TITANIUM ALLOY MATERIAL, STRUCTURAL MEMBER, AND CONTAINER FOR RADIOACTIVE WASTE

It is an object of the invention to provide a titanium alloy material that exerts excellent corrosion resistance at a low cost in non-oxidizing environment such as a sulfuric acid environment, high temperature neutral chloride environment, or high temperature neutral chloride environment containing fluoride, a structural member using the titanium alloy material, and a container for radioactive waste using the titanium alloy material. Disclosed are a titanium alloy containing ruthenium (Ru): 0.005-0.10 mass %, palladium (Pd): 0.005-0.10 mass %, nickel (Ni): 0.01-2.0 mass %, chromium (Cr): 0.01-2.0 mass %, vanadium (V): 0.01-2.0 mass %, with the remainder including titanium (Ti) and inevitable impurities, and a structural member and a container for radioactive waste using the titanium alloy material.

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Description
BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a low-cost titanium alloy excellent in corrosion resistance, more specifically, relates to a titanium alloy material suitable for use in non-oxidizing environment such as sulfuric acid environment, high temperature neutral chloride environment, or high temperature neutral chloride environment containing fluoride, a structural member using the titanium alloy material, and a container for radioactive waste using the titanium alloy material.

2. Description of the Related Art

Because titanium is excellent in corrosion resistance, it is used in various fields such as a chemical plant, marine structure, and building materials. Corrosion resistance of titanium largely depends on stability of a passive film formed on the surface in a usage environment. In an environment of an oxidizing acid such as nitric acid and ordinary temperature chloride such as seawater, titanium forms a stable passive film on the surface and exerts excellent corrosion resistance. However, because oxidizability of environment (sulfuric acid, highly concentrated brine, and the like) is low, a stable passive film mainly of titanium oxide may not be formed sufficiently, and corrosion resistance may not become so excellent.

To cope with such problem of corrosion resistance in non-oxidizing environment, alloys whose corrosion resistance is further improved by adding various alloy elements to titanium have been developed. For example, Ti—Pd alloy is an alloy excellent in corrosion resistance even in non-oxidizing environment. The reason is that Pd makes a potential of titanium noble, and the condition of the passive film becomes more stable. Industrially, Ti-0.15 mass % Pd alloy has been standardized as ASTM Grade 7 or Grade 11, and has been used in a field such as an oil refinery and petrochemical plant where extremely high corrosion resistance is required. However, the Ti-0.15 mass % Pd alloy has a problem of increasing a material cost because expensive Pd is contained by comparatively large amount.

As more inexpensive titanium alloy exerting excellent corrosion resistance, a titanium alloy has been developed in which small amount of platinum group elements that exert corrosion resistance improving effect by shift of the potential to the nobler direction as Pd does are compositely added, and other alloy elements are further added. For example, Ti-0.05 mass % Pd-0.3 mass % Co alloy has been developed and has been standardized as ASTM Grade 30 and Grade 31. Also, JP-A-H4-308051 discloses a titanium alloy added with platinum group elements, chromium (Cr), and nickel (Ni), and JP-A-2000-248324 discloses a titanium alloy whose corrosion resistance is improved by making the ratio of palladium (Pd) to platinum group elements other than palladium (Pd) appropriate.

However, conventional titanium alloy materials have such problems as described below.

Ordinarily, when a titanium alloy is used as a building material usable in an air atmosphere, there is not any problem such as severe pitting corrosion and crevice corrosion, however, there is a case that surface discoloration by corrosion is taken up as a landscape problem. Also, to cope with an acid-rain environment in an industrial area and the like exposed to a sulfuric acid acidic condition, further improvement of corrosion resistance at a low cost is demanded.

Further, needs of a titanium alloy in high temperature neutral chloride environment such as a condenser of a thermoelectric or nuclear power plant and a heat-transfer pipe of a desalination plant are high, however its using environment has become severe and further improvement of corrosion resistance is demanded. Particularly, there are many cases of generation of crevice corrosion by occurrence of chloride concentration in a structural gap forming part or in a state in which adhering substances are attached on the surface of a titanium alloy, and improvement of crevice corrosion resistance is demanded.

Also, in a container for transportation or disposal of radioactive waste generated from nuclear power-related facilities such as nuclear fuel manufacturing facilities, nuclear power plants, and nuclear fuel reprocessing facilities, the metal surface temperature of the container may occasionally rises to 100° C. or above by heat generation of the radioactive waste. Accordingly, it is presumed that, in transportation or disposal, the surface of the container is formed of a high concentration solution in which chloride, fluoride or the like, that is a corrosion promoting factor, is concentrated due to the evaporation of moisture, and is subjected to a severe corrosive environment. Further, it is known that fluoride corrodes titanium in an acidic region of pH 6 or below, and corrosion resistance in an acidic chloride environment containing fluoride becomes a problem as well.

