JPH055106A - Production of alloy sintered body - Google Patents

Abstract

PURPOSE:To obtain an alloy sintered body having high surface hardness and excellent wear resistance and hardly causing chipping and cracking by a method with suitability for mass production. CONSTITUTION:A green compact formed by compacting Al-contg. ferrite alloy powder to a prescribed shape is sintered in a nonoxidizing atmosphere and alumina is deposited on the surface of the resulting sintered body by heat treatment in an atmosphere of oxidizing gas.

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-based sintered body which can be applied to blades, gears, shafts and other parts requiring wear resistance.

[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 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.

In the case of using an alloy material, on the other hand, a metal material that is awarded as a super hard material has excellent toughness, but has a surface hardness (Hv = 1100) of that of a ceramic sintered product. It is considerably lower than that of 2000 or more), 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 metal to form a composite film. Specifically, a film of TiN, ZrN or the like is formed on the metal surface by a method such as a sputtering method or a CVD method. In this case, between the 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, so that the mutual adhesion strength is small, 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.

[0004]

In view of the above circumstances, the present invention makes it possible to obtain an alloy-based sintered body having a large surface hardness, excellent wear resistance, and less likely to be chipped or cracked. It is an object to provide a method having suitability for mass production.

[0005]

In order to solve the above-mentioned problems, in the method for producing an alloy-based sintered body of the present invention, a molded body obtained by molding a ferrite alloy powder containing Al into a predetermined shape is placed in a non-oxidizing atmosphere. The alumina component is deposited on the surface by sintering and heat treatment in an oxidizing gas atmosphere.

Examples of the non-oxidizing atmosphere include an inert gas atmosphere as defined in claim 2, a reducing gas atmosphere as defined in claim 3, and a vacuum atmosphere as defined in claim 4. The temperature of heat treatment during sintering in a non-oxidizing atmosphere is
As in claim 4, a temperature range of 1300 to 1400 ° C is preferable. 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 is narrowed.

As a ferrite alloy containing Al, Fe
There are -Cr-Al-based alloys, Fe-Cr-Ni-Al-based alloys, and the like. The hardness of the base material of these alloys is Hv = 200 depending on the kind and content of the metal elements constituting the alloy.
It is less than or equal to or more than Hv = 300, and its value is different. Even if the Fe-Cr-Al-based alloy generally satisfies the toughness, the hardness is Hv = 200 or less, and therefore it is not suitable for applications requiring hardness (for example, mechanical parts such as gears and shafts).

Therefore, the type of the ferrite alloy containing Al is selected according to the application. The Fe-Cr-Ni-Al alloy is suitable for applications requiring a hardness of Hv = 300 or more, and in particular, its composition is Cr: 20 to 35% by weight: N.
i: 2 to 25% by weight, Al: 2 to 8% by weight, Ti: 0.
5% by weight or less, any one or more of Zr, Y, Hf, Ce, La, Nd and Gd: 0.05 to
1.0% by weight, Fe: Fe-Cr-Ni- with the balance
Al-based ferrite alloy is most suitable. Cutlery, or
It is easy to obtain a sintered product suitable for mechanical parts such as gears and shafts that require abrasion resistance. As a matter of course, the ferrite alloy containing Al of the present invention is the Fe--Cr--Ni--
It is not limited to the Al-based ferrite alloy.

The present invention will be described in more detail below. First, for example, Cr: 20 to 35% by weight: Ni: 2
-25 wt%, Al: 2-8 wt%, Ti: 0.5 wt% or less, Zr, Y, Hf, Ce, La, Nd and Gd.
Any one or two or more of the above: 0.05 to 1.0
A ferrite alloy powder containing Al is obtained by dissolving all components in a blending ratio of wt% and the balance being substantially Fe, for example, by atomizing by an atomizing method or atomizing an alloy by a mechanical grinding method. ..

The ferrite alloy powder containing Al 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 product shaped according to the purpose of use, and is different from a base material such as an ingot which is subjected to processing such as grinding in the next step. To give an example of an organic binder,
Organic compounds such as polyvinyl alcohol (PVA) and ethylene glycol may be mentioned.

The pressure during molding is 400 in the case of the present invention.
There is also the application of a low pressure of about MPa, usually 400 to 1
It is selected from the range of about 000 MPa or about 450 to 600 MPa. However, the molding pressure is 400M
If it is less than Pa, it tends to be difficult to obtain dimensional accuracy.
Next, this compact is sintered by heat treatment in a non-oxidizing atmosphere. Heat treatment is 1250-14
It is carried out at 00 ° C (preferably 1300 to 1400 ° C). Within this heat treatment temperature range, sufficient hardness (Hv = about 300) and tensile strength of 100 kg / mm without forming a liquid phase
The above can be obtained, and a base material having sufficient strength can be obtained as a mechanical part.

