer each have a compound titanium layer mixed with a compound formed by C and Ti to Ti dissolved with at least O and C including: preparing a rolling process of rolling both faces of a titanium base material; and performing rolling of the titanium base material on one face, and on the other face by a condition different from that of the other surface in the rolling process to make an average C concentration in a region of 4 nm or more and 50 nm or less from the surface of the first surface layer higher by 3 atm% or more than the average C concentration of the second surface concentration.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a titanium plate and a titanium plate. [Background technology]

[0002] For example, solid polymer fuel cells have been attracting attention as power sources for mobility including automobiles, power generation facilities for homes and businesses, and batteries for portable devices such as mobile phones and personal computers. The above-mentioned fuel cells generally consist of a plurality of cells, each of which is a unit in which a solid polymer electrolyte membrane is sandwiched between a pair of gas diffusion membranes, and a pair of separators is arranged on the outside of the solid polymer electrolyte membrane and the pair of gas diffusion membranes to sandwich the electrolyte membrane and the pair of gas diffusion membranes.

[0003] In the fuel cell, hydrogen is passed through one gas diffusion membrane of the cell and air (oxygen) is passed through the other gas diffusion membrane to generate electricity, and the generated electricity is extracted by the separator. In addition, in the fuel cell, multiple cells are stacked to obtain high voltage, and the separator also serves as an electrical connector connecting the cells in series.

[0004] In addition, cooling water is passed between the stacked cells, i.e., between the opposing separators of adjacent cells, to discharge heat generated by the power generation of the cells. The separators must maintain their electrical conductivity even in an environment where the cooling water flows. For this reason, the separators are required to be both electrically conductive and corrosion-resistant to the cooling water.

[0005] As a sheet material for this separator, a titanium sheet material has been proposed that combines electrical conductivity and corrosion resistance by stably thinning the passive film (see JP 2014-192039 A).

[0006] The titanium sheet is manufactured by cold-rolling a raw titanium sheet using an organic rolling oil. This rolling process forms a surface layer on both sides of the titanium substrate layer, consisting of either a compound-mixed titanium layer less than 1 μm thick, in which O, C, and N are dissolved in Ti and a compound formed by at least one element selected from O, C, and N and Ti, or the compound-mixed titanium layer and a passivation film less than 5 nm thick formed on the surface. Because the compound-mixed titanium layer prevents the regeneration of the passivation film, the insulating passivation film can be consistently thin, ensuring the corrosion resistance of titanium while reducing contact resistance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-192039 Summary of the Invention [Problem to be solved by the invention]

[0008] The titanium sheet has excellent corrosion resistance against cooling water, especially when the surface layer has a high C concentration. However, a high C concentration in the surface layer reduces the workability of the titanium sheet. For this reason, it is difficult to achieve both corrosion resistance and workability.

[0009] The present invention has been made in light of the above-mentioned circumstances, and an object of the present invention is to provide a method for manufacturing a titanium plate material and a titanium plate material that achieves both high levels of corrosion resistance and workability. [Means for solving the problem]

[0010] The conventional titanium plate material described above is manufactured by rolling, and has a uniform surface layer formed on both sides. The inventors noticed that when a titanium plate material is used as, for example, a separator for a fuel cell, corrosion resistance is required on one side, not both sides. That is, the inventors came up with the idea of ​​providing surface layers with different C concentrations on both sides to produce a titanium plate material with excellent corrosion resistance and workability. After extensive research, the inventors discovered that the C concentration of the surface layers on both sides can be changed by intentionally setting different conditions on both sides when rolling a titanium base material, and thus completed the present invention.

[0011] That is, a method for producing a titanium plate according to one embodiment of the present invention includes a plate-shaped titanium base layer, a first surface layer formed on one surface of the titanium base layer, and a second surface layer formed on the other surface of the titanium base layer, wherein the first surface layer and the second surface layer are compound titanium layers comprising Ti in which at least O and C are solid-solved, and a compound formed by C and Ti, and the method further includes a rolling step of rolling both surfaces of the titanium base material, wherein the rolling of the titanium base material is performed under different conditions for the one surface and the other surface, thereby making the average C concentration in the range of 4 nm to 50 nm from the surface of the first surface layer 3 atm % or more higher than the average C concentration in the second surface layer.

