JP2000328104A - Sintering method of ferrous sintered alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce sintering time while completely sintering and sufficiently assuring product strength. SOLUTION: In a sintering method of a ferrous sintered alloy in which green compact made of ferrous powder is subjected to induction heating to sinter, a first activation treatment in which the green compact is held in a temperature range between 473 to 673 K and a second activation treatment in which the green compact is held in a temperature range between 973 to 1273 K are executed in a period from stating of heating till the green compact reaches a maximum temperature. Holding time in the above temperature range is 30 to 120 seconds and an average heating rate except holding time in the above temperature range is made to be <=40 K /second.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of sintering an iron-based sintered alloy by heating and sintering an Fe-based green compact by using induction heating. It relates to technology that enables rapid heating while heating.

[0002]

2. Description of the Related Art In recent years, manufacturing processes have been shortened, speeded up, and automated in various industrial fields, and labor saving and unmanned operation have rapidly become transparent. On the other hand, in the manufacturing process of sintered mechanical parts, the sintering process requires a lot of production time, man-hours, and energy consumption, and shortening and speeding up this process is not limited to other fields,
There is a feeling that the process is significantly delayed compared to the processes before and after the process. For example, in a general mesh belt type continuous furnace, 3.
Energy of 5 to 4.0 kWh / kg is required. Further, a large amount of an inert gas of 0.5 to 1 m ³ / kg is introduced for controlling the atmosphere in the furnace, which also imposes a heavy burden on the economy. Therefore, it can be said that performing sintering in a short time is urgently required to reduce the manufacturing cost of sintered parts.

[0003] As a method of performing sintering in a short time, electric current sintering or discharge sintering (sps) is currently applied to some hardly sinterable materials. And there are few applications to general iron-based or copper-based sintered machine parts. This is because it is considered that it is extremely difficult to apply these methods to general sintered machine parts while maintaining the current productivity and economy. Therefore, in recent years, a sintering method using induction heating has attracted attention as a method capable of sintering in an extremely short time. In this induction sintering method, it is possible to raise the temperature rapidly even with an iron-based material, and it is considered to be considerably more effective than the current treatment from the viewpoint of energy saving.

[0004]

However, when the temperature is increased by induction heating, the molten material is efficiently heated and rapidly heated, whereas in the case of a green compact, induction heating is started. Because the temperature rises slowly for a while,
It is known that much time is required to raise the temperature to the 073K region (powder and powder metallurgy, Vol. 27, No. 6,
issue). The time period during which the temperature rise is slow is called the incubation period, and varies depending on the induction coil output, the frequency used, the shape of the induction coil, the shape of the compact, the material composition, etc., but reaches the maximum temperature after the subsequent temperature rise. Longer than the time
This is a major problem in the induction sintering method, in which there is a strong demand for shortening the entire sintering process.

[0005] As described above, the induction sintering method has a problem of incubation period. Therefore, simply shortening the time required to reach the maximum temperature by increasing the output of the induction coil becomes insufficient and the sintering of the sintered product becomes insufficient. The problem of insufficient strength occurs. Therefore,
An object of the present invention is to reduce the time required for the sintering step while improving the material strength of a sintered product by setting the optimum conditions from the start of heating to cooling.

[0006]

A first method of sintering an iron-based sintered alloy according to the present invention is directed to a method of sintering an iron-based sintered alloy by induction-heating and sintering an Fe-based green compact. From the start of heating until the green compact reaches the maximum temperature, 973 ~
It is characterized in that a second activation process for maintaining the temperature in a temperature range of 1273 K is performed.

