WO2019181449A1

WO2019181449A1 - Surface treatment method, production method of sintered body with oxide film, and sintered body with oxide film

Info

Publication number: WO2019181449A1
Application number: PCT/JP2019/008296
Authority: WO
Inventors: 剛志門村
Original assignee: 日本電産株式会社
Priority date: 2018-03-22
Filing date: 2019-03-04
Publication date: 2019-09-26

Abstract

[Problem] To provide a surface treatment method which can form an oxide film that has a surface with high smoothness and that exhibits excellent an rust prevention effect, a production method for producing a sintered body with said oxide film, and a sintered body with an oxide film. [Solution] In this surface treatment method, a sintered body of a raw material powder containing raw material particles containing Fe is heated in an oxidizing environment at a maximum temperature of 450-900°C for a prescribed time to form an oxide film on the surface thereof. The prescribed time is preferably 0.5 minutes to 1 hour. Further, the oxidizing environment preferably contains oxygen gas and an inert gas, and the ratio of the oxygen gas and the inert gas at the time when the maximum temperature is reached is preferably 1:9-1:30, by volume.

Description

Surface treatment method, method for producing sintered body with oxide film, and sintered body with oxide film

The present invention relates to a surface treatment method, a method for producing a sintered body with an oxide film, and a sintered body with an oxide film.

Conventionally, steam treatment has been used for sealing treatment for the purpose of preventing rust. In this method, an oxide film of Fe ₃ O ₄ (black rust) covering the surface of the sintered body is formed by using high-pressure steam in a processing temperature range of 550 to 600 ° C. (see, for example, Patent Document 1). ).
In addition, for products that require high hardness due to the nature of the product (especially gears, etc.), the hardness is adjusted by performing (gas) soft nitriding or carburizing treatment after the steam treatment.

JP 2012-031965 A

An object of the present invention is to provide a surface treatment method capable of forming an oxide film having a highly smooth surface and exhibiting an excellent rust prevention effect, and sintering with an oxide film capable of producing a sintered body provided with such an oxide film. It is providing the manufacturing method of a body, and a sintered compact with an oxide film.

In the exemplary invention of the present application, a sintered body of raw material powder containing raw material particles containing Fe is heated in an oxidizing atmosphere at a maximum temperature of 450 to 900 ° C. for a predetermined time to form an oxide film on the surface. A surface treatment method characterized by:

In addition, another exemplary invention of the present application includes a step of compression molding raw material powder containing raw material particles containing Fe to obtain a molded body, a step of firing the molded body to obtain a sintered body, And heating the sintered body at a maximum temperature of 450 to 900 ° C. for a predetermined time in an oxidizing atmosphere to form an oxide film on the surface thereof, thereby obtaining a sintered body with an oxide film. It is a manufacturing method of the sintered compact with an oxide film.

Furthermore, another exemplary invention of the present application includes a sintered body of raw material powder containing raw material particles containing Fe, and an oxide film that covers the surface of the sintered body and has an average thickness of 5 μm or more. It is a featured sintered body with an oxide film.

According to the exemplary invention of the present application, an oxide film having a highly smooth surface and exhibiting an excellent antirust effect can be formed.

It is the top view (a) and sectional view (b) which show typically composition of a sintering gear concerning one embodiment of the present invention. It is a figure which shows schematic structure of the shaping | molding apparatus used in manufacturing a sintered gear.

Hereinafter, a surface treatment method, a method for producing a sintered body with an oxide film, and a sintered body with an oxide film according to the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 1 is a plan view (a) and a cross-sectional view (b) schematically showing the configuration of a sintered gear according to an embodiment of the present invention, and FIG. 2 shows a molding apparatus used to manufacture the sintered gear. It is a figure which shows schematic structure.

Below, the case where a sintered compact is used as a sintered gear is demonstrated as a representative.
The direction parallel to the central axis of the sintered gear (the direction perpendicular to the paper surface of FIG. 1A) is the “axial direction”, the direction orthogonal to the central axis is the “radial direction”, and the axis is centered on the central axis. The surrounding direction is called “circumferential direction”.
A sintered gear 1 shown in FIG. 1 includes a disc-shaped gear body 2 and a plurality of teeth 3 that are arranged along the circumferential direction of the gear body 2 and project radially outward. The plurality of teeth 3 are provided at substantially equal intervals.