[0012] In this method for producing a titanium plate, the rolling step involves rolling the titanium base material on both sides under different conditions. By rolling the titanium base material on both sides under different conditions in this way, the average C concentration in the first surface layer can be made 3 atm% or more higher than the average C concentration in the second surface layer. Therefore, the titanium plate produced by this method for producing a titanium plate has both high levels of corrosion resistance and workability.

[0013] The condition is preferably the roll peripheral speed. By setting the roll peripheral speed as the condition in this manner, it is possible to easily make the average C concentration of the first surface layer 3 atm % or more higher than the average C concentration of the second surface layer.

[0014] Preferably, the condition is the roll roughness. By setting the condition to the roll roughness in this manner, it becomes possible to easily make the average C concentration in the first surface layer 3 atm % or more higher than the average C concentration in the second surface layer.

[0015] The condition is preferably the roll diameter. By setting the condition to the roll diameter in this manner, it is possible to easily make the average C concentration in the first surface layer 3 atm % or more higher than the average C concentration in the second surface layer.

[0016] A titanium plate according to another embodiment of the present invention comprises a plate-shaped titanium base layer, a first surface layer formed on one surface of the titanium base layer, and a second surface layer formed on the other surface of the titanium base layer, wherein the first surface layer and the second surface layer comprise compound titanium layers in which Ti in which at least O and C are solid-solved is mixed with a compound formed by C and Ti, and the average C concentration in a range of 4 nm to 50 nm from the surface of the first surface layer is higher than the average C concentration of the second surface layer, and the difference therebetween is 3 atm% or more.

[0017] The titanium plate has a high average C concentration in the first surface layer, and therefore has excellent corrosion resistance, particularly on the first surface layer side. Furthermore, the average C concentration in the second surface layer is lower than the average C concentration in the first surface layer by at least the lower limit, which prevents deterioration in the workability of the titanium plate. Therefore, the titanium plate has both high levels of corrosion resistance and workability.

[0018] The average C concentration of the first surface layer is preferably 12 atm% or more. By setting the average C concentration of the first surface layer to be equal to or greater than the lower limit, the corrosion resistance of the first surface layer side can be further improved.

[0019] The average C concentration of the second surface layer is preferably 12 atm% or less. By setting the average C concentration of the second surface layer to the upper limit or less in this way, the workability of the titanium plate can be further improved.

[0020] The average thickness of the first surface layer and the second surface layer is preferably less than 1 μm. By making the average thickness of the first surface layer and the second surface layer less than the upper limit, it is possible to prevent cracks from occurring in the titanium plate during processing.

[0021] The first and second surface layers preferably have a passivation film formed on the outer surface of the compound titanium layer, and the average thickness of the passivation film is preferably less than 5 nm. By having the first and second surface layers have a passivation film formed on the outer surface of the compound titanium layer, the corrosion resistance of the titanium plate can be further improved. Furthermore, by setting the average thickness of the passivation film to less than the upper limit, an increase in the contact resistance of the titanium plate can be prevented.

[0022] The average thickness of the titanium plate is preferably 0.02 mm or more and 0.4 mm or less. By setting the average thickness of the titanium plate within this range, it is easy to achieve both strength and workability of the titanium plate.

[0023] The titanium plate material is particularly suitable for use as a separator for a fuel cell.

[0024] Here, the "average carbon concentration" refers to the carbon concentration measured by XPS in a range of 4 nm to 50 nm deep from the surface, and the integrated average calculated over the entire range. Note that the region less than 4 nm deep from the surface was removed because it is susceptible to the influence of impurities adhering to the surface of the titanium plate. Furthermore, according to the findings of the present inventors, the region 50 nm deep from the surface is the region that significantly affects the corrosion resistance and workability of the titanium plate.

