JP2005314769A - Alloy material of high melting-point metal having high strength and high toughness due to carbonization, and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a Mo-based material obtained by a reported carbonization method is still insufficient in high temperature strength and toughness. <P>SOLUTION: The alloy material of a high melting-point metal having high strength and high toughness is produced by carbonizing a workpiece of the alloy material comprising one element among Mo, W and Cr as a parent phase, and at least one element among Ti, Zr, Hf, V, Nb and Ta as a dissolved metal; and includes carbon segregated in a grain boundary and carbide particles of a dissolved metal dispersedly precipitated in the matrix, by the carbonization treatment with the use of a carbon source containing oxygen gas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a high-temperature heat-resistant material, in particular, a carbide particle dispersion strengthened high-strength and high-toughness refractory metal-based alloy material having one of Mo, W and Cr as high-melting-point metals as a parent phase, and a method for producing the same About.

Currently, as a refractory metal-based heat-resistant alloy, Plansee TZM alloy (maximum operating temperature 1400 ° C) in which Ti, Zr, and C are added to Mo is used almost exclusively, but this alloy is difficult to process. It is.

Mo alloys, once heated above their recrystallization temperature (1000-1300 ° C.), are reproducible, resulting in low temperature brittleness and reduced strength at high temperatures. . As a method for strengthening the crystal grain boundary of the Mo-based material, the present inventors have reported a study on a carbonization treatment method in which a small amount of carbon is deposited and then carbon is diffused by vacuum heating (Non-Patent Document 1). ). In addition, the present inventors have reported a research on a material structure control and a toughening method by carbonizing a TZM alloy using dilute CO gas (Non-patent Document 2). In addition, the inventors
A study on the material structure when the recrystallized Mo-Ti alloy was subjected to CO gas heat treatment was reported (Non-patent Document 3).

Satoshi Hoshika et al. "Powder and Powder Metallurgy" 49 (2002) 32-36 Naoki Nomura et al. “Abstracts of the 2002 Fall Meeting of the Powder and Powder Metallurgy Association” (2002) 201 Naoki Nomura et al. “Abstracts of the 2003 Fall Meeting” (2003) 31

The Mo-based material obtained by the carbonization method reported by the present inventors is still insufficient in terms of high temperature strength and toughness.

For many years, the present inventors have conducted research on microstructure control and toughening by carbonization treatment of Mo-based materials, and show ductility that can withstand static bending at a low temperature of at least −100 ° C. The inventors have succeeded in developing a refractory metal alloy material having a high temperature strength at least twice as high as that of a commercially available pure Mo material.

That is, in the present invention, (1) one of Mo, W, and Cr is used as a parent phase, and Ti, Zr, H
A carbonized material of an alloy processed material in which at least one of f, V, Nb, and Ta is a solute metal, carbon segregated at grain boundaries by carbonization using a carbon source in which oxygen coexists, and dispersion A high-strength, high-toughness refractory metal-based alloy material characterized by containing precipitated solid solution metal carbide particles.

The present invention also provides (2) a high-strength, high-toughness refractory metal alloy material according to the above (1), wherein the surface portion of the alloy material maintains a processed structure and the inside is a recrystallized structure. It is.

The present invention is also characterized in that (3) Mo is a parent phase, Ti is a solute metal, and DBTT (ductility-brittle transition temperature) is −110 ° C. Refractory metal-based alloy material.

Furthermore, the present invention provides (4) one of Mo, W, and Cr as a parent phase, and Ti, Zr, Hf
(1) or (2), wherein carbonization using a carbon source in which oxygen coexists is performed in a multi-stage on an alloy processed material in which at least one of V, N, and Ta is a solid solution metal. ) For producing a refractory metal alloy material.

In the present invention, (5) the first stage carbonization treatment is performed at a temperature lower than the recrystallization upper limit temperature of the alloy processed material and at a temperature lower than the recrystallization lower limit temperature − (minus) 200 ° C. Particles are dispersedly formed, and then the second stage carbonization treatment is performed at a temperature equal to or higher than the recrystallization lower limit temperature of the alloy processed material obtained by the first stage carbonization treatment, and the carbide formed by dispersion formation by the first stage carbonization treatment (4) The method for producing a refractory metal-based alloy material according to (4), wherein the particles are grown and stabilized.