The sintered gear 1 is composed of a sintered body of raw material powder. The configuration of the raw material powder will be described in detail later.
The size of the sintered gear 1 is not particularly limited because it is designed according to the application to be used, but when the sintered gear 1 is a gear for a robot hand (high-precision gear), for example, the following Designed as such.
The tip circle diameter (indicated by “D” in FIG. 1) of the sintered gear 1 is preferably about 3 to 15 mm, more preferably about 5 to 10 mm. The number of teeth of the sintered gear 1 is preferably about 15 to 40, more preferably about 20 to 35.

Therefore, the module indicating the size (tooth thickness) of the teeth 12 is preferably about 0.15 to 0.3 mm, and more preferably about 0.15 to 0.25 mm. Even such a small (high accuracy) sintered gear 1 can be manufactured with high dimensional accuracy by using the raw material powder of the present invention.
The tooth width of the tooth 12 (indicated by “W” in FIG. 1) is preferably about 1 to 10 mm, and more preferably about 2 to 5 mm.

1 is a so-called spur gear, the present invention is not limited to this, and may be, for example, a screw gear, a bevel gear, a worm gear, a hypoid gear, or the like.
Such a sintered gear 1 is manufactured as follows.
Hereinafter, a method for manufacturing the sintered gear 1 (a method for manufacturing a sintered gear) will be described.

The method for manufacturing a sintered gear according to the present embodiment includes: [1] a molding step of compression molding raw material powder to obtain a molded body having a shape corresponding to the sintered gear 1, and [2] firing the molded body. And a firing step for obtaining a sintered body, and [3] a surface treatment step (corresponding to the surface treatment method of the present invention) for heat-treating the sintered body to form an oxide film covering the surface thereof. Hereinafter, each process will be described sequentially.

[1] Molding process First, a molding apparatus and raw material powder are prepared.
The shaping | molding apparatus 10 shown in FIG. 2 is provided with the shaping | molding die 20 and the feeder 30 which accommodated the raw material powder.
The molding die 20 includes a die 21 having a through hole 211 that penetrates in the thickness direction, and an upper punch 22 and a lower punch 23 that are inserted into the through hole 211 of the die 21. The shape of the inner peripheral surface of the die 21 that defines the through-hole 211 corresponds to the shape (uneven shape) of the outer peripheral surface of the sintered gear 1 to be manufactured.

In the molding apparatus 10, first, the tip of the lower punch 23 is inserted below the through hole 211 of the die 21, and a cavity (space) 212 is formed by the die 21 and the lower punch 23 (FIG. 2A )reference). Next, the feeder 30 is slid on the die 21 so as to cover the cavity 212 with the feeder 30, and the raw material powder is filled into the cavity 212 from the feeder 30 (see FIG. 2B). Thereafter, the feeder 30 is slid on the die 21 so as to be retracted from the cavity 212, the tip of the upper punch 22 is inserted into the cavity 212, and the raw powder is compressed by the lower punch 23 and the upper punch 22. (See FIG. 2C).

The raw material powder used to manufacture the sintered gear 1 is preferably configured as follows.
The raw material powder includes raw material particles having a particle size of a module [mm] or less of the sintered gear 1. With this configuration, the raw material particles can be filled not only into the tooth root portion of the cavity 212 but also into the tooth tip portion as necessary and sufficient.
In particular, in this embodiment, when the minimum particle size of the raw material particles is A [mm] and the maximum particle size is B [mm], the particle size of the raw material particles is adjusted so that B / A is 10 or less. Has been. That is, it is adjusted so that the difference in particle size of the raw material particles contained in the raw material powder does not become large.

B / A is preferably 7 or less, more preferably about 2 to 4. By adjusting B / A to the said range, the remarkable fall of the fluidity | liquidity of raw material powder can be prevented. Thereby, raw material powder can be stably supplied to the cavity 212 and can be filled with high density. Further, in this case, it is possible to prevent the amount of the raw material particles to be discarded from being excessively increased, and to suppress an increase in the cost of the raw material powder and consequently the manufacturing cost of the sintered gear 1.
The maximum particle size B of the raw material particles is preferably not more than half that of the module of the sintered gear 1, and more preferably about 0.35 to 0.45 times the module. Thereby, the filling density to the tooth tip part of the cavity 212 of a raw material particle can be raised more.