SUMMARY OF THE INVENTION

The present invention has been developed in view of the problems described above and its object is to provide a titanium alloy material that exerts excellent corrosion resistance at a low cost in non-oxidizing environment such as a sulfuric acid environment, high temperature neutral chloride environment, or high temperature neutral chloride environment containing fluoride, a structural member using the titanium alloy material, and a container for radioactive waste using the titanium alloy material.

As a result of investigations on improvement of corrosion resistance in non-oxidizing environment, the inventors have found out that composite addition of ruthenium (Ru) and palladium (Pd) is most effective with respect to platinum group elements, and corrosion resistance is optimized when nickel (Ni), chromium (Cr), and vanadium (V) are compositely added in addition thereto, which will be described more specifically below.

As described above, composite addition of ruthenium (Ru) and palladium (Pd) is effective in making a potential of titanium noble to form a stable passive film mainly of titanium oxide on the surface. In this regard, by compositely adding nickel (Ni), chromium (Cr), and vanadium (V) at the same time of adding ruthenium (Ru) and palladium (Pd), surface concentration of ruthenium (Ru) and palladium (Pd) on the surface of the titanium alloy in non-oxidizing environment is promoted, and the effect of formation of a stable passive film comes to be exerted greatly even if ruthenium (Ru) and palladium (Pd) are in small amount. Also, nickel (Ni) is an element forming stable oxide even in non-oxidizing environment and contributing to improvement of corrosion resistance. Further, nickel (Ni), chromium (Cr), and vanadium (V) form a stable protective film of composite fluoride on the surface of the titanium alloy in an environment containing fluoride, and contribute to improvement of corrosion resistance. It is contemplated that excellent corrosion resistance is exerted by a multiplier effect of the individual additive elements described above.

Also, it has been found out that addition of aluminum (Al), silicon (Si), and iron (Fe) in an appropriate amount in addition to the elements described above is effective in improvement of corrosion resistance against fluoride, and that more excellent corrosion resistance is obtained by further adding osmium (Os), rhodium (Rh), iridium (Ir), and platinum (Pt) in an appropriate amount.

That is, a titanium alloy material according to an embodiment of the invention contains ruthenium (Ru): 0.005-0.10 mass palladium (Pd): 0.005-0.10 mass %, nickel (Ni): 0.01-2.0 mass %, chromium (Cr): 0.01-2.0 mass %, vanadium (V): 0.01-2.0 mass %, with the remainder including titanium (Ti) and inevitable impurities.

According to such a configuration, because the titanium alloy material contains a predetermined amount of ruthenium (Ru) and palladium (Pd), a potential of titanium is made noble, and a stable passive film mainly of titanium oxide is formed on the surface. Also, by containing a predetermined amount of nickel (Ni), chromium (Cr), and vanadium (V), surface concentration of ruthenium (Ru) and palladium (Pd) on the surface of the titanium alloy is promoted in non-oxidizing environment, formation of a stable passive film is promoted, and a stable protective film of composite fluoride is formed on the surface of the titanium alloy in an environment containing fluoride. Further, by containing a predetermined amount of Ni, a stable oxide is formed on the surface of the titanium alloy in non-oxidizing environment.

It is preferable that the titanium alloy material according to an embodiment of the invention further contains at least one member selected from the group consisting of aluminum (Al): 0.005-2.0 mass %, silicon (Si): 0.005-2.0 mass %, and iron (Fe): 0.005-2.0 mass %.

According to such a configuration, because the titanium alloy material selectively contains further a predetermined amount of aluminum (Al), silicon (Si), andiron (Fe), corrosion resistance against fluoride is further improved, and strength is also enhanced.

It is preferable that the titanium alloy material according to an embodiment of the invention further contains at least one member selected from the group consisting of osmium (Os): 0.005-0.10 mass %, rhodium (Rh): 0.005-0.10 mass %, iridium (Ir): 0.005-0.10 mass %, and platinum (Pt): 0.005-0.10 mass %.

According to such a configuration, because the titanium alloy material selectively contains further a predetermined amount of osmium (Os), rhodium (Rh), iridium (Ir), and platinum (Pt), a potential of titanium is made noble, and a stable passive film mainly of titanium oxide is formed on the surface. Thereby, corrosion resistance in non-oxidizing environment is further improved.

A structural member according to an embodiment of the invention is characterized to use the titanium alloy material described above.

According to such a configuration, because the titanium alloy material excellent in corrosion resistance in non-oxidizing environment such as sulfuric acid environment, high temperature neutral chloride environment, or high temperature neutral chloride environment containing fluoride is used, the structural member becomes excellent in corrosion resistance in non-oxidizing environment.

A container for radioactive waste according to an embodiment of the invention is characterized to use the titanium alloy material described above.

