JPWO2014115845A1 - Titanium alloy with excellent corrosion resistance in environments containing bromine ions - Google Patents

Abstract

Provided is a low-cost titanium alloy having corrosion resistance equal to or higher than that of the prior art, excellent corrosion resistance to an environment containing bromine ions, and low cost. Titanium alloy used in an environment containing bromine ions, in mass%, platinum group element: 0.01 to 0.10%, rare earth element: less than 0.001 to 0.02%, O: 0 to 0 A titanium alloy containing less than 1% by mass with the balance being Ti and impurities. Instead of a part of Ti, one or more selected from the group consisting of Ni, Co, Mo, V, Cr and W may be contained. It is desirable to contain platinum group elements: 0.01 to 0.05% by mass%. Moreover, it is desirable to contain rare earth elements: 0.001 to less than 0.02% by mass%.

Description

The present invention relates to a titanium alloy, and more particularly, to a titanium alloy having excellent corrosion resistance (such as crevice corrosion resistance and acid resistance in an environment containing bromine ions) and economy.

Titanium is actively utilized in the field of aircraft, etc., taking advantage of its light and strong characteristics. Titanium has excellent corrosion resistance, and therefore has been widely used for chemical industrial equipment materials, thermal / nuclear power generation equipment materials, and seawater desalination equipment materials. .

However, the environment in which titanium can exhibit high corrosion resistance is limited to oxidizing acid (nitric acid) environments and neutral chloride environments such as seawater. Crevice corrosion resistance under high-temperature chloride environments, hydrochloric acid, etc. The corrosion resistance in the non-oxidizing acid solution (hereinafter, unless otherwise specified, these corrosion resistances are collectively referred to simply as “corrosion resistance”) is not sufficient. In order to solve this problem, titanium alloys containing platinum group elements in titanium (hereinafter referred to as “platinum group element-containing titanium alloys”) have been proposed, standardized, and used in various applications. .

Specifically, in the field of soda industry, the anode electrode used for electrolysis is used in high concentration brine containing 20 to 30% hydrochloric acid at a high temperature of 100 ° C. or higher. In the anode electrode, a platinum group element-containing titanium alloy is used at a site where crevice corrosion is a problem.

In the field of Ni refining industry, the reaction vessel is exposed to a high concentration sulfuric acid solution at a high temperature exceeding 100 ° C. containing slurry. As a material for the reaction vessel, a platinum group element-containing titanium alloy is used.

In the field of heat exchangers, heat transfer tubes used in the salt production field are exposed to high temperature and high concentration salt water, and heat transfer tubes used for heat exchange of incinerator exhaust gas are exposed to exhaust gas containing chlorine, NO _x , and SO _x. It is. A platinum group element-containing titanium alloy is used for these heat transfer tubes.

In the petrochemical industry, a reaction vessel of a desulfurization apparatus used for petroleum refining is exposed to high-temperature hydrogen sulfide. In such a reaction vessel or the like, a platinum group element-containing titanium alloy is used.

In addition, it has been studied to apply a platinum group element-containing titanium alloy to a fuel cell separator material by taking advantage of its excellent corrosion resistance.

Gr., Which is a Ti-0.15Pd alloy. No. 7 (“Gr.” (Grade) is based on the ASTM standard. The same applies hereinafter) is a titanium alloy developed so that corrosion resistance can be obtained in the above-described applications. Pd contained in this titanium alloy can reduce the hydrogen overvoltage and maintain the natural potential in the passive region. That is, Pd eluted from this alloy due to corrosion is re-deposited and deposited on the surface of the alloy, thereby reducing the hydrogen overvoltage of this alloy and maintaining the natural potential in the passive region. Shows corrosion resistance.

However, Gr. 7 is very expensive (for example, according to the Nihon Keizai Shimbun morning edition dated December 13, 2012, 1905 yen / g), its field of use was limited.

In order to solve this problem, as disclosed in Patent Document 1 below, the Pd content is 0.03 to 0.1% by mass, Gr. A titanium alloy (Gr. 17) having excellent crevice corrosion resistance while being reduced as compared with 7 is proposed and put into practical use.

Patent Document 2 listed below contains a total of 0.01 to 0.12% by mass of one or more platinum group elements as a titanium alloy that can be manufactured at low cost while suppressing a decrease in corrosion resistance, and contains Al, Cr, Zr. , Nb, Si, Sn, and Mn, a titanium alloy containing 5% by mass or less in total is disclosed. In the use at the time of development of the titanium alloy, sufficient corrosion resistance is obtained when Pd is in the range of 0.01 to 0.12% by mass. However, for applications that require further improvement in properties in recent years, corrosion resistance has become insufficient, particularly when the Pd content is less than 0.05% by mass. In addition, there is an increasing demand for further cost reduction in applications at the time of development.

However, according to Non-Patent Document 1 below, in the Ti—Pd alloy, by adding Co, Ni or V as the third element, the crevice corrosion resistance is improved, but sufficient crevice corrosion resistance is obtained. From this point of view, the Pd content is required to be 0.05% by mass or more.

For cost reduction, materials that actively utilize the least expensive Ru among the platinum group elements have been developed. Patent Document 3 below discloses a titanium alloy to which 0.005 to 0.2 mass% of Ru is added. As shown in Examples in this document, in order to obtain sufficient crevice corrosion resistance, the amount of Ru added to the titanium alloy has to be 0.05% by mass or more.

