JPH08193201A - Method for producing Y2O3-dispersed Cr-based alloy - Google Patents

Abstract

PURPOSE: To produce a Cr-base alloy in which Y2 O3 alone is dispersed finely and uniformly as oxide by crushing an alloy in which Y is dispersed in a Cr- base metal and then heating the resulting powder to a specific temp. in the air to oxidize the Y into Y2 O3 . CONSTITUTION: An alloy, in which Y is nearly uniformly dispersed in a Cr-base metal containing Fe, etc., is refined by vacuum melting. At this time, preffered Y content is about 0.2-2.0wt.%. An ingot of this alloy is mechanically crushed into a powder of about 100μm. This powder is heated at 800-1000 deg.C under the air atmosphere. By this procedure, Y dispersed in the Cr, Fe, etc., in the alloy is selectively oxidized into Y2 O3 , without oxidizing them. By this method, the alloy, in which Cr oxide, Fe oxide, etc., do not exist practically and fine Y2 O3 is uniformly dispersed in a Cr-base metal, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an alloy in which fine Y ₂ O ₃ is uniformly dispersed in a Cr-based metal matrix.

[0002]

The applicant has previously proposed a Cr-based oxide dispersion strengthened heat-resistant sintered alloy (Japanese Patent Laid-Open No. 4-325651).
The raw material powder used for this sintered alloy is particles in which fine Y ₂ O ₃ particles are uniformly dispersed in a matrix of Cr-based metal.

The particles are produced under an Ar gas atmosphere by using an attritor device (high energy type ball mill). A large amount of steel balls are pre-loaded in the tank of the attritor device, and Cr-based metal powder and Y ₂ O ₃ are placed in the tank.
Add powder. These powders are subjected to a severe impact from the steel balls due to the high speed rotation of the stirring rod, and are repeatedly compressed, crushed, and adhered, and as a result, the average particle size in the Cr-based metal is about 0.
Fine Y ₂ O ₃ having a size of 1 μm or less is forcedly infiltrated (mechanical alloying) in the solid state, and particles having a structure in which Y ₂ O ₃ is uniformly dispersed in the Cr-based metal matrix are obtained. The metal base of these particles is strengthened by the effect of finely dispersing Y ₂ O ₃ , and the alloy obtained by sintering this has high strength at high temperatures.

As the Cr-based metal powder to be charged into the attritor, an ingot of Cr-based metal melted in the air is usually crushed. In atmospheric melting, Cr, F in molten metal
The e component reacts with oxygen to unavoidably generate Cr oxide and Fe oxide. When the molten metal is solidified, these oxides do not disperse uniformly in the metal structure, but exist as segregation in grain boundaries and grains.

By the way, when Cr-based metal powder containing Cr oxide and Fe oxide in the composition is mechanically alloyed with Y ₂ O ₃ powder, the Y ₂ O ₃ particles are produced by the attritor device as described above. While mechanically alloyed by sufficient stirring inside and finely dispersed in the metal matrix, Cr oxide, Fe oxide, etc. remain as segregation. If an oxide exists as segregation in the metal matrix without being finely dispersed, it adversely affects the strength. Therefore, oxides other than Y ₂ O ₃ that enter the metal matrix in the solid state should be minimized. Is desirable.

[0006]

The object of the present invention is to provide Cr
An object of the present invention is to provide a method for producing an alloy in which fine Y ₂ O ₃ is uniformly dispersed without substantially containing Cr oxide, Fe oxide and the like in the base metal matrix.

[0007]

According to the present invention, an alloy in which Y (yttrium) is substantially uniformly dispersed in a Cr base metal is melted by vacuum melting, and the powder obtained by crushing the alloy is converted into air. Heat treatment at a temperature of 800 to 1000 ° C. in an atmosphere,
By oxidizing Y dispersed in the Cr-based alloy and converting it into Y ₂ O ₃ , fine Y ₂ O ₃ is uniformly dispersed in the matrix of the Cr-based alloy.

As the Cr-based metal, (a) a metal substantially composed of Cr, (b) Fe: 20% (weight%, hereinafter the same) or less, and a balance substantially composed of Cr, (c) Al, Mo. , W, N
b, Ta, Hf and at least one selected from the group consisting of Al-Ti in a total amount of 10% or less, the balance being a metal substantially consisting of Cr, or (d) Al, Mo, W, N
b, Ta, Hf and at least one selected from the group consisting of Al-Ti in a total amount of 10% or less, Fe: 20
% Or less, and a metal substantially consisting of Cr as the balance.

The content of Y ₂ O ₃ in the Cr-based metal is 0.
Y to be mixed with Cr-based metal so as to be 2 to 2.0% by weight
It is desirable to adjust the amount of If it is less than 0.2%, the effect of finely dispersing Y ₂ O ₃ cannot be expected, and if it is more than 2.0%, Y ₂ O ₃ may aggregate during use at a temperature higher than 1350 ° C.

[0010]

Since the Cr base metal and Y are melted by vacuum melting, Y is not oxidized, and an alloy uniformly dispersed in the Cr base metal in the state of Y is obtained. The powder obtained by crushing this Cr-based alloy was heated to 8
When heat-treated at a temperature of 00 to 1000 ° C., Y evenly dispersed in the alloy reacts with oxygen, and Y is oxidized to Y.
₂ O ₃ is produced, and an alloy powder having a structure in which fine Y ₂ O ₃ is uniformly dispersed in the base of the Cr-based alloy is obtained.

