KR20120072235A - Fe-based oxide dispersion strengthened alloy, and manufacturing method thereof - Google Patents

Abstract

PURPOSE: A ferritic oxide dispersion reinforced alloy and a manufacturing method thereof are provided to obtain a ferritic oxide dispersion reinforced alloy, in which Y2O3 nano particles are evenly dispersed, without a mechanical alloy method by employing a spray casting method. CONSTITUTION: A method for manufacturing a ferritic oxide dispersion reinforced alloy, using a spray casting method, comprises a first step of preparing molten metal including 80-90weight% of Fe and 10-20weight% of Cr, a second step of dropping the molten metal and spraying inert gas and Y2O3 nano particles through a gas sprayer(40) to form droplets(50), and a third step of stacking the droplets formed out of the Y2O3 nano oxide particles on a substrate(60) to form alloy billet.

Description

Ferritic Oxide Dispersion Strengthened Alloy, And Manufacturing Method Thereof

The present invention relates to a ferritic oxide dispersion strengthened alloy (Fe-based Oxide Dispersion Strengthened Alloy), and more particularly, to an oxide dispersion-reinforced Fe-based alloy for a nuclear power plant material by a spray casting process and a manufacturing method thereof.

Recently, in order to increase energy efficiency in the power plant field, we are promoting ultra-high temperature, high pressure, and large-scaled power generation of existing power generation facilities. Also, interest in power generation using nuclear energy is increasing as a steady research to overcome energy resource depletion and environmental problems. have.

Nuclear power plants include light water reactors, heavy water reactors, rapid growth reactors and fusion reactors. Among them, light reactors and heavy reactors are currently in operation, but rapid growth reactors and fusion reactors are still in the research stage for practical use.

As one of the materials for nuclear power generation, ferritic alloys that are conventionally used cannot obtain sufficient high temperature strength at a high temperature of 500 ° C or higher. The research and development of the field is actively progressing.

Oxides uniformly dispersed to a fine size of less than 100 nanometers are very stable at high temperatures and hinder the movement of dislocations, thereby dramatically improving high temperature strength. Since the oxide dispersion hardened alloys are difficult to uniformly disperse fine oxides in the alloy by conventional casting methods, coarse raw material powders and fine oxide powders of several tens of micrometers are high-energy attritors. Or it is produced by mechanical alloying (mechanical alloying) through a crushing and mixing process that is repeated in the closed container such as a ball mill (ball mill) and the fracture and pressure welding between the steel balls. The raw alloy powder and the oxide powder added in the mechanical alloying method are very uniformly mixed by a high energy milling process, and the oxide is pulverized to a size of several tens to several tens of nanometers.

Briefly describing the manufacturing process of the oxide dispersion-reinforced alloy by mechanical alloying, first, the known alloy powder and Y ₂ O ₃ powder are pulverized, mixed and sealed together through mechanical alloying, and then degassed. Then, the resultant is hot isostatic press (HIP) and then the dispersion strengthening alloy is prepared through a hot extrusion or rolling process.

Disadvantages of the method of manufacturing the oxide dispersion reinforced alloy using mechanical alloying are that the time required for the high energy milling process is very long, ranging from 2 to 3 days or more, mass production is not easy, and mechanical friction and collision with a ball or a container Due to this, it is reported that the raw alloy is susceptible to contamination by the constituents of the ball and the container. In addition, the raw material alloy powder should be produced by a gas injection method, and the alloy is produced by a multi-step compounding process, which causes an increase in manufacturing cost.

Therefore, if it is possible to produce an oxide dispersion strengthening alloy of the same level through an economic method other than the mechanical alloying process, it is expected that it is possible to further improve productivity and minimize the incorporation of impurities in the alloy.

The present invention was devised to solve the above problems of the prior art, and an object thereof is to provide a Fe-based oxide dispersion strengthening alloy in which Y ₂ O ₃ nanoparticles are uniformly dispersed and a method of manufacturing the same.

Method for producing a ferrite-based oxide dispersed alloy using a spray casting process according to the present invention, the first step of preparing a molten metal containing iron and chromium, inert gas and Y through a gas atomizer while dropping the molten metal A second step of forming droplets by injecting ₂ O ₃ oxide nanoparticles, and a third step of stacking the droplets in which the Y ₂ O ₃ oxide nanoparticles are dispersed on a substrate disposed below the gas atomizer to form an alloy billet Steps.

