JP6620468B2 - Titanium material and cell member for polymer electrolyte fuel cell containing the same - Google Patents

Description

  The present invention relates to a titanium material and a cell member for a polymer electrolyte fuel cell including the same. The polymer electrolyte fuel cell is used, for example, as a power source for mounting on automobiles or for home use. A cell member is a member which comprises the cell of a polymer electrolyte fuel cell, for example, is a separator or a baffle plate.

  A fuel cell is a cell that generates a direct current using hydrogen and oxygen, and is made into a solid electrolyte type, a molten carbonate type, a phosphoric acid type, and a solid polymer type depending on the constituent material of the electrolyte part of the fuel cell. Broadly divided.

  Among these fuel cells, phosphoric acid fuel cells operating near 200 ° C. and molten carbonate fuel cells operating near 650 ° C. have reached the commercial stage. Furthermore, due to the progress of technological development in recent years, solid polymer fuel cells that operate near room temperature and solid electrolyte fuel cells that operate at 700 ° C. or higher are used in small-sized power sources for automobiles or homes, or for commercial use. It is starting to be put on the market as a power source for buildings.

FIG. 1A is a perspective view of the entire fuel cell, and FIG. 1B is an exploded perspective view of a fuel cell (single cell).
As shown in FIGS. 1A and 1B, the fuel cell 1 is an assembly of single cells. As shown in FIG. 1B, the unit cell has a fuel electrode membrane (anode) 3 laminated on one surface of the solid polymer electrolyte membrane 2 and an oxidant electrode membrane (cathode) 4 laminated on the other surface. The separators 5a and 5b are stacked. A typical material constituting the solid polymer electrolyte membrane 2 is a fluorine ion exchange resin membrane having a hydrogen ion (proton) exchange group.

  The fuel electrode film 3 and the oxidant electrode film 4 include a diffusion layer made of carbon paper or carbon cloth made of carbon fiber, and a catalyst layer provided so as to be in contact with the surface of the diffusion layer. The catalyst layer includes a particulate platinum catalyst, catalyst-supporting carbon, and a fluororesin having a hydrogen ion (proton) exchange group. An MEA (Membrane Electrode Assembly) may be used in which the fuel electrode film 3 and the oxidant electrode film 4 are bonded to the solid polymer electrolyte membrane 2 and configured as an integral member.

  Separator 5a, 5b may be called a bipolar plate. The rectifying plate is a member for rectifying or distributing fuel gas or oxidizing gas, and is sometimes called a porous plate, fins, or mesh.

  A fuel gas (hydrogen or a hydrogen-containing gas) A flows through a flow path 6 a that is a groove formed in the separator 5 a, whereby the fuel gas is supplied to the fuel electrode film 3. In the fuel electrode film 3, the fuel gas permeates the diffusion layer and contacts the catalyst layer. Further, an oxidizing gas B such as air is flowed through the flow path 6b which is a groove formed in the separator 5b, whereby the oxidizing gas is supplied to the oxidant electrode film 4. In the oxidant electrode film 4, the oxidizing gas passes through the diffusion layer and contacts the catalyst layer. By supplying these gases, an electrochemical reaction occurs, and DC power is generated between the fuel electrode film 3 and the oxidant electrode film 4.

The main functions required for a separator of a polymer electrolyte fuel cell are as follows.
(1) Function as “flow path” for uniformly supplying fuel gas or oxidizing gas into the surface of the battery (2) Water generated on the cathode side together with a carrier gas such as air and oxygen after the reaction, and fuel Function as a “flow path” for efficiently discharging the battery out of the system (3) Contact with the electrode film (anode 3 and cathode 4) to form an electrical path, and further, electrical between two adjacent single cells Function as “connector” (4) Function as “partition wall” between the anode chamber of one cell and the cathode chamber of the adjacent cell between adjacent cells

  So far, carbon plate materials have been studied as separator materials at the laboratory level. However, the carbon plate material has a problem that it is easily broken, and further has a problem that the machining cost for flattening the surface and the machining cost for forming the gas flow path are very high. These problems make it difficult to commercialize solid polymer fuel cells.

Among the carbon materials, the thermally expansive graphite processed product is remarkably inexpensive, and thus has attracted the most attention as a material for a separator of a polymer electrolyte fuel cell. However, problems to be solved in the future include, for example, the following.
・ Responding to increasingly strict dimensional accuracy requirements ・ Aging deterioration of organic resin that occurs during fuel cell application ・ Carbon corrosion that progresses under the influence of battery operating environment ・ Hydrogen permeation called cross leak ・ Fuel Unexpected cracking accident during battery assembly and use

  Apart from these graphite-based materials, attempts have been made to apply metal sheets to separators for the purpose of reducing costs and improving crack resistance and mass productivity for graphite-based materials. .

  Patent Document 1 discloses a fuel cell separator that is made of a metal member and that is directly gold-plated on a contact surface with an electrode of a unit cell. Examples of the material constituting the metal member include stainless steel, Al, and Ni-Fe alloy, and examples of the stainless steel include SUS304. This separator is gold plated. Therefore, the electrical contact resistance value between the separator and the electrode is low, and the conduction of electrons from the separator to the electrode is good. Thereby, in the fuel cell of patent document 1, it is supposed that an output voltage will become large.

  Patent Document 2 discloses a polymer electrolyte fuel cell including a separator made of a metal material on which a passive film is easily generated by contact with the atmosphere. Examples of the metal material include stainless steel and Ti alloy. A passive film always exists on the surface of the metal used for the separator. For this reason, it becomes difficult for the surface of a metal to be chemically attacked, and the ratio of what is ionized among the water produced | generated by the fuel cell is reduced. Thereby, in the fuel battery cell of patent document 2, the fall of electrochemical reactivity is supposed to be suppressed. Further, Patent Document 2 also shows that the contact resistance value is lowered by removing the passive film at a portion in contact with the electrode film of the separator and forming a noble metal layer.

  Patent Document 3 discloses a titanium material for an upper plate of a camera. This titanium material has H: 0.002 mass% or less, N: 0.007 mass% or less, Fe: 0.02-0.06 mass%, O (oxygen): 0.03-0.06 mass% And the balance is titanium, the crystal grain size is 4 to 7, and the elongation is 45% or more.

  In order to mold the camera upper plate, it is required that the moldability is extremely excellent. When manufacturing the camera upper plate, processing (integral molding) including steps such as blanking, drawing a plurality of times, engraving, drilling, and edge cutting is performed. According to Patent Document 3, if the crystal grain size of the titanium material to be processed is 4 (the crystal grain size is 40 to 45 μm), no cracks are generated when the camera upper plate is processed. On the other hand, in the titanium material having a crystal grain size exceeding 7, cracks are remarkably generated. For example, in a titanium material having a crystal grain size of 8 or 10 (crystal grain size is 25 to 30 μm), cracks are generated during the forming process of the upper plate. Therefore, it cannot be applied as a product. However, when the crystal grain size is less than 4, it is considered that rough skin (wrinkles) occurred in the processed part.

  Patent Document 4 discloses a method for producing a pure titanium thin plate by repeating cold rolling and annealing. In this method, the final annealing is performed as continuous annealing at 600 to 800 ° C. in an air atmosphere for 2 to 6 minutes, thereby adjusting the average crystal grain size of the product to 3 to 60 μm and improving the surface gloss. It is said that a pure titanium sheet in a suppressed state is obtained. After final annealing, pickling is performed. According to this method, it is said that it is possible to suppress the occurrence of defects in which the surface undulates during molding, as compared with a vacuum annealed material.

