JP2019203173A - Method for manufacturing test sintered body - Google Patents

Abstract

To provide a method for manufacturing a test sintered body allowing for manufacturing a test sintered body for finding out a proper forming condition in a short time.SOLUTION: A method for manufacturing a test sintered body comprises a preparation step that prepares a raw material powder containing a ferrous powder, a formation step that makes a green compact by press-forming the raw material powder, and a test-sintering step that test-sinters the green compact by high-frequency induction heating.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a test sintered body.

  As a method for manufacturing an iron-based sintered member used for automobile parts or general machine parts, for example, a method for manufacturing a sintered body of Patent Document 1 is known. In this method for producing a sintered body, a pre-fired body is produced by pre-baking a compact body obtained by press-molding metal powder at a temperature lower than the main firing temperature before the main firing (main sintering). The calcined body has high mechanical strength as compared with the molded body before calcining, and is hardly chipped by machining. The calcined body is easy to machine because it has lower hardness than the sintered body after main calcining. Therefore, it is easy to manufacture a pre-fired body having a predetermined shape, and thus a sintered body (sintered member).

JP 2007-77468 A

  It is desired to produce a sintered member that is substantially free of defects such as cracks in a short time. For this purpose, it is necessary to find an appropriate molding condition in a short time that can produce a green compact with substantially no wrinkles. However, if the molding conditions have been confirmed through pre-baking and main baking as in the prior art, it takes a long time to find appropriate molding conditions. This is because the calcination and the main calcination are generally performed by atmospheric heating, and thus the rate of temperature increase is slow. Therefore, there is room for further improvement in order to efficiently produce a sintered member that is practically free from wrinkles.

  Accordingly, an object of the present invention is to provide a method for producing a test sintered body that can produce a test sintered body for finding appropriate molding conditions in a short time.

The manufacturing method of the test sintered body according to the present disclosure is as follows.
A preparation step of preparing a raw material powder containing iron-based powder;
A molding step of pressure-molding the raw material powder to produce a green compact,
A test sintering step in which the green compact is subjected to test sintering by high-frequency induction heating.

  The method for producing a test sintered body according to the present disclosure can produce a test sintered body for finding an appropriate molding condition in a short time.

<< Description of Embodiments of the Present Invention >>
First, the contents of the embodiments of the present invention will be listed and described.

(1) A method for producing a test sintered body according to an aspect of the present invention includes:
A preparation step of preparing a raw material powder containing iron-based powder;
A molding step of pressure-molding the raw material powder to produce a green compact,
A test sintering step in which the green compact is subjected to test sintering by high-frequency induction heating.

  According to said structure, a test sintered compact can be manufactured in a short time. This is because high-frequency induction heating can raise the temperature rapidly.

  As will be described in detail below, the test sintered body can be produced in a short time, so that the time required to find an appropriate molding condition for producing a green compact having substantially no defects such as cracks can be shortened. Therefore, a green compact with substantially no wrinkles can be produced in a short time, and the sintered compact with substantially no wrinkles can be produced in a short time by subjecting the green compact to a main sintering. Therefore, the productivity of the sintered member substantially free from wrinkles can be increased.

  The test sintered body can be used for a flaw detection step (details will be described in an embodiment described later) for detecting the presence or absence of flaws such as cracks. By examining the presence or absence of wrinkles in the test sintered body, the presence or absence of wrinkles in the green compact can be determined. This is because if wrinkles are formed in the green compact, the wrinkles are substantially maintained in the test sintered body that has undergone the subsequent test sintering step. Depending on the wrinkle detection method, the test sintered body is checked for the presence of wrinkles rather than the presence of wrinkles on the green compact itself. This is because it is difficult to be destroyed during the detection operation, and it is easy to perform the wrinkle detection operation.