Patent Document 4 listed below discloses a system material in which Ru and Ni are added in addition for the purpose of further improving corrosion resistance. This material has not only crevice corrosion resistance but also excellent corrosion resistance in an environment containing a non-oxidizing acid such as sulfuric acid or hydrochloric acid. Ti-0.06Ru-0.5Ni, which is an alloy within the composition range shown in Patent Document 4 below, is Gr. It has been standardized as 13 and put into practical use as a corrosion-resistant titanium alloy. However, by adding Ni, a Ti ₂ Ni compound is precipitated in the titanium alloy. Due to this compound precipitation, the titanium alloy has a workability such as elongation of Gr. There was a problem that it was inferior to 17.

In addition to these problems, when an inexpensive raw material (saline solution) is used when the Ti—Pd alloy is applied to an anode application for electrolysis, bromine is contained in the raw material. ), Crevice corrosion, which was thought to be impossible when using normal saline, may occur. Further, for example, corrosion caused by bromine (bromine ions) may occur in a chemical plant. For this reason, the titanium alloy which shows the excellent corrosion resistance also in the environment containing a bromine ion was calculated | required.

Here, Patent Document 5 and Patent Document 6 disclose materials in which a platinum group, a rare earth element, and a transition element are added in combination. However, these are all titanium alloys for ultra-high vacuum containers or ultra-high vacuum containers. In these Patent Documents 5 and 6, the reason why platinum group and rare earth elements are added is that, in an ultra-high vacuum, the effect of suppressing the phenomenon in which gas components dissolved in the material are diffused and released to the vacuum side. To get. The platinum group has an action of trapping hydrogen and the rare earth element trapping oxygen in the titanium alloy. In these Patent Documents 5 and 6, transition elements of Co, Fe, Cr, Ni, Mn, and Cu are essential elements in addition to the platinum group and rare earth elements. The transition element is said to have a role of fixing atomic hydrogen adsorbed on the vacuum vessel surface by the platinum group. However, none of these Patent Documents 5 and 6 considers corrosion resistance, and does not mention corrosion resistance in an environment containing bromine ions.

Japanese Patent Publication No. 4-57735 International Publication No. 2007/077645 Japanese Patent Publication No.62-56219 Japanese Examined Patent Publication No. 62-20269 JP-A-6-65661 JP-A-6-64600

Hideaki Yuki, 1 other, “Low Alloy Titanium SMI-ACE with Excellent Crevice Corrosion Resistance”, Society of Materials, Corrosion and Corrosion Prevention Committee, September 12, 2001 Chihiro Taki, “Characteristics and Use Cases of Corrosion Resistant Titanium Alloy TICOREX”, Nippon Steel Technical Report, 2001, No. 375, pp. 73-77 Tatsuhiro Okada, “Pitting corrosion potential of titanium in bromide solution”, DENKI KAGAKU, 1981, 49, No. 9, pp. 584-588

This invention is made | formed in view of said problem, and it aims at obtaining the titanium alloy excellent in corrosion resistance, especially the corrosion resistance with respect to the environment containing a bromine ion.

Furthermore, a titanium alloy cheaper than the prior art was realized by not containing expensive Pd among platinum group elements but containing Ru which is cheaper than Pd.

In order to achieve the above-mentioned object, the present inventors have clarified (i) a mechanism in which corrosion resistance is manifested in a Ti—Pd alloy, and studied to contain an element that promotes a surface state preferable for improving corrosion resistance. Further, in the case of a Ti—Ru alloy, investigations were made on improving the corrosion resistance. (ii) In addition, the present inventors have studied to obtain corrosion resistance equivalent to or better than that of the conventional platinum group element with a low content of platinum group elements and excellent corrosion resistance in an environment where bromine ions are present.

FIG. 1 is a schematic diagram for explaining a mechanism of corrosion resistance development of a Ti—Pd alloy and a Ti—Pd—Co alloy. The surfaces of Ti—Pd alloy and Ti—Pd—Co alloy are active in the initial state before being immersed in the solution. When immersed in an acid solution such as boiling hydrochloric acid, Ti and Pd on the surface, or Ti, Pd and Co are dissolved, and dissolved Pd, or Pd and Co are precipitated on the surface and concentrated. Thereby, the hydrogen overvoltage of the titanium alloy as a whole is lowered. For this reason, this titanium alloy is maintained at a passive region potential and exhibits excellent corrosion resistance.

The present inventors have investigated the Ti—Ru alloy and confirmed that the corrosion resistance of the Ti—Ru alloy is secured by the same mechanism as that of Ti—Pd. However, when Pd and Ru of the same addition amount are compared under the same other conditions, the effect of improving the corrosion resistance is greater with Pd. In order to obtain the same corrosion resistance, it became clear that more Ru needs to be added.

In the above-mentioned Patent Document 4 and Non-Patent Document 2, Ru and Ni are added in combination, and Ti ₂ Ni _1-x Ru _x (a compound in which a part of Ni in Ti ₂ Ni is substituted with Ru in a titanium base material) It is disclosed that high corrosion resistance can be obtained without adding a lot of Ru. However, a titanium alloy added with a large amount of Ni has a problem that workability such as elongation is inferior.

The inventors of the present invention have prepared an alloy base material that is generated at an early stage after the immersion in the solution so that Ru can be rapidly and uniformly deposited on the surface and concentrated after the Ti—Ru alloy is immersed in the acid solution. We searched for a new additive element that promotes dissolution of. By including such a new additive element in the Ti—Ru alloy, if the alloy base material dissolves early in the active state after being immersed in the acid solution, the Ru in the solution near the surface of the alloy It is considered that a sufficient amount of Ru precipitates and concentrates on the surface of the alloy immediately after increasing the ion concentration to bring the alloy to the passive region potential. Hereinafter, precipitation of such an amount of Ru on the alloy surface is referred to as “Ru precipitation concentration”. Even if the Ru content of the alloy is low, if Ru precipitation enrichment occurs, the hydrogen overvoltage of the Ti—Ru alloy decreases rapidly, and the Ti—Ru alloy becomes more noble and stable (passive region). Potential).