Here, the molten metal in the first step, 80% by weight or more and 90% by weight or less of iron; And at least 10% by weight and at most 20% by weight of chromium. In addition, in the second step, the Y ₂ O ₃ oxide nanoparticles are preferably sprayed so as to be in the composition ratio range of 0.1 wt% or more and 3.0 wt% or less with respect to the total weight of the finally formed ferritic oxide dispersion strengthening alloy. The size of the Y ₂ O ₃ oxide nanoparticles is preferably in the range of 10 nm or more and 100 nm or less.

Further, in the first step, it is preferable to keep the molten metal within a temperature range of 1500 ° C or higher and 1650 ° C or lower. In addition, the inert gas injected through the gas atomizer in the second step is preferably nitrogen gas or argon gas. At this time, the injection pressure of the gas atomizer is preferably in the range of 4bar or more and 8bar or less.

In addition, in the third step, as the droplets are stacked, it is preferable to stack the substrates while lowering them within a speed range of 0.8 mm / s or more and 1.5 mm / s or less.

The ferritic oxide dispersion strengthening alloy according to the present invention can be prepared by the spray casting process described above. In particular, the ferritic oxide dispersion strengthening alloy includes iron (Fe) as a main component; At least 10 wt% and at most 20 wt% chromium (Cr); And at least 0.1 wt% and at most 3.0 wt% Y ₂ O ₃ ;

According to the manufacturing method of the Fe-based oxide dispersed reinforced alloy using the spray casting process according to the present invention has the following effects.

According to the present invention, it is possible to produce an oxide dispersion reinforced alloy having excellent corrosion resistance and high temperature strength without using mechanical alloying method. In addition, the existing complex manufacturing process can be simplified, and impurities such as milling vessels or balls do not occur as in the mechanical alloying process, and mass production can be performed, thereby greatly reducing the process cost required for manufacturing the alloy. have.

In particular, the technology of manufacturing alloys by simultaneously injecting nanoparticles during the spray casting process is a new technology that has not been reported worldwide yet, and it is possible to enhance the localization of materials and system export competitiveness by securing source technology.

1 is a schematic diagram illustrating a method for producing a Fe-based oxide dispersed strengthening alloy by a spray casting process according to the present invention.
Figure 2 is a microstructure photograph of Fe-17Cr-0.3Y ₂ O ₃ oxide dispersion reinforced alloy billet prepared by the spray casting process according to the present invention.
Figure 3 is a TEM microstructure photograph of the inside of the grains of Fe-17Cr-0.3Y ₂ O ₃ oxide dispersion reinforced alloy billet prepared by the spray casting process according to the present invention, (a) is a bright field image, (b) is implied It represents nocturnal.

The present invention relates to a method for producing a Fe-based oxide dispersion reinforced alloy using a spray casting process and to a Fe-based oxide dispersed reinforced alloy produced by the same, hereinafter with reference to the accompanying drawings will be described in detail a preferred embodiment according to the present invention; do.

First, the spray casting process according to the present invention is a new solidification technique capable of manufacturing rod-shaped, plate-like or tubular shaped bodies by spraying molten droplets using high-pressure gas and laminating them onto a molded substrate before the molten droplets are completely solidified. The rapid solidification effect can be obtained through the formation of fine droplets, and a uniform microstructure can be formed through the final reaction solidification process on the substrate surface. Metallurgically, it is possible to form a characteristic microstructure of fine isotropic grains with a high molding density of more than 98% and no segregation.

In the spray casting process according to the present invention, the molten metal is first sprayed by spraying a high-pressure inert gas using a gas injector while freely dropping the molten metal through a nozzle of several millimeters in diameter. The sprayed droplets reach the substrate while being cooled by the high-speed, low-temperature injection gas while falling. Reached droplets are classified according to size into fully coagulated microparticles, semi-melt droplets and coarse droplets in liquid form.

The droplets in various states react with the stack to form a thin layer of solid or semi-melt state on the surface of the stack, and the remaining liquid phase is solidified by thermal conduction with the substrate and convection gas. As the stacking continues, the substrate is lowered at a constant speed to maintain a constant distance between the nozzle of the molten metal and the stacking surface, thereby controlling the heat capacity and the liquid fraction of the stacking surface constantly.

