JP2000248324A - CORROSION RESISTANT Ti ALLOY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Ti alloy less expensive than the presently used Ti-0.15Pd alloy and having excellent corrosion resistance and also to provide a corrosion resistant Ti alloy having cold workability (press workability) equal or superior to that of the Ti-0.15Pd alloy and further a corrosion resistant Ti alloy excellent also in hydrogen absorption resistance. SOLUTION: The Ti alloy excellent in corrosion resistance can be obtained by providing a composition consisting of, by mass (the same applies to the following), 0.020-0.050% Pd, one or more platinum group elements other than Pd in an amount one-third (in mass ratio) the amount of Pd or more, and the balance permissible components and Ti. To obtain the corrosion resistant Ti alloy excellent in cold formability, it is desirable to provide a composition consisting of 0.020-0.050% Pd, 0.01-0.03% Ir and/or Pt, <=0.05% Fe, <=0.05% O, and the balance permissible elements and Ti. Further, in addition to cold formability and corrosion resistance, hydrogen absorption resistance can also be imparted by regulating the amount of Pd to <=0.030%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a corrosion-resistant Ti alloy,
The present invention relates to a member using the corrosion-resistant Ti alloy.

[0002]

2. Description of the Related Art Pure Ti is generally known to have better corrosion resistance than stainless steel and copper alloys, but causes corrosion in high-temperature, high-concentration non-oxidizing acids. In addition, crevice corrosion may occur in a high-temperature and high-concentration aqueous chloride solution. As a method for preventing such corrosion, a method of adding an alloying element, adding an oxidizing agent to a corrosive environment, or performing a surface treatment has been studied. Among them, the addition of alloying elements is the most reliable method, and platinum group elements such as Pd and Ru are considered to be effective. The reason for this is that Pd or Ru has a small hydrogen generation overpotential, and thus promptly promotes the positive polarization of titanium. That is, the oxidation reaction of Ti + 2H ₂ O → TiO ₂ + 4H ⁺ + 4e ⁻ progresses rapidly on the surface of titanium, and a passive oxide film TiO 2 is formed to improve the corrosion resistance. Concretely, T-0.15Pd alloy (ASTM Grade 7,11)
i-alloys have been developed and used in fields such as petroleum refining and petrochemical plants. However, the Ti-0.15Pd alloy has a problem that the material cost is increased because a relatively large amount of expensive Pd is added. Furthermore, when the amount of Pd contained in the Ti alloy is large, Pd oxide (commonly called Pd black) is generated on the surface during pickling,
Since the pickling is hindered, it is necessary to pass through the pickling line many times, which increases the manufacturing cost.

Therefore, recently, P
In order to minimize the addition of d and Ru, and to compensate for the deterioration of corrosion resistance, a Ti alloy containing a small amount of an iron group element that does not impair workability has been developed.For example, Ti-0.
05Pd-0.3Co alloy (ASTMGrade 30,31;
No. 9423) and Ti-0.5Ni-0.05Ru alloy (ASTM G
rade 13, 14, 15; Japanese Patent Publication No. 62-20269). These alloys limit the amount of addition of expensive platinum group elements such as Pd and Ru to suppress the cost increase, and to the extent that corrosion resistance deterioration caused by a decrease in the amount of platinum group element added is not significantly impaired in workability. It is supplemented by adding an additive element (Ni, Mo, Co, etc.) that contributes to the improvement of corrosion resistance. However, the addition of the above-mentioned elements for improving corrosion resistance inevitably lowers the workability, and requires corrosion resistance, such as plate-type heat exchangers and battery case members in the soda electrolysis industry, and relatively severe cooling such as bulging. It was difficult to use the above-mentioned Ti alloy for members subjected to cold working. Therefore, for applications requiring cold workability as well as corrosion resistance, a Ti-0.15Pd alloy which does not add a corrosion resistance improving element such as Ni, Mo, Co, etc. which impairs the workability, although it is expensive. (ASTM Grade 11) has to be used.