According to such a configuration, because the titanium alloy material excellent in corrosion resistance in non-oxidizing environment such as sulfuric acid environment, high temperature neutral chloride environment, or high temperature neutral chloride environment containing fluoride is used, the container for radioactive waste becomes adaptable even to a severe corrosion environment of radioactive waste.

The titanium alloy material according to an embodiment of the invention exerts excellent corrosion resistance even in non-oxidizing environment such as sulfuric acid environment, high temperature neutral chloride environment, or high temperature neutral chloride environment containing fluoride. Also, it is inexpensive and excellent in economy.

The structural member according to an embodiment of the invention is suitably used for members of an oil refinery, petrochemical plant, marine structure, building materials and the like, for example, a condenser for a thermoelectric or nuclear power plant and a heat-transfer pipe of a desalination plant and the like which are exposed to non-oxidizing environment.

Because the container for radioactive waste according to an embodiment of the invention can adapt even to severe corrosive environment by radioactive waste, it becomes a suitable container for transportation or disposal of radioactive waste.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to FIG. 1C are schematic drawings showing test pieces used in Examples.

 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, the titanium alloy material, structural member, and container for radioactive waste according to an embodiment of the invention will be described in detail.

<Titanium Alloy>

The titanium alloy material according to an embodiment of the invention contains ruthenium (Ru): 0.005-0.10 mass %, palladium (Pd): 0.005-0.10 mass %, nickel (Ni): 0.01-2.0 mass %, chromium (Cr): 0.01-2.0 mass %, and vanadium (V): 0.01-2.0 mass %, with the remainder including titanium (Ti) and inevitable impurities.

The titanium alloy material may further contain at least one member selected from the group consisting of aluminum (Al), silicon (Si), and iron (Fe) by a predetermined amount, and, in addition, may yet further contain at least one member selected from the group consisting of osmium (Os), rhodium (Rh), iridium (Ir), and platinum (Pt) by a predetermined amount.

The reasons of limiting the composition will be described below.

(Ruthenium (Ru): 0.005-0.10 mass %)

Ruthenium (Ru) is an additive element effective in making a potential of titanium noble and forming a stable passive film mainly of titanium oxide on the surface of a titanium alloy in non-oxidizing environment. In order to exert such effects, it is necessary to contain ruthenium (Ru) by 0.005 mass % or more. On the other hand, if ruthenium (Ru) content exceeds 0.10 mass %, such effects saturate, which is not preferable from viewpoint of a cost because (Ru) is an expensive element. Therefore ruthenium (Ru) content is made 0.005-0.10 mass %. Also, ruthenium (Ru) content is preferably 0.008 mass % or more, more preferably 0.010 mass % or more. Further, ruthenium (Ru) content is preferably 0.095 mass % or less, more preferably 0.090 mass % or less.

(Palladium (Pd): 0.005-0.10 mass %)

Palladium (Pd) is an additive element effective in making a potential of titanium noble and forming a stable passive film mainly of titanium oxide on the surface of a titanium alloy in non-oxidizing environment, and particularly, the effect becomes noticeable by co-existence with ruthenium (Ru). In order to exert such effects of palladium (Pd), it is necessary to contain palladium (Pd) by 0.005 mass % or more. On the other hand, if palladium (Pd) content exceeds 0.10 mass %, such effects saturate, which is not preferable from viewpoint of a cost because palladium (Pd) is an expensive element. Therefore palladium (Pd) content is made 0.005-0.10 mass %. Also, palladium (Pd) content is preferably 0.008 mass % or more, more preferably 0.010 mass % or more. Further, palladium (Pd) content is preferably 0.095 mass % or less, more preferably 0.090 mass % or less.

(Nickel (Ni): 0.01-2.0 mass %)

Nickel (Ni) is an element that promotes surface concentration of ruthenium (Ru) and palladium (Pd) in non-oxidizing environment by co-existence with chromium (Cr) and vanadium (V). Also, nickel (Ni) is an element that forms stable oxide on the surface of titanium alloy in non-oxidizing environment, and is an element that forms a protective film of stable composite fluoride on the surface of a titanium alloy in an environment containing fluoride and contributes to improvement of corrosion resistance. In order to exert such effects, it is necessary to contain nickel (Ni) by 0.01 mass % or more. However, if an amount of addition becomes excessive, weldability and hot workability deteriorate, and therefore nickel (Ni) content is made 2.0 mass % or less. Accordingly, nickel (Ni) content is made 0.01-2.0 mass %. Also, nickel (Ni) content is preferably 0.03 mass % or more, more preferably 0.05 mass % or more. Further nickel (Ni) content is preferably 1.95 mass % or less, more preferably 1.90 mass % or less.

