JP3076696B2 - α + β type titanium alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an α + β type titanium alloy.

[0002]

2. Description of the Related Art Titanium alloys having characteristics of light weight and high strength have been widely used in the space and aircraft fields. Especially Ti-6
Α + β type titanium alloy represented by Al-4V has strength,
It has well-balanced mechanical properties such as ductility and toughness, and has been used particularly frequently among titanium alloys. In recent years, research and development to apply the α + β type titanium alloy having excellent material properties to automobile parts and the like have been actively conducted. However, most of the existing α + β type titanium alloys are Ti
-6Al-4V is an Al-V titanium alloy using expensive V as an alloy element, as a result,
There was a disadvantage that the price of the alloy was significantly increased. Further, Ti-6Al-4V is inferior in hot and cold workability, and has a disadvantage that the production cost is further increased.

In order to make up for this drawback, Al-Fe based titanium alloys in which expensive V is replaced by Fe which is inexpensive and improves hot workability have been studied. For example, in 1984, Deutsche Gesellsch
`` Titanium Science an published by aftfur Metallkunde EV
d Technology "on page 1335.
Fe and “Advanced Materials & Pro” published in 1993.
cesses ", p. 43, Ti-6Al-1.7Fe-
Like 0.1Si, the fatigue characteristics required for reciprocating / rotating parts such as automobile engine parts are Ti-6Al-
An alloy having a hot workability equal to or higher than 4V and superior to Ti-6Al-4V has been devised. However, these alloys have better hot workability than Ti-6Al-4V, but have a slightly lower hot deformation resistance.
It cannot be said that it is particularly excellent, and the cold workability is insufficient, and it has been desired to provide more excellent workability.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a conventional Al
An object of the present invention is to provide a titanium alloy having the same fatigue strength as that of an Fe-based titanium alloy and a higher hot or cold workability.

[0005]

[MEANS FOR SOLVING THE PROBLEMS]
The present invention provides (1)In mass%,1.4% or more and not 2.1%
Full Fe, Al of 4.4% or more and less than 5.5%, and residual titanium
Α + β type titanium alloy consisting of
(2) A part of Fe of the alloy according to the above (1) isIn mass%,
Less than 0.15% Ni, less than 0.25% Cr, 0.2
Α + β-type titanium alloy replaced by at least one of Mn of less than 5%
Gold, (3)In mass%,0.05% or more and 0.25%
(1) and (2), which further contain less than
Α + β type titanium alloy described above. Here, the impurity is
It cannot be removed in processes such as refining, melting, spreading and heat treatment.
Or a small amount of elements mixed in these processes
0.1% or less of C, N, H, 0.3% or less of O, etc.
Corresponds to this.

[0006]

The present inventors have conducted intensive studies on the effects of Al and Fe on the workability and fatigue properties of titanium alloys. As a result, as the addition amount of Al or Fe increases,
At room temperature, the tensile strength increased, but the fatigue strength was found to be hardly affected by the amount added above a certain amount. That is, when a certain amount or more of Al is added, the room temperature tensile temperature increases as the amount of Al added increases, but the fatigue strength hardly increases.
When Fe exceeds a certain amount, the tensile strength increases as the amount of Fe added increases, but the fatigue strength hardly increases.

The reason is as follows. Al strengthens the α phase, but on the other hand induces a smooth local slip, where fatigue cracks tend to occur, leading to early fracture.
Therefore, even if the tensile strength increases, the fatigue strength does not increase much. In particular, in a titanium alloy containing less than a few% of Fe, the occurrence of the local slip is 5.5% or more of A
Occurs frequently in alloys containing l.

On the other hand, in a titanium alloy containing Al, when the amount of Fe is increased, the ratio of the β phase increases and the ratio of the α phase relatively decreases. Since Al is an element that is concentrated in the α phase, α
When the phase is reduced, Al is concentrated in the α phase and local slip is induced. Therefore, even if the tensile strength is increased, the fatigue properties are not improved. Such a phenomenon occurs when the amount of Fe added is 2.1%.
It becomes remarkable when it exceeds.

