JP3353836B2 - Iron powder for powder metallurgy, its production method and iron-base mixed powder for powder metallurgy - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an iron powder for powder metallurgy, a method for producing the same, and an iron-based mixed powder for powder metallurgy. Related to powder that exhibits

BACKGROUND ART In general, powder metallurgy is a technique in which a metal powder is pressurized in a mold to form a molded body, and the molded body is sintered to produce a mechanical part or the like. For example, when using iron powder as the metal powder,
The iron powder is mixed with Cu powder, graphite powder and the like, and the above-described molding and sintering are performed to obtain a sintered body having a density of usually about 5.0 to 7.2 g / cm ³ . By using such powder metallurgy, mechanical parts having fairly complicated shapes can be manufactured with high dimensional accuracy. However, when manufacturing a mechanical part having strict dimensional accuracy, the sintered body may be further subjected to machining such as cutting or drilling.

In addition, powder metallurgy products, that is, sintered products are generally inferior in machinability, so they are used for cutting compared to cutting ingots (for example, materials obtained by rolling slabs manufactured by continuous casting). Tool life is reduced. For this reason, there is a problem that the cost for the machining is increased. The cause of the low machinability of the sintered body is the pores contained in the sintered body. This is because the pores cause intermittent cutting, or the thermal conductivity of the sintered body decreases, and the temperature of the cut portion increases.

Therefore, in order to improve the machinability of the sintered body, conventionally, S
And MnS were often mixed with iron powder. These S and MnS
This is because the chip is easily broken or a thin film of S or MnS is formed on the rake face of the tool, and the thin film exerts a lubricating action during cutting.

For example, Japanese Patent Publication No. 3-25481 discloses that 0.1 to 0.5% by weight M
In addition to pure iron containing n and Si, C, etc., S is further added to 0.03-0.0
We propose iron powder for powder metallurgy, which is produced by atomizing molten steel with 7% by weight of water or gas. However, the machinability of the sintered body manufactured using the iron powder is improved only about two times less than that of the sintered body manufactured using the conventional iron powder, and further improvement has been demanded.

JP-A 61-253301 discloses that C: 0.10% by weight or less, Mn: 2.0% by weight or less, oxygen: 0.30% by weight or less, Cr: 0.10 to 5.0% by weight, Ni: 0.10 to 5.0% by weight %, Si: 2.0
% By weight, Cu: 0.10 to 10.0% by weight, Mo: 0.01 to 3.0% by weight, W: 0.01 to 3.0% by weight, V: 0.01 to 2.0% by weight, Ti: 0.005
~ 0.50% by weight, Zr: 0.005 ~ 0.50% by weight, Nb: 0.005 ~ 0.50
%, P: 0.03 to 1.0% by weight and B: 0.0005 to 1.0% by weight, and contains one or more of the components, and further contains S: 1.0% by weight or less as necessary, and the balance Proposed an alloy steel powder consisting essentially of Fe.

However, this alloyed steel powder was obtained by water atomizing iron powder obtained by roughly reducing iron oxide such as iron ore and mill scale with fine coke and molten steel separately prealloyed with a number of metal elements. The mother alloy powder is mixed, and then the mixed powder is finish-reduced for production. Therefore, this alloy steel powder
Not only is it manufactured by a very complicated method, but also contains a large amount of a large number of alloying elements, so that it is expensive. The mother alloy powder obtained by the above-mentioned water atomization was C: 0.50% by weight or less, Mn: 5.0% by weight or less, and the oxygen content: 1.5% by weight.
% By weight, Cr: 0.10 to 20.0% by weight, Ni: 0.15 to 2%
0.0% by weight, Si: 5.0% by weight or less, Cu: 0.15 to 20.0% by weight,
Mo: 0.015 to 15.0% by weight, W: 0.015 to 15.0% by weight, V: 0.015
~ 5.0 wt%, Ti: 0.01 ~ 2.0 wt%, Zr: 0.01 ~ 2.0 wt%, Nb: 0.01 ~ 2.0 wt%, P: 0.04 ~ 2.0 wt%, and
B: Contains one or more of a component group consisting of 0.0010 to 2.0% by weight, further contains S: 4% by weight or less as needed, and the balance substantially consists of Fe.