The present invention also provides (6) the refractory metal alloy material according to (4) or (5) above, wherein carbonization is performed using an inert gas containing 0.1 to 5% by volume of CO. Manufacturing method.

The present inventor conducted a carbonization treatment using a carbon source in which oxygen coexists with a refractory metal processed material in which a metal element is dissolved in a matrix phase, thereby causing grain boundary strengthening due to grain boundary segregation of carbon by carburization. As well as the phenomenon of dispersion and precipitation of solid solution metal carbide particles due to intragranular diffusion of carbon (
We have found that internal carbonization occurs.

When the CO gas heat treatment is performed by gradually increasing the temperature from a low temperature (for example, 1000 ° C.), internal carbonization occurs. When heat treatment is suddenly performed at a high temperature, the MoC ₂ film is difficult to be formed and oxygen can be diffused. However, when it is performed at a low temperature, a very thin MoC ₂ film is formed on the surface of the processed material. As a result, the diffusion of oxygen into the processed material is hindered. As a result, only carbon from the interface between the MoC ₂ film and the processed material can be diffused, and internal carbonization is considered to occur. For example, C
When a similar heat treatment is performed with an argon gas containing 2% by volume of H ₄ gas, a very thick MoC ₂ film is formed regardless of the heat treatment temperature, and the material becomes brittle. Coexisting with MoC
₂ Formation of film (carbonization reaction of Mo itself) is suppressed. Therefore, in the case of multi-stage carbonization,
Although the MoC ₂ film is produced, the rate of the production reaction is significantly slower than that of the atmosphere containing CH ₄ gas or the like, so that it is considered that not only the grain boundary diffusion of carbon but also the intragranular diffusion of carbon becomes possible. The carbide particles thus produced not only increase the resistance to high-temperature deformation of the refractory metal-based composite material, but also have a pinning effect to prevent the movement of crystal grain boundaries.

The alloy material obtained by carbonization has a structure in which a processed structure such as rolling is maintained at least on the surface, and carbide particles of solid solution metal are dispersed and precipitated from the surface to the inner layer by carburization. Thus, the strength is increased by segregation of grain boundaries of carbon, and the recrystallization temperature is improved by precipitation hardening of carbide particles, which is more than twice as high as that of a conventional commercially available pure Mo material in a high temperature region around 1500 ° C. Shows strength characteristics. In addition, the low temperature ductility is improved and the ductile-brittle transition temperature (DBT
T) is, for example, a Mo-1.0 wt% Ti alloy and is −110 ° C. Therefore, it can withstand static bending at a low temperature of at least -100 ° C. The same Mo-Ti alloy recrystallized at a high temperature is -50 ° C, and this is simply carbonized under the same conditions.
-70 ° C.

Normally, when an impact three-point bending test with a high deformation speed is performed, the DBTT shifts to the high temperature side, and in some cases, it may become room temperature or higher. Considering that maintenance (secondary processing) is performed at room temperature, the lower the DBTT in the static three-point bending test, the better. The DBTT in the static test is -70 considering the impact resistance near room temperature. It cannot be said that ℃ is sufficient.

The present invention provides a refractory metal alloy material having high strength and high toughness. Since the processed structure such as rolling maintained on the surface portion of the alloy material has an effect of inhibiting the propagation of cracks, the impact resistance is also excellent. Furthermore, by processing the alloy material into an arbitrary shape and then performing a heat treatment using a carbon source in which oxygen coexists, it is possible to easily cope with a complex shape product processed in advance. Also,
Multi-stage carbonization of ingots before processing, etc., and incorporation into product processing processes such as ingots can significantly reduce the hot processing temperature for subsequent forging, etc., so a significant reduction in processing energy can be expected . .

In the refractory metal-based alloy material of the present invention, Ti, Zr, Hf, V,
Nb and Ta are suitable. Since these metals easily form carbides, they are suitable as additive elements for internal carbonization in Group 6A metals. The content is about 0.1 to 5.0 wt%
More preferably, it is about 0.3 to 2.0 wt%. If it is less than 0.1 wt%, there are too few precipitated particles and recrystallization cannot be suppressed. If it exceeds 5.0 wt%, the material after carbonization becomes brittle and practically difficult to use.