[0025] The term "average thickness" refers to the arithmetic mean value of thicknesses measured at 10 random points. [Effects of the Invention]

[0026] As described above, the method for manufacturing a titanium plate according to the present invention can provide the titanium plate with high levels of both corrosion resistance and workability. Furthermore, the titanium plate according to the present invention has high levels of both corrosion resistance and workability. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the configuration of a titanium plate according to one embodiment of the present invention. [Figure 2] FIG. 2 is a flow diagram showing a method for producing a titanium plate according to one embodiment of the present invention. [Figure 3] FIG. 3 is a schematic side view showing a rolling device used in the rolling step of FIG. [Figure 4] FIG. 4 is a graph showing the measurement results of the average C concentration when the peripheral speed ratio is changed in the example. [Figure 5] FIG. 5 is a graph showing the measurement results of the average C concentration when the roughness ratio is changed in the example. [Figure 6] FIG. 6 is a graph showing the measurement results of the average C concentration when the roll diameter ratio is changed in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0028] A method for manufacturing a titanium plate and a titanium plate according to one embodiment of the present invention will be described below.

[0029] [Method of manufacturing titanium sheets] A method for manufacturing a titanium plate according to one embodiment of the present invention can manufacture a titanium plate 1 shown in Fig. 1, which is itself one embodiment of the present invention. The titanium plate 1 comprises a plate-shaped titanium base layer 10, a first surface layer 20 formed on one surface of the titanium base layer 10, and a second surface layer 30 formed on the other surface of the titanium base layer 10, and the first surface layer 20 and the second surface layer 30 have compound titanium layers (first compound titanium layer 21 and second compound titanium layer 31) in which titanium (Ti) in which at least oxygen (O) and carbon (C) are solid-solved is mixed with a compound formed by C and Ti.

[0030] As shown in Figure 2, the method for producing a titanium plate includes a rolling step S1 and a heat treatment step S2. The method for producing a titanium plate does not require an annealing step for reducing the C concentration in the compound titanium layer. Because the method for producing a titanium plate does not require the annealing step, it is possible to improve yield, reduce production costs, and improve productivity.

[0031] <Rolling process> In the rolling step S1, both sides of the titanium base material X are rolled as shown in Fig. 3. Specifically, in the rolling step S1, cold rolling is performed using an organic rolling oil. The rolling step S1 can be performed using a rolling mill 2 shown in Fig. 3.

[0032] The titanium base material X can be produced by a manufacturing method including the steps of blooming forging an ingot of pure titanium or a titanium alloy, hot rolling the blooming forged titanium material, and cold rolling the hot-rolled titanium material. An annealing step or an acid pickling step may be included between the hot rolling and cold rolling steps as needed.

[0033] The lower limit of the average thickness of the titanium base material X before rolling is preferably 0.2 mm, more preferably 0.3 mm, from the viewpoint of the strength of the titanium plate material 1 to be produced. On the other hand, the upper limit of the average thickness of the titanium base material X before rolling is preferably 1 mm, more preferably 0.8 mm, from the viewpoint of the workability of the titanium plate material 1 to be produced.

[0034] When the titanium base material X is exposed to the atmosphere, a thin passive film of about 10 nm or more and 20 nm or less is formed on its surface.

[0035] The organic rolling oil is not particularly limited as long as it contains carbon, and examples thereof include mineral oils such as neat oil, synthetic oils such as ester oil, and fats and oils.

[0036] The rolling mill 2 has an upper roll 2a that rolls the titanium base material X from above, and a lower roll 2b that vertically faces the upper roll 2a with the titanium base material X sandwiched therebetween and rolls the titanium base material X from below. The rolling mill 2 rolls both sides of the titanium base material X with the upper roll 2a and the lower roll 2b while transporting the titanium base material X from one side to the other (in the direction of the arrow in FIG. 3). This rolling elongates and thins the titanium base material X.

[0037] The rolling speed (transport speed of the titanium base material X) can be, for example, 50 m / min or more, but from the viewpoint of productivity, the rolling speed is preferably 100 m / min or more.

[0038] The present inventors have found that by applying an appropriate pressure during rolling in the rolling step S1, a compound titanium layer can be formed on each of both surfaces of the titanium base material X, in which compounds formed by C and Ti are mixed with Ti in which at least O and C are solid-solved. That is, the compound titanium layer is formed during this rolling step S1.