Accordingly, the present applicant has proposed water atomized steel powder containing S, Cr, and Mn as disclosed in Japanese Patent Application Laid-Open Nos. 7-233401 and 7-233402, and has improved machinability of a sintered body. The abrasion resistance has been improved somewhat. At this time, when this steel powder is sintered, graphite remains in the pores of the sintered body, and at the same time, MnS precipitates in the iron particles, so that the machinability of the sintered body is dramatically increased. I made it. The residual graphite is
It is considered that Cr and S suppress the diffusion of graphite into the iron powder particles during sintering.

However, even in such a steel powder and has the H ₂ contained in the atmospheric gas during sintering, the cutting and wear resistance of the sintered body has lowered, further improvements are eager I was

Further, the present applicants filed Japanese Patent Application No. 7-15368, B: 0.001 to
0.03% by weight, Cr: 0.02 to 0.07% by weight, Mn: less than 0.1% by weight,
It has been proposed that by sintering iron powder containing at least one of S, Se and Te in a total amount of 0.03 to 0.15% by weight, the amount of residual graphite is further increased and the machinability is improved.

However, the maximum amount of residual graphite was about 0.42% by weight, and no improvement in machinability was observed with an iron powder composition in which the composition of the iron powder exceeded 0.03% by weight and the content of Mn exceeded 0.1% by weight.

Therefore, there has been a demand for iron powder capable of obtaining a sintered steel containing a large amount of graphite in the sintered body.

DISCLOSURE OF THE INVENTION In view of such circumstances, the present invention provides an iron powder for powder metallurgy capable of producing a sintered body exhibiting more excellent machinability and abrasion resistance, a method for producing the same, and other methods. It is an object of the present invention to provide a mixed powder to which the powder of (1) is added.

The present inventors have studied to further improve the machinability and wear resistance of a sintered body with reference to the descriptions in JP-A-7-233401 and JP-A-7-233402.
That is, diligent efforts have been made to find an alloy element that increases the amount of residual graphite compared to the sintered body described in the above publication. As a result, a new finding was obtained that when the molten steel containing B containing 100 ppm or less of oxygen was atomized with water and sintered using iron powder, the amount of residual graphite in the sintered body was significantly increased. Further, the point of the present invention lies in that a certain amount or more of B is segregated on the surface of the iron powder. The present invention embodies this finding, that is, contains B: more than 0.03 to 0.3% by weight, Cr: 0.07% by weight or less, and Mn: less than 0.3% by weight, with the balance being Fe and unavoidable impurities. An iron powder for powder metallurgy, wherein the intensity ratio of B to Fe in the emission spectrum obtained by measuring the surface by Auger electron spectroscopy is 0.05 or more.

Further, the present invention provides that the composition contains at least one selected from S, Se and Te in a total amount of 0.001% by weight to less than 0.20% by weight, or Mo: 0.05 to 3.5% by weight. This is an iron powder for powder metallurgy.

Furthermore, the present invention is, in the iron powder, a MoO ₃ powder 0.05 to 0.7
It is also an iron-based mixed powder for powder metallurgy, wherein 0.05 to 0.7% by weight of WO ₃ powder and / or WO ₃ powder is mixed.

In addition, the present invention provides a method for producing iron powder for powder metallurgy, comprising: B: more than 0.03 to 0.3% by weight, Cr: 0.07% by weight or less, Mn: less than 0.3% by weight, oxygen: 100 ppm or less, with the balance being Is a method for producing iron powder for powder metallurgy, comprising using molten steel containing Fe and unavoidable impurities, subjecting the molten steel to water atomization to obtain a powder, and sequentially subjecting the powder to dehydration drying and reduction.

In addition, the present invention further provides that the composition of the molten steel contains one or more selected from S, Se and Te in a total content of 0.001% by weight to less than 0.20% by weight, or a Mo content of 0.05 to 3.5% by weight. A method for producing iron powder for powder metallurgy.

ADVANTAGE OF THE INVENTION According to this invention, the iron powder for powder metallurgy which can manufacture easily the sintered compact which has the outstanding machinability and wear resistance compared with the former is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of an emission spectrum obtained by measuring the surface of iron powder according to the present invention by Auger electron spectroscopy.

FIG. 2 is a diagram showing an example of the concentration distribution of each element at each position in the depth direction from the surface of the iron powder measured by Auger electron spectroscopy. The sputtering time on the horizontal axis corresponds to the distance in the depth direction from the surface of the iron powder.

