JP3135691B2 - Low thermal expansion super heat resistant alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used as a composite material with gas turbine parts, ceramics and cemented carbide,
The present invention relates to a super heat-resistant alloy which is excellent in high-temperature strength and requires a low coefficient of thermal expansion.

[0002]

2. Description of the Related Art Conventionally, alloys for applications requiring a low coefficient of thermal expansion include Fe-36% Ni-based invar alloys and Fe-42% Ni.
There are known 42-based nickel alloys and Fe-29% Ni-17% Co-based Kovar alloys. Although these alloys have a low coefficient of thermal expansion, they have low strength at room temperature and high temperature, and therefore cannot be used for parts requiring strength.

[0003] On the other hand, an alloy having a coefficient of thermal expansion smaller than that of an ordinary austenitic alloy and having an increased high-temperature strength by adding a precipitation strengthening element such as Al, Ti, or Nb, though not as high as that of the above alloys. As
No. 67, No. 67, and a series of improved alloys of the Incoloy 903 alloy are disclosed in
-30729, JP-A-50-30730, U.S. Patent
4200459, JP-A-59-56563, JP-A-60-56
128243, JP-A-53-6225, JP-A-50
-30728, JP-B-63-43457, U.S. Patent
An alloy disclosed in, for example, Japanese Patent No. 4006011 is known.

[0004]

In recent years, as the operating temperature of gas turbine components has risen, the strength of the gas turbine components has been increased from room temperature to high temperature, and the clearance provided between various components and members has been maintained at a constant level from room temperature to high temperature. The demand for sustainable materials,
There is a tendency that demands for improving the bondability between low thermal expansion materials such as ceramics and cemented carbide and metal materials are increasing. One example of the application is a turbo collar for joining a shaft part and a wing part (usually ceramics) of a turbine rotor of an automobile. Other applications include parts such as gas turbine compressor cases, exhaust cases, and sealing materials; aluminum die-casting sleeves consisting of a ceramic inner cylinder and an outer cylinder made of a low thermal expansion super heat-resistant alloy; or a cemented carbide and base metal. As a cushioning material, there is a cemented carbide blade using a low thermal expansion super heat resistant alloy. Conventionally, Incoloy 903 disclosed in Japanese Patent Publication No. 41-2767 has been put to practical use to meet such needs.
No. 3 became a problem because it became clear that the notch sensitivity was significantly increased at an operating temperature of about 500 ° C. In fact, this kind of low-thermal-expansion super-heat-resistant alloy often has several stress-concentrated parts in practical products, and if the notch strength of that part is lower than the strength of the smooth surface, it will be longer than the designed fracture life. Will also result in significantly faster destruction. Such a decrease in notch strength is most sensitive at temperatures around 500 ° C. in this type of alloy, so in a 500 ° C. smooth-notch composite creep rupture test, the notch breaks earlier than the smooth part. Materials have extremely limited practical use conditions. Therefore, it is important that the notch rupture strength exceeds the smooth rupture strength in the 500 ° C. smooth-notch composite creep rupture test.

A series of improved alloys in this regard include:
JP-A-50-30729 and JP-A-50-3 mentioned above
No. 0730, U.S. Pat. No. 4,2004,591, JP-A-59-565.
No. 63, JP-A-60-128243, JP-A-53-6
No. 225, JP-A-50-30728, JP-B-63-4
No. 3457, U.S. Pat. No. 4,0060,11 and the like have been proposed, and among these improvements, Incoloy 909 has been put to practical use. Incoloy 909 is certainly Incoloy 9
03, the notch breaking strength is excellent, but 700 to 8
Instability of the tissue during high temperature heating at about 00 ° C,
Alternatively, there has been a problem that the age hardening property during short-time high-temperature heating, such as brazing treatment with ceramics or cemented carbide, is insufficient, and the hardness is insufficient. On the other hand, Cr addition has been studied as one of the techniques for improving the notch sensitivity of Incoloy 903, but F which has been conventionally studied has been studied.
In the e-Co-Ni matrix composition range, the addition of Cr unnecessarily increases the coefficient of thermal expansion, but cannot add a sufficient amount of Cr to improve notch sensitivity and oxidation resistance. It has not been converted.