(Chromium (Cr): 0.01-2.0 mass %)

Chromium (Cr) is an element that promotes surface concentration of ruthenium (Ru) and palladium (Pd) in non-oxidizing environment by co-existence with nickel (Ni) and vanadium (V). Also, chromium (Cr) is an element that forms a protective film of stable composite fluoride on the surface of titanium alloy in an environment containing fluoride and contributes to improvement of corrosion resistance. In order to exert such effects, it is necessary to contain chromium (Cr) by 0.01 mass % or more. However, if an amount of addition becomes excessive, weldability and hot workability deteriorate, and therefore chromium (Cr) content is made 2.0 mass % or less. Accordingly, chromium (Cr) content is made 0.01-2.0 mass %. Also, chromium (Cr) content is preferably 0.03 mass) or more, more preferably 0.05 mass % or more. Further, chromium (Cr) content is preferably 1.95 mass % or less, more preferably 1.90 mass % or less.

(Vanadium (V): 0.01-2.0 mass %)

Vanadium (V) is an element that promotes surface concentration of ruthenium (Ru) and palladium (Pd) in non-oxidizing environment by co-existence with nickel (Ni) and chromium (Cr). Also, vanadium (V) is an element that forms a protective film of stable composite fluoride on the surface of a titanium alloy in an environment containing fluoride and contributes to improvement of corrosion resistance. In order to exert such effects, it is necessary to contain vanadium (V) by 0.01 mass % or more. However, if an amount of addition becomes excessive, weldability and hot workability deteriorate, and therefore vanadium (V) content is made 2.0 mass %, or less. Accordingly, vanadium (V) content is made 0.01-2.0 mass %. Also, vanadium (V) content is preferably 0.03 mass % or more, more preferably 0.05 mass % or more. Further vanadium (V) content is preferably 1.95 mass % or less, more preferably 1.90 mass % or less.

(At least one member selected from the group consisting of aluminum (Al): 0.005-2.0 mass %, silicon (Si): 0.005-2.0 mass %, and iron (Fe): 0.005-2.0 mass %)

Aluminum (Al), silicon (Si) and iron (Fe) are not elements effective in improvement of corrosion resistance against hydrochloric acid and sulfuric acid, but are elements that become effective in improvement of corrosion resistance against fluoride and in enhancement of strength by adding a trace amount. In order to exert such effects, it is necessary to contain them by 0.005 mass % or more respectively. However if they are added excessively, corrosion resistance in an acidic environment largely deteriorates, workability also largely deteriorates, and therefore the upper limit of their content is made 2.0 mass %. Accordingly, when aluminum (Al), silicon (Si) and iron (Fe) are to be added, the content is made 0.005-2.0 mass % respectively. Also, the content of aluminum (Al), silicon (Si) and iron (Fe) is preferably 0.008 mass % or more, and more preferably 0.010 mass % or more respectively. Further, it is preferably 1.95 mass % or less, more preferably 1.90 mass % or less respectively.

(At least one member selected from the group consisting of osmium (Os): 0.005-0.10 mass %, rhodium (Rh): 0.005-0.10 mass %, iridium (Ir): 0.005-0.10 mass %, and platinum (Pt): 0.005-0.10 mass %)

Osmium (Os), rhodium (Rh), iridium (Ir), and platinum (Pt) are elements that promote formation of stable passive film by making a potential of titanium noble, and contribute to improvement of corrosion resistance. In order to exert such effects, it is necessary to contain 0.005 mass % or more respectively. However if they are added excessively, workability largely deteriorates, and therefore the upper limit of their content is made 0.10 mass %. Accordingly, when osmium (Os), rhodium (Rh), iridium (Ir), and platinum (Pt) are to be added, the content is made 0.005-0.10 mass % respectively. Also, the content of osmium (Os), rhodium (Rh), iridium (Ir), and platinum (Pt) is preferably 0.008 mass % or more, and more preferably 0.010 mass % or more respectively. Further, it is preferably 0.095 mass % or less, more preferably 0.090 mass % or less respectively.

(Remainder: titanium (Ti) and inevitable impurities)

The composition of the titanium alloy material is as described above and the remainder is titanium (Ti) and inevitable impurities. The inevitable impurities are allowable within a scope not impairing various characteristics of the titanium alloy. For example, if nitrogen (N) is up to approximately 0.03 mass %, carbon (C) is up to approximately 0.08 mass %, hydrogen (H) is up to approximately 0.02 mass %, and oxygen (O) is up to approximately 0.3 mass %, there is not anyproblem in containing these elements, and corrosion resistance improvement effect of the invention can be secured as well.

<Method for Manufacturing>

Next, an example of a method for manufacturing the titanium alloy material according to an embodiment of the invention will be described.

