JPH07233401A - Atomized steel powder and sintered steel with excellent machinability and dimensional accuracy - Google Patents

Abstract

PURPOSE:To produce atomized steel powder capable of obtaining a sintered steel small in the dispersion of dimensional variation and excellent in machinability after sintering by forming a specified compsn. in which S, Cr and Mn are compositely added and the content of O is controlled. CONSTITUTION:This atomized steel powder contains, by weight, 0.005 to 0.3% S, 0.03 to <0.1% Cr, 0.03 to 0.5% Mn and 0.3% O, and the balance Fe (compsn. 1). This compsn. may moreover be incorporated with one or more kinds among <=4.0% Ni, <=4.0% Mo, <=0.05% Nb, <=0.5% V, <=0.1% Si and <=0.1% Al (compsn. 2). The compsn. 1 or 2 may be formed into alloy powder by mixing one or more kinds among <=5.0% Ni source, <=3.0% Mo source and <=5.0% Cu source thereto, executing heat treatment and diffusedly sticking the same thereto. Moreover, the same powder may be added with 0.4 to 1.5% graphite and be subjected to compacting and sintering. By using this steel powder, the sintered steel having a structure in which graphite is precipitated into pores of the sintered steel by >=0.05% and MnS having <=5mum grain size is present in the grains of iron and on the grain boundaries can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to atomized steel powder for powder metallurgy and its sintered steel, especially for powder metallurgy which has little variation in dimensional change during sintering and has excellent machinability after sintering. The present invention relates to atomized steel powder and its sintered steel.

[0002]

2. Description of the Related Art Iron powder for powder metallurgy generally has a density of 5.0 to 7.2 g / cm ³ by adding and mixing Cu powder, graphite powder, etc., compression molding in a mold and sintering. It is used for manufacturing machine parts. In such a mechanical part manufacturing process, a process of manufacturing iron powder itself, a process of mixing iron powder with copper powder or graphite powder, and a long process of transportation, transportation, molding, sintering, etc. There is a problem that the dimensions of the sintered body tend to vary, and for this reason, there is often a step for performing dimension correction called sizing after sintering.

However, a sintered body produced by adding Cu powder, graphite powder, etc. to iron powder has a high strength and is sufficient for spring back of the sintered body even if sizing for dimensional correction is performed. There is a problem that the dimension correction cannot be achieved. Further, it is desirable that the sizing process can be omitted from the viewpoint of cost and lead time of shortening the process as much as possible.

Therefore, in order to secure the dimensional accuracy without depending on the sizing, a technique for improving the dimensional accuracy by defining the particle size composition of powder, as disclosed in Japanese Patent Publication No. 56-12304, Japanese Patent Laid-Open No. 142342/1993 proposes a technique for predicting and controlling dimensional change during sintering from the shape of powder. On the other hand, regarding the influence of the composition of iron powder on the dimensional change, see Japanese Patent Publication
No. 1 discloses 0.1-0.5 wt% (hereinafter abbreviated as%) of Mn and Si,
0.03 to 0.07% S in pure iron powder that contains C and the balance is iron
A technique for reducing sintering strain by adding and reducing the dimensional defect rate after sizing is disclosed.

Regarding the effect of adding S to the iron powder, in addition to the effect of the sintering strain of Japanese Patent Publication No. 3-25481 mentioned above, the machinability of the sintered body is improved by including the same. In most cases, S was added to iron powder in Japanese Patent Publication No. 54-457, Japanese Patent Publication No. 47-39832, Japanese Patent Publication No. 56-45964, Japanese Patent Publication No. 61-253301, etc. Although there is an example in which the machinability is improved by adding it to, no technique has been proposed for improving the stability of dimensional change.

From the above, the present inventors have decided to grasp the stability of dimensional change from the actual operation aspect. That is, Cu powder, graphite powder, lubricant, etc. are added to iron powder, and after mixing for homogenization, during transfer operation for container replacement, or transportation, handling during supply to the molding apparatus system, etc. However, the added Cu powder or graphite powder tends to vary due to segregation, which causes a problem that the dimensional change during sintering greatly fluctuates. In addition, the dimensional changes were greatly influenced by changes in the sintering conditions such as the sintering time and the sintering temperature. There is no technique disclosed in the past, including Japanese Patent Publication No. 3-25481, as a method for solving the problem that the dimensional change varies due to inevitable fluctuation factors in actual operation.

As described above, powder metallurgical products with strict dimensional accuracy are cut and processed after sintering for dimensional correction, but powder metallurgical products are generally inferior in machinability and are processed as compared with ingot products. It has a problem that the life of the tool is short, resulting in a high machining cost. Deterioration of machinability in powder metallurgy products is said to be caused by intermittent cutting due to pores contained in the powder metallurgy products or increase in cutting temperature due to a decrease in thermal conductivity.

In order to improve machinability, it is often the case that free-cutting components such as S and MnS are mixed with iron powder. This is S
This is to improve the machinability by the effect of facilitating the breakage of chips of MnS or MnS, or by forming a thin cutting edge of S or MnS on the tool to lubricate the rake face of the tool. Japanese Patent Publication No. 4-72905 discloses that Mn: 0.1-0.9%, Cr: 0.1
~ 1.2%, Mo: 0.1-1.0%, Cu: 0.1-2.0% and
Ni: Two or more of 0.1-2.0% of metals and Nb, A
containing at least one of l and V and S, and C and Si
A free-machining sintered forged part containing is disclosed.