When manufacturing the high precision (small) sintered gear 1 as described above, the specific value of the maximum particle size B of the raw material particles is preferably about 0.1 to 0.25 mm. More preferably, it is about 0.2 mm. In this case, the specific value of the minimum particle diameter A of the raw material particles is preferably about 0.02 to 0.05 mm, and more preferably about 0.025 to 0.04 mm.
By setting the minimum particle size A and the maximum particle size B of the raw material particles in the above ranges, the raw material particles can be produced without reducing the fluidity of the raw material powder even when the sintered gear 1 with high precision is manufactured. The tooth tip portion of the cavity 212 can be sufficiently filled.
Here, the particle diameter of the raw material particles can be measured, for example, from a projected image by a laser.

The raw material particles can be produced using, for example, an atomizing method such as a pulverizing method, a water atomizing method, a gas atomizing method, a reduction method, a carbonyl method, or the like.
The constituent material of the raw material particles is a Fe (iron) simple substance, a metal material containing Fe such as an alloy containing Fe as a main component and an arbitrary element. Examples of elements added to the alloy include Cr (chromium), Mo (molybdenum), Mn (manganese), Ni (nickel), Cu (copper), W (tungsten), V (vanadium), and Co ( Cobalt), Si (silicon), C (carbon), and the like.

Such raw material powder may contain a lubricant. Thereby, the fluidity | liquidity of raw material powder can be improved more.
Examples of the lubricant include fatty acids such as stearic acid, metal salts thereof, derivatives thereof (eg, amides, esters, etc.), fluorine resins, and the like. These compounds can be used individually by 1 type or in combination of 2 or more types.
In this case, the amount of lubricant contained in the raw material powder is not particularly limited, but is preferably 5% by mass or less, more preferably about 0.1 to 3% by mass.

In addition, in this embodiment, since the raw material particle | grains with a relatively small particle size are removed, the fluidity | liquidity of the raw material powder itself which does not contain a lubricant is high. Therefore, the fluidity of the raw material powder can be adjusted to a sufficiently high value by containing a small amount (about 0.1 to 0.5% by mass) of a lubricant.
The specific fluidity of the raw material powder is preferably about 25 to 50 sec / 50 g, more preferably about 30 to 40 sec / 50 g. A raw material powder having such a fluidity can be supplied to the cavity 212 with high stability. Here, the fluidity can be measured in accordance with a metal powder-fluidity measurement method defined in JIS Z 2502 (2012).

The pressure at which the raw material powder is compressed (molding pressure) is not particularly limited, but is preferably about 0.5 to 3 tons, and more preferably about 1 to 2 tons.
As described above, the molded body 11 having a shape corresponding to the sintered gear is obtained in the cavity 212.
Thereafter, the die 21 and the lower punch 23 are relatively approached, and the molded body 11 is discharged from the cavity 212.

[2] Firing step Next, the obtained molded body 11 is fired to obtain a sintered body.
By this sintering, in the molded body 11, diffusion occurs at the interface between the raw material particles, leading to sintering. At this time, the molded body 11 is entirely contracted to obtain a high-density sintered body. In the present invention, since the raw material powder as described above is used, the effect is particularly high.
The firing temperature is not particularly limited because it is set depending on the composition, particle size, and the like of the raw material powder used in the production of the molded body 11, but is preferably about 950 to 1300 ° C., and preferably about 1000 to 1200 ° C. Is more preferable.

The firing time is preferably about 0.2 to 3 hours, and more preferably about 0.5 to 2 hours.
Moreover, the atmosphere at the time of baking is not particularly limited, but examples include an air atmosphere, an oxidizing atmosphere, a reducing atmosphere, an inert atmosphere, or a reduced pressure atmosphere obtained by reducing these atmospheres.
Since the sintered body obtained in this way has extremely high dimensional accuracy, the sintered gear 1 can be formed without performing secondary processing such as forging and cutting. The secondary processing refers to processing that mechanically changes the shape of the sintered body, and the secondary processing does not include surface treatment (heating treatment) described later.

