JPH0745681B2 - Reduced iron powder with excellent machinability and mechanical properties after sintering - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an iron powder as a raw material for a sintered machine part, etc., and particularly aimed at an advantageous improvement in machinability and mechanical properties after sintering. It is a thing.

Sintered machine parts used for automobiles, precision machinery, and household appliances, etc. do not undergo machining such as cutting because they have the feature that they can be manufactured to a predetermined size and shape by molding and sintering. Was the principle.

However, in recent years, as the shape has become more complicated and high dimensional accuracy has come to be required, the number of cases in which cutting such as drilling, end face cutting, and grooving is unavoidably increased after sintering. It was

Unlike molten steel, voids remain inside sintered steel, which causes intermittent cutting when cutting, and the voids serve as a heat insulating material and deteriorate thermal conductivity, resulting in higher cutting temperatures. Therefore, it is generally said that the tool life is shorter than that of molten steel. Therefore, a sintered steel having excellent machinability has been desired.

(Prior Art) As a method for improving the machinability of sintered steel, a method of adding S, Pb, Se and Te, which are free-cutting components, and their compounds to sintering raw material powder (Japanese Patent Laid-Open No. -80409) or B
Method of adding aSO ₄ , BaS (Japanese Patent Publication No. 46-39564), C
A method of adding aS or CaSO ₄ (Japanese Patent Publication No. 52-16684) has been proposed.

(Problems to be Solved by the Invention) Among the above-mentioned matters, S, for example, is widely known as a free-cutting component of molten steel, but is not necessarily compatible with sintered steel. That is, when S is added to the sintering raw material powder, S tends to react with hydrogen in the sintering atmosphere to generate hydrogen sulfide during sintering, which not only damages the brick and the heating element of the sintering furnace. In addition, the dimension after sintering becomes large and the mechanical properties are significantly deteriorated.

Further, Pb has an extremely low melting point of about 330 ° C., and since it does not form a solid solution in iron, it is difficult to uniformly disperse it in sintered steel, and in addition, there is a problem of Pb pollution during sintering, which is preferable. Absent.

In addition, even in Se and Te, the compounds thereof, that is, the selenium compound and the telluride, generate hydrogen selenide and hydrogen telluride which are both toxic during sintering, like S.

On the other hand, since BaSO ₄ and CaSO ₄ change into BaS and CaS during sintering and become hygroscopic after sintering, there is a problem that the sintered steel is easily rusted.

In addition, when the above additives are added to the iron powder after finishing reduction, the formability of the iron powder when molded (given by the ratler value)
However, the dimensional change after sintering was significantly different from that without addition, and mechanical properties such as tensile strength and impact value were always deteriorated. Therefore, it is difficult to change the mold, and it is difficult to apply it to parts that require strength.

By the way, iron powder as a sintering raw material, so-called reduced iron powder and irregular shaped powder such as electrolytic iron powder, and atomized powder, there are almost spherical powder such as carbonyl powder, among them, the present invention with respect to the former, It is an object of the present invention to solve the above problems in a particularly advantageous manner, and to propose a reduced iron powder that is harmless during sintering and is excellent in machinability and mechanical properties after sintering.

(Means for Solving the Problems) The inventors have found that MgO—SiO ₂ -based composite oxides and glasses are effective as free-cutting components that do not cause adverse effects during sintering of reduced iron powder, and further It was found that the presence of the free-cutting component in the particles of the reduced iron powder is effective in preventing deterioration of mechanical properties after sintering.

The present invention is based on the above findings. That is, the present invention is a reduced iron powder obtained through rough reduction and subsequent finish reduction, wherein a free-cutting component consisting of MgO-SiO ₂ -based composite oxide powder and / or glass powder is incorporated into the particles of the reduced iron powder. It is a reduced iron powder having excellent machinability and mechanical properties after sintering, which is characterized by containing 0.1 to 1.5% by weight of the reduced iron powder in the existing form.

In the present invention, the MgO-SiO ₂ -based composite oxide powder has a MgO / SiO ₂ molar ratio of 0.5 to 5.0, and talc, serpentine, etc. are advantageously suitable.

