JP2001158931A - Cr BASE HEAT RESISTANT MATERIAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a heat resistant material having high strength at higher temperature compared to the case of a material used as the conventional heat resistant material and moreover having toughness higher than that of ceramics. SOLUTION: This Cr base heat resistant material is obtained by melting and solidifying a raw material mixture prepared in such a manner that B and Re are added to Cr, and the composition after the melting and solidifying is controlled to the one of 5 to 30 mol% B, 5 to 35 mol% Re, and the balance Cu and has a composite structure of a Cr phase in which Re is entered into solid solution and a Cr2B phase in which Re is entered into solid solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant material used for gas turbines, boilers, etc., which require performance such as strength, toughness (ductility), creep resistance, oxidation resistance, and high temperature corrosion resistance (corrosion resistance). High-temperature structural materials).

[0002]

2. Description of the Related Art Conventional heat-resistant materials (high-temperature structural materials) include metals represented by iron and Ni and ceramics represented by alumina and silicon nitride. The former metal material has high strength and high toughness, but is generally inferior to ceramics such as alumina and silicon nitride in terms of oxidation resistance and corrosion resistance, and the latter has high strength, oxidation resistance and corrosion resistance. However, there is a problem that it lacks toughness. Among the metallic materials, a Ni-based superalloy is a representative high-temperature structural material. This material has a good balance of strength (particularly high-temperature strength), toughness, creep resistance, oxidation resistance, and corrosion resistance, and is often used for high-temperature structural members such as gas turbines and boilers that require these characteristics. . In recent years, to further improve energy conversion efficiency,
There is a strong demand for higher service temperatures of materials. In gas turbines and the like, the melting point of Ni-based superalloys (about 1300
Air cooling or the like has been devised so that it can be used at an ambient temperature of 1500 ° C. exceeding 1500 ° C.). However, at present, the Ni-based superalloy can no longer respond to the demand for further improvement of the service temperature.

Therefore, use of a material having a higher melting point than that of a Ni-based superalloy can be considered. For metals, W (melting point about 3380
C) and Mo (melting point: about 2630 ° C.), but most of the high melting point metals have poor oxidation resistance and cannot be used. There are Cr (melting point about 1890 ° C) and Pt (melting point about 1770 ° C) as oxidation resistant high melting point metals, but these are low in strength in a single phase, exhibit low temperature brittleness, and are expensive. Is one of the issues. Nevertheless, with respect to Cr which is cheaper than Pt, several heat-resistant alloys have been developed as disclosed in, for example, JP-A-8-291355 and JP-A-9-3583. However, these Cr-based heat-resistant alloys are single-phase, have low strength, and have insufficient oxidation resistance and corrosion resistance. Other high melting point materials include ceramics such as alumina and silicon nitride, but as described above, poor toughness is a major problem. Cermet, which is a composite material of metal and ceramics, attempts to take advantage of the advantages of metal and ceramics, and most of them are manufactured by a powder sintering method. However, when the cermet material produced by the powder sintering method has a large number of grain boundaries and is used at a high temperature, there is a problem that grain boundary slip occurs and creep resistance cannot be sufficiently exhibited.

[0004]

SUMMARY OF THE INVENTION In view of the state of the art, the present invention provides a heat resistant material which has higher strength at higher temperatures than metal materials used as conventional heat resistant materials and has higher toughness than ceramics. It is an object of the present invention to provide a heat-resistant material having excellent creep characteristics.

[0005]

According to the present invention, (1) B and Re are added to Cr and the composition after melt-solidification is B: 5 to 30.
Mol%, Re: 5-35 mol%, and a composite of a Cr phase in which Re is dissolved and a Cr ₂ B phase in which Re is dissolved, obtained by melting and solidifying a raw material mixture prepared so that the remainder is Cr. And (2) the composite structure is a structure in which a Cr phase in which Re is dissolved and a Cr ₂ B phase in which Re is dissolved are oriented in one direction. (1) The Cr-based heat-resistant material according to the above (1).