In the case of Ti-Ru alloy having a low Ru content, if such a new additive element is contained, if the alloy base material is rapidly dissolved in the initial active state, such an additive element is not contained. As compared with the above, the Ru ion concentration and Ti ion concentration near the surface are increased, and Ru precipitation concentration occurs. Therefore, it is considered that the hydrogen overvoltage of the alloy quickly decreases and can be maintained at the passive region potential.

On the other hand, in a Ti-Ru alloy having a high Ru content and containing this new additive element, if damage such as wrinkles occurs on the surface of the alloy in the use environment, It is considered that the Ru precipitation concentration on the surface proceeds more rapidly than in the case of the conventional titanium alloy, the hydrogen overvoltage of the alloy reaches the passive region, and the damage is repaired. Therefore, the effect that corrosion starting from damage hardly progresses can be expected.

As shown in Non-Patent Document 3, pitting corrosion and crevice corrosion occur in pure titanium under an environment containing bromine. Crevice corrosion has been considered not to occur in Ti—Pd titanium alloys, but may occur in chloride environments containing bromine ions. As a result of various studies on this problem, the present inventors have found that the resistance to corrosion caused by bromine is improved by concentrating Ru on the surface.

Based on the above inference and knowledge, the present inventors have found that an element that promotes dissolution of the alloy base material that occurs at an early stage after the alloy is immersed in the solution, that is, the Ru precipitation concentration on the surface of the Ti—Ru alloy. An experiment was conducted to search for an element that promotes crystallization (the above-mentioned “new additive element”).

As a result, the present inventors have found that the rare earth element corresponds to such an element, and further selected from the group consisting of Ni, Co, Mo, Cr, V and W together with Ru and the rare earth element 1. It has been found that the resistance to corrosion caused by bromine is further improved by a synergistic effect when more than seeds are contained. In addition, although Ru was demonstrated, it is thought that the resistance with respect to the corrosion resulting from a bromine improves similarly about other platinum group elements, such as Pd.

The rare earth element itself does not have the effect of improving the corrosion resistance of the alloy. In this respect, the rare earth element is different in action from the additive elements disclosed in Patent Documents 2 to 4 and Non-Patent Document 1.

  Further, the uses of the alloys of Patent Documents 5 and 6 and the action of elements are different from those of the present invention. That is, the action of rare earth elements in both inventions of Patent Documents 5 and 6 will be described in a comparative form (content is% by weight).

  Patent Documents 5 and 6: Titanium alloys have large oxygen solid solubility. When used in high vacuum applications, rare earth elements are added to fix oxygen as an oxide for the purpose of suppressing solute oxygen from diffusing through the alloy and being released in a gaseous state to the vacuum atmosphere. In order to obtain this effect, 0.02% is the lower limit of the rare earth element. In addition, if added over 0.5%, the ductility is lowered due to the precipitated oxide. Therefore, the upper limit of rare earth elements is set to 0.5%.

  The present invention; when a titanium alloy containing a platinum group element is immersed in an aqueous chloride solution environment, dissolution occurs in the active state region, and the platinum group element precipitates and concentrates on the surface, so that the entire alloy has a passive region potential. Transition to (nominal potential). Rare earth elements have the effect of shortening the potential noble time and increasing the surface concentration of platinum group elements. In order to obtain this effect, it is desirable that the rare earth element is in the solid solution range of the titanium alloy. The lower limit for obtaining the effect is 0.001%, and the upper limit is 0.1%. This is because if it exceeds 0.1%, a compound of titanium and rare earth is generated, and the corrosion resistance may be deteriorated.

  The role of rare earth elements in Patent Documents 5 and 6 is to generate an oxide by reacting with oxygen dissolved in a titanium alloy. On the other hand, in the present invention, the action is in promoting the enrichment of platinum group elements on the surface of the titanium alloy in a wet corrosion environment, and the action is completely different. Further, in the present invention, a desirable rare earth element component is in a solid solution range, and has a rare earth content that is small compared to Patent Documents 5 and 6.

The present invention has been completed based on this finding, and the gist of the following (1) to (7) titanium alloys.

(1) A titanium alloy used in an environment containing bromine ions, and in mass%, platinum group element: 0.01 to 0.10%, rare earth element: less than 0.001 to 0.02%, O: A titanium alloy containing 0 to less than 0.1% by mass with the balance being Ti and impurities.

(2) Instead of a part of Ti, containing one or more selected from the group consisting of Ni, Co, Mo, V, Cr and W, the Ni content is 1.0 mass% or less, The Co content is 1.0 mass% or less, the Mo content is 0.5 mass% or less, the V content is 0.5 mass% or less, and the Cr content is 0.5 mass% or less. The titanium alloy according to (1), wherein the titanium alloy content is not more than mass% and the W content is not more than 0.5 mass%.

(3)
The titanium alloy according to (1) or (2), which contains, in mass%, a platinum group element: 0.01 to 0.05%.

(4)
The titanium alloy according to any one of (1) to (3), wherein the platinum group element is Ru.

(5) The titanium alloy according to any one of (1) to (4), wherein the rare earth element is Y.

(6) The titanium alloy according to any one of (1) to (5), wherein the O content is less than 0.05% by mass.

(7)
Titanium alloy of any one of (1)-(6) used for a chemical plant apparatus.

The titanium alloy of the present invention has excellent corrosion resistance, particularly corrosion resistance in an environment containing bromine ions. If Ru, which is an inexpensive platinum group element, is used, the raw material cost of the titanium alloy is reduced. When the platinum group element content is high (for example, higher than 0.05% by mass), when damage occurs to remove the passive film due to surface flaws, etc., corrosion starts from this damage. It becomes difficult.