The glass powder refers to powder of soda lime glass, borosilicate glass, lead glass and the like.

In the present invention, it is important that the reduced iron powder contains a specific amount of the free-cutting component in the form existing in the grain. First
The reduced iron powder of the present invention is schematically shown in FIGS. (A) and (b). In the figure, 1 represents particles, 2 represents free-cutting components, and in FIG. In b), prior to the rough reduction, free-cutting components are added to the respective raw material reduced iron powders, and between the concave portions of the particles 1 and / or between the fine particles 1 ′ which mutually coalesce under high temperature rough reducing conditions, The free-cutting component 2 was added to each.

In the present invention, the form shown in FIGS. 1 (a) and 1 (b) is referred to as "form in which free-cutting components are present in the grains of reduced iron powder".

(Created for) MgO-SiO ₂ composite oxide, as shown in the equilibrium diagram of the MgO and SiO ₂ in FIG. 2, MgO is (shown below simply%) 35 wt% rapidly melting point degree It is characterized by the fact that it is decreasing, and for that reason, stacking magnesia bricks and silica bricks has been prohibited for many years in steelmaking furnaces. The reason is that if the silica brick exceeds 30%, a liquid phase of 1543 ° C is generated.

As described above, the temperature locally reached during cutting of sintered steel is higher than that of molten steel. Therefore, in this invention,
By including MgO-SiO ₂ -based composite oxide powder with a composition that produces a liquid phase of 1543 ° C in sintered steel, a liquid phase of 1543 ° C appears on the cutting tool surface during cutting and adheres to the cutting tool. It is thought that the life of the cutting tool will be greatly improved at the same time as it controls the cutting edge and lubricates it.

In addition, so-called glass such as soda lime glass, borosilicate glass, lead glass, etc. also has a melting temperature of 1350 to 1800 ° C depending on the type, but since it gradually begins to soften before the melting temperature, MgO-SiO ₂ composite Similar to oxides, glass adheres to the cutting tool surface during cutting, protects and lubricates the cutting tool, and prevents the diffusion reaction of carbon between the cutting tool and sintered steel, greatly improving the cutting tool life. I think that the.

Further, by simultaneously adding MgO-SiO ₂ -based composite oxide powder and glass powder, the number of types of oxide liquid phase adhering to the cutting tool increases, and it is possible to improve the life of the cutting tool over a wide range of cutting conditions. it can.

As described above, the MgO—SiO ₂ composite oxide and glass have the same action and effect and are the same effect substance.

All of the above free-cutting components are thermally stable MgO during sintering.
Since it contains oxides such as SiO ₂ and SiO ₂ as a main component, it does not generate harmful gas during sintering, and does not damage the bricks in the furnace of the sintering furnace, the heating element, or the pipes. Therefore, it does not affect the dimensional change after sintering at all.

Even if MgO-SiO ₂ composite oxide powder and glass powder, which are free-cutting components that are harmless during sintering and do not adversely affect the dimensions after sintering, even after atomization iron powder or reduced iron powder, finish reduction When added to the iron powder, the formability of the iron powder deteriorates, and mechanical properties such as tensile strength, elongation and impact value after sintering are deteriorated. This is because in the case of atomized iron powder, the shape of the iron powder particles is relatively spherical and there is no unevenness on the surface. Therefore, as shown in FIG. Since the direct contact between powder particles is obstructed and the additive acts as a notch, the formability of iron powder and the mechanical properties after sintering are reduced. In the case of reduced iron powder, Fig. 3 As shown in (b), since there are more irregularities on the surface than the atomized iron powder and it has an irregular shape as a whole, even if some additives enter the recesses on the surface, the rest are iron powder other than the recesses. The particles remain attached to the surface of the particles, which also hinders direct contact between the iron powder particles during molding, resulting in deterioration of the moldability of the iron powder and mechanical properties after sintering.