  Patent Document 5 discloses a method for appropriately adjusting the grain size of a titanium material depending on the content and the content of Fe and O and the conditions of batch annealing according to required performance and quality. According to Patent Document 5, the crystal grain size is 4 to 5 for a plate material that requires stretch formability, and 5.5 to 6.5 when it is necessary to prevent roughening in addition to the stretch formability. It is disclosed that the roll formability is 8 to 11 when manufacturing requires roll formability.

  Patent Document 6 contains, by mass%, Fe: 0.035 to 0.100%, O: 0.010% or more and less than 0.030%, the balance is made of titanium and impurities, and the crystal grain size is 8. A pure titanium plate that is between 0 and 11.5 is shown. The material of the titanium plate is obtained by electron beam melting or vacuum arc melting, and is excellent in formability.

  Patent Document 7 contains, by mass, Fe: more than 0.1 and 0.5 or less, and O: 0.03 or more and 0.1 or less, the balance is made of titanium and impurities, and the crystal grain size is 10 or more. A titanium material is disclosed. This titanium material is said to be excellent in formability.

  In Patent Document 8, Fe: more than 0.10% and less than 0.60%, O: more than 0.005% and less than 0.20%, C: less than 0.015%, N: A titanium material containing less than 0.015% and H: less than 0.015%, the balance being titanium and impurities is disclosed. In this titanium material, Fe is contained more than O, a two-phase structure of α phase and β phase is formed, and the circle equivalent average particle diameter of α phase is set to 10 μm or less.

  In Patent Document 9, a titanium material containing, by mass%, Fe: 0.15% or less (not including 0%) and O: 0.15% or less (not including 0%) is press-molded. Processing to a titanium plate by the method is disclosed. The average crystal grain size of the α phase of the titanium plate is said to be 10 to 200 μm.

  Patent Document 10 contains, by mass%, Fe: 0.15% or less (excluding 0%) and O: 0.15% (excluding 0%), with the balance being from Ti and impurities. A titanium plate is disclosed. In Patent Document 10, a crystal orientation and a crystal grain size are defined for a titanium material, and this titanium plate is said to be excellent in press formability with high yield strength. As for the crystal grain size, the average crystal grain size of the top 100 crystal grains among the crystal grains present in a square having a side of 1 mm on the surface of the titanium plate is 10 to 200 μm. The ratio of the proof stress in the rolling direction of the titanium plate to the proof stress in the vertical direction of rolling of the titanium plate is 0.75 or more.

  Patent Document 11 discloses a titanium plate containing, by mass%, Fe: 0.04 to 0.10% and O: 0.07 to 0.20%, with the balance being Ti and impurities. Yes. This titanium material is said to be excellent in formability such as press working.

  In Patent Document 12, in mass%, O: 0.07 to 0.20%, Fe: 0.04 to 0.10%, N: 0.001% or more and less than 0.02%, C: A titanium plate containing less than 0.015% (including 0%) and the balance being Ti and impurities is disclosed. In this titanium material, the O content [% O] and the Fe content [% Fe] satisfy [% O] + 0.12 × [% Fe] ≧ 0.080, and have high strength and excellent moldability. It is said that.

  Patent Document 13 includes mass%, O: 0.03% or more and less than 0.08%, Fe: 0.015% or more and less than 0.055%, and N: 0.001% or more and less than 0.02%. And a titanium plate containing C: less than 0.015% (including 0%), the balance being Ti and impurities. In this titanium material, the O content [% O] and the Fe content [% Fe] satisfy [% O] + 0.12 × [% Fe] <0.080 and are excellent in formability. ing.

  Patent Document 14 discloses a titanium plate containing 0.04 to 0.06% Fe and 0.07 to 0.11% O in mass%, with the balance being Ti and impurities. . This titanium material is said to have high yield strength and excellent formability such as press working.

  Patent Document 15 discloses a purified gas comprising at least one of hydrogen, paraffin hydrocarbon, ammonia, halogen, and carbon monoxide when a raw material is melted to obtain titanium or a titanium alloy by an electron beam melting method. Is introduced into an electron beam melting chamber to reduce impurity elements such as O and Fe.

  In Patent Document 16, Al is added to a titanium raw material containing O, and these are melted by an electron beam, so that O contained in the titanium raw material is vapor-phase deoxidized as an oxide of Al. A method is described. Further, in Patent Document 16, a further insufficient amount of Al is added to a titanium raw material in which Al and O remain, and these are dissolved by an electron beam, so that O contained in the titanium raw material is used as an oxide of Al. A method for deoxidizing titanium by vapor phase deoxidation is also disclosed.

  In Patent Document 16, as an example, after a titanium sample having an initial O content of 10% by mass and an Al content of 10% by mass was brought into a molten state for 6 minutes, substantially all of the metal Al was O 2. It has been described that the O content was halved. As another example, Al was added to a titanium sample having an initial O content of 1.1% by mass and a titanium sample having an initial O content of 0.12% by mass and melted for 5 minutes. As a result, it was shown that the O content decreased to 0.5% by mass and less than 0.05% by mass, respectively. At that time, the Al addition rate relative to the total weight of the initial sample was 20% by mass and 5.5% by mass, respectively. Patent Document 16 does not describe the Al content of the titanium material after adding Al and maintaining the molten state.

JP-A-10-228914 JP-A-8-180883 Japanese Examined Patent Publication No. 7-62194 Japanese Patent Publication No. 64-1546 Japanese Patent Laid-Open No. 10-317118 Japanese Patent No. 4388503 JP 2009-161816 A Japanese Patent No. 4605514 Japanese Patent No. 5123910 Japanese Patent No. 5385038 Japanese Patent No. 5400824 Japanese Patent No. 5427154 Japanese Patent No. 5444182 Japanese Patent No. 5654933 JP-A-9-25522 Japanese Patent No. 2651945

  However, in Patent Documents 1 to 16, in titanium material, workability suitable for manufacturing a separator or a current plate that is a cell member of a polymer electrolyte fuel cell, and corrosion resistance required for these members are described. It has not been fully studied to achieve both.

  Accordingly, an object of the present invention is to provide a titanium material that is excellent in workability suitable for mass production of a cell member of a polymer electrolyte fuel cell and has excellent corrosion resistance required as a cell member. . Another object of the present invention is to provide a solid polymer fuel containing a titanium material having excellent processability suitable for producing a cell member of a polymer electrolyte fuel cell and having excellent corrosion resistance required as a cell member. It is providing the battery cell member.

  As the workability, in particular, the punching processability that can sufficiently suppress the generation of burrs that occur when forming a through hole by punching, or the stretch formability that can form a cell member having a precise flow path configuration by press molding. The purpose is to improve.

  The gist of the present invention is the following (A) titanium material and the following (B) solid polymer fuel cell member.

(A) In mass% or mass ppm,
Fe: 0.010% or more and 0.100% or less,
O: 0.005% or more and 0.110% or less, and Al: more than 1.0 ppm and 1000 ppm or less, with the balance consisting of Ti and impurities,
The impurities are
C: 0.015% or less,
N: 0.001% or more and 0.020% or less, and H: 0.015% or less,
A titanium material having an α-phase average crystal grain size of 6.5 μm or more and 100 μm or less.

(B) A cell member for a polymer electrolyte fuel cell comprising the titanium material of (A).

  The titanium material of the present invention is excellent in workability suitable for producing a cell member of a polymer electrolyte fuel cell and excellent in corrosion resistance required as a cell member. Since the cell member of the present invention contains such a titanium material, it can have a predetermined shape, exhibits high corrosion resistance and exhibits excellent battery performance when used in a polymer electrolyte fuel cell. To do.