Since this sintered forged part has almost reached the true density, it has few pores, and it is considered that the decrease in the thermal conductivity due to the pores and the deterioration in the machinability due to the intermittent cutting are small, but the density is 5.0 to 7.2 g. No mention is made of general sintered parts containing pores of / cm ³ . As a conventional technique for iron powder for powder metallurgy containing S, Japanese Patent Publication No. 3-25481 discloses a composition of pure iron powder containing a small amount of Mn (0.1 to 0.5%), Si, C, etc., and the balance being iron. , And S is 0.03
Disclosed is a powder for powder metallurgy, which is manufactured by adding it to a molten metal of 0.07% and spraying it with water or gas. However
A powder for powder metallurgy in which Cr and S are simultaneously added to a molten metal and sprayed has not been proposed yet.

[0010]

SUMMARY OF THE INVENTION In view of the above drawbacks of the prior art, the object of the present invention is to reduce the dimensional change during sintering without impairing the compressibility, which makes it possible to omit the sizing step and, in particular, to the added graphite. A powder that has small dimensional change during sintering due to variation in quantity and small dimensional change during sintering due to variation in sintering time, and that has excellent machinability of the sintered steel. An atomized steel powder for metallurgy and a sintered steel thereof.

[0011]

In order to achieve the above-mentioned object, the present inventors have extensively studied the effect of additional elements on the variation of dimensional change during sintering, and as a result, S, Cr and Mn
Atomic steel powders and sintered steels, which have excellent machinability and have significantly reduced dimensional change fluctuations by controlling the amount of O, are found.

Further, the inventors of the present invention produced an iron powder for powder metallurgy by water-spraying molten steel containing an appropriate amount of Cr, S, and Mn, and obtained a sintered body structure with good machinability obtained by using this iron powder. Was observed in detail. Then, in the sintered body structure having a composition of Cr and free S (a form in which only S is detected when observed with an X-ray microanalyzer), C whose diffusion is suppressed during sintering is contained. Residual graphite is precipitated at grain boundaries and pores, and at the same time, fine MnS particles with a particle size of 5 μm or less are also deposited. This residual graphite and MnS act as a composite to act as a lubricant on the tool rake surface during machining. It was confirmed that the tool life was extended.

Based on the above findings, the inventor of the present invention has a new machinability improving mechanism which has a small variation in dimensional change during sintering and is different from the machinability improving mechanisms proposed so far. In addition, we propose a steel powder for powder metallurgy and a sintered steel having excellent compressibility. The present invention is S: 0.005-0.3 wt
%, Cr: 0.03 to less than 0.1 wt%, Mn: 0.03 to 0.5 wt% and O: 0.3 wt% or less, and the balance is Fe and inevitable impurities, and excellent in machinability and dimensional accuracy. Atomized steel powder, Ni: 4.0 wt% or less, Mo: 4.0
wt% or less, Nb: 0.05 wt% or less, V: 0.5 wt% or less, Si:
Atomized steel powder containing at least one selected from the group of 0.1 wt% or less and Al: 0.1 wt% or less. In these atomized steel powders, Ni source: 5.0 wt% or less, Mo source: 3.0 wt%
% Or less and Cu source: 5.0 wt% or less selected from the group, and heat treated to diffuse and adhere to the alloy steel powder having excellent machinability and dimensional accuracy. These alloy steel powders have S: 0.005 to 0.3 wt% and Cr: 0.03 to 0.
Less than 1 wt%, Mn: 0.03 to 0.5 wt% and O: 0.3 wt% or less, and Ni: 5.0 wt% or less, Mo: 3.0 wt% or less and
Cu: 1 or more selected from the group of 5.0 wt% or less, the balance being Fe
And unavoidable impurities, and S: 0.
005 to 0.3 wt%, Cr: 0.03 to less than 0.1 wt%, Mn: 0.03 to
0.5 wt% and O: 0.3 wt% or less, and Ni: 9.0 wt%
Below, Mo: 7.0 wt% or less, Cu: 5.0 wt% or less, Nb: 0.05
wt% or less, V: 0.5 wt% or less, Si: 0.1 wt% or less, and
Al: at least one selected from the group of 0.1 wt% or less, the balance being Fe
And an unavoidable impurity. The Ni source is Ni powder, the Mo source is Mo powder, MoO ₃ powder, and the Cu source is
Cu powder can be used.

Further, according to the present invention, graphite is added to these steel powders.
Sintered steel with excellent machinability and dimensional accuracy, characterized by the addition of 4 to 1.5% and forming and sintering.
0.5 to 4.0% by weight may be mixed, and the structure has a structure in which 0.05% or more of graphite is deposited in the pores of the sintered steel, and the structure in which MnS with a particle size of 5 μm or less is present in the iron particles and in the grain boundaries. Is.

[0015]

By including Cr and S in the atomized steel powder, the dimensional change during sintering becomes stable, and graphite remains in or precipitates in the pores and grain boundaries of the sintered steel to improve the machinability. Two effects are obtained. First,
Regarding the stabilizing effect of dimensional change, considering the results of various experiments conducted by the present inventors, the following two actions can be considered for the action due to the presence of Cr and free S. First of all,
When Cr and free S coexist in the iron powder, the diffusion of C from the graphite added during sintering into the iron powder particles is suppressed,
Even if the amount of added graphite changes, the amount of C that penetrates and diffuses into the iron powder is kept constant. Factors that determine the dimensional change during sintering include C expansion due to diffusion of C into γ particles during sintering, and Fe-
In the Cu-C system, it is important that the degree of penetration of Cu between iron particles (so-called Cu expansion) depends on the amount of C solid solution of γ particles. Therefore, in the sintering of the powder of the present invention, Fe-
The C expansion in the C system and the Cu expansion amount and the C expansion amount in the Fe-Cu-C system can be reduced with respect to variations in the amount of added graphite. As a second effect, it was found that the presence of Cr and free S in the iron powder suppresses the dimensional change even if the sintering time changes during sintering. This is probably because the shrinkage associated with charcoal is suppressed.

