JPH07157803A - Water atomized iron powder for powder metallurgy and production thereof - Google Patents

Abstract

PURPOSE:To produce an iron powder for powder metallurgy, minimal in the range of fluctuation in dimensional change at the time of sintering, at a low manufacturing cost by successively applying water atomization and drying to a molten steel having specific composition under specific conditions. CONSTITUTION:A molten steel, having a composition consisting of, by weight, <=0.01% C, <=O.30% Mn, <=0.30% Ni, <=0.01% Cr, =0.05%, in total, of P and S, and the balance essentially upon, is atomized in an atomizing atmosphere of <=5.0vol.% oxygen concentration by using a water jet of a pressure of 4-20MPa to undergo water atomization. The iron powder prepared by water atomization is dried at 100-300 deg.C in a nonoxidizing atmosphere, in an H2 atmosphere, or in vacuum. By the above procedure, the water atomized iron powder, in which the hardness of the cross section of a grain is regulated to Hv80-250 and the surface of a grain is covered with the oxide reducible in a sintering atmosphere and which has <=1.0wt.% oxygen content, can be obtained. By this method, the water atomized iron powder for powder metallurgy, capable of producing a sintered compact excellent in dimensional accuracy, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called water atomized iron powder for powder metallurgy produced by a spraying method using water and a method for producing the same.

[0002]

2. Description of the Related Art Generally, the manufacturing process of water atomized iron powder is
Atomizing process of spraying molten steel adjusted to obtain the desired composition with high-pressure water, annealing softening and quenching structure by the atomizing process, annealing softening / reduction process of reducing and removing oxide film on the particle surface, the annealing softening / reduction It consists of a crushing step of crushing the powder agglomerated by the steps, and there is a limit to cost reduction as long as this manufacturing step is protected.

In the case of producing a sintered part using this iron powder, a step of further adding a lubricant or additive alloy component powder to the iron powder and press-molding, a step of sintering the compact at a high temperature, Further, it comprises a sizing process for adjusting the dimensions, and the whole process becomes longer. In these steps, it is necessary to reduce the cost, for example, to reduce the manufacturing cost of automobile parts, and many efforts have been made for that purpose.

However, in order to fundamentally reduce the cost, it is necessary to basically omit the steps. In particular, omitting the annealing softening / reduction process shortens the process,
Greatly reduces costs by reducing equipment costs, labor costs, and utility costs. However, if the annealing softening / reduction step is omitted, the iron powder is usually hard to form due to the quenching structure when it is water-atomized and dried, and a considerable amount of oxygen is brought into the iron powder that is the sintering material. Therefore, this process was not omitted because oxygen impairs the properties of the sintered parts and the sintered products, and oxygen is generally considered to be harmful to the sintered parts.

For example, Japanese Patent Application Laid-Open No. 51-20760 discloses a method for producing iron powder using a converter or a vacuum decarburizer for smelting molten steel, but the powder is annealed after water atomizing and drying. -Includes a reduction process. In addition, Japanese Patent Publication No. 56-45963 discloses that a so-called finishing powder that has undergone an annealing / reduction process,
A method for improving the characteristics of iron powder by mixing atomized raw iron powder that has not been subjected to a reduction step is disclosed. In this invention, although positively trying to use the atomized raw iron powder that does not go through the annealing / reduction process, the predetermined characteristics are not obtained with the atomized raw iron powder that does not go through the annealing / reduction process. It is shown.

Further, in Japanese Patent Laid-Open No. 63-157804, an attempt is made to simplify the manufacturing process of atomized iron powder by adding alcohol or the like to spray water to suppress oxidation and carburization during spraying as much as possible. However, although the obtained iron powder has a low oxygen content,
Since the C content is 0.01% or more, and quenching easily occurs at the cooling rate by water atomization, it is impossible to mold as it is, and the annealing softening process is essential.

On the other hand, in the process of manufacturing a sintered part using iron powder, it is necessary to make the dimensional change constant or as small as possible in the manufacturing process. In particular, if the dimensional accuracy can be ensured without depending on the sizing, the process can be omitted and the cost can be reduced. Therefore, efforts are being made to omit the sizing process. For example, Japanese Examined Japanese Patent Sho 56-12304
Japanese Patent Publication No. 3-142342 discloses and proposes a technique for improving dimensional accuracy from a particle size distribution of powder, and Japanese Patent Publication No. 3-142342 a technique for predicting and controlling a dimensional change during sintering from the shape of powder.

[0008] However, the iron powder for powder metallurgy is added with Cu powder, graphite powder, and other lubricants. However, the Cu powder added by a transfer operation for container replacement or transportation,
Graphite powder tends to segregate, and the composition tends to vary. Therefore, due to these factors, the dimensional change during sintering tends to fluctuate, and a sizing step as a post-treatment was indispensable to correct the fluctuation.

[0009]

SUMMARY OF THE INVENTION The first object of the present invention is to:
In view of such drawbacks of the conventional technique, it is an object of the present invention to provide a technique for omitting the iron powder manufacturing process and supplying an inexpensive water atomized iron powder for powder metallurgy. The second object of the present invention is to
The purpose is to reduce the cost of iron powder production while ensuring compressibility. A third object of the present invention is to reduce the manufacturing cost of the raw material powder and to provide a water atomized iron powder for powder metallurgy in which the dimensional change during sintering is stable, and in particular the dimensional variation after sintering is small with respect to the variation in the graphite content. To provide.