[0009] As described above, from the viewpoint of fatigue characteristics, it is necessary to set 5.
The addition of 5% or more of Al and 2.1% or more of Fe means that more alloy elements are added than necessary.
In addition, it is generally known that Al deteriorates hot and cold workability, and it is desirable that the amount of Al added is small in order to improve hot and cold workability. In addition, the lower the amount of Fe added, the lower the room temperature tensile strength, the higher the ductility, and the better the cold workability.

However, when the amount of Al added is less than 4.6 % or the amount of Fe added is less than 1.4%, local slip hardly occurs, but the tensile strength at room temperature becomes small, so that slip deformation occurs. Readily occur, resulting in reduced fatigue properties. For the above reasons, 1.4% or more and less than 2.1% of Fe, 4.6 % or more and less than 5.5% of Al
, It is possible to produce a titanium alloy having the same fatigue strength as that of a conventional Al-Fe-based titanium alloy and higher hot and cold workability.

In the present invention 2, a part of Fe of the alloy described in the present invention 1 is reduced to less than 0.15% of Ni, 0.25%.
% Or less of Mn and less than 0.25% of Mn. In this method, a part of Fe is replaced with an element which is inexpensive and has a function similar to that of Fe if the amount is small. Here, the upper limits of the added amounts of Ni, Cr, and Mn are 0.15%, 0.25%, and 0.25%, respectively.
The reason is that if these elements are added at or above the indicated upper limit, the intermetallic compound phase (Ti2Ni, T
iCr2, TiMn) is easily formed, which causes an extreme decrease in fatigue strength and cold workability. Also, N
The total amount of i, Cr, Mn, and Fe is 1.4% or more and 2.1%
Must be less than.

The reason for this is the same as in the case where Fe alone is added. If it is less than 1.4%, the tensile deformation at room temperature becomes small, so that slip deformation easily occurs, and as a result, the fatigue characteristics are reduced. The reason is that, when the total amount is less than 2.1%, sufficient fatigue strength has already been obtained, and even if it is further added, the fatigue strength is not so much improved, and further addition is useless. In addition, ductility is reduced by an increase in room temperature tensile strength, and as a result, cold workability is reduced.

According to the third aspect of the present invention, 0.05% or more of 0.1% or more is used.
Less than 25% of Si was added to the alloys of Inventions 1 and 2. In general, it is known that a small amount of Si improves the creep characteristics of a titanium alloy, and the creep characteristics of the alloys described in Inventions 1 and 2 are also improved by the addition of Si. However, the effect does not appear unless 0.05% or more is added, and if 0.25% or more is added, Ti
And a compound phase of Si precipitate at the interface between the α phase and the β phase, and the fatigue properties and cold workability are significantly reduced.

[0014]

EXAMPLE An ingot having the components shown in Table 1 was produced in an amount of about 5 kg using a plasma melting furnace, which was further heated at 900 ° C.
It was rolled into a wire having a diameter of 12 mm, air-annealed at 750 ° C. for 1 hour, and air-cooled. Using a test piece cut from this wire, a room temperature tensile test, a cold rolling test, a high temperature high speed tensile test, a rotating bending fatigue test, and a creep test were performed.

The cold workability is a limit cold rolling rate at which porosity is generated in a sample, the hot workability is a reduction value at 900 ° C., and the fatigue property is that the material breaks even after 1 × 10 ⁷ repetitions. The strength that did not exist was defined as fatigue strength, and the creep properties were evaluated by the amount of strain when a load of 540 MPa was applied at 400 ° C. for 300 hours. All tests were performed in air, and the room temperature tensile test was performed at a strain rate of 1 × 10 −4.
The s ^-1 high-speed high-speed tensile test was performed at a strain rate of 5 s ^-1 .
The cold rolling was performed using a high-speed roll of 180 mm in diameter at a rolling reduction of 5% per pass. Table 2 shows various test results of the samples shown in Table 1.

[0016]

[Table 1]

[0017]

[Table 2]

Test Nos. 1 and 2 have compositions similar to typical Al-Fe-based titanium alloys described in the section of "Prior Art" and correspond to conventional examples. Both have a high room temperature tensile strength of 990 MPa or more and a high fatigue strength of 500 MPa or more, but can only perform cold rolling at a rolling reduction of 10% or less. %, The hot workability is insufficient.