The error between the dimension in the radial direction of the sintered gear 1 to be manufactured and the dimension in the radial direction of the obtained sintered body is 6σ, preferably 0.02 mm or less, more preferably 0.005 to 0. About .015 mm. By using the raw material particles having a particle size as described above, it is possible to obtain the sintered gear 1 with high dimensional accuracy.

[3] Surface treatment step Next, the sintered body is heated in an oxidizing atmosphere at a maximum temperature of 450 to 900 ° C. for a predetermined time to form an oxide film (Fe ₃ O ₄ : black rust) on the surface. Surface treatment is performed.
By this surface treatment, the sintered gear 1 is sealed, and the smoothness of the surface is increased. As a result, the slidability of the surfaces of the teeth 3 of the sintered gear 1 is further improved. Further, since the oxide film is formed on the surface, the sintered gear 1 with the oxide film is increased in size by the thickness of the oxide film, so that the dimensional error with the sintered gear 1 to be manufactured is further reduced. Can do.

The maximum temperature of the surface treatment may be about 450 to 900 ° C., preferably about 550 to 850 ° C., and more preferably about 650 to 800 ° C. When the maximum temperature is set, the surface treatment time can be shortened.
The predetermined time (treatment time) is set according to the maximum temperature and is not particularly limited, but is preferably about 0.5 minutes to 1 hour, more preferably about 0.5 to 30 minutes. More preferably, it is about 1 to 10 minutes. By performing the surface treatment at the maximum temperature for such time, an oxide film having a sufficient thickness is formed.

An oxidizing atmosphere is an atmosphere containing a relatively large amount of oxidizing gas, excluding a water vapor atmosphere. The oxidizing atmosphere preferably contains oxygen gas and inert gas. With this configuration, the final hardness of the sintered gear 1 (sintered gear 1 with oxide film) can be controlled by appropriately selecting the type of inert gas. Therefore, the hardness of the sintered gear 1 can be easily adjusted according to the product standard.
Examples of the inert gas include rare gases such as argon gas, nitrogen gas, and the like. These gases can be used alone or in combination of two or more.

Moreover, it is preferable to start supplying the inert gas into the oxidizing atmosphere after the heating of the sintered gear 1 is started so that the ratio of the oxygen gas is reduced. Thereby, it is possible to prevent the surface oxidation of the sintered gear 1 from proceeding rapidly, in other words, the surface oxidation can proceed under mild conditions. For this reason, an oxide film with little variation in thickness and quality is formed.
When the maximum temperature is reached, the ratio of the oxygen gas to the inert gas is preferably about 1: 9 to 1:30, more preferably about 1:12 to 1:25 in terms of volume ratio. By making the ratio of oxygen gas and inert gas at the time of reaching the maximum temperature within the above range, the generation of Fe ₂ O ₃ (red rust) can be suppressed.

The average thickness of the formed oxide film is preferably 5 μm or more, more preferably about 7.5 to 25 μm, and further preferably about 10 to 20 μm. Thereby, a rust prevention effect can be improved more. Such a relatively thick oxide film is difficult to form by a conventional method using water vapor.
As described above, the sintered gear 1 and the sintered gear 1 with an oxide film (sintered body with an oxide film) covering the surface of the sintered gear 1 and having an oxide film having an average thickness of 5 μm or more are obtained. It is done.

The oxide film formed in this way has a small surface roughness (Ra) and high smoothness, and thus has excellent slidability. Therefore, breakage of the sintered gear 1 due to sliding of other members can be suitably prevented, that is, durability can be improved.
Further, the Vickers hardness of the oxide film is preferably about 400 to 750 Hv, and more preferably about 450 to 600 Hv. An oxide film having such hardness has particularly high slidability.
According to such surface treatment, the conventional water vapor treatment and hardness adjustment treatment can be performed simultaneously in one step. Since the resulting oxide film is dense, a high antirust effect is expected.

As mentioned above, although the surface treatment method of this invention, the manufacturing method of the sintered compact with an oxide film, and the sintered compact with an oxide film were demonstrated based on suitable embodiment, this invention is not limited to these.
Further, the sintered gear 1 is not only an industrial machine part such as a robot hand, but also, for example, an automobile part, a bicycle part, a railway vehicle part, a marine part, an aircraft part, a space transportation part, etc. It is used for parts for electronic equipment such as parts for transportation equipment, parts for personal computers and parts for portable terminals, parts for electric equipment such as refrigerators, washing machines and air conditioners, parts for plants, parts for watches, and the like.

