JPH06200342A - High corrosion resistance and high rigidity Ti alloy and its manufacturing method - Google Patents

Abstract

PURPOSE:To obtain a highly corrosion resistant high rigidity Ti alloy excellent in corrosion resistance and rigidity by specifying a composition consisting of Al, B, O, platinum group elements, and Ti and crystallizing or precipitating metal borides in a matrix. CONSTITUTION:This alloy is a highly corrosion resistant high rigidity Ti alloy which has a composition consisting of, by weight, 5.5-10% Al, 0.5-3.0% B, <=0.25% O, 0.005-0.25%, in total, of one or more kinds among platinum group elements, and the balance Ti with inevitable impurities and where metal borides are crystallized and/or precipitated in a matrix. This Ti alloy has corrosion resistance equal to or higher than that of conventional corrosion resisting Ti alloy and rigidity as high as >= about 13000kgf/mm<2> Young's modulus, without deteriorating hot workability. If necessary, this alloy can further contain 0.1-5.0% of Ni or Co, further <=20% of one or more elements among Sn, Zr, and Hf, and further one or more beta-phase stabilizing elements among V, Mo, and W in the range satisfying V equivalent =V+15/10Mo+15/6.3Cr+15/4Fe+15/9Ni+15/25W<=15%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high corrosion resistance and high rigidity Ti alloy suitable for a material for parts which is used in a severe corrosive environment and is required to have high rigidity, and a method for producing the same.

[0002]

2. Description of the Related Art Since Ti alloys are lightweight, have high strength, and have excellent corrosion resistance and heat resistance, their application to various materials for machine parts has been promoted. Ti has excellent corrosion resistance in a corrosive environment of an oxidizing acid such as nitric acid, but the corrosion resistance in a corrosive environment of a reducing acid such as sulfuric acid or hydrochloric acid is not sufficient, and in order to improve this,
It has been conventionally known that a platinum group element (Ru: ruthenium, Pd: palladium, Os: osnium, Ir: iridium, Rh: rhodium and Pt: platinum) may be added.

For example, as JIS 11 to 13 types, 0.12 to 0.25% Pd as a platinum group element (hereinafter, "%" means "% by weight" unless otherwise specified) The Ti alloy to be contained is specified, and JP-A-62-107041 and JP-A-62-149836 also propose a Ti alloy containing a platinum group element with high corrosion resistance. Further, Japanese Patent Laid-Open No. 63-114931 proposes a Ti alloy for oil well environment, in which a trace amount of one or more platinum group elements is added, or a Ni alloy is added in addition to one or more platinum group elements. , Co,
Corrosion resistance is improved by adding a small amount of W or the like.

By the way, in order to utilize the excellent corrosion resistance of the Ti alloy, the above-mentioned high corrosion resistance Ti is used for the shaft portion of the turbine and the chemical agitator used in a corrosive environment.
When the alloy is applied, insufficient rigidity as a mechanical part has often been a problem. By the way, these high corrosion resistance Ti
The Young's modulus of the alloy is about 1 / th that of steel materials that are normally used.
It was about 2.

Conventionally, a composite material using a Ti alloy as a matrix has been studied as a means for improving and improving the rigidity of a highly corrosion resistant Ti alloy. As such a composite material, for example,
There is a fiber reinforced Ti alloy in which fibers having a high Young's modulus such as SiC, C and Al ₂ O ₃ are mixed in a titanium alloy.

[0006]

However, in the conventional means for improving the rigidity by making a composite material using a highly corrosion resistant Ti alloy as a matrix, a high Young's modulus fiber is used, resulting in a significant increase in cost. Also, when activated titanium and fibers react, a fragile reaction layer is generated at the interface,
It was not possible to produce a corrosion-resistant Ti alloy having the desired rigidity because the mechanical properties were rather deteriorated.