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the content of Cr and Mn in iron powder is suppressed to a low level, and instead, B is positively contained, and B is added to the surface of the iron powder.
Was segregated. As a result, the amount of residual graphite in the sintered body manufactured from the iron powder was increased as compared with the conventional sintered body, and the machinability was further improved. At the same time, the self-lubricating action of the residual graphite improves the wear resistance of the sintered body. This is because when atomizing molten steel containing B with water, a part of B is easily oxidized by water and precipitates as B-based oxide on the surface of iron powder, and this B-based oxide is It is considered that the amount of residual graphite increases in order to suppress the diffusion of C into the powder.

The first point of the present invention is to atomize molten steel having an oxygen content of 100 ppm or less, and the second point is that the degree of segregation of B on the surface of iron powder is defined as described in the claims. Due to these two points, the amount of residual graphite was increased with a high B composition and a low S composition as compared with Japanese Patent Application No. 7-15368, thereby further improving the machinability and the abrasion resistance. In particular,
It was found that when the amount of graphite in the sintered body was 1% by weight or more, the abrasion resistance was significantly improved.

In the present invention, the above effects are promoted by using the above B in combination with S, Se, and Te. And then Mo
An iron powder containing iron was also proposed. It should be noted that mixing MoO ₃ powder with the iron powder according to the present invention further improves the machinability of the sintered body, rather than including Mo by pre-alloying at the stage of molten steel. Also, WO ₃ powder has the same effect as MoO ₃ powder, and was therefore added to the present invention.

Therefore, iron powder for powder metallurgy according to the present invention, or an iron-based mixed powder, as usual, mixed with copper powder or graphite powder to form a pressed compact, and when the compact is sintered, a large amount of residual graphite A sintered body containing excellent cutability and wear resistance can be easily obtained. The reason for limiting the content of each element will be described below.

B: more than 0.03 to 0.3% by weight A part of B added to the molten steel precipitates as an oxide on the surface of the iron powder when the molten steel is atomized with water. When the iron powder compact is sintered, the oxide suppresses the diffusion of carbon into the iron powder particles, and increases the amount of residual graphite in the sintered compact. As a result, the machinability and wear resistance of the sintered body are improved. Furthermore, B-based oxide is very stable and does not react with H _2, even if the sintering in a hydrogen atmosphere, in JP-A 7-233401 JP described as steel powder, the sintered body The machinability does not decrease. It should be noted that even if a method in which Fe-B alloy powder is simply mixed with iron powder containing no B, the amount of residual graphite in the sintered body does not increase,
There was no improvement in the machinability of the sintered body.

When B is contained in an amount exceeding 0.03% by weight, the amount of residual graphite increases remarkably and the machinability and wear resistance of the sintered body are further improved. Therefore, in the present invention, the lower limit is 0.03% by weight or more. . On the other hand, when the content of B exceeds 0.3% by weight, a part of B forms a solid solution in the iron powder particles and the hardness of the sintered body increases, and the machinability thereof decreases. I do.

B on the iron powder surface: the intensity ratio of B to Fe in the emission spectrum measured by Auger electron spectroscopy is 0.05 or more. B is, as described above, segregated on the surface of the iron powder. This has the effect of increasing the amount of residual graphite in the sintered body. B segregated on the surface of the iron powder can be confirmed by measurement by Auger electron spectroscopy. FIG. 1 shows an example of an emission spectrum obtained by the measurement.

The inventors obtained the intensity ratio of B to Fe from the spectrum as shown in FIG. Specifically, as shown in the figure, Fe Pea whose electron energy corresponds to 703 eV (horizontal axis)
This is the ratio between the k-to-peak value and the peak-to-peak value of B at the 179 eV position. And according to the inventors' research, this intensity ratio
In the case of 0.05 or more, the amount of residual graphite in the sintered body increased,
Below 0.05, it was not observed. Therefore, in the present invention, the condition of the iron powder is to have an intensity ratio of 0.05 or more.

As an item to be confirmed, FIG. 2 shows an example of the concentration distribution of each element in the depth direction from the iron powder surface measured by Auger electron spectroscopy. In addition, the sputtering time on the horizontal axis is a scale indicating the distance in the depth direction from the surface of the iron powder. In FIG. 2, the B concentration on the surface of the iron powder was 17 atomic%. Also,
With the enrichment at the surface of B, oxygen is also enriched, and it is likely that B exists in the form of B ₂ O ₃ .