Furthermore, the sintered body is not limited to the sintered gear 1 and can be a component that allows other members to slide on the surface of the oxide film. Examples of such parts include bearings and cylinders.

Next, examples of the present invention will be described.
1. Manufacture of sintered gear with oxide film

(Example 1)
[A] First, raw material particles containing Fe as a main component (maximum particle size B: 0.212 mm, manufactured by Höganäs) were prepared.
[B] Next, particles having a particle diameter of less than 0.032 mm were removed from the raw material particles using a sieve. Therefore, B / A is 6.6.

[C] Next, the raw material particles and N, N′-ethylenebisstearamide (manufactured by Kao Corporation, “KAO WAX EB-FF”) as a lubricant are mixed for 30 minutes with a V-type mixer, and the raw material is mixed. A powder was obtained. The amount of N, N′-ethylenebisstearamide contained in the raw material powder was adjusted to 0.2% by mass. Moreover, when the fluidity of the obtained raw material powder was measured using a fluidity measuring device (in-house manufactured, based on JIS Z 2502 (2012)), it was 30 sec / 50 g.
Next, this raw material powder was compression molded using a molding apparatus shown in FIG. 2 to obtain a molded body. The pressure during compression molding was 1.1 ton and the temperature was room temperature.

[D] Next, the obtained molded body was fired at 1200 ° C. for 1 hour in an air atmosphere to obtain a sintered gear (sintered body). The shape of the sintered gear was a tip diameter 9 mm, a module 0.3 mm, and 27 teeth. The result of measuring the dimensional error in the thickness direction of the sintered gear with a micrometer at this point. It was 0.02 mm at 6σ.

[E] Next, the obtained sintered gear was housed in a furnace, and heating was started. At this time, supply of air and argon gas into the furnace was also started. The maximum temperature was set to 750 ° C., and this maximum temperature was maintained for 10 minutes. Further, the supply amount of argon gas was sequentially increased, and the ratio of oxygen gas and inert gas when reaching the maximum temperature of 750 ° C. was set to be 1:15 in volume ratio.
In this way, an oxide film was formed on the surface of the sintered gear. As a result, a sintered gear with an oxide film was obtained.

(Example 2)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the maximum temperature during the surface treatment was 600 ° C. and was maintained at this maximum temperature for 15 minutes.
(Example 3)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the maximum temperature during the surface treatment was set to 450 ° C. and was maintained at this maximum temperature for 40 minutes.

Example 4
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the maximum temperature during the surface treatment was 850 ° C. and was maintained at this maximum temperature for 5 minutes.
(Example 5)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the maximum temperature during the surface treatment was 900 ° C. and was maintained at this maximum temperature for 1 hour.
(Example 6)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the shape of the sintered gear was 6 mm in tip diameter, 0.2 mm in module, and 28 teeth. In addition, the result of having measured the dimensional error in the radial direction of a sintered gear with a factory microscope (measurement microscope). It was 0.02 mm at 6σ.

(Comparative Example 1)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the maximum temperature during the surface treatment was 400 ° C. and was maintained at this maximum temperature for 1.5 hours.
(Comparative Example 2)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the maximum temperature during the surface treatment was 1000 ° C. and this maximum temperature was maintained for 1 minute.
(Comparative Example 3)
A sintered gear with an oxide film was formed in the same manner as in Example 1 except that instead of the combination of air and argon gas, heat treatment was performed on the sintered gear at 600 ° C. for 15 minutes using water vapor. Got.

2. Measurement and evaluation 2-1. Measurement of Average Thickness of Oxide Film The average thickness of the oxide film formed in each example and each comparative example was measured by a cross-sectional observation method.
2-2. Measurement of surface hardness About the sintered gear with an oxide film obtained in each Example and each comparative example, the surface Vickers hardness was measured using the micro Vickers hardness meter.

2-3. Evaluation of Rust Prevention Effect In each example and each comparative example, 10 sintered bodies with oxide films were manufactured. 5% by mass of salt water was sprayed on each oxide film-attached sintered gear, and the surface condition was visually observed over time.
Then, the degree of occurrence of red rust was evaluated according to the following four-stage evaluation criteria.