[0004] Titanium is frequently used as a condenser pipe for thermal and nuclear power plants, a pipe for a high-temperature and high-pressure chemical plant such as urea synthesis, and a heat transfer pipe for a seawater desalination apparatus. And may cause accidents due to hydrogen embrittlement. Tokuhei 4-57735
According to the publication, since the Ti-0.15Pd alloy contains a large amount of Pd, the hydrogen absorption resistance is not sufficient as compared with pure titanium, so the Pd content is in the range of 0.03 to 0.1%. Adjusted Ti alloy [for example, Ti-0.05Pd alloy (ASTM G
r.16,17)] has been proposed. However, in actual use, since the hydrogen absorption of titanium is complicatedly related to the surface state (roughness, finishing method), crystal grain size and use environment, the Pd content is controlled to 0.03 to 0.1%. Even when a Ti alloy was used, hydrogen absorption sometimes occurred.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been widely used at present.
An object of the present invention is to provide a Ti alloy exhibiting excellent corrosion resistance at a lower cost than a -0.15 Pd alloy.
An object of the present invention is to provide a corrosion-resistant Ti alloy having a cold workability (pressing property) equal to or higher than that of a 15Pd alloy and a corrosion-resistant Ti alloy excellent in hydrogen absorption resistance.

[0006]

The corrosion-resistant Ti alloy according to the present invention, which has solved the above problems, has a Pd of 0.020 to 0.0
50% (mean% by mass, the same applies hereinafter)
At least one platinum group element other than d is contained at a mass ratio of 1/3 or more to Pd, and the balance consists of an allowable component and Ti. The platinum group element other than Pd is Ir. And / or Pt is preferred. Further, the content of the platinum group element other than Pd is desirably 0.01 to 0.03%, and the content of Pd is desirably 0.030% or less.

In order to obtain a corrosion-resistant Ti alloy excellent in cold formability, Pd is set to 0.020 to 0.050%, and
r and / or Pt are contained in an amount of 0.01 to 0.03%, the Fe content is 0.05% or less, and the O content is 0.0
It is desirable that the balance be 5% or less and the balance be an allowable component and Ti. Such a corrosion-resistant Ti alloy having excellent cold formability is suitable for a plate-type heat exchanger member or an electrolysis tank component. Further, in this composition range, the amount of Pd is set to 0.030.
% Or less, hydrogen absorption resistance can be imparted in addition to cold formability and corrosion resistance.

Further, in order to obtain a corrosion-resistant Ti alloy which does not require the cold formability as described above but is required to have excellent hydrogen absorption resistance, Pd is set to 0.020 to 0.030.
%, The content of platinum group elements other than Pd is set to 0.01 to 0.03%, and the Fe content is set to 0.1%.
It is preferable that the O content is 0.4% or less and the O content is 0.4% or less, with the balance being an allowable component and Ti. Such a corrosion-resistant Ti alloy having excellent hydrogen absorption resistance is used for heat exchanger tubes and other piping. It is suitable as a tube.