In atomized iron powder, a method of adding to the iron powder before finish reduction or as described in JP-B-52-36750, the additives are mixed in the molten metal and atomized, cooled, and solidified to produce a composite powder. It is also possible to produce iron powder excellent in machinability by the method described above or the method of mixing additives with a spray medium and spraying as in JP-A-61-17703, but these also have the following problems. There is. That is, the method of adding to the iron powder before finish reduction is that the additive adhered to the surface of the relatively spherical iron powder particles has no metallurgical binding force with the iron powder particles as shown in FIG. 3 (c). Since most of them are easily removed by magnetic separation after finish reduction, even if additives are added, no additive remains in the iron powder after finish reduction, so that there is no effect of improving machinability. In addition, in the method of adding to the molten metal or the spray medium, as shown in FIG. 3 (d), some of the additives are included inside the iron powder particles, and some of them are firmly attached to the surface of the iron powder particles. . Additives firmly attached to the surface of the iron powder particles are not removed by the subsequent magnetic separation and remain on the surface of the iron powder particles, which interferes with the direct contact between the iron powder particles when the iron powder is molded. And the mechanical properties after sintering are reduced.

On the other hand, in the present invention, the additive is added before the crude reduction or finish reduction of the reduced iron powder. By doing so, for example, in the addition before rough reduction, as shown in FIG. 1 (b), the additive adhered to the surface of the iron oxide is confined between the iron powder particles due to the sintering of the iron oxide during the rough reduction. To be On the other hand, the additive that is not confined between the iron powder particles and adheres to the surface is not metallurgically adhered to the iron oxide powder, and thus is easily removed by the magnetic separation in the subsequent step. Therefore, there is no additive on the surface of the iron powder particles, and an iron powder in which an oxide exists in the particles of the reduced iron powder is formed. This does not hinder the direct contact between the iron powder particles when the iron powder is molded, and thus does not deteriorate the moldability of the iron powder and the mechanical properties after sintering. Moreover, when additives are added to the reduced iron powder before finish reduction, FIG. 1 (a)
As shown in, the additive adheres to the concave portion and the smooth portion on the surface of the iron powder particles, but the additive adhered to the smooth portion is removed by magnetic separation after finish reduction. Therefore, it is possible to obtain an iron powder that does not interfere with the direct contact between the iron powder particles when the iron powder is molded, and thus does not add the moldability of the iron powder and the mechanical properties after sintering.

The reasons for limitation will be described below.

In either case of adding MgO-SiO ₂ composite oxide powder and glass powder alone or both, if less than 0.1%, there is almost no effect, while if it exceeds 1.5%, the compressibility of iron powder is extremely poor. Therefore, it was set to 0.1 to 1.5%.

MgO / SiO ₂ molar ratio in the MgO-SiO ₂ composite oxide powder 0.5
As shown in the equilibrium diagram of Fig.2, the amount of liquid phase at 1543 ℃ decreases, so the effect of sticking to the cutting tool during cutting, protecting and lubricating the cutting tool, and The effect of preventing the carbon diffusion reaction with the binding steel is reduced,
Since the life of the cutting tool is shortened, it is preferable to set the MgO / SiO ₂ molar ratio to about 0.5 to 5.0.

The particle size of the MgO-SiO ₂ -based composite oxide powder or glass powder is preferably as fine as possible in order to be present in the particles of iron powder, but 325 mesh (0.044 mm) or less is sufficient.

(Example) Example 1 Talc powder (33% MgO-) having 325 mesh or less on a mill scale.
60% SiO ₂ ) was added 0.1%, 0.5%, 1.0% and 1.5% respectively, and coarse reduction was performed in coke at 1150 ° C. for 44 hours, then crushed to 100 mesh or less, and 900 ° C. for 1 hour after magnetic reduction. The iron powder was applied and magnetically selected.

Separately, mill scale was roughly reduced in coke at 1150 ° C. for 44 hours, the obtained pulverized powder was magnetically separated, and 0.1%, 0.5%, 1.0%, 1.5% and 2.0% of talc powder of 325 mesh or less were added, respectively. After that, finish reduction was performed at 900 ° C. for 1 hour, and magnetic separation was performed to obtain iron powder.