973 to 1273K (700 to 1000
° C) as shown in the iron phase diagram.
Is the transformation temperature from to .gamma.Fe. In the present invention, the ferrite in the material is austenitized by keeping the material in this temperature range. Further, by maintaining the temperature at such a temperature, the diffusion of graphite contained in the material into the matrix is promoted. Therefore, by appropriately setting the cooling conditions, the sintered product can have a high-strength structure such as pearlite and bainite. In addition, when rapid heating is performed, the gas adsorbed on the powder is sealed in the tissue by sintering soon after the gas is released, and remains as pores. In the present invention, the gas is released during holding.
As described above, in the present invention, austenitization, diffusion of graphite, and degassing are promoted by maintaining the temperature within the above-mentioned temperature range, so that the material strength can be improved even when the temperature raising rate is increased. Hereinafter, preferred embodiments of the present invention will be described.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When powder is mixed, it is common to add a metal soap such as zinc stearate, a wax, etc. as a lubricant when press-molding a green compact. Then, it is considered that such a lubricant increases the electric resistance of the green compact and causes the above-mentioned incubation period. According to “Powder and Powder Metallurgy, Vol. 27, No. 6,” the holding temperature at which the effect of releasing such a lubricant is obtained is 473 K (200 ° C.) or more, and the holding temperature is 673 K (40 ° C.).
It has been clarified that even if the temperature exceeds 0 ° C.), no further improvement in the effect can be expected. Therefore, during the period from the start of heating to the time when the green compact reaches the maximum temperature, 473 to 67
It is desirable to perform the first activation process in which the temperature is maintained in a temperature range of 3K. In some cases, a lubricant is applied to a press molding die without mixing a lubricant with the powder to form a green compact. In this case, the first activation processing is unnecessary.

The time of the above-mentioned first and second activation processes is as follows:
It is desirably 30 to 120 seconds. According to the study by the present inventors, if the holding time is less than 30, the effects of austenitization and degassing are insufficient, and if the holding time exceeds 120 seconds, no further effect can be expected. It is more preferable that the time for the first and second activation processes is 90 to 120 seconds. It is desirable that the average heating rate excluding the time during which the temperature is maintained in the above temperature range is 40 K / sec or less. According to the study of the present inventors, it has been found that when the average heating rate exceeds 40 K / sec, sintering becomes insufficient and the radial crushing strength decreases.

[0010] In the cooling process from the maximum temperature, 10
The cooling rate from 73K to 673K is desirably 4 to 40K / sec. By setting the cooling rate, the structure of the sintered product can be made into high-strength bainite. When the cooling rate exceeds 40 K / sec, the metal structure becomes a brittle martensite structure, and when the cooling speed is less than 4 K / sec, the metal structure remains pearlite.

Further, in the case of sintering by rapid heating, the reaction does not proceed sufficiently at a normal sintering temperature (about 1400 K) due to a high heating rate, and sintering becomes incomplete. According to the study of the present inventor, all the metal structures became pearlite at the sintering temperature of 1523 to 1573K, but it became clear that the surface of the sintered product was thermally deformed at 1573K. Therefore, the sintering temperature is 1503-1 to 20K lower than the above temperature range.
It is estimated that 555K is good.

The Fe-based green compact in the present invention is:
For example, it refers to a powder mainly composed of Fe-C and mixed with additional elements such as Cu, Ni, and Mo, and a powder obtained by compression molding an alloy steel powder composed of such an element. Further, the amount of the lubricant contained in the green compact is desirably as small as possible because it increases the electric resistance and hinders the induction heating.
Therefore, it is preferable that the green compact is formed by applying a lubricant to the cavity surface of the press molding die without adding a lubricant such as metal soap or wax to the powder. Alternatively, even when a lubricant is added to the powder, it is desirable that the weight ratio to the green compact be 0.2% or less. When the amount of the lubricant is 0.2% by weight or less, the influence on the electric resistance is small, and the step of removing the lubricant inside the green compact before the induction heating can be omitted. If the method of applying a lubricant to the cavity surface is used, the content of the lubricant is 0.2% by weight or less.

By setting the lubricant contained in the green compact to 0.2% by weight or less, the fluidity of the powder particles at the time of molding can be improved, and the inside of the green compact can be improved. The dispersion of the density is very small, so that the dimensional accuracy after induction sintering can be improved. When the green compact is induction-heated, the green compact may be directly heated (self-heating), or the green compact is housed in a heating medium such as a carbon container and the heating medium is self-generated. To heat the compact.

[0014]

Hereinafter, the present invention will be described in more detail with reference to specific examples. 1. The sample used in the examples was 10 mm square in cross section and 60 mm in length.
Rod-shaped impact test piece (JIS Z2442) and outer diameter 2
7.03mm, inner diameter 16.03mm and height 10mm
Ring-shaped test piece. The chemical components of the sample are
In the former, Cu: 1.5%, C: 1.0%, Fe:
The balance is as follows: Cu: 1.5%, C: 0.8% by weight,
Fe: The powder was blended so as to be the remainder, and the green compact was formed by mold lubrication to reduce the amount of lubricant contained in the green compact as much as possible. The molding density is 6.8 g / cm ³
And was fixed.