[0006] In view of the above problems, the present invention provides a low thermal expansion super heat resistant alloy Incoloy 90 which has been put to practical use.
The present invention provides a novel low thermal expansion super heat resistant alloy having low thermal expansion properties at the same level as No. 3 or Incoloy 909 and having both high age hardening properties and notch breaking strength, which cannot be obtained with these alloys.

[0007]

Means for Solving the Problems In order to solve the above problems, the present inventor conducted experiments on Fe-Co-Ni alloys, and as a result, contributed to the improvement of age hardening property and the improvement of notch sensitivity. Has the optimum addition range of Cr and a low coefficient of thermal expansion comparable to that of the conventional alloy even by such addition of Cr.
In addition, an appropriate amount of La that helps refine the crystal grains and improve the notch strength
To find out the proportions of Fe, Co and Ni for precipitating the ves phase and the proper addition ranges of Ti, Nb and Al for precipitating a more stable and age-hardenable gamma prime phase,
As a result, the inventors have invented an alloy having both high high-temperature strength and a low coefficient of thermal expansion, which are not found in conventional alloys.

That is, according to the present invention, C 0.2%
Hereinafter, Si 1.0% or less, Mn 1.0% or less, Cr 0.5 to 4.0%,
Al 0.25-1.0%, Ti 0.5-2.5%, Nb 3.0-6.0%, B
0.02% or less, Ni is 24% or more and less than 30%, and Co is 20 to 28%, and the remainder is a low thermal expansion super heat resistant alloy characterized by being substantially composed of Fe, excluding impurities. At 0.1% or less, Si 1.0% or less, Mn 1.0% or less, C
r 0.5-4.0%, Al 0.25-1.0%, Ti 0.5-2.5%, Nb
One or two of Ta and Nb + 1 / 2Ta at 3.0 to 6.0
%, B 0.01% or less, Ni 27% or more and less than 30%, and Co 20
A low thermal expansion super-heat-resistant alloy consisting essentially of Fe except for impurities, and more desirably 0.1% or less of C, 1.0% or less of Si, and 1.0% or less of Mn in weight%. , Cr 0.5-2.95%, Al 0.25-1.0%, Ti 0.5-2.5
%, One or two of Nb and Ta are 3.0% by Nb + 1 / 2Ta.
6.0%, B 0.01% or less, Ni 27-29.8% and Co 20-2
It is a low-thermal-expansion super-heat-resistant alloy consisting essentially of Fe, containing 5% and the remainder excluding impurities.

[0009]

The reasons for limiting the components of the alloy of the present invention will be described below. C combines with Ti and Nb to form carbides and prevents coarsening of crystal grains and contributes to the improvement of strength. However, excessive addition exceeding 0.2% results in too much Ti and Nb carbides to strengthen precipitation. While reducing Ti and Nb acting as elements,
C is set to 0.2% or less to increase the coefficient of thermal expansion of the alloy. A desirable range of C is 0.1% or less.

[0010] Si is an essential additive element in addition to its effect as a deoxidizing agent, because it promotes the precipitation of a Laves phase useful for refining crystal grains and improving the grain boundary shape, but excessive addition exceeding 1%. Causes deterioration in hot workability and high-temperature strength, so 1.
Limit to 0% or less. Mn is included in the alloy because it is added as a deoxidizing agent, but excessive addition is undesirable because it increases the coefficient of thermal expansion of the alloy. Therefore, Mn is 1.0
% Or less.

In the present invention, Cr plays an important role in improving age hardenability and improving notch sensitivity. That is, Cr forms a solid solution in the matrix to promote the precipitation of the gamma-prime phase, which is a precipitation strengthening phase, so that sufficient strength can be obtained even by aging for a short time, and the crystal grain boundaries considered to be one of the causes of notch sensitivity. Increases oxidation resistance. For this purpose, Cr needs to be at least 0.5% or more. Excessive addition of more than 4% can reduce Fe, Co, and N constituting the matrix.
No matter how the ratio of i is adjusted, sufficient low thermal expansion characteristics cannot be obtained, so the content is limited to 0.5 to 4.0%. Desirable Cr
Ranges from 0.5 to 2.95%

Al is (Ni, Co) ₃ (Al, T
A fine gamma-prime phase having a composition of i, Nb) having a diameter of about several tens of nanometers is precipitated, and the high-temperature tensile strength is significantly improved.
When the concentration of Al in the gamma prime phase decreases, 700
At a high temperature of about 800 ° C., the gamma-prime phase becomes unstable, and a hexagonal η phase and an orthorhombic δ phase are precipitated, resulting in a decrease in strength at room temperature and high temperature. Therefore, in order to precipitate a stable gamma prime phase, A
l requires a minimum addition of 0.25% or more, but an excessive addition exceeding 1% precipitates a large amount of the gamma prime phase and lowers hot workability, so it is limited to 0.25 to 1.0%.