The present inventors first added B (boron) to oxidation-resistant Cr, one of the refractory metals, and melt-solidified the Cr and Cr ₂ B phases to solve the above-mentioned problems. Proposed a Cr-B-based melt-solidified material consisting of (Japanese Patent Application No. 10-541).
No. 54). The present invention is further based on the results of various studies on the improvement of the strength characteristics of the Cr-B-based melt-solidified material, and by adding Re (rhenium) to the Cr-B-based melt-solidified material, It is a solution to the problem.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION From the Cr-B binary phase diagram,
And Cr ₂ B (corresponding to Cr-33.3 mol% B) have a eutectic reaction, and the material obtained by melting and solidifying the eutectic composition is a layered material composed of a Cr phase and a Cr ₂ B phase. Alternatively, a complex structure unique to a rod-shaped eutectic system is formed. When an appropriate amount of Re was added to this system, Re partially dissolved in the Cr ₂ B phase, but mainly dissolved in the Cr phase, and the Cr phase in which Re was dissolved and Re was substituted and dissolved in part of Cr. A composite material comprising the Cr ₂ B phase is obtained.

[0008] The amount of B to be added is preferably 5 to 30 mol%, more preferably 10 to 20 mol%, and most preferably 13.5 mol% which is a eutectic composition from the viewpoint of homogeneity of solidified structure.
It is. When importance is placed on the strength and hardness of the material, the addition amount thereof may be larger than 13.5 mol% so that the volume fraction of the hard phase, Cr ₂ B phase, increases. When emphasis is placed on ductility, the addition amount is 13.
It may be 5 mol% or less. However, when the content exceeds 33 mol%, the Cr phase disappears, and Cr ₂ B, Cr ₅ B ₃ and Cr
Since a structure consisting of a hard and brittle chromium boride phase such as B is formed and ductility (toughness) which is one of the important properties of the structural material is impaired, the amount of B added is limited to about 30 mol%. When emphasis is placed on ductility, the amount of B added may be reduced so that the volume fraction of the Cr ₂ B phase is reduced. However, if the amount of B is small, the effect of the Cr ₂ B phase acting as a strengthening phase is small, so it is preferable that the amount is about 5 mol% or more.

If the amount of Re added is too large, Cr
About 35 mol% from forming a Re-based compound
Is the limit. Further, if the addition amount is small, there is no effect of improving the strength properties, so the addition amount is desirably 5 mol% or more.

[0010] The Cr-based heat-resistant material of the present invention, Cr-Re
The method for producing the -B-based melt-solidified material may be any method as long as it goes through a melt-solidification process. As B and Re to be added to Cr, in addition to pure B lump and pure Re powder, Cr-B-based compounds such as CrB, Cr ₂ B and CrB ₂ and Re ₃ B, Re ₇ B ₃ , ReB _{2 and the} like Re-B
A series compound can also be used.

In the Cr-Re-B-based melt-solidified material of the present invention, the creep characteristics can be further improved by orienting the constituent phases, Cr phase and Cr ₂ B phase, in one direction. Examples of a method for orienting the tissue include a unidirectional solidification method such as a Bridgman method, a Czochralski method, and a floating zone melting method, but these methods are not limited thereto.

[0012]

EXAMPLES Hereinafter, the effects of the present invention will be demonstrated by specific examples of the present invention. (Example 1) The composition was Cr-26.0 mol% Re-13.
A mixture of Cr, B and Re so that the content becomes 5 mol% B
A melt-solidified material was produced by an arc melting method in an r atmosphere. In this example, pure B lumps and pure Re were added to B and Re additions.
Powder was used. FIG. 1 shows a typical structure photograph of the obtained melt-solidified material. The constituent phases are mainly Cr and C by X-ray diffraction.
It could be confirmed that it consisted of r ₂ B phase. Analysis by EPMA confirmed that Re was present in both the Cr phase and the Cr ₂ B phase, but it was confirmed that Re was mainly present in the Cr phase. The proportion of Re present in the Cr phase was about 35 mol%. From these results, in the structure photograph of FIG. 1, the bright contrast portion is the Cr phase in which Re is dissolved, and the dark contrast portion is the Cr ₂ B phase in which Re is dissolved. A bending test piece was processed from the molten and solidified material, and a bending test was performed at room temperature. As a comparative material, a melt-solidified material produced under the same conditions with a composition of Cr-13.5 mol% B was used.