First, various metal and alloys are molten, and a titanium alloy ingot having the composition described above is manufactured. After the ingot obtained is forged at 950-1,050° C. heating temperature, it is hot rolled at 800-900° C. to obtain a predetermined sheet thickness. Then, after performing annealing at 700-900° C. for 10-60 minutes, the titanium alloy material of a predetermined thickness is manufactured by cold rolling.

<Structural Member>

The structural member according to an embodiment of the invention uses the titanium alloy material described above.

As described above, the titanium alloy material according to an embodiment of the invention is excellent in corrosion resistance in non-oxidizing environment such as sulfuric acid environment, high temperature neutral chloride environment, or high temperature neutral chloride environment containing fluoride, and therefore can be used as a member of an oil refinery, petrochemical plant, marine structure, building materials and the like exposed to such environment. For example, it can be used in such a usage as a condenser for a thermoelectric or nuclear power plant and a heat-transfer pipe of a desalination plant.

<Container for Radioactive Waste>

The container for radioactive waste according to an embodiment of the invention uses the titanium alloy material described above.

As described above, in a container for transportation or disposal of radioactive waste generated from nuclear power-related facilities such as nuclear fuel manufacturing facilities, nuclear power plants, and nuclear fuel reprocessing facilities, the metal surface temperature of the container becomes high by heat generation of the radioactive waste, a high concentration solution in which chloride, fluoride or the like, that is a corrosion promoting factor, is concentrated is formed, and the container is subjected to a severe corrosive environment.

Thus, by employing the titanium alloy material according to an embodiment of the invention, the container for radioactive waste becomes adaptable even to such a severe corrosive environment as described above.

EXAMPLES

Next, the titanium alloy material, structural member, and container for radioactive waste according to an embodiment of the invention will be described more specifically comparing Examples satisfying the requirement of an embodiment of the invention and comparative examples not satisfying the requirement of an embodiment of the invention.

(Manufacture of Sample)

Approximately 500 g in total of various metals and alloys of melting material is molten using a vacuum arc melting furnace, and various titanium alloy ingots were manufactured. Chemical composition is as shown in Table 1 (with the remainder being titanium (Ti) and inevitable impurities). After the ingot obtained was forged at the heating temperature of 1,000° C., it was hot rolled at 870° C. to obtain a sheet thickness of 5 mm. Then, after performing annealing at 750° C. for 20 minutes, a titanium alloy sheet material of 3 mm thickness was manufactured by cold rolling. From the titanium alloy sheet material obtained, test pieces A (TP-A in FIG. 1A) of 50 mm length×30 mm width×2 mm thickness and test pieces B (TP-B in FIG. 1B) of 30 mm length×30 mm width×2 mm thickness were cut out.

Also, in order to hang down the test piece in a corrosion test, a hole of 3 mm diameter was bored in an end of TP-A. Further, in order to test the crevice corrosion characteristic, a crevice corrosion test piece (sample) C (FIG. 1C, FIG. 1D) was manufactured by overlaying TP-A and TP-B of same material each other and fastening them by a bolt. In the crevice corrosion test piece C, a test solution intrudes into a matching face (gap) of TP-A and TP-B, salt concentration and lowering of pH occur, a corrosive condition severer than that of the outside the gap is brought about, and corrosion develops (crevice corrosion) according to the kind of the crevice corrosion test piece C. The crevice corrosion test piece C was manufactured by boring a hole of 5 mm diameter in the center of TP-A and TP-B, and by fastening them by a bolt and nut made of pure titanium. The fastening torque was set to 8.5 N·m, a thread part of the bolt made of pure titanium was covered with a silicone tube, and contact between different metals between TP-A or TP-B and the bolt/nut was prevented by interposing a washer made of polytetrafluoroethylene (PTFE) (PTFE washer). Also, all of TP-A and TP-B were polished by a wet type rotary polisher to SiC#600 on all surfaces, were subjected to water washing and acetone washing, and were tested thereafter.

(Method of Corrosion Test)

Corrosion resistance was evaluated in 3 kinds of non-oxidizing solutions of (1) sulfuric acid aqueous solution, (2) salt water, and (3) salt water containing fluoride as a corrosive environment. With respect to the corrosive environment (1), an immersion corrosion test was performed in a boiling 5% H2SO4 aqueous solution, and evaluation was made based on a weight loss due to corrosion obtained from the variation of mass prior to and after the immersion test. Immersion time was 72 hours. First, the test solution was poured into a round bottom flask with 1 L capacity, was heated by a mantle heater, and boiled. After the solution was boiled, a test piece (TP-A) was hung as a sample using a string made of PTFE and was immersed. At that time, a cooling pipe was arranged in the flask and evaporation of the solution was prevented. The liquid volume of the test solution was 1 L per one test piece (sample). For the test, 5 pieces were tested for each of the titanium alloy materials No. 1-40 shown in Table 1, and the average value of 5 pieces was calculated with respect to the weight loss due to corrosion. Also, the mass after the test was measured after the test piece A after immersion was subjected to water washing, acetone washing, and drying thereafter.