By these actions, the variation in dimensional change during sintering is suppressed, but this is exhibited only when Cr and free S coexist as described in the section of Examples.
Even if only one of the elements satisfies the composition range of the present invention, a sufficient effect cannot be obtained. As described above, it is unclear in what principle Cr and free S exert the above-mentioned two effects, but since each element alone does not exert this effect, it is considered that they mutually influence each other. Conceivable.

Next, the effect of improving the machinability will be described. Mn
In sintered steel that has a structure in which graphite is precipitated in the pores along with S, the graphite that precipitates in the pores acts as a lubricant on the tool rake surface during machining, and cutability is greatly improved by suppressing interrupted cutting . Such a machinability improving mechanism is a novel one which is completely different from the previously proposed one using MnS and the like, and the machinability is remarkably improved as compared with the case where MnS is present alone.

Based on such a premise, the inventors of the present invention develop a steel powder having excellent machinability in order to develop Cr, Mn, and S-containing atomized steel powder containing Cr in an amount of 0.03% or more, and its calcination. Focusing on the binding steel, we conducted intensive studies. As a result, Mn was 0.03%
It has been discovered that when the content of Cr is 0.5% or less, the coexistence of Cr with Mn and S causes graphite to remain in the pores in an amount of 0.05% or more and the average size thereof is 10 μm or more. The average size of graphite remaining in the pores is 10 μm or more, and the amount is 0.05 μm.
%, And at the same time MnS having a grain size of 5 μm or less is precipitated in the iron grains and at the grain boundaries, the machinability is dramatically increased.

It has been well known in the field of ingots that it is necessary to increase the size of free-cutting inclusions such as MnS in order to improve machinability. However, in the conventional technique of powder metallurgy, MnS deposited is as small as 5 μm or less, and about 1 μm on average, and it is difficult to significantly improve the machinability. Further, the added graphite is completely diffused into the iron particles during sintering, and hardly remains in the pores of the sintered body.

The main inclusions responsible for free-cutting in the present invention are residual graphite and MnS, and the contribution of residual graphite is particularly large. The average size of the residual graphite according to the present invention is 10 μm or more, which is 10 times or more the size of MnS 2. When such residual graphite is contained in an amount of 0.05% or more, it is very effective in improving machinability. However, if MnS hardly precipitates, for example, if Mn is less than 0.03%, the improvement in machinability is relatively small,
It was found that a sintered steel with excellent machinability can be obtained by the synergistic effect of MnS and residual graphite of 0.05% or more.

In order to obtain the steel powder of these components, it is difficult to change the component composition of the reduced iron powder to increase Cr and S. Also in the case of atomized powder, simply add pure iron molten steel to S
It cannot be obtained only by adding. That is, by controlling the desulfurization reaction in a converter or an electric furnace, or by actively adding it to match the amount of S to the target, and after finishing refining, add Cr in the ladle (usually 0.01% if not added). Hereinafter, this can be achieved for the first time by spraying a steel powder by a water atomizing method or the like and then controlling the amount of oxygen in a subsequent step such as drying or reduction annealing.

In order to produce a sintered steel having a structure in which graphite exists in the pores of the sintered body, the S content is 0.005 to 0.3%, and Cr is
Content 0.03 to less than 0.1%, O content 0.3% or less, Mn content 0.03
~ 0.5%, graphite powder in the powder produced by the water atomizing method, characterized in that the balance is Fe and inevitable impurities,
It can be easily obtained by mixing copper powder and zinc stearate, molding with a molding machine used in ordinary powder metallurgy, and sintering in a nitrogen atmosphere. The sintered steel thus obtained has a S content of 0.005 to 0.3%, a Cr content of 0.03 to less than 0.1%, and a Mn content of 0.03.
~ 0.5%, C content 0.4 ~ 1.5%, balance Fe and unavoidable impurities, has a structure in which residual graphite and MnS are present in the pores, and is a sintered steel with excellent machinability and dimensional accuracy. When 1% of zinc stearate as a lubricant is added to the steel powder of the present invention and molding is carried out at a molding pressure of 5 t / cm ² , a powder compact density of 6.85 g / cm ³ or more is obtained.

In the sintered steel in which graphite is precipitated in the pores proposed in the present invention, the synergistic effect of Cr and S during sintering partially suppresses the diffusion of graphite into γ grains during sintering, It is obtained by leaving graphite in the pores after sintering. Thus Cr and S
It can be seen that a peculiar ferrite-perlite structure in which graphite remains in the pores can be obtained by the synergistic action with. Further, if an appropriate amount of elements such as Ni, Mo, Nb and V is further added to the above atomized steel powder, the strengthening action of these elements causes
It is possible to obtain atomized steel powder and sintered steel having high strength and excellent dimensional accuracy and machinability. Addition of Al, Si, etc. is also effective in further improving the machinability. In addition, if elements such as Ni, Mo, and Cu are mixed on the surface of the above-mentioned steel powder and heat-treated to diffuse and adhere, compression molding is easy, and even higher strength is obtained by sintering and dimensional accuracy and machinability are improved. Excellent sintered steel can be obtained.

