JP2003064434A - Ti BASED HEAT RESISTANT MATERIAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Ti based heat resistant material which has excellent heat resistance. SOLUTION: This Ti based heat resistant material has a composition containing, by mass, 16 to 21% Nb, 10 to 16% Al, V or/and Mo by 2 to 7% in the total content of both and 0.03 to 1.0% Si, and the balance Ti with inevitable impurities. It is possible that a part of Nb is substituted with <=5% Ta, and the total content of Nb and Ta is 16 to 21%, and also, the total content of C, N and O contained as inevitable impurities is preferably controlled to <=0.10%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Ti-based heat-resistant material which is lightweight and has high strength and excellent heat resistance,
More specifically, Ti, which is superior in heat resistance to conventional Ti-based heat-resistant materials containing a Ti ₃ Al intermetallic compound as a base,
Base heat resistant material.

[0002]

2. Description of the Prior Art Near α type Ti alloys are lightweight and have high strength, and therefore, intake / exhaust valves for automobile engines, disks and blades for compressors for aircraft engines,
In addition, it is widely used as a material for various structural members that are required to have light weight and heat resistance.

However, the near α type Ti alloy has a service temperature of 5
The temperature is set to 0 to 600 ° C. For example, in the case of an automobile engine, using it for an exhaust valve whose operating temperature rises higher than that of an intake valve is necessary in the case of an automobile engine for a large vehicle whose temperature environment is relatively gentle. limited. As a material having higher heat resistance than this near α-type Ti alloy,
A Ti-based heat resistant material based on a TiAl intermetallic compound having a high service temperature of 800 to 900 ° C. is known.

However, there is a problem that this intermetallic compound is brittle at room temperature. Further, this intermetallic compound is poor in hot workability, and when manufacturing a structural member using this, it is difficult to carry out hot rolling, for example, and a casting method has to be adopted, so it was manufactured. There is a problem in the quality stability of the members. Thus, in recent years, Ti containing Ti ₃ Al intermetallic compound as a base has replaced TiAl intermetallic compound.
Base heat resistant materials are drawing attention as heat resistant materials.

The Ti-base heat-resistant material containing this Ti ₃ Al intermetallic compound as a base has a service temperature of about 800 ° C.
Although it is slightly lower than that of the TiAl intermetallic compound, it is significantly higher than that of the near α-type Ti alloy, and T
It is industrially useful because hot working, which is practically impossible with iAl metal compounds, can be performed (Japanese Patent Laid-Open No. 56-201).
No. 38).

[0006]

Recently, demands for improving high temperature strength of heat resistant materials have been increasing. The same applies to the Ti-based heat-resistant material containing the Ti ₃ Al intermetallic compound as a base. In order to meet the above-mentioned demands, the present invention aims to provide a Ti-based heat-resistant material based on a Ti ₃ Al intermetallic compound, which is superior in high-temperature strength and high-temperature creep strength to the conventional ones.

[0007]

In order to achieve the above object, in the present invention, Nb: 16 to 21% by mass,
Al: 10 to 16% by mass, V or / and Mo: 2 to 7% by mass in total of both, Si: 0.03 to 1.0% by mass, and the balance consisting of Ti and inevitable impurities. A featured Ti-based refractory material is provided.

In the Ti-based heat-resistant material, part of Nb may be replaced by Ta: 5 mass% or less, and the total amount of Nb and Ta may be 16 to 21 mass%. Further, in the Ti-based heat-resistant material, C contained as an unavoidable impurity
The total content of N and O is preferably 0.10% by mass or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION
₃ Al alloy designed so that Si exists in the matrix composed of Al intermetallic compound. One of the general methods for improving the high temperature creep strength is to strengthen the grain boundaries by forming grain boundary precipitates in the matrix. However, in that case, the grain boundary slip in the material is suppressed, and the Ti ₃ Al intermetallic compound, which originally has a lower room temperature ductility than the near α-type Ti alloy, is practically used because the room temperature ductility is reduced due to the suppression of the grain boundary slip. There is a possibility that it will not be a proper material.

Therefore, in the present invention, the design concept is to improve the heat resistance of the Ti-base heat-resistant material based on the Ti ₃ Al intermetallic compound by allowing Si to exist in the base. Si is Ti ₅ Si _{3 at the} grain boundary.
Although it is an element that produces, there is a tendency to segregate at the grain boundaries even in the solid solution state, and it has the effect of suppressing grain boundary slip and at the same time making the crystal grains finer.

That is, Ti ₃ Al containing Si
In the case of the intermetallic compound, even if the grain boundary slip is suppressed by the grain boundary strengthening, on the other hand, the ductility is improved due to the refinement of the crystal grains, and the decrease in the ductility of the material due to the grain boundary strengthening is compensated. Therefore, by adding Si to the material, it becomes possible to improve the high temperature tensile strength and the high temperature creep strength while maintaining the room temperature ductility.