With respect to the corrosive environment (2), the crevice corrosion test piece (sample) was immersed in a boiling 20% NaCl aqueous solution, and whether crevice corrosion in the matching face of the crevice corrosion test piece C had occurred or not was investigated. First, in the same manner as above-referenced (1), the test solution was poured into a round bottom flask with 1 L capacity, was heated by a mantle heater, and was boiled. After the solution was boiled, the crevice corrosion test piece C was hung as a sample by a PTFE string and was immersed. The immersing time was 30 days. At that time, a cooling pipe was arranged in the flask and evaporation of the solution was prevented. The liquid volume of the test solution was 1 L per one test piece (sample). For the test, 5 pieces were tested for each of the titanium alloy materials Nos. 1-40 shown in Table 1, and the crevice corrosion occurrence probability (=number of the test pieces in which crevice corrosion occurred/5×100(%)) was obtained. Also, with respect to whether crevice corrosion had occurred or not, the case in which a corrosion hole of 10 μm or more depth was observed when the crevice corrosion test piece C after the test was disassembled and washed was determined as the crevice corrosion had occurred.

With respect to the corrosive environment (3), an immersion corrosion test was performed in a boiling 20% NaCl+0.01% NaF aqueous solution whose pH value had been adjusted to 4.0, and evaluation was made based on a weight loss due to corrosion obtained from the variation of mass prior to and after the immersion test. Immersion time was 30 days. First, HCl was properly added to 20% NaCl+0.01% NaF aqueous solution, and pH value of the solution was adjusted to 4.0. Then, the test solution was poured into a round bottom flask with 1 L capacity, heated by a mantle heater, and boiled. After the solution was boiled, a test piece A (TP-A) was hung as a sample using a PTFE string, and was immersed. At that time, a cooling pipe was arranged in the flask and evaporation of the solution was prevented. The liquid volume of the test solution was 1 L per one test piece (sample). For the test, 5 pieces were tested for each of the titanium alloy materials Nos. 1-40 shown in Table 1, and the average value of 5 pieces was calculated with respect to the weight loss due to corrosion. Also, the mass after the test was measured after the test piece A after immersion was subjected to water washing, acetone washing, and drying.

With respect to these corrosion tests in two kinds of non-oxidizing solutions of (1) sulfuric acid aqueous solution and (3) salt water containing fluoride, the weight loss due to corrosion of each sample was represented by a relative value when the weight loss due to corrosion of No. 35 (pure titanium) was defined as 100. Also, as an overall evaluation, when occurrence of crevice corrosion was not observed (the crevice corrosion occurrence probability was zero) in the salt water of (2), one in which both of the relative values of the weight loss due to corrosion in each acid solution of above-referenced (1) and (3) were 2 or less (the weight loss due to corrosion was less than 1/50 of that of No. 35) was defined to be very good in corrosion resistance (⊚⊚), one in which either one or more of the relative values was more than 2 and 5 or less (the weight loss due to corrosion was more than 1/50 and 1/20 or less of that of No. 35) and both of them were 5 or less was defined to be good in corrosion resistance (⊚), and one in which either one or more of the relative values was more than 5 and 10 or less (the weight loss due to corrosion was more than 1/20 and 1/10 or less of that of No. 35) and both of them were 10 or less was defined to be slightly good in corrosion resistance (∘). Further, one in which occurrence of crevice corrosion was observed (the crevice corrosion occurrence probability was 20 or more) and either one or more of the relative value of the weight loss due to corrosion in each acid solution of above-referenced (1) and (3) was more than 10 (the weight loss due to corrosion was more than 1/10 of that of No. 35) and less than 100 was defined to be bad in corrosion resistance (Δ). The weight loss due to corrosion (100) of No. 35 (pure titanium) was defined to be very bad (x).

The chemical composition of the sample is shown in Table 1, and the result of the corrosion test is shown in Table 2. Also, in Table 1, those not satisfying the scope of an embodiment of the prevention was shown by adding an underline to the value, and those not containing the component is shown by “-”.