FIG. 1 shows that Cu: 1.5%, C:
1.0%, Fe: shows the fluidity of powder when zinc stearate as a lubricant is added to the remaining powder mixture while changing the compounding amount. As can be seen from FIG. 1, when the amount of the lubricant added is 0.2% by weight or less, the fluidity of the powder particles is very good. Therefore, by setting the amount of the lubricant to 0.2% by weight or less, the density variation inside the compact is minimized, and the dimensional accuracy after induction heating can be improved. In this example, the induction heating was performed without removing the lubricant inside the green compact.

[0016] 2. Sample sintering In this embodiment, a high-frequency heating apparatus shown in FIG. 2 (manufactured by Fuji Denki Koki / THERMMASTER Z: PCD control, PR
Thermocouple). The high-frequency heating device shown in FIG. 1 includes jigs 2 and 2 for holding a sample S and an induction coil 3 surrounding the sample S inside a vacuum chamber 1, and has an output of 15 kW and a frequency of 100 kHz ± 10%. , 1
In a vacuum of about 0 ^-4 torr, the heating rate is 5 to 50 K /
It is variable in the range of s.

[0017] 3. Example 1: Investigation of sintering temperature FIG. 4 shows that the temperature rising rate was constant at 5 K / s using an impact test piece (JIS Z2442), and the sintering temperatures were 1523 K and 15
The outer surface of the sample at 73K and 1623K (Ed
ge) and the microstructure of the center (Center). 1623
In K, linear cementite is observed at the center. The sample melted due to this abnormal precipitation of cementite. On the other hand, the samples of 1523 and 1573K were almost all pearlite, but the sample surface of 1573K was deformed. Therefore, the sintering temperature is the lowest at 1523.
K constant.

[0018] 4. Example 2: Examination of heating rate FIG. 5 shows the microstructure of an impact test piece in which the sintering temperature was set to 1523 K and the heating rate was changed to 5 K / sec, 10 K / sec and 50 K / sec in Example 1. Is shown. When the rate of temperature rise is as fast as 50 K / sec, there is more ferrite than the other two. This is considered to be because graphite cannot react sufficiently due to a high temperature rising rate. The heating rate is 5K / sec,
The sample at 10 K / sec is almost entirely pearlite. However, although the pearlite rate is high at any of the heating rates, it seems that a large amount of unreacted graphite is present.

Therefore, carbon analysis was performed by EPMA on the samples having a heating rate of 5 K / sec and 10 K / sec. FIG. 6 shows the result. In the sample with a heating rate of 10 K / sec, more unreacted graphite was observed than in the sample with a heating rate of 5 K / sec. From this, simply raising the temperature of the sample
Unless the heating rate was set to 5 K / sec or less, it was confirmed that the diffusion of graphite was insufficient and sintering was not complete.

Next, the maximum temperature was kept constant at 1523 K, the heating rate was kept constant at 5 K / sec, and the holding time at the maximum temperature was changed to 60 seconds and 300 seconds for comparison. FIG. 7 shows an electron micrograph of the structure of the impact test piece in that case. Retention time 60
In the second sample, the shape of powder particles still remains in the center, and ferrite is often seen on the outer surface. From this fact, it was found that when the sintering temperature was 1523 K and the temperature was raised at a rate of 5 K / sec, the holding time had to be 300 seconds. About 9
It takes minutes, and the object of the present invention of shortening the sintering time cannot be achieved.

[0021] 5. Example 3: Rate of temperature rise on radial crushing strength
Influence of Cooling Time Using a ring-shaped sample, ordinary induction sintering in which the temperature was raised from room temperature to the maximum temperature was performed, and the relationship between the radial crushing strength and the heating rate and the relationship between the radial crushing strength and the cooling time were examined. FIG. 8 shows the result. In the following description, “cooling time” refers to the time required for cooling from 1073K to 673K, as shown in FIG. As can be seen from this figure, when the heating rate is 5 K / sec, 10 K / sec and 20 K / sec, when the cooling time is as fast as 10 or 20 sec, about 950 N / mm
² and average crushing strength when sintered in a normal continuous furnace (about 83
3N / mm ² ). This is presumably because, even when the inside of the sample was not completely sintered, the microstructure of the sample surface became bainite due to the rapid cooling time, and thus exceeded the average radial crushing strength in a continuous furnace.
On the other hand, in the sample subjected to the rapid heating at 50 K / sec, even if the cooling time was changed, the radial crushing strength of the ordinary continuous furnace was considerably lower. This is presumably because the rate of temperature rise is high and graphite cannot diffuse sufficiently. From the above results, it is thought that in normal induction sintering, the heating rate can be increased to about 30 K / sec by increasing the cooling rate. However, as described below, the problem of incomplete sintering occurs. Remains.