[0039] After the rolling step S1 or the heat treatment step S2, for example, the titanium plate material 1 may be exposed to the atmosphere, which may cause a passive film (first passive film 22 and second passive film 32) to be reformed on the surface of the compound titanium layer, as shown in Fig. 1. The layer consisting of the compound titanium layer and the passive film is the surface layer (first surface layer 20 and second surface layer 30). Note that if a passive film is not reformed on the surface of the compound titanium layer, the surface layer will consist of only the compound titanium layer.

[0040] In the method for producing a titanium plate, in the rolling step S1, the titanium base material X is rolled under different conditions on one side and the other side, so that the average C concentration in the range of 4 nm to 50 nm from the surface of the first surface layer 20 is made 3 atm% or more higher than the average C concentration in the second surface layer 30. Hereinafter, the one side will be described as the lower surface of the titanium base material X (the surface on the side of the lower roll 2b) and the other side as the upper surface of the titanium base material X (the surface on the side of the upper roll 2a), but this correspondence may be reversed.

[0041] The above condition can be the roll peripheral speed. By using the roll peripheral speed as the above condition, it is possible to easily increase the average C concentration of the first surface layer 20 by 3 atm % or more compared to the average C concentration of the second surface layer 30. When the roll diameters are the same, the roll peripheral speed can be replaced with the roll rotation speed. As the roll rotation speed increases, the roll peripheral speed increases. Conversely, when the roll rotation speeds are the same, the roll peripheral speed can be replaced with the roll diameter. In this case, as the roll diameter increases, the roll peripheral speed increases. Alternatively, the peripheral speed can be changed by adjusting both. Below, an example will be described in which the roll diameters are the same and the roll peripheral speed is changed depending on the roll rotation speed.

[0042] When changing the roll peripheral speed by the roll rotation speed, specifically, the rotation speed of the lower roll 2b is lowered relative to the upper roll 2a, and the peripheral speed of the lower roll 2b is reduced. In other words, the peripheral speed of the roll (lower roll 2b) used to roll the first surface layer 20, in which the C concentration is desired to be increased, is set lower than the peripheral speed of the roll (upper roll 2a) used to roll the second surface layer 30. In the rolling step S1, the titanium base material X is thick and short before rolling, but is thinned (stretched) after rolling. Therefore, as the titanium base material X becomes thinner during rolling, the conveyance speed of the titanium base material X increases relative to the conveyance speed of the titanium base material X before rolling. The rotation speeds of the upper roll 2a and the lower roll 2b are set so that the peripheral speeds of the upper roll 2a and the lower roll 2b are intermediate between the conveyance speeds before and after rolling. In other words, as the conveyance speed of the titanium base material X increases during rolling, the initially slow conveyance speed eventually matches the peripheral speed of the rolls, and then the conveyance speed increases. Here, when the rotation speed of the lower roll 2b is made lower than that of the upper roll 2a, the point at which the peripheral speed of the lower roll 2b and the transport speed of the titanium base material X coincide will be located upstream of the point at which the peripheral speed of the upper roll 2a and the transport speed of the titanium base material X coincide. The inventors have found that when this coincidence point is located upstream, the region where the material moves faster relative to the roll becomes larger, making it easier to incorporate C into the compound titanium layer and increasing the planar C concentration on the side of the lower roll 2b where the peripheral speed is slower, i.e., the first surface layer 20.

[0043] The lower limit of the ratio of the peripheral speed (rotation speed) of the lower roll 2b to the peripheral speed (rotation speed) of the upper roll 2a (rotation speed ratio) is preferably 0.6, more preferably 0.7. On the other hand, the upper limit of the rotation speed ratio is preferably 0.9, more preferably 0.85. If the rotation speed ratio is below the lower limit, it will be impossible to set the rotation speeds of the upper roll 2a and the lower roll 2b so that the peripheral speeds of the upper roll 2a and the lower roll 2b are intermediate between the conveying speeds before and after rolling, which may make it impossible to perform stable rolling. Conversely, if the rotation speed ratio exceeds the upper limit, it may be impossible to ensure a sufficient difference in the average C concentration between the first surface layer 20 and the second surface layer 30.