As described above, since the rigidity of the conventional corrosion-resistant Ti alloy is as low as about 1/2 of that of steel materials, parts requiring high rigidity as mechanical parts, such as the shaft of a turbine or the shaft of a chemical stirrer. It was not easy to apply the conventional corrosion resistant Ti alloy to. Here, an object of the present invention is to have a corrosion resistance equal to or higher than that of a conventional corrosion-resistant Ti alloy without impairing the hot workability, and a high rigidity having a Young's modulus of 13000 kgf / mm ² or more. It is to provide a Ti alloy and a manufacturing method thereof.

[0008]

By the way, one of the inventors of the present invention was previously described in Japanese Patent Application No. 4-212880, Al: 5.5.
-10%, B: 0.5-3.0%, O: 0.07-0.25%, if necessary, one or more of Sn, Zr and Hf: 20% or less, and V equivalent = V + (15/10) Mo + ( 15 / 6.3) Cr + (15 /
4.0) Fe + (15/36) Nb + (15/9) Ni + (15/25) One or more β-phase stabilizing elements that make W less than 15%, the balance Ti and inevitable impurities. We proposed a high-rigidity Ti alloy in which metal borides crystallize or precipitate in the alloy matrix.

To this high-rigidity Ti alloy, Al and O are added in appropriate amounts in order to improve Young's modulus, and one or more of Sn, Zr and Hf are added in order to improve high temperature strength and creep resistance. By further adding a β-phase stabilizing element and dispersing titanium boride particles with a high Young's modulus in the matrix, hot working is possible and tensile strength: 90 kgf / mm ² or more, Young's modulus : We provide high-rigidity Ti alloys of 13000 kgf / mm ² or more.

The present inventors cannot improve the corrosion resistance of the high rigidity Ti alloy proposed in Japanese Patent Application No. 4-212880 to provide a high corrosion resistance and high rigidity Ti alloy that can achieve the above object. As a result of further studies, the high-rigidity Ti alloy proposed by Japanese Patent Application No. 4-212880 may be added with a platinum group element, which is one of the conventional techniques for improving the corrosion resistance of Ti alloys. Based on this finding, the present invention has been completed.

The gist of the present invention is as follows.
l: 5.5-10%, B: 0.5-3.0%, O: 0.25% or less, R
u, Pd, Os, Ir, Rh and Pt One or more platinum group elements consisting of six: 0.005 to 0.25% in total, balance Ti
A highly corrosion-resistant and high-rigidity Ti alloy having an alloy composition of unavoidable impurities and having a metal boride crystallized and / or precipitated in its Ti alloy matrix.

The above-mentioned high corrosion resistance and high rigidity Ti alloy according to the present invention further comprises one or two of Ni and Co in a total amount of 0.1.
When the content is up to 5.0%, the hydrogen overvoltage of the Ti alloy can be lowered and the corrosion resistance can be improved, like the platinum group element. High corrosion resistance and high rigidity Ti alloy according to these inventions,
Further, by containing 20% or less in total of one or more selected from the group consisting of Sn, Zr and Hf, the high temperature strength can be increased and the high heat resistance can be improved.

Further, high corrosion resistance and high rigidity Ti according to the present invention.
For the alloy, β composed of V, Mo, Cr, Fe, Ni and W so that the V equivalent represented by the following formula is 15% or less.
By containing at least one phase stabilizing element, it is possible to improve rigidity, heat treatment property and hot workability.

[0014]

[Equation 2] V equivalent = V + (15/10) Mo + (15 / 6.3) Cr + (15/4) Fe + (15/9) Ni + (15/25) W ・ ・ ・ ・ ・ Incidentally, this V equivalent is , The effect of the β-phase stabilizing element in the degree of decrease in β transformation point is converted into V content. Further, if one or more of V, Mo and W are used as the β-phase stabilizing element, the corrosion resistance can be further improved.

[0015]

The operation of the present invention will be described in detail below. All essential additive elements and optional additive elements in the high corrosion resistance and high rigidity Ti alloy according to the present invention are roughly classified into (1) a corrosion resistance expressing component element and (2) a high rigidity expressing component element and (3) a high temperature strength expressing component. Element and (4) Become a high hot workability manifesting element element. Therefore, each is divided. In addition, in the high corrosion resistance and high rigidity Ti alloy according to the present invention, the corrosion resistance expressing component element and the high rigidity expressing component element do not react with each other and independently improve the characteristics.