FIG. 9 shows a comparison of micro-woven fabrics in the case where the normal induction sintering shown in FIG. 8 has a heating rate of 20 K / sec and a cooling time different from 10 seconds and 50 seconds. Looking at the braid near the surface of the sample (Outside), it can be seen that the sample of 10 seconds compared to the cooling time of 50 seconds is partially bainite. In addition, the sample middle part (Middle) and the inner part (Insi
In de), almost no difference such as lamella spacing, graphite and pores is observed between the samples having the cooling time of 10 seconds and 50 seconds. Therefore, the reason for exceeding the average radial crushing strength when the sample of 10 seconds was sintered in a normal continuous furnace is that the matrix on the surface of the sample was strengthened due to bainite, and the radial crushing strength was increased. It is considered to be the same as the one with an insufficient cooling time of 50 seconds in that the sintering is incomplete. As described above, at a relatively low heating rate even in normal induction sintering, the strength tends to increase when the cooling time is fast. Not considered suitable for product manufacturing.

[0023] 6. Example 4: First activation treatment A first activation treatment of maintaining the temperature at 523K for 60 seconds during the temperature rise was performed. FIG. 10 shows the relationship between the radial crushing strength and the cooling time, and the relationship between the radial crushing strength and the heating rate of the sample subjected to the first activation treatment whose main purpose is the removal of oxides, moisture and adsorbed gas and the use of a delubricating agent. When the heating rate is as low as 5 and 10 K / sec, any cooling rate exceeds the radial crushing strength of the sample sintered in the continuous furnace. This tendency was not normal induction sintering. However, when the heating rate is 20K / sec and 50K
As fast as / s, cooling times were significantly below normal strength at 50 and 100 seconds. It is considered that when the cooling time is short, the strength was increased because the matrix was partially strengthened by bainite formation, as in the result of FIG. 9, but when the cooling time was slow, the heating rate was fast. It is considered that the sintering did not proceed sufficiently to the inside only by the first activation treatment, and the strength was lowered.

Next, FIG. 11 shows a microstructure in which the first activation treatment was performed at a heating rate of 20 K / sec and a cooling time of 10 and 50 sec. As in FIG. 9, the vicinity of the sample surface (Outsid
Looking at the structure of e), it is considered that the sample with a cooling time of 10 seconds became bainite compared with the cooling time of 50 seconds, which exceeded the average radial crushing strength in a normal continuous furnace. However, there were still many unreacted graphite. ing. In addition, the sample center (Middle), inside (Insi
In de), it can be seen that the pores are large and the sintering is insufficient. These tendencies were almost the same as those of the normal induction sintering microstructure shown in FIG. 9, but the amount of graphite tended to decrease.
For this reason, the temperature rise rate is 5 to 1 in the first activation process alone.
Although the reference value was cleared at 0K, it was found that a sintered part could not be manufactured at a higher heating rate. However, the effects of degassing and delubricating are exhibited by using the second activation treatment described below in combination.

[0025] 7. Example 5: Second activation treatment A second activation treatment in which the temperature was maintained at 1223 K for 60 seconds during the temperature rise was performed. FIG. 12 shows a similar relationship of the sample which has been subjected to the second activation treatment whose main purpose is degassing and graphite diffusion. Samples with heating rates of 5, 10 and 20 K / sec exceeded the average radial crush strength in a continuous furnace at any cooling time. It is considered that this was because the sintering proceeded sufficiently inside the sample by performing the second activation treatment. Samples with a heating rate of 50 K / sec showed higher values as a whole as compared with FIGS. 8 and 10, but did not exceed the average radial crushing strength in a continuous furnace. This is presumably because even if the second activation treatment is performed, if the heating rate is 50 K / sec, graphite cannot sufficiently diffuse. On the other hand, the limit of the heating rate seems to be about 30 K / sec as in FIG. However, sufficient radial crushing strength was obtained at a fairly wide range of cooling rates, indicating the effectiveness of this second activation treatment.