  If the presence or absence of wrinkles in the green compact is known, the suitability of the molding conditions of the green compact can be determined. That is, when there are wrinkles in the green compact, the molding conditions are inappropriate. When there are substantially no wrinkles in the green compact, the molding conditions are appropriate. When the molding conditions are inappropriate, it is necessary to review the molding conditions and find an appropriate molding condition for producing a green compact having substantially no wrinkles. This is because if the green compact with the wrinkles is subjected to main sintering, the wrinkles that are the starting point of fracture are substantially maintained, and thus a sintered member with low strength is produced.

  To find the proper molding conditions, set the molding conditions to produce a green compact until the wrinkle detection result is “no wrinkle” → test-sinter the green compact to The operation of “preparation → detection of wrinkles of test sintered body” is repeated as one cycle. Since the test sintered body can be manufactured in a short time, the time of one cycle (cycle time) can be shortened. In particular, the time required for the test sintering step among the cycle times is likely to be the longest. Therefore, the ability to manufacture the test sintered body in a short time is effective in reducing the cycle time. That is, the suitability of the molding conditions of the green compact can be determined in a short time. Thereby, appropriate molding conditions for producing a compacted body substantially free from wrinkles can be obtained in a short time. The operation of finding the appropriate molding conditions must be performed, for example, every time at least one of the shape, size, and material of the sintered member to be manufactured is changed. If an appropriate molding condition is found, a sintered compact substantially free from wrinkles can be manufactured by subjecting the green compact to main sintering without test sintering.

  In other words, since the test sintered body can be manufactured in a short time, an appropriate molding condition can be obtained in a short time, and a compacted body substantially free of wrinkles can be manufactured in a short time, and the flaws free of flaws can be produced. The binding member can be manufactured in a short time. Therefore, the productivity of the sintered member substantially free from wrinkles can be increased.

  In addition, as will be described in detail below, since the test sintered body can be manufactured in a short time, it is possible to suppress a decrease in the productivity of the green compact and to greatly reduce energy waste in the production process.

  Regardless of the test sintering method, the molding apparatus is stopped without being operated during the period from the start of the test sintering process (completion of the molding process) to the completion of the soot detection process (while no soot detection result is output). On the other hand, this sintering furnace keeps the furnace temperature at the sintering temperature of the green compact even if there is no green compact to be sintered. This is to prevent the raw material powder from being wasted by preventing the compacting body from being produced under inappropriate molding conditions by stopping the molding apparatus. On the other hand, by maintaining the furnace temperature of the main sintering furnace at a predetermined temperature, the temperature of the sintering furnace is lowered and the time required for raising the temperature again to the predetermined temperature is reduced, thereby reducing the work efficiency. It is for suppressing.

  However, if the manufacturing time of the test sintered body is long as in the prior art, it takes a long time to obtain appropriate molding conditions, so the down time of the molding apparatus becomes longer, and the productivity of the green compact is increased. This reduces the productivity of the sintered member. Moreover, the holding time of the furnace temperature becomes long, and a huge amount of energy is wasted.

  On the other hand, according to the method for producing a test sintered body according to one aspect of the present invention, since the test sintered body can be produced in a short time, the appropriate molding conditions can be obtained in a short time as described above. The down time of the apparatus can be shortened, and the holding time of the furnace temperature of the sintering furnace can be shortened. Therefore, it is possible to suppress a reduction in productivity of the green compact and to greatly reduce energy waste in the production process.

(2) As one form of the manufacturing method of the said test sintered compact,
In the test sintering step, the temperature rising rate of the green compact may be 5 ° C./second or more.

  According to said structure, since a temperature increase rate is sufficiently quick, a test sintered compact can be manufactured in a short time.

(3) As one form of the manufacturing method of the said test sintered compact,
A holding time at the test sintering temperature of the green compact is 1 second or more and 240 seconds or less.

  If the holding time is 1 second or longer, the green compact can be sufficiently heated, so that a test sintered body can be manufactured. In addition, since the holding time is moderately long, it is easy to produce a test sintered body with high strength. If the holding time is 240 seconds or less, the holding time is reasonably short, so that the test sintered body can be easily manufactured in a short time.