[0010]

According to the present invention, the hardness of the particle cross section is Hv80 to 25 when sprayed with water and dried.
The water atomized iron powder for powder metallurgy has a particle size of 0, the surface of the particles is covered with a reducible oxide in a sintering atmosphere, and the oxygen content is 1.0 wt% or less. In addition, the iron powder,
Particles with a particle cross-sectional shape factor of 2.5 or less expressed by the square of the perimeter of the particle cross-section divided by the product of the cross-sectional area and 4π, including 10% or more by number of particles A water atomized iron powder for powder metallurgy having 10 to 30 wt% and containing 20 wt% or more of particles of less than 45 μm.

In addition to oxygen, the iron powder contains impurities such as C: 0.01 wt% or less, Mn: 0.30 wt% or less, Ni: 0.30 wt% or less, Cr: 0.30 wt% or less, and the total of P and S. : 0.05 wt% or less, and the balance is water atomized iron powder for powder metallurgy, which is substantially iron. The iron powder is a powder metallurgical water atomized iron powder further containing Mo: 5.0 wt% or less and Nb: 0.20 wt% or less.

Further, in any of the above iron powders, an element that is more easily oxidized than iron (hereinafter referred to as an easily oxidizable element) is further contained, and 20% or more of the easily oxidizable element is oxidized and is oxidized in a sintering atmosphere. It is a water atomized iron powder for powder metallurgy that forms an irreducible oxide and covers the particle surface. Further, as the easily oxidizable element, Si: 0.01 to 0.1 wt%, Al: 0.003 to 0.05 wt%, V: 0.008 to 0.
A water atomized iron powder for powder metallurgy containing one or more of 5 wt% Ti: 0.003 to 0.1 wt% and Zr: 0.008 to 0.1 wt%.

The total amount of the above oxidizable elements is 0.00
Water atomized iron powder for powder metallurgy with 3 to 0.5 wt%.
Further, the present invention, C: 0.01 wt% or less, Mn: 0.30 wt% or less, N
i: 0.30wt% or less, Cr: 0.30wt% or less, total of P and S: 0.050w
A manufacturing method of water atomized iron powder for powder metallurgy, characterized in that molten steel made of iron is sprayed using a water jet with a pressure of 4 to 20 MPa and then dried, and then directly used for powder metallurgy. .

In the present invention, Mo: 5.0 wt% or less, Nb: 0.2
0 wt% or less, C: 0.01 wt% or less, Mn: 0.30 wt% or less, N
i: 0.30wt% or less, Cr: 0.30wt% or less, total of P and S: 0.050w
A manufacturing method of water atomized iron powder for powder metallurgy, characterized in that molten steel made of iron is sprayed using a water jet with a pressure of 4 to 20 MPa and then dried, and then directly used for powder metallurgy. .

Production of water atomized iron powder for powder metallurgy using molten steel containing 0.003 to 0.5 wt% in total of easily oxidizable elements in addition to the components specified in the above method for producing water atomized iron powder for powder metallurgy. Is the way. Further, in the above manufacturing method, the easily oxidizable element is Si, Ti, V, or A.
A method for producing a water atomized iron powder for powder metallurgy, which is one or more selected from l and Zr.

In the above method for producing water atomized iron powder for powder metallurgy, the oxygen concentration in the atomizing atmosphere is 5.0 vol%.
The iron powder obtained by water atomization is 100% in a non-oxidizing atmosphere, an H ₂ atmosphere, or a vacuum.
A method for producing water atomized iron powder for powder metallurgy, which comprises performing a drying treatment at a temperature of up to 300 ° C.

[0017]

The present invention has been completed on the basis of this finding by studying the conventional techniques and finding that the softening annealing / reduction step is not necessarily required under certain conditions. Conventionally, there are two reasons that the softening annealing / reduction process is performed. One is that the raw iron powder in the water atomized state has high hardness and is inferior in compressibility as it is and cannot be used for powder metallurgy, so it is necessary to soften the quenched structure generated when water atomized by annealing. There was

The compressibility means the green compact density obtained when compacted at a certain constant molding pressure, which is an evaluation index of the green compact characteristics often used in the field of powder metallurgy. good. Another is that iron powder particles are covered with a hard oxide film such as FeO in the water atomized state, and if it is left as it is, the moldability deteriorates and the strength of the sintered body decreases, so that the hard oxide film can be removed. Was needed. Here, the formability is the green compact strength indicated by the ratler value, and is a green compact property evaluation index that is commonly used in the field of powder metallurgy, like the compressibility. Incidentally, it is preferable that the Ratler value is small.

However, according to the research results of the present inventors,
It has been found that if the following conditions are satisfied, a material having satisfactory compressibility, moldability, and sinterability can be obtained. That is, first, it was found that in order to secure the compressibility in the state of the water atomized raw iron powder, the hardness of the particles should be lowered. For example, C: 0.007wt%, Mn: 0.005wt%, Ni: 0.03wt%, Cr:
Vickers hardness of Hv is 0.017wt%, Si: 0.008wt%, P: 0.003wt%, S: 0.002wt% and the balance is substantially Fe.
(100) is as low as 107. Add 1.0 wt% zinc stearate powder as a lubricant to this powder, and mix with a mold to obtain 5 t / cm ²
By molding in the molding pressure, green density is obtained of excellent value of 6.81 g / cm ^3, the particle cross-section hardness, iron powder which has undergone any of the characteristics of the softening annealing and reduction according to the prior art green density The same excellent value was obtained.