In the present invention, the term "allowable component" means, in addition to general unavoidable impurities, an element which is allowed to be contained within a range that does not adversely affect the properties of the corrosion-resistant Ti alloy according to the present invention. It may be included if it is within the allowable range of each element. As unavoidable impurities,
Examples include Fe, O, N, H, C, Ni, and Cr. These elements are trace components contained in titanium oxide as a raw material and elements derived from a stainless steel container used for manufacturing titanium sponge.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors, when designing the component composition of a Ti alloy, set the addition amount of Pd, which has the highest ability to improve the corrosion resistance of Ti among the platinum group elements, in view of the cost reduction. Various Ti alloys were set to be 02 to 0.05%, and various platinum group elements other than Pd were added singly or in combination, and the corrosion resistance and cold workability of each Ti alloy were repeatedly evaluated. . As a result, when one or more platinum group elements other than Pd are contained so that the mass ratio to Pd is 1/3 or more, the total amount of platinum group elements other than Pd is replaced with Pd, and Pd alone is used. The present inventors have found that the corrosion resistance is improved rather than the case where it is added, and arrived at the present invention. This effect has not been clearly elucidated at this time, but it is due to the fact that platinum group elements other than Pd chemically bond with Pd and Ti, resulting in a substance having a lower hydrogen overvoltage than Pd. It is thought that it is because.
The reason why the corrosion resistance is improved when the ratio (mass ratio) of the other platinum group element to Pd is 1/3 or more is not clear at present, but in the case of this range. It is presumed that a substance having a low hydrogen overvoltage is produced efficiently and more. The ratio (mass ratio) of the other platinum group element to Pd is not more than 2 because it is too high, which adversely affects the formability and impairs the economic efficiency.

In the Ti alloy according to the present invention, Pd is required to be 0.020% or more in order to obtain a sufficient effect of improving corrosion resistance. On the other hand, if the upper limit of Pd is too large, the cost is high, and Pd oxide is generated on the surface during pickling with nitric hydrofluoric acid to inhibit pickling. In order to improve the hydrogen absorption resistance, the content is desirably 0.030% or less.

The platinum group elements other than Pd include Ir, P
There are t, Ru, Re, Rh, and Os, and when these are added to Ti, although the degree varies depending on the individual elements, as the addition amount increases, the structure becomes finer and the cold workability deteriorates. Therefore, while ensuring corrosion resistance, it is necessary to add an element effective for corrosion resistance in order to obtain good formability. At that time, select an additive element that does not contribute as much as possible to microstructural refinement. It is also necessary.
Then, the present inventors examined the crystal grain refining ability of each platinum group element added in a complex manner to the Ti-Pd alloy. As a result, it was found that the miniaturization ability of Ir was the smallest, followed by the miniaturization ability of Pt. The greatest ability to refine crystal grains is R
u, and Re, Rh, and Os were between Pt and Ru. Since Re, Os, and Rh are expensive elements, a titanium alloy excellent in formability and corrosion resistance can be obtained by adding one or two types of Ir or Pt to a titanium alloy containing Pd. Among them, particularly preferred is Ti
This is the case where Ir is solely added to the Pd alloy. In addition,
If the cost aspect is ignored, Re,
It is also effective to add one or more of Rh and Os.

[0013] Incidentally, Fe and O (oxygen) in the Ti alloy are unavoidable impurities, and when their content increases, the structure becomes finer and leads to an increase in strength, so that the formability is significantly adversely affected. Therefore, the contents of Fe and O are both desirably 0.10% or less, and more desirably 0.05% or less. However, in applications where moldability need not be taken into account, the content may be up to 0.4%.

Further, in the present invention, in addition to the inevitable impurities contained in the raw material sponge titanium, as long as the properties of the corrosion-resistant Ti alloy according to the present invention are not adversely affected,
Other elements may be included. For example,
N, H, C, Ni, Cr, and the like can be cited as allowable components. In applications requiring formability, these are approximate values, but N: 0.02% or less, H: 0.01% or less. ,
C: 0.02% or less, Ni: 0.05% or less, Cr:
If it is 0.05% or less, it may be contained. In addition, although it depends on the degree of formability required, other elements than these elements are generally included, but if the total amount is 0.1% or less,
It may be included. When used in applications where moldability is not so required, the corrosion-resistant Ti according to the present invention is used.
Various elements exceeding the upper limit may be contained as long as the properties of the alloy are not adversely affected.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention, and any design change based on the above and following gist will be described. Are included within the technical scope of

[0016]

Example 1 A pure titanium plate (O: 0.04%, Fe: 0.03%) of JIS Class 1 (equivalent to ASTM Gr.1) was used as a melting raw material, and the components of each metal powder shown in Table 1 were used. It is contained in varying proportions, melted in a vacuum arc melting furnace, and cast ingots (approximately 50
0 g). Thereafter, a plate for evaluation was prepared in the following steps.

