WO1997014523A1 - Iron powder for powder metallurgy, process for producing the same, and iron-base powder mixture for powder metallurgy - Google Patents

Abstract

Iron powder and iron-base powder mixture for powder metallurgy, which can provide sinters excellent in machinability and wear resistance. The iron powder contains 0.03-0.3 wt.% boron, at most 0.07 wt.% chromium, less than 0.3 wt.% manganese, and the balance consisting of iron and unavoidable impurities, and has an intensity ratio of boron to iron of at least 0.05 in the spectrum of the powder surface as determined by Auger electron spectroscopy. The powder serves to increase the amount of graphite remaining in sinters to thereby improve the machinability and wear resistance thereof. Another iron powder is prepared by adding sulfur, selenium, tellurium, molybdenum or the like to the above powder. These powders are mixed with MoO3 or WO3 powder to develop a so-called iron-base powder mixture. It is produced by water-atomizing the above powders while adjusting the oxygen content of molten steel to 100 ppm or below.

Description

 Description Iron powder for powder metallurgy, manufacturing method and iron-base mixed powder for powder metallurgy

 The present invention relates to an iron powder for powder metallurgy, a method for producing the powder, and an iron-based mixed powder for powder metallurgy, and more particularly to a powder that exhibits excellent machinability and abrasion resistance when formed into a sintered body. .

 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, use iron powder for metal powder

If you are 10, C u powder iron powder, mixing the graphite powder and the like, shaped as described above, was sintered, usually from 5.0 to 7. Sintered body having a density of about 2 g / cm ³ To By using such powder metallurgy, machine parts with fairly complex shapes can be manufactured with high dimensional accuracy. However, when manufacturing mechanical parts with strict dimensional accuracy, the sintered body may be subjected to further machining such as cutting or drilling.

I D

 In addition, powder metallurgy products, that is, sintered bodies, generally have poor machinability, so they are more suitable for cutting than in the case of cutting ingots (for example, materials obtained by rolling flakes manufactured by continuous sintering). The life of the tool used is shortened. For this reason, there is a problem that the cost during the machining is increased. The cause of the low machinability of the sintered body is due to 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 cutting portion increases.

Therefore, in order to improve the machinability of the sintered body, S and MnS have conventionally been often mixed with iron powder. These S and MnS facilitated chip breaking Alternatively, 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 molten steel containing pure iron containing 0.1 to 0.5% by weight of Mn and Si, C, etc., and further adding 0.03 to 0.07% by weight of S. It has proposed iron powder for powder metallurgy manufactured by atomizing with water or gas. However, the machinability of the sintered body manufactured using this iron powder has been improved only slightly less than twice that of the sintered body manufactured using the conventional iron powder, and further improvement has been demanded. .

 Japanese Patent Application Laid-Open No. 61-253301 discloses that C: 0.10% by weight or less, n: 2.0% by weight or less, oxygen: 0.30% by weight or less, and Cr: 0.10% by weight. — 5.0% by weight, Ni: 0.10-5.0% by weight, Si: 2.0% by weight or less, Cu: 0.10-1.0% by weight, Mo: 0.01 -3.0% by weight, W: 0.01 -3.0% by weight, V: 0.001 to 2. ◦% by weight, Ti: 0.005 to 0.50% by weight, Zr: 0 005-0. 50% by weight, Nb: 0.005—0.50% by weight, P: 0.03 to 1.0% by weight and B: 0.0005-1.0% by weight We proposed an alloy steel powder containing one or more of these, and if necessary, containing S: 1.0% by weight or less, with the balance substantially consisting of Fe.

However, this alloy powder is made by water atomizing iron powder obtained by roughly reducing iron oxide such as iron ore and mill scale with fine powder coke and molten steel separately pre-alloyed with many metal elements. The obtained mother alloy powder is mixed, and after that, the mixed powder is finish-reduced for production. Therefore, this alloy steel powder was not only manufactured by a very complicated method, but also contained a large amount of many alloying elements, so that it was expensive. The master alloy powder obtained by the above-mentioned water atomization was as follows: C: 0.50% by weight or less, Mn: 5.0% by weight or less, oxygen content: 1.5% by weight or less, and Cr: 0.10% or less. ~ 20.0% by weight, Ni: 0.15 ~ 20.0 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:

0.01 to 5.0% by weight, Ti: 0.01 to 2.0% by weight, Zr:

0.01 to 2.0% by weight, Nb: 0.01 to 2.0% by weight, P: 0.04 to 2.0% by weight, and B: 0.0010 to 2.0% by weight. Contains one or more members of the group, and optionally contains S: 4% by weight or less, with the balance substantially consisting of Fe.

