JPH0665672A - Production of ferritic alloy sintered body - Google Patents

Abstract

PURPOSE:To provide the method capable of obtaining a ferritic alloy sintered body in which a ceramic film increasing its surface hardness and wear resistance is securely adhered to the surface as well as chipping and cracking are hard to generate and having the aptitude for mass production. CONSTITUTION:As for the method for producing the ferritic alloy sintered body, Fe-Cr-Ni-Al ferritic alloy powder having a compsn. contg., by weight, 15 to 40% Cr, 2 to 25% Ni, 2 to 8% Al, >1.0 to 2.5% of one or >= two kinds among Zr, Y, Ce, Hf, La, Nd and Gd and 0 to 0.5% Ti, and the balance Fe is compacted. This green compact is sintered in a nonoxidizing atmosphere and is subjected to heat treatment in an atmosphere of an oxidizing gas to precipitate alumina components onto the surface.

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 a ferrite alloy sintered body applicable to parts requiring abrasion resistance such as blades, gears, shafts and chucks.

[0002]

2. Description of the Related Art Conventionally, ceramic materials or alloy materials have been used for such applications. Use of Ceramic Material There is a ceramic sintered product obtained by mixing a raw material ceramic powder and an organic binder, molding the mixture into a predetermined shape by injection molding or direct pressure molding, removing the binder by heat treatment, and then sintering. The sintered product manufactured in this manner has a hardness as high as Hv = 2000 or more, but has a defect that it is easily chipped or cracked because it has no toughness.

On the other hand, when an alloy material is used, a metal material that is praised as a superhard material has excellent toughness, but has a surface hardness (Hv = 1100) of that of a ceramic sintered product (Hv = 2000). It is considerably lower than the above), and it cannot be said that the abrasion resistance is sufficient. Therefore, attempts have been made to improve wear resistance by forming a film having wear resistance on the surface of a metal to form a composite film. Specifically, for example, by a method such as a sputtering method or a CVD method,
A film of TiN, ZrN or the like is formed on the metal surface.
In this case, between the metal film formed on the surface of the metal and the metal, there is a boundary surface that is uniquely formed when a heterogeneous material is compounded, and thus the mutual adhesion strength is weak, and It is practically difficult to make the thickness sufficiently thick and the thickness is limited, so that there is a problem that sufficient abrasion resistance cannot be secured.

Therefore, the inventors of the present invention have a large surface hardness,
In order to find a method which is suitable for mass production and which can obtain a ferrite alloy sintered body which is excellent in abrasion resistance and is less likely to be chipped or cracked, investigations were conducted from various angles. As a result, Fe-Cr-Ni-Al
Achievement of the objective if the alumina component is deposited on the surface by sintering a molded body of ferrite ferrite alloy powder in a specified shape in a non-oxidizing atmosphere and heat-treating it in an oxidizing gas atmosphere. It turned out that considerable progress was seen. On the surface of the obtained sintered body, a hard and sufficiently thick ceramic coating containing an alumina component as a main component is formed on the surface by heat treatment in an oxidizing gas atmosphere. However, this ceramic film is not sufficient in terms of adhesion and it cannot be said to be perfect, and it was found that there is room for improvement.

[0005]

SUMMARY OF THE INVENTION Therefore, according to the present invention, there is provided a ferrite alloy sintered body in which a ceramic coating which enhances surface hardness and abrasion resistance is firmly adhered to the surface, and moreover, cracks and cracks are hard to occur. It is an object to provide a method capable of obtaining a body and suitable for mass production.

[0006]

In order to solve the above problems, in the method for producing a ferrite alloy sintered body of the present invention,
Cr: 15-40% by weight: Ni: 2-25% by weight, A
1: 2 to 8% by weight, Zr, Y, Ce, Hf, La, Nd
And any one or more of Gd: 1-2.
5% by weight (however, 1.0% by weight is not included), Ti: 0
Fe-Cr- having a composition of 0.5% by weight and Fe: balance
A compact formed by molding a Ni-Al ferrite alloy powder is sintered in a non-oxidizing atmosphere, and then heat-treated in an oxidizing gas atmosphere to deposit an alumina component on the surface.