[0044] The condition can also be the roll diameter. By using the roll diameter as the condition in this way, it is possible to easily make the average C concentration in the first surface layer 20 higher than the average C concentration in the second surface layer 30 by 3 atm % or more.

[0045] When the roll diameter is set as the above condition, the roll peripheral speed is kept constant, and the roll diameter of the lower roll 2b is set larger than that of the upper roll 2a. In other words, the roll diameter of the roll (lower roll 2b) used to roll the first surface layer 20, in which the C concentration is desired to be increased, is set larger than the roll diameter of the roll (upper roll 2a) used to roll the second surface layer 30. The inventors have found that a smaller roll diameter makes it difficult for C to be incorporated, and conversely, a larger roll diameter makes it easier for C to be incorporated.

[0046] The upper limit of the ratio of the diameter of the lower roll 2b to the diameter of the upper roll 2a is preferably 5, and more preferably 3. If the roll diameter ratio exceeds the upper limit, the average C concentration in the first surface layer 20 becomes relatively too high, which may cause cracks in the titanium sheet 1 during processing. On the other hand, the lower limit of the roll diameter ratio is not particularly limited, and may be any value greater than 1.0, for example, 1.1.

[0047] Alternatively, the condition can be the roll roughness. By using the roll roughness as the condition, it is possible to easily make the average C concentration in the first surface layer 20 higher than the average C concentration in the second surface layer 30 by 3 atm % or more.

[0048] The inventors have found that lowering the roll roughness makes it difficult for C to be incorporated, and conversely, increasing the roll roughness makes it easier for C to be incorporated. In other words, the roll roughness of the roll (lower roll 2b) that rolls the first surface layer 20, in which the C concentration is desired to be increased, is made larger than the roll roughness of the roll (upper roll 2a) that rolls the second surface layer 30.

[0049] The surface of the upper roll 2a is preferably substantially a mirror finish. By making the surface of the upper roll 2a substantially a mirror finish in this way, it becomes difficult for C to be taken in. Here, "mirror finish" means that the roughness is 0.2 μm or less. The "roughness" of the roll means the arithmetic mean roughness Ra defined in JIS-B-0601:2013.

[0050] By increasing the surface roughness of the lower roll 2b relative to the upper roll 2a, C can be more easily incorporated. The lower limit of the roughness ratio of the lower roll 2b to the roughness of the upper roll 2a is preferably 20, more preferably 40. On the other hand, the upper limit of the roughness ratio is preferably 500, more preferably 100. If the roughness ratio is below the lower limit, the difference in the average C concentration between the first surface layer 20 and the second surface layer 30 may not be sufficiently ensured. Conversely, if the roughness ratio exceeds the upper limit, the roughness of the lower roll 2b may become too large, making it impossible to uniformly roll the titanium base material X.

[0051] Furthermore, the above conditions can also be set to a lubricated state. In this case, the lubricated state is set so that the roll (lower roll 2b) that rolls the first surface layer 20, in which the C concentration is desired to be increased, is less slippery than the roll (upper roll 2a) that rolls the second surface layer 30. For example, an organic rolling oil can be used as a lubricant for the upper roll 2a, and water can be used for the lower roll 2b. Alternatively, a lubricant can be used for the upper roll 2a, and no lubricant can be used for the lower roll 2b (non-lubricated).

[0052] These conditions may be used alone or in combination. Furthermore, the above conditions are not limited to the roll peripheral speed, roll roughness, and lubrication state, and other conditions may also be employed. For example, the same effect can be achieved even when the conditions are such that the roll diameters are differentiated regardless of the peripheral speed (for example, at a constant peripheral speed).

[0053] <Heat treatment process> In the heat treatment step S2, the rolled material obtained in the rolling step S1 is heat treated. The heat treatment is performed under predetermined heat treatment conditions, and the mechanical properties of the obtained rolled material are adjusted. Note that if adjustment of the mechanical properties is not necessary, this step can be omitted.