(1) Corrosion resistance-producing component element Platinum group element: In the present invention, one or two or more platinum group elements consisting of 6 kinds of Ru, Pd, Os, Ir, Rh and Pt are added as an essential addition element in an amount of 0.005. ~ 0.25% contained. Industrially practical platinum group elements are Ru and Pd, but Os, Ir, Rh and Pt can also be used. These elements have the effect of improving the corrosion resistance of the titanium alloy,
0.005% in total when added alone or in combination
If it is not above, the effect of improving the corrosion resistance does not appear. On the other hand, although the corrosion resistance improves as the content of the platinum group element increases, if the total content exceeds 0.25%, the corrosion resistance improving effect tends to be saturated, and the platinum group element is an extremely expensive element. The cost just increases.
Therefore, in the present invention, the total amount of one or more platinum group elements added is limited to 0.005% or more and 0.25% or less.
Desirably, it is 0.05 to 0.2%.

Ni, Co: In the present invention, both Ni and Co are optional elements, and in order to improve the corrosion resistance, it is desirable that the base contains Ni and / or Co.
When Ni and / or Co are contained in a total amount of 0.1% or more in the coexistence with the above-mentioned platinum group element, they have the effect of lowering the hydrogen overvoltage of the Ti alloy and improving the corrosion resistance, like the platinum group element. Play. However, if the content of these elements exceeds 5.0%, the workability of the Ti alloy is significantly reduced. Therefore, in the present invention, the content of Ni and / or Co is 0.1
% To 5.0% or less is desirable. More preferably, it is 0.3 to 1.0%.

V, Mo, W: V, Mo, and W are one of the high hot workability-expressing component elements described later, and if at least one of these elements is added as required, the corrosion resistance is also improved. If the added amount is small, there is no corrosion resistance improving effect,
The effect is exhibited when the V equivalent is 0.05% or more. However, as will be described later, the Young's modulus decreases when the V equivalent exceeds 15%, so one or more of V, Mo, and W is 0.05 to 15%.
Is desirable.

(2) High rigidity component element Al: In the present invention, Al is an essential additive element. Al is an α-phase stabilizing element and significantly improves Young's modulus by solid solution hardening. The effect of improving the Young's modulus is not exhibited when the content is less than 5.5%, while when it exceeds 10%, Ti ₃ Al
A large amount of (α ₂ phase) is generated, and the ductility in both hot and cold is deteriorated. Therefore, in the present invention,
The Al content is limited to 5.5% or more and 10% or less. It is preferably 6.5% or more and 8.5% or less.

B: In the present invention, B is an essential additive element. B is titanium boride (Ti
B) crystallizes and / or precipitates, and has the effect of improving the Young's modulus of the Ti alloy. TiB has a Young's modulus of 50,000
Since it is more than kgf / mm ² and has a very high Young's modulus as compared with Ti, when dispersed in a Ti alloy, the Young's modulus of the Ti alloy should be improved according to a compound rule proportional to the volume of particles in the Ti alloy. You can When the B content is less than 0.5%, the amount of TiB crystallized and / or precipitated is small and the Young's modulus is not improved. On the other hand, if the B content exceeds 3.0%, the TiB dispersion amount increases, so that the Young's modulus improvement amount increases, but the ductility in both hot and cold regions remarkably decreases. Therefore, in the present invention, the B content is limited to 0.5% or more and 3.0% or less. Desirably, it is 0.7 to 2.0%.

According to the confirmation results of the present inventors, B
When the content is 1.0%, about 5% by volume of titanium boride is crystallized and / or precipitated and dispersed in the matrix, and B
When the content is 3.0%, about 15% by volume (titanium boride) is dispersed.

According to the present invention, as will be described later, a neutral type element and / or a β-phase stabilizing element may be blended. In such a case, each additive element is solid-dissolved in the matrix. . However, most of Zr and Hf are solid-solved in the matrix, but crystallize and / or precipitate as a metal boride in a slight amount. The metal borides at that time are zirconium boride and hafnium boride.
However, due to the small amount and the Young's modulus of the boride itself is lower than that of titanium boride,
These do not contribute to the improvement of Young's modulus.