When one or more selected from the group consisting of Ni, Co, Mo, Cr, V and W is contained instead of a part of Ti, resistance to a high-concentration chloride environment containing bromine is obtained. It is done.

When the O content is less than 0.05% by mass, good workability is obtained.

Among rare earth elements, Y is inexpensive. When the rare earth element is Y, the raw material cost is reduced.

It is a schematic diagram for demonstrating the corrosion-resistant expression mechanism of a Ti-Pd (-Co) alloy. It is a schematic diagram of the test piece for a crevice corrosion test, (a) is a top view, (b) is a side view. It is a schematic diagram which shows the state of the test piece at the time of using for a crevice corrosion test (ASTM G78). It is a graph which shows the relationship between Y content and corrosion rate of Ti alloy containing Pd0.02% in Example 2 (96-hour average). It is a graph which shows the change of the surface Pd density | concentration after the boiling hydrochloric acid test of Ti alloy containing Pd0.02% in Example 2. FIG.

As described above, the titanium alloy of the present invention is in mass%, platinum group element: 0.01 to 0.10%, rare earth element: less than 0.001 to 0.02%, O: 0 to 0.1 mass. %, With the balance being Ti and impurities. Hereinafter, the present invention will be described in detail.

1. Platinum group element The platinum group element has an effect of reducing the hydrogen overvoltage of the titanium alloy and maintaining the natural potential in the passive region, and is an essential component for the titanium alloy having corrosion resistance. The titanium alloy of the present invention contains, for example, Ru among these platinum group elements. Ru is a preferable element from the viewpoint of ensuring low cost and economy as compared with other platinum group elements. At the market price in January 2012, Ru is about 1/6 of Pd.

Although the mechanism is not clear, according to the results of the study by the present inventors, the titanium alloy is added with a platinum group element and a rare earth element in a complex manner. The effect which suppresses is acquired. In this invention, the content rate of a platinum group element shall be 0.01-0.10 mass%. When the content of the platinum group element is less than 0.01% by mass, the corrosion resistance of the titanium alloy becomes insufficient, and corrosion may occur in a high concentration chloride aqueous solution at a high temperature. On the other hand, even if the content of the platinum group element is higher than 0.10% by mass, improvement in corrosion resistance cannot be expected, raw material costs increase, and workability is inferior.

Considering the balance between workability and corrosion resistance, the content of platinum group elements having β-stabilizing action such as Ru is preferably set to 0.01 to 0.05 mass%, for example. This is because the titanium alloy of the present invention has the same corrosion resistance as that of a conventional titanium alloy having a platinum group element content higher than 0.05% by mass even in this range of platinum group element content. However, in the case where the titanium alloy is damaged so that the passive film is removed by soot or the like, the higher the Ru content of the titanium alloy, the more fresh it is caused by soot or the like, as described above for the Ti-Ru alloy. Ru precipitation concentration on the surface proceeds promptly. Therefore, the higher the Ru content, the faster the potential at the site where wrinkles occur and the surface is repaired (restoration of the passive film), so that corrosion starting from the damage occurs. Hateful. When the Ru content is higher than 0.05% by mass, the titanium alloy of the present invention is suitable for applications in severe usage environments where the passive film may be damaged.

2. Rare earth elements 2-1. Reasons for Inclusion of Rare Earth Elements The present inventors have examined the inclusion of trace amounts of various elements that are easily dissolved in a high-concentration chloride aqueous solution environment at a high temperature in a Ti-0.04 mass% Ru alloy. A titanium alloy containing such an element was immersed in an aqueous chloride solution and dissolved in the active state region. And it was investigated whether the effect which makes the whole alloy transfer to the electric potential of a passive region by promoting the precipitation density | concentration of Ru on the surface of this titanium alloy was investigated. As a result, the element in which this effect was recognized was a rare earth element.

As a result of further investigation, the Ru content in the Ru-containing titanium alloy is not limited to 0.04% by mass, but in the range of 0.01 to 0.05% by mass, and more than 0.05% by mass. It was found that the same effect can be obtained even in the case of high. That is, by adding a rare earth element to a titanium alloy having a Ru content in the range of 0.01 to 0.10% by mass, the titanium alloy can be quickly brought into contact with Ti and Ru immediately after being exposed to a corrosive environment. It was found that the Ru ion concentration in the solution near the surface of the titanium alloy can be rapidly increased (Ru precipitation concentration occurs). The Ru-containing titanium alloy containing rare earth elements is easier to obtain the efficiency of precipitating Ru on the surface than the Ru-containing titanium alloy not containing rare earth elements, and the dissolution amount (corrosion amount) of the entire titanium alloy is small. Also, Ru can be precipitated efficiently and is excellent in corrosion resistance. In addition, although Ru was demonstrated, it is thought that the resistance with respect to the corrosion resulting from a bromine improves similarly about other platinum group elements, such as Pd.

The rare earth elements include Sc, Y, light rare earth elements (La to Eu), and heavy rare earth elements (Gd to Lu). As a result of the study by the present inventors, the above-mentioned effect was recognized when any rare earth element was used. Further, it is not necessary to contain only one kind of element as a rare earth element, such as a mixed rare earth element (Misch metal, hereinafter also referred to as “Mm”) or didymium alloy (alloy consisting of Nd and Pr) before separation and purification. Even when a rare earth element mixture or compound was used, the above-described effects were observed.

Considering the above, it is economical to use La, Ce, Nd, Pr, Sm, Mm, didymium alloy, and Y (particularly Y) which are easily available and relatively inexpensive among rare earth elements. preferable. Mm and didymium alloys can be used in the present invention in any rare earth element composition ratio as long as they are commercially available.