FIG. 1A is a perspective view of the entire fuel cell. FIG. 1B is an exploded perspective view of the fuel battery cell. FIG. 2 is a perspective view of an example of a truncated cone molded product obtained by drawing a titanium material. FIG. 3 is a graph showing the relationship between the average crystal grain size of the titanium material and the amount of die wear after 2 million drilling shots. FIG. 4 is a diagram showing the relationship between the number of perforation shots and the height of burrs caused by the punching of the titanium material (coil).

  The inventor has studied a metal separator having excellent corrosion resistance. At that time, even when used as a separator for a polymer electrolyte fuel cell for a long time, metal elution from the surface of the metal separator is extremely small, contamination with MEA metal ions hardly progresses, catalyst performance decreases, and polymer The target corrosion resistance is that the film performance hardly deteriorates.

  Metals examined for separators include general-purpose SUS304 and SUS316L, their gold-plated materials, M2B or M23C6 type conductive metal precipitate-dispersed stainless steel, stainless steel with conductive fine particle coating or coating treatment, surface The modified stainless steel and titanium materials were used. As a result of the examination, the following knowledge was obtained.

  Stainless steel is a material that is excellent in mass productivity and has both corrosion resistance and workability. In this respect, it can be a candidate for a material for a cell member of a polymer electrolyte fuel cell. However, in a fuel cell using stainless steel, the degree of elution of metal ions varies depending on the structure of the fuel cell or the skill in controlling operation and stoppage. Under conditions where metal ions are likely to elute, even if the stainless steel surface is kept passive, metal ions elute gradually from the stainless steel, causing irreparable damage to the solid polymer membrane and the catalyst. May give. In this case, the performance of the polymer electrolyte fuel cell is greatly deteriorated.

  Titanium is a very expensive material, but it is one of the few commercially available highly corrosion-resistant metal materials that hardly cause metal elution even in the environment within the polymer electrolyte fuel cell. In other words, if the cost is neglected and only the corrosion resistance is emphasized, titanium is a solid polymer in that the degree of elution of metal ions is not influenced by the structure of the fuel cell or the skill of control of operation and suspension. It is a material that is extremely suitable as a constituent material of a cell member for a fuel cell.

  However, regarding workability, titanium is generally inferior to stainless steel. However, it is known that the workability of titanium varies greatly depending on the type and content of trace elements in the material. In particular, Fe, O, and N, which are impurity elements mixed in the manufacturing process, greatly affect the workability of titanium. In addition, a trace amount of H in titanium greatly affects cracking and embrittlement. However, reducing the impurity content and reducing the manufacturing cost are contradictory requirements.

  In pure titanium, if the content ratio of Fe and O is too high, the proof stress becomes too high, and the press formability and elongation properties become poor. On the other hand, a fuel cell is used in a state in which a large number (for example, several hundreds) of cells are stacked and fastened, and when the content of Fe and O in pure titanium is too low, the yield strength becomes too low and the fuel cell is fastened. Depending on the load, the separator or the current plate may buckle.

  The mechanical properties required for titanium materials differ depending on how the separator or the current plate is used in the polymer electrolyte fuel cell and the processing method applied to manufacture the cell members. . When manufacturing a separator or a current plate, a punching (shearing) process, a stretch forming process, a drawing process, a bending process, and the like are appropriately performed. Depending on what kind of processing is performed, it is necessary to give the titanium material mechanical characteristics suitable for the processing. The mechanical properties of the titanium material are preferably adjusted by Fe content, O content, annealing temperature, temper rolling (skin pass rolling) after final annealing, and the like.

  Titanium materials used in these cell members have excellent local elongation characteristics and rough skin occurs at the overhang forming part in order to prevent warping and rough skin from forming due to forming a separator or current plate. It is preferable that it is difficult. For that purpose, adjustment of the average crystal grain size (crystal grain size) is extremely important.

  A material used for a cell member which is manufactured only by a punching (shearing) process and a bending process and hardly subjected to a stretch forming process is required to be less likely to generate burrs and cracks. Such a material does not require high local stretch performance, for example, the stretch performance required for a cell member that is subjected to a stretch forming process for forming a flow path. Further, since one machining is performed in a very short time and the machining is repeatedly performed at a high speed, the durability life of a die (for example, a punching blade) used for the punching is also regarded as important. As determined by the inventor, it is preferable that the titanium material to be processed is one that can achieve a durable life of more than 2 million dies used for punching.

  It is difficult to obtain a titanium material by melting and refining it in a melting furnace or crucible lined with an oxide-based refractory like a steel material. This is because Ti is very easy to bond with O, so it is melted in a vacuum or in an inert gas atmosphere. In such an atmosphere, the oxide refractory is easily reduced by Ti and suffers from erosion. by. For this reason, the titanium material is usually dissolved using a water-cooled copper mold.

  As a method for melting a titanium ingot that is a raw material for a titanium material, various special melting techniques with different heating methods have been developed. The current mainstream melting methods are vacuum arc resolving (VAR), plasma arc melting (PAM), vacuum induction melting (VIM), and electron beam melting (VIM). This is an EBM (Electron Beam Melting) method.

  In the EBM method, it is possible to perform melting using more scrap than in the VIM method or the like. As described above, the Fe content and the O content of the titanium material greatly affect the workability. For this reason, it is important to control the Fe content and the O content in the production of the titanium material. Since the O content of scrap is not constant, the establishment of a technique for controlling the O content when adding a large amount of scrap is one of the important development issues.

  In the EBM method, the temperature of a portion (hereinafter referred to as “fire point”) where an electron beam is incident on the surface of a molten metal (hereinafter also referred to as “molten metal”) exceeds 2000 ° C., and is locally 2,000. It is several hundred degrees Celsius. In addition, since the electron beam has a large current, a vortex having a high flow velocity is formed in the molten metal near the fire point due to the magnetic field generated by the current, and the renewal speed of the molten metal surface is increased.

O (oxygen) in Ti is thermodynamically stable and is very difficult to remove. The temperature of the molten metal at the hot spot is a high temperature exceeding 2000 ° C., and in this portion, it is usually difficult to thermodynamically deoxidize O as Ti oxide vapor by the concentration of O by the amount of Ti evaporation. It is. The present inventor studied deoxidation as CO gas, deoxidation as Si oxide vapor, deoxidation as Al oxide vapor, and the like as deoxidation methods from molten titanium. As a result, it was judged that the most effective means for removing O in the molten titanium was to add Al and deoxidize it as Al ₂ O vapor.

In titanium dissolution by the EBM method performed under reduced pressure (vacuum), when the Al concentration in the molten metal is high, Al oxide mainly composed of Al ₂ O rapidly evaporates at the fire point and in the vicinity thereof. Deoxidation proceeds. Therefore, the electron beam melting in the presence of Al is effective as a method for reducing the O concentration and a method for controlling the O concentration when melting titanium in which a large amount of scrap is added.

The present invention has been obtained based on these findings and an original technical idea.
As described above, the titanium material of the present invention is, by mass%, Fe: 0.010% or more and 0.100% or less, O: 0.005% or more and 0.110% or less, and Al: exceeding 1.0 ppm. It contains 1000 ppm or less, and the balance consists of Ti and impurities. The impurities include C: 0.015% or less, N: 0.001% or more and 0.020% or less, and H: 0.015% or less. The average crystal grain size of the α phase is 6.5 μm or more and 100 μm or less.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In the following, regarding the chemical composition, “%” is mass%, and “ppm” is mass ppm.