When the relationship between hardness and compressibility was investigated,
It was found that when the cross-section hardness of the iron powder particles was Hv250, a green compact with a sufficient green compact density was obtained. The lower the particle cross-section hardness, the better the impact on the compressibility. However, attempting to industrially achieve a Hv value of less than 80 unnecessarily increases the refining cost of the molten metal and is not practical. Therefore, in the present invention, the hardness of iron powder particles in cross section is set to Hv80 to 250. The preferred hardness is Hv 120-250.

The cross-sectional hardness of such iron powder particles is C in the iron powder.
It can be obtained by reducing the components such as For example, as shown in Fig. 1, if the C content in the iron powder is reduced, the hardness decreases and approaches that of the finished and annealed iron powder. The results of investigating the influence of molten steel composition in relation to hardness are as follows. If the C content is 0.01 wt% or less, the quenched structure does not appear even with water atomization, but the C content is 0.01 wt%
If it exceeds, the hardness of the powder will increase. More preferably, the C content is 0.005 wt% or less.

Mn, Ni, and Cr have a great influence on the compressibility, and when the C content is 0.01 wt% or less, Mn is 0.40 wt% or less, Ni is 0.40 wt% or less, and Cr is 0.40 wt% or less. The hardness of raw iron powder after spraying and drying was measured by water atomization by changing the value with the results, and when the hardness of Mn, Ni, and Cr exceeded 0.30 wt%, the hardness Hv (100) of raw iron powder exceeded 250. However, press molding in a mold becomes difficult, and a sufficient green compact density cannot be obtained. Therefore, in the present invention, the amount of Mn, Ni, Cr is 0.30 wt%
Below. It is preferable that the content of these elements be 0.1 wt% or less, but if they are unnecessarily lowered due to the steelmaking technology, the cost will increase.

It is desirable to reduce P and S as much as possible, but if the total amount is 0.05 wt% or less, there is no adverse effect. oxygen
The presence of (O) has traditionally been severely limited and therefore removed by the reduction process. However, according to the knowledge of the present inventors, it was found that the presence of O does not cause any harm in sintering unless it exceeds a certain range. That is, unless the O content exceeds 1.0 wt%, the compressibility and moldability of the iron powder do not deteriorate. In this case, O is generally present in the form of FeO, and within the above range, it is acceptable because it is reduced to Fe in the reducing atmosphere in the sintering process and causes no particular trouble in the sintering process. One of the features of the present invention is that the oxygen is allowed to exist. The oxygen content as an oxide reduced in the above step is 0.5 wt%
The following is particularly preferable in terms of moldability.

To reduce the amount of oxygen after water atomizing and drying to 1.0 wt% or less, the amount of oxygen in the atmosphere during water atomizing should be 5 vol.
Must be less than or equal to%. Further, for drying after water atomization, it is necessary to set the drying atmosphere to a non-oxidizing atmosphere such as H ₂ , N ₂ or vacuum. In the present invention, Mo or / and Nb are preferably added as an iron powder composition. This is because they both help improve the compressibility of iron powder.

Regarding the amount of Mo, when the content is 0.05 to 5.0 wt%, the compressibility is improved, the sintering is further promoted, and the strength of the sintered body is improved. However, if it exceeds 5.0 wt%, the compressibility is drastically reduced, which is not preferable. Similarly, with respect to Nb, addition of 0.005 to 0.2 wt% improves the compressibility. However, if added in excess of 0.2 wt%, the compressibility will drop sharply.

In the present invention, basically, a satisfactory iron powder for sintering can be obtained depending on the hardness and oxygen content of the iron powder particles, but in the water atomized state, a partially quenched structure is generated, Harder than the hardness (Hv: 80-100) of iron powder that has undergone the general annealing softening / reduction process due to the introduction of strain due to rapid cooling. Therefore, in order to give better compressibility, it is preferable to pay attention to the shape of the particles forming the iron powder.

In the present invention, the particle shape is expressed using a particle shape coefficient. The shape factor is represented by a value obtained by dividing the square of the peripheral length of the particle cross-sectional shape by the product of the cross-sectional area and 4π, and becomes 1 when the cross-section is a perfect circle. According to the experimental results of the present inventors, for example, selecting a particle size of 75 μm or more and less than 106 μm,
If the particles constituting the particle size include particles with a particle cross-sectional shape factor of 2.5 or less by 10% or more in number, even if the particle cross-sectional hardness exceeds Hv200, the composition of Fe-1.0wt% solid lubricant is 5t / cm.
^With a molding pressure of ² , a powder density of 6.70 g / cm ³ or more can be obtained. It was previously unthinkable that relatively round particles were required to increase the green density.