The reasons for limiting the components will be described below. S
Is contained in order to suppress the diffusion of C into the γ grains due to the synergistic action of Cr and S, and to form a sintered steel structure in which graphite remains in the pores after sintering. The reason for limiting the amount of S to 0.005% or more is that if it is less than 0.005%, C diffuses entirely into the iron powder particles, the amount of graphite precipitated in the grain boundary pores is small, and the above-mentioned lubricating action cannot be obtained, so cutting This is because the dimensional accuracy is poor. The reason for limiting the content to 0.3% or less is that when added in excess of 0.3%, the compressibility decreases, the diffusion amount of C into the iron powder particles decreases, the ferrite single phase increases, and the strength decreases. This is because. When the S content is 0.05 to 0.15%, the dimensional change during sintering is further stabilized and excellent machinability is obtained.

Cr is contained in order to suppress the diffusion of C into the γ grains by a synergistic action with S and form a sintered steel structure in which graphite remains in the pores after sintering. Cr content of 0.03% or more
The reason for limiting the content to less than 0.1% is that if the Cr content is less than 0.03%, the above machinability improvement effect is also absent and the dimensional accuracy is inferior, while if it is 0.1% or more, compressibility and dimensional accuracy decrease. This is because A more preferable range of Cr content is
It is 0.06 to 0.09%. Within this range, the dimensional change during sintering is further stabilized, and excellent machinability can be obtained.

The reason for limiting the O content to 0.3% or less is 0.3.
This is because if it exceeds%, the compressibility decreases and the strength deteriorates. Mn is added as the Mn source of MnS 2. Mn amount from 0.03 to 0.
The reason for limiting the content to 5% is that if it is less than 0.03%, the precipitation of MnS is small and the machinability is not significantly increased. Also, if it exceeds 0.5%, the compressibility deteriorates. The more preferable range of the amount of Mn is 0.05 to 0.15%, and in this range, more excellent machinability can be obtained.

Graphite: 0.4 to 1.5% Graphite is added in order to obtain a desired strength by solid solution in steel which is a general purpose, and in the present invention, it is added as a graphite source remaining in pores. The amount of graphite to be added is 0.4 to 1.5%. When it is less than 0.4%, the strength becomes low, and when it exceeds 1.5%, proeutectoid cementite precipitates and the machinability deteriorates.
Therefore, it is preferably set to 0.6 to 1.2%. If Cr, Mn, and S are particularly preferable in this range, the average size of graphite in the sintered steel is 10 μm or more, and the machinability is improved.

That is, the steel powder of the present invention is used as an ordinary Fe--C type, Fe
Sintering with the —Cu—C system makes it possible to obtain a sintered steel containing MnS and residual graphite existing in the pores and having excellent machinability. The sintered forged steel containing almost no pores of Japanese Patent Publication No. 4-72905 described above has improved machinability due to S. Due to MnS of the present invention and residual graphite present in the pores,
It is completely different from the technology for improving the machinability of sintered steel containing pores.

Further, while the C content of the sintered forged steel of Japanese Patent Publication No. 4-72905 is 0.4%, in the present invention, residual graphite is generated and at the same time, carbon which forms a solid solution in the matrix is secured. Therefore, the amount of graphite added is as large as 0.4 to 1.5%. As described above, the size of residual graphite and MnS particles has a great effect on machinability. In the steel powder obtained by the present invention, the residual graphite is 0.05% or more, and the size thereof is 10 μm or more on average, and at the same time, MnS is about 1 μm in size, so that the machinability is excellent.

As a prealloy, Si and Al are similar to Cr and S
It has the effect of preventing carburization and the precipitation of MnS from molten steel.
SiO that becomes the precipitation site when₂, Al₂O₃The effect of precipitating
Add because it has fruit. Si and Al were set to 0.1% or less
Is SiO above 0.1%₂, Al ₂O₃Too many, cut
Machinability drops sharply. If the amount of Si or Al added is small,
In that case, the effect of addition is small.
0.01% to 0.03% of each is preferable.

As a prealloying component, Ni, Mo, Nb, and V are added to enhance the hardenability or to obtain a desired strength by the precipitation effect, as in the case of ordinary alloy steel powder. Further, Nb and V are added to improve the compressibility because the atomized steel powder is likely to be spheroidized by the addition thereof and the compressibility is improved by adding an appropriate amount.
The amount of Ni added is 4% or less, and the amount of Mo added is 4% or less because if they exceed 4%, the machinability deteriorates due to solid solution hardening. It is preferable to add 0.1% or more and 2.0% or less of each, because the improvement of strength and the further improvement of dimensional accuracy are recognized.

The amount of Nb added is 0.05% or less, and V is 0.5% or less. This is because if they exceed 0.05% and 0.5%, respectively, the machinability and the compressibility are deteriorated due to the generated carbide or precipitation strengthening. The preferred range is 0.01% or more, respectively.
03% or less, 0.1% or more and 0.4% or less. As a diffusion alloy component, Ni, Mo, and Cu are used to obtain a desired strength, like ordinary alloy steel powder. The addition amounts of Ni, Mo, and Cu are 5%, 3%, and 5% or less, respectively, in consideration of the relationship with the amount of prealloying components of atomized steel powder. 5% and 3 respectively
%, If it exceeds 5%, the machinability is deteriorated due to the solid solution hardening. 0.1 to 4.0, 0.1 to 2.0, 0.5 to 2.
It is preferable to diffuse and adhere in the range of 0%. The reason for this is that improvement in strength can be recognized by diffusing and adhering 0.1, 0.1, and 0.5% or more, respectively. Also, each 4,
The reason for this is not clear, but the dimensional accuracy is further improved by diffusing and adhering it by 2% or less.