Fe-Cr-Ni-Al in the present invention
Series ferrite alloy powder (hereinafter referred to as "ferrite alloy powder"
Is abbreviated) Cr: 25-35 wt%: Ni: 2-25
% By weight, Al: 2 to 8% by weight, Zr, Y, Ce, Hf,
Any one or more of La, Nd and Gd: 1 to 2.5% by weight (however, 1.0% by weight is not included),
The composition is preferably composed of Ti: 0 to 0.5% by weight and Fe: balance, Cr: 25 to 35% by weight: Ni: 1.
5-25% by weight, Al: 2-8% by weight, Zr, Y, C
e, Hf, La, Nd, and any one or more of Gd: 1 to 2.5% by weight (however, 1.0% by weight is not included), Ti: 0 to 0.5% by weight, It is more preferable that the composition is Fe: balance.

Examples of the non-oxidizing atmosphere in the present invention include an inert gas atmosphere and a reducing gas atmosphere in addition to the vacuum atmosphere. The heat treatment temperature during sintering in a non-oxidizing atmosphere is preferably in the temperature range of 1300 to 1400 ° C. Of course, the heat treatment temperature at the time of sintering is not limited to this range, but if it deviates from the temperature range of 1300 to 1400 ° C., there is a disadvantage that the applicable molding pressure range becomes narrow.

The present invention will be described in more detail below. First, Cr: 15-40% by weight: Ni: 2-25% by weight, Al: 2-8% by weight, Zr, Y, Ce, Hf, L
Any one or more of a, Nd and Gd:
1 to 2.5% by weight (excluding 1.0% by weight), T
i: 0 to 0.5% by weight, Fe: all the components are dissolved in a blending ratio of substantially Fe, and for example, by atomizing by an atomizing method, or by pulverizing an alloy by a mechanical grinding method. , Obtain ferrite alloy powder.

The ferrite alloy powder thus obtained is mixed with an organic binder and molded (shaped) into a predetermined shape by a mold by a method such as injection molding or direct pressure molding to obtain a molded body. This molded product is a product or a product shaped according to the intended use, and is different from a base material such as an ingot which is subjected to processing such as grinding in the next step.
Examples of the organic binder include organic compounds such as polyvinyl alcohol (PVA) and paraffin wax.

The pressure during molding is 400 in the case of the present invention.
There is also application of a low pressure of about MPa, usually 400 to 1
It is selected from the range of about 000 MPa or about 650 to 850 MPa. However, the molding pressure is 400M
If it is less than Pa, there is a tendency that the dimensional accuracy and the like cannot be obtained sufficiently. Next, this molded body is sintered by being heat-treated (baked) in a non-oxidizing atmosphere. The heat treatment is performed at 1250 to 1400 ° C (preferably 1300 to 14
00 ° C). Within this heat treatment temperature range, sufficient hardness and tensile strength can be imparted without generating a liquid phase, and a base material having sufficient strength as a mechanical component can be obtained.

The reason why the heat treatment is performed in a non-oxidizing atmosphere is that if oxidation occurs, the sintering does not proceed and the toughness of the alloy cannot be secured. In the case of an inert gas atmosphere,
For example, an inert gas such as argon or helium is used. In the case of a reducing gas atmosphere, for example, hydrogen gas is used. Since the base material of the thus obtained sintered body is a sintered body of ferrite alloy powder unlike ceramics, it does not cause cracking or chipping before alumina precipitation, and is used for mechanical processing such as grinding and polishing. There is an advantage that machining or electric discharge machining can be easily performed. Therefore, if necessary, machining or electric discharge machining can be performed before alumina precipitation.