O: In the present invention, O is an essential additive element, which stabilizes the α phase and improves Young's modulus like Al. It is not necessary to set the lower limit of the content because even if the amount is a small amount, such an effect is exhibited, but if the content exceeds 0.25%, the cold ductility of the Ti alloy is significantly reduced. Therefore, in the present invention, the O content is limited to 0.25% or less. Desirably 0.10%
It is above 0.20%.

In addition to Al and O, C and N are known as α-phase stabilizing elements, and these elements have Young's modulus improving effect like Al and O, but C is 0.3%. As described above, the addition of a trace amount of N of 0.1% or more significantly reduces the cold ductility of the Ti alloy. Therefore, in the present invention, it is desirable that neither C nor N be added.

(3) High temperature strength developing component elements Sn, Zr, Hf: In the present invention, these elements are optional addition elements, and at least one element is contained if necessary. Preferred combinations include Sn and Zr (and / or
Hf). Sn, Zr, Hf are all neutral type elements,
It acts as a solid solution strengthener for Ti alloys. Although the Young's modulus improvement effect is small, the high temperature strength can be increased and the application range of Ti alloy can be expanded. Therefore, it is desirable to add them in order to improve the properties of both high heat resistance and high Young's modulus. When the addition amount of these elements is small, the effect of deteriorating the ductility in both hot and cold is small and there is no problem. Become. Therefore, in the present invention, Sn,
It is desirable that the total content of one or more Zr and Hf is 20% or less. More preferably, it is 1 to 12%.

These additional elements, which are neutral type elements, are mostly present in a solid solution form in the titanium alloy matrix according to the present invention. However, although Zr and Hf are small, some of them combine with boron and contribute to the formation of metal borides. In the case of Zr, its content is about 7/8 as a solid solution and about 1/8 contributes to the formation of metal borides. Similarly, in the case of Hf, it is considered that 3/4 forms a solid solution and about 1/4 contributes to metal boride formation.

(4) High hot workability-producing component element β-phase stabilizing element: Examples of the β-phase stabilizing element include:
V, Mo, Cr, Fe, Ni, W, etc. are known, but in the present invention, these β-phase stabilizing elements are optional addition elements, and at least one or two or more elements are added as necessary. It Although these β-phase stabilizing elements lower the Young's modulus, they have the effect of suppressing the formation of Ti ₃ Al, so that they can contain more Al, which has the Young's modulus improving effect in the present invention. Further, it also has the effect of improving the heat treatment property and decreasing the β transus (the temperature at which the β phase is transformed into the α + β phase) to improve the hot workability.

Of the β-phase stabilizing elements, V which is a solid solution type,
Mo has a large Young's modulus lowering effect, while eutectoid Cr and Fe have a smaller Young's modulus lowering effect. However, if any β-phase stabilizing element is added in such a large amount that it becomes a β-phase single phase, the Young's modulus significantly decreases, which is not preferable. Therefore, in the range where the Young's modulus is not extremely lowered, that is, in the total of at least one β-phase stabilizing element, the V equivalent by the above equation is 15
It is desirable to add in the range of not more than%. It is preferably 1 to 10%. In addition, the individual addition amount of each element corresponding to V equivalent: 15% is Mo: 10%, Cr: 6.3%, Fe: 4
%, Ni: 9%, W: 25%.

Compositions other than the above are Ti and inevitable impurities. In addition, there are N, H, etc. as unavoidable impurities,
For example, a total amount of 1% or less is acceptable. In particular, it is preferable to limit H: 0.05% or less and N: 0.1% or less for reasons of room temperature ductility.

The high corrosion resistance and high rigidity Ti alloy of the present invention having the above composition has the high rigidity proposed by Japanese Patent Application No. 4-212880.
It is possible to further improve and improve the corrosion resistance while maintaining the high rigidity characteristic of Ti alloy. Therefore, for example, it is suitable as a material for a shaft of a turbine or a shaft of a chemical agitator used in a corrosive environment. Next, a method for producing a titanium alloy according to the present invention will be described.