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 as an 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 sintered body thus obtained is a sintered body of ferrite alloy powder, which is different from ceramics, it does not cause cracks or chips before precipitation of alumina, 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% due to 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 dimensional accuracy is difficult to obtain. 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 and 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 higher than 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 surface layer (alumina film) containing alumina as a main component is attached.
Al alloy type sintered product 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 aluminum element is easily oxidized when heat-treated in an oxidizing gas atmosphere and is made of alumina having high hardness. This is because ceramic can be produced. The alloy-based sintered body thus obtained has a large surface hardness because it has a surface layer 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. In contrast to the fact that sufficient abrasion resistance cannot be obtained because the film thickness of the coating layer is limited,
The surface layer containing alumina as a main component according to the present invention has high adhesion strength to the base material because the root of the alumina is stretched in the base material, and the thickness of the surface layer can be increased to 10 to 50 μm. .. Furthermore, it is possible to shape it into the desired shape through the steps of molding and sintering, and to manufacture it without the need for machining such as inefficient cutting. In this 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.

Articles to which the method of the present invention can be applied include the following. [Cutters used for home] Blades of electric razors, hair clippers (especially pet hair clippers and garden tree hair clippers that can bite small stones, etc.), blades of mowers, cooking mixers, cutters, etc. , Knives, scissors, saw blade for DIY carpenters, etc.

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

[0018]

In the alloy-based sintered body obtained by the manufacturing method of the present invention, the alumina component forming the surface layer is formed by rooting in the alloy filling the interior, so that the adhesion between the surface layer and the alloy is high. And the precipitation of alumina on the surface has the effect of increasing the surface hardness, and the alloy filling the interior of the sintered body has the effect of increasing the toughness of the sintered body.

[0019] Further, the step of molding and sintering into a desired shape improves the economical efficiency and the mass productivity required for industrial production, and therefore 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, it is possible to improve dimensional accuracy. It is also applicable when accuracy is required.

[0020]

Embodiments of the present invention will be described below. The present invention is not limited to the following embodiments. -Example 1-Cr: 24% by weight, Ni: 4% by weight, Al: 3.5% by weight, Zr: 0.05% by weight, and the balance: Fe were alloyed in a high frequency melting furnace. 1 to 2 m of the finished ingot
After rolling to a thickness of m, the obtained plate was cut into chips of 2 to 3 mm square, and then pulverized to obtain a ferrite alloy powder of 50 mesh or less.

PVA was mixed with this powder as a binder to form a slurry, which was then filled in a cavity for molding a gear around which ridges are arranged in parallel, and the gear before sintering was molded by direct pressure molding. This raw gear, which is a compact, was sintered in an argon gas atmosphere at 1250 ° C. for 5 hours to obtain a sintered compact. Next, heating was performed at 1150 ° C. for 10 hours in the atmosphere to deposit alumina on the surface, and as a result, a target gear having a gray surface was obtained.

Table 1 shows the surface hardness of the alumina-precipitated sintered body, the hardness of the internal alloy (shown as the base metal hardness), and the content of the alumina component on the surface. In addition,
When the cross section of the surface layer was observed with an electron microscope, it was confirmed that the alumina had a state in which the protrusions of the needle streak penetrated the alloy inside as it progressed inward from the surface.

-Example 2-Cr: 30% by weight, Ni: 21% by weight, Al: 6% by weight, Ti: 0.5% by weight, Zr: 0.2% by weight, balance:
An alloy having a composition of Fe was melted in a high-frequency melting furnace, the resulting ingot was made into a ferrite alloy powder by an atomizing method, and then molding, sintering and heat treatment were performed in the same manner as in Example 1.

Table 1 shows the surface hardness of the obtained sintered body, the hardness of the alloy (shown as the base metal hardness), and the content of the alumina component on the surface. When the cross section of the surface layer was observed with an electron microscope, it was confirmed that the needle-like protrusions penetrated the alloy inside as the alumina progressed inward from the surface. -Example 3-Cr: 26% by weight, Ni: 21% by weight, Al: 6.5% by weight, Zr: 0.2% by weight, balance: Fe was prepared by melting in an induction melting furnace. After the ingot was made into a ferrite alloy powder by an atomizing method, a gear before sintering was molded by the same method as in Example 1. The green gear, which is a compact, was sintered in a hydrogen gas atmosphere at 1350 ° C. for 5 hours to obtain a sintered compact. Next, heating was performed at 1150 ° C. for 10 hours in the atmosphere to deposit alumina on the surface, and as a result, a target gear having a gray surface was obtained.