Next, the structure of the sintered steel according to the present invention will be described. According to the present invention, graphite is formed in the pores of the sintered steel, and MnS is precipitated in the iron particles or in the grain boundaries, so that the graphite precipitated in the pores is lubricated on the tool rake surface during cutting. The action as an agent and the suppression of intermittent cutting greatly improve the machinability. Such a machinability improvement mechanism is a novel one, which is completely different from the ones using MnS etc. that have been proposed so far.

Further, by finely dispersing MnS having a particle size of 5 μm or less into the fine MnS particles, the fine MnS particles exert a pinning effect on the growth of the γ phase during sintering, and the sintered body structure becomes finer. , S is hardly recognized as compared with the case where S and S are not contained. The present invention, which compensates for the deterioration of strength by the composite machinability improving mechanism using graphite precipitated in such pores and fine MnS and the strengthening mechanism using fine MnS, has been proposed in the field of powder metallurgy in the past. This is a new sintered steel that is completely different from the one using MnS powder.

[0035]

EXAMPLES The present invention will now be described in detail based on examples. (Example 1) An example of the invention and a comparative example according to claim 1 will be described below. Table 1 shows the chemical composition of the atomized steel powder used in the invention examples and the comparative examples. These steel powders are produced by water-spraying molten steel, and the raw powder is produced at 140 ° C in a nitrogen atmosphere at 60 ° C.
After minute drying, the product was reduced in a pure hydrogen atmosphere at 930 ° C. for 20 minutes, and then pulverized and classified to produce.

[0036]

[Table 1]

The dimensional change during sintering was as follows: pure iron powder mixed with graphite powder and copper powder, Fe-2.0% Cu-0.8% Gr (graphite) and Fe-2.0
Two levels of graphite,% Cu-1.0% Gr, were investigated. Fe-
Sintered dimensions of 2.0% Cu-0.8% Gr (compacted powder compact) and Fe-2.0
The variation width (A) was defined as the ratio of the difference between the sintered dimension of% Cu-1.0% Gr (based on the green compact). The sample shape at this time is a ring cylinder shape with an outer diameter of 60 mmφ, an inner diameter of 25 mmφ, and a height of 10 mm.
Sintering was performed for 20 minutes in a nitrogen atmosphere at 1130 ° C. with a green compact density of 6.85 g / cm ³ . In addition, in the case of Fe-2.0% Cu-0.8% Gr composition, the sintering dimension when the sintering time is 30 minutes (compacted powder compact)
And the ratio of the difference from the sintering dimension (compacted powder compact) when the sintering time was 20 minutes was defined as the variation width (B).

The compressibility was evaluated by adding stearic acid to each steel powder.
Molding pressure 5t / cm with 1% lead added ²11φ × 10mm
The molding density was used when the bullet was molded. Cutting
The evaluation of the property is a cylindrical shape with an outer diameter of 60 mmφ and a height of 10 mm.
Density 6.85 g / cm³And sinter for 20 minutes in a nitrogen atmosphere at 1130 ℃
After that, using a HSS drill with a diameter of 1 mmφ, 10,000 rpm,
Processing until processing becomes impossible under the condition of 0.012 mm / rev
The average number of drilled holes (average value of 3 drills) is the tool life.
Evaluated.

Table 2 shows the analytical values of the sintered steel obtained by molding and sintering the atomized steel powder shown in Table 1 and the results of tool life, tensile strength and dimensional change rate. The compact density of the commercially available pure iron powder was 6.86 g / cm ³ , the tensile strength of the sintered steel obtained by molding and sintering the scrap was 42 kgf / mm ² , and the tool life was 30 times. S amount is 0.
005-0.3%, Cr content 0.03-0.1%, Mn content 0.03-
From the steel powder characterized by 0.5%, O content of 0.3% or less, and balance Fe and unavoidable impurities, the S content is 0.005 to 0.3.
%, Cr content 0.03 to less than 0.1%, Mn content 0.03 to 0.5%, C
If you make a sintered steel that is characterized by 0.4-1.5% amount of Cu, 0.5-4.0% Cu amount if necessary, balance Fe and unavoidable impurities, it is 10 times more than commercial pure iron powder. It can be seen that the above tool life and tensile strength of 47 kgf / mm ² or more are simultaneously satisfied. Also, as is clear from Table 2, Cr is 0.03 to 0.1%
If the steel powder has a suitable range of less than less than 0.1%, the variation width (A) is 0.1% or less and the variation width (B) is 0.01%.
The following excellent dimensional accuracy is shown.