Here, the particle shape was typified by particles having a particle size of 75 μm or more and less than 106 μm, and the reason why the coarse powder having a particle size of 75 μm or more makes a large contribution to the compressibility and the fine powder was excluded. This is because the particle size of 75 μm or more and less than 106 μm causes the largest weight when performing normal sieving in powder metallurgy. Such particles having a particle diameter of 75 μm or more and less than 106 μm are required to be 10 to 30 wt%. The reason is that if it is less than 10 wt%, the compressibility becomes poor, and if it exceeds 30 wt%, the strength decreases.

On the other hand, if the particle shape is round, the strength of the sintered body generally tends to decrease. This problem is less than 45 μm (-325
The problem can be solved by making fine particles of (mesh) present in an amount of 20 wt% or more. For example, Fe-2.0wt% Cu-0.8wt% graphite is mixed with solid lubricant, and after compaction molding, at 1130 ℃ for 20 minutes, N ₂
A tensile strength of 250 N / mm ² or more can be obtained in a sintered body having a sintering density of 6.80 g / cm ³ obtained by sintering in an atmosphere.
However, if the particle size of less than 45 μm (−325 mesh) exceeds 50 wt%, the compressibility is deteriorated, which is not preferable.

Thus, it is possible to control the green compact density and sintered body strength of the raw iron powder of the present invention by the shape of particles having a particle size of 75 μm or more and less than 106 μm and the amount of particles less than 45 μm (-325 mesh). Become. Such a particle shape and particle size distribution shows that when the pressure of the water spray of molten steel is 4 MPa or more and 20 MPa or less,
A water to molten steel ratio of 5 to 15 is obtained. Water pressure is 20MPa
When it exceeds, the energy of water becomes large and the molten steel is pulverized excessively, so that the cooling rate becomes large and the obtained particles are likely to have an irregular shape. That is, spherical particles that improve the compressibility as described above cannot be obtained. On the other hand, if the water pressure is less than 4 MPa, the energy of water is small, and therefore molten steel cannot be finely pulverized. That is, the amount of fine powder for ensuring strength is insufficient.

Drying of the raw iron powder after the water atomizing is carried out in the range of 100 to 300 ° C. in the same manner as in the usual water atomizing iron powder production.
It is preferably performed in a non-oxidizing atmosphere. By the way, when manufacturing a sintered body using iron powder, improvement in dimensional accuracy is required. The inventors of the present invention have studied this problem and found that the presence of a certain amount of oxide that is not reduced in the atmosphere of the sintering process on the surface of the iron powder particles significantly improves the dimensional accuracy of the sintered part. found.

That is, in the molten steel, easily oxidizable elements (Si, A
(l, V, Ti, Zr), the FeO due to oxidation during atomization
It has been found that the generation of iron is suppressed, and an iron powder having a unique surface structure in which oxides of these easily oxidizable elements are generated on the surface can be obtained. This is because even if the amount of oxygen in the spray atmosphere is slightly reduced when spraying molten steel, each oxidizable element in the iron powder is selectively oxidized by the slight amount of residual oxygen, and an oxide film is formed on the surface of the iron powder. It is considered that it works as a protective film.

The reason why the dimensional accuracy is improved by allowing the oxide of the easily oxidizable element to exist on the surface of the iron powder has not been clarified yet, but it is considered as follows. In other words, if the above oxides are present on the surface of iron powder, the amount of C that penetrates and diffuses into the iron powder due to the diffusion of C from the added graphite into the iron powder particles during sintering will increase the amount of added graphite and the particle size. It is considered that it is kept almost constant regardless of the change, and as a result, the so-called Cu expansion amount is also stabilized.

As a result, it is possible to suppress variations in dimensional changes of the Fe-Cu-C system, which are sensitive to variations in graphite powder. At the same time, the addition of this easily oxidizable element
Oxygen existing as O 2 is reduced, whereby the formability of the iron powder can be further improved. As an example, FIG. 2 shows the relationship between the dissolved Al content of molten steel and the O 2 content of atomized raw iron powder.

Here, the oxidizable element is typically Si,
Al, V 2, Ti, and Zr, which can be added alone or in combination. The preferred ranges in the case of adding each element alone are as follows. Si: 0.01-0.1wt%, Al: 0.003-0.05wt%, V: 0.008-0.
5 wt% Ti: 0.003 to 0.1 wt%, Zr: 0.008 to 0.1 wt% When the oxidizable elements are added, the total amount of them is preferably 0.003 wt% or more and 0.5 wt% or less. . If these easily oxidizable elements are less than the lower limit, there is substantially no effect of reducing the oxygen content, while if they exceed the upper limit,
This is because the O 2 content increases and the sintering strength rapidly decreases.

In order to obtain the effect of improving the dimensional accuracy as described above, it is necessary that the oxidation ratio of the easily oxidizable element contained is 20% or more. This is because if it is less than 20%, the effect of reducing the fluctuation range of the dimensional change during sintering with respect to the variation in the amount of added graphite is small. However, even in this case, in order to maintain the formability, the O 2 content in the iron powder is limited to 1.0% wt or less, preferably 0.5 wt% or less.

As described above, easily oxidizable elements (Si, Al, V,
(Ti, Zr) is added to molten steel to form an appropriate oxide film on the surface of iron powder, the oxygen (O ₂ ) concentration in the atmosphere is sprayed with water in a non-oxidizing gas of 5 vol% or less, Hydrogen, nitrogen,
Alternatively, it is dried at 100 to 300 ° C in vacuum.