[Titanium material of the present invention]
<Chemical composition>
Essential elements in the titanium material of the present invention are Ti, Fe, O, and Al. This titanium material may contain a noble metal as an optional element. Hereinafter, each element will be described.

Fe :: 0.010% or more and 0.100% or less Fe is generally contained as an impurity in a titanium material, but is an additive element (conditioning element) that is effectively used in the titanium material of the present invention. . In the titanium material, Fe is a β-phase stabilizing element, and part of it is solid-solved in the α-phase, but many form a β-phase, and depending on the heat treatment conditions, as TiFe which is an intermetallic compound It precipitates and functions to suppress crystal grain growth. By adjusting the Fe content and the O content, the yield strength can be increased while suppressing a decrease in ductility of the titanium material. In addition, by suppressing the crystal grain growth, it is possible to suppress the generation of burrs during cutting or punching hole formation, and the effect of reducing the wear of the mold can be expected.

  However, if the Fe content exceeds 0.100%, the moldability cannot be ensured even if the O content in the material is reduced. On the other hand, if the Fe content is less than 0.010%, the yield strength is too low and the material becomes soft and easily buckled, and it becomes difficult to secure a raw material that can reduce the Fe content, and the low industrial scale. Cost stable mass production becomes difficult. For this reason, in the titanium material of the present invention, the lower limit of the Fe content is 0.010% and the upper limit is 0.100%. The Fe content is preferably 0.020% or more and 0.100% or less, and more preferably 0.030% or more and 0.100% or less.

O (oxygen): 0.005% or more and 0.110% or less O is generally contained as an impurity in a titanium material, but is an additive element that is effectively utilized in the titanium material of the present invention. As an example of the method for producing the titanium material of the present invention, Al is added during electron beam melting, and vapor phase (vapor) deoxidation is performed with Al. In this case, as a result, although depending on the melting raw material including the scrap to be used, the O content may be lower than that of a normal titanium material currently on the market.

The cell member of the polymer electrolyte fuel cell assumed as the main application of the titanium material of the present invention is required to have the following characteristics at the same time.
・ Excellent mass productivity ・ Inexpensive ・ Excellent corrosion resistance ・ Good formability when processed as a cell member (for example, warpage and burrs are unlikely to occur) ・ Highly durable mold What can be done? When the fuel cell is assembled by fastening the cell, it has a material strength (yield strength) that is difficult to buckle

  In order to satisfy such a requirement, the O content needs to be 0.005% or more and 0.110% or less. That is, if the O content is less than 0.005%, the material strength is insufficient, the titanium material becomes soft and is easily buckled, and the local stretchability is too high at the time of punching, so that burrs are conspicuously generated. become. Further, if the O content in the titanium material is lowered to less than 0.005%, the manufacturing cost becomes too high, and it cannot be a material for the above-mentioned use assumed in terms of mass productivity and cost. On the other hand, when the O content exceeds 0.110%, even if the content of other elements such as Fe is adjusted, the material strength and proof stress are too high, and the elongation performance becomes inferior, Overhang forming for forming a flow path as a cell member for a fuel cell becomes difficult. On the other hand, when the O content exceeds 0.110%, the life of the mold is shortened, making it unsuitable for mass production. The O content is preferably 0.010% or more and 0.060% or less.

Al: more than 1.0 ppm and not more than 1000 ppm Al is a metal element that is not usually added in JIS 1, 2, 3, 11 and other titanium materials. Al is an additive element actively utilized. As will be described later, when the titanium material of the present invention is manufactured, Al can be positively added as a deoxidizing element during melting to adjust the O content of the titanium material. Depending on such a manufacturing method, it is difficult to stably mass-produce titanium materials with an Al content of 1.0 ppm or less. In the material of the present invention, when the Al content is 1.0 ppm or less, it is difficult to stably obtain desired mechanical properties and workability. For this reason, Al content rate shall exceed 1.0 ppm.

  On the other hand, if the Al content exceeds 1000 ppm (0.100%), it becomes difficult to form a cell member of a fuel cell into a predetermined shape, and corrosion resistance cannot be ensured. For this reason, the Al content is set to 1000 ppm or less, preferably 100 ppm or less, and more preferably 20 ppm or less.

  The Al content of the titanium material can be quantitatively analyzed by a titanium-ICP emission spectroscopic analysis method standardized in JIS H1632-2. The content of less than 10 ppm can be quantitatively analyzed by glow discharge mass spectrometry. Thereby, it is possible to analyze with an accuracy of 0.01 ppm. As a measuring device, VG9000 manufactured by FI ELEMENT may be used.

Hereinafter, the impurity element will be described.
C: 0.015% or less (including 0%)
In the titanium material of the present invention, C is an impurity. C tends to adhere to the surface of the titanium material due to contamination from rolling oil used in the rolling process. When C exists in the surface layer of the titanium material, TiC or TiCN is generated on the surface of the titanium material in the annealing process. TiC and TiCN are both high-hardness intermetallic compounds, which cause the damage of the mold to be accelerated. Therefore, the C content is set to 0.015% or less (including 0%). The C content is preferably 0.010% or less.

N: 0.001% or more and 0.020% or less In the titanium material of the present invention, N is an impurity. By absorbing N from the atmosphere in the annealing process, the N content of the titanium material is likely to increase, and in this case, TiN is generated. TiN is a high-hardness intermetallic compound, and causes damage to the mold faster. For this reason, N content rate shall be 0.001% or more and 0.020% or less. The N content is preferably 0.015% or less, and more preferably 0.010% or less.

H: 0.015% or less In the titanium material of the present invention, H is an impurity. H is inevitably absorbed into the titanium material by pickling, annealing in the manufacturing process of the titanium material, electrolytic treatment performed as necessary. H causes hydrogen embrittlement and hydrogen cracking of the titanium material. For this reason, the H content is set to 0.015% or less, preferably 0.010% or less.

Other impurities: Ca
The titanium material of the present invention may contain several ppm of Ca as impurities. In the production method described later, when an Al sheath-CaCl ₂ interior cored wire is used as an Al source to be added to the molten titanium, the obtained titanium material contains Ca as an impurity. Ca, like Al, has a stronger bonding force with O than Ca, and Ca oxide has a high vapor pressure, so it is easily removed from a high-temperature titanium melt. For this reason, in many cases, Ca does not remain above 10 ppm in the titanium material.

Noble metal: 0.25% or less Noble metal is not an essential additive element in the titanium material of the present invention. However, in order to improve corrosion resistance and electrical contact resistance performance, noble metal is contained instead of a part of Ti. Also good. Here, the noble metal is one or more of Au, Ag, Pt, Pd, and Ru. If the precious metal is contained exceeding 0.25%, an increase in material cost cannot be ignored. For this reason, when the titanium material of this invention contains a noble metal, the content rate shall be 0.25% or less.

  As a reference example, consider the case where a rare earth element is contained in the titanium material of the present invention. Since rare earth elements have a very strong bonding force with O, inclusion of rare earth elements in a titanium material is effective for fixing O in the titanium material. When producing such a titanium material, the rare earth element may be added to the molten titanium. In this case, the rare earth element reacts with O remaining in the molten titanium to form a fine oxide of the rare earth element, and the grain refinement of the titanium material can be controlled. However, since the vapor pressure is low, it cannot be expected that gas phase (vapor) deoxidation will proceed. The rare earth element may be added as an Al cored wire that contains the rare earth element.