On the other hand, Test Nos. 3, 5, 6, and 8, which are Examples of the present invention 1, all have a room temperature tensile strength of 99.
Although it is a low value of 0 MPa or less, the fatigue strength shows a high value of 500 MPa or more.
Is equivalent to This is because local slip, which causes fatigue cracking, was suppressed by specifying the amounts of Al and Fe to be added.

In addition, each of these samples has a critical cold rolling reduction of 15% or more and a hot drawing of 70% or more.
It also has high cold and hot workability. This is due to the effect of improving the hot and cold workability by specifying the amount of Al added, and the effect of increasing the ductility and improving the cold workability by designing the low room temperature tensile strength. .

However, on the other hand, Test No. 4 which is a comparative example,
7 has a low fatigue strength of 500 MPa or less,
Test No. 9 is inferior in cold and hot workability. This is because, in Test Nos. 4 and 7, the amounts of Al and Fe added were lower than the ranges of the present invention 1, so that the room temperature tensile strength was reduced and slip deformation was easily caused, and as a result, the fatigue properties were reduced. In Test No. 9, the hot and cold workability was reduced because the amount of Al added was larger than the range of the first invention.

In Table 1, test numbers 10, 1
Nos. 2, 14, 16, and 18 represent a part of Fe as Ni, Cr, Mn.
This is an example of the second embodiment of the present invention. Table 2
As shown in Table 2, each of them has a high fatigue strength of 500 MPa or more, a high critical cold rolling reduction of 15% or more, and a hot drawing of 70% or more. It is an excellent material. In this way, a part of Fe
i, Cr, Mn can be substituted, but Ni, C
r and Mn are added in amounts of 0.15%, 0.25%,
When it is 0.25% or more, fatigue strength and cold workability are reduced as in Test Nos. 11, 13, and 15.

This is because, when added above the indicated upper limit, the intermetallic compound phases (Ti ₂ Ni, TiCr ₂ , T
iMn), resulting in an extreme decrease in fatigue strength and cold workability. Test No. 17 has a very high tensile strength at room temperature, but has a fatigue strength of Test No. 16
Is equivalent to When the total amount of Fe, Cr, Mn, and Ni exceeds the upper limit of 2.1% of the present invention 2, the tensile strength at room temperature is increased, but the fatigue strength is not so much improved. The addition is useless.

In addition, the ductility at which the tensile strength at room temperature is increased is reduced, and the cold workability is significantly reduced. In Test No. 19, the fatigue strength was a low value of 500 MPa or less. This is because the total amount of Fe, Cr, Ni, and Mn was lower than the lower limit of the present invention 2, and the room temperature tensile strength was low. Sliding deformation easily occurs, and as a result, fatigue properties are reduced.

Test Nos. 21 and 22 are examples of the present invention 3 in which Si is added for the purpose of improving the creep characteristics of Test No. 3. As shown in Table 2, the creep characteristics are improved as compared with Test No. 3, and have the same creep resistance as Test No. 2 in which 0.1% of Si is added in the conventional example.

However, Test No. 20, in which the amount of Si added was less than the range of the present invention 3, showed almost no effect of improving the creep characteristics, and Test No. In No. 23, the compound phase of Ti and Si precipitates at the interface between the α phase and the β phase, and the fatigue properties and the cold workability are significantly reduced. Test No. 24 is an example in which Si was added to improve the creep properties of Test No. 16, but the creep properties were improved while maintaining excellent fatigue properties, cold workability, and hot workability.

[0027]

According to the present invention, the conventional A
It is possible to produce a titanium alloy having the same fatigue strength and creep resistance as an l-Fe titanium alloy, and having a high hot or cold workability equivalent to or higher than that.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-308052 (JP, A) JP-A-4-358036 (JP, A) JP-A-5-209251 (JP, A) JP-A-2- 22435 (JP, A) JP-A-4-202729 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 14/00

Claims (3)

(57) [Claims] An α + β-type titanium alloy comprising 1.4% or more and less than 2.1% of Fe, 4.6 % or more and less than 5.5% of Al, the balance of titanium and impurities by mass% . 2. A part of Fe, in mass%, is less than 0.15% Ni, less than 0.25% Cr, less than 0.25% M.
2. The α + β titanium alloy according to claim 1, wherein at least one of n is substituted. 3. The α + according to claim 1, further comprising Si in an amount of 0.05% or more and less than 0.25% by mass%.
β type titanium alloy.