In the qualitative analysis of iron powder by Auger electron spectroscopy employed in the present invention, the acceleration voltage of the primary electron beam was set at 10
kV and a beam current of 1.1 μA. The reading of the measured data was 1.00 eV / step, 50 msec / step, the integration was performed 11 times, and a 5-point differentiation was performed to obtain a differential spectrum.

Cr: 0.07% by weight or less Cr easily forms an oxide and covers the surface of the iron powder to inhibit the surface segregation of B. Therefore, the content of Cr must be kept as low as possible. Further, Cr forms carbides, increases the hardness of the sintered body, and lowers the machinability. Therefore, in the present invention, Cr is set to 0.07% by weight or less. In consideration of the machinability and wear resistance of the sintered body and the manufacturing cost, a preferable range is 0.02 to 0.06% by weight.

Mn: less than 0.3% by weight Mn is an element that reduces residual graphite. Further, Mn in the iron powder particles combines with S, Se, and Te to form a compound, and reduces S, Se, and Te, which are effective for increasing the residual graphite in the sintered body. Further, Mn forms an oxide to cover the surface of the iron powder and inhibits segregation on the surface of B. Therefore, when the content is 0.3% by weight or more, the amount of residual graphite in the sintered body is reduced, and the machinability is reduced. At the stage of adjusting molten steel composition
In view of the refining cost required for reducing the amount of Mn and the machinability of the sintered body, a preferable range is 0.07 to 0.15% by weight.

Total of one or more of S, Se, and Te: 0.001 to 0.20% by weight
Less than S, Se and Te are contained to increase the amount of residual graphite in the sintered body. The total amount is 0.001-0.20% by weight
Limited to less than. When the content is 0.20% by weight or more, soot is generated at the time of sintering, and mechanical parts as products tend to be rusted. On the other hand, when the content is 0.001% by weight or less, there is no effect of increasing the amount of residual graphite.

Mo: 0.05 to 3.5% by weight Mo is contained to increase the strength of the iron powder. However, if the amount is less than 0.05% by weight, no improvement in strength is observed, and if it exceeds 3.5% by weight, the machinability of the sintered body is sharply reduced. From the viewpoint of strength and machinability, a preferable range is 0.4 to 0.7% by weight.

MoO ₃ powder: 0.05 to 0.7% by weight, WO ₃ powder: 0.05 to 0.7% by weight Any one or more of MoO ₃ and WO ₃ powder are mixed with the iron powder according to the present invention,
Used to form new powder metallurgy mixes. The purpose of mixing is to improve the machinability of the sintered body and to increase the strength by solution hardening. If the mixing amount of the MoO ₃ powder and the WO ₃ powder is less than 0.05, the above effect is not recognized. If the mixing amount exceeds 0.7% by weight, bainite is generated in the iron particles and the strength of the sintered body is reduced. For this reason, the mixing amounts were all in the range of 0.05 to 0.7% by weight.

In addition, when one or more of MoO ₃ powder and WO ₃ powder, graphite powder and copper powder are mixed with iron powder, a known segregation prevention treatment (Japanese Patent Application Laid-Open No. 1-165701, Japanese Patent Application Laid-Open No. −4720
It is more preferable to mix them after the application. This is because MoO ₃ powder and WO ₃ powder are homogeneously mixed with iron powder, so that Mo and W are more uniformly dissolved in iron powder in the sintered body than in a simple mixing method. As a result, after sintering, the ferrite phase in the iron particles becomes finer, and the strength of the sintered body is 15% by weight compared to the case of manufacturing by a simple mixing method.
Increase to the extent.

Oxygen in molten steel: 100 ppm or less The iron powder according to the present invention is formed by atomizing molten steel adjusted to the above composition range with water. At that time, the amount of oxygen (O) in the molten steel is set to 100 ppm or less, preferably 70 ppm or less. If the amount of O in the molten steel exceeds 100 ppm, B becomes B ₂ O ₃ and becomes slag before atomizing, and the amount of B effective for iron powder decreases. Therefore, the amount of O in the molten steel is kept as low as possible, and B is dissolved in the molten steel and then atomized.
It is important to oxidize B with water and segregate it as B or B ₂ O ₃ on the iron powder surface.

The iron powder formed by the water atomization is then subjected to dry dehydration and reduction as usual, and then pulverized and classified into iron powder.