Table 1 shows the results of the bending test of the manufactured samples. The Cr-Re-B-based melt-solidified material of the present invention is twice as strong as the Cr-B-based melt-solidified material of the comparative material,
It is clear that the strength characteristics are improved by adding Re.

[0014]

[Table 1]

(Example 2) Cr-2 produced in Example 1
About 100 g of a melt-solidified material having a composition of 6.0 mol% Re-13.5 mol% B was inserted into an alumina tanman tube having an inner diameter of about 12 mm, and a temperature of 1850 ° C. and a holding time of 1 in an Ar atmosphere.
A rod-shaped melt-solidified material (ordinary solidified material) was produced under melt-solidification conditions at a time and a temperature-falling rate of 10 ° C./min. Similarly, C
About 100 g of the melt-solidified material of r-13.5 mol% B was inserted into an alumina protective tube having an inner diameter of about 11 mm, and this was fished in a vertical tubular furnace having a central maximum temperature of 1850 ° C and a temperature gradient of about 50 ° C / cm. It was lowered and moved downward from the upper part at about 30 mm / h to produce a unidirectional solidified material. The macrostructure of the normally solidified material is composed of equiaxed grains, and the microstructure within the grains is R
e had a structure in which a Cr phase and a Cr ₂ B phase in which a solid solution was formed were randomly oriented in a layered or rod shape. The macrostructure of the unidirectionally solidified material is composed of columnar crystal grains in which crystal grains are grown in the solidification direction, and the microstructure in the crystal grains is a structure in which the Cr ₂ B phase is oriented to some extent in the solidification direction (the longitudinal direction of the Cr ₂ B phase). Was a structure grown in the solidification direction at an aspect ratio of 2 or more). Further, creep test pieces were processed from two types of melt-solidified materials, and subjected to a creep test at a temperature of 950 ° C. and a stress of 400 MPa in the atmosphere.

Table 2 shows the creep test results of these two types of melt-solidified materials together with the test results of an example of the comparative material Cr-B-based directional solidified material and an example of the Ni-based superalloy. Both the Cr-Re-B type normal solidified material and the unidirectional solidified material produced in this example have a longer rupture time than the Ni-based superalloy and the Cr-B type unidirectional solidified material and are superior in creep characteristics. It is apparent that the creep characteristics have been improved by doing so. Further, it can be seen that the Cr-Re-B-based unidirectionally solidified material has a longer rupture time than the ordinary solidified material, and the creep characteristics are further improved by orienting the structure.

[0017]

[Table 2]

[0018]

The Cr-based heat-resistant material comprising a Cr-Re-B-based melt-solidified material according to the present invention is a Cr-B-based melt-solidified material which has higher strength and higher toughness than conventional metal materials and does not contain Re. It is a heat-resistant material that is more excellent in high-temperature strength and creep characteristics. Further, by orienting the Cr phase and the Cr ₂ B phase in which Re, which is a constituent structure, is dissolved in one direction,
Further, the creep characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a structural photograph of a Cr—Re—B-based melt-solidified material of the present invention obtained in Example 1.

Claims (2)

[Claims] 1. A raw material mixture prepared by adding B and Re to Cr and adjusting the composition after melt solidification to B: 5 to 30 mol%, Re: 5 to 35 mol%, and the balance to Cr. Characterized by having a composite structure of a Cr phase in which Re is dissolved and a Cr ₂ B phase in which Re is dissolved, obtained by
Base heat resistant material. 2. The Cr-based composite according to claim 1, wherein the composite structure is a structure in which a Cr phase in which Re is dissolved and a Cr ₂ B phase in which Re is dissolved are oriented in one direction. Heat resistant material.