[0054] <Advantages> In this titanium plate manufacturing method, in the rolling step S1, the titanium base material X is rolled under different conditions on each side. By rolling the titanium base material X under different conditions on each side in this manner, the average C concentration in the first surface layer 20 can be made 3 atm % or more higher than the average C concentration in the second surface layer 30. Therefore, the titanium plate 1 manufactured by this titanium plate manufacturing method has both high levels of corrosion resistance and workability.

[0055] [Titanium plate] 1 includes a plate-shaped titanium substrate layer 10, a first surface layer 20 formed on one surface of the titanium substrate layer 10, and a second surface layer 30 formed on the other surface of the titanium substrate layer 10. The titanium substrate 1 is particularly suitable for use as a separator for a fuel cell.

[0056] <Titanium substrate layer> The titanium substrate layer 10 is a layer made of metallic titanium and has a recrystallized structure. Having such a recrystallized structure reduces the electrical resistance of the titanium substrate layer 10 itself, thereby enabling the contact resistance of the titanium sheet 1 to be reduced. While it is preferable that the entire titanium substrate layer 10 has a recrystallized structure, a portion of the titanium substrate layer 10 may have a recrystallized structure. If even a portion of the titanium substrate layer 10 has a recrystallized structure and electrical continuity is ensured, the contact resistance of the titanium sheet 1 can be reduced.

[0057] The material of the titanium substrate layer 10 may be either pure titanium or a titanium alloy, such as pure titanium of types 1 to 4 specified in JIS-H-4600, and titanium alloys such as Ti—Al alloy, Ti—Ta alloy, Ti-6Al-4V alloy, and Ti—Pd alloy. Of these, pure titanium is preferred.

[0058] <Surface layer> The first surface layer 20 and the second surface layer 30 have a compound titanium layer (first compound titanium layer 21 and second compound titanium layer 31) in which Ti in which at least O and C are solid-solved is mixed with a compound formed by C and Ti, and a passivation coating (first passivation coating 22 and second passivation coating 32) formed on the outer surface of the compound titanium layer.

[0059] The average thickness of each of the first surface layer 20 and the second surface layer 30 is preferably less than 1 μm, more preferably less than 500 nm, and even more preferably less than 300 nm. On the other hand, the lower limit of the average thickness is preferably 30 nm, more preferably 50 nm. If the average thickness of the first surface layer 20 and the second surface layer 30 is equal to or greater than the upper limit, cracks may occur in the titanium plate 1 during processing. Conversely, if the average thickness of the first surface layer 20 and the second surface layer 30 is less than the lower limit, corrosion resistance may be insufficient.

[0060] In the compound titanium layer, C in the compound or dissolved C is likely to bond to Ti before O in the air, and therefore the titanium in the surface layer does not readily react with O in the air, making it difficult for the passive film to become thick on the surface layer.

[0061] Specifically, the average thickness of the passivation film is preferably less than 5 μm, more preferably less than 3 nm, and even more preferably less than 1 nm. By setting the average thickness of the passivation film to be less than the upper limit, an increase in the contact resistance of the titanium plate 1 can be suppressed.

[0062] The average C concentration in the range of 4 nm to 50 nm from the surface of the first surface layer 20 is higher than the average C concentration in the second surface layer 30. The lower limit of the difference between the average C concentration in the first surface layer 20 and the average C concentration in the second surface layer 30 is 3 atm%, more preferably 4 atm%, and even more preferably 4.5 atm%. On the other hand, the upper limit of the difference in the average C concentrations is preferably 10 atm%, more preferably 7 atm%. If the difference in the average C concentrations is below the lower limit, it may be difficult to achieve high levels of both corrosion resistance and workability. Conversely, if the difference in the average C concentrations exceeds the upper limit, the average C concentration in the first surface layer 20 becomes too high, which may cause cracks in the titanium plate 1 during processing.

[0063] The lower limit of the average C concentration in the first surface layer 20 is preferably 12 atm%, more preferably 13 atm%. On the other hand, the upper limit of the average C concentration in the first surface layer 20 is preferably 16 atm%, more preferably 15 atm%. If the average C concentration in the first surface layer 20 is below the lower limit, the corrosion resistance of the first surface layer 20 may be insufficient. Conversely, if the average C concentration in the first surface layer 20 exceeds the upper limit, cracks may occur in the titanium plate 1 during processing.