(4) As one form of the manufacturing method of the said test sintered compact,
The atmospheric temperature at the time of the test sintering of the said compacting body is 380 degreeC or more and less than 1250 degreeC.

  If the said atmospheric temperature is 380 degreeC or more, a compacting body can fully be heated and a test sintered compact can be manufactured. In addition, since the ambient temperature is moderately high, it is easy to produce a test sintered body with high strength. If the said atmospheric temperature is less than 1250 degreeC, since temperature is not too high, temperature rising time can be shortened and it is easy to manufacture a test sintered compact in a short time.

<< Details of Embodiment of the Present Invention >>
Details of the embodiment of the present invention will be described below.

[Method for producing test sintered body]
The method for producing a test sintered body according to the embodiment includes a preparation step of preparing a raw material powder of the test sintered body, a forming step of pressure-molding the raw material powder to create a green compact, and a green compact And a test sintering process for test sintering. One of the features of the method for producing the test sintered body is that the test sintering is performed using a specific method in the test sintering process. Hereinafter, details of each process will be described.

[Preparation process]
In the preparation step, raw material powder containing iron-based powder is prepared. Examples of the iron-based powder include any one of the following powders (a) to (d).
(A) Pure iron powder only (b) Mixed powder containing both the pure iron powder and alloying element powder (c) Iron alloy powder only (d) Composite powder containing both the mixed powder and iron alloy powder

(A: Pure iron powder only)
As the pure iron powder, for example, water atomized powder, gas atomized powder, carbonyl powder, and reduced powder can be used. As for the average particle diameter of pure iron powder, 20 micrometers or more and 200 micrometers or less are mentioned, for example. By making the average particle size of the pure iron powder within the above range, it is easy to handle and press-mold. By setting the average particle size of the pure iron powder to 20 μm or more, it is easy to ensure fluidity. By setting the average particle size of the pure iron powder to 200 μm or less, it is easy to obtain a sintered body having a dense structure. As for the average particle diameter of pure iron powder, 50 micrometers or more and 150 micrometers or less are mentioned further. The “average particle size” is a particle size (D50) at which the cumulative volume in the volume particle size distribution measured by a laser diffraction particle size distribution measuring device is 50%. This also applies to the average particle size of alloying element powder and iron alloy powder described later.

(B: mixed powder)
The mixed powder includes the pure iron powder and the alloying element powder. The alloying element powder is a powder that reacts with pure iron powder to form an iron alloy when the mixed powder is pressed and sintered. Examples of the alloying element powder include a powder of at least one alloying element selected from Ni, Cu, Cr, Mo, Mn, and C. The alloying element improves the hardenability and contributes to the improvement of the mechanical properties of the sintered member. Among the alloying elements, the content of Ni, Cu, Cr, Mn, and Mo powders is more than 0% by mass and 10.0% by mass or less when the mixed powder is 100% by mass, and 5.0%. The mass% or less, especially 0.1 mass% or more and 2.0 mass% or less are mentioned. On the other hand, the content of the C powder is more than 0% by mass and 2.0% by mass or less, and further 0.1% by mass or more and 1.0% by mass or less when the raw material powder is 100% by mass. The average particle size of each alloying element powder is preferably smaller than the average particle size of pure iron powder. If it does so, since it is easy to disperse | distribute each alloying element powder uniformly between pure iron particles, alloying will advance easily. The content of the pure iron powder in the mixed powder is, for example, 90% by mass or more and further 95% by mass or more when the mixed powder is 100% by mass.