As described above, Ti and Nb first combine with C to form a carbide, and the remaining Ti and Nb combine with Al and Ni and Co together with Al to form a gamma prime phase as described below. To strengthen the alloy. Ti precipitates a gamma prime phase together with Ni, Co, Al, and Nb by aging treatment, and remarkably improves high-temperature tensile strength. The Ti content required for this is at least 0.5%, but excessive addition exceeding 2.5% destabilizes the gamma-prime phase, increases the thermal expansion coefficient and lowers the hot workability. 0.5-2.
Limited to 5%.

Similarly to Ti, Nb is Nb by aging treatment.
Precipitates a gamma prime phase together with i, Co, and Al, and significantly improves hot strength. Some Nb has a diameter of several μm
A small amount of Laves phase precipitates at the grain boundaries and inside the grains, enabling the crystal grains to be refined, and also has the effect of increasing the strength of the grain boundaries, significantly improving the high-temperature tensile strength and the notch creep rupture strength at around 500 ° C. Has the effect of causing. Therefore Nb is 3.0
% Or more, but excessive addition exceeding 6.0% increases the thermal expansion coefficient and decreases the hot workability, so
Nb is limited to 3.0 to 6.0%. Also, Ta is an element of the same family as Nb and has twice the atomic weight of Nb.
Substitution is possible in the range of + 1 / 2Ta ≦ 6.0.

B segregates at the crystal grain boundaries to increase the grain boundary strength,
Since it contributes to the improvement of hot workability and notch creep rupture strength at around 500 ° C, even a very small amount is effective. But 0.02
Excessive addition of B in excess of% results in the formation of a boron compound, conversely lowering the initial melting temperature of the alloy and impairing the hot workability, so is limited to 0.02% or less. Desirable range of B is
0.01% or less.

Ni forms a matrix together with Co and Fe, and the ratio of Fe to Co and Ni significantly affects the coefficient of thermal expansion of the alloy and the form of precipitation of intermetallic compounds. The alloy of the present invention contains a large amount of precipitation strengthening elements such as Ti, Nb and Al in order to provide the highest level of high-temperature strength among conventional alloys. It was found that both high temperature tensile strength and low coefficient of thermal expansion were compatible. Further, Fe, Co, and Ni of the alloy of the present invention are used.
With respect to the amount and ratio of the alloy, the precipitation amount of the fine spherical Laves phase is much larger than that of the conventional alloy, which is useful for strengthening the grain boundary and has the effect of increasing the notch creep rupture strength at around 500 ° C. The Ni amount required for that purpose is 24% or more. If the Ni content is less than 24%, the austenite phase becomes unstable, and the precipitation of the gamma prime phase becomes insufficient, whereby the aging response becomes dull and the high-temperature strength decreases. Conversely, Ni of 30% or more increases the coefficient of thermal expansion and reduces the amount of precipitation of the Laves phase, which makes it difficult to refine crystal grains and strengthen grain boundaries.
The object of the present invention cannot be achieved. Therefore, Ni is 2
It is important that it is 4% or more and less than 30%. A desirable Ni range is 27% or more and less than 30%, and more preferably 27 to 2%.
9.8%.

Co, like Ni, forms a matrix together with Fe, and serves to lower the coefficient of thermal expansion and precipitate the La-ves phase. Therefore, Co needs to be added in an amount of 20% or more.
Conversely, if Co exceeds 28%, the thermal expansion coefficient increases and the high-temperature strength decreases due to excessive Laves phase precipitation, so Co is set in the range of 20 to 28%. Desirable range of Co is 2
0 to 25%.