 Accordingly, the applicant of the present invention has disclosed Japanese Patent Application Laid-Open No. 7-233401

As disclosed in Japanese Patent Publication No. 402, a water atomized steel powder containing S, Cr, and Mn was proposed, and the cutability and wear resistance of the sintered body were somewhat improved. 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. Revealed. This residual graphite was considered to suppress the diffusion of graphite into the Cr and S iron powder particles during sintering.

However, even with such steel powder, if the atmosphere gas during sintering contains H ₂ , there is a problem that the cutability and wear resistance of the sintered body are reduced, and further improvement is desired. I was

 Furthermore, the present applicants have filed Japanese Patent Application No. 7-15368, B: 0.001--0.

3% by weight, Cr: 0.02 to 0.07% by weight, Mn: Less than 0.1% by weight, contains a total of at least one of S, Se and Te in a range of 0.03 to 0.15% by weight It has been proposed that sintering the iron powder to be added further increases the amount of residual graphite and improves machinability.

 However, the maximum amount of residual graphite is about 0.42% by weight, and the composition of iron powder with B: more than 0.03% by weight and Mn: more than 0.1% by weight shows improvement in machinability. I couldn't.

Therefore, an iron powder that can obtain a sintered steel containing a large amount of graphite in the sintered body is desired. Had been. 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 wear resistance, a method for producing the same, and other powders added to the iron powder. It is intended to provide a mixed powder added.

 The present inventors have studied on further improving 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, the present inventors have made intensive efforts to find an alloy element that increases the amount of residual graphite from the sintered body described in the above publication. As a result, a new finding that when sintering using iron powder obtained by atomizing molten steel containing B with oxygen below IOOP pm with water significantly increases the amount of residual graphite in the sintered body. Was obtained. Further, the point of the present invention lies in that a certain amount or more of B is biased toward the surface of the iron powder. The present invention embodies this finding.

 B: 0.03-0.3% by weight,

 Cr: 0.07% by weight or less,

 Mn: less than 0.3% by weight,

 And the balance consists of Fe and unavoidable impurities, and the intensity ratio of B to Fe in the emission spectrum obtained by measuring the surface by Auger electron spectrometry is 0.05 or more. This is an iron powder for powder metallurgy.

 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% to less than 0.20% by weight, or Mo: 0.2% by weight. 05-3.5 Iron powder for powder metallurgy characterized by containing 5% by weight.

Furthermore, the present invention is, in the iron powder, powders, characterized in that a mixture of MO0 ₃ powder and 0.05 to 0.7 wt%及beauty or W0 ₃ powder 0.05 to 0.7 wt% It is also an iron-based mixed powder for metallurgy.

 In addition, the present invention relates to a method for producing iron powder for powder metallurgy,

 B: 0.03-0.3% by weight,

 Cr: 0.07% by weight or less,

 Mn: less than 0.3% by weight,

 Oxygen: 1 O O ppm or less,

Using molten steel in which the balance is Fe and unavoidable impurities, water-atomizing the molten steel into powder, and sequentially subjecting the powder to dehydration drying and reduction, It is a manufacturing method.

 In addition, the present invention relates to the above composition of molten steel,

 At least one selected from the group consisting of S, Se, and Te should contain 0.001% by weight to less than 0.20% by weight, and Mo should contain 0.05% to 3.5% by weight. A method for producing iron powder for powder metallurgy characterized by the following.

 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 FIGURES

 FIG. 1 is a view showing an example of a luminescent spectrum obtained by measuring the surface of the iron powder according to the present invention by an 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 horizontal axis of the sputtering time 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 Cr and Mn contents in the iron powder are suppressed to a low level, and instead, B is positively contained so that B is biased on the surface of the iron powder. The result As a result, the amount of residual graphite in the sintered body produced 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 the molten steel containing B is atomized with water, part of B is easily oxidized by water and precipitates as B-based oxide on the surface of the iron powder, and this B-based oxide is being sintered. It is thought that the amount of residual graphite increases because the diffusion of C into iron powder is suppressed.