In the case of the conventional ceramic material, it is difficult to obtain the dimensional accuracy due to the shrinkage of about 20% accompanying the sintering, but it is difficult to process it, and it is difficult to improve the dimensional accuracy in the post-processing. Even in the case of super hard materials, post-processing such as cutting and grinding is not easy, and it is difficult to obtain dimensional accuracy. In either case, it is not suitable for use where precision is required.

However, in the case of the present invention, as described above, the dimensional accuracy can be improved by machining such as grinding or polishing or electric discharge machining without causing cracks or chips before the precipitation of alumina. Therefore, the present invention can be sufficiently applied to a place where dimensional accuracy is required. Next, this sintered body is heat-treated at a temperature exceeding 1000 ° C., for example, in the atmosphere or an oxidizing gas atmosphere such as oxygen gas to deposit an alumina (aluminum oxide) component on the surface. By this heat treatment, for example, Fe-Cr-Ni with a ceramic film (alumina film) containing alumina as a main component is attached.
-Al ferrite alloy sintered body is completed.

Here, the reason why the component deposited on the surface of the alloy forming the sintered body is limited to alumina is that the Al element is easily oxidized when heat-treated in an oxidizing gas atmosphere, and is made of alumina having high hardness. This is because a ceramic film can be generated. The alloy sintered body thus obtained has a large surface hardness because it has a ceramic coating containing alumina as a main component, and is excellent in toughness because the base material that fills the inside of the sintered body is an alloy. In addition, when a ceramic coating is formed on the metal surface by a sputtering method or a CVD method, since a boundary surface is formed between the coating and the metal base material, the adhesion strength between the coating and the base material is small, and Sufficient wear resistance cannot be obtained because the film thickness of the coating is limited, whereas the ceramic coating containing alumina as a main component according to the present invention has a root of alumina in the base material and is not Has a high adhesion strength, and the thickness of this ceramic coating is 10
It can be increased to ˜50 μm, and sufficient abrasion resistance can be obtained. Furthermore, it is possible to shape into the desired shape through the steps of molding and sintering, and it is possible to manufacture without processing such as inefficient cutting, in which case it is required for industrial production. It can be said that the economy and the effect of mass production are remarkable.
In other words, it is suitable for mass production.

Next, the reasons for limiting the content of the elements contained in the ferrite alloy powder in the present invention will be explained. The ferrite alloy powder of the present invention is a Fe-based alloy powder containing a large amount of ferrite-forming elements Cr and Al and austenite-forming element Ni, and the reason why the alloy is mainly in the ferrite phase is as follows. Is. Ferrite phase alloys are dense and dense alumina (Al ₂
This is because the O ₃ ) film is easily formed, but the austenite phase alloy does not uniformly form a film containing alumina as a main component and is peeled off.

[Cr: 15 to 40 wt%] Cr is necessary for forming a dense and uniform ceramic film containing alumina as a main component on the alloy surface, but since the alloy of the present invention contains Ni, Even if Ni is the lower limit and Al is the upper limit, 15 wt% is necessary to make the alloy into a ferrite phase.
% Or more of Cr is required. The formation of the ceramic coating is incomplete in the alloys in which the Ni content is near the lower limit, the Al content is near the upper limit, and the Cr content is less than 15 wt%. Therefore, the lower limit of Cr is 15 wt%. Moreover, since the tendency of embrittlement becomes stronger as the Cr content in the alloy increases, the upper limit of Cr is 40.
wt%.

[Ni: 2 to 25 wt%] Ni is presumed to precipitate fine NiAl in the alloy and improve the mechanical properties (eg hardness) of the base material. Is an essential element for precipitating NiAl. 2wt to be effective enough to improve mechanical properties
% Or more of Ni is required. If the amount of Ni increases, Ni
Although it is convenient for the precipitation of Al, if the content of Ni, which is an austenite-forming element, is increased, it is accompanied by Cr.
It is necessary to increase the content of Al and Al. But,
If the amount of Ni exceeds 25 wt%, the amount of Cr must be increased, and if it is made brittle, the upper limit of Ni is 25 wt%.