As the carbon source in which oxygen coexists, for example, dilute CO gas can be used. The dilute CO gas is preferably an inert gas containing about 0.1 to 5% by volume of CO. C
If the O concentration is higher than 5% by volume, the refractory metal is carbonized, which is not desirable. The dilute CO gas can easily control the carbon potential, and the formation of a hard and brittle carbide layer on the alloy material surface can be suppressed by adjusting the carbon concentration.

The carbonization treatment is possible not only with dilute CO gas, but also by a method in which a carbon source such as solid carbon or hydrocarbon is placed around the refractory metal alloy material and oxygen is allowed to coexist. For example, if the processed material is not directly in contact with the carbon source and the carbon powder is placed in the vicinity of the processed material and heat treatment is performed while evacuating with a rotary pump or the like, it is the same as when dilute CO gas is used. Reaction occurs. Under conditions where the degree of vacuum is not so good, a trace amount of oxygen in the atmosphere reacts with carbon, resulting in CO 2.
Gas is generated and will be involved in the reaction. A similar reaction occurs even if a processed material is embedded in a mixed powder of carbon powder and alumina powder and reacted in a low vacuum state. However,
When a solid carbon source is used, when the heating temperature is low, a hard and brittle refractory metal carbide layer is likely to be formed on the surface of the work material, and therefore a carbonization method using dilute CO gas is more preferable.

The recrystallization temperature of the alloy work material mainly depends on the preparation conditions of the alloy material such as the degree of work, and has a certain range of the recrystallization upper limit value and lower limit value. For example, Mo-1.0 wt% Ti alloy work material Then 950-
It is about 1020 ° C. The temperature at which recrystallization occurs decreases as the degree of processing increases.

The carbonization treatment is a first stage carbonization treatment of the alloy processed material, below the upper limit recrystallization temperature of the alloy,
And it heats at the temperature of recrystallization minimum temperature -200 degreeC or more, and disperse-forms the carbide particle of a solid solution metal element. The reason why the recrystallization upper limit temperature is not higher than that is that the material is recrystallized and brittle when carbonized at a temperature higher than that, and the recrystallization lower limit temperature minus 200 ° C. or higher is used.
This is because at a temperature lower than this, the diffusion rate of carbon is too slow and it is difficult to carbonize internally to a practically sufficient depth.

Next, as the second stage carbonization treatment, heating is performed at a temperature equal to or higher than the recrystallization lower limit temperature of the alloy processed material obtained by the first stage carbonization treatment, and the carbide particles dispersed and formed by the first stage carbonization treatment are grown as grains. To stabilize.

The number of stages of the multi-stage carbonization treatment may be at least two, but as the carbonization treatment after the third stage, heating is performed at a temperature equal to or higher than the recrystallization lower limit temperature of the alloy processed material obtained in the preceding stage carbonization treatment. Thus, a method of further growing and stabilizing the carbide particles dispersed and formed by the carbonization treatment in the previous stage can also be carried out.

For example, when the first stage carbonization is performed at 900 ° C., the gradient of the distribution density of precipitated TiC particles from the surface to the inside occurs in the obtained internal carbonized layer (the number of surface portions is large and the number inside is small). .
As a result, the recrystallization temperature in the dilute CO gas atmosphere of the inner carbonized layer obtained by the first stage carbonization is
Near the surface is the highest (for example, 1300 ° C (recrystallization upper limit temperature)), and the tip of the inner carbonized layer is the lowest (
For example, 950 ° C. (recrystallization lower limit temperature).

The thickness of the internal carbonized layer obtained by the first stage carbonization defines the theoretical maximum thickness that can leave the processed structure such as rolling as it is, but leaves the processed structure such as rolled to the maximum extent. Therefore, it is necessary to increase the precipitation density of TiC particles near the tip of the inner carbonized layer obtained by the first stage carbonization by setting the second stage carbonization directly above the recrystallization lower limit temperature and to increase the size of the TiC particles. is there. As a result, the recrystallization lower limit temperature after the second stage carbonization (recrystallization temperature near the tip of the inner carbonized layer)
Rises. Of course, if the second stage carbonization is performed at a temperature higher than the first stage carbonization temperature and lower than the recrystallization lower limit temperature, it is possible to leave the thickest processed structure such as rolling, but the number of carbonization steps increases. The time will be too long. The same can be said for the third and subsequent carbonization processes.