Example 1 Production of 10 kinds of atomized iron powder whose iron powder composition contains B: 0.031 to 0.10% by weight, Cr: 0.02 to 0.04% by weight, Mn: 0.06 to 0.07% by weight, with the balance being Fe and inevitable impurities. did. That is, there are five types of iron powders according to the present invention and four types of iron powders (hereinafter referred to as comparative examples) for comparing performance results. The method for producing these iron powders is as follows.

First, molten steel having a predetermined composition at a temperature of 1630 ° C. was atomized with water to obtain powder. This powder is placed under nitrogen atmosphere at 140
After drying at a temperature of ℃ for 60 minutes, 930 under pure hydrogen atmosphere
A reduction treatment was performed at a temperature of ° C. for 20 minutes. Then, the powder taken out of the reduction furnace after cooling was pulverized and classified.
Nos. 1 to 6 shown in FIG.

Further, in the same production method, an iron powder containing 0.02 to 0.10% by weight of S in addition to the composition of the iron powder was produced. These are Nos. 7 to 10 shown in Table 1. The oxygen content of the molten steel before atomization was adjusted to 40 to 200 ppm by adding iron carbide.

The emission spectra of the surfaces of Nos. 1 to 10 produced in this manner were measured by Auger electron spectroscopy, and from the spectra, the peak-to-peak value of Fe (703 eV) and the peak value of Pe
The intensity ratio of the k-to-Peak value (179 eV) was calculated. The measuring method and the measuring conditions are as described above.

Next, 1.2% by weight of graphite powder and 2.0% by weight of copper powder were mixed with these iron powders, and 1 part by weight of zinc stearate was added to 100 parts by weight of the mixed powder.
It was pressurized to a cm ³ to obtain a cylindrical molded body. Then, these compacts were sintered at a temperature of 1130 ° C. for 20 minutes in a nitrogen stream containing 10% by volume of hydrogen.

The amount of residual graphite in the obtained sintered body was determined by an infrared absorption method from a filtrate obtained by dissolving a part (sample) of the sintered body with nitric acid and filtering the residue through a glass filter. In addition, the cutability of each sintered body is determined separately by using these iron powders.
A cylindrical sintered body having a diameter of 60 mm and a height of 10 mm was manufactured, and the sintered body was evaluated as a test piece. Specifically, first, the diameter is 2mm
Rotate a φ Heiss drill at 10,000 rpm and 0.012 mm / rev to make many holes in the test piece. Then, the average number of holes (three drills and the average value) of holes drilled before the drill cannot be drilled is determined, and the larger the value (the longer the life of the tool used) is, the better the machinability is. It was done.

Table 1 summarizes the characteristics of the iron powder and the sintered body described above.
Shown in

As is clear from Table 1, the sintered body manufactured from the iron powder for powder metallurgy according to the present invention has oxygen in the molten steel set to 100 ppm or less, and is measured on the iron powder surface by Auger electron spectroscopy. All the intensity ratios of B to Fe in the obtained spectrum are 0.
It is 05 or more. Further, the amount of residual graphite in the sintered body was larger than that in the comparative example, and the machinability was greatly improved.

Example 2 Atomized iron powder having the composition shown in Table 2 was separately manufactured.
That is, the six types of iron powder according to the present invention (No. 11, 12, 16, 18, 23,
24), 3 types of iron-based mixed powder (Nos. 13, 14 and 17), Comparative Example 4
Type (No. 19 to 22). Table 2 also shows the amount of oxygen in the molten steel before water atomization.

After treating the iron powder and the iron-based mixed powder in the same manner as in Example 1, the peak of Fe on the iron powder surface was measured by Auger electron spectroscopy.
The spectrum intensity ratio of the Peak-to-Peak value of B (179 eV) to the -to-Peak value (703 eV) was measured. Further, under the same conditions as in Example 1, the compact was sintered, and the obtained graphite was measured for the residual graphite amount and the machinability was evaluated.

Table 2 shows that the sintered body produced from the atomized iron powder or the iron-based mixed powder according to the present invention has a large amount of residual graphite, a long tool life, and excellent machinability.