[0038]

【Example】

(Example 1, Comparative Example 1) C: 0.002 wt%, Mn: 0.002 by refining molten steel in a converter and decarburizing with a vacuum decarburizer
wt%, Ni: 0.006wt%, Cr: 0.013wt%, Si: 0.005wt%, P:
A melt of 0.002 wt% and S: 0.002 wt% was melted. Add this melt to 7.
Water atomization was performed under the conditions of a water pressure of 5 MPa and a water / molten steel ratio of 10.
The obtained powder was dried at 125 ° C. in an N ₂ atmosphere, and then classified to 1000 μm or less without annealing / reduction.

The powder hardness was measured by Vickers hardness with a load of 100 g to measure the powder cross section. The particle cross-sectional shape factor was measured using an image processing device. Dense density is iron powder with zinc stearate
1.0 wt% was added and mixed, and a tablet having a diameter of 11.3 mm was formed at a pressure of 5 t / cm ² and measured. Sintered body strength is iron powder, Cu powder,
After molding the mixed powder of graphite powder and solid lubricant,
The tensile strength was measured at a sintered density of 6.80 g / cm ³ and an Fe-2.0% Cu-0.8% C composition obtained by sintering in a propane-modified gas atmosphere for 1 minute.

In Comparative Example 1, the same treatment was carried out using a commercially available water-atomized iron powder for powder metallurgy that had been subjected to reduction annealing. Table 1 shows the chemical composition of the iron powder, and Table 2 shows the powder hardness and the strength of the sintered body. The particle size distribution of the atomized iron powder used in Example 1 is less than 45 μm: 26.3 wt%, less than 63 μm to 45 μm: 1.
3.5 wt%, less than 75 μm to 63 μm: 4.7 wt%, less than 106 μm to 75 μm: 15.6 wt%, less than 150 μm to 106 μm: 15.1 wt
%, Less than 180 μm to 150 μm: 7.0 wt%, less than 250 μm to 1
The composition is 80 μm: 9.7 wt% and less than 1000 μm to 250 μm: 8.2 wt%.

[0041]

[Table 1]

[0042]

[Table 2]

Although the example 1 was not annealed or reduced, the powder hardness, the green compact density and the properties of the sintered body were almost the same as those of the conventional iron powder of the comparative example 1. (Examples 2 to 12, Comparative Examples 2 to 9) After refining in a converter or an electric furnace, using a vacuum degassing device, C: 0.002 to 0.032 wt%,
Mn: 0.38 wt% or less, Ni: 0.41 wt% or less, Cr: 0.42 wt% or less, S
i: 0.005-0.020wt%, P: 0.001-0.025wt%, S: 0.002-
A 0.03 wt% molten metal was melted. This molten metal was water atomized under the conditions of a water pressure of 3 to 25 MPa and a water / molten steel ratio of 10. The obtained powder was dried at 125 ° C. in a N ₂ atmosphere except for Comparative Example 7. Comparative Example 7 was dried in air at 125 ° C. All raw iron powders were classified to 1000 μm or less without being annealed or reduced.

Particle hardness, shape factor of particle cross section of raw iron powder,
The green compact density and the sintered body strength were measured by the same methods as in Example 1. Table 3 shows the chemical composition of raw iron powder for Examples 2 to 12 and Comparative Examples 2 to 9, and Table 4 shows powder hardness, spray water pressure, particle size 75 to
Ratio of particles less than 106 μm (wt%) and shape factor
Number ratio of 2.5 or less, particle size less than 45 μm (-325 mesh)
And the green density and the sintered body strength without finish reduction.

[0045]

[Table 3]

[0046]

[Table 4]

In each of Examples 2 to 12, practical green compact density and sintered body strength were shown, but in Comparative Examples 2 to 7, since the composition of the raw iron powder exceeds the proper range, the particle hardness is Hv ( 100) 250 or more, and a compacting density of 6.70 g / cm ³ or more was not obtained at a molding pressure of 5 t / cm ² . In Comparative Example 8, since the spray pressure exceeds the proper range, the shape factor among particles having a particle size of 75 to less than 106 μm is used.
A ratio of 2.5 or less was 10% or less, and a compacting density of 6.70 g / cm ³ or more could not be obtained at a molding pressure of 5 t / cm ² . In Comparative Example 9, since the spraying pressure was below the proper range, the particles of less than 45 μm became 20 wt% or less, and the sintered body strength of 300 N / mm ² could not be obtained at the sintered body density of 6.80 g / cm ³ . (Examples 13 to 25, Comparative Examples 10 to 19) After refining in a converter or an electric furnace, using a vacuum degassing device, C: 0.002 to 0.03 wt%,
Mn: 0.4 wt% or less, Ni: 0.4 wt% or less, Cr: 0.4 wt% or less, S
i: 0.006-0.02wt%, P: 0.007-0.025wt%, S: 0.002-
A molten metal containing 0.03 wt%, Mo: 6.0 wt% or less, and Nb: 0.3 wt% or less was melted. This molten metal was water atomized under the conditions of a water pressure of 3 to 25 MPa and a water / molten steel ratio of 10. The obtained powder was dried at 125 ° C. in an N ₂ atmosphere except for Comparative Example 19. Comparative Example 19 was dried in air at 125 ° C. All raw iron powders were classified to 1000 μm or less without being annealed or reduced.