Further, as a comparative example, rough reduction, magnetic separation, finish reduction, and magnetic separation were performed on a mill scale under the same conditions as above, and 0.1%, 0.5%, 1.0%, 1.5% and 2.0% of talc powder were respectively added to the obtained iron powder.
Was added.

To these iron powders containing talc and iron powders without talc, 2% of electrolytic copper powder, 0.5% of natural graphite powder were added in the inner frame, and 1% of zinc stearate as a solid lubricant was added in the outer frame.
Fig. 4 shows the properties of the green compact when these iron powders were compacted at a compacting pressure of 5 t / cm ² .

As is apparent from the figure, the powder density and the ejection force decrease with the addition amount of talc at any addition position. The ratler value increases (becomes worse) with the amount of talc added
Although there is a tendency, the talc powder added to the iron powder before the crude reduction and before the finish reduction, which is the present invention, is only slightly worse than the addition after the finish reduction. The reason for this will be described later.

In Fig. 5, the mixed powder was molded into a JSPM standard tensile test piece and a Charpy impact test piece with a green density of 6.8 g / cm ³ , and a flow rate of 4
After dewaxing at 600 ° C for 30 minutes in a decomposed ammonia gas atmosphere of / min, sinter at 1130 ° C for 30 minutes to change the dimensions,
The results of measuring tensile strength, elongation and impact value are shown. The dimensional change was measured in the length direction of the Charpy impact test piece before and after sintering.

As is clear from the figure, the dimensional change is almost constant regardless of the addition amount of talc at any addition position. Regarding the tensile strength, those added after finishing reduction significantly decreased with the addition amount of talc, whereas the additions before rough reduction and addition before finish reduction of the present invention hardly decreased. This is similar to the Ratler value was that when talc powder was added after finish reduction, talc adhered to the surface of the iron powder particles to prevent direct contact between the iron powder particles, resulting in a decrease in tensile strength, On the other hand, if talc is added between the iron powder particles or present in the recesses on the surface of the iron powder particles when added before rough reduction or finish reduction, it does not interfere with the direct contact between the iron powder particles. The decrease is small. For the same reason, the elongation and impact value of the iron powder to which talc was added before rough reduction and finish reduction did not deteriorate much.

In Fig. 6, cutting test pieces with an inner diameter of 20 mm, an outer diameter of 60 mm, and a height of 30 mm were molded and sintered under the same conditions as the above-mentioned tensile test, and then three were connected to perform a cutting test. The result of having measured the amount of abrasion and surface roughness (average roughness Ra) is shown. Here, the cutting conditions were as follows.

Depth: 1.0 mm Feed: 0.1 mm / rev. Cutting speed: 200 m / min Cutting distance: 1272 m Cutting tool: Carbide JIS P10 class From Fig. 6, the amount of talc addition and the amount of lateral flank wear can be seen at any addition position. You can see that it is decreasing. This is because the wear amount of the cutting tool is affected only by the addition amount of talc, and there is no difference depending on the addition position. The surface roughness has a similar tendency.

It was found that the amount of talc added is preferably 0.1 to 1.5%, judging from the properties of the green compact, the properties of the sintered body and the amount of lateral flank wear.

On the other hand, even as a comparative example, atomized iron powder at the time of atomizing the talc powder addition position, before finish reduction and after finish reduction,
Divide each, the amount of talc added is 0.1%, 0.5%,
It was adjusted to 1.0%, 1.5% and 2.0% and added. It should be noted that talc can be added in any amount when added before and after finish reduction, but when added during atomization, it is difficult to add any amount, so talc raw powder dispersed in water The amount of talc-added atomized powder is changed by the pencil jet method at a water pressure of 150 kg / cm ² and a flow rate of 230 / min. 0 for each.
It is adjusted to 1%, 0.5%, 1.0%, 1.5% and 2.0%. All finish reductions were performed at 950 ° C. for 1 hour, and magnetic separation was performed after atomization and finish reduction.