Temper annealing (heating at 1000 ° C. for 2 hours) → hot rolling (heating at 850 ° C., about 20 ^t × 40 ^w → about 5 ^t × 40 ^w ) →
Annealing (850 ° C, 30 minutes) → shot blasting → pickling (dropping about 1 mm in thickness) → cold rolling (about 4 ^t × 40 ^w → about 1.
2 ^t × 40 ^w ) → salt immersion (520 ° C, 3 minutes) → pickling (about 1.2 ^t × 40 ^w → about 1.0 ^t × 40 ^w ) As a general corrosion test, in a 5% boiling hydrochloric acid aqueous solution A 24-hour immersion test was performed to calculate the corrosion rate. Table 1 shows the results
It is described together.

[0018]

[Table 1]

No. 1 to 9 are platinum group elements other than Pd.
Pd is contained in a mass ratio of 1/3 or more to d.
No. 3 containing no more than 1/3 of the platinum group element other than Pd in mass ratio to Pd. Nos. 11 and 13 had a lower corrosion rate, and Pd was a single additive. Corrosion rate is smaller than 14 and 15. No. Nos. 10 and 12 contain platinum group elements other than Pd in a mass ratio to Pd of 1/3 or more, but have a Pd content of less than 0.020% and are inferior in corrosion resistance.

Example 2 A pure titanium plate (O: 0.04%, Fe: 0.03%) of JIS Class 1 (equivalent to ASTM Gr.1) was used as a melting raw material, and the component ratio of each metal powder shown in Table 2 was used. And melted in a vacuum arc melting furnace to form an ingot (approximately 50
0 g). Thereafter, a plate for evaluation was prepared in the following steps.

Temper annealing (heating at 1000 ° C. for 2 hours) → hot rolling (heating at 850 ° C., about 20 ^t × 40 ^w → about 5 ^t × 40 ^w ) →
Annealing (850 ° C, 30 minutes) → shot blasting → pickling (removing about 1 mm in thickness) → cold rolling (about 4 ^t × 40 ^w → about 0.
7 ^t × 40 ^w ) → salt immersion (520 ° C, 3 minutes) → pickling (about 0.7 ^t × 40 ^w → about 0.5 ^t × 40 ^w ).

In evaluating the corrosion resistance, the corrosion rate was calculated by performing an immersion test in a 2% boiling hydrochloric acid aqueous solution for 24 hours, and evaluated as follows. The results are shown in Table 2. ◎: Corrosion rate less than 0.1 mm / year ：: Corrosion rate 0.1 mm / year or more and 0.5 mm / year
Less than Δ: Corrosion rate 0.5 mm / year or more and less than 1 mm / year ×: Corrosion rate 1 mm / year or more.

For the evaluation of the hydrogen absorption resistance, a cathode charge method was used. In this test, a Pt electrode 1 and a strip-shaped test piece 2 (10 mm × 50 mm, 1 m thick) were placed in a sulfuric acid aqueous solution (0.05 M, 30 ° C.).
m) were arranged at an interval of 50 mm, and hydrogen was generated from the cathode side was absorbed by the test piece by applying a current of 10 mA / cm ² between them for 6 hours using a constant current DC power supply. . In this test, a plurality of electrolysis containers 3 were connected in series as shown in FIG. 1 in order to process several test pieces in one test. In order to unify the influence of the surface state of the test pieces on hydrogen absorption, the surfaces of all the test pieces were subjected to # 400 wet emery polishing. The amount of hydrogen absorbed was calculated from the amount of hydrogen before the test and the amount of hydrogen after the test, and evaluated as follows. The analysis of the amount of hydrogen after the test was conducted by heating the above-mentioned hydrogen absorption sample at 400 ° C. for 1 hour in the air.
This was performed after the hydrogen-enriched layer formed on the surface was uniformly diffused in the inner direction of titanium. ◎: Hydrogen absorption less than 50 ppm ：: Hydrogen absorption 50 ppm or more and less than 100 ppm Δ: Hydrogen absorption 100 ppm or more and less than 200 ppm ×: Hydrogen absorption 200 ppm or more.