<Crystal grain size and average crystal grain size>
“Crystal grain size” refers to a grain size number standardized by JIS G 0551. The “average crystal grain size” is a circle-equivalent diameter calculated based on the number of crystal grains per 1 mm ² obtained according to JIS G 0551, assuming that all the crystal grains are circles of the same diameter.

  In the titanium material of the present invention, the average crystal grain size of the α phase is 6.5 μm or more and 100 μm or less (corresponding to crystal grain size number 4 to 11.5). If the average crystal grain size of the α phase is within this range, it is possible to perform general processing on the titanium material.

  However, more specifically, when this titanium material is processed (including molding) into a solid polymer fuel cell member, the preferred range of the average crystal grain size (crystal grain size) of the titanium material depends on the processing method. different. For example, the processing of a cell separator of a polymer electrolyte fuel cell is mainly performed by an overhang forming process in order to generate a channel composed of peaks and valleys. In this case, the average crystal grain size of the α phase is preferably 35 μm or more and 100 μm or less (corresponding to crystal grain size numbers 4 to 7). On the other hand, the processing of the rectifying plate for cells of the polymer electrolyte fuel cell is mainly performed by bending and punching (shearing). In this case, the average crystal grain size of the α phase is preferably 10 μm or more and 30 μm or less (corresponding to a crystal grain size number of 7.5 to 11). This is because there is a large difference in the stretch formability and the height of burrs that can be generated along the end face of the punched portion, depending on the crystal grain size of the titanium material.

  As the average crystal grain size of the α phase increases, the local elongation of the titanium material increases. When the average crystal grain size of the α phase is 35 μm or more and 100 μm or less, since the local elongation is large, the stretch forming process can be favorably performed on the titanium material. On the other hand, when the average crystal grain size of the α phase exceeds 100 μm, cracks, wrinkles, and rough skin tend to occur when the titanium material is formed.

  On the other hand, when a titanium material having an α-phase average crystal grain size of 30 μm or more is subjected to a punching process, burrs may be prominent, and the life of the mold to be used tends to be shortened. More specifically, since the punching process of the titanium material proceeds by shearing and breaking, if the local elongation is too large, it is difficult to break, and as a result, high burrs are likely to occur. When the burr height is large, if the punching process is performed at high speed, the tip temperature of the punching blade rises, and the titanium punching residue adheres to the blade tip. The oxide generated thereby promotes wear of the cutting edge.

  When press forming is performed on the titanium material to be processed in addition to punching (shearing) processing, if the average crystal grain size of the α phase is too small, cracks are likely to occur during press forming. If the average crystal grain size of the α phase is 10 μm or more and 30 μm or less, it is possible to achieve both punching workability and stretch forming workability in the titanium material. The generation of burrs is particularly suppressed when the average crystal grain size of the α phase is 12 μm or more and 28 μm or less, and the durability of the mold becomes the highest.

  When the polymer electrolyte fuel cell is, for example, mounted on an automobile, 800 cells are used per vehicle. When two cell members are used in one cell, 1600 cells per vehicle are used. In the case where three cell members are used for one cell per vehicle, 2400 cell members are used. When the durability of the mold deteriorates rapidly due to the occurrence of burrs, it is necessary to secure a spare mold for replacement and frequently exchange the mold during processing. For this reason, it is very important that the mold has high durability during mass production. In order to increase the durability of the mold, measures such as selection of the mold material, adjustment of the mold clearance, and application of lubricating oil are taken, but the crystal grain size of the titanium material to be processed can be adjusted. Very important.

[Method for producing titanium material of the present invention]
The method for producing the titanium material of the present invention is not limited to the one described below.
First, an example of a raw material melting method in producing the titanium material of the present invention will be described.

  The titanium material of the present invention is assumed to be manufactured in large quantities in the future as a material for a polymer electrolyte fuel cell to be mounted on an automobile. In this respect, it is preferable to melt by the EBM method that can use a large amount of titanium scrap and return scrap among the above-described melting methods. In particular, a melting method in which a molten raw material containing a large amount of scraps and return scraps is continuously agglomerated into billets while continuously or semi-continuously supplied to a fire point, for example, a dredging method EBM method is the most. This is the preferred method.

In the case of melting by the EBM method, for example, an Al source is charged into the molten titanium, and Al is reacted with O in the molten titanium, so that O can be removed from the surface of the molten titanium as Al oxide vapor. When thermodynamic calculation is performed using the value of the degree of vacuum in the chamber in which electron beam melting is performed, from the surface of the molten metal where the molten metal temperature exceeds 2000 ° C., it is vaporized as Al oxide gas (considered as Al ₂ O). From this molten metal, metal Ti is also vaporized, but the vapor pressure of the Al oxide gas is about two orders of magnitude higher, and most of the gas exhausted from the chamber becomes the Al oxide gas.

  Further, in the vicinity of the hot spot, the molten metal is rotated at high speed (stirring) due to the magnetic field of the high-current electron beam, and the renewal speed of the molten metal surface is increased. Due to the above factors, by depressurizing the inside of the chamber, Al vapor phase deoxidation proceeds efficiently at and near the fire point.

  On the other hand, at a portion of 1500 ° C. or less away from the fire point on the surface of the molten metal, the vapor pressure of the Al oxide is low, so the evaporation rate of the Al oxide is low, and most of the added Al stays in the molten metal. As described above, the evaporation rate of the Al oxide varies depending on the temperature of the molten metal surface, and thus varies depending on the distance from the fire point. For this reason, the Al concentration in the molten titanium can be controlled by the addition position of the Al source.

  Rather than increasing the Al concentration of the entire titanium melt, by increasing the Al concentration only at the fire point and its vicinity, the added Al can efficiently contribute to the evaporation of Al oxide, that is, deoxidation. Can do. For this purpose, the Al source is not charged into the melting tank at the same time as the titanium melting raw material, but is directly and continuously charged into the hot spot and the molten pool portion around it, so that the Al concentration is hot. And it is preferable to make it high only in the vicinity thereof.

As the Al source, for example, an aluminum shot, an aluminum wire, or a cored wire with an Al exterior / CaCl ₂ interior can be used. The Al source in the form of a wire can be directly charged into the molten metal using, for example, an automatic wire feeder. The Al concentration of the molten metal can be adjusted by the Al addition position, the Al addition amount, and the degree of vacuum in the melting tank.

  You may perform cold rolling and annealing with respect to the solidified titanium material. Cold rolling may be performed in several passes. You may perform temper rolling (skin pass rolling) with respect to the titanium material after annealing (after final annealing in the case of performing annealing multiple times).

As the rolling reduction of the titanium material during cold rolling increases, the internal strain of the titanium material increases. Here, the “reduction ratio” is (1−t ₁ / t ₀ ) × 100 (%), where t ₀ is the thickness before cold rolling and t ₁ is the thickness after cold rolling. expressed. When the internal strain of the titanium material is increased, the strength (yield strength) is increased and the local elongation characteristics are decreased. Such mechanical properties can be adjusted by annealing after cold rolling.

  By performing skin pass rolling on the titanium material, the stretch forming performance is reduced, but the occurrence of burrs during cutting or punching can be suppressed. If the rolling reduction is too large, the workability is lowered. For this reason, the rolling reduction by skin pass rolling is preferably 0.05% or more and less than 15%, more preferably 0.05% or more and less than 10%, and more preferably about 1 to 3%. preferable.