TABLE 1 Chemical composition (mass %), (Remainder: Ti and inevitable impurities) No. Ru Pd Ni Cr V Al Si Fe Os Rh Ir Pt 1 0.050 0.020 0.012 0.33 0.12 — — — — — — — 2 0.050 0.021 0.49 0.011 0.13 — — — — — — — 3 0.050 0.020 0.50 0.54 0.012 — — — — — — — 4 0.005 0.020 0.50 0.15 0.21 0.12 — — — — — — 5 0.025 0.020 0.40 0.15 0.15 — 0.005 — — — — — 6 0.024 0.020 0.39 0.14 0.15 — — 0.053 — — — — 7 0.024 0.020 0.40 0.15 0.21 0.017 0.016 — — — — — 8 0.024 0.020 0.39 0.14 0.15 0.005 — 0.055 — — — — 9 0.024 0.020 1.02 2.0 0.05 — 0.015 0.022 — — — — 10 0.024 0.020 1.00 0.05 2.0 0.019 0.015 0.022 — — — — 11 0.10 0.020 0.09 0.54 0.12 — — — 0.029 — — — 12 0.050 0.10 0.10 0.54 0.12 — — — — 0.030 — — 13 0.050 0.020 0.10 0.54 0.12 — — — — — 0.030 — 14 0.050 0.020 0.09 0.54 0.12 — — — — — — 0.030 15 0.050 0.020 0.20 0.55 0.09 — — — 0.019 0.005 — — 16 0.050 0.020 0.20 0.55 0.10 — — — 0.019 — 0.005 — 17 0.050 0.020 0.20 0.55 0.10 — — — 0.019 — — 0.005 18 0.050 0.020 2.0 0.55 0.10 — — — — 0.050 0.049 — 19 0.050 0.020 0.11 0.55 0.10 — — — — 0.049 — 0.049 20 0.050 0.020 0.11 0.54 1.01 — — — 0.005 0.015 0.015 — 21 0.050 0.020 0.11 0.55 1.01 — — — 0.015 0.015 — 0.015 22 0.050 0.020 0.11 0.54 1.01 — — — 0.015 — 0.015 0.015 23 0.050 0.005 0.12 0.55 1.01 — — — — 0.015 0.014 0.015 24 0.050 0.020 0.11 0.55 1.01 — — — 0.010 0.009 0.009 0.009 25 0.015 0.012 0.055 0.050 0.19 — — 0.022 0.10 — — — 26 0.015 0.012 0.055 0.050 0.19 0.049 — 0.022 — 0.10 — — 27 0.014 0.012 0.055 0.050 0.19 — 0.091 0.022 — — 0.10 — 28 0.015 0.012 0.055 0.050 0.19 0.016 0.015 0.022 — — — 0.10 29 0.050 0.017 0.45 0.090 0.08 — — 0.0051 0.010 — 0.012 — 30 0.050 0.017 0.45 0.090 0.08 — — 2.0 — 0.011 0.010 — 31 0.025 0.051 0.85 1.01 0.89 2.0 0.009 — — 0.010 — 0.010 32 0.024 0.051 0.85 1.01 0.90 0.010 2.0 — 0.010 — 0.010 0.010 33 0.025 0.050 0.85 1.01 0.89 0.005 — — 0.010 0.010 0.010 — 34 0.025 0.051 0.85 1.01 0.89 0.050 0.077 0.099 0.008 0.008 0.008 0.008 35 — — — — — — — — — — — — 36 0.004 0.019 0.50 0.18 0.20 — — — — — — — 37 0.049 0.003 0.50 0.20 0.20 — — — — — — — 38 0.050 0.018 0.004 0.15 0.25 — — — — — — — 39 0.051 0.020 0.51 0.004 0.23 — — — — — — — 40 0.050 0.020 0.50 0.19 0.004 — — — — — — —

TABLE 2 (3) Boiling 20% NaCl + 0.01% (1) Boiling 5% H2SO4 (2) Boiling 20% NaCl NaF Weight loss due to corrosion Crevice corrosion occurrence Weight loss due to corrosion Overall No. (relative value) probability (%) (relative value) evaluation 1 4.2 0 9.2 ◯ 2 4.3 0 9.3 ◯ 3 4.1 0 9.5 ◯ 4 5.0 0 6.8 ◯ 5 4.1 0 5.5 ◯ 6 7.5 0 5.4 ◯ 7 4.9 0 5.9 ◯ 8 7.0 0 5.8 ◯ 9 6.9 0 5.1 ◯ 10 6.5 0 5.2 ◯ 11 2.0 0 3.9 ⊚ 12 2.0 0 3.8 ⊚ 13 2.0 0 4.3 ⊚ 14 1.9 0 4.2 ⊚ 15 1.8 0 4.0 ⊚ 16 1.9 0 3.9 ⊚ 17 1.8 0 4.0 ⊚ 18 1.8 0 3.8 ⊚ 19 1.8 0 3.9 ⊚ 20 1.7 0 4.0 ⊚ 21 1.7 0 4.0 ⊚ 22 1.9 0 4.1 ⊚ 23 2.9 0 4.0 ⊚ 24 1.6 0 3.7 ⊚ 25 1.2 0 1.1 ⊚⊚ 26 1.1 0 1.1 ⊚⊚ 27 1.2 0 1.0 ⊚⊚ 28 1.1 0 1.0 ⊚⊚ 29 0.9 0 1.2 ⊚⊚ 30 1.1 0 1.0 ⊚⊚ 31 0.82 0 0.92 ⊚⊚ 32 0.80 0 0.91 ⊚⊚ 33 0.78 0 0.87 ⊚⊚ 34 0.85 0 0.85 ⊚⊚ 35 100 100 100 X 36 30 60 71 Δ 37 35 80 82 Δ 38 20 40 65 Δ 39 18 40 64 Δ 40 11 20 51 Δ