2-2. Rare earth element content The range of the rare earth element content in the titanium alloy of the present invention is 0.001 to less than 0.02 mass%. If the content of the rare earth element is 0.001% by mass or more, in the active state region of the Ti-platinum group element alloy, Ti, the platinum group element, and the rare earth element are simultaneously dissolved in the chloride aqueous solution, The effect of promoting the precipitation of platinum group elements on the alloy surface is sufficiently obtained.

The upper limit of the rare earth element content is less than 0.02% by mass because not only the effect is saturated even if the rare earth element is contained more than this content, but the compound that does not form when the rare earth element is not contained is Ti. This is because it may be formed in the alloy. This compound is preferentially dissolved in an aqueous chloride solution to cause pit-like corrosion in the Ti-platinum group element alloy. Therefore, the Ti-platinum group element alloy produced by this compound is inferior in corrosion resistance as compared with the case where no rare earth element is contained.

The rare earth element content in the Ti-platinum group element alloy is preferably below the solid solubility limit of α-Ti shown in the phase diagram or the like. For example, the solid solubility limit of Y in α-Ti is 0.02% by mass (0.01 at%). Therefore, when Y is contained, the Y content is preferably less than 0.02% by mass. Moreover, according to the said nonpatent literature 4, the solid solubility limit in the alpha-Ti of La is as very large as 2.84 mass% (1 at%). However, even when La is contained, the content of La is set to less than 0.02% by mass from the viewpoint of ensuring economic efficiency.

3. O (oxygen) The titanium alloy of the present invention contains less than 0.1% by mass of O. The reason why the O content is less than 0.1% by mass is to ensure good workability in addition to corrosion resistance. Ti has a large oxygen solid solubility, and Ti (JIS type 2 to 4 type titanium) having a high solid solution oxygen concentration is intentionally used for applications requiring high strength. However, the solid solution of oxygen is effective for increasing the strength, but on the other hand, the workability may be deteriorated. For this reason, in consideration of workability in addition to corrosion resistance and economy, the upper limit of the O content is set to 0.1% by mass. When applied to applications that do not require high strength, or applications where workability is important, the O content is preferably less than 0.05% by mass.

4). Ni, Co, Mo, V, Cr, and W In the titanium alloy of the present invention, one or more of Ni, Co, Mo, V, Cr, and W may be contained instead of part of Ti. In this case, combined with the effects of the platinum group element and the rare earth element, the corrosion resistance of the titanium alloy in an environment containing bromine ions can be improved.

When these one or more elements are contained, the content is Ni: 1.0 mass% or less, Co: 1.0 mass% or less, Mo: 0.5 mass% or less, V: 0.5 mass% Hereinafter, Cr: 0.5 mass% or less, W: 0.5 mass% or less.

5. Impurity elements As impurity elements in the titanium alloy, Fe, O, C, H, and N mixed from raw materials, melting electrodes, and the environment, and Al, Zr, Nb, Si, Sn mixed when scrap is used as a raw material, Mn and Cu are mentioned. There is no problem even if these impurity elements are mixed in as long as they do not significantly impair the effects of the present invention. Specifically, the amount that does not significantly inhibit the effect of the present invention is Fe: 0.3 mass% or less, O: less than 0.1 mass%, C: 0.18 mass% or less, H: 0.015 mass %: N: 0.03 mass% or less, Al: 0.3 mass% or less, Zr: 0.2 mass% or less, Nb: 0.2 mass% or less, Si: 0.02 mass% or less, Sn: 0.2% by mass or less, Mn: 0.01% by mass or less, Cu: 0.1% by mass or less, and the total of these elements is 0.6% by mass or less.

In order to confirm the crevice corrosion resistance and workability (bendability and elongation) of the titanium alloy of the present invention, the following tests were conducted and the results were evaluated.

1. Test method 1-1. Sample Table 1 shows the sample used in the test and its composition (analytical values for elements other than Ti, where Ti is the balance (bal.)).

As samples used for the test, comparative materials (sample numbers 1 to 4), which are conventional materials, examples of the present invention (sample numbers 5 to 8 corresponding to claim 1, and sample numbers 12 to 18 corresponding to claim 2) Although not a conventional material, a titanium alloy of an example outside the scope of the present invention (hereinafter simply referred to as “example outside the scope of the present invention”; sample numbers 9 to 12) was prepared as a sample of the plate material. Comparative materials 1 to 3 were obtained in the city, and samples other than these (including comparative material 4) were produced in a laboratory. The comparative material 4 employs a Ti—Ru alloy composition disclosed in Patent Document 3 “excellent in crevice corrosion resistance and bending workability”.

1-1-1. Composition of sample Comparative material 1 is Gr. 7. Comparative material 2 is Gr. 17, Comparative material 3 is Gr. 13. Comparative materials 1 to 4 are all alloys that do not contain rare earth elements.

Hereinafter, the characteristics of the samples of the examples of the present invention and examples outside the scope of the present invention will be described. Invention Examples 1 and 4: The Ru content is less than 0.05 mass%, and the oxygen content is less than 0.05 mass%. Invention Example 2: The Ru content is less than 0.05% by mass, and the oxygen content is 0.05% by mass or more. Invention Example 3: The Ru content is 0.05% by mass or more and the oxygen content is less than 0.05% by mass. Invention Example 5: Contains Ni. Invention Example 6: Contains Co. Invention Example 7: Contains Cr. Invention Example 8: Contains Mo. Invention Example 9: W is contained. Invention Example 10: V is contained. Invention Example 11: Contains Cr, Co, Mo, W, and V. Invention Examples 1 to 11 have a rare earth element content of less than 0.02%. Example 1 outside the scope of the present invention: The O content exceeds 0.10% by mass, which is outside the scope of the present invention. Example 2 outside the scope of the present invention: It is outside the scope of the present invention in that the Ru content is less than 0.01% by mass. Example 3 outside the scope of the present invention: It is outside the scope of the present invention in that the rare earth element content is 0.02% by mass or more.