As a result of the above carbonization treatment, the material surface portion has a characteristic structure such as rolling, and the inside has a characteristic two-layer structure having a recrystallized structure. The amount of carbon segregating at grain boundaries is about 30 to 150 ppm (wt%), and if it is less than this, the effect of strengthening grain boundaries cannot be expected. Almost all of the solid solution metal precipitates as carbides in the inner carbonized layer.

As a test piece, rolled Mo-1.0wt% Ti alloy (1.0mm thickness x 2.5mm width x 25mm length)
Was used. This alloy rolled material had a recrystallization lower limit temperature of 900 ° C. and an upper limit temperature of 1020 ° C. This was carbonized using a dilute CO gas atmosphere in a first stage at 1000 ° C. for 16 hours, a second stage at 1200 ° C. for 16 hours, and a third stage at 1400 ° C. for 16 hours. The concentration of CO gas was Ar / CO = 49/1 (CO concentration 2% by volume). The recrystallization lower limit temperature and the upper limit temperature are 1050 ° C. and 1300 ° C. after the first stage treatment, and 1250 ° C. and 1 after the second stage treatment, respectively.
500 ° C., 1450 ° C. and 1600 ° C. after the third stage treatment.

In FIG. 1, the optical microscope structure of the test piece after a process is shown. It can be seen that a fine rolling structure is maintained from the surface to around 75 μm. In FIG. 2, the TEM structure | tissue of the test piece after a process is shown.
The final carbide size was plate-like particles having a length of about 100 nm. FIG. 3 shows the results of the three-point bending test. The DBTT (ductility-brittle transition temperature) of the carbonized material with multistage lean CO gas was about -110 ° C. When the recrystallized material is carbonized with CO gas at 1400 ° C. for 16 hours, the DBTT is −70 ° C., and it can be seen that the low temperature ductility is very excellent.

The refractory metal-based alloy material of the present invention has heat resistance superior to that of the current TZM alloy, and is used as a heat-resistant structural material corresponding to an ultra-high temperature environment. Specifically, for example, bolts and nuts for ultra-high temperature members, heaters for ultra-high temperature furnaces, filaments, reflectors, boats and heat sinks for firing semiconductor components, hot working molds and dies, gas injection nozzles for aerospace Examples thereof include a rapid solidification mold of molten metal and an injection mold.

3 is a drawing-substituting photograph showing an optical microscope structure of a test piece after processing in Example 1. FIG. 2 is a drawing-substituting photograph showing a TEM structure of a test piece after processing in Example 1. FIG. 3 is a graph showing the results of a three-point bending test of a test piece after treatment in Example 1. FIG.

Claims (6)

A carbonized material of an alloy processed material in which one of Mo, W, and Cr is a parent phase and at least one of Ti, Zr, Hf, V, Nb, and Ta is a solute metal, A high-strength, high-toughness, high-melting-point metal alloy material comprising carbon that has been segregated at grain boundaries by carbonization using a carbon source in which carbon coexists, and carbide particles of solute metal that has been dispersed and precipitated. The high-strength and high-toughness refractory metal alloy material according to claim 1, wherein the surface portion of the alloy material maintains a processed structure and the inside is a recrystallized structure. The refractory metal-based alloy material according to claim 1 or 2, wherein Mo is a parent phase, Ti is a solute metal, and DBTT (ductility-brittle transition temperature) is -110 ° C. Using a carbon source in which oxygen coexists in an alloy processed material in which one of Mo, W, and Cr is a parent phase and at least one of Ti, Zr, Hf, V, Nb, and Ta is a solute metal. The method for producing a refractory metal-based alloy material according to claim 1 or 2, wherein the carbonization is performed in multiple stages. The first stage carbonization treatment is performed at a temperature lower than the recrystallization upper limit temperature of the alloy processed material and at a temperature lower than the recrystallization lower limit temperature − (minus) 200 ° C. to disperse and form solid solution metal carbide particles, 2
Performing the stage carbonization treatment at a temperature equal to or higher than the lower recrystallization lower limit temperature of the alloy processed material obtained by the first stage carbonization treatment, and growing and stabilizing the carbide particles dispersed and formed by the first stage carbonization treatment. The method for producing a refractory metal-based alloy material according to claim 4. 6. The method for producing a refractory metal alloy material according to claim 4 or 5, wherein carbonization is performed using an inert gas containing 0.1 to 5% by volume of CO.

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