[0018]

【Example】

(Example 1) Table 1 shows the chemical compositions of the alloys of the present invention, comparative alloys and conventional alloys. The alloys of the present invention and conventional alloys are melted in a vacuum induction melting furnace to form a 10 kg ingot,
1150 ° C x 20hrs homogenization treatment, then heating temperature
The sample was forged at 1100 ° C. to obtain a 30 mm square sample. Thereafter, all the alloys except for the conventional alloy No. 21 were subjected to a solution treatment in which the alloy was kept at 982 ° C. × 1 hour and air-cooled, and a solution treatment in which No. 21 was kept at 930 ° C. × 1 hour and air-cooled.

[0019]

[Table 1]

The conventional alloy No. 21 is Incoloy 903, No.
22 is Incoloy 909, Incoloy 903 (No.
In the case of only 1), the recrystallization temperature of the alloy was low and crystal grains were easy to grow, so the solution treatment temperature was 930 ° C, which was lower than other alloys. The aging conditions were set at 850 to simulate practical bonding conditions for brazing with ceramics and cemented carbide.
After holding at 30 ° C. for 30 minutes, the furnace was cooled to 650 ° C. at a cooling rate of 100 ° C./h and air-cooled. This heat treatment is performed using the conventional Incoloy 903.
This is a high-temperature, short-time heat treatment as compared with the standard aging treatment of Incoloy 909 and Incoloy 909. Among the alloys shown in Table 1, the microstructure photographs of the alloy No. 4 of the present invention, the conventional alloys No. 21 and No. 22 after the heat treatment are shown in FIG. FIG. 1 shows that the alloy No. 4 of the present invention has fine crystal grains, and fine Laves phase is uniformly distributed in the grain boundaries and in the grains. On the other hand, in the conventional alloy No. 21 (Incoloy 903), although the solution treatment temperature was lowered, the crystal grains became coarse, and the precipitation of Laves phase like the alloy of the present invention was not observed in the grain boundaries and in the grains. I can't. In addition, in the conventional alloy No. 22 (Incoloy 909), a needle-like δ phase was observed in the grains in addition to a small amount of the Laves phase due to the high-temperature aging treatment. Sufficient tensile strength at normal and high temperatures cannot be obtained.

(Example 2) Table 2 shows the room-temperature tensile properties, 500 ° C tensile properties, and 500 ° C of the alloys of the present invention, comparative alloys and conventional alloys.
Smooth-notched composite creep rupture characteristics and 30 ° C to 400 ° C
The average thermal expansion coefficient up to is shown. Tensile test at room temperature, 500 ℃
In both cases, based on the test method specified by the ASTM method, the test was performed on a reduced tensile test specimen of A370 having a parallel portion diameter of 6.35 mm and a distance between gauge points of 25.4 mm. In addition, the smooth-notch composite creep rupture test was performed based on the test method specified in the ASTM method, and the diameter of both the smooth part and the notch part was 4.52 mm, and the distance between the gauge points of the smooth part was 18.08 mm.
453 No. 9 test pieces were used. Initial Stress at test temperature 500 ° C. is a No.21 and 22 only 50 kgf / mm ^2, and all other is 80 kgf / m
The test was conducted in the initial stress of m ^2. When the rupture time exceeded 200 hours, the stress was increased by 5 kgf / mm ² every 8 to 16 hours to force the rupture.

[0022]

[Table 2]

Table 2 shows the initial stress and the stress at the time of final rupture (in the column of rupture stress), the total test time up to rupture (in the column of rupture life), and the value of elongation when ruptured in a smooth part. In the case of breakage at the notch, the symbol "N" was described in the column of elongation. Measurement of thermal expansion coefficient is 5mm in diameter and 19.5m in length
The average coefficient of thermal expansion from 30 ° C. to 400 ° C. was determined using a test piece of m.