1-1-2. Raw materials used for the preparation of the samples The raw materials used for the preparation of the titanium alloy are commercially available pure Ti sponge for industrial use (JIS type 1), ruthenium (Ru) powder (purity 99.9% by mass) manufactured by Kishida Chemical Co., Ltd. The wrought yttrium (Y) (purity 99.9% by mass) and bulk Mm (mixed rare earth elements) were manufactured. The rare earth element ratio in Mm was La: 28.6% by mass, Ce: 48.8% by mass, Pr: 6.4% by mass, and Nd: 16.2% by mass.

1-1-3. Sample preparation method The above raw materials are weighed at a predetermined ratio for each sample to be prepared, and melted (melted) in an argon atmosphere in an arc melting furnace to prepare five ingots (weight per ingot is 80 g). Thereafter, all of these five ingots were redissolved together to prepare a square ingot having a thickness of 15 mm. This square ingot was redissolved for homogenization, and a square ingot having a thickness of 15 mm was produced again. That is, the dissolution was performed three times in total.

Since any square ingot contains a small amount of Pd and rare earth elements, heat treatment was performed under the following conditions in order to reduce segregation of each element and to homogenize the elements in the alloy. Atmosphere: Vacuum (<10 ⁻³ Torr) Temperature: 1100 ° C. Time: 24 hours

The heat-treated square ingot was rolled under the following conditions to obtain a plate material having a thickness of 2.5 mm. β-phase region hot rolling: Rolling so that the heating temperature is 1000 ° C. and the thickness is reduced from 15 mm to 9 mm. α + β phase region hot rolling: The plate material after the β phase region hot rolling is rolled so that the heating temperature is 875 ° C. and the thickness is reduced from 9 mm to 2.5 mm.

The plate material obtained by rolling was annealed at 750 ° C. for 30 minutes in a vacuum to remove strain. A test piece used for the following test was obtained from the obtained hot-rolled sheet by machining.

1-2. Crevice Corrosion Resistance Test A crevice corrosion resistance test was performed using the obtained test piece.

1-2-1. FIG. 2 is a schematic diagram of a test piece for a crevice corrosion test, wherein (a) is a plan view and (b) is a side view. As shown in the figure, this test piece has a thickness of 2 mm and a width and a length of 30 mm. A hole having a diameter of 7 mm is formed in the center of the test piece. Further, one surface (front surface) of the test piece is polished with emery paper having a particle size of # 600.

FIG. 3 is a schematic diagram showing a state of a test piece when subjected to a crevice corrosion resistance test. The test piece 1 was sandwiched by clevis (spacer) 2 made of polytrifluoride ethylene from both sides. In the center of the clevis 2, a hole is formed corresponding to the hole of the test piece 1. A plurality of grooves are formed on one surface of the clevis 2, and the surface on which the grooves are formed is brought into contact with the test piece 1. By this groove, a gap is formed between the test piece 1 and the clevis 2.

The bolt 3 was inserted into the hole of the test piece 1 and the hole of the clevis 2, the nut 4 was fitted to the bolt 3, and the test piece 1 and the clevis 2 were tightened. The bolt 3 and the nut 4 are obtained by oxidizing pure Ti bolts and nuts in the atmosphere by heating with a burner. The torque during tightening was 40 kgf · cm.

1-2-2. Crevice corrosion resistance test in an environment substantially free of bromide ions Using the test piece in the above-described state shown in FIG. 3, a crevice corrosion resistance test was performed in accordance with the multi-clevis test defined by ASTM G78. Specifically, the test piece is immersed in a 250 g / L NaCl aqueous solution (pH = 2; pH is adjusted with hydrochloric acid), and the aqueous solution is kept in an air-saturated liquid state at 150 ° C. using an autoclave device. The test was conducted as described above. The test time was 500 hours.

After the test, count the number of parts where crevice corrosion occurred in the test piece, and measure the amount of increase / decrease in the test piece weight (the value obtained by subtracting the weight of the test piece before the test from the weight of the test piece after the test). went. The weight per test piece before the test was about 7 g.

1-2-3. Crevice corrosion resistance test in an environment containing bromine ions Add a sodium bromide reagent to the NaCl aqueous solution used to perform the above-mentioned "crevice corrosion resistance test in an environment that does not substantially contain bromine ions", and the bromine ion concentration A test under the same conditions as in the “crevice corrosion resistance test in an environment containing substantially no bromine ions” and an evaluation were performed, except that an aqueous solution containing 0.01 mol / L was used for the corrosion test.

1-3. Investigation of workability The workability of the material was evaluated by a bending test and a tensile test. The test conditions are as follows.

1-3-1. Bending test Specimens were prepared by rolling and annealing a plate material having a thickness of 2.0 mm to 2.5 mm to 0.5 mm by rolling, and having a size and shape in accordance with JIS Z 2204 (with a width of 20 mm). A piece having a length of 60 mm) was cut out, and the surface of the piece was polished with # 600 emery paper in a direction perpendicular to the rolling direction.

The bending test was performed by a method based on JIS Z 2248, and the T-direction adhesion bendability was evaluated.

1-3-2. Tensile test The test piece 1 for the crevice corrosion resistance test described above, which was not subjected to the crevice corrosion resistance test, was subjected to ASTM half size test pieces with a plate thickness of 2 mm in parallel with the rolling longitudinal direction. Two were cut out per each. About the cut-out test piece, the tensile test was done using the autograph tensile tester by Shimadzu Corporation. The tensile speed was 0.5% / min until the yield strength, and 5 mm / min thereafter. The average value of the breaking elongation measured for the two test pieces was taken as the elongation in the L direction of the sample.