Ti sponge which is a melting material, pure Al, electrolytic S
n, Zr sponge, pure Hf, Al-V master alloy, Al-Mo master alloy,
And Cr, V, pure Ni, pure W, pure Co, and platinum group elements
(For example, pure Pd and / or pure Ru) are individually selected and mixed in a predetermined amount, and in order to crystallize / precipitate and disperse a metal boride for improving Young's modulus,
A low melting point Al boride (melting point 1720 ° C) and / or Fe boride (melting point 1650 ° C) is mixed as a B source in the raw material, which does not easily cause unmelting, and then non-consumable electrode melting such as arc melting or VAR It may be alloyed as a melt by melting. The amount of oxygen can be adjusted depending on the type of Ti sponge, but if a large amount is added, TiO ₂ may be used.

When TiB ₂ is used as the B source, the melting point is 3225 ° C., so that it becomes unmelted in VAR melting, and there is a problem in melting such as side arc generation. Further, even when the non-consumable electrode is melted, TiB ₂ may be undissolved, and a good quality ingot in which crystallized substances and / or precipitates of metal borides are dispersed cannot be obtained. Also, B alone has a melting point of 2100.
C. and similar problems may occur. Therefore, when using these, it is necessary to use a melting method having higher energy, such as electron beam melting.

Therefore, in the case of VAR melting, by using at least Al boride and / or Fe boride as a raw material for melting the B source, the metal boride is uniformly crystallized in the matrix after solidification and cooling after melting. Eject and / or precipitate. The dispersed particles have a matrix density (approximately 4.
Since it is almost equal to 5), segregation etc. does not occur, and it is extremely uniformly dispersed. Furthermore, since such metal borides are dispersed particles that have been crystallized and / or precipitated, the particles produced are extremely stable, and even when heat treatment such as hot working or heat treatment is performed, the particles between the matrix and the metal borides are It does not cause a reaction layer and does not deteriorate the alloy.

The alloy ingot thus produced can be hot-worked at a temperature of, for example, 1000 to 1200 ° C. to be a forged or rolled material. Further, it is possible to adjust mechanical properties to desired values by heat treatment such as annealing.
Further, the present invention will be described in detail with reference to examples, but this is an example of the present invention and the present invention is not limited thereto.

[0035]

EXAMPLES Ti alloys having the compositions shown in Tables 1-1 and 1-2 were melted twice by a melting method using a small VAR apparatus having a capacity of 15 kg to prepare an ingot having a diameter of 140 mm and a length of 220 mm. The raw materials used are Ti sponge, Zr sponge, electrolytic S
n, Al-V mother alloy, Al-Mo mother alloy, pure Al, pure Hf, pure Cr, A
l Boride powder, Fe boride powder, Pure Ni, Pure W, Pure Pd,
It was pure Co.

In order to disperse the metal boride in the matrix, titanium boride powder was used for VAR dissolution, but the titanium boride powder was not dissolved in the ingot and a uniform ingot was obtained. There wasn't. Table 2-
1 and No. 1 to No. 37 in Table 2-2 are examples of the present invention, No. 3
8 to No. 48 are comparative examples, and No. 49 to No. 51 are conventional examples of existing α, (α + β) and β type alloys.

The ingot obtained in this manner is used for 1150
A bar material having a diameter of 30 mm and a length of 4500 mm was obtained by heating to ℃ and forging and hot rolling between 1200 and 900 ℃.
Regarding the test materials in which cracking occurred due to hot working at this time, the hot workability was considered to be poor, and “X” is shown in Table 2-1 and Table 2-2.

Each of the test materials obtained in this manner was 950
After heat treatment of ℃ × 1hr → AC, diameter 6 × distance between gauges 30 (m
m) tensile test piece, Young's modulus measurement test piece of 12 mm diameter x 150 mm length, hydrochloric acid corrosion test piece of 10 mm x 20 mm x 20 mm,
Hot upsetting test pieces having a diameter of 8 mm and a length of 12 mm were collected and subjected to various tests.