 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 defines the degree of segregation of B on the surface of the iron powder as described in the claims. On the point. Due to these two points, compared with Japanese Patent Application No. 7-153 638, the amount of residual graphite was increased with a high B composition and a low S composition, and the machinability was further improved. Abrasion resistance was improved. . 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.

Further, in the present invention, the above effects are promoted by using the above B in combination with S, Se, and Te. He also proposed iron powder containing Mo. Contact name The M o, rather than be contained by pre-alloyed with the molten steel stage, who mix the M o 0 ₃ powder to the iron powder according to the present invention described above is, even more machinability of the sintered body Improve. Further, W 0 ₃ powder also exhibits the same effect as the M o 0 ₃ powder was added to the present invention.

 Therefore, the iron powder for powder metallurgy or the iron-based mixed powder according to the present invention is mixed with copper powder or graphite powder as usual to form a compact, and when the compact is sintered, a large amount of residual graphite is obtained. A sintered body excellent in machinability and abrasion resistance contained in the steel can be easily obtained. The reason for limiting the content of each element will be described below. B: 0.3 to 0.3% by weight

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 body. Let As a result, the machinability and wear resistance of the sintered body are improved. Further, since the B-based oxide is very stable and does not react with H ₂ , even if the sintering is performed in a hydrogen atmosphere, the B-based oxide is similar to the steel powder described in Japanese Patent Application Laid-Open No. In addition, the machinability of the sintered body does not decrease. It should be noted that the method of simply mixing Fe-B alloy powder with iron powder containing no B does not increase the amount of residual graphite in the sintered body. There was no improvement in machinability and the like.

 When B is contained in an amount of 0.3% by weight or more, the amount of residual graphite increases remarkably, and the machinability and wear resistance of the sintered body are further improved. Is the lower limit. On the other hand, if 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. Is the upper limit.

 B on iron powder: The intensity ratio of B to Fe in the luminescent spectrum measured by Auger electron spectroscopy is 0.05 or more.

 B, as described above, has an effect of increasing the amount of residual graphite in the sintered body by being present on the surface of the iron powder in a biased manner. B segregated on the surface of the iron powder can be confirmed by measuring by Auger electron spectroscopy. FIG. 1 shows an example of the 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, the peak-to-peak value of Fe corresponding to the electron energy of 703 eV (horizontal axis), and the peak value of B at the position of 179 eV -to-Peak value ratio. According to the research of the inventor, the amount of residual graphite in the sintered body increased when the strength ratio was 0.05 or more, but was not recognized when the strength ratio was less than 0.05. 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 Auge electron spectroscopy. Note that the horizontal axis The aging time is a measure of the distance in the depth direction from the surface of the iron powder. In FIG. 2, the B concentration on the iron powder surface was 17 atomic%. Further, the thickening together with the surface of B, the oxygen are also enriched with, B is Ru seems to be present in B ₂ 0 ₃ forms.

 In the qualitative analysis of iron powder by Auger electron spectroscopy employed in the present invention, the accelerating voltage of the primary electron beam was 10 kV and the beam current was 1. I wA. In addition, the measured data was read as 1. O OeV st step and 50 ms e c st step, the integration was performed once, and a 5-point differentiation was performed to obtain a differential spectrum.

 Cr: 0.07% by weight or less

 Since Cr easily forms oxides and covers the surface of the iron powder and inhibits surface segregation of B, its content must be kept as low as possible. Cr forms carbides and increases the hardness of the sintered body to reduce machinability. Therefore, in the present invention, Cr is set to 0.07% by weight or less. A preferable range is 0.02 to 0.06% by weight in consideration of the machinability and wear resistance of the sintered body and the production cost.

 Mn: less than 0.3% by weight

 Mn is an element that reduces residual graphite. In addition, 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 in increasing the residual graphite in the sintered body. In addition, Mn forms oxides to cover the surface of the iron powder and inhibits segregation on the surface of B. For this reason, if 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. The preferred range is from 0.07 to 0.15% by weight in view of the refining cost required for reducing the amount of Mn in the step of adjusting the molten steel component and the machinability of the sintered body.

Total of one or more of S, Se, and Te: 0.001 to 0.20% by weight S, Se, and Te are included to increase the amount of residual graphite in the sintered body. The total amount is limited to 0.001 to less than 0.20% by weight. If the content exceeds 0.20% by weight, "soot" is generated during sintering, and the mechanical parts as products become too hot. Therefore, this value was set as the upper limit. On the other hand, if the content is less than 0.001% by weight, there is no effect of increasing the amount of residual graphite, so the content is limited to the above range.