According to Tables 1 and 2, the alloys Nos. 1 to 9 and 31 to 35 of the present invention all have excellent tensile strength at room temperature and 500 ° C., and have a smooth-notched composite creep rupture at 500 ° C. In the tests, it can be seen that the notch strength exceeded the strength of the smooth portion, and that the breaking stress was high, in each case of breaking at the smooth portion. Further, in the average coefficient of thermal expansion from room temperature to 400 ° C., all of the alloys of the present invention show a value of 8.5 × 10−6 / ° C. or less, which is as low as that of the conventional alloys No. 21 and No. 22. It can be seen that they also have a coefficient of thermal expansion. On the other hand, the comparative alloy No. 10 is the alloy No. 9 of the present invention.
It is probable that despite the almost similar composition except that the Ni content was slightly higher at 30% or more as compared with, the Laves phase was insufficiently precipitated to cause breakage at the notch.

Comparative alloy No. 11 has a higher Ni and lower Co matrix composition than the alloy of the present invention.
Although the alloy contained in No. 25 has a high tensile strength at room temperature and high temperature with this composition, the Laves phase does not precipitate because the Ni / Co ratio is too high, and the crystal grains become coarse. Notch breakage occurs, and the coefficient of thermal expansion is inferior to that of the alloy of the present invention. Since the comparative alloy No. 12 has a composition that does not contain Cr with respect to the alloy of the present invention, the aging at high temperature for a short time does not sufficiently precipitate the gamma prime phase, and is inferior in strength to the alloy of the present invention. Further, since the intergranular oxidation resistance is lowered, a fracture occurs at the notch. Further, Comparative Alloy No. 13 has higher Cr than the alloy of the present invention, and provides good room-temperature and high-temperature tensile strength, but has too high a coefficient of thermal expansion.

Also, a conventional alloy No. 21 (Incoloy 903)
Although the same strength as the alloy of the present invention can be obtained only at room temperature and at a tensile strength of 500 ° C., the notch strength at 500 ° C. is extremely low. The notch sensitivity of No. 21 (Incoloy 903) is abnormally high because Nb is slightly low and the proportion of Fe, Co and Ni is not sufficient to cause precipitation of the Laves phase. It is considered that the cause is that the grain boundary strength is not sufficiently maintained. Conventional alloy No. 22 (Incoloy 909) is an alloy in which Al of No. 21 (Incoloy 903) is reduced and Nb is increased, and Laves has the same ratio of Fe, Co and Ni as No. 21. Precipitation of the phase occurs, and the notch rupture strength is certainly improved. But,
Since Al is not contained, a stable gamma-prime phase cannot be precipitated when high-temperature aging is performed, and the strength is clearly lower than that of the alloy of the present invention.

[0027]

When the alloy of the present invention is used for gas turbine parts, ceramic joint parts, cemented carbide joint parts, etc., it simultaneously satisfies high high-temperature strength and low thermal expansion characteristics which cannot be obtained with conventional alloys. Thus, it is possible to adapt to structural materials which require high strength from room temperature to high temperature and a constant clearance provided between various members and components from room temperature to high temperature. In addition, when joining a low thermal expansion material such as ceramics and cemented carbide to a structural material, a highly reliable and highly reliable joint can be obtained.

[Brief description of the drawings]

FIG. 1 is an optical microscopic microstructure photograph of an alloy No. 4 of the present invention, a conventional alloy No. 21, and a conventional alloy No. 22 after heat treatment.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Ide 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-2-70040 (JP, A) JP-A-4-218642 (JP, A) Special Table Hei 6-500361 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 30/00-30/06 C22C 38/00-38/58

Claims (2)

(57) [Claims] (1) In weight%, C is 0.1% or less, SI is 1.0%.
Below, Mn 1.0% or less, Cr 0.5 to 4.0%, Al 0.25 to
1.0%, Ti 0.5 to 2.5%, one or two of Nb and Ta
Seeds are 3.0-6.0% at Nb + 1 / 2Ta, B 0.01% or less, Ni 2
A low-thermal-expansion super-heat-resistant alloy containing 7% or more but less than 30% and Co of 20 to 25%, with the balance being substantially Fe, excluding impurities. 2. In % by weight, C: 0.1% or less, Si: 1.0%
Below, Mn 1.0% or less, Cr 0.5-2.95%, Al 0.25
-1.0%, Ti 0.5-2.5%, one or two of Nb and Ta are 3.0-6.0% by Nb + 1 / 2Ta, B 0.01% or less, Ni
A low-heat-expansion super-heat-resistant alloy containing 27 to 29.8% and 20 to 25% Co, with the balance being substantially Fe, excluding impurities.