Table 1 shows the surface hardness of the alumina-precipitated sintered body, the hardness of the internal alloy (shown as the base metal hardness), and the content of the alumina component on the surface. In addition,
When the cross section of the surface layer was observed with an electron microscope, it was confirmed that the alumina had a state in which the protrusions of the needle streak penetrated the alloy inside as it progressed inward from the surface.

Reference Examples 1 and 2 The hardness (in this case, the surface hardness and the base material hardness) of SKH5, which is a superhard metal material, and alumina, which is a ceramic material, are shown in Table 1 as Reference Examples 1 and 2, respectively. Write together.

[0027]

[Table 1]

-Example 4-Cr: 32% by weight, Ni: 21% by weight, Al: 6.5% by weight, Zr: 0.8% by weight, the balance: Fe, dissolved in the following proportions and atomized by atomization. Fe-Cr-Ni-
An Al-based ferrite alloy powder was obtained. The alloy powder thus obtained and PVA for the binder are mixed, and 45
It was molded at a pressure of 0 MPa. Then, the molded body was sintered by being heat-treated at 1350 ° C. for 3 hours in a vacuum, and then ground and precisely adjusted to a predetermined shape. Next, in an atmosphere, heat treatment is performed at 1150 ° C. for 20 hours and heat treatment at 1250 ° C. for 30 minutes to form an alumina film, which is air-cooled and then Fe—Cr—Ni—Al-based sintered product (alloy-based sintering Got the body).

Example 5-A Fe-Cr-Ni-Al-based sintered product was obtained in the same manner as in Example 4 except that the molding pressure was 600 MPa. -Example 6-Cr: 24% by weight, Ni: 4% by weight, Al: 3.5% by weight, Zr: 0.05% by weight, the balance being substantially Fe so that the components are melted in a high frequency melting furnace. As a result, an alloy ingot was obtained. After rolling this ingot to a thickness of 1 to 2 mm and cutting this plate into chips of 2 to 3 mm square,
Mechanically crushed and Fe-Cr-Ni with 50 mesh or less
-Al type ferrite alloy powder was obtained.

The alloy powder thus obtained and PVA for a binder were mixed and molded at an appropriate pressure in the range of 1000 MPa. Then, the molded body was heat-treated at 1300 ° C. for 5 hours in an argon gas atmosphere to sinter it, followed by grinding to accurately match it with a predetermined shape. Next, in the atmosphere, heat treatment at 1150 ° C. for 20 hours and heat treatment at 1250 ° C. for 30 minutes are performed to form an alumina film, which is air-cooled and then Fe—Cr—Ni—A.
An l-based sintered product was obtained.

Example 7-Cr: 35% by weight, Ni: 21% by weight, Al: 7% by weight, Zr: 0.4% by weight, the balance being substantially Fe, dissolved in a high frequency melting furnace, Fe-Cr-Ni-Al ferrite alloy powder was obtained by atomizing by atomization method. Alloy powder thus obtained and PV for binder
A was mixed and molded at an appropriate pressure in the range of 700 MPa. Then, the formed body is vacuumed at 1350.
After heat treatment at 4 ° C. for 4 hours to sinter, it was ground and adjusted to a predetermined shape. Next, in the atmosphere, heat treatment at 1150 ° C. for 20 hours and 1250 ° C.
A heat treatment was applied for 30 minutes to form an alumina film, which was air-cooled to obtain a Fe-Cr-Ni-Al-based sintered product.

Example 8 F was prepared in the same manner as in Example 7 except that the molding pressure was 900 MPa and the heat treatment temperature for sintering was 1300 ° C.
An e-Cr-Ni-Al-based sintered product was obtained. -Example 9-The alloy powder used in Example 4 was classified to 30 μm or less, and about 10% by weight of paraffin wax,
Knead with a binder containing stearic acid as the main component, and
It was injection-molded into a predetermined shape at 50 ° C. The obtained molded body was held in vacuum at 400 ° C. for 50 hours to be degreased. The degreased molded body is held in vacuum at 1350 ° C. for 3 hours to be sintered, then oxygen gas is fed into the furnace and held at 1250 ° C. for 30 minutes to deposit an alumina film on the surface, Fe
A -Cr-Ni-Al-based sintered product was obtained.