(C: iron alloy powder only)
The iron alloy powder has a plurality of iron alloy particles containing iron as a main component and containing one or more additive elements selected from the above alloying elements. That is, examples of the additive element include Ni, Cu, Cr, Mo, Mn, and C. Iron alloys are allowed to contain inevitable impurities. Specific iron alloys include stainless steel, Fe-C alloy, Fe-Cu-Ni-Mo alloy, Fe-Ni-Mo-Mn alloy, Fe-Cu alloy, Fe-Cu-C alloy. Fe-Cu-Mo alloy, Fe-Ni-Mo-Cu-C alloy, Fe-Ni-Cu alloy, Fe-Ni-Mo-C alloy, Fe-Ni-Cr alloy, Fe-Ni -Mo-Cr alloy, Fe-Cr alloy, Fe-Mo-Cr alloy, Fe-Cr-C alloy, Fe-Ni-C alloy, Fe-Mo-Mn-Cr-C alloy, etc. Can be mentioned.

  As for iron content in an iron alloy, when an iron alloy is 100 mass%, 90 mass% or more, Furthermore, 95 mass% or more is mentioned. The total content of additive elements in the iron alloy is more than 0% by mass and 10.0% by mass or less, and further 0.1% by mass or more and 5.0% by mass or less. The content of C in the iron alloy is more than 0% by mass and 2.0% by mass or less, and further 0.1% by mass to 1.0% by mass. C may not be included as an additive element of the iron alloy but may be included in the raw material powder as a powder. That is, the raw material powder may contain C powder in addition to the iron alloy powder.

  As for the average particle diameter of iron alloy powder, 20 micrometers or more and 200 micrometers or less are mentioned similarly to the average particle diameter of the above-mentioned pure iron powder, for example.

(D: Composite powder)
The composite powder includes both the above mixed powder and the above iron alloy powder. That is, the composite powder includes pure iron powder, alloying element powder, and iron alloy powder. The total content of iron contained in the pure iron powder and the iron alloy in the composite powder is 90% by mass or more, and further 95% by mass or more when the total composite powder is 100% by mass. The total content of the alloying element powder in the composite powder and the additive elements in the iron alloy is 1% by mass or more, and further 2% by mass or more and 10% by mass or less when the total composite powder is 100% by mass. It is done.

(Content)
The content of the iron-based powder in the raw material powder is, for example, 90% by mass or more when the raw material powder is 100% by mass, and further 93% by mass or more, 95% by mass or more, particularly 97% by mass or more, 99 The mass% or more is mentioned.

(Other)
<lubricant>
The raw material powder may have a lubricant. The lubricant improves the lubricity at the time of molding the raw material powder and improves the moldability. Examples of the lubricant include higher fatty acids, metal soaps, fatty acid amides, higher fatty acid amides, and the like. Examples of the metal soap include zinc stearate and lithium stearate. Examples of fatty acid amides include stearic acid amide, lauric acid amide, and palmitic acid amide. Examples of the higher fatty acid amide include ethylene bis stearic acid amide. The presence form of the lubricant is not limited to a solid form, a powder form, or a liquid form. As the lubricant, at least one of these can be used alone or in combination. The content of the lubricant in the raw material powder is, for example, 0.1% by mass to 2.0% by mass, and further 0.3% by mass to 1.5% by mass, when the raw material powder is 100% by mass. The following are mentioned, and 0.5 mass% or more and 1.0 mass% or less are mentioned especially.

<binder>
The raw material powder may contain an organic binder. Examples of the organic binder include polyethylene, polypropylene, polymethyl methacrylate, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyamide, polyester, polyether, polyvinyl alcohol, vinyl acetate, paraffin, and various waxes. The content of the organic binder is 0.1% by mass or less when the raw material powder is 100% by mass. If it does so, since the ratio of the metal powder contained in a molded object can be increased, it will be easy to obtain a compact compacted object. When no organic binder is contained, it is not necessary to degrease the green compact in a subsequent step.