The Ti-based heat-resistant material of the present invention was developed on the basis of the above design concept. In this case, a Ti ₃ Al metal compound as a base and Si existing in the base coexist. The composition is set as follows in consideration of the condition. Al: 10 to 16 mass% Al is a component necessary to generate a Ti ₃ Al intermetallic compound as a base, and its content is 10 mass%.
When the amount is less than the above, the amount of Ti ₃ Al intermetallic compound produced is small and the proportion of the near α-type Ti alloy in the material is large, so that the high temperature strength is lowered. Further, when the content exceeds 16 mass%, the amount of TiAl intermetallic compound produced increases and the hot workability decreases, so the content of Al is 10 to 10.
16% by mass. The preferable content rate of Al is 12.0.
˜15.0% by mass.

Si: 0.03 to 1.0% by mass Si is a component added to improve heat resistance such as high temperature strength and high temperature creep strength, but it also has an effect of refining crystal grains and has ductility. It is a component that also contributes to the improvement of. If the content is less than 0.03% by mass, the effect of improving heat resistance and ductility cannot be sufficiently obtained, and if it exceeds 1.0% by mass, the effects are saturated and Ti ₅ S
i ₃ intermetallic compounds are generated, which rather deteriorates heat resistance. Therefore, the Si content is 0.03 to
It is set to 1.0% by mass. The preferable content rate of Si is 0.0
It is 5 to 0.5 mass%.

Nb: 16 to 21% by mass Nb is a component added to stabilize the high temperature β phase of the Ti ₃ Al intermetallic compound and to secure the hot workability of the material. When the content rate is less than 16% by mass,
The above-mentioned effect cannot be sufficiently obtained, and when it exceeds 21% by mass, the amount of Ti ₃ Al intermetallic compound is relatively reduced and the high temperature strength is lowered, so that the Nb content is 1%.
6 to 21% by mass. The preferred Nb content is 1
It is 7.0 to 20.0 mass%.

V or / and Mo: 2 to 2 in total amount of both
Either 7 or 7% by mass of V and Mo is added. V
And Mo are components added to stabilize the high temperature β phase of the Ti ₃ Al intermetallic compound and to secure the hot workability of the material, and at the same time, are added to increase the high temperature creep strength. It is the ingredient to do. If the total amount of V and Mo is 2% by mass or less, the above-mentioned effects cannot be sufficiently obtained, and if it exceeds 7% by mass, Ti ₃ A is relatively produced.
Since the amount of 1-intermetallic compound produced is reduced and the high temperature strength is reduced, the total amount of V and Mo is set to 2 to 7 mass%. The preferable total amount of V and Mo is 2.0 to 5.0 mass%.

The Ti-based heat-resistant material of the present invention may further contain Ta in addition to the above components. In that case, the content rate is preferably set as follows. Ta: 5 mass% or less, and 16 to 2 in the total amount of Nb and Ta
1% by mass In the Ti-based heat-resistant material of the present invention, Ta can replace a part of Nb, stabilize the β phase which is a high temperature phase of the Ti ₃ Al intermetallic compound, and heat the material. It is a component added to ensure inter-workability. However, if its content exceeds 5 mass%, Ta is a heavy element,
Since the specific gravity of the material increases and weight segregation occurs during manufacturing, the Ta content is 5% by mass or less. In that case, Ta is an element that replaces a part of Nb, so Nb and T
The total amount of a is in the range of the Nb content when Ta is not added, that is, 16 to 21% by mass. In addition, the preferable content rate of Ta is 0.3 to 3.5 mass%.

Further, in the Ti-based heat-resistant material of the present invention,
It is preferable that the sum of the content rates of C, N, and O contained as unavoidable impurities is regulated as follows. C, N and O: The total amount of C, N and O is 0.10% by mass or less. C, N and O contained as unavoidable impurities respectively deteriorate the toughness of the Ti ₃ Al intermetallic compound, especially at low temperatures. Therefore, the total amount of C, N and O is 0.10% by mass.
It is regulated below. Specifically, the content ratios of these components can be regulated by selecting blended raw materials, for example, sponge Ti.

Although C, N and O are unavoidable impurities, if it is possible to remove any one or more of them from the material, the removable element is Of course, you can remove it.

[0019]

EXAMPLES Examples 1-9, Comparative Examples 1, 2 T having the chemical composition shown in Table 1 by a levitation furnace
An i alloy ingot was melted. Temperature 1 for each ingot
After hot forging at 200 ° C to make a round bar with a diameter of 20 mm, this round bar was annealed at a temperature of 1000 ° C for 2 hours and then air-cooled, and then a tensile test piece (parallel part diameter 6.25 mm, between gauges) Distance of 25 mm) is cut into 3 pieces each at room temperature and 8
A tensile property test at 50 ° C. was performed.

