JPH02277746A - Wear-resistant low thermal expansion sintered alloy and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the sintered alloy having low thermal expansion properties and excellent wear resistance and strength in which carbide such as NbC is uniformly and finely dispersed into a matrix alloy phase constituted of an invar alloy by subjecting alloy powder obtd. from an alloy molten metal having prescribed compsn. to pressure sintering. CONSTITUTION:At first, alloy powder of which one or more kinds of MC-type carbide among NbC, TaC, TiC, ZrC and HfC are uniformly and finely dispersed into a matrix constituted of a well-known invar alloy is manufactured by subjecting a molten metal having prescribed compsn. to rapid solidifying treatment by a gas atomizing method or the like. At this time, as for the amounts of carbide-forming elements (such as Nb) and carbon, the amounts determined stoichiometrically so as to be present as MC-type carbide in the alloy are regulated as the standard. Next, the above alloy powder is subjected to pressure sintering to manufacture the above sintered alloy. Furthermore, as for the manufacture of the alloy powder, rapid solidifying treatment having about >=10<3> deg.C/sec cooling rate is preferably executed, and, as for the pressure sintering, HIP is preferably executed. Moreover, the average grain size of the carbide is preferably regulated to about <=5mum and the amt. of the carbide to about 2 to 10 volume.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a sintered alloy that is optimal for precision machinery, equipment parts, etc. that require low thermal expansion and wear resistance, and a method for producing the same. be.

[Conventional technology]

As is well known, many metal 1 alloys expand in volume as the temperature rises, and those with a large coefficient of thermal expansion have large volumetric expansions and contractions as the temperature changes.

Due to their reliability, parts for precision machinery and equipment have extremely low coefficients of thermal expansion near room temperature. A so-called invar type alloy is often used.

Typical examples of invar type alloys include nickel-iron alloy, 36% Ni-Fe alloy, 31% Ni-5% G
O-F e alloy (super invar), 54% Co-10% Cr-Fe alloy, which is a stainless steel invar alloy, and the like are known. In addition to the above, N1-Co-
It is known that low thermal expansion characteristics can be obtained in a specific composition range in Or-Fe alloys.

The above-mentioned invar type alloys satisfy the requirements for precision machinery and equipment parts in terms of thermal expansion properties.

There was a problem that wear resistance or mechanical strength was insufficient.

In order to improve wear resistance, etc., it is possible to add carbide-forming elements to conventional Invar alloys, but this results in a significant deterioration of the low thermal expansion properties.

In view of the above, by regulating the content of Ni (or Ni and Co) within a specific range, low thermal expansion characteristics can be maintained even when carbide-forming elements are added.
Ni 26.5-28.5%, Co 13-15%
, CrO, S-t%, GO, 45-0,55%, V
O,4-0,6%, Mo O,8-1,2%, M
n 0.3% or less, SLo, 3% or less, remainder substantially F
A cast alloy consisting of E is disclosed in JP-A No. 50-30728, and similar alloys are disclosed in JP-A-55-122855 and JP-A-55-122855.
No. 128565 and the like.

In addition, various proposals have been made to precipitate graphite in nickel-iron-based low thermal expansion cast iron to provide both low thermal expansion characteristics and wear resistance (for example, Journal of Precision Engineering, Vol. 51, No. 5).
Special issue of “Iron-Nickel Alloy” published on May 5, 1985,
JP-A-62-284038, JP-A No. 62-284039, etc.).

[Problem to be solved by the invention]

However, the above-mentioned low thermal expansion cast iron is a cast iron with large crystal grains and a coarse structure, so even if the thermal expansion characteristics are titrated, the wear resistance and strength are insufficient, and improvement of the layer has been desired. .

The present invention provides a wear-resistant, low thermal expansion alloy having low thermal expansion characteristics and excellent wear resistance and strength.

[Means for solving the problem] The present inventors have considered improving the wear resistance of Invar alloys by dispersing carbides.

The problem here is that, as mentioned above, if the carbide-forming element is solidly dissolved in the matrix, the low thermal expansion characteristics will be impaired.

However, on the other hand, if the carbide-forming element does not form a solid solution in the base but exists in the alloy as a carbide, low thermal expansion characteristics can be maintained.

The present inventor conducted various studies on one or more points and found that if a carbide-forming element has a low carbide formation free energy, that is, it is easy to form a carbide, it will preferentially form a carbide rather than form a solid solution in the base. It was found that low thermal expansion characteristics can be maintained.

The present invention was made based on the above findings.

In the base alloy phase consisting of Invar alloy, NbC, TaCt
One or two of T x Cy Z r C+ Hf C
This is a wear-resistant, low thermal expansion sintered alloy characterized by having more than one type of MC type carbide uniformly and finely dispersed.

The present invention will be explained in detail below.

The carbide dispersed in the alloy of the present invention is NbC.