2. Test result 2-1. Table 2 shows the results of the crevice corrosion resistance test. In Table 2, the results of the crevice corrosion resistance test in an environment containing substantially no bromine ions are shown in the column labeled “250 g / L-NaCl pH = 2 150 ° C.”. The results of the crevice corrosion resistance test in an environment containing bromine ions are shown in the column labeled “250 g / L-NaCl Br0.01 mol / L pH = 2 150 ° C.”.

Regarding “corrosion rate” in Table 2, “40” in the denominator is the number of gaps formed between the test piece 1 and the clevis 2 by the groove of the clevis 2. The number of molecules is the number of portions where corrosion has occurred in the portion corresponding to the gap on the surface of the test piece 1.

The test results in the above “environment substantially free of bromine ions” are as follows. Samples that did not corrode at all for 40 gaps were all of the inventive examples (Inventive Examples 1-4 and 5-11), Comparative Materials 1-3, and Examples 1, 3 outside the scope of the invention. there were. In these samples, oxidation coloring was observed in portions other than the portion corresponding to the gap, and a slight weight increase due to this oxidation was recognized.

Samples in which crevice corrosion was observed were Comparative Material 4 (the material described in Patent Document 3) and Example 2 outside the scope of the present invention (a material having a lower Ru content than that within the scope of the present invention). . Regarding these samples, a white corrosion product was observed in a portion corresponding to the gap in the test piece, and a weight loss of corrosion exceeding 40 mg occurred.

The results of the test in the above “environment containing bromine ions” are as follows. Samples in which no corrosion occurred at all for 40 gaps were all of the examples of the present invention (Invention Examples 1 to 4 and 5 to 11), and Examples 1 and 3 outside the scope of the present invention. In these samples, oxidation coloring was observed in portions other than the portion corresponding to the gap, and a slight weight increase due to this oxidation was recognized.

Samples in which crevice corrosion was recognized were Comparative materials 1 to 4 and Example 2 outside the scope of the present invention. Of these samples, the comparative material 4 and Example 2 outside the scope of the present invention have particularly large corrosion weight loss.

It turns out that the example of this invention shows the outstanding corrosion resistance (crevice corrosion resistance) with respect to any of the chloride environment which does not contain a bromine ion substantially, and the chloride environment which contains a bromine ion.

2-2. Workability Table 3 shows the results of a bending test (contact bending) and a tensile test.

In Table 3, the meanings of the symbols described in the column of “T direction tight bend” are as follows. ○: No cracking occurred. (Triangle | delta): The fine crack was recognized by either test piece. X: Cracks were observed in any of the test pieces.

About the comparative materials 1 and 3, a crack generate | occur | produces by T direction contact | adherence bending, and L direction elongation is small. That is, the workability of the comparative materials 1 and 3 is low. About the comparative material 2, crack generation | occurrence | production is not recognized by T direction close_contact | adherence bending, but L direction elongation shows the big value equivalent to a JIS1 seed material. About the comparative material 4, although the L direction elongation shows the big value equivalent to a JIS1 seed material, the fine crack was recognized on the surface of the test piece by the T direction adhesion bending.

In Invention Examples 1, 3, 4 and 8, no crack was observed in the T-direction contact bending, and the L-direction elongation was 50% or more, which was equivalent to JIS class 1 titanium. On the other hand, in the inventive examples 2, 5, 6, 7, 9, 10 and 11, the L-direction elongation is less than 50%, which is lower than those of the other invention examples, and the surface is fine by T-direction contact bending. Cracks occurred. Thus, the inventive examples 2, 5, 6, 7, 9, 10 and 11 are inferior in workability to the inventive examples 1, 3, 4, and 8. Invention Example 8 is slightly inferior in L-direction elongation as compared to Invention Examples 1, 3, and 4.

About Example 1 outside the scope of the present invention, the L direction elongation was poor, and cracking occurred in the T direction close contact bending. In Example 2 outside the scope of the present invention, both the results of T-direction contact bending and L-direction elongation were good. In Example 3 outside the scope of the present invention, cracks occurred in the T-direction contact bending, although the L-direction elongation was large.

Workability generally tends to improve as the O content is lower and the content of Ni, Cr, Co, Mo, W, and V is lower. Inventive Examples 1, 3, and 4 have better processability than Inventive Example 2, whereas the O content of Inventive Examples 1, 3, and 4 is less than 0.05% by mass. Thus, it is considered that the O content in Invention Example 2 corresponds to 0.05% by mass or more (however, it is less than 0.1% by mass and within the scope of the present invention). . Inventive Examples 5 to 11 are inferior in workability compared to Inventive Examples 1, 3, and 4 because Inventive Examples 5 to 11 contain Ni, Cr, Co, Mo, W, or V. it is conceivable that.

The rare earth element content of Example 3 outside the scope of the present invention exceeds the range of the rare earth element content in the present invention (0.01 to 0.10% by mass), and this sample contains a compound containing rare earth elements. It was generated. The cracks generated in the T-direction close contact bending of Example 3 outside the scope of the present invention are presumed to have originated from this compound.

3. Comprehensive evaluation Each sample was comprehensively evaluated in consideration of the test results and economic efficiency. Table 4 shows the result of calculating the cost of the platinum group element in the raw material cost based on the ratio of the platinum group element contained in the sample. In the calculation, the platinum group element metal price was set to 1905 yen / g for Pd and 300 yen / g for Ru.