In the same way as the reduced iron powder mentioned above, the electrolytic copper powder is added to the obtained iron powder.
%, Natural graphite powder 0.5% in the inner frame, zinc stearate 1
% Each was added in the outer frame. Fig. 7 shows the characteristics of the green compact at a molding pressure of 5 t / cm ² . As is clear from the figure, the powder density decreases with the amount of talc added at the time of atomization and addition after finish reduction, but not so much with the addition before finish reduction. This is because when added before finish reduction, atomized iron powder is relatively spherical, so it does not fit into the recess like reduced iron powder, and most of the talc is removed by magnetic separation after finish reduction. The density does not drop so much. The output value varies widely,
At the time of atomization and after the addition of finish reduction, it tends to decrease with the addition amount of talc, but in the addition before the finish reduction, the added talc is mostly removed by magnetic separation after the finish reduction, so there is not much change.

FIG. 8 shows the characteristics of a sintered body obtained by sintering the reduced iron powder under the same conditions. As is clear from the figure, the dimensional change is almost constant regardless of the addition amount of talc at any addition position. Regarding the tensile strength, when it is added before finish reduction, it does not decrease much with the addition amount of talc for the reason described above. When added during atomization and after finish reduction, it decreases with the amount of talc added. The same tendency was observed for elongation and impact value.

FIG. 9 shows the result of the cutting test. As is clear from the figure, when added before finish reduction, talc is largely removed by magnetic separation after finish reduction as in the case of tensile strength, so the amount of lateral flank wear does not decrease.

As described above, in the atomized iron powder, talc is strongly adhered to the inside of the particle and the particle surface when added during atomization, and talc firmly adhered to the particle surface is not removed by the magnetic separation after atomization or the magnetic separation after finish reduction. Since the direct contact between the iron powder particles is hindered, the strength is reduced. Further, if added before finish reduction, atomized iron powder does not have an irregular shape like reduced iron powder, but since it is close to a spherical shape, most of talc is removed by magnetic separation after finish reduction, so there is no addition effect. If added after finishing reduction, talc adheres to the surface of the iron powder particles as in the case of the reduced iron powder and prevents direct contact between the iron powder particles.

Example 2 MgO having a composition shown in Table 1 was fired by adding various reagents MgO or SiO ₂ to talc (talc) having a composition of 33% MgO-60% SiO _2.
—SiO ₂ -based composite oxide powder was prepared.

This MgO-SiO ₂ composite oxide powder is mill scale 0.1%, 0.3%, 0.5%, 0.75%, 1.0%, 1.3%, 1.6%, respectively.
And 2.0% were added, and crude reduction and finish reduction were performed under the same conditions as in Example 1 to obtain reduced iron powder. To these iron powders, 2% of electrolytic copper powder and 0.5% of natural graphite powder were added in an inner frame, and zinc stearate was added in an outer frame of 1%.

Fig. 10 shows the characteristics of the green compact molded at a molding pressure of 5 t / cm ² .
From the figure, it can be seen that the powder density and the ejection force decrease with the addition amount of the MgO-SiO ₂ composite oxide powder, and the Ratler value deteriorates.

Next, sintering was performed under the same conditions as in Example 1, and after sintering, dimensional change, tensile strength, elongation and impact value were measured. The results are shown in FIG. From the figure, it is understood that the dimensional change hardly changes with the addition amount, but the tensile strength, the elongation and the impact value decrease with the addition amount, and sharply decrease when the addition amount exceeds 1.5%.

Horizontal逃面wear amount of the cutting tool after the cutting test in FIG. 12, and the surface roughness, showing the relationship between MgO-SiO ₂ composite oxide powder amount. Obviously lateral逃面wear amount and surface roughness as the figure is decreased with MgO-SiO ₂ composite oxide powder amount.

Example 3 Talc having a composition of 33% MgO-60% SiO ₂ and reagent MgO or SiO ₂
Was added and fired to prepare MgO—SiO ₂ composite oxide powder having the composition shown in Table 2.