[Molding process]
In the forming step, the raw powder is pressure formed to produce a green compact. Examples of the shape of the green compact include a shape along the final shape of the sintered member, specifically, a columnar shape, a cylindrical shape, and the like. For the production of the green compact, an appropriate molding device (mold) that can be molded into the above-mentioned shape is used. For example, it is possible to use a die capable of uniaxial pressing so as to be press-formed along the axial direction of a column or cylinder. The higher the molding pressure, the higher the density of the green compact, and the higher the strength of the test sintered body. The molding pressure is, for example, 400 MPa or more, further 500 MPa or more, and particularly 600 MPa or more. Although the upper limit of a shaping | molding pressure is not specifically limited, For example, 2000 Mpa or less is mentioned, Furthermore, 1000 Mpa or less is mentioned, Especially 900 Mpa or less is mentioned. The green compact may be appropriately cut. A known process can be used for the cutting process.

[Test sintering process]
In the test sintering step, the green compact is heated to produce a test sintered body. For this heating, high frequency induction heating is used. Since high-frequency induction heating can increase the temperature rapidly, the green compact can be raised to a predetermined temperature in a short time. Therefore, the test sintered body can be manufactured in a short time. For the high-frequency induction heating, for example, a high-frequency induction heating apparatus including a power source capable of adjusting output and frequency, a coil connected to the power source, and a storage container that is disposed in the coil and stores the compacted body is used. Yes (not shown). The high-frequency induction heating device preferably further includes a gas supply path for supplying an inert gas into the storage container and a gas discharge path for discharging the gas outside the storage container. Then, the green compact can be test sintered in a non-oxidizing atmosphere. Examples of the inert gas include nitrogen gas and argon gas. In this test sintering process, a temperature raising process, a high temperature holding process, and a cooling process are sequentially performed.

(Heating process)
In the temperature raising process, the production time of the test sintered body can be shortened as the rate of temperature rise in the temperature range below the test sintering temperature is increased. The temperature rising rate is preferably 5 ° C./second or more, for example. Then, since the temperature rising rate is sufficiently fast, the test sintered body can be manufactured in a short time. The heating rate is preferably 10 ° C./second or more, and more preferably 15 ° C./second or more. Although the upper limit of the said temperature increase rate is not specifically limited, For example, 50 degrees C / sec or less is mentioned. The heating rate can be adjusted by adjusting the output and frequency of the power source of the high-frequency induction heating device.

(High temperature holding process)
The holding time at the atmospheric temperature (test sintering temperature) during the test sintering of the green compact is, for example, preferably from 1 second to 240 seconds, although it depends on the atmospheric temperature (test sintering temperature). If the holding time is 1 second or longer, the green compact can be sufficiently heated, and a test sintered body can be produced. In addition, since the holding time is moderately long, it is easy to produce a test sintered body with high strength. If the holding time is 240 seconds or less, the holding time is reasonably short, so that the test sintered body can be easily manufactured in a short time. The holding time is further preferably 10 seconds or longer and 150 seconds or shorter, and particularly preferably 30 seconds or longer and 90 seconds or shorter.

  The test sintering temperature of the green compact is not particularly limited as long as the strength is such that the test sintered body is not destroyed in the soot detection step described later. For example, the test sintering temperature is preferably 400 ° C. or higher and 1250 ° C. or lower. When the test sintering temperature is 400 ° C. or higher, the green compact can be sufficiently heated, and the test sintered body can be manufactured. In addition, since the test sintering temperature is moderately high, it is easy to produce a test sintered body with high strength. By being able to manufacture a test sintered body having a high strength, it is easy to perform the soot detection step described later. Furthermore, a test sintered body having a high strength can be expected to be used for a destructive test and a strength test. If the test sintering temperature is 1250 ° C. or lower, the temperature is not excessively high, so that the temperature raising time can be shortened and the test sintered body can be easily manufactured in a short time. The test sintering temperature is preferably 450 ° C. or more and 1200 ° C. or less, and particularly preferably 500 ° C. or more and 1185 ° C. or less.