In Table 4, “Platinum group element cost” is the cost (yen) of the platinum group element occupying 1 kg of the titanium alloy, and “Platinum group element relative cost” is when the platinum group element cost of the comparative material 1 is 100. It is a cost ratio of the platinum group element of each sample. Assuming the above metal price, the cost of the platinum group element of the present invention example is 1/10 or less of the cost of the platinum group element of the comparative material 1, and the cost of the platinum group element of the comparative material 2 Even if it compares, it is 1/4 or less.

Table 5 shows the results of comprehensive evaluation of the comparative material and the inventive example.

In Table 5, each evaluation item is evaluated in three stages: ○ (excellent), Δ (slightly inferior), and x (inferior).

As described above, with respect to workability, the present invention may be slightly inferior (Example 2 of the present invention), and the workability may be when the O content is 0.05 mass% or more, or with Ni, Cr, Co, Mo. , W, or V is considered to be worse. Therefore, when used for applications where workability is important, the titanium alloy of the present invention has an O content of less than 0.05% by mass and substantially contains Ni, Cr, Co, Mo, W, and V. Shall not.

With respect to items other than workability, the present invention is all excellent.

On the other hand, the comparative materials are inferior with respect to any of the evaluation items. In particular, regarding the crevice corrosion resistance in an environment containing bromine ions, any of the comparative materials is at a level that can be substantially used. Absent.

2.1 Composition of Titanium Alloy Used in Example 2 The following confirmation experiment was conducted to clarify the optimum rare earth content and to confirm that Ru among platinum group species has excellent bromine corrosion resistance. Table 6 shows the composition of the titanium alloy used in Example 2. An alloy having the composition shown in Table 6 was obtained according to the method for preparing the sample shown in Example 1.

The comparative materials 5 and 6 have rare earth elements less than 0.001%, both of which are outside the scope of the present invention. A titanium alloy plate for crevice corrosion test shown in FIG. 2 was obtained from the materials shown in Table 6 by machining, and a crevice corrosion test piece shown in FIG. 3 was constructed using the test piece. The torque during tightening was 40 kgf · cm. The crevice corrosion test piece was subjected to a crevice corrosion test in an environment containing bromine ions shown in 1-2-3.

Table 7 shows the results obtained as a result of the 500 hour crevice corrosion test. In the comparative material 5 containing no rare earth, many crevice corrosion was observed, and 325 mg of corrosion weight loss was recognized. Moreover, crevice corrosion was recognized also by the comparative material 6 with insufficient rare earth, and 32 mg of corrosion weight loss was recognized. The desirable rare earth content in an environment containing bromide ions is considered to be 200 ppm or less. Invention Examples 12 to 15 having rare earth contents within the scope of the present invention had no crevice corrosion, and the corrosion weight loss was small.

Next, crevice corrosion test pieces of the materials of the present invention 16-19 having different Ru contents were subjected to a crevice corrosion test in an environment containing bromine ions shown in 1-2-3. In addition, an Erichsen test defined in JISZ2247 was conducted to investigate the press formability of materials.

In the test, a plate material of 2 mm thickness and 90 mm × 90 mm was prepared, a steel ball having a diameter of 20 mm was pushed into the plate material, and the punch stroke when the crack reaching the back surface occurred was defined as the Erichsen value. For lubrication, graphite grease was used, and a molding test was conducted at a speed of 5 mm / min. The results are shown in Table 8.

In any of the present inventions 16 to 18, no crevice corrosion was observed, and excellent corrosion resistance was exhibited in a solution environment containing bromide ions. It should be noted that the Erichsen value indicating the moldability slightly decreased when the Ru content exceeded 0.05%. On the other hand, there was a tendency that the corrosion weight loss decreased as the Ru content increased. In order to achieve both excellent corrosion resistance and moldability, Ru is preferably in the range of 0.01 to 0.05%.

  From the above experimental facts, it has been found that, within the range of the present invention, better corrosion resistance can be obtained when the rare earth element content is in the range of 0.001 to less than 0.02%. In addition, excellent moldability can be secured when the Ru content is 0.01 to 0.05%.

The titanium alloy of the present invention can be applied to facilities and equipment used in an environment where corrosion resistance in an environment containing bromine ions is required (in particular, a high-temperature and high-concentration chloride environment).

(2) Instead of a part of Ti, it contains one or more selected from the group consisting of Ni, Co, Mo, V, Cr and W, the Ni content is 0.12 % by mass or less, The Co content is 0.18 mass% or less, the Mo content is 0.11 mass% or less, the V content is 0.19 mass% or less, and the Cr content is 0.18 mass%. The titanium alloy according to (1), wherein the titanium alloy is not more than mass% and the W content is not more than 0.14 mass%.

Claims (7)

A titanium alloy used in an environment containing bromine ions, and in mass%, platinum group element: 0.01 to 0.10%, rare earth element: less than 0.001 to 0.02%, O: 0 to 0 A titanium alloy containing less than 1% by mass with the balance being Ti and impurities. Instead of a part of Ti, it contains one or more selected from the group consisting of Ni, Co, Mo, V, Cr and W, the Ni content is 1.0 mass% or less, and the Co content The rate is 1.0 mass% or less, the Mo content is 0.5 mass% or less, the V content is 0.5 mass% or less, and the Cr content is 0.5 mass% or less. The titanium alloy according to claim 1, wherein the W content is 0.5 mass% or less.   The titanium alloy according to claim 1 or 2, which contains, in mass%, a platinum group element: 0.01 to 0.05%.   The titanium alloy according to any one of claims 1 to 3, wherein the platinum group element is Ru. The titanium alloy according to claim 1, wherein the rare earth element is Y. The titanium alloy according to any one of claims 1 to 5, wherein the O content is less than 0.05 mass%.   The titanium alloy of any one of Claims 1-6 used for a chemical plant apparatus.

Images