It is selected from one or more of TaCrTictZrCtHfC. This includes Nb, Ta, Ti, Zr,
This is because Hf has a smaller free energy of carbide formation than V, Cr, etc., which are known as other carbide forming elements, and does not adversely affect the low thermal expansion characteristics.

Among the carbide-forming elements mentioned above, Nb is the most desirable as a carbide-forming element in the alloy of the present invention because it easily forms carbides, the coefficient of thermal expansion of the carbide itself is small, and the carbide is difficult to form a solid solution in the matrix.

If the content of carbide dispersed in the matrix is too large, the material will become brittle and difficult to process, and if it is too small, the wear resistance will be insufficient. Considering the above, 2-10% for volumetric clouds.
It is desirable to do so.

Further, the smaller the size of the carbide, the better for improving wear resistance and strength, and it is desirable that the average particle size is 5 μI or less.

In addition, even when using a carbide-forming element with a small carbide-forming free energy as described above, it is inevitable that a small amount of the carbide-forming element will be solid-dissolved in the base, and in the present invention, no carbide-forming element is dissolved in the base at all. It does not mean that. However, it is important that the carbide-forming elements are dispersed as carbides without being dissolved in the base as much as possible.

As the base Invar alloy, a wide variety of conventionally known Invar alloys can be used.

As a particularly suitable alloy.

(1) 32 to 39% Ni by weight, the balance being substantially Fe
(2) an alloy consisting of 29-38% Ni, 10% or less Co, and the balance substantially Fe; (3) an alloy consisting of 54-59% Co, 8-11% Cr by weight;
Hereinafter, an alloy in which the remainder substantially consists of Fe is mentioned. By dispersing the carbide employed in the present invention in the above alloy, it is possible to obtain a thermal expansion coefficient of 4X10'/'C or less, which is sufficient for precision machinery and equipment.

In the alloy (1), 36% Ni-Fe and (2
), the coefficient of thermal expansion can be minimized by blending the ingredients to 31%Ni-5%Co-Fe. The alloy (3) is effective for applications requiring corrosion resistance.

The reason why the compositions of the alloys (1) to (3) are limited is as follows.

This is because if any of them is outside the above range, it will not be possible to satisfy the desired low thermal expansion characteristics.

In addition, Mn is added for the purpose of improving the processing characteristics of the alloy.

It is permissible to incorporate a small amount of Sl, Se, and Mo into a solid solution as long as low thermal expansion characteristics are satisfied.

The alloy of the present invention as described above is most suitably produced by pressurizing and sintering a preliminary alloy powder obtained from a molten alloy having a predetermined composition.

That is, although it is possible to produce an alloy with the same composition as the present invention by a so-called melting method or a method in which invar alloy powder and carbide powder are mixed and then pressure sintered, both of them are dispersed in the base. While it is not possible to sufficiently refine carbides, gas atomization methods yield a pre-alloy powder in which extremely fine and uniform carbides are dispersed, and the carbide morphology of the alloy produced by sintering this powder also becomes extremely uniform and fine. It is from.

The method for manufacturing the alloy of the present invention will be specifically described below.

First, MC type carbide (
Specifically, a preliminary alloy powder in which one or more of NbC, TaC, TiC, ZrC, and HfC is uniformly and finely dispersed is prepared.

This preliminary alloy powder is produced by rapidly solidifying a molten alloy having a predetermined composition.

In order to make the average particle size of carbide 5 μm or less.

It is necessary to apply a rapid solidification treatment method that has a cooling rate of 103° C./see or higher for the molten alloy.

Examples of the rapid solidification treatment methods include inert gas atomization, water atomization, single-rotation roll method, and other widely known metal powder manufacturing methods.

Among the alloy powders obtained by the above rapid solidification treatment, it is desirable to use fine-grained ones.

This is because the finer the particles, the faster the solidification cooling rate and the finer the carbide particle size.

According to the studies of the present inventors, an alloy with a sufficiently fine carbide grain size can be obtained if the mesh size is 100 mesh or less.

Next, as a method of pressure sintering, hot isostatic pressing (HI
P), hot pressing, hot back rolling, hot back forging, etc. can be applied. Among these, HIP is the most desirable from the viewpoint of sintering density, etc. In the case of 6HIP, the gas pressure is 5
It is carried out under the conditions of 00 atm or more and a heating temperature of 1000 to 1300°C, but it goes without saying that the specific conditions should be set depending on the alloy composition, etc.

Further, after HIP is completed, hot working such as hot forging or rolling may be further performed.

〔Example〕

The present invention will be explained below based on examples.

Example 1 In this example, the base alloy phase & 36% Ni-Fe alloy were used.
NbC is selected as the carbide and its amount is varied.