Example 10 An injection-molded article obtained in the same manner as in Example 9 was degreased by holding it at 500 ° C. for 50 hours in an argon gas atmosphere. The degreased molded body was heated to 1350 ° C. in an argon gas atmosphere for 3 hours.
After holding for a time to sinter, the gas in the furnace was replaced with oxygen gas, and the furnace was held at 1250 ° C. for 30 minutes to deposit an alumina film on the surface to obtain a Fe—Cr—Ni—Al-based sintered product. It was

-Example 11-F was prepared in the same manner as in Example 9 except that the alloy powder used in Example 7 was classified and the alloy powder having a particle size of 30 μm or less was used.
An e-Cr-Ni-Al-based sintered product was obtained. Examples 4-11
The state of the alumina coating, the hardness of the base metal and the dimensional accuracy of the sintered product were examined. The results of the examination are shown in Table 2. In Table 2,
A circle in the dimensional accuracy data column indicates that the error is within 5%.

[0035]

[Table 2]

From the results shown in Table 2, it is clearly understood that the sintered products of Examples 4 to 11 have good dimensional accuracy, large surface hardness and are durable. Note that FIG. 1 is an optical microscope photograph (magnification 700 times) showing a metal structure near the surface of the alumina-coated Fe—Cr—Ni—Al-based sintered product of Example 4.
In the photograph of FIG. 1, a white background portion having black spots occupying substantially the lower half is a base material, a black background layer above the base material is an alumina film, and a black background layer above the black background layer is a protective Ni film. FIG. 2 shows the Fe-Cr-Ni-Al with alumina coating of Example 4.
It is an optical microscope photograph (magnification 700 times) showing the metallographic structure inside the system sintered product. FIG. 3 schematically shows the metal structure of the vicinity of the surface of the sintered product of Example 4. As shown in FIG. 2, in the base material portions of FIGS. 1 and 2, the black portion is a cavity, the gray portion is a NiAl phase, and the white portion is a ferrite phase. Further, in FIG. 3, the alumina film 2 is formed on the surface of the base material 3, and the protective film N is formed on the alumina film 2.
1 illustrates a configuration with an i-film 3.

Further, in Example 4, when the processing temperature for sintering was 1200 ° C., there was a tendency that the base material hardness was difficult to be sufficient. Then, in Example 6, an Fe-Cr-Ni-Al-based sintered product was obtained in exactly the same manner except that the molding pressure was set to 350 MPa, but the dimensional accuracy (the error exceeds 5%), the base metal hardness and the The alumina coating state tended to be considerably inferior to that of Example 6.

[0038]

As described above, according to the present invention, it is possible to obtain a useful alloy-based sintered body having a high surface hardness and excellent abrasion resistance in which chipping and cracking are unlikely to occur, and
It is very useful because it is suitable for mass production. Further, when the ferrite alloy powder containing Al having the composition described in claim 6 is used, an alloy-based sintered body suitable for an application in which both surface hardness and base material hardness are required, such as mechanical parts, can be reliably obtained. There is an advantage that.

[Brief description of drawings]

FIG. 1 is an optical micrograph (magnification: 700 times) showing a metal structure near the surface of a sintered product of Example 4.

FIG. 2 is an optical micrograph (magnification: 700 times) showing the metallographic structure inside the sintered product of Example 4.

FIG. 3 is an explanatory diagram showing an outline of a metal structure near the surface of the sintered product of Example 4.

[Explanation of symbols]

 1 Protective Ni film 2 Alumina film 3 Base material

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

Claims (1)

Claim: What is claimed is: 1. A ferrite alloy powder containing Al is molded into a predetermined shape, a compact is sintered in a non-oxidizing atmosphere, and heat-treated in an oxidizing gas atmosphere to form alumina on the surface. A method for producing an alloy-based sintered body, which comprises depositing components. 2. The method for producing an alloy-based sintered body according to claim 1, wherein the non-oxidizing atmosphere is an inert gas atmosphere. 3. The method for producing an alloy-based sintered body according to claim 1, wherein the non-oxidizing atmosphere is a reducing gas atmosphere. 4. The method for producing an alloy-based sintered body according to claim 1, wherein the non-oxidizing atmosphere is a vacuum atmosphere. 5. 1300 to 1400 in a non-oxidizing atmosphere
Sintering is performed by heating at a temperature of ° C.
5. The method for producing an alloy-based sintered body according to any one of 1 to 4. 6. The composition of the ferrite alloy powder containing Al is such that Cr: 20 to 35% by weight: Ni: 2 to 25% by weight,
Al: 2 to 8% by weight, Ti: 0.5% by weight or less, Zr,
Any one or more of Y, Hf, Ce, La, Nd and Gd: 0.05 to 1.0% by weight, Fe:
The method for producing an alloy-based sintered body according to any one of claims 1 to 5, which comprises the balance.