After polishing and etching each test material, the structure of the matrix was observed with a metallurgical microscope. The above test results are summarized in Table 1. The values of tensile strength and elongation in the table are average values. From this table it is clear that:

[0021]

[Table 1]

1) Conventional near α-type Ti containing no Nb
Comparative Example 1, which is a 6242S-Ti alloy having an alloy base, is extremely inferior in tensile strength at 850 ° C. as compared with Examples 1 to 9 which include a Ti ₃ Al intermetallic compound as a base 2). Comparative Example 2, which has a chemical composition similar to that of Example 1 except that it does not substantially contain Si, is the same as Example 1
Compared with No. 9, both tensile strength and elongation at room temperature and 850 ° C. are inferior. 3) Examples 4 to 6 in which a part of Nb is replaced by Ta show equivalent tensile properties at room temperature and high temperature as compared with Examples 1 to 3. 4) Compared with Examples 1 to 6, Examples 7 to 9 in which the total amount of O, N and C is regulated to 0.10 mass% or less are particularly excellent in elongation at room temperature.

Examples 10 to 13 and Comparative Examples 3 and 4 In the same plasma melting furnace (PP), only the Si content was changed and the other components except Ti were kept in the same amount.
After melting in C), it is further melted in a vacuum arc melting furnace (VAR), and chemical composition: Ti-18.6% Nb-14.2% Al-3.0% V-
1.8% Mo-x% Si-0.05% O-0.01% C
-0.01% N (however, x: 0.01, 0.10, 0.18, 0.3
2, 0.70 and 1.51. ) Having a weight of 100
Six types of ingots having a weight of 240 kg and a diameter of 240 mm were melted.
This ingot was hot-forged at a temperature of 1200 ° C. to form a billet having a diameter of 80 mm, which was then cut and cared for.
It was hot rolled at 0 ° C. And the temperature of this round bar is 1000
After annealing for 2 hours at ℃ and air cooling, the rotating bending fatigue test piece and creep rupture test piece were machined and
Bending fatigue limit of 10 ⁷ times at 50 ° C and 730-8
The creep rupture property at 50 ° C. was measured.

The rotary bending fatigue test piece had a diameter of parallel portion of 8
mm, the parallel portion length was 22 mm, and the crepe breaking test piece had a parallel portion diameter of 6 mm. The measurement results are shown in FIGS.
The horizontal axis of the creep rupture characteristics in FIG. 2 is the following expression: LP = (T + 273) (20 + log (t)) (where T is the test temperature (° C.) and t is the creep rupture time (h)). Represented LP (Larson-Mil
It is a value obtained by dividing the (ler parameter) value by 1000.

From these results, the following is clear. 5) As shown in FIG.
Compared with Comparative Example 3 in which the Si content is low, room temperature and 8
The rotary bending fatigue limit at 50 ° C is improved. Especially, at a high temperature of 850 ° C., it is improved by about 10%, which is very useful as a heat resistant material. 6) As shown in FIG.
A solid line that approximately represents the relationship between the LP value and the stress at
When compared with Comparative Example 3 having a low Si content or Comparative Example 4 having a high Si content, the solid line of the example is located above the broken line of the comparative example, and the example is compared. Better creep rupture properties than the examples. Therefore, for example, under the same stress, the time required for creep rupture in the example is longer than that in the comparative example, and it is clear that the example is more useful as a heat-resistant material.

[0026]

As is apparent from the above description, the Ti-based heat-resistant alloy of the present invention has a limited chemical composition and contains an appropriate amount of Si, whereby the high temperature strength and high temperature creep strength are improved, Furthermore, the tensile properties and fatigue limit at room temperature and high temperature are also improved.

In the Ti-base heat-resistant alloy of the present invention, part of Nb may be replaced by Ta, and the total amount of C, N, and O contained as unavoidable impurities is regulated so that the temperature is particularly high at room temperature. Can improve the elongation at.

[Brief description of drawings]

FIG. 1 is a graph showing fatigue limit characteristics in Examples and Comparative Examples.

FIG. 2 is a graph showing high temperature creep rupture characteristics in Examples and Comparative Examples.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Michio Okabe             2-30, Daido-cho, Minami-ku, Nagoya-shi, Aichi             Daido Steel Co., Ltd. Technology Development Laboratory

Claims (3)

[Claims] 1. Nb: 16 to 21 mass%, Al: 10
16% by mass, V or / and Mo: 2 to the total amount of both
7 mass%, Si: 0.03 to 1.0 mass%, and the balance consisting of Ti and inevitable impurities, a Ti-based heat-resistant material. 2. The Ti-based heat-resistant material according to claim 1, wherein a part of Nb is replaced by Ta: 5 mass% or less, and the total amount of Nb and Ta is 16 to 21 mass%. 3. The Ti-based heat-resistant material according to claim 1, wherein the total amount of C, N and O contained as unavoidable impurities is 0.10 mass% or less.