Through the above process, it is possible to obtain a fine and uniform microstructure through the effect of quench solidification and the reaction solidification process on the substrate surface. In addition, segregation can be minimized and the characteristic microstructure of fine isotropic grains can be formed. These microstructure features have the advantage of eliminating the subsequent processing or molding process with the improvement of mechanical properties of the final product. In addition, since the production from molten metal to semi-finished molded bodies is possible in a single process in a short time, compared to the production of alloys through mechanical alloying, complicated manufacturing steps can be omitted, making the alloy much more economical.

Hereinafter, the present invention will be described in detail through examples. However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited by the following examples.

Referring to FIG. 1, a raw material alloy having a composition ratio of 80 wt% or more and 90 wt% or less of iron (Fe) and 10 wt% or more and 20 wt% or less of chromium (Cr) using the induction melting furnace 10 is used. Dissolve in molten metal. Thereafter, this molten metal is supplied to the tundish 20. On the other hand, the molten metal supplied to the tundish 20 serves to continuously supply the gas atomizer 40 through the molten metal outlet 21.

In addition, the gas atomizer 40 is connected to the gas supply pipe 41 so that a high-speed gas jet is ejected into the molten metal. In the gas atomizer 40, Y ₂ O ₃ nanoparticles are uniformly injected into the injection gas by the particle injector 42 additionally installed in the gas supply pipe 41 while the high pressure injection gas is sprayed. . At this time, it is preferable that the weight ratio of the injected Y ₂ O ₃ particles be in the range of 0.1% to 3.0% with respect to the finally formed ferritic oxide dispersion strengthening alloy, and the size of the particles is preferably 10 nm or more and 100 nm or less. The molten metal contacted with the high pressure inert gas injected through the gas atomizer 40 is atomized into fine droplets 50.

Meanwhile, a metal substrate 60 is horizontally positioned below the gas atomizer 40, and the falling droplets 50 are continuously stacked on the substrate 60 to form an alloy billet. Here, the substrate 60 is rotated by the motor 61, which is a rotating means, to induce uniform stacking of the droplets, and the diameter of the billet can be easily controlled by adjusting the tapping speed of the molten metal, that is, the falling speed of the substrate.

When molten metal flows out from the tundish 20, the most suitable temperature of the alloy molten metal is 1500 ° C to 1650 ° C, and nitrogen gas or argon gas may be used as the injection gas, but nitrogen gas is used in consideration of economical efficiency. Is most preferred. The reason for controlling the temperature of the alloy molten metal in the range of 1500 ° C to 1650 ° C is that when the temperature of the alloy molten metal is less than 1500 ° C, since the temperature is low and the solidification is rapid, droplets are difficult to form during gas spraying, and it is difficult to be deposited on the substrate. This is because when the molten metal exceeds 1650 ° C., the molten metal may be overheated, causing a problem that the droplets may not be deposited on the substrate and flow down.

In addition, in order to prevent oxidation of the molten metal, it is necessary to block the inflow of the external air by using the airtight member 30 so that the molten metal tapping into the molten metal outlet does not come into contact with external air.

In addition, the pressure of the injection gas is suitable 4bar ~ 8bar, if the injection gas pressure is less than 4bar, the droplet size is coarse, the structure of the billet alloy is not uniform, while if the pressure exceeds 8bar, the back pressure around the gas atomizer It is formed and operation is not smooth.

The substrate is lowered when alloy droplets of uniformly dispersed Y ₂ O ₃ nanoparticles are deposited onto the substrate. At this time, when the lowering speed of the substrate is less than 0.8mm / s, the thickness of the alloy layer to be laminated may be formed too thick. On the other hand, when it exceeds 1.5 mm / s, the droplets are difficult to be easily laminated. Therefore, the lowering speed of the substrate is preferably limited to 0.8 ~ 1.5mm / s range.

Fe-17Cr-0.3Y ₂ O ₃ oxide dispersion strengthened alloy billet was prepared using the above conditions, and the microstructure observation results are shown in FIG. 2. As shown in FIG. 2, the present embodiment prepared by the spray casting process formed a microstructure of equiaxed crystals having a grain size of 20 to 30 μm, and the formation of the secondary phase was effectively suppressed and very uniform with little porosity and segregation. One microstructure could be obtained.