These MgO-SiO ₂ -based composite oxide powders were pulverized to 325 mesh or less, and 0.75% each was added to the mill scale to perform crude reduction at 1150 ° C for 44 hours, and then pulverized to 100 mesh or less, Magnetically selected. Further, the product was subjected to finish reduction in H ₂ at 900 ° C. for 1 hour, crushed, and then magnetically selected again (Examples A to
D, Comparative Examples E, F). As a comparative example, a reduced iron powder containing no MgO—SiO ₂ added was also prepared by performing rough reduction, pulverization, magnetic separation, finish reduction, crushing, and magnetic separation on the same mill scale under the same conditions (Comparative Example G). The apparent density of each iron powder was adjusted to 2.5 g / cm ³ .

2% of electrolytic copper powder and 0.5% of natural graphite powder were mixed with these iron powders, and 1.0% of zinc stearate as a solid lubricant was mixed with the mixed powder in the outer frame. Table 3 shows the properties of the green compact when molded at a molding pressure of 5 t / cm ² .

As is clear from the table, all of the symbols A to F in which the additive was added to the mill scale had the green compact density lower by 0.06 to 0.10 g / cm ³ than the symbol G without the additive. The output and the ratler value are the same as G.

After that, a tensile test piece of the JISPM standard with a powder density of 6.8 g / cm ^{3 and} a ring test piece for cutting test with an inner diameter of 20 mm, an outer diameter of 60 mm and a height of 30 mm were molded, and 600 mm in a decomposed ammonia gas atmosphere with a flow rate of 4 / min. After dewaxing at 30 ° C for 30 minutes, sintering at 1130 ° C for 30 minutes, dimensional change after sintering, tensile strength, elongation, impact value, and lateral flank wear amount of the cutting tool after cutting test, The surface roughness was measured. Here, the cutting conditions of the cutting test were as follows.

Depth …… 1.0mm Feed …… 0.1mm / rev. Cutting speed …… 200m / min Cutting distance …… 1272m Cutting tool …… Cemented Carbide JIS P10 Class Dimensional change after sintering, tensile strength, elongation and impact value It is shown in FIG. The dimensional changes, tensile strengths, elongations and impact values of Examples A to D and Comparative Examples E and F are the same as those of the additive-free (Comparative Example G), and the MgO / SiO ₂ molar ratio is unchanged.

Horizontal逃面wear amount of the cutting tool after the cutting test with MgO-SiO ₂ molar ratio, the relationship between the surface roughness shown in FIG. 13. As is clear from the figure, the amount of lateral flank wear is significantly improved by adding the MgO-SiO ₂ composite oxide, and in particular the MgO / SiO ₂ molar ratio is
Those of 0.5 to 5.0 are excellent. The same applies to the surface roughness.

Example 4 0.55% of talc powder of 325 mesh or less was added to a mill scale, and coarse reduction was performed in a coke at 1150 ° C. for 44 hours, followed by crushing.
Finishing reduction was performed at 0 ° C. for 1 hour to obtain iron powder.

Separately from this, an iron powder in which 0.55% of talc was added after rough reduction was applied to the mill scale and an iron powder in which 0.55% of talc was added after rough reduction and finish reduction were performed on the mill scale were also prepared.

As a comparative example, talc powder of 325 mesh or less is dispersed in water, water atomized with a pencil jet method at a water pressure of 150 kg / cm ² , and a flow rate of 230 / min, classified to 100 mesh, dried and then subjected to a finishing reduction at 950 ° C for 1 hour. gave. Since the analyzed amounts of Si and Mg of the obtained iron powder were 0.17% and 0.056%, respectively, by adding an arbitrary amount of talc to the atomized iron powder, Si,
It was expected that the iron powder contained 0.54 to 0.56% of talc in comparison with the results of Mg analysis. Further, iron powder was prepared by atomizing water by a usual method and adding 0.55% of talc powder of 325 mesh or less before and after finish reduction, respectively. An iron powder without addition of talc powder was also prepared.

2% electrolytic copper powder and 0.5% natural graphite powder to these iron powders
In the inner frame, zinc stearate was added 1% in the outer frame.

Table 4 shows the properties of the green compact at a pressure forming force of 5 t / cm ² .

