WO2019167722A1

WO2019167722A1 - Iron powder for powder metallurgy

Info

Publication number: WO2019167722A1
Application number: PCT/JP2019/006090
Authority: WO
Inventors: 祐司谷口; 北条　啓文; 西田　智
Original assignee: 株式会社神戸製鋼所
Priority date: 2018-02-28
Filing date: 2019-02-19
Publication date: 2019-09-06
Also published as: CN111741822B; KR20200121858A; EP3760343A4; EP3760343A1; JP7057156B2; JP2019147997A; CN111741822A; KR102507938B1

Abstract

An iron powder for powder metallurgy according to one embodiment of the present invention has a composition that contains 0.005% by mass or less of C, 0.030% by mass or less of Si, 0.020% by mass or less of P, 0.020% by mass or less of S, 0.15% by mass or less of O and 3.0% by mass or less of the total of Mn, Ni, Mo and Cr, with the balance being made up of Fe and unavoidable impurities; and this iron powder for powder metallurgy has a tap density of from 3.90 g/cm³ to 4.20 g/cm³ (inclusive).

Description

Iron powder for powder metallurgy

The present invention relates to iron powder for powder metallurgy.

Powder metallurgy is widely used in which metal parts are formed by sintering metal powders after compacting. In powder metallurgy, in general, the mechanical strength of the obtained metal sintered body can be increased by increasing the density of the green compact, that is, by reducing the porosity of the green compact. In powder metallurgy, by increasing the strength of the green compact, the dimensional accuracy of the resulting sintered metal can be improved and the yield can be increased.

JP-A-4-173901 describes that the density of the green compact can be increased by relatively increasing the apparent density of the iron powder for powder metallurgy, that is, the bulk specific gravity of the powder in a stationary state. However, this publication further describes that if the apparent density is increased beyond a certain level, the strength of the green compact becomes insufficient. However, as a result of verification by the present inventors, in the limit region where the strength reduction of the green compact starts to become a problem, the magnitude relation of the apparent density of the iron powder for powder metallurgy having the same composition and the magnitude relation of the density of the green compact However, it turned out that it is not rare to reverse.

If the molding pressure at the time of compacting is increased, the density of the compact is increased and the strength of the compact is improved. However, an increase in the molding pressure causes inconveniences such as shortening the life of the mold, so that the production efficiency of metal parts decreases.

JP-A-4-173901

In view of the above inconveniences, an object of the present invention is to provide iron powder for powder metallurgy from which a high-strength sintered body can be obtained.

The iron powder for powder metallurgy according to one embodiment of the present invention made to solve the above-mentioned problems is, C is 0.005 mass% or less, Si is 0.030 mass% or less, P is 0.020 mass% or less, T has a composition in which S is 0.020% by mass or less, O is 0.15% by mass or less, the total of Mn, Ni, Mo and Cr is 3.0% by mass or less, and the balance is Fe and inevitable impurities. density of 3.90 g / cm ³ or more 4.20 g / cm ³ or less.

The iron powder for powder metallurgy is excellent in compressibility at the time of compaction molding because it is easy to rearrange the iron powder particles so as to be in the closest packed state by setting the tap density within the above range. The strength of the finally obtained sintered body is large.

In the iron powder for powder metallurgy, the content of particles passing through a plain weave wire mesh having an average opening of 45 μm is preferably 10% by mass or more and 20% by mass or less. Thereby, sufficient intensity | strength is obtained with the green compact and sintered compact of the said iron powder for powder metallurgy.

Here, “tap density” is a value measured according to JIS-Z2512 (2012).

As described above, the powder metallurgy iron powder according to one embodiment of the present invention has a high density of a green compact, and a high-strength sintered body can be obtained.

It is a graph which shows the relationship between the tap density of the iron powder for powder metallurgy, and the density of a green compact. It is a graph which shows the relationship between the tap density of the iron powder for powder metallurgy, and the Rattler value of the green compact.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[Iron powder for powder metallurgy]
In the iron powder for powder metallurgy according to an embodiment of the present invention, C is 0.005 mass% or less, Si is 0.030 mass% or less, P is 0.020 mass% or less, and S is 0.020 mass% or less. , O is 0.15 mass% or less, the total of Mn, Ni, Mo and Cr is 3.0 mass% or less, the balance is Fe and inevitable impurities, and the tap density is 3.90 g / cm ^3. This is 4.20 g / cm ³ or less.

<C (carbon)>
C is an element that hardens particles of the iron powder for powder metallurgy. C can also harden iron powder particles by combining with other impurities to form fine carbides. If the iron powder particles become hard, it becomes difficult to be deformed at the time of compacting, so that the moldability is lowered and the density of the compact is lowered. Therefore, the upper limit of the C content in the iron powder for powder metallurgy is 0.005% by mass, preferably 0.003% by mass, and more preferably 0.002% by mass.