[0026] 8. Embodiment 6: First and Second Activation Process FIG. 3 is a diagram showing a temperature change when both the first and second activation processes are performed. FIG. 13 shows a similar relationship of the sample at that time. Also in this case, as in the case of FIG. 12, the heating rate is 5 K / sec, 10 K / sec and 20 K / sec.
The sample at K / s significantly exceeded the normal radial crushing strength at any cooling time and was about 50% more than in FIG.
N / mm ² showed a higher value. That is, it has been found that this activation treatment is very effective, and the strength can be remarkably improved by combination. However, FIG.
Samples with a heating rate of 50 K / sec as in FIG.
Although it shows a high value as a whole as compared with, the average radial crushing strength in the continuous furnace was not exceeded. Therefore, as described below, in order to examine the fastest heating time, the limit of the heating rate of the sample that has been subjected to the second activation process and the first activation process was examined.

FIG. 15 is similar to FIG. 12 and FIG.
The microstructure when the heating rate is 20 K / sec and the cooling time is 50 seconds is shown. Although some unreacted graphite remains on the outside surface, the inside is almost entirely pearlite compared to FIG. Also, it can be seen that the lamella spacing of the center part (Middle) and the inner part (Inside) is also small. As described above, in the induction sintering, the activation treatment is considered to be very effective also from the observation result of the microstructure. However, the difference between performing only the second activation treatment and performing the first and second activation treatments was not clearly recognized in the microstructure.

9. Example 7: Optimal sintering conditions FIG. 14 shows the limit of the heating rate in order to finish sintering within several minutes, which is the final purpose of the present experiment. As shown in the figure, the temperature increase rate of the sample subjected to the second activation treatment is limited to about 30 to 35 K / sec, and the sample subjected to the first and second activation treatments is limited to about 35 to 40 K / sec. there were. As a result, in the fastest sintering, if the cooling process is not taken into account, the heating time is 30 seconds and the activation time is 60 seconds (second activation processing).
And 120 seconds (first and second activation treatments), the maximum temperature holding time was 60 seconds, and it was found that sintering was completed within 2.5 to 3.5 minutes. That is, according to this embodiment,
It has been confirmed that the heating rate in the present invention is preferably 40 K / sec or less.

FIG. 16 shows that the time of the second activation process is 60 to 1
The relation between the radial crushing strength changed up to 50 seconds and the holding time is shown. When the temperature was maintained at 1223 K for 90 seconds or more in the second activation treatment, a sample sufficiently exceeding the strength level in a normal continuous furnace was obtained even at a heating rate of 40 K / sec. In this, the first and second activation processes were performed with a holding time of 90 seconds or more (FIG. 1).
The result was even better than the result shown in 3), and the effect of the second activation treatment was clearly shown. However, as is apparent from the figure, even when the holding time exceeds 120 seconds, almost no increase in the radial crushing strength is observed, so it was confirmed that the holding time should be 120 seconds or less.

FIG. 17 shows a case where the heating rate is 30K in FIG.
/ Second, the holding time of the second activation process is 90 seconds,
The microstructure of the sample changed to 120 seconds and 150 seconds is shown. As in FIG. 14, unreacted graphite is present on the sample surface side (Outside), but the inside is substantially sintered. Although the heating time is as fast as 30 K / sec as compared with FIG. 14, the microstructures such as the pore ratio and the lamella spacing are almost the same. Further, although the pearlite ratio is slightly increased as the holding time is increased, the holding time is considered to be sufficient for 90 seconds because there is almost no difference in radial crushing strength. That is, the holding time is 90 to 120.
Seconds are preferred.