  The atmospheric temperature during the test sintering of the green compact is preferably 380 ° C. or higher and lower than 1250 ° C. If the test sintering temperature of the green compact meets 400 ° C or higher, the ambient temperature during the test sintering of the green compact satisfies 380 ° C or higher. Similarly, if the test sintering temperature of the green compact satisfies 1250 ° C. or lower, the ambient temperature during the test sintering of the green compact satisfies less than 1250 ° C. The ambient temperature during the test sintering is preferably 430 ° C. or more and 1185 ° C. or less, and particularly preferably 480 ° C. or more and less than 1185 ° C. The atmospheric temperature is the temperature of the atmosphere in the storage container, and is the temperature measured with a thermocouple (diameter: Φ3.5 mm) disposed within 8.5 mm from the compact. Since the atmosphere in the storage container is warmed by the heat of the compacted body heated by induction, the ambient temperature is often a little lower than the temperature of the compacted compact itself heated by induction. .

(Cooling process)
The temperature lowering rate in the cooling process of the test sintering process is not particularly limited and can be appropriately selected. As for the said temperature fall rate, 1 degree-C / sec or more is mentioned, for example. Then, since the temperature drop rate is fast, the test sintered body can be manufactured in a short time. The temperature lowering rate is preferably 5 ° C./second or more, more preferably 15 ° C./second or less. As for the upper limit of the said temperature fall rate, 50 degrees C / sec or less is mentioned, for example.

[Usage]
The method for producing a test sintered body according to the embodiment is to produce various types of general structural parts (sintered parts such as sprockets, rotors, gears, rings, flanges, pulleys, bearings, and other mechanical parts). Can be suitably used. The test sintered body manufactured by the method for manufacturing a test sintered body according to the embodiment can be suitably used for a soot detection process described later. Moreover, although explanation is omitted, this test sintered body is expected to be usable for a destructive test and a strength test, depending on its strength.

(Wrinkle detection process)
In the flaw detection step, the presence or absence of flaws such as cracks in the test sintered body is detected. If wrinkles of the test sintered body are detected, it is understood that wrinkles are present in the green compact. This is because wrinkles of the compacted body are substantially maintained in the test sintered body even after the subsequent test sintering process. That is, if there is a flaw in the test sintered body, it is found that the molding conditions of the green compact are inappropriate. If there is no flaw in the test sintered body, the molding conditions of the green compact are appropriate. I understand.

  The soot detection method is not particularly limited as long as it can detect soot in the test sintered body. Examples of the wrinkle detection method include at least one of magnetic particle inspection, eddy current inspection, ultrasonic inspection, laser flaw inspection, and image recognition.

  In the magnetic particle flaw detection, the presence or absence of wrinkles can be detected by magnetizing the test sintered body and observing the change in the magnetic powder pattern adhered thereto. Eddy current flaw detectors detect wrinkles using changes in current. For example, when a detection coil that has passed an alternating current is brought close to the test sintered body, a certain eddy current flows through the test sintered body. The current value changes. The change can detect the presence or absence of wrinkles. An ultrasonic flaw detector detects wrinkles using reflection of ultrasonic waves. For example, the ultrasonic wave transmitted from the ultrasonic sensor is reflected on the surface of the test sintered body, received by the ultrasonic sensor, and converted into a voltage. Since there is a difference in the converted voltage depending on the presence or absence of wrinkles, the presence or absence of wrinkles can be detected from this voltage difference. The laser soot inspection device detects soot using reflection of laser light. For example, when the surface of the test sintered body is irradiated with laser light, the laser light receiving position reflected by the presence or absence of wrinkles changes. The wrinkles can be detected from the difference between the reflected laser light receiving positions. The image recognition device detects wrinkles using an image captured by the imaging device. For example, wrinkles can be detected by recognizing the shape of the wrinkles by image processing (such as binarization processing).

[Function and effect]
The method for producing a test sintered body according to the embodiment is to test-sinter a green compact by high-frequency induction heating, thereby increasing the rate of temperature increase during test sintering. The test sintered body can be manufactured in a short time.