Figure 3 is a TEM (scanning electron microscope) microstructure observation results inside the grains of the present embodiment. As shown in FIG. 3, the present example confirmed that fine Y ₂ O ₃ particles having a size of 20 nanometers or less were dispersed very uniformly inside the grains. As the very fine Y ₂ O ₃ particles are uniformly distributed, the high temperature mechanical properties of the alloy can be greatly improved.

In order to evaluate the mechanical properties of the billet prepared by the present invention and the alloy prepared by the conventional mechanical alloying method, a tensile test was performed at room temperature and 600 ° C., and the results are shown in Table 1.

division Manufacturing method Composition of alloys Yield strength (MPa) Elongation
(%) Yield strength
(600 ℃) Elongation
(600 ℃) Example 1 Spray casting Fe-12Cr-0.3Y ₂ O ₃ 810 ± 22 20 ± 2 230 ± 10 40 ± 6 Example 2 Spray casting Fe-17Cr-0.3Y ₂ O ₃ 840 ± 26 25 ± 2 250 ± 10 46 ± 5 Comparative Example 1 Mechanical Alloying Fe-12Cr-0.3Y ₂ O ₃ 800 ± 38 14 ± 3 210 ± 13 32 ± 6 Comparative Example 2 Mechanical Alloying Fe-17Cr-0.3Y ₂ O ₃ 820 ± 41 18 ± 4 220 ± 15 30 ± 7

As shown in Table 1, it can be seen that Example 1 and Example 2 according to the present invention has a superior room temperature and high temperature tensile strength compared to Comparative Example 1 and Comparative Example 2 of the same composition, respectively. In addition, it can be seen that the elongation is also superior to the alloy produced by the conventional mechanical alloying method as the internal casting such as pores or segregation is suppressed through the spray casting process and exhibits a fine and uniform microstructure.

Although a preferred embodiment of the present invention has been described so far, those skilled in the art will be able to implement in a modified form without departing from the essential characteristics of the present invention. Therefore, the embodiments of the present invention described herein are to be considered in descriptive sense only and not for purposes of limitation, and the scope of the present invention is shown in the appended claims rather than the foregoing description, and all differences within the equivalent scope of the present invention Should be interpreted as being included in.

10: Induction Melting 20: Tundish
21: molten metal outlet 30: airtight member
40: gas atomizer 41: gas supply pipe
42: particle injector 50: melt droplets
60: substrate 61: motor

Claims (10)

As a manufacturing method of ferritic oxide dispersion strengthening alloy using a spray casting process,
A first step of preparing a molten metal containing iron and chromium,
A second step of forming droplets by spraying inert gas and Y ₂ O ₃ oxide nanoparticles through a gas atomizer while dropping the molten metal;
And depositing the droplets on which the Y ₂ O ₃ oxide nanoparticles are dispersed on a substrate disposed under the gas atomizer to form an alloy billet.
The method of claim 1,
In the first step, the molten metal may include 80 wt% or more and 90 wt% or less of iron; And 10% by weight or more and 20% by weight or less of chromium.
The method of claim 1,
In the second step, the Y ₂ O ₃ oxide nanoparticles are injected so that the composition ratio range of 0.1% by weight or more and 3.0% by weight or less with respect to the total weight of the ferrite-based oxide dispersion strengthening alloy finally formed Method for producing oxide dispersed hard alloy.
The method of claim 1,
The size of the Y ₂ O ₃ oxide nanoparticles in the second step is a method for producing a ferritic oxide dispersion strengthening alloy, characterized in that the range of 10nm or more and 100nm or less.
The method of claim 1,
The method of claim 1, wherein the molten metal is maintained in a temperature range of 1500 ° C. or higher and 1650 ° C. or lower.
The method of claim 1,
In the second step, the inert gas is nitrogen gas or argon gas manufacturing method of ferritic oxide dispersion strengthening alloy, characterized in that.
The method of claim 1,
The injection pressure of the gas atomizer in the second step is a method for producing a ferritic oxide dispersion strengthening alloy, characterized in that the range of 4bar or more and 8bar or less.
The method of claim 1,
As the droplets are laminated in the third step, the substrate is laminated while lowering within a speed range of 0.8 mm / s or more and 1.5 mm / s or less.
A ferritic oxide dispersion strengthening alloy produced by the manufacturing method according to any one of claims 1 to 8.
10. The method of claim 9,
Iron (Fe) as a main component; At least 10 wt% and at most 20 wt% chromium (Cr); And at least 0.1 wt% and at most 3.0 wt% of Y ₂ O ₃ .

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