<Si (silicon)>
Si is an element that easily binds to oxygen, and forms an oxide film on the particle surface of the iron powder for powder metallurgy. Since the oxide film made of Si is not easy to reduce, the strength of the obtained sintered body is lowered. Moreover, since Si has the effect | action which hardens iron powder particle | grains, it reduces the compressibility (density and intensity | strength of a compact) of the said iron powder for powder metallurgy. For this reason, as an upper limit of content of Si, it is 0.030 mass%, 0.020 mass% is preferable, and 0.015 mass% is more preferable.

<P (phosphorus)>
P is an element that hardens iron powder particles and lowers compressibility. For this reason, as an upper limit of content of P, it is 0.020 mass%, 0.017 mass% is preferable, and 0.015 mass% is further more preferable.

<S (sulfur)>
S is an element that hardens iron powder particles and lowers compressibility. For this reason, as an upper limit of content of S, it is 0.020 mass%, 0.015 mass% is preferable, and 0.010 mass% is further more preferable.

<O (oxygen)>
O is an element that hardens iron powder particles and lowers compressibility. For this reason, as an upper limit of content of O, it is 0.15 mass%, 0.12 mass% is preferable, and 0.10 mass% is more preferable.

<Mn (manganese), Ni (nickel), Mo (molybdenum), Cr (chromium)>
Mn, Ni, Mo and Cr are elements added to improve the strength of a sintered body obtained by compacting and sintering the iron powder for powder metallurgy. However, if the content of these elements becomes too large, the iron powder particles become too hard and the compressibility may be insufficient. For this reason, as an upper limit of total content of Mn, Ni, Mo, and Cr, it is 3.0 mass%, 2.5 mass% is preferable and 2.0 mass% is more preferable.

<Tap density>
The tap density is an index representing the ease of rearrangement of iron powder particles. If the true specific gravity is constant, the larger the tap density value, the easier the iron powder particles are rearranged into a packed state with a smaller porosity. For this reason, the higher the tap density, the higher the compressibility and the easier the compacting, and a compact with a higher density can be obtained at a relatively low pressure. On the other hand, when the tap density is excessively large, the adhesion between the iron powder particles is insufficient, and the strength of the obtained green compact may be insufficient. Therefore, the lower limit of the tap density of the powder metallurgical iron powder, a 3.90 g / cm ^3, preferably ^{3.95g / cm 3, 3.97g / cm} 3 is more preferable. On the other hand, the upper limit of the tap density of the powder metallurgical iron powder, a 4.20 g / cm ^3, preferably ^{4.15g / cm 3, 4.10g / cm} 3 is more preferable.

<Particle size distribution>
As a minimum of the content rate of the particle | grains which pass through the plain weave metal mesh of 45 micrometers of average openings in the said iron powder for powder metallurgy, 10 mass% is preferable and 12 mass% is more preferable. On the other hand, the upper limit of the content of particles passing through a plain weave wire mesh with an average opening of 45 μm in the iron powder for powder metallurgy is preferably 20% by mass, and more preferably 18% by mass. If the content of particles passing through a plain weave wire mesh with an average opening of 45 μm in the powder metallurgy iron powder is less than the lower limit, the strength of the sintered body of the powder metallurgy iron powder may be insufficient. Conversely, when the content of particles passing through a plain weave wire mesh with an average opening of 45 μm in the iron powder for powder metallurgy exceeds the above upper limit, the strength of the green compact finally obtained may be insufficient.

<Dense density>
As a lower limit of the density of the green compact obtained when 0.75% by mass of zinc stearate is added to the iron powder for powder metallurgy and molded at a molding pressure of 7 tf / cm ² , 7.20 g / cm ³ is Preferably, 7.22 g / cm ³ is more preferable. If the density of the green compact is less than the lower limit, the strength of the finally obtained sintered body may be insufficient.

<Strength of compact>
As an upper limit of the Rattler value, which is an index of the strength of a green compact obtained by adding 0.75% by mass of zinc stearate to the iron powder for powder metallurgy and molding at a molding pressure of 7 tf / cm ² 0.75% is preferable, and 0.70% is more preferable. If the Rattler value of the green compact exceeds the upper limit, the green compact strength may be insufficient, and the dimensional accuracy and yield of the sintered body may be insufficient. The “Rattler value” is a value measured according to JSPM standard 4-69.

<Manufacturing method>
The iron powder for powder metallurgy includes a water atomizing process in which water is sprayed into molten iron prepared in the above-described composition, and a reducing process in which the powder obtained in the water atomizing process is heated in a reducing gas atmosphere. And a pulverization step of pulverizing the iron powder solidified in the reduction step.

(Water atomization process)
In the water atomization step, fine iron powder is obtained by spraying water onto the molten iron flowing down from the furnace. In this water atomization step, the tap density of the obtained iron powder for powder metallurgy is adjusted within the above-mentioned range by adjusting the water pressure of the water to be sprayed. Specifically, the tap density of the iron powder for powder metallurgy obtained as the water pressure increases is reduced.

(Reduction process)
In the reduction step, the iron powder oxidized in the water atomization step is reduced by heating in a reducing gas environment.

As the reducing gas, for example, hydrogen gas, ammonia gas, or butane gas can be used.