[Al: 2 to 8 wt%] Al is a fine N
It is an essential element for precipitating iAl in the alloy and for forming a ceramic film containing alumina as a main component on the alloy surface by high temperature oxidation treatment. In order to form a dense and uniform film, it is necessary to contain 2 wt% or more of Al. The increase of Al content is advantageous for the precipitation of NiAl and the formation of a ceramic film, but if it exceeds 8 wt%, the workability of the alloy decreases, so the upper limit of Al is 8 wt%.
%.

[One or more of Zr, Y, Ce, Hf, La, Nd and Gd: (total)
1 to 2.5% by weight (however, 1% by weight is not included; that is, the range is more than 1% by weight and 2.5% by weight or less)] Any one of these elements is selectively added. , Mixed in the ceramic film to improve the brittleness of the film and disperse as internal oxide particles in the alloy immediately below the film to improve the adhesion of the film. In previous studies by the inventors, it was thought that the total content of Zr, Y, Ce, Hf, La, Nd and Gd should be 1% by weight or less, but if the content is 1% by weight or less, Since it oxidizes before the heat treatment for precipitation of the alumina component, the root of the ceramic coating containing alumina as the main component is about 30 or less per 1 mm in cross-section observation, and particularly 10 at less than 0.05% by weight. This is less than this level and the adhesion of the film is not sufficient. In the case of the present invention, since the content exceeds 1% by weight, the method of rooting the film is appropriate and the adhesion is high. However, if the content exceeds 2.5% by weight, the main component of the film is zirconia (Hv = 1500).
And other components, the hardness of the ceramic coating is Hv = 1.
It falls below about 700, and sufficient surface hardness cannot be secured.

[Ti: 0 to 0.5% by Weight] Ti is added as required, and has the advantage that it forms a fine intermetallic compound and serves to strengthen the alloy. However,
If the content exceeds 0.5% by weight, the characteristics of the ceramic coating may be impaired, so the upper limit is made 0.5% by weight.

[Fe: Remainder] In addition to the above components, Fe occupies. However, it is not limited to the case where the balance is completely Fe, and there may be inevitable impurities (such as Si) present in Fe. Examples of articles to which the method of the present invention can be applied include the following. [Cutters used for household use] Blades of electric razors, hair clippers (especially pet hair clippers and garden tree clippers for gardens that may bite small stones, etc.), blades for mowers, cooking mixers, cutters, etc. , Swords, scissors, saw blade for DIY carpenters, etc.

[Blade used for business] Various band saw blades,
Tools such as rotary blades, cutting tools, dies, screws for kneading machines, etc. [Abrasion resistant parts] Electric drill blades, drill chuck parts, gears, rotary shafts, bearings, etc.

[0024]

In the alloy sintered body obtained by the production method of the present invention, since the alloy composition of the ceramic alloy powder is appropriate, a thick ceramic film containing an alumina component as a main component is formed on the surface and the surface hardness is high. Wear resistance is sufficient. And the ceramic coating is Zr, Y, Ce, H
Since the contents of f, La, Nd and Gd are appropriate,
The alumina component forming the film has a function of increasing the adhesion force between the film and the alloy by sufficiently forming a root in the alloy filling the inside, and thus the adhesion of the ceramic film is high.

In addition, the alloy filling the interior of the sintered body has a high toughness and does not cause cracking or chipping. Then, the step of molding and sintering into a desired shape improves the economical efficiency and mass productivity required for industrial production, and thus suitability for mass production comes out. Further, since the alloy sintered body after sintering but before alumina precipitation can be processed so as to accurately match a predetermined shape without causing chips or cracks, dimensional accuracy can be improved. It is also applicable when precision is required.