Since the free energy for producing Y oxide (Y ₂ O ₃ ) is much lower than that of Cr oxide and Fe oxide, Y ₂ O ₃ is present in the presence of oxygen. Is preferentially generated. The generation of Cr oxide or the like can be prevented by terminating the heat treatment when almost all of Y has changed to Y ₂ O ₃ .

[0012]

EXAMPLE Cr: 1.7 kg, Fe: 0.3 kg, Y: 20 g were melted in a vacuum melting furnace to obtain an alloy ingot in which Cr, Fe and Y were mixed almost uniformly. Next, this alloy ingot was mechanically pulverized to prepare an alloy powder having an average particle size of about 100 μm. This alloy powder was heat-treated in the atmosphere at 1000 ° C. for 10 hours. The obtained powder is designated as test powder 1.

Next, a Cr-Fe alloy having an average grain size of about 100 μm
2 kg of (Cr85%, Fe15%) powder and 20 g of Y ₂ O ₃ powder having an average particle size of about 1 μm were put into the tank of the attritor device, and 4
Mechanical alloying treatment was performed for 8 hours. The Cr-Fe alloy powder used was melted in the air. The obtained powder is designated as test powder 2. As the attritor device, MA-1D manufactured by Mitsui Chemicals, Inc. was used, and 17.5 kg of 3 / 8-inch SUJ-2 steel balls were loaded in the tank.
r gas was introduced.

2 kg of the above-mentioned Cr-Fe alloy powder
And 20 g of Y ₂ O ₃ powder were kneaded substantially uniformly in a mortar. The obtained powder is designated as test powder 3.

A metal can was filled with the above-mentioned test powder, and after deaeration and sealing in a known manner, HIP sintering was performed to obtain a diameter.
A 30 mm × 50 mm long sintered body was obtained. HIP was carried out under the conditions of a temperature of 1250 ° C., a pressure of 118 MPa, and a time of 2 hours, using Ar gas as a pressure medium.

A high temperature cyclic compression test was carried out on the obtained three kinds of sintered bodies, and the high temperature creep strength was examined by the deformation amount. The test was performed in an electric furnace at 1350 ° C. by repeatedly raising and lowering a ram and applying a compressive load of 9.8 MPa. The load repeating pattern is a load of compressive load of 9.8 MPa for 5 seconds, no load for 5 seconds (load state to no load state 1 second, no load state 3 seconds, no load state to load state 1 second) Of 10
The amount of deformation (unit:%) was examined by applying a compressive load to the sintered body 10,000 times in a second cycle. The amount of deformation was determined by the following equation, where L1 is the length before the test and L2 is the length after the test. Amount of compressive deformation (%) = (L1-L2) / L1 x 100

The test results of the deformation amount are as follows. Sintered body of test powder 1: 0.1% Sintered body of test powder 2: 0.1% Sintered body of test powder 3: 20% or more In addition, the sintered body of test powder 3 is a repetition number of 1000 times. Since the amount of deformation reached 20%, the test was stopped at that point.

From the above test results, it is understood that the sintered body of the test powder 3 has a larger deformation amount than the sintered bodies of the test powders 1 and 2. It is considered that this is because the test powder 3 was obtained by simply mixing Y ₂ O ₃ in the mortar.

The sintered bodies of the test powders 1 and 2 have a very small amount of deformation. It is considered that the small amount of deformation is due to the fact that fine Y ₂ O ₃ is uniformly dispersed in the matrix of the Cr—Fe alloy in both sintered bodies, and the matrix metal is strengthened.

Y ₂ O ₃ is dispersed in the alloy matrix of the test powder 1 because it is Y dispersed in the alloy composition by vacuum melting.
However, in the subsequent heat treatment step, it reacts with oxygen and is oxidized to generate Y ₂ O ₃ . Note that the oxide produced in the heat treatment step is substantially only the oxide of Y.
The oxide of Y, that is, Y ₂ O ₃ , has much lower free energy for oxide formation than the oxides of Cr and Fe.
₂ O ₃ is preferentially generated.

Therefore, the test powder 1 contains Cr oxide and F.
It is considered that almost no e oxide was contained. On the other hand, as the test powder 2, since the Cr-Fe alloy prepared by melting in the air was used, as described above, in the composition thereof, C
The r oxide and the Fe oxide are present as segregation.

Under the above test conditions, no difference in the amount of deformation was observed between the sintered bodies of the test powders 1 and 2 depending on the presence or absence of Cr oxide and Fe oxide. However, as described above, theoretically, it is desirable that as few oxides as segregation be present.

[0023]

According to the method of the present invention, a Cr-based alloy powder in which fine Y ₂ O ₃ is uniformly dispersed in a Cr-based metal matrix can be produced. The sintered body of this powder has excellent high-temperature strength and is suitable as a skid button for a walking beam heating furnace. Further, unlike the Cr-based metal melted in the air, since the composition does not contain oxides such as Cr, it is possible to prevent the strength from decreasing due to the inclusion of segregation of these oxides.

Claims (1)

[Claims] 1. An alloy in which Y is substantially uniformly dispersed in a Cr-based metal is melted by vacuum melting, and the powder obtained by crushing the alloy is heated to a temperature of 800 to 1000 ° C. in an air atmosphere. To heat Y, and oxidize Y dispersed in the Cr-based alloy to Y
By varying the ₂ O _3, characterized in that to uniformly distribute the fine Y ₂ O ₃ to the base of the Cr-based alloy, Y ₂ O ₃ Preparation of dispersion Cr-based alloy.