As is clear from the table, in the reduced iron powder, the ratler value of the one to which the talc powder was added before the rough reduction and after the finish reduction which are examples is slightly incompressible as compared with the iron powder without the additive, but is 0.7. The values were almost the same as those in the% range and no addition. In atomized iron powder, those added during atomization and after finish reduction deteriorated until the ratler value exceeded 1%,
On the other hand, the one added before the finishing reduction showed almost the same ratler value as the iron powder without addition because the added talc powder was removed by the magnetic separation after the finishing reduction.

Next, a green compact having a green compact density of 6.8 g / cm ³ was sintered in decomposed ammonia gas at 1130 ° C. for 30 minutes. Table 5 shows the dimensional change after sintering, tensile strength, elongation, impact value, and the lateral flank wear amount and surface roughness of the cutting tool after the cutting test.

As is clear from the table, in the reduced iron powder, the amount of tool wear is small even though the addition before rough reduction and the addition before finish reduction of the example have the same strength level as the iron powder without addition. Therefore, it is understood that the iron powder of the present invention can improve the machinability without lowering the formability and the machinability after sintering.

On the other hand, the one added after finishing reduction has low strength because the direct contact between the iron powders is disturbed, and the tool wear amount is also small. In atomized iron powder, when atomizing,
The iron powder added after finishing reduction has low strength and less tool wear. The iron powder added before finish reduction had the same strength as the additive-free powder and the amount of tool wear. This is because if talc powder is added before the finish reduction of atomized iron powder, most of the talc powder is removed by magnetic separation after finish reduction.

Example 5 A talc powder having a composition of 33% MgO-60% SiO ₂ was added to a mill scale at 0.7.
5% was added. Separately, 73% SiO ₂ -13% Na ₂ O-10% C
aO-4% MgO composition soda glass powder on a mill scale 0.7
5% was added. These raw powders were placed in coke at 1150 ℃, 4
After rough reduction for 4 hours, it was ground to 100 mesh or less and magnetically selected. Further, finish reduction was performed in H ₂ at 900 ° C. for 1 hour, and after crushing, magnetic separation was performed again. As a comparative example, the same mill scale to which nothing was added was subjected to rough reduction, pulverization, magnetic separation, finish reduction, crushing, and magnetic separation under the same conditions to prepare a reduced iron powder having an apparent density almost equal to that of the example. 2% of electrolytic copper powder and 0.5% of natural graphite powder were mixed with these three kinds of iron powders, and 1.0% of zinc stearate as a solid lubricant was mixed with this mixture in the outer frame.

Table 6 shows the properties of the green compact at a molding pressure of 5 t / cm ² .

In the example, the green compact density is slightly low, but the ejection force and the ratler value are the same.

After that, the tensile test piece and Charpy impact test piece of the JSPM standard with a powder density of 6.8 g / cm ³ and an inner diameter of 20 mm, an outer diameter of 60 mm and a height of 30 mm
The ring test piece for cutting test was molded, dewaxed at 600 ° C for 30 minutes in a decomposed ammonia gas atmosphere at a flow rate of 4 / min, and then sintered at 1130 ° C for 30 minutes to change the dimensions after sintering.
The tensile strength, the elongation, the impact value, the lateral flank wear amount of the cutting tool after the cutting test, and the surface roughness were measured. Here, the conditions of the cutting test are as follows.

Depth …… 1.0mm feed …… 0.1mm / rev. Cutting speed …… 200m / min Cutting distance …… 1272m Cutting tool …… Cemented Carbide JIS P10 The above results are shown in Table 7.

It can be seen that in the examples, the tensile strength and the impact value are almost the same as those without addition, but the lateral flank wear amount is almost halved. The surface roughness is also improved.

Example 6 The MgO—SiO ₂ -based composite oxide powder represented by the symbol A in Table 1 and 73% SiO ₂ -13% Na ₂ O-10% CaO-4% MgO composition soda glass powder used in Example 2 were used. Mix 1: 1 and add 0.75% of this mixed powder to the mill scale. As a comparative example, the reduced iron powder of Comparative Example G of Example 2 was prepared.