Particle hardness, shape factor of particle cross section of raw iron powder,
The green compact density and the sintered body strength were measured by the same methods as in Example 1. In Tables 5 and 6, for Examples 13 to 25 and Comparative Examples 10 to 19, the chemical composition of the raw iron powder, the hardness of the powder, the spray pressure, and the particle size of 75 to 106.
Ratio of particles less than μm (wt%) and shape factor of 2.5
The following ratios of the number of particles, ratios of particles less than 45 μm, green density and sintered body strength are shown.

[0049]

[Table 5]

[0050]

[Table 6]

All Examples 13 to 25 are practically compacted.
Degree, and the strength of the sintered body were shown.
Exceeds the proper range, the particle hardness becomes 250 or more,
5t / cm ² 6.70 g / cm at molding pressure³The above green density is obtained
I couldn't. In Comparative Example 17, the spray pressure exceeded the proper range.
Therefore, a shape factor of 2.5 or more among particles with a particle size of 75 to less than 106 μm
Lower ratio is 10% or less, 5t / cm² 6.70 at molding pressure
g / cm³The above green compact density was not obtained. Comparative Example 18 is a jet
Since the fog pressure does not reach the proper range, particles smaller than 45 μm
20wt% or less, 6.80g / cm³At a sintered body density of 30
0 N / mm²No sintered body strength was obtained. Comparative Example 19 is dry
Since the conditions are inappropriate and the amount of raw iron powder oxygen exceeds the proper range,
300 N / mm²No sintered body strength was obtained. (Examples 26 to 30, Comparative Examples 20 to 22) Refining in a converter or electric furnace
After smelting, using a vacuum degasser, C: 0.01 wt% or less, Mn:
0.1 wt% or less, Ni: 0.1 wt% or less, Cr: 0.1 wt% or less, Si: 0.
02wt% or less, P: 0.02wt% or less, S: 0.02wt% or less, Al: 0.1w
A melt of t% or less was melted. This molten metal with a water pressure of 12 MPa
Water was atomized under the condition of a water / molten steel ratio of 10. The powder obtained
To N₂It was dried at 125 ° C in the atmosphere. Any raw iron powder is baked
Classified to 250 μm or less without blunting or reducing.

Table 7 shows the particle hardness, the ratio of particles of 75 to less than 106 μm, the ratio of particles having a shape factor of 2.5 or less, the chemical composition of iron powder, the green density, the ratler value, the tensile strength and the impact value. Show. In each of Examples 26 to 30, the oxygen amount was 0.4 wt% or less because it contained an appropriate amount of Al, and as a result, 6.7 g / cm ³
More green density, 400 N / mm ² or more sintered body strength and 1.5%
The following Ratler values are shown. Comparative Examples 20 and 22 have a green density
Although it is 6.78 g / cm ³ or more, since the amount of Al exceeds the appropriate range, the ratler value is 1.5% or more and the formability is deteriorated. Further, in Comparative Example 21, the hardness exceeds 250, so the green density is 6.5 g / cm ³ or less.

[0053]

[Table 7]

(Examples 31 to 37, Comparative Examples 23 to 26) After refining in a converter or an electric furnace, C: 0.01 wt% was obtained using a vacuum degassing device.
% Or less, Mn: 0.1 wt% or less, Ni: 0.1 wt% or less, Cr: 0.1 wt%
Below, P: 0.02wt% or less, S: 0.02wt% or less, Si + Ti + Zr: 0.2
A molten metal of 4 wt% or less was melted. This molten metal was water atomized at a water pressure of 13 MPa. The obtained powder is heated at 125 ° C in N ₂ atmosphere.
Dried in. All raw iron powders were classified to 250 μm or less without annealing or reduction.

The chemical composition and atomizing conditions of molten steel and atomized raw iron powder are shown in Table 8, particle hardness, the ratio of particles having a particle size of 75 to less than 106 μm, and the ratio of particles having a shape factor of 2.5 or less,
Table 9 shows the green density, ratler value, tensile strength, and impact value. In Examples 31 to 37, the oxygen content is 0.5 wt% or less because all of Si, Ti, and Zr are contained in appropriate amounts, and as a result, the sintered body strength of 400 N / mm ² or more and 1.5% or less. The Ratler value is shown. In Comparative Example 23, since the amounts of Si, Ti, and Zr are less than the lower limit of the appropriate range, the ratler value is 1.5% or more, and the formability is deteriorated. In Comparative Example 24, the particle hardness exceeds 250, so the green density is
It is less than 6.5g / cm ³ . Further, in Comparative Examples 25 and 26 in which the amounts of Si and Ti exceed the proper ranges, the strength of the sintered body is lowered.

[0056]

[Table 8]

[0057]

[Table 9]

(Example 38, Comparative Example 27) C: 0.00 was obtained by refining molten steel in a converter and decarburizing it using a vacuum decarburizing apparatus.
4wt%, Mn: 0.03wt%, Ni: 0.005wt%, Cr: 0.01wt%, Si: 0.0
A melt of 06wt%, P: 0.008wt%, S: 0.006wt%, Al: 0.004wt% was melted and a water jet with a water pressure of 13MPa produced an N concentration of 0.5% N.
Water atomized in ₂ atmospheres. After drying the obtained powder at 180 ° C in an H ₂ atmosphere, it is heated at 25 ° C without annealing or reduction.
It was classified to 0 μm or less.