Inventive Examples 7 and 8 had Cr of 0.06 to 0.09% and S
Is 0.05 to 0.15%, Mn is a preferred range of 0.05 to 0.15%,
With regard to dimensional stability, the variation width (A) is 0.05% or less and the variation width (B) is 0.005% or less, which is extremely excellent in dimensional stability and the tool life exceeds 600 times. Comparative Example 1 is a normal pure iron powder, but its machinability is extremely poor and its dimensional stability is also poor. In Comparative Example 2, the S content is less than 0.005% and the machinability is
Inferior dimensional stability. Comparative Example 3 shows that the compressibility is low when the S content exceeds 0.3%. Comparative Example 4 has Mn of 0.03%
If it is less than 1, no significant improvement in machinability is observed. Comparative Example 5
It shows that the compressibility is poor when Mn exceeds 0.5%.
Comparative Example 6 shows that if the Cr content is less than 0.03%, the machinability and dimensional stability are poor. Comparative Example 7 shows that the machinability is poor when the Cr content is 0.1% or more, and Comparative Example 8 shows that the compressibility is poor when the O content of the steel powder exceeds 0.3%.

[0041]

[Table 2]

Example 2 An example of the invention and a comparative example for claim 2. Table 3 shows the chemical composition of the atomized steel powder used in the invention examples and the comparative examples. These steel powders were produced by drying raw powder obtained by spraying molten steel with water in a nitrogen atmosphere at 140 ° C for 60 minutes, reducing it in a pure hydrogen atmosphere at 930 ° C for 20 minutes, and then pulverizing and classifying. .

[0043]

[Table 3]

[0044]

[Table 4]

The compressibility was evaluated by adding stearic acid 1 to each steel powder.
% Of the composition (Fe-1.0% ZnSt), the molding density was obtained when a tablet of 11φ × 10 mm was molded at a molding pressure of 7 t / cm ² . The machinability was evaluated by mixing graphite powder and zinc stearate with the powder shown in Table 3 Fe-0.9% Gr-1.
90% φ with 0% ZnSt and a powder density of 7.00 g / cm ³ .
A cylinder having a height of 10 mm was formed and sintered at 1130 ° C. for 20 minutes in a nitrogen atmosphere. After sintering, an average number of holes (average of three drills) machined until it became impossible to machine under conditions of 10,000 rpm and 0.012 mm / rev using a HSS drill with a diameter of 4 mm was evaluated as the tool life. .

The dimensional change rate during sintering was evaluated according to Example 1. Table 3 shows the results of the powder compact density, tool life and dimensional change rate. Atomized steel powder satisfying the requirements of claim 2 was mixed with Fe-0.9% Gr-1.0% ZnSt for 1150
Sintering for 30 minutes in a nitrogen atmosphere at ℃ shows good dimensional accuracy with tool life of 100 times or more, variation width (A) of 0.10% or less, and variation width (B) of 0.01% or less. ing.

Inventive Examples 17, 19, 21, 25 and 26 had a Cr content of 0.
06-0.09%, S 0.05-0.15%, Mn 0.05-0.15%, Ni 2% or less, Mo 2% or less, Si 0.01-0.
03%, Al 0.01-0.03%, V 0.1-0.4%, Nb 0.01
It is a preferable range containing one or more of 0.03% to 0.03%, and the dimensional stability satisfies the variation width (A) of 0.05% or less and the variation width (B) of 0.05% or less, which is extremely excellent in dimensional stability. , The tool life exceeds 300 times.

Comparative Example 9 shows that if the amount of S is less than 0.005%, the machinability and dimensional stability deteriorate. Comparative Example 10 shows that the compressibility is poor when the S content exceeds 0.3%. Comparative Example 11
Indicates that if the Cr content is less than 0.03%, the machinability and dimensional stability are poor. Comparative Example 12 shows that if the Cr content is 0.1% or more, the compressibility and dimensional stability are poor. In Comparative Example 13 (Al-containing), when the Mn content is less than 0.03%, the effect of inclusion such as improvement of machinability is not recognized, and in Comparative Example 14, the Mn content exceeds 0.5%, the compressibility is lowered. There is. Comparative Examples 15 and 16 show that the compressibility decreases when the Ni content and Mo content exceed 4.0%, respectively.
It was confirmed that the addition of Ni and Mo is preferably 0.1% or more, and the strength is improved as compared with the case where each element is not added. Comparing Comparative Example 17 and Invention Example 13, the compressibility is improved by adding an appropriate amount of Nb, but if it exceeds 0.05%, the machinability and the compressibility are rather deteriorated. Comparing Comparative Example 18 with Invention Example 19, the compressibility is improved by adding an appropriate amount of V, but 0.5%
If it exceeds, the machinability and compressibility deteriorate. Comparing Comparative Example 19 with Example 26, the machinability is improved by adding an appropriate amount of Si, but if it exceeds 0.1%, the compressibility and the machinability are rather deteriorated. Comparing Comparative Example 20 with Example 27, the machinability is improved by the addition of an appropriate amount of Al, but if it exceeds 0.1%, the machinability is deteriorated.

(Embodiment 3) An invention example and a comparative example of claim 3 are described. Table 4-1 shows the chemical composition and the amount of diffused adhesion of the atomized steel powder (base powder) used in the invention examples and the comparative examples. These steel powders were obtained by spraying molten steel with water and drying the powder in a nitrogen atmosphere at 140 ° C for 60 minutes, then reducing it in a pure hydrogen atmosphere at 930 ° C for 20 minutes, then pulverizing and classifying it. A base powder containing S, Cr, Mn, O and the balance Fe and inevitable impurities was produced. Then, a predetermined amount of this original powder was mixed with Ni powder, MoO ₃ powder, and Cu powder with a V-type mixer. The mixed powder was heated at 900 ° C. for 30 minutes in an ammonia decomposition atmosphere gas, gradually cooled, and then pulverized and classified to obtain a powder having a chemical composition shown in Table 4-2.