 Mo: 0.05-3.5% by weight

 Mo is included 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.

Mo 0 ₃ powder:. 0.05 to 0 7% by weight, W0 ₃ powder:. 0.05 to 0 7% by weight of any one or more

MO0 ₃ and W0 ₃ flour, then mixed with the iron powder according to the present invention is utilized to form the novel powder冶gold for mixed powder. The purpose of the mixing is to improve the machinability of the sintered body and to increase the strength by solid solution hardening. Mixing amount of Mo 0 ₃ powder and WO ₃ powder is at less than 0.05, the effect is not observed, and when it exceeds 0.7 wt%, bainite in the iron particles are generated, the sintered body Strength decreases. For this reason, the mixing amounts were all in the range of 0.05 to 0.7% by weight.

Further, the iron powder, MO0 ₃ powder, W0 ₃ when mixed and any one or more of graphite powder and copper powder powder, known segregation prevention treatment thereto (JP-1 - 1 657 01 JP It is more preferable to mix after applying. It, MO0 ₃ powder, W0 ₃ powder is homogeneously mixed iron powder Runode, compared with the simple mixing method, because Mo in the sintered body, the formation of a solid solution in the iron powder W is uniform quality . As a result, after sintering, the ferrite phase in the iron particles becomes finer, and the strength of the sintered body is increased by about 15% by weight as compared with the case where it is manufactured by a simple mixing method. 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 oxygen (0) content in the molten steel should be 100 ppm or less, preferably 70 ppm or less. If the amount of 0 in the molten steel exceeds 100 ppm, B becomes B ₂ 〇 ₃ before atomization and turns into slag, and the amount of B effective for iron powder decreases. Accordingly, the suppressed as low as possible 0 amount in the molten steel, B was § Bok Mize from dissolving in the molten steel, it is important that the B with water by oxidizing to segregate the iron powder surface as B and B ₂ 0 ₃ is there.

 The iron powder formed by water atomization is then dried, dehydrated and reduced as usual, and then crushed and classified into iron powder.

Example 1

 Iron powder composition: B: 0.02 to 0.10% by weight, Cr: 0.02 to 0.04% by weight, Mn: 0.06 to 0.07% by weight, the balance being Fe and inevitable Nine kinds of atomized iron powder were produced. That is, there are five types of iron powder according to the present invention and four types of iron powder (hereinafter, referred to as comparative examples) for comparing the performance. 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 a powder. This powder was dried under a nitrogen atmosphere at a temperature of 140 ° C. for 60 minutes, and then subjected to a reduction treatment in a pure hydrogen atmosphere at a temperature of 93 (TC temperature for 20 minutes. After cooling, the powder was taken out of the reduction furnace. The powder thus obtained was pulverized and classified to obtain Nos. 1 to 6 shown in Table 1.

 Further, an iron powder containing S: 0.02 to 0.10% by weight in addition to the composition of the iron powder was manufactured by the same manufacturing method. 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 surfaces of Nos. 1 to 9 produced in this way were analyzed by Auger electron spectroscopy. And the intensity ratio of the Peak-to-Peak value of B (179 eV) to the Peak-to-Peak value of Fe (703 eV) is measured from the spectrum. Calculated. The measurement method and measurement 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. Pressure was applied to a density of 6.85 gXcm ³ to obtain a columnar molded body. These compacts were sintered at a temperature of 1130 ° C. for 20 minutes under 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 machinability of each sintered body was evaluated separately by using these iron powders to produce a columnar sintered body with an outer diameter of 60 m πιφ and a height of 1 Omm, and evaluating the sintered body as a test piece. Valued. Specifically, first, a high-speed steel drill with a diameter of 2 mmΦ is rotated under the conditions of 10000 rpm and 0.012 mmZreV, and a number of holes are drilled in the test piece. Then, the average number of holes drilled before the drill cannot be drilled (the average value of three drills) is obtained, and the larger the value (the longer the life of the tool used), the better the machinability. It was.