《Test example》
The difference in production time due to the difference in the production method of the test sintered body was evaluated.

[Sample No. 1-No. 3]
Sample No. 1-No. Two test sintered bodies were prepared in the same manner as in the above-described test sintered body manufacturing method through a preparation process, a molding process, and a test sintering process. Sample No. 1-No. Each of the test sintered bodies 3 has a different kind of raw material powder prepared in the preparation process.

[Preparation process]
Sample No. As the raw material powder 1, pure iron powder was prepared. The average particle diameter (D50) of the pure iron powder is 65 μm.

  Sample No. As the raw material powder 2, a mixed powder containing Fe powder, Cu powder and C powder was prepared. The average particle diameter (D50) of the Fe powder is 65 μm, the average particle diameter (D50) of the Cu powder is 22 μm, and the average particle diameter (D50) of the C powder is 18 μm. The content of each powder was such that the content of Cu powder was 2 mass%, the content of C powder was 0.8 mass%, and the content of Fe powder was the balance.

  Sample No. As the raw material powder 3, a mixed powder containing Fe powder, Ni powder, Mo powder, Cu powder, and C powder was prepared. The average particle diameter (D50) of the Fe powder is 65 μm, the average particle diameter (D50) of the Ni powder is 10 μm, the average particle diameter (D50) of the Mo powder is 10 μm, and the average particle of the Cu powder The diameter (D50) is 22 μm, and the average particle diameter (D50) of the C powder is 18 μm. The content of each powder is such that the content of Ni powder is 4% by mass, the content of Mo powder is 0.5% by mass, the content of Cu powder is 1.5% by mass, and the content of C powder is The content was 0.5% by mass, and the content of Fe powder was the balance.

[Molding process]
The raw material powder was pressure-molded to produce a compacted body (outer diameter: 34 mm, inner diameter: 20 mm, height: 10 mm). The molding pressure was 600 MPa.

[Test sintering process]
The green compact was heated by high frequency induction to produce a test sintered body. In this example, a power source capable of adjusting output and frequency, a coil (wire diameter: 10 mm, inner diameter: 50 mm) connected to the power source, a storage container that is disposed in the coil and stores the green compact, and a storage container A high-frequency induction heating apparatus including a gas supply path for supplying inert gas to the inside and a gas discharge path for discharging gas to the outside of the storage container was used. The storage container is made of a material (ceramics) that is not induction-heated. Nitrogen gas was used as the inert gas. In the test sintering process, a temperature rising process, a high temperature holding process, and a cooling process were sequentially performed. Each process was performed while measuring the ambient temperature. The measurement of the atmospheric temperature was performed with a thermocouple (diameter: Φ3.5 mm) arranged within 8.5 mm from the green compact in the storage container.

(Heating process)
In the temperature raising process, the temperature was raised with the output and frequency of the power source of the high-frequency induction heating apparatus kept constant without changing the way. Here, the temperature increase rate (° C./second) was set to 5 ° C./second or more. Specifically, the output was approximately 6.0 kW and the frequency was 3.5 kHz.

(High temperature holding process)
In the high temperature holding process, the green compact was held at a predetermined temperature for a predetermined time. Sample No. 1-No. In No. 3, when the measured atmospheric temperature became the temperature shown in Table 1, the atmospheric temperature was held for the time shown in Table 1. Here, the output of the power source of the high frequency induction heating apparatus was adjusted so as to maintain the ambient temperature.

(Cooling process)
In the cooling process, the test sintered body was cooled by spraying a cooling gas (nitrogen gas) on the test sintered body. Here, the temperature decrease rate (° C./second) was set to 1 ° C./second or more.