In addition, the pressability test was performed in the following manner: 0.5 ^t × 40 ^w ×
Using a 150 ^l size cut plate, corrugated plate pressing was performed with the mold shown in FIG. 2, and the moldability was evaluated based on the presence or absence of cracks.
The press test was performed at room temperature using a lubricating oil for press.

The results are shown in Table 2.

[0026]

[Table 2]

No. Nos. 1 to 8 are examples of the present invention, which were excellent in corrosion resistance and hydrogen absorption resistance, did not have fine crystal grains, and were excellent in press moldability.

No. Nos. 9 to 11 have a large content of O and Fe. Nos. 12 to 14 have a large amount of Ir and / or Pt, and the press formability is no. Although not as excellent as 1 to 8, it exhibited excellent characteristics with respect to corrosion resistance and hydrogen absorption resistance. No. In No. 15, Ru was contained, but the corrosion resistance and press formability were no. Not as good as 1-8. No. Nos. 16 and 17 are low in Ir or Pd and have no corrosion resistance. Not as good as 1-8. No. No. 18 has a large amount of Pd, and the hydrogen absorption resistance is No. 18; Not as good as 1-8. No. 19 to 21 are pure titanium and have insufficient corrosion resistance.

[0029]

As described above, the present invention can provide a Ti alloy exhibiting excellent corrosion resistance at a lower cost than the Ti-0.15 Pd alloy generally used at present, and a Ti-0.15 Pd alloy can be provided. It has become possible to provide a corrosion-resistant Ti alloy having a cold workability (pressability) equal to or higher than that of an alloy, and a corrosion-resistant Ti alloy excellent in hydrogen absorption resistance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an experimental method of a cathode charging method performed in an example.

FIG. 2 is an explanatory view showing an experimental method of press formability.

Claims (10)

[Claims] Claims: 1. Pd is contained in an amount of 0.020 to 0.050 mass%, and at least one platinum group element other than Pd is contained in a mass ratio of not less than 1/3 to Pd, with the balance being an allowable component and Ti A corrosion-resistant Ti alloy comprising: 2. The corrosion-resistant Ti alloy according to claim 1, wherein the platinum group element other than Pd is Ir and / or Pt. 3. The content of a platinum group element other than Pd is 0.0
The corrosion-resistant Ti alloy according to claim 1, wherein the content is 1 to 0.03 mass%. 4. The corrosion-resistant Ti alloy according to claim 1, wherein the content of Pd is 0.030% by mass or less. 5. A composition containing 0.020 to 0.050 mass% of Pd, 0.01 to 0.03 mass% of Ir and / or Pt, and 0.05 mass% or less of Fe content. A corrosion-resistant Ti alloy excellent in cold formability, characterized in that the O content is 0.05% by mass or less, and the balance consists of an allowable component and Ti. 6. A member for a plate-type heat exchanger, comprising the corrosion-resistant Ti alloy according to claim 5. 7. An electrolysis tank component comprising the corrosion-resistant Ti alloy according to claim 5. 8. An alloy containing 0.020 to 0.030% by mass of Pd, 0.01 to 0.03% by mass of a platinum group element other than Pd, and a Fe content of 0.4% by mass or less. , O content is 0.4% by mass or less, and the balance consists of an allowable component and Ti. 9. A heat exchanger tube comprising the corrosion-resistant Ti alloy according to claim 8. 10. A piping tube comprising the corrosion-resistant Ti alloy according to claim 8.