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

As is evident 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 of 100 ppm or less, and is measured on the surface of the iron powder by Auger electron spectroscopy. The intensity ratio of B to Fe in the spectrum obtained in this way is all 0.05 or more. In addition, the amount of residual graphite in the sintered body was larger than that in the comparative example, and the machinability was greatly improved. 97/14523

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 ¾ 1

 * Inevitable impurities Example 2

0 Separately, atomized iron powder having the composition shown in Table 2 was produced. There are six types of iron powder according to the present invention (No. 11, 12, 16, 18, 23, 24) and four types of iron-based mixed powder (o. 13, 14, 15). And 17), and 4 comparative examples (o. 19-22). Table 2 also shows the elemental content in the molten steel before water atomization.

5 After treating these iron powder and iron-base mixed powder in the same manner as in Example 1, the peak-to-peak value of Fe on the iron powder surface (703_, eV The peak intensity ratio of the Peak-to-Peak value (179 eV) of B with respect to) was measured. Further, the compact was sintered under the same conditions as in Example 1, and the amount of residual graphite and the machinability of the obtained sintered body were evaluated.

Table 2 shows that the sintered body manufactured 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.

Table 2

* Inevitable impurities

Example 3

Water atomized iron powder having the composition shown in Table 3 was produced in the same manner as described above. They are four types of iron powder according to the present invention (Nos. 25 to 28) and three types of comparative examples (Nos. 29 to 31). 2% by weight of graphite powder and 15% by weight of copper powder are added to these iron powders, and 1% by weight of zinc stearate is further mixed as a lubricant, and the mixture is pressed to a density of 6.85 g / cm ³ and molded. Created body. Next, the molded body was sintered at a temperature of 1130 ° C. for 20 minutes in an atmosphere of RX gas (end temperature).

 Table 3 also shows the amount of residual graphite in the sintered body and the vector intensity ratio between Fe and B by the above-mentioned Auge spectroscopy. In addition, a cylindrical test specimen with an inner diameter of 1 ΟηιπιφΧ outer diameter of 20 mmΦ and a height of 8 mm was manufactured for each sintered body, and an S 45C shaft of 1 OmmΦ was placed inside the cylinder, with clearance from the hole wall. Inserted at 20 wm. Then, the abrasion resistance test was performed by rotating the shaft at a peripheral speed of 1 OOmZmin under a dry 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 were seized was used as an index of the wear resistance of the sintered body.

The iron powder Nos. 25 to 28 according to the present invention had wear resistance of a load of 4 kgfZcm ² or more. When the amount of graphite in the sintered body is 1% by weight or more, the abrasion 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 The abrasion resistance of the sintered body manufactured using this was inferior to the iron powder according to the present invention. Good 3

 * Inevitable impurities

Industrial potential

 The powdered metallurgy iron and the iron-based mixed powder according to the present invention, when consolidated into a consolidated compact, has improved machinability and abrasion property of the consolidated body as compared with conventional iron powder and mixed powder. . Therefore, if these powders are used and mechanical parts are manufactured by powder metallurgy, the dimensional accuracy of the mechanical parts will increase and the life will be prolonged. It is.

Claims

 1 B: 0.03-0.3% by weight, Cr: 0.07% by weight or less, Mn: Less than 0.3% by weight, the balance being Fe and unavoidable impurities. When the ratio of the peak value of peak to peak value of B in the emission spectrum obtained by measuring the surface by Auger electron spectroscopy is greater than 0.05, An iron powder for powder metallurgy characterized by the fact that: Enclosure  2. The iron for powder metallurgy according to claim 1, further comprising at least one selected from S, Se and Te in a total amount of 0.01% to less than 0.2% by weight. powder. 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. Iron powder according to claim 1 or 2, characterized in that the mixed Mo 0 ₃ powder and 0.05 to 0. 7% by weight and / or W0 ₃ powder 0.05 to 0.7 wt% Iron-based mixed powder for powder metallurgy. 5. In the method of manufacturing iron powder for powder metallurgy, B _: 0.03-0.3% by weight, Cr _: 0.07% by weight or less, Mn: less than 0.3% by weight, oxygen: 100 ppm or less A method for producing iron powder for powder metallurgy, comprising: using molten steel in which the balance is Fe and inevitable impurities, using water as a powder, and subjecting the powder to dehydration drying and reduction sequentially. . 6. In addition, the composition of the molten steel should be one or more selected from S, Se and Te. 6. The method for producing iron powder for powder metallurgy according to claim 5, wherein the total content of the above is 0.001% to less than 0.20% by weight. 7. The method for producing an iron powder for powder metallurgy according to claim 5, wherein Mo is further contained in the composition of the molten steel in an amount of 0.05 to 3.5% by weight.