Example 3 Water atomized iron powder having the composition shown in Table 3 was produced in the same manner as described above. It is the four types of iron powder according to the present invention (No.
8) and three comparative examples (Nos. 29 to 31). To these iron powders, 2% by weight of graphite powder and 15% by weight of copper powder were added, and 1% by weight of zinc stearate was mixed as a lubricant to obtain a density.
Pressure was applied to 6.85 g / cm ³ to form a molded body. Next, the molded body is placed under an atmosphere of RX gas (endothermic gas).
It was sintered at a temperature of 1130 ° C. for 20 minutes.

Table 3 also shows the residual graphite content of the sintered body and the spectral intensity ratio between Fe and B by the Auger spectroscopy described above. Also,
A cylindrical test specimen having an inner diameter of 10 mmφ, an outer diameter of 20 mmφ, and a height of 8 mm was manufactured from each sintered body, and an S45C shaft having a diameter of 10 mmφ was inserted into the cylinder with a clearance of 20 μm from the hole wall. Then, the abrasion resistance test was carried out by rotating the shaft at a peripheral speed of 100 m / min under a drying condition and gradually increasing the contact load from a low load. That is, the contact load when the shaft and the inner wall of the cylinder are seized is used as an index of wear resistance of sintering resistance.

The iron powder Nos. 25 to 28 according to the present invention had a wear resistance of 4 kgf / cm ² or more. Thus, the amount of graphite in the sintered body is 1
When it is at least% by weight, the wear resistance is remarkably improved. On the other hand, No. 29 of the iron powder used as a comparative example had little segregation of B, and No. 30 did not contain B, and No. 31 contained excessive B, so it was manufactured using them. The wear resistance of the obtained sintered body was inferior to the iron powder according to the present invention.

INDUSTRIAL APPLICABILITY The iron powder for powder metallurgy and the iron-based mixed powder according to the present invention are sintered into a compact, and when sintered, the machinability and wear resistance of the sintered body are reduced by the conventional iron powder and mixed powder. Better than powder. Accordingly, if mechanical parts are manufactured by powder metallurgy using these powders, the dimensional accuracy of the mechanical parts is increased, and the life of the mechanical parts is prolonged. Therefore, the present invention is very useful industrially.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yang Sekiaki 3-10 Koganecho, Niigata City, Niigata Prefecture Mitsubishi Materials Corporation Niigata Works (56) References JP-A-8-176604 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) B22F 1 / 00,9 / 08 C22C 33/02 C22C 38/00-38/60

Claims (8)

(57) [Claims] 1. The composition contains B: more than 0.03 to 0.3% by weight, Cr: 0.07% by weight or less, Mn: less than 0.3% by weight, the balance being Fe and unavoidable impurities, and Auger electron spectroscopy of the iron powder surface. An iron powder for powder metallurgy, wherein a ratio of a Peak-to-Peak value of B to a Peak-to-Peak value of Fe in an emission spectrum obtained by a method is 0.05 or more. 2. The iron powder for powder metallurgy according to claim 1, further comprising one or more selected from S, Se and Te in a total amount of 0.001% by weight to less than 0.2% by weight. 3. The iron powder for powder metallurgy according to claim 1, further comprising Mo: 0.05 to 3.5% by weight in a weight ratio. 4. The iron powder according to claim 1 or 2, wherein MoO ₃ powder is added to the iron powder.
0.05 to 0.7 wt% and / or WO ₃ powder for powder metallurgy iron-based mixed powder, characterized in that the mixing 0.05-0.7% by weight. 5. The method according to claim 1, wherein the molten steel having oxygen (O) of 100 ppm or less is atomized with water.
The iron-based mixed powder for powder metallurgy according to any one of the above. 6. A method for producing iron powder for powder metallurgy,
b: Over 0.03% to 0.3% by weight, Cr: 0.07% by weight or less, Mn: less than 0.3% by weight, oxygen: 100 ppm or less, with the balance being Fe and unavoidable impurities using molten steel, and water atomizing the molten steel. A method for producing an iron powder for powder metallurgy, wherein the powder is subjected to dehydration drying and reduction sequentially. 7. The composition of the molten steel further comprises S, Se and
The method for producing iron powder for powder metallurgy according to claim 6, wherein one or more kinds selected from Te are contained in a total of 0.001% by weight to less than 0.20% by weight. 8. The composition of the molten steel according to claim 8, further comprising 0.05 to 3.
The method for producing iron powder for powder metallurgy according to claim 6, wherein the iron powder is contained in an amount of 5% by weight.