The outline of each test is as follows. Tensile test: A normal temperature tensile test method was used. Young's modulus measurement: E = 4 ρL ² f ² (L:
The Young's modulus was obtained from the length of the sample, ρ: bulk density, f: resonance frequency.

Hydrochloric acid corrosion test: The corrosion weight loss was measured by immersing in a 5 wt% HCl boiling solution for 20 hours, and the corrosion weight loss was converted into mm / year to evaluate the corrosion resistance. Hot upsetting test: This is a test for grasping hot workability. A test piece with a diameter of 8 mm and a length of 12 mm is 1.
Two levels of compression tests of 70% and 85% were performed at a strain rate of ⁰ sec ^-1 , and those with no cracks at 70% compression were marked with "○", and those without cracks even at 85% compression were marked with "◎" Table 2 -1 and Table 2-2.

Table 1-1, Table 1-2, Table 2-1 and Table 2
-2, the inventive examples have a higher Young's modulus and excellent corrosion resistance as compared with the conventional examples (Nos. 49 to 51). No.19 ~ 25,
When β-phase stabilizing elements such as Cr, V, and Mo are added as in No. 34 and No. 35, effects such as improvement of room temperature strength and improvement of hot workability are recognized.

Further, No. 15 to 18, No. 25, No. 33 and
It can be seen that the high temperature strength is improved by adding Sn, Zr and Hf as in No.35. On the other hand, if the composition is out of the range of the present invention, the Young's modulus decreases, for example, No. 38, No. 42, No. 43 and No. 46, and the corrosion resistance decreases as No. 48. No.39 to 41, No.44, No.45 and No.47
As described above, the bar cannot be manufactured due to its poor hot ductility.

[0043]

[Table 1-1]

[0044]

[Table 1-2]

[0045]

[Table 2-1]

[0046]

[Table 2-2]

[0047]

As described in detail above, according to the present invention,
A Ti alloy having extremely high rigidity and corrosion resistance while maintaining sufficient mechanical strength and hot workability is provided. Therefore, for example, the Ti alloy can be applied to mechanical parts such as a shaft of a chemical stirrer and a shaft of a turbine that require high rigidity in a corrosive environment.

Claims (6)

[Claims] 1. By weight%, Al: 5.5-10%, B: 0.5-
3.0%, O: 0.25% or less, one or two or more platinum group elements: 0.005 to 0.25% in total, with an alloy composition consisting of the balance Ti and unavoidable impurities, and a metal boride crystal in the Ti alloy matrix. A high-corrosion-resistant, high-rigidity Ti alloy characterized by being formed and / or precipitated. 2. The high corrosion resistance and high rigidity Ti alloy according to claim 1, wherein the alloy composition contains one or two kinds of Ni and Co: 0.1 to 5.0% by weight in total. 3. The alloy composition further comprises Sn, Zr and
One or more selected from the group consisting of Hf: in total
The high corrosion resistance and high rigidity Ti alloy according to claim 1 or 2, wherein the Ti alloy contains 20% by weight or less. 4. The alloy composition according to claim 1, further comprising one or more β-phase stabilizing elements in an amount of 15% by weight or less in V equivalent determined by the following formula. Item 5. A highly corrosion-resistant and highly rigid Ti alloy according to any one of Items 3. [Equation 1] V equivalent = V + (15/10) Mo + (15 / 6.3) Cr + (15/4)
Fe ＋ (15/9) Ni ＋ (15/25) W 5. The β-phase stabilizing element is one or more of V, Mo and W, and the V equivalent is 0.05 to 15% by weight.
The high corrosion resistance and high rigidity Ti alloy according to claim 4. 6. A smelting process using at least Al boride and / or Fe boride as a B source in a raw material, and crystallizing and / or precipitating a metal boride in a Ti alloy matrix during solidification or heat treatment. High corrosion resistance and high rigidity Ti according to any one of claims 1 to 5.
Alloy manufacturing method.