Alloy powders (samples (1) to (4)) having the components shown in Table 1 were produced by a gas atomization method. Carbide-forming element (N
b) and the amount of carbon were based on the amount stoichiometrically determined to exist as MC type carbide in the alloy.

The obtained alloy powder was classified to 100 mesh or less, filled into capsules, and then hot isostatically pressed at 1100° C. and 10 QO atmospheric pressure to compact it. This sintered body is heated to t too°C
After hot forging at a temperature of , test pieces were cut out and their thermal expansion coefficient, strength, wear resistance, and microstructure were examined.

Table 3 shows each characteristic value.

Figure 1: A is a microstructure photograph (400x magnification) of sample (1), B is a microstructure photograph (400x magnification) of sample (2), and Figure 2 is a scanning electron microscope photograph of sample (1) (A) and sample (2) (B). A microstructure photograph (magnification: 1000 times) is shown, and it was confirmed that NbC with an average particle size of approximately IμI was uniformly dispersed in the matrix.

Comparative materials shown in Table 2 include a 36Ni-Fe alloy (sample (5)) manufactured by forging an ingot, and an alloy (sample (2)) that has the same composition as the alloy of the present invention (sample (2)) and is produced by an ingot process. Sample (6)) and 36N with graphite precipitated and dispersed
A cast product of i-Fe alloy (sample (7)) was prepared and evaluated in the same manner, and its properties were compared with that of the alloy of the present invention.

Table 3 × Coefficient of thermal expansion is the value at 25 to 150°C *Wear characteristics indicate the specific wear amount when the Okoshi type wear test was conducted under the following conditions.

Testing machine: Okoshi type rapid wear tester Compatible material: JIS SK4 equivalent material (Hardness HRC56) Friction load: 6.8kg Friction distance: 400m Friction speed: 1.96m/see Sample (1) shown in Table 3 4) In the alloy of the present invention, as the amount of carbides increases, the strength and wear resistance properties tend to improve, but as the amount of carbides increases, the coefficient of thermal expansion also tends to increase. Furthermore, if the amount of carbide is less than 2vol%, it is presumed that the strength and wear resistance properties superior to those of the conventional materials used as comparative materials cannot be obtained.

Regarding the thermal expansion characteristics, there is a tendency for the coefficient of thermal expansion to increase as the amount of carbide increases, but the alloys of the present invention were all low thermal expansion alloys with a coefficient of thermal expansion of 4X10-'/'C or less.

When we observed the microstructure of sample (6) produced by forging an ingot of an alloy with the same targeted components as the alloy of the present invention (2), we found that the carbide size was approximately 10 μm and segregation was observed. . The strength and wear resistance properties of this sample (6) are far inferior to the alloy of the present invention (2) in which fine carbides are uniformly and finely dispersed.

In addition, the alloy of the present invention is a sample (5) which is a general invar alloy.
), it has much improved strength and wear resistance, and even compared to sample (7), which is an alloy made of invar alloy with spheroidal graphite cast iron dispersed, it has lower thermal expansion characteristics, strength, and wear resistance. Are better.

Example 2 This example uses the alloy of sample (2) of Example 1 as a base, changes the Ni or C content, and investigates the effects thereof.

Table 4 shows the chemical composition etc. of the alloys used. Note that the manufacturing method is the same as in Example 1.

Table 5 shows the results of investigating various characteristics in the same manner as in Example 1.

Table 5 × Wear characteristics shows the specific wear amount when the Okoshi type wear test was conducted under the following conditions.

Testing machine: Okoshi type rapid wear tester Compatible material: JIS SKA equivalent material (hardness HRC56) Friction load: 6.8kg Friction distance: 400m Friction speed: 1.96m/see Samples (8) or 10 in Table 5 ), NbC
In the present alloy in which 5Vo1% is dispersed, in order to obtain a low thermal expansion property with a thermal expansion coefficient of 4X10''/'C or less, the Ni content of the base alloy must be in the range of approximately 36 to 39%. it is conceivable that.

In addition, from the results of samples (11) and (12), the thermal expansion coefficient of the alloy (sample (11)) with C'h<0.2% less than the stoichiometrically calculated C content tends to increase. However, it can be said that the alloy containing 0.2% more C (sample (12)) has almost no variation in the coefficient of thermal expansion.

This is thought to be because Nb, which cannot combine with C as NbC in alloys with a small amount of C, becomes solid solution in the matrix and impairs the low thermal expansion characteristics of the matrix, but in alloys with a large amount of C, it cannot combine with Nb. Although C forms a solid solution in the base, C does not harm the thermal expansion characteristics compared to Nb, so it is thought that an increase of about 0.2% will not cause any change in the thermal expansion coefficient. This is 1 normal invar alloy is 0.1%
This is also inferred from the fact that it contains a certain amount of C.

Incidentally, since the mechanical strength increases as the amount of C in the base increases, applications requiring mechanical strength may be handled by increasing the amount of C from the stoichiometric amount.