The compacted density is 1. If zinc stearate is added to raw iron powder.
0 wt% was added and mixed, and the mixture was molded into tablets having a diameter of 11.3 mm at a pressure of 5 t / cm ² and measured. Sintered body strength is raw iron powder, Cu powder,
A mixture of graphite powder and zinc stearate as a lubricant was molded into a JSPM standard tensile test piece and then sintered at 1130 ℃ for 20 minutes in a propane metamorphic gas atmosphere (compacted powder density 6.86g). / cm ³ , composition Fe-2.0% Cu-0.8% Gr), the tensile strength was measured. Fe-2.0% Cu-0.8% Gr and Fe-2.0% Cu-1.0% Gr
The dimensional change during sintering was examined for the two levels of graphite, and the difference between the dimensional changes in sintering was defined as the “dimensional change fluctuation range”. The sample shape at this time is 60φ in outer diameter, 25φ in inner diameter, and height.
The ring shape was 10 mm, the green density was 6.8 g / cm ^3, and sintering was performed at 1130 ° C. in a propane metamorphic gas atmosphere for 20 minutes.

In Comparative Example 27, the same treatment was performed using a commercially available water-atomized iron powder for powder metallurgy that had been subjected to reduction annealing. Table 10 shows the chemical composition of iron powder, the oxidation ratio of easily oxidizable elements,
Table 11 shows the particle cross-section hardness, the ratio of particles less than 75 to 106 μm,
Among them, the ratio of particles with a shape factor of 2.5 or less, the green compact density, the sintered body strength, and the dimensional fluctuation range are shown. Example 38 is annealed,
Although not subjected to reduction, the green density is comparative
Not only is it almost the same as the conventional iron powder of No. 27, but the variation width of dimensional change is superior to that of Comparative Example 27.

[0061]

[Table 10]

[0062]

[Table 11]

(Examples 39 to 53, Comparative Examples 28 to 31) After refining in a converter or an electric furnace, C: 0.01 wt% was obtained using a vacuum degassing device.
Below, Mn: 0.1wt% or less, Ni: 0.1wt% or less, Cr: 0.1wt% or less, P: 0.02wt% or less, S: 0.02wt% or less, Si + Al + Ti + V: 1.0
Melt of less than wt% was melted. This molten metal was water atomized at a water pressure of 100 kgf / cm ² in a N ₂ atmosphere with an oxygen concentration of 10% or less. The obtained raw iron powder was dried in H ₂ and N ₂ at 100 to 300 ° C. in vacuum, and then classified to 250 μm or less without annealing and reduction.

The green compact density, the strength of the sintered body, and the variation range of the dimensional change of the sintered body were measured by the same method as in Example 38. Examples in Table 12
39-53 and Comparative Examples 28-31 chemical composition of raw iron powder,
Oxidation ratio of easily oxidizable elements, particle cross-section hardness, 75-106 μm
The ratio of particles having a shape factor of less than 2.5, the ratio of particles having a shape factor of 2.5 or less, the compact density, the strength of the sintered body, and the dimensional change fluctuation range are shown.

[0065]

[Table 12]

All of Examples 39 to 51 showed practical green compact density and sintered body strength. Furthermore, the dimensional change fluctuation range is 0.
It showed a good dimensional accuracy of 1% or less. In Example 52, Si + Al +
Ti + V amount, in Example 53, the oxidization ratio of the oxidizable element was out of the appropriate range, so the dimensional change fluctuation range was large, but the compressibility, the sintered body strength showed a practical value. .

On the other hand, in the comparative example, the green compact density is 6.7 g / cm ^3.
Although the above compressibility can be obtained, only the strength of the sintered body is low because the amounts of Si, Al, Ti, and V each exceed the proper range. (Examples 54-69, Comparative Examples 32-38) After refining in a converter or an electric furnace, using a vacuum degassing device, C: 0.022 wt% or less, Mn: 0.3
wt% or less, Ni: 0.3 wt% or less, Cr: 0.3 wt% or less, P: 0.003
~ 0.02wt%, S: 0.002-0.015wt%, Mo: 4.0wt% or less, Nb:
A melt containing 0.3 wt% or less and Si + Al + Ti + V + Zr: 0.7 wt% or less was melted. This molten metal was sprayed with water having a water pressure of 8 to 16 MPa in a nitrogen atmosphere having an oxygen concentration of 8% or less and dried at 130 to 280 ° C. in hydrogen, nitrogen or vacuum. All raw iron powders were classified to 250 μm or less without annealing or reduction.

The green compact density, the strength of the sintered body, and the variation range of the dimensional change of the sintered body were measured in the same manner as in Example 37. Table 13 Examples
54-69 and the chemical composition of raw iron powder for Comparative Examples 32-38,
Table 14 spraying conditions, drying conditions, oxidation ratio of easily oxidizable elements,
The powder hardness, the ratio of particles having a particle size of 75 to less than 106 μm, of which the shape factor is 2.5 or less, the ratio of less than 45 μm, and the green compact density without finish reduction and the sintered body strength and dimensional change fluctuation range are shown. .