[0064] The upper limit of the average C concentration in the second surface layer 30 is preferably 12 atm%, and more preferably 10 atm%. If the average C concentration in the second surface layer 30 exceeds the upper limit, the workability of the titanium plate 1 may be insufficient. On the other hand, the lower limit of the average C concentration in the second surface layer 30 is not particularly limited, but can be, for example, 3 atm%.

[0065] The lower limit of the average thickness of the titanium plate 1 is preferably 0.02 mm, more preferably 0.05 mm, and even more preferably 0.08 mm. On the other hand, the upper limit of the average thickness of the titanium plate 1 is preferably 0.4 mm, more preferably 0.3 mm, and even more preferably 0.2 mm. If the average thickness of the titanium plate 1 is below the lower limit, the strength may be insufficient. Conversely, if the average thickness of the titanium plate 1 exceeds the upper limit, the workability of the titanium plate 1 may be reduced. Furthermore, by keeping the average thickness of the titanium plate 1 within the above range, the titanium plate 1 can be suitably used as a separator for a fuel cell.

[0066] <Advantages> The titanium plate 1 has a high average C concentration in the first surface layer 20, and therefore has excellent corrosion resistance, particularly on the side of the first surface layer 20. Furthermore, the titanium plate 1 has an average C concentration in the second surface layer 30 that is 3 atm % or more lower than the C concentration in the first surface layer 20, which prevents a decrease in the workability of the titanium plate 1. Therefore, the titanium plate 1 has both high levels of corrosion resistance and workability.

[0067] [Other embodiments] The present invention is not limited to the above-described embodiment.

[0068] In the above embodiment, the titanium plate manufacturing method includes a rolling step and a heat treatment step, but the titanium plate manufacturing method may further include other steps. For example, it may include a press working step (press working step) after the heat treatment step (after the rolling step if the heat treatment step is not included) or a conductive layer forming step (conductive layer forming step).

[0069] In the above embodiment, the surface layer of the titanium plate material has a passive film. However, the surface layer may not have a passive film, i.e., may be composed of only a titanium compound layer. [Example]

[0070] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0071] <No.1> In a laboratory, titanium base material X was rolled using a rolling mill 2 shown in Figure 3. The roughness of both the top roll 2a and the bottom roll 2b was mirror-finished, and the ratio of the rotation speed of the bottom roll 2b to the rotation speed of the top roll 2a was set to 1.0. The top roll 2a and the bottom roll 2b had the same diameter, and this ratio of the rotation speeds was the ratio of the peripheral speeds. That is, in No. 1, the peripheral speed ratio was 1.0, the roughness ratio was 1, and the roll diameter ratio was 1.0 (see Table 1).

[0072] The rolling was performed using neat lubricant in two passes to obtain No. 1 titanium plate. In the first rolling pass, the reduction ratio was 14.6 and the tension condition was 12.8 kgf / 4.6 cm. 2 , rolling time = steady 2 minutes, in the second rolling, reduction rate = 13.9, tension condition = 15.0 kgf / 5.3 cm 2 The rolling time was set to 2 minutes.

[0073] <No.2、No.3> The ratio of the rotation speed of the lower roll 2b to the rotation speed of the upper roll 2a was adjusted to obtain the peripheral speed ratio shown in Table 1. Except for this, rolling was carried out in the same manner as in No. 1 to obtain titanium plate materials No. 2 and No. 3.

[0074] <No.4、No.5> By increasing the roughness of the lower roll 2b, the roughness ratio of the lower roll 2b to the roughness of the upper roll 2a was set to the value shown in Table 1. Except for this, rolling was performed in the same manner as in No. 1 to obtain titanium plate materials No. 4 and No. 5.

[0075] <No.6~No.9> Rolling was carried out in the same manner as No. 1, except that the peripheral speed ratio was kept at 1 and the roll diameter ratio of the lower roll 2b to the roll diameter of the upper roll 2a was set to the value shown in Table 1, to obtain titanium plate materials No. 6 to No. 9.