As shown in Tables 1 and 2, because the titanium alloy materials Nos. 1-34 satisfied the scope of an embodiment of the invention, occurrence of crevice corrosion in salt water was not observed and the weight loss due to corrosion in sulfuric acid aqueous solution and salt water containing fluoride was 1/10 or less of that of pure titanium of No. 35 in all of them, and they resulted to be excellent in corrosion resistance. Corrosion resistance of them is exerted by composite addition of ruthenium (Ru), palladium (Pd), nickel (Ni), chromium (Cr), and vanadium (V).

On the other hand, because Nos. 35-40 did not satisfy the scope of an embodiment of the invention, the results were as follows.

Because No. 35 was of pure titanium, it was inferior in corrosion resistance.

Although the titanium alloy materials of Nos. 36-40 improved in corrosion resistance when compared to pure titanium of No. 35, occurrence of crevice corrosion in salt water was observed, and reduction in the weight loss due to corrosion was not sufficient.

Because each of ruthenium (Ru) and palladium (Pd) content of No. 36 and No. 37 was less than the lower limit value, a potential of titanium was not made so noble, formation of a stable passive film was not sufficient, and the both were inferior in corrosion resistance.

Because each of nickel (Ni), chromium (Cr) and vanadium (V) content of Nos. 38-40 was less than the lower limit value, surface concentration of ruthenium (Ru) and palladium (Pd) was not promoted, a potential of titanium was not made so noble, formation of a stable passive film was not sufficient, and they were inferior in corrosion resistance. Also, in the salt water containing fluoride, formation of a protective nickel (Ni), chromium (Cr) and vanadium (V) composite fluoride film was not sufficient, and they were inferior in corrosion resistance. Further, because nickel (Ni) content of No. 38 was less than the lower limit value, a stable oxide was not formed also.

As described above, all of the titanium alloy material according to an embodiment of the invention have excellent corrosion resistance in non-oxidizing environment and are suitable to a structural member. Particularly, because they are superior to conventional titanium alloy materials added with a trace amount of platinum group (Nos. 36-40) in corrosion resistance in salt water containing fluoride, they are suitable to a container for radioactive waste used for transportation or disposal of radioactive waste disposed to a high concentration solution environment in which chloride, fluoride and the like are concentrated.

Although the titanium alloy material, structural member, and container for radioactive waste according to an embodiment of the invention were described above in detail referring to embodiments and Examples, the object of the invention is not limited to the contents described above. Also, it is needless to say that the contents of the invention can be widely modified, altered, or the like based on the above description.

Claims

1. A titanium alloy material comprising 0.005-0.10 mass % of ruthenium (Ru), 0.005-0.10 mass % of palladium (Pd), 0.01-2.0 mass % of nickel (Ni), 0.01-2.0 mass % of chromium (Cr), 0.01-2.0 mass % of vanadium (V), with the remainder including titanium (Ti) and inevitable impurities.

2. The titanium alloy material according to claim 1 further comprising at least one member selected from the group consisting of 0.005-2.0 mass % of aluminum (Al), 0.005-2.0 mass % of silicon (Si), and 0.005-2.0 mass % of iron (Fe).

3. The titanium alloy material according to claim 1 further comprising at least one member selected from the group consisting of 0.005-0.10 mass % of osmium (Os), 0.005-0.10 mass % of rhodium (Rh), 0.005-0.10 mass % of iridium (Ir), and 0.005-0.10 mass % of platinum (Pt).

4. The titanium alloy material according to claim 2 further comprising at least one member selected from the group consisting of 0.005-0.10 mass % of osmium (Os), 0.005-0.10 mass % of rhodium (Rh), 0.005-0.10 mass % of iridium (Ir), and 0.005-0.10 mass % of platinum (Pt).

5. A structural member using the titanium alloy material of any one of claims 1 to 4.

6. A container for radioactive waste using the titanium alloy material of any one of claims 1 to 4.

Patent History
Publication number: 20100322817
Type: Application
Filed: Apr 30, 2010
Publication Date: Dec 23, 2010
Applicant: Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) (Kobe-shi)
Inventors: Shinji SAKASHITA (Kobe-shi), Kyosuke FUJISAWA (Kobe-shi)
Application Number: 12/771,147
Classifications
Current U.S. Class: Vanadium Containing (420/420); Chromium Or Molybdenum Containing (420/421)
International Classification: C22C 14/00 (20060101);