  The rate of temperature increase, the rate of temperature decrease, and the elapsed time were determined from the transition (temperature profile) of the ambient temperature from the temperature increase process to the cooling process in each sample. The rate of temperature increase was determined as the rate in the ambient temperature range (from 25 ° C. to 1135 ° C.) corresponding to the temperature of the green compact from the temperature increase start to the test sintering temperature. The rate of temperature decrease was determined as the rate in the ambient temperature range (from 1135 ° C. to 200 ° C.) corresponding to the time from the start of cooling (sintering completion) to the completion of cooling. The elapsed time was determined as the time from the start of temperature rise to the completion of the test sintering (start of cooling) and the time from the start of temperature rise to the completion of cooling. These results are shown together in Table 1.

[Sample No. 101-No. 103]
Sample No. 101-No. Each of the test sintered bodies of Sample No. 103 was the same as Sample No. 1, except that an atmosphere sintering furnace was used in the test sintering process. 1-No. It was produced in the same way as 3. The temperature and time shown in Table 1 were set as the temperature of the green compact during the test sintering and the holding time at that temperature, respectively. The temperature of the green compact was measured with a temperature sensor (radiation thermometer R-4601 manufactured by Anritsu Keiki Co., Ltd.). Sample No. From the temperature profile of No. 101, sample no. Similarly to 1 and the like, the temperature increase rate, the temperature decrease rate, and the elapsed time were obtained. The results are shown in Table 1.

[Density measurement]
The apparent density (g / cm ³ ) of the test sintered body of each sample was measured by the Archimedes method. The apparent density of the test sintered body is “(dry weight of test sintered body) / {(dry weight of test sintered body) − (weight in water of oil immersion material of test sintered body)} × density of water”. I asked for it. The weight in water of the oil-immersed material of the test sintered body is the weight of a member obtained by immersing the test sintered body immersed in oil and immersed in water. Table 2 shows the measurement results of the apparent density of the test sintered body of each sample.

[Evaluation of strength]
The strength of the test sintered body of each sample was evaluated. The strength was evaluated by measuring the crushing strength and the Rockwell hardness HRB.

[Compression strength]
The measurement of the crushing strength was performed in accordance with “Sintered bearing-crushing strength test method JIS Z 2507 (2000)”. Specifically, two plates are arranged on the cylindrical test sintered body so as to face each other in the radial direction, the test piece is sandwiched between these plates, and a load is applied to one plate. . And the maximum load when a cylindrical test sintered compact fractures | rupture was calculated | required, and this maximum load (n = 3 average) was evaluated as crushing strength (MPa). The results are shown in Table 2.

[Rockwell hardness]
The measurement of Rockwell hardness HRB was performed based on "Rockwell hardness test-test method JIS Z 2245 (2016)". Here, three locations were measured for each of the upper and lower end surfaces of the test sintered body, and the average values of the upper and lower end surfaces were determined. The intervals along the circumferential direction between the measurement points on each end face were made uniform. The results are shown in Table 2.

  As shown in Tables 1 and 2, Sample No. 1-No. 3 is sample No. 101-No. In a shorter time than 103, Sample No. 101-No. It was found that a test sintered body having a density equivalent to 103 and a strength equivalent to 103 can be produced. Therefore, it can be seen that a high-strength test sintered body can be produced in a short time by high-frequency induction heating.

  The present invention is not limited to these exemplifications, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

Claims (4)

A preparation step of preparing a raw material powder containing iron-based powder;
A molding step of pressure-molding the raw material powder to produce a green compact,
A test sintered body manufacturing method comprising: a test sintering step of performing test sintering of the green compact by high frequency induction heating.   The method for producing a test sintered body according to claim 1, wherein in the test sintering step, the temperature rising rate of the green compact is 5 ° C./second or more.   The method for producing a test sintered body according to claim 1 or 2, wherein a holding time of the green compact at a test sintering temperature is 1 second or more and 240 seconds or less.   The method for producing a test sintered body according to any one of claims 1 to 3, wherein an atmospheric temperature during the test sintering of the green compact is 380 ° C or higher and lower than 1250 ° C.