  In the above manufacturing process, the average crystal grain size of the titanium material (α phase) is adjusted mainly by the contents of Fe, O, and Al and the conditions of the rolling and annealing processes. Specifically, the higher the content of at least one of Fe, O, and Al, the greater the rolling reduction during rolling, the lower the annealing temperature, and the shorter the annealing time, the more titanium. The average crystal grain size of the material can be adjusted small.

[Cell member of the present invention]
The cell member of the present invention preferably has a surface roughness of 0.12 μm or more and 4 μm or less (preferably 3 μm or less) with an Ra value standardized by JIS B 0601-1982. If the surface roughness is less than 0.12 μm due to the passive film formed on the surface of the titanium material, the electrical contact resistance becomes high, and as a separator for a polymer electrolyte fuel cell cell, a current plate, etc. It is difficult to use. By setting the surface roughness to 0.12 μm or more, the contact resistance can be reduced to some extent. This is because the surface roughness of the cell member such as the separator and the current plate is increased, and the cell member and the fuel electrode film and the oxidant electrode film, which are other constituent members of the cell, or the MEA including them. This is because the number of contact points and the contact area increase. Even if the roughness exceeds 4 μm and is too large, the contact resistance value increases. This is because the number of contact points and the contact area between the cell member and the fuel electrode film and the oxidant electrode film, which are other components of the cell, or the MEA including them are reduced.

[Method for producing cell member of the present invention]
The cell member can be manufactured by appropriately performing the above-described stretch forming process, folding process, punching process, etc. on the foil-like titanium material.

  When adjusting the surface roughness of the cell member, the surface treatment of the cell member, for example, a spray etching process or an immersion process using an acid solution containing hydrofluoric acid is performed with an acid solution after the molding process is completed. The surface roughness tends to increase as the surface treatment time increases and as the temperature or concentration of the acid solution used in the treatment increases. Titanium fluoride remaining on the surface after the treatment becomes an oxide during operation of the fuel cell incorporating the cell member, resulting in an increase in contact resistance. For this reason, it is preferable to perform the final surface roughness adjustment in an acid solution that does not contain hydrofluoric acid.

The cell member may be subjected to the following surface treatment.
(1) Applying a conductive layer containing a noble metal (at least one of Au, Ag, Pt, Pd, and Ru) to the outermost layer on at least one surface of the cell member by plating or painting.
(2) A conductive layer containing at least one of graphite powder, carbon powder, carbon fiber, and carbon nanotube is applied to the outermost layer on at least one surface of the cell member by coating treatment or electrodeposition treatment.

<First embodiment>
In order to confirm the effect of the present invention, a sample of a titanium material was prepared, and corrosion resistance and workability were evaluated. Table 1 shows the chemical composition of the material used to produce the titanium material.

  All the materials were obtained by melting the raw materials. Melting was performed by melting the raw material in the chamber of the vacuum melting apparatus by the EBM method. The Fe content and O content of the material were adjusted by the following method. First, as a raw material, it was confirmed that the first sponge titanium in which the Fe content and the O content were confirmed to be lower than the target values, and the Fe content and the O content were higher than the target values. Second sponge titanium and a return scrap material with known Fe content and O content were prepared.

  The 1st and 2nd sponge titanium was produced by the crawl method. Then, the first sponge titanium was melted by the EBM method, and the second sponge titanium and the return scrap material were added to the resulting molten metal. The Fe content and the O content were adjusted according to the ratio of the amount of the dissolved first sponge titanium, the added second sponge titanium, and the amount of the return scrap material.

  An appropriate amount of aluminum wire was put into the molten metal during melting using a wire addition device installed in a vacuum melting apparatus chamber. In the molten pool, the aluminum wire was directly put into a hot spot and a high temperature part exceeding 2000 ° C. in the vicinity thereof. Thereby, gas phase (evaporation) deoxidation with Al oxide was performed, the Al concentration and O concentration in the molten metal were adjusted, and the Al content rate and O content rate of the material were adjusted.

  The materials of Sample Nos. 1 to 10 shown in Table 1 were melted in a small electron beam melting furnace and agglomerated in a water-cooled copper mold to obtain an ingot. The ingot was a slab having a mass of 10 kg, a thickness of 45 mm, and a width of 100 mm. The slab was soaked at 850 ° C. in an electric furnace in an air atmosphere, then hot rolled to a thickness of 5.3 mm, and allowed to cool to obtain a hot rolled sheet. Subsequently, this hot-rolled sheet was annealed by holding it at 700 ° C. for 30 minutes in an atmospheric furnace, and then air-cooled.

  After completely removing the scale of this hot-rolled sheet by machining, it was cold rolled until the thickness became 0.5 mm to obtain a titanium material to be evaluated. In the course of cold rolling, an intermediate annealing treatment was performed once in an argon atmosphere. The average crystal grain size (crystal grain size) of the titanium material was adjusted according to the annealing conditions and the rolling reduction during the cold rolling. In the production of the titanium material according to the embodiment of the present invention, the α-β two-phase region cooling for the fine graining is made by utilizing the fact that the two-phase structure of the α phase and the β phase is obtained by setting the temperature of the intermediate annealing. Hot rolling was performed. Both hot rolling and cold rolling in the examples of the present invention were performed in the same direction with respect to the titanium material.

  The obtained titanium material was subjected to final annealing in a vacuum furnace. The final annealing was performed in a temperature range of 500 to 800 ° C. after the inside of the furnace was once made an argon atmosphere and then evacuated. The holding time was 4 hours in all cases.

  The titanium material sample obtained through the above steps was evaluated for corrosion resistance as a cell member of a polymer electrolyte fuel cell by the following procedure. First, the surface of the sample was wet-polished with No. 600 emery abrasive paper, and then continuously immersed in a holding solution at 70 ° C. for 96 hours, and the weight loss due to immersion was measured. The corrosion resistance of the material was evaluated. The titanium material sample used for the evaluation was a test piece having a width of 30 mm and a length of 40 mm. Two test pieces were prepared for each sample of the titanium material, and the corrosion weight loss was obtained for each of these test pieces, and these were averaged to obtain the corrosion weight loss of the titanium material. The holding solution was prepared by adding 30 ppm of fluorine ions to an aqueous sulfuric acid solution adjusted to pH 3. This evaluation condition can be said to be an environment simulating a typical polymer electrolyte fuel cell.

  Tables 2-1 and 2-2 show the numbers of the materials used (see Table 1), the final annealing temperature (heating temperature), and the corrosion weight loss.

  It was confirmed that the titanium materials using the materials 7 to 9 whose Al content exceeds 1000 ppm, that is, the titanium materials of Comparative Examples 7 to 34 have a small amount of corrosion weight loss regardless of the heat treatment conditions. This is presumed to be because the corrosion resistance of Ti was reduced because the titanium material contained Al exceeding 1000 ppm. When the surface of these titanium materials after the corrosion resistance evaluation was subjected to surface analysis using a Quantara SXM scanning X-ray photoelectron spectrometer manufactured by ULVAC-PHI, it was confirmed that Al oxide was generated. In order to obtain sufficiently high corrosion resistance, it can be judged that the Al content of the titanium material is preferably 1000 ppm or less.

  The crystal grain size of each titanium material was measured by a method according to JIS G 0551, and the average crystal grain size was determined as the equivalent circle crystal grain size from the value of the crystal grain size.

  About each titanium material, the Erichsen test based on JISZ2247 was implemented, the Erichsen value (molding height) was measured, and the stretch moldability was evaluated.