[0026]

Embodiments of the present invention will be described below. The present invention is not limited to the embodiments described below. -Example 1-Cr: 32.0 wt%, Ni: 21.0 wt%, Al:
6.5% by weight, Zr: 2.0% by weight, balance: substantially F
The alloy of composition e was melted in a high-frequency melting furnace and pulverized by an atomizing method to obtain a ferrite alloy powder.

PVA for a binder was mixed with the obtained powder and then molded at a pressure of 700 MPa. Then, the molded body was heat-treated and sintered in a vacuum at 1350 ° C. for 3 hours, and then ground to obtain a predetermined shape. Then, after heat treatment in air at 1150 ° C. for 20 hours, heat treatment in air at 1250 ° C. for 30 minutes is performed to precipitate an alumina component to form a ceramic film on the surface, and then air cooling is performed to produce Fe—Cr—Ni. An Al-based ferrite alloy sintered product was obtained.

When the cross section of this sintered product was observed with an optical microscope, the ceramic film was deposited so as to take roots on the base material, and the frequency of the roots of this ceramic film was about 70 per 1 mm, which is very large. Admitted. -Example 2-Cr: 35.0 weight%, Ni: 21.0 weight%, Al:
7.0% by weight, Zr: 1.2% by weight, balance: substantially F
The alloy of composition e was melted in a high-frequency melting furnace and pulverized by an atomizing method to obtain a ferrite alloy powder.

PVA for a binder was mixed with the obtained powder and then molded at a pressure of 800 MPa. Then, in vacuum, the molded body was heat-treated and sintered at 1350 ° C. for 4 hours, and then ground so as to have a predetermined shape. Then, after heat treatment in air at 1150 ° C. for 20 hours, heat treatment in air at 1250 ° C. for 30 minutes is performed to precipitate an alumina component to form a ceramic film on the surface, and then air cooling is performed to produce Fe—Cr—Ni. -Al
A sintered ferrite ferrite alloy product was obtained.

When the cross section of this sintered product was observed with an optical microscope, the ceramic film was deposited so as to take roots on the base material, and the frequency of the roots of this ceramic film was about 40 per 1 mm, which is considerably large. Admitted. -Example 3-Cr: 33.0 wt%, Ni: 21.0 wt%, Al:
5.8% by weight, Zr: 1.5% by weight, balance: substantially F
The alloy of composition e was melted in a high-frequency melting furnace and pulverized by an atomizing method to obtain a ferrite alloy powder. Then, this alloy powder was classified, and about 1
A 0 wt% paraffin wax and a binder containing stearic acid as a main component were kneaded and injection-molded at a temperature of 150 ° C. to obtain a molded product having a predetermined shape.

The obtained molded product was first subjected to 400
After degreasing by holding at a temperature of 50 ° C for 50 hours, hold at 1350 ° C for 3 hours in vacuum to sinter the molded body, and then feed oxygen gas into the furnace and hold at 1250 ° C for 30 minutes. After the alumina component was deposited to form a ceramic film on the surface, it was air-cooled to obtain a Fe-Cr-Ni-Al ferrite alloy sintered product.

When the cross section of this sintered product was observed with an optical microscope, the ceramic film was deposited so as to form a root on the base material, and the frequency of the root of this ceramic film was about 60 per 1 mm, which is very large. Admitted. -Comparative Example 1-Cr: 35.0 wt%, Ni: 21.0 wt%, Al:
An alloy having a composition of 7.0% by weight and the balance: Fe was substantially melted in a high-frequency melting furnace and pulverized by an atomizing method to obtain a ferrite alloy powder.