FIG. 18 shows the microstructure of the sample in which the heating rate was constant at 40 K / sec and the holding time of the second activation treatment was changed to 90, 120 and 150 seconds. FIG.
Although the number of pores is slightly larger than that of No. 7, the pore rate, the lamellar interval, and the like are almost the same even though the heating time is as fast as 40 K / sec as compared with FIG. Has become. Further, although the pearlite ratio slightly increased as the holding time became longer, there was almost no difference in the radial crushing strength as in FIG. 17, so that the holding time of 90 seconds was sufficient. As a result, even if the radial crushing strength and the microstructure are observed, it is considered that by performing the second activation treatment for 90 seconds, it is possible to manufacture a sintered part equivalent to or more than the current continuous furnace.

[0032]

As described above, according to the present invention, the second activation treatment in which the green compact is maintained at a temperature in the range of 973-1273 K from the start of heating until the green compact reaches the maximum temperature. Therefore, the effect is obtained that the sintering can be completed and the sintering time can be significantly reduced while sufficiently securing the product strength.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of lubricant added to powder used in an embodiment of the present invention and the fluidity.

FIG. 2 is a cross-sectional view showing an induction heating device used in an embodiment of the present invention.

FIG. 3 is a diagram showing a temperature change in a sintering step in an example of the present invention.

FIG. 4 is an electron micrograph showing a microstructure of a sample in Example 1.

FIG. 5 is an electron micrograph showing a microstructure of a sample in Example 2.

FIG. 6 is a photograph showing an EPMP analysis result of a sample in Example 2.

FIG. 7 is an electron micrograph showing a microstructure of another sample in Example 2.

FIG. 8 is a diagram showing the relationship between the cooling time and the rate of temperature rise of the sample and the radial crushing strength in Example 3.

FIG. 9 is an electron micrograph showing a microstructure of a sample in Example 3.

FIG. 10 is a diagram showing a relationship between a cooling time and a heating rate of a sample and a radial crushing strength in Example 4.

FIG. 11 is an electron micrograph showing a microstructure of a sample in Example 4.

FIG. 12 is a diagram showing the relationship between the cooling time and the rate of temperature rise of the sample and the radial crushing strength in Example 5.

FIG. 13 is a diagram showing the relationship between the cooling time and the rate of temperature rise of another sample and the radial crushing strength in Example 5.

FIG. 14 is an electron micrograph showing a microstructure of a sample in Example 6.

FIG. 15 is a diagram showing a relationship between a temperature rising rate of a sample and a radial crushing strength in Example 7.

FIG. 16 is a diagram showing the relationship between the holding time of the second activation treatment of the sample and the radial crushing strength in Example 7.

FIG. 17 is an electron micrograph showing a microstructure of a sample in Example 7.

FIG. 18 is an electron micrograph showing a microstructure of another sample in Example 7.

Claims (9)

[Claims] 1. A sintering method for induction-heating and sintering a Fe-based green compact, wherein a temperature range of 973 to 1273K is maintained after the heating is started until the green compact reaches a maximum temperature. A sintering method for an iron-based sintered alloy, wherein a second activation treatment is performed. 2. The method according to claim 1, wherein a first activation process for maintaining the green compact in a temperature range of 473 to 673 K is performed after the heating is started and before the green compact reaches a maximum temperature. The sintering method of the iron-based sintered alloy described in the above. 3. The holding time in the temperature range is 30 to 1
The method for sintering an iron-based sintered alloy according to claim 1, wherein the time is 20 seconds. 4. The method for sintering an iron-based sintered alloy according to claim 1, wherein an average heating rate excluding a time during which the temperature is maintained in the temperature range is set to 40 K / sec or less. 5. The method according to claim 1, wherein the cooling process from the highest temperature comprises 10
The method for sintering an iron-based sintered alloy according to any one of claims 1 to 4, wherein the cooling rate from 73K to 673K is 4 to 40K / sec. 6. The green compact contains 0.2% by weight therein.
The method for producing an iron-based sintered alloy according to any one of claims 1 to 5, further comprising a lubricant such as the following metal soap or wax. 7. The method according to claim 1, wherein the induction heating is performed without removing a lubricant contained in the green compact.
7. The method for producing an iron-based sintered alloy according to any one of claims 6 to 6. 8. The method for producing an iron-based sintered alloy according to claim 1, wherein the green compact does not contain a lubricant such as metal soap or wax therein. . 9. The green compact is heated by directly causing the green compact to self-heat by the induction heating, or by causing a heating medium containing the green compact to self-generate heat. Item 10. The method for producing an iron-based sintered alloy according to any one of Items 1 to 8.