  In addition, each titanium material was subjected to stretch forming with drawing. The punch used had a diameter of 20 mm and a shoulder radius of 1 mm, and the die used had a hole diameter of 50 mm and a shoulder radius of 1 mm. Using these punches and dies, a blank of titanium material having a size of 100 mm was formed into a truncated cone shape having a height of 20 mm.

  FIG. 2 is a perspective view of an example of a truncated cone molded product obtained by drawing a titanium material. For some titanium materials, body wrinkles 12 occurred on the side surfaces of the truncated cone molded product 11. About each titanium material, the generation | occurrence | production condition of the body flaw 12 (the wrinkle occurrence condition of a vertical wall) was evaluated.

  About the rough skin by processing, the sample surface after the Erichsen test and the sample surface after the stretch forming processing test were observed by magnifying 50 times, and the rough skin occurrence state of these samples was comprehensively evaluated.

  Assuming that it is processed into a cell member of a polymer electrolyte fuel cell, the same shape as the separator flow path is formed on the titanium material by press molding using a press mold and a 80-ton capacity press. A test to form a groove having The press-molding die is for forming a serpentine-type flow path. The width of the crest and trough of the flow path are both 0.8 mm, the depth is 0.4 mm, and the shoulder radius is It was 0.15 mm. About each titanium material, the presence or absence of the crack generation by press molding was evaluated (component molding comprehensive evaluation). The titanium material of the comparative example using the materials 9 and 10 was not suitable as a material for the cell member of the polymer electrolyte fuel cell because the end face crack occurred during the cold rolling and the surface roughness was remarkable. Judging as appropriate, these titanium materials were not evaluated except for the corrosion resistance evaluation shown in Tables 2-1 and 2-2.

  In Tables 3-1 and 3-2, the numbers of the materials used (see Table 1), the final annealing temperature (heating temperature), the α grain size (grain size number), and the average grain size determined from this grain size. , Yield strength and elongation, and results of moldability evaluation are shown.

  The mechanical properties of the titanium material are greatly influenced by the Fe content and the O content. Referring to Table 1, the O contents of the materials 1 to 8 were all as low as 0.010 to 0.031% by mass. The Fe content of the materials 1, 3 and 4 is as low as 0.034 to 0.0036% by mass, the Fe content of the materials 2 and 5 to 7 is 0.074 to 0.096% by mass, the material 1, Higher than the Fe content of 3 and 4. In the materials 2 and 5 to 7, the heating temperature at the time of final annealing is about 595 ° C., and at a higher temperature, the β phase is precipitated in the α phase at the time of heating, and the β phase precipitation ratio varies depending on the heating temperature. At lower temperatures, no β phase precipitated in the α phase during heating.

  From Table 3-1 and Table 3-2, it can be seen that the titanium material having a height of 10 mm or less in the Eriksen test had a problem during flow path molding. For this reason, as an Erichsen test result, it can be said that the titanium material which has an Erichsen value of 10 mm or less in Table 3-1 and Table 3-2 is not favorable.

  All of the titanium materials of Comparative Examples 1 to 6 had an average crystal grain size of less than 6.5 μm, the Eriksen test results were not good, and cracks were generated in the overall evaluation of the member molding. Therefore, it can be seen that the average crystal grain size needs to be 6.5 μm or more.

  Materials 7 and 8 both have an Al content higher than 1000 ppm, and titanium materials using materials 7 and 8 are cracked and wrinkled in the Erichsen test, the stretch forming test, and the flow path formation test using a press. , And / or rough skin occurred frequently. These titanium materials are not good in the results of corrosion resistance evaluation (see Table 2-2). Therefore, it is understood that the Al content of the titanium material needs to be 1000 ppm or less.

On the other hand, the evaluation results of the materials satisfying the following requirements (i) to (viii) were good.
(i) Fe content: 0.010% or more and 0.100% or less
(ii) O content: 0.005% or more and 0.110% or less
(iii) C content: 0.015% or less (including 0%)
(iv) N content: 0.001% to 0.020%
(v) H content: 0.015% or less
(vi) Al content: more than 2.0ppm and 1000ppm or less
(vii) The balance of the titanium material is made of Ti and impurities.
(viii) Average crystal grain size of α phase: 6.5 μm or more and 100 μm or less (corresponding to crystal grain size number 4 to 11.5)

  Moreover, about the Example whose average crystal grain diameter of (alpha) phase is 10 micrometers or more and 30 micrometers or less (equivalent to the crystal grain size number 7.5-11), and the average crystal grain diameter of (alpha) phase are not in this range, and comparison The evaluation results were good compared to the examples.

<Second embodiment>
The raw materials were melted by electron beam melting, and titanium ingots of materials 11 to 14 shown in Table 1 were produced on a mass production scale, one for each composition. During the electron beam melting, an aluminum wire was introduced at and near the fire point to adjust the O concentration and Al concentration of the molten metal. Each ingot had a mass of 3 tons, a thickness of 200 mm, and a width of 530 mm. All of the ingots had an Al content of 1.3 to 4.8 ppm, an O content of 0.031 to 0.098%, and an Fe content of 0.045 to 0.095%.

  After cleaning the surface of these ingots, an antioxidant was applied and processed into a slab having a thickness of 55 mm and a width of 560 mm by hot forging. The heating temperature during the hot forging was 1050 ° C. The slab was divided into three in the longitudinal direction during hot forging to obtain a slab for hot rolling. The surface of each slab is subjected to surface shaving and completely removed from wrinkles, and then an antioxidant is applied and heated and maintained at 730 ° C. in an electric furnace. Hot rolling was performed to obtain a hot rolled coil having a thickness of 4.8 mm.

  These hot-rolled coils were subjected to an intermediate annealing process that was held at 700 ° C. for 5 minutes in a continuous sheet-type annealing furnace, and subsequently descaling was performed by a continuous pickling process. This coil was cold-rolled and finished to a thickness of 0.5 mm.

  After the obtained coil was divided into three in the length direction, a short-time heat treatment capable of actual production was performed using a bright annealing furnace dedicated to titanium. The heating temperature was 800 ° C., and the heating time was 1.5 minutes, 3 minutes, and 6 minutes for the three divided coils, respectively. After this heat treatment (bright annealing), each coil was subjected to skin pass rolling so that the reduction rate was 1.2% only for the 60 m region, and a material for confirming the skin pass effect was obtained.

  The material 15 in Table 1 is a JIS type 1 standard titanium coil material procured from the city. This titanium coil material has a bright annealing specification and can be judged as a mass-produced material, but the annealing conditions are unknown. The plate thickness of the titanium coil material was 0.5 mm. The chemical composition of the titanium coil material was as follows. The Fe content was 0.032%, the O content was 0.049%, and the Al content was 0.16 ppm, both of which were regarded as normal impurity contents. It was also confirmed that the C content, N content, and H content were at a level that can be regarded as a normal impurity content. From the appearance of this titanium coil material, it was judged that skin pass rolling was not performed at the time of production.

  About each titanium material, the JIS13B tensile test piece was extract | collected along the coil longitudinal direction, and the tensile strength and elongation were measured at normal temperature. Further, in each titanium material, for each of the part that was not subjected to skin pass rolling and the part that was subjected to skin pass rolling, the Erichsen test and the stretch forming test were performed in the same manner as the titanium materials shown in Table 3-1 and Table 3-2. And the flow path formation test by the press was performed, and the same evaluation was performed. Furthermore, the punching process test was done about the part which did not perform the skin pass rolling of each titanium material.