[Evaluation criteria]
A: The occurrence of red rust is hardly confirmed even after 24 hours of salt spray.
B: The occurrence of some red rust is confirmed after 24 hours of salt spray.
C: Many red rusts are observed after 24 hours of salt spray.
D: Generation of many red rusts is confirmed after 8 hours of salt spray.
These measurement results and evaluation results are shown in Table 1 below together with the composition of the raw material powder.

As described above, an oxide film having a sufficient thickness was obtained by subjecting the sintered gear to heat treatment in the temperature range of 450 to 900 ° C. The sintered gear provided with such an oxide film had a high surface hardness. It was also found that the surface roughness of the oxide film was small and the surface was smooth. These are considered to be involved in the high rust prevention effect.
On the other hand, an oxide film having a sufficient thickness could not be obtained by performing heat treatment outside the above temperature range or by performing heat treatment using water vapor. The sintered gear provided with such an oxide film has a surface hardness that is not as high as expected. In addition, the surface roughness of the oxide film was large, and thus the antirust effect was low.
From the results of the antirust effect, the Vickers hardness of the oxide films of Examples 2 and 3 is about 500 to 550 Hv, the Vickers hardness of the oxide films of Examples 4 and 5 is about 450 to 500 Hv, and Comparative Examples 1 and 2 The Vickers hardness of the oxide film is estimated to be less than 400 Hv.

DESCRIPTION OF SYMBOLS 1 ... Sintered gear 11 ... Molded object 2 ... Gear main body 3 ... Teeth 10 ... Molding device 20 ... Mold 21 ... Die 211 ... Through-hole 212 ... Cavity 22 ... Upper punch 23 ... Lower punch 30 ... Feeder

Claims

A surface treatment characterized in that a sintered body of raw material powder containing raw material particles containing Fe is heated in an oxidizing atmosphere at a maximum temperature of 450 to 900 ° C. for a predetermined time to form an oxide film on the surface. Method.
2. The surface treatment method according to claim 1, wherein the predetermined time is 0.5 minute to 1 hour.
The oxidizing atmosphere includes oxygen gas and inert gas;
3. The surface treatment method according to claim 1, wherein a ratio of the oxygen gas and the inert gas at the time when the maximum temperature is reached is 1: 9 to 1:30 in volume ratio.
The surface treatment method according to claim 3, wherein after the heating of the sintered body is started, the supply of the inert gas into the oxidizing atmosphere is started so as to reduce the ratio of the oxygen gas.
The surface treatment method according to claim 1, wherein an average thickness of the oxide film is 5 μm or more.
Compression molding raw material powder containing raw material particles containing Fe to obtain a molded body;
Firing the molded body to obtain a sintered body;
Heating the sintered body at a maximum temperature of 450 to 900 ° C. for a predetermined time in an oxidizing atmosphere to form an oxide film on the surface thereof, thereby obtaining a sintered body with an oxide film. The manufacturing method of the sintered compact with an oxide film characterized.
The sintered body is a sintered gear;
The raw material particles have a particle size of the sintered gear module [mm] or less;
The method for producing a sintered body with an oxide film according to claim 6, wherein B / A is 10 or less, where A [mm] is the minimum particle size of the raw material particles and B [mm] is the maximum particle size.
The method for producing a sintered body with an oxide film according to claim 7, wherein the module of the sintered gear is 0.15 to 0.3 mm.
The sintered body with an oxide film according to claim 7 or 8, wherein after obtaining the sintered body, the sintered body is used as the sintered gear without subjecting the sintered body to secondary processing. Production method.
10. The error between the radial dimension of the sintered gear to be manufactured and the radial dimension of the obtained sintered body is 0.02 mm or less at 6σ. Of manufacturing a sintered body with an oxide film.
A sintered body of raw material powder containing raw material particles containing Fe;
A sintered body with an oxide film, which covers the surface of the sintered body and has an oxide film having an average thickness of 5 μm or more.
The sintered body with an oxide film according to claim 11, wherein the oxide film has a Vickers hardness of 400 to 750 Hv.
The sintered body with an oxide film according to claim 11 or 12, wherein the surface of the oxide film is a surface on which another member slides.
The sintered body with an oxide film according to claim 11, wherein the sintered body is a sintered gear.