[0050]

[Table 5]

[0051]

[Table 6]

Evaluation of compressibility and machinability was carried out in the same manner as in Example 2. The dimensional change during sintering was also evaluated in the same manner as in Example 2. Table 4-1 summarizes the results of the green compact density, tool life, and dimensional change rate. Alloy steel powder satisfying the requirements of claim 3 was mixed with Fe-0.9% Gr-1.0% ZnSt for 1150
If sintered for 30 minutes in a nitrogen atmosphere at ℃, in the invention example, the tool life is 100 times or more, the variation width (A) is 0.10% or less, and the variation width (B) is 0.01% or less. It shows the accuracy.

Inventive Examples 29, 35 and 36 have a Cr content of 0.06 to 0.09%,
Steel powder with S content of 0.05 to 0.15% and Mn content of 0.05 to 0.15% is mixed with one or more of Ni source amount of 4% or less, Mo source amount of 2% or less, and Cu source amount of 2% or less, and heat treated. It is a suitable range of alloy steel powder that is diffused and adhered, and the dimensional stability has a variation width (A) of 0.05%.
Below, the variation width (B) also satisfies 0.005% or less,
Excellent dimensional stability and tool life of over 300 times.

Comparative Example 21 shows that if the S content is less than 0.005%, the machinability and dimensional stability are reduced. Comparative Example 22 is S
If the amount exceeds 0.3%, the compressibility is inferior. Comparative example
No. 23 shows that if the Cr content is less than 0.03%, the machinability and dimensional stability are poor. Comparative Example 24 shows that if the Cr content is 0.1% or more, the compressibility and the dimensional stability are poor. In Comparative Example 25, the amount of Mn is
If it exceeds 0.5%, the compressibility is poor. In addition, the amount of Mn is 0.03
If it is less than%, the effect is not recognized in terms of compressibility, machinability and dimensional accuracy. Comparative Examples 26, 27 and 28 are Ni source amount, Mo
It shows that the machinability deteriorates when the source amount and the Cu source amount exceed 5.0, 3.0 and 5.0%, respectively. It was confirmed that the strength is improved by adding the Ni source amount and the Mo source amount preferably 0.1% or more and the Cu source amount preferably 0.5% or more as compared with the case where each element is not added.

(Embodiment 4) An invention example and a comparative example of claim 4. Tables 5-1 and 6-1 show the chemical composition and the amount of diffused adhesion of the atomized steel powder (original powder) used in the invention examples and the comparative examples. These steel powders were obtained by spraying molten steel with water and drying the powder in a nitrogen atmosphere at 140 ° C for 60 minutes, then reducing it in a pure hydrogen atmosphere at 930 ° C for 20 minutes, and then pulverizing and classifying it. A base powder was produced in which the alloy components shown in the base powder part and the balance were Fe and inevitable impurities. Next, this original powder was mixed with Ni powder and Mo powder.
A predetermined amount of O ₃ powder and Cu powder were mixed with a V-type mixer. The mixed powder was heated at 900 ° C. for 30 minutes in an ammonia decomposition atmosphere gas, then gradually cooled, and then pulverized and classified to obtain powders having chemical compositions shown in Table 5-2 and Table 6-2.

[0056]

[Table 7]

[0057]

[Table 8]

[0058]

[Table 9]

[0059]

[Table 10]

Evaluation of compressibility, machinability, and dimensional stability was in accordance with Example 2. Table 5-1 and Table 6-1 show the results of the green compact density, tool life, and sintering dimensional change. An alloy steel powder satisfying the requirements of claim 4 was mixed with Fe-0.9% Gr-1.0% ZnSt.
Sintering for 30 minutes in a nitrogen atmosphere at 1150 ° C will improve tool life.
A good dimensional accuracy of 00 times or more, the variation width (A) of 0.10% or less, and the variation width (B) of 0.01% or less is shown. Inventive Examples 42, 43, 46 the amount of Cr is 0.06-0.09.
%, S amount is 0.05 to 0.15%, Mn amount is 0.05 to 0.15%, and
Ni content 2.0% or less, Mo content 2.0% or less, Si content 0.01-0.03%,
Al amount 0.01-0.03%, V amount 0.1-0.4%, Nb amount 0.01-0.03
% Of pre-alloyed steel powder containing at least one Ni content of 4.0% or less, Mo content of 2.0% or less, and Cu content of 2.0% or less, heat treated and diffusion-bonded alloy steel in a suitable range. Since it is a powder, the dimensional stability has a variation width (A) of 0.05% or less,
Also, the variation width (B) is less than 0.005%, which is extremely excellent in dimensional stability, and the tool life exceeds 300 times.