Example 3 In this example, Example 1 and Example 2 contain N as a carbide.
While bC was used, other carbides such as HfC were used.

Table 6 shows the chemical compositions of the alloys used. In addition.

The manufacturing method is the same as in Example 1.

Table 7 shows the results of various characteristics investigated in the same manner as in Example 1.

From Table 7, it can be seen that even when Hf, Ta, Ti, or Zr is used as the carbide element, properties equivalent to those using Nb as the carbide can be obtained.

Table 7 X Thermal expansion coefficient is the value at 25-150° C. × Abrasion characteristics shows the specific wear amount when the Odate type abrasion test was conducted under the following conditions.

Testing machine: Odate type rapid abrasion tester Compatible material: JIS SK4 equivalent material (hardness [1RC56)
Friction load: 6.8 kg Friction distance: 400 m Friction speed: 1.96 m/see Example 4 This example differs from Example Work to Example 3 in that 36N i-Fe alloy was used as the base alloy phase. , which was evaluated using other invar type alloys.

Table 8 shows the chemical composition of the alloy used, and the manufacturing method is the same as in Example 1.

In addition, alloys having the compositions shown in Table 9 were obtained by a melting process and used as comparative materials.

Table 10 shows the results of various characteristics investigated in the same manner as in Example 1.

From Table 10, it can be seen that the alloy of the present invention can significantly improve wear resistance, strength, etc., compared to alloys produced by conventional melting methods, without significantly deteriorating the low thermal expansion properties.

Table 9 X Thermal expansion coefficients are values at 25 to 150° C. × Wear characteristics indicate the specific wear amount when the Odate type wear test was conducted under the following conditions.

Testing machine: Odate type rapid abrasion tester Compatible material: JIS SK4 equivalent material (hardness: IRC56)
Friction load: 6.8 kg Friction distance: 400 m Friction speed: 1,96 m/sec [Effects of the invention] As explained above, the alloy of the present invention has been used in the field of precision machinery where thermal expansion of parts is avoided. It can be used for moving parts, etc., where low thermal expansion alloys cannot be used due to their lack of wear resistance.

By using this alloy, it is expected that the accuracy and life of precision machinery will be improved.

[Brief explanation of drawings]

Figures 1A and B are photos of metal microstructures (400x magnification) taken with an optical microscope of sample (1) and sample (2) in the example, respectively, and Figures 2A and B are photos of the sample (400x) in the example, respectively.
1) and sample (2) taken with a scanning electron microscope (1000x magnification).

Claims (1)

[Claims] 1. In the base alloy phase consisting of an invar alloy, NbC, Ta
One or more MCs of C, TiC, ZrC, and HfC
A wear-resistant, low thermal expansion sintered alloy characterized by uniform and finely dispersed carbides. 2. Average grain size of carbide is 5 μm or less, amount of carbide is volume %
2. The wear-resistant, low thermal expansion sintered alloy according to claim 1, wherein the wear-resistant, low thermal expansion sintered alloy has a content of 2 to 10%. 3. A claim in which the base alloy phase is an alloy consisting of 32 to 39% Ni by weight and the remainder substantially Fe, and has a coefficient of thermal expansion from room temperature to 150°C of 4 x 10^-^6/°C or less. The wear-resistant, low thermal expansion sintered alloy according to item 1. 4. The base alloy phase is Ni29-38% by weight%, Co1
2. The wear-resistant, low thermal expansion sintered alloy according to claim 1, which is an alloy consisting of 0% or less and the remainder substantially Fe, and has a coefficient of thermal expansion from room temperature to 150°C of 4×10^-^6°C or less. 5. Base alloy phase is Co54-59%, Cr8 in weight%
~11% or less, the balance substantially consisting of Fe,
Thermal expansion coefficient from room temperature to 150℃ is 4 x 10^-^6
2. The wear-resistant, low thermal expansion sintered alloy according to claim 1, wherein the wear-resistant, low thermal expansion sintered alloy has a temperature of at most /°C. 6. A method for producing a wear-resistant, low thermal expansion sintered alloy according to claims 1 to 4, wherein an alloy powder is produced from a molten alloy adjusted to have a final composition, and then the alloy powder is pressure sintered. A method for producing a wear-resistant, low thermal expansion sintered alloy characterized by the following: 7. The method for producing a wear-resistant, low thermal expansion sintered alloy according to claim 6, wherein the production of the alloy powder is a rapid solidification treatment having a cooling rate of 10^3°C/sec or more. 8. The method for producing a wear-resistant, low thermal expansion sintered alloy according to claim 6, wherein the pressure sintering is hot isostatic pressing. 9. The method for producing a wear-resistant, low thermal expansion sintered alloy according to claim 6, wherein hot working is carried out after hot isostatic pressing.