PVA for a binder was mixed with the obtained powder and then molded at a pressure of 800 MPa. Then, in vacuum, the molded body was heat-treated and sintered at 1350 ° C. for 4 hours, and then ground to obtain a predetermined shape. Then, after heat treatment in air at 1150 ° C. for 20 hours, heat treatment in air at 1250 ° C. for 30 minutes is performed to precipitate an alumina component to form a ceramic film on the surface, and then air cooling is performed to produce Fe—Cr—Ni. An Al-based ferrite alloy sintered product was obtained.

When the cross section of this sintered product was observed with an optical microscope, the ceramic coating was deposited parallel to the base metal.
There was almost no part where the roots were bulged and deposited. Further, the ceramic coating may be peeled off depending on the cooling rate after the formation of the ceramic coating in the oxygen atmosphere. -Comparative Example 2-Cr: 33.0 wt%, Ni: 21.0 wt%, Al:
An alloy having a composition of 3.2% by weight, Zr: 2.7% by weight, and the balance: Fe was melted in a high-frequency melting furnace and pulverized by an atomizing method to obtain a ferrite alloy powder. Then, this alloy powder was classified, and about 10% by weight was added to the alloy powder having a size of 30 μm or less
The paraffin wax and the binder containing stearic acid as main components were kneaded and injection molded at a temperature of 150 ° C. to obtain a molded product having a predetermined shape.

The obtained molded product was first subjected to 400
After degreasing by holding at a temperature of 50 ° C for 50 hours, hold at 1350 ° C for 3 hours in vacuum to sinter the molded body, and then feed oxygen gas into the furnace and hold at 1250 ° C for 30 minutes. After forming a ceramic film on the surface, air-cool it to Fe
A -Cr-Ni-Al ferrite alloy sintered product was obtained. When the cross section of this sintered product was observed with an optical microscope, the ceramic film was deposited so as to take roots on the base material, and the frequency of the roots of this ceramic film was very large, about 90 per 1 mm. . However, this ceramic coating contains zirconia as a main component and has a low hardness, and therefore does not have sufficient surface hardness.

With respect to the sintered products of Examples and Comparative Examples, the number of roots of the ceramic coating and the surface hardness were measured. The measurement results are as follows. Number of roots of ceramic coating (pieces / mm) Surface hardness (HV) Example 1 70 1900 Example 2 40 2000 Example 3 60 1950 Comparative example 1 2100 Comparative example 2 90 1700 It can be clearly seen that the resulting product has a sufficient surface hardness and the ceramic film is deposited in a sufficiently tense state, and the film has good adhesion.

[0037]

In the alloy sintered body obtained by the manufacturing method of the present invention, since the alloy composition of the ceramic alloy powder is appropriate, a thick ceramic film containing an alumina component as a main component is formed on the surface. With high hardness and sufficient wear resistance, and proper content of Zr, Y, Ce, Hf, La, Nd, and Gd, the ceramic film is well rooted in the alloy. Because of this, the adhesion of the ceramic coating is high, and in addition, the alloy inside the sintered body has high toughness and does not cause cracks or chips.
In addition, the manufacturing method of the present invention is very useful because it is suitable for mass production and has sufficient dimensional accuracy.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigekazu Shozusawa 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works Co., Ltd. (72) Hajime Kojima, 1048, Kadoma, Kadoma City, Osaka Matsushita Electric Works Co., Ltd. (72) Inventor Masao Tanahashi 1048 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works Co., Ltd.

Claims (1)

[Claims] 1. Cr: 15-40% by weight, Ni: 2-2
5% by weight, Al: 2 to 8% by weight, Zr, Y, Ce, H
Any one or more of f, La, Nd and Gd: 1 to 2.5% by weight (but not including 1.0% by weight), Ti: 0 to 0.5% by weight, Fe: A compact formed by molding a Fe-Cr-Ni-Al ferrite alloy powder having the composition of the balance is sintered in a non-oxidizing atmosphere, and then heat-treated in an oxidizing gas atmosphere to form alumina on the surface. A method for producing a ferrite alloy sintered body, in which components are precipitated.