Comparative Example 29 shows that if the S content is less than 0.005%, the machinability and dimensional stability are reduced. Comparative Example 30 shows that if the S amount exceeds 0.3%, the compressibility is poor. Comparative Example 31
Indicates that if the Cr content is less than 0.03%, the machinability and dimensional stability are poor. In Comparative Example 32, when the Cr amount is 0.1% or more, the compressibility is
Shows poor dimensional stability. Comparative Example 33 has an Mn content of 0.5.
When it exceeds%, the compressibility is inferior. In addition, the amount of Mn is 0.03
If it is less than%, no improvement in machinability was observed. Comparative example 3
Nos. 4 and 35 show that compressibility and machinability deteriorate when the Ni content and Mo content of the original powder exceed 4.0%, respectively. Also the original powder Ni
If the amount of Mo and the amount of Mo are less than 0.1%, the strength is not improved as compared with the case where each element is not added, and it is not practical in terms of alloy cost. Compared with Comparative Example 36 and Invention Example 40, the addition of Nb improves the compressibility and machinability, but if it exceeds 0.05%, the compressibility and machinability are rather reduced. Comparative Example 37 and Invention Example
Compared with 41, the addition of V improves the compressibility,
If it exceeds 0.5%, the machinability and compressibility deteriorate. Comparative Example 38
When compared with Invention Example 46, the machinability is generally improved by the addition of Si, but if it exceeds 0.1%, the machinability is rather deteriorated. Comparing Comparative Example 39 with Invention Example 42, the machinability is generally improved by the addition of Al, but if it exceeds 0.1%, the machinability is rather deteriorated. According to Comparative Examples 40, 41, 42
It can be seen that the machinability deteriorates when the amounts of Ni, Mo and Cu exceed 5.0%, 3.0% and 5.0%, respectively. The Ni content and Mo content of the diffusion-adhering species are preferably 0.1% or more, and the Cu content is 0.5%.
It was confirmed that the above-mentioned addition improves the strength as compared with the case where each element is not added.

(Embodiment 5) It is an invention example and a comparative example of claims 5 and 6. Table 7-1 shows atomized steel powder (original powder)
The composition and the amount of diffusive deposition of the above are shown. Then, alloy steel powder having the composition shown in Table 7-2 was mixed with graphite and 1.0% zinc stearate, and after mixing, the green compact density was 6.85.
It was sintered at 1130 ° C. for 20 minutes in a nitrogen atmosphere at g / cm ³ .
Table 7 summarizes tool life and dimensional stability. The tool life and dimensional stability were evaluated in the same manner as in Examples 1 and 2.

[0063]

[Table 11]

[0064]

[Table 12]

The amount of residual graphite was quantified by infrared absorption method after filtering the nitric acid-dissolved residue with a glass filter. See also Electr
An on-probe X-ray Miccroanalyzer (hereinafter referred to as EPMA) was used for surface analysis of Mn and S, and the simultaneous output of these two elements confirmed the precipitation of MnS. Inventive Examples 47 to 50 are cases in which the amount of added graphite during sintering is 0.4 to 1.5%, exhibiting excellent dimensional stability with a tool life of 300 times or more and a variation width (B) of 0.01% or less. In Comparative Example 43, the amount of added graphite is 0.4%
It was found that the dimensional stability was poor, and Comparative Example 44 had an added graphite amount of more than 1.5% and had poor machinability.

In the example of the present invention, the residual graphite was 0.05% or more, and as a result of C mapping by EPMA, graphite was concentrated and remained in the pores, and MnS was precipitated in the entire structure. The fracture surface of the tensile test piece is observed and Emergy Dispersive
When the size of 50 inclusions containing Mn and S confirmed by X-ray Spectroscopy (hereinafter referred to as EDX analysis) was measured, all were 5 μm or less. From these facts, the steel powder of each invention example satisfying the requirements of the present invention has graphite having pores and having a structure in which MnS of 5 μm or less exists in iron particles and grain boundaries, and has excellent machinability, dimensional stability, and strength. Excellent sintered steel can be easily obtained.

[0067]

According to the present invention, atomized steel powder and sintered steel excellent in machinability, dimensional accuracy and wear resistance can be manufactured.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (31) Priority claim number Japanese Patent Application No. 5-337325 (32) Priority date Hei 5 (1993) December 28 (33) Priority claim country Japan (JP) (72) Inventor Kuniaki Ogura 1st Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation High-Tech Research Institute

Claims (6)

[Claims] 1. S: 0.005-0.3 wt%, Cr: 0.03-0.1
Atomized steel powder excellent in machinability and dimensional accuracy, characterized by less than wt%, Mn: 0.03 to 0.5 wt% and O: 0.3 wt% or less, and the balance being Fe and unavoidable impurities. 2. In addition to the composition according to claim 1, further Ni:
4.0 wt% or less, Mo: 4.0 wt% or less, Nb: 0.05 wt% or less,
V: 0.5 wt% or less, Si: 0.1 wt% or less and Al: 0.1 wt%
% Or less selected from the group consisting of at least one atomized steel powder having excellent machinability and dimensional accuracy. 3. The atomized steel powder according to claim 1, further comprising Ni
Source: 5.0 wt% or less, Mo source: 3.0 wt% or less and Cu source: 5.
An alloy steel powder excellent in machinability and dimensional accuracy, characterized by mixing one or more kinds selected from the group of 0 wt% or less, heat-treating and diffusing and adhering. 4. The atomized steel powder according to claim 2, wherein Ni
Source: 5.0 wt% or less, Mo source: 3.0 wt% or less and Cu source: 5.
An alloy steel powder excellent in machinability and dimensional accuracy, characterized by mixing one or more kinds selected from the group of 0 wt% or less, heat-treating and diffusing and adhering. 5. A steel having excellent machinability and dimensional accuracy, characterized in that 0.4 to 1.5 wt% of graphite is further added to the steel powder according to claim 1, 2, 3 or 4 to form and sinter. Steel. 6. The graphite in the pores of the sintered steel is 0.05 wt% or more,
The sintered steel having excellent machinability and dimensional accuracy according to claim 5, having a structure in which MnS having a grain size of 5 μm or less is present in the iron particles and at grain boundaries.