[0069]

[Table 13]

[0070]

[Table 14]

Examples 54 to 69 all showed practical green compact density and sintered body strength. Further, Examples 54 to 66 showed good dimensional accuracy with a dimensional change fluctuation range of 0.1% or less. On the other hand, in the comparative example, only the powder compact density or the sintered body strength was low because it exceeded the appropriate range of the invention.

[0072]

INDUSTRIAL APPLICABILITY The iron powder for powder metallurgy of the present invention does not require an annealing / reduction process after water spraying as compared with the conventional water atomized iron powder for powder metallurgy and can be molded in a raw iron powder state. Further, the iron powder for powder metallurgy of the present invention, compared with the iron powder for conventional powder metallurgy, Cu, when sintered with graphite addition, the variation of the sintering dimensional change due to the variation of the graphite addition amount is small, resulting Since a sintered body having excellent dimensional accuracy can be manufactured, the sizing step can be omitted. For these reasons, by using the iron powder of the present invention, the manufacturing process of the sintered part can be shortened, and the manufacturing cost of the sintered part can be reduced without impairing the characteristics of the sintered part. You can do it economically.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the hardness of atomized raw iron powder and the C content in the iron powder.

FIG. 2 is a characteristic diagram showing a relationship between oxygen content and iron content in iron powder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Minor Nitta, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Technical Research Division, Kawasaki Steel Co., Ltd. (72) Kazuo Higuchi, 1 Kawasaki-cho, Chuo-ku, Chiba Address Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Makino Raiseshi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Yoshiaki Maeda Kawasaki-cho, Chuo-ku, Chiba City No. 1 Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Koichi Komamura No. 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Kawasaki Steel Co., Ltd. Chiba Works

Claims (12)

[Claims] 1. A particle having a particle cross-section hardness of Hv80 to 250 when sprayed with water and dried, and the particle surface is covered with a reducible oxide in a sintering atmosphere, Water atomized iron powder for powder metallurgy having an oxygen content of 1.0 wt% (hereinafter referred to as wt%) or less. 2. The particle according to claim 1, which has a particle shape factor of 2.5 or less expressed by a value obtained by dividing the square of the perimeter of the particle cross-sectional shape by the product of the cross-sectional area and 4π, and 10% or more in number. Diameter
Water atomized iron powder for powder metallurgy containing 10 to 30 wt% of particles less than 75 to 106 μm and 20 wt% or more of particles less than 45 μm. 3. The impurity according to claim 1 or 2, wherein C: 0.01 wt% or less, Mn: 0.30 wt% or less, Ni:
0.30wt% or less, Cr: 0.30wt% or less, sum of P and S: 0.05wt%
Water atomized iron powder for powder metallurgy, including the following, with the balance being essentially iron. 4. The water atomized iron powder for powder metallurgy according to claim 3, further containing Mo: 5.0 wt% or less and Nb: 0.20 wt% or less. 5. The sintered body according to claim 1, further comprising an element that is more easily oxidized than iron (hereinafter referred to as an easily oxidizable element), and 20% or more of the easily oxidizable element is oxidized. Water atomized iron powder for powder metallurgy that forms an irreducible oxide in the atmosphere and covers the particle surface. 6. The oxidizable element according to claim 5, wherein Si: 0.01-0.1 wt%, Al: 0.003-0.05 wt%, V: 0.008-0.
Water atomized iron powder for powder metallurgy containing one or more of 5 wt% Ti: 0.003 to 0.1 wt% and Zr: 0.008 to 0.1 wt%. 7. The water atomized iron powder for powder metallurgy according to claim 6, wherein the total amount of easily oxidizable elements is 0.003 to 0.5 wt%. 8. C: 0.01 wt% or less, Mn: 0.30 wt% or less, Ni:
0.30wt% or less, Cr: 0.30wt% or less, total of P and S: 0.050wt%
Hereinafter, a method for producing a water atomized iron powder for powder metallurgy, characterized in that molten steel consisting of iron as the balance is sprayed using a water jet having a pressure of 4 to 20 MPa, dried and then used as it is for powder metallurgy. 9. Mo: 5.0 wt% or less, Nb: 0.20 wt% or less, and C: 0.01 wt% or less, Mn: 0.30 wt% or less, Ni: 0.30 wt% or less,
Cr: 0.30 wt% or less, total of P and S: 0.050 wt% or less, the balance is iron molten steel is sprayed using a water jet with a pressure of 4 to 20 MPa, dried, and then directly used for powder metallurgy. A method for producing a water atomized iron powder for powder metallurgy. 10. In addition to the components defined in claim 8 or claim 9, a total amount of easily oxidizable elements is 0.003 to.
A method for producing a water atomized iron powder for powder metallurgy using molten steel containing 0.5 wt%. 11. The easily oxidizable element according to claim 10,
A method for producing a water atomized iron powder for powder metallurgy, which is one or more selected from Si, Ti, V 2, Al and Zr. 12. The method for producing a water atomized iron powder for powder metallurgy according to claim 11, wherein the oxygen concentration in the atomizing atmosphere is adjusted.
Water atomized iron powder for powder metallurgy, which is 5.0 vol% or less, and the iron powder obtained by water atomization is dried at a temperature of 100 to 300 ° C in a non-oxidizing atmosphere, an H ₂ atmosphere, or a vacuum, respectively. Manufacturing method.