(Crushing process)
In the pulverization step, the iron powder solidified into a cake by the reduction treatment is pulverized by a mill. By sufficiently pulverizing the iron powder, the particle size distribution of the obtained iron powder for powder metallurgy is assumed to conform to the particle size distribution of the iron powder obtained in the water atomization step, thereby ensuring a desired tap density.

As the mill used in this pulverization step, for example, a hammer mill, a feather mill or the like can be used.

In this pulverization step, it is preferable that the pulverized iron powder is classified with a wire mesh and large particles are reintroduced into the mill.

<Advantages>
The iron powder for powder metallurgy is excellent in compressibility at the time of compaction molding because it becomes easy to rearrange the iron powder particles so as to increase the apparent density by setting the tap density within the above range. And a green compact having sufficient strength can be obtained. For this reason, the sintered compact with a large intensity | strength can be efficiently manufactured by using the said iron powder for powder metallurgy.

[Other Embodiments]
The said embodiment does not limit the structure of this invention. Therefore, in the above-described embodiment, the components of each part of the above-described embodiment can be omitted, replaced, or added based on the description and common general knowledge of the present specification, and they are all interpreted as belonging to the scope of the present invention. Should.

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not construed as being limited based on the description of the examples.

Molten iron was prepared using an electric furnace, and the molten iron flowed down from the electric furnace was pulverized by a water atomization method in which water was injected into the molten iron. At this time, the pressure of the water ^jet, low pressure 30kgf / cm 2 ~ 60kgf / cm 2, of 60kgf / cm 2 ~ 90kgf / cm 2 medium ^pressure, 90 kgf / cm 2 of ~ 120 kgf / cm ² for three high-pressure Selected by range. Next, the obtained iron powder is dehydrated and dried, and the coarse powder is removed by a wire mesh having a mesh opening of 425 μm, followed by a reduction treatment in a temperature range of 880 ° C. to 980 ° C. for 30 minutes to 60 minutes in a decomposed ammonia gas atmosphere. Was given. Then, the iron powder that has been reduced and solidified into a cake is pulverized with a hammer mill and a feather mill, sieved with a wire mesh of 425 μm, 250 μm, or 180 μm. 1-No. 9 was obtained.

Prototype No. of powder metallurgy powder obtained in this way 1-No. Nine compositions were analyzed. The contents of C and S were measured using a carbon / sulfur analyzer “CS-244” manufactured by LECO. The content of O was measured using an oxygen / nitrogen analyzer “TC-400” manufactured by LECO. The content of elements other than C, S, and O was measured using an ICP issuance analyzer “ICPV-5500” manufactured by Shimadzu Corporation. Prototype No. 1-No. The analysis results of the composition of 9 are shown in Table 1.

Furthermore, prototype No. of iron powder for powder metallurgy 1-No. The particle size distribution of 9 and the tap density were measured. The particle size distribution was measured by a screening test based on JIS-Z8815 (1994). The tap density was measured according to JIS-Z2512 (2012).

Prototype No. of iron powder for powder metallurgy 1-No. The powder in which zinc stearate 0.75% was added and mixed as a lubricant to No. 9 was compacted at a molding pressure of 7 tf / cm ² to produce a cylindrical compact with a diameter of 11.28 mm and a height of 10 mm. did. The density and Rattler value of the obtained green compact were measured. The density of the green compact was measured according to JIS-Z2501 (2000). Further, the Rattler value of the green compact was measured according to JSPM standard 4-69.

Prototype No. of iron powder for powder metallurgy 1-No. No. 9 particle size distribution and tap density, and prototype No. of iron powder for powder metallurgy 1-No. Table 2 summarizes the density and the Rattler value of the green compact.

In addition, Fig. 1 shows a prototype No. of iron powder for powder metallurgy. 1-No. 9 shows the relationship between the tap density and the density of the green compact, and FIG. The relationship between the tap density of 1 to 9 and the Rattler value of the green compact is shown.

As shown in the figure, it was confirmed that the tap density, the density of the green compact, and the Rattler value are all in a substantially proportional relationship. More specifically, the density of the green compact is set to 7.20 g / cm ³ or more at which sufficient strength can be obtained after sintering, and the Rattler value of the green compact is 0.75% in which cracks and chips are within an allowable range. the order or less, that the tap density of the powder metallurgy iron powder may be set to 3.90 g / cm ³ or more 4.20 g / cm ³ or less was confirmed.

The iron powder for powder metallurgy according to one embodiment of the present invention can be suitably used for manufacturing mechanical parts such as gears.

Claims

C is 0.005 mass% or less,
Si is 0.030 mass% or less,
P is 0.020% by mass or less,
S is 0.020% by mass or less,
O is 0.15% by mass or less,
The total of Mn, Ni, Mo and Cr is 3.0 mass% or less, and the balance is Fe and inevitable impurities,
Tap density 3.90 g / cm 3 or more 4.20 g / cm 3 for powder metallurgy iron powder or less.
The iron powder for powder metallurgy according to claim 1, wherein the content of particles passing through a plain weave wire mesh having an average mesh size of 45 µm is 10% by mass or more and 20% by mass or less.