[0076] [Table 1]

[0077] For titanium plate materials No. 1 to No. 9, the average carbon concentration was measured in the range of 4 nm to 50 nm from the surface of the upper surface layer and the lower surface layer. The results are shown in Figures 4 to 6. Note that the average carbon concentration of No. 1 was measured using XPS, while Nos. 2 to 9 were measured using EPMA and converted to XPS results.

[0078] From the graph in Figure 4, which shows the results for No. 1 to No. 3, where the peripheral speed ratio was changed, it can be seen that No. 1, which had the same peripheral speed ratio, had the same average C concentration on the top and bottom surfaces, whereas No. 2 and No. 3, which had different peripheral speed ratios, were able to increase the average C concentration on the bottom surface, where the peripheral speed was lower, by 3 atm% or more.

[0079] From the graph in Figure 5, which shows the results for No. 1, No. 4, and No. 5, where the roughness ratio was changed, it can be seen that No. 1, which has the same roughness ratio, has the same average C concentration on the top and bottom surfaces, whereas No. 4 and No. 5, which have different roughness ratios, have an average C concentration on the bottom surface, where the roughness is greater, that is 3 atm% or more higher.

[0080] From the graph in Figure 6, which shows the results for No. 1 and No. 6 to No. 9, which had different roll diameters, it can be seen that No. 1, which had the same roll diameter, had the same average C concentration on the top and bottom surfaces, whereas No. 6 to No. 9, which had different roll ratios, had a larger roll diameter and the average C concentration on the bottom surface was increased by 3 atm% or more. [Industrial Applicability]

[0081] The method for producing a titanium plate material of the present invention can achieve high levels of both corrosion resistance and workability in the resulting titanium plate material. Furthermore, the titanium plate material of the present invention achieves high levels of both corrosion resistance and workability. [Explanation of symbols]

[0082] 1 Titanium plate 10 Titanium substrate layer 20 1st surface layer 21 First compound titanium layer 22 First passive film 30 2nd surface layer 31 Second compound titanium layer 32 Second passive film 2. Rolling equipment 2a Upper Roll 2b Lower Roll X Titanium base material

Claims

1. A method for producing a titanium plate material comprising: a plate-shaped titanium substrate layer; a first surface layer formed on one surface of the titanium substrate layer; and a second surface layer formed on the other surface of the titanium substrate layer, wherein the first surface layer and the second surface layer have compound titanium layers in which at least O and C are solid-solved in Ti and a compound formed by C and Ti are mixed, a rolling step of rolling both sides of the titanium base material by cold rolling using an organic rolling oil; In the rolling step, the titanium base material is rolled under different conditions for the one surface and the other surface, thereby making the average C concentration in the range of 4 nm to 50 nm from the surface of the first surface layer 3 atm % or more higher than the average C concentration in the second surface layer; A method for producing a titanium plate material, wherein the above conditions are any one of roll peripheral speed, roll roughness, and roll diameter, or a combination thereof.

2. a plate-shaped titanium substrate layer; a first surface layer formed on one surface of the titanium substrate layer; a second surface layer formed on the other surface of the titanium substrate layer; Equipped with the first surface layer and the second surface layer each have a compound titanium layer in which at least O and C are solid-solved in Ti and a compound formed by C and Ti are mixed, an average C concentration in a range of 4 nm to 50 nm from the surface of the first surface layer is higher than the average C concentration in the second surface layer; The difference is 3 atomic % or more.

3. 3. The titanium plate according to claim 2, wherein the average carbon concentration in the first surface layer is 12 atm % or more.

4. 4. The titanium plate material according to claim 2, wherein the average carbon concentration in the second surface layer is 12 atm % or less.

5. 5. The titanium plate according to claim 2, wherein the first surface layer and the second surface layer have an average thickness of less than 1 μm.

6. the first surface layer and the second surface layer have a passivation film formed on an outer surface of the compound titanium layer, 6. The titanium plate material according to claim 2, wherein the average thickness of the passive film is less than 5 nm.

7. The titanium plate material according to any one of claims 2 to 6, having an average thickness of 0.02 mm or more and 0.4 mm or less.

8. The titanium plate material according to any one of claims 2 to 7, which is used as a separator for a fuel cell.

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