  In Table 4, the results of the same evaluation as the titanium materials shown in Table 3-1 and Table 3-2 for the portions that were not subjected to skin pass rolling of each titanium material were the numbers of the materials used (see Table 1), And the final annealing time (holding time). Table 5 shows the results of the same formability evaluation as the titanium materials shown in Table 3-1 and Table 3-2 for each titanium material, together with the number of the material used and the final annealing time (holding time). Show.

  As shown in Table 3-1 and Table 3-2 and Table 4, Table 3-1 and Table 3-2 show the results shown in Tables 3-1 and 3-2 by short-time annealing at 800 ° C. for 1.5 to 6 minutes in the examples shown in Table 4. It was confirmed that the obtained titanium material had the same characteristics as the long-time annealing held at 535 to 735 ° C. for 4 hours in the examples shown. Depending on the evaluation items, these titanium materials exhibited characteristics superior to the material 15 (commercial product) shown as the comparative example 38. This result can be determined to be due to the fact that in the examples of the present invention, the O concentration was adjusted using Al during melting. The titanium material of the present invention can be produced without any problem even in a mass production line that is required to be excellent in productivity because good characteristics can be obtained even by short-time annealing. As shown in Table 5, it was confirmed that the titanium material after the skin pass rolling also has good characteristics.

<Third embodiment>
For the titanium material shown in Table 4 (coil having a thickness of 0.5 mm and a width of 560 mm), slitting was performed with a width of 31 mm over the entire length of the portion not subjected to skin pass rolling. Fifteen coils having a length of 0.5 mm and a width of 31 mm were collected. These coils were punched (perforated), and the behavior of burrs and the dies used for the punching, particularly the durability of the punch edge, were investigated. The punch and die were produced by processing HAP40 manufactured by Hitachi Metals Tool Co., Ltd., which is a commercially available tool steel.

  The punched hole shape was a square having a side of 2.000 mm (corner R was 0.050 mm). The coil was continuously drilled by a progressive feed method in a pattern in which two punched holes were simultaneously drilled in a row along the width direction of the coil. The feed pitch was 3 mm, and the clearance between the punch and the die was set to 6.5% of the plate thickness. The punching press speed was 230 spm, and punching was performed 2 million times (2 million shots). No stamping oil was used. An 80-ton capacity press was used for drilling.

  Table 6 shows the results of the punching test together with the number of raw materials used, the α phase crystal grain size (grain size number), and the average crystal grain size determined from this crystal grain size.

  FIG. 3 is a diagram showing the relationship between the average crystal grain size of the titanium material and the die wear after 2 million shots. The die wear amount is the sum of the punch wear amount and the die wear amount. FIG. 4 is a diagram showing the relationship between the number of perforation shots and the height of burrs caused by the punching of the titanium material (coil). The legend of FIG. 4 shows the average crystal grain size of each titanium material.

From FIG. 3, the following can be understood.
(1) When the average crystal grain size is around 15 μm, the wear amount of the mold becomes the smallest.
(2) When the average crystal grain size is larger than 15 μm, the wear amount of the mold increases as the average crystal grain size increases.

The following can be seen from FIG.
(3) In Examples and Comparative Examples in which the average crystal grain size is larger than 30.8 μm (Example 38), the burr height tends to increase as the number of drilling shots increases.
(4) In Examples and Comparative Examples in which the average crystal grain is smaller than 28.3 μm (Example 35), the burr height remains at 8 μm or less even when the number of drilling shots exceeds 1.2 million.

  From the results of (1) to (4) above, it can be seen that excellent mold durability can be secured by setting the average crystal grain size to 10 μm to 30 μm.

<Fourth embodiment>
Two coils having a thickness of 0.5 mm and a width of 240 mm were sampled from the coil after skin pass (Examples 36, 39, and 42 and Comparative Example 36) manufactured in the second example by slitting. did. A separator for a cell of a polymer electrolyte fuel cell was produced from this coil using a progressive press die and a 250-ton capacity press.

  These separators are sprayed with an aqueous solution of 10% by mass nitric acid and 4% by mass hydrofluoric acid, and the temperature of the liquid is adjusted to 45 ° C., and surface pickling is performed. To 0.15 μm. After pickling, washing was performed with a 5% by mass aqueous hydrochloric acid solution, followed by washing with water. The separator surface was thinly sprayed with a conductive paint composed of carbon powder, conductive carbon nanotubes, and a conductive organic resin. The separator was formed with three serpentine-type flow paths, and the widths of the crests and troughs of the flow path part were each 1 mm and the depth was 0.6 mm.

A single cell of a polymer electrolyte fuel cell was assembled using these separators and a commercially available standard Japan Gore MEA, and an evaluation test was performed on the single cell. First, for these single cells, constant current operation at a current density of 0.1 A / cm ² was performed for 2000 hours. This is a condition that simulates the operation evaluation environment of a home stationary fuel cell. During operation, the utilization rate of hydrogen and oxygen was constant at 40%.

  For comparison, a separator made of SUS316L having a thickness of 0.1 mm was prepared by subjecting the surface to a cyan bath gold plating treatment with an average basis weight of 50 nm. This separator had a surface roughness adjusted to an Ra value of 0.30 μm by an acid solution treatment before the cyan bath gold plating treatment. This surface roughness is a size that is judged to be preferable in carrying out the present invention. Using this separator, a single cell of a polymer electrolyte fuel cell was assembled in the same manner as described above, and this single cell was operated under the same conditions.

  With respect to the single cell of the above polymer electrolyte fuel cell, the cell voltage after 2000 hours of operation was measured. Table 7 shows the titanium material (see Table 1), the final annealing heating temperature and holding time, the results of the separator molding operation evaluation, and the cell voltage after operating the unit cell of the polymer electrolyte fuel cell for 2000 hours ( Hereinafter, it is referred to as “cell voltage after operation”).

  The cell voltage under the evaluation conditions was about 0.788 V immediately after the operation, but gradually decreased. It can be judged that a cell whose cell voltage can be maintained higher is better as a polymer electrolyte fuel cell. In this evaluation, a cell voltage after operation exceeding 0.750 V is determined to be good. In all of the examples of the present invention, the cell voltage after operation was good because the same performance as that of the gold-plated material using the cyan bath (Comparative Example 42) was obtained. In Comparative Example 40, the cell voltage after operation was less than 0.750V. The cell of Comparative Example 40 was disassembled after the evaluation was completed, and the surface of the separator was subjected to surface analysis using a scanning X-ray photoelectron spectrometer, and it was confirmed that a slight amount of Al oxide was adhered. It was. This Al oxide was generated by the elution of Al from the separator during the operation of the cell, and it was considered that the cell voltage was thereby lowered.

    1: Fuel cell 5a, 5b: Separator

Claims (5)

In mass% or mass ppm,
Fe: 0.010% or more and 0.100% or less,
O: 0.005% or more and 0.110% or less, and Al: more than 1.0 ppm and 1000 ppm or less, with the balance consisting of Ti and impurities,
The impurities are
C: 0.015% or less,
N: 0.001% or more and 0.020% or less, and H: 0.015% or less,
A titanium material having an α-phase average crystal grain size of 6.5 μm or more and 56.2 μm or less. The titanium material according to claim 1,
A titanium material containing 0.25% or less of a noble metal instead of a part of Ti. The titanium material according to claim 1 or 2,
A titanium material having an α-phase average crystal grain size of 10 μm or more and 30 μm or less. The titanium material according to claim 1 or 2,
A titanium material having an average crystal grain size of an α phase of 35 μm or more and 56.2 μm or less . A cell member for a polymer electrolyte fuel cell, comprising the titanium material according to any one of claims 1 to 4.

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