To these iron powders, 2% of electrolytic copper powder, 0.5% of natural graphite powder was added in the inner frame, and 1% of zinc stearate was added in the outer frame. Table 8 shows the properties of the green compact at a molding pressure of 5 t / cm ² .

In the example, the powder density is lower than that of the comparative example because the iron powder particles contain the additive. Table 9 shows the dimensional change, tensile strength, elongation and impact value after sintering.

From the table, it can be said that there is almost no difference in mechanical properties after sintering between the example and the comparative example.

Fig. 13 shows the results of examining the lateral flank wear amount and surface roughness of the cutting tool after cutting while changing the cutting speed to 50, 75, 100, 150 and 200 m / min. As is clear from the figure, the lateral flank wear amount shows a smaller amount at any cutting speed than the comparative example, and the composite of MgO-SiO ₂ -based complex oxide powder and soda glass powder is shown. It shows that the additive is effective over a wide range of cutting conditions. Regarding the surface roughness, in the comparative example, the cutting speed increased and the surface roughness decreased, which is the same as what is said for the molten steel. The example shows a maximum at a cutting speed of 150 m / min. The reason for this seems to be that the deposits on the cutting tool during cutting have an effect.

(Effects of the Invention) By using the iron powder of the present invention, the dimensional change and mechanical properties after sintering can be made to be the same as those of the conventional iron powder without causing damage to the brick in the sintering furnace and the heating element during sintering. It is possible to obtain a sintered machine part having excellent machinability while maintaining the same level, and the effect is great.

[Brief description of drawings]

FIG. 1 is a schematic diagram of reduced iron powder of the present invention, FIG. 2 is an equilibrium diagram of MgO—SiO ₂ system, FIG. 3 is a schematic diagram of iron powder of a comparative example, and FIG. 4 is reduction. Fig. 5 is a graph showing the relationship between the talc addition amount in the iron powder, the green compact density of the green compact, the ejection force and the ratler value. Fig. 5 shows the talc addition amount in the reduced iron powder, the dimensional change of the sintered body, and the tensile strength. FIG. 7 is a graph showing the relationship between strength, elongation, and impact value, and FIG. 6 is a graph showing the relationship between the amount of talc added in the reduced iron powder, the lateral flank wear amount after the cutting test, and the surface roughness, FIG. Is a graph showing the relationship between the amount of talc added in atomized iron powder and the density, ejection force and ratler value of the green compact, FIG. 8, talc addition amount in atomized iron powder, dimensional change of sintered body, and tensile strength. Fig. 9 is a graph showing the relationship between strength, elongation and impact value. Fig. 9 shows talc in atomized iron powder. A graph showing the relationship between the addition amount, the lateral flank wear amount after the cutting test, and the surface roughness, FIG. 10 shows the addition amount of the MgO-SiO ₂ -based complex oxide powder and the green compact density, the ejection force and the ratler value. Fig. 11 is a graph showing the relationship with Fig. 11, Fig. 11 is a graph showing the relationship between the amount of MgO-SiO ₂ composite oxide powder added and dimensional change, tensile strength, elongation and impact value, and Fig. 12 is MgO. A graph showing the relationship between the amount of addition of -SiO ₂ -based complex oxide powder and the amount of lateral flank wear, surface roughness, Fig. 13 shows the MgO / SiO ₂ molar ratio and dimensional change, tensile strength, elongation and Graph showing the relationship with the impact value, FIG. 14 is a graph showing the relationship between the MgO / SiO ₂ molar ratio and the lateral flank wear amount after the cutting test, and the surface roughness, and FIG. 15 is a graph showing the relationship after the cutting test. 6 is a graph showing the relationship between the amount of lateral flank wear and surface roughness. 1 ... particle, 2 ... free-cutting component

Claims (1)

[Claims] 1. A reduced iron powder obtained by rough reduction and subsequent finish reduction, wherein a free-cutting component consisting of MgO—SiO ₂ -based composite oxide powder and / or glass powder is incorporated into the reduced iron powder. The reduced iron powder having excellent machinability and mechanical properties after sintering, characterized in that it is contained in the form of 0.1 to 1.5% by weight relative to the reduced iron powder.