JP2002146402A - Iron-based powder and iron-based powdery mixture for warm molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide iron-based powder and an iron-based powdery mixture in which the amount of green density to be enhanced is high in warm molding. SOLUTION: The iron based powder has powder hardness of <=90 by Visckers hardness and, preferably, has a composition containing <=0.008% C, <=0.08% O and <=0.002% N, and the balance substantially iron. One or more kinds selected from Ni, Mo and Cu may be contained so as to be partially alloyed. The above iron based powder is mixed with powder for alloying and lubricant powder or, further, powder for improving machinability to form a powdery mixture. The powdery mixture is subjected to warm compacting to form a compact in which the amount of density to be enhanced is large, and having high density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron-based powder suitable for sintered parts, and particularly to an iron-based powder and an iron suitable for warm compaction, which have a large improvement in green density during warm compaction. It relates to base mixed powder.

[0002]

2. Description of the Related Art Powder metallurgy technology is capable of manufacturing parts having complicated shapes in near net shape with high dimensional accuracy and greatly reducing cutting costs. Has been adopted. Moreover,
Recently, there has been a demand for powder metallurgy products to have higher strength in order to reduce the size and weight of parts. In particular, there is a strong demand for higher strength of iron-based powder products (iron-based sintered members).

To increase the strength of the iron-based sintered member, it is effective to increase the density of the sintered member by increasing the density of the compact. As the density of the sintered member increases, the number of porosity in the member decreases, and mechanical properties such as tensile strength, impact value, and fatigue strength improve. As a molding method for increasing the density of a molded article, for example, Japanese Unexamined Patent Publication
-156002, JP-B-7-103404, U.S. Patent No.
No. 5,256,185 and U.S. Pat.
A warm forming technique for forming a metal powder while heating it is disclosed. By applying these warm forming technologies, Fe
-4Ni-0.5Mo-1.5Cu partially alloyed steel powder mixed with 0.5 mass% graphite powder and 0.6 mass% lubricant mixed iron-based powder
7.30Mg when molded at a temperature of 150 ° C and a pressure of 686MPa
It is said that a molded article having a density of about / m ³ is obtained.

[0004]

In such a warm forming technique, an iron-based mixed powder is pre-heated to a predetermined temperature of about 70 to 200 ° C., supplied to a metal mold, and subjected to pressure molding. Body. According to this technology, it is said that the green compact density of a compact is improved by effects such as improvement of plastic deformability of iron-based powder (iron powder, alloyed steel powder) due to temperature rise and promotion of particle rearrangement due to melting of lubricant. ing.

[0005] However, even if the above-mentioned warm compacting technique is applied, there is a limit to the improvement of the green compact density of the compact as long as the conventional iron-based powder is used. There was a problem with the demand for conversion. The present invention
An object of the present invention is to provide an iron-based powder and an iron-based mixed powder which are advantageous in solving the above-mentioned problems of the prior art and have a high compaction density improvement ratio during warm compaction and have excellent warm compactibility. In the present invention, “excellent in warm moldability” means that the difference between the green compact density at room temperature molding and the green compact density at warm molding is 0.07 Mg / m ^3.
As mentioned above, it means that the green compact density improvement amount in warm forming is large.

[0006]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have studied various factors affecting the green density of a compact. As a result, the present inventors have found that the iron-based powder used in the conventional warm compaction technology has not been specially considered for warm compaction, and the plastic deformation ability of the iron-based powder in the warm state is poor. Not always enough,
Therefore, it was considered that the density of the green body was not sufficiently improved during the warm forming.

Accordingly, the present inventors have further studied various factors affecting the plastic deformability of the iron-based powder in the warm state. As a result, by reducing the powder hardness of the iron-based powder to a predetermined hardness or less, specifically, by setting the Vickers hardness to 90 or less, the plastic deformability of the iron-based powder in a warm state is improved, It has been found that high-density compacts can be obtained by warm compaction.

The present invention has been made based on the above findings. That is, a first aspect of the present invention is an iron-based powder for warm forming, wherein the powder hardness is 90 or less in Vickers hardness.
In the present invention, the iron-based powder has a C content of 0.008% by mass.
%, O: 0.08% or less, N: 0.002% or less, and the balance is preferably substantially iron. In the first aspect of the present invention, the iron-based powder further comprises It is preferable that the alloy is a partially alloyed iron-based powder in which one or more of Ni: 6% or less, Mo: 2% or less, and Cu: 3% or less by mass are diffused and adhered.

In the second aspect of the present invention, any one of the above-described iron-based powders is used, and the alloy-based powder, the lubricant powder, and further the machinability improving powder are mixed with the iron-based powder. This is an iron-based mixed powder for warm forming characterized by the following.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The iron-based powder of the present invention has a Vickers hardness Hv of 90 or less. Powder hardness is Hv
When the hardness exceeds 90, the plastic deformability of the powder during warming decreases, and the density improvement during warm forming decreases. For this reason, the powder hardness of the iron-based powder is limited to 90 or less in Vickers hardness Hv. Preferably, the Vickers hardness Hv is 85 or less.

The hardness of the iron-based powder can be determined, for example, by embedding the iron-based powder in a resin, polishing the resin, and measuring the Vickers hardness Hv of the cross section of the iron-based powder under a load of 100 g. In the iron-based powder of the present invention, C: 0.008
% Or less, O: 0.08% by mass or less, N: 0.002% by mass or less, and the Vickers hardness Hv is preferably 90 or less by reducing interstitial solid solution elements of C, O and N.

C: 0.008% by mass or less C is an element that forms an interstitial solid solution in the iron-based powder and hardens the powder, and is preferably reduced as much as possible. If the content exceeds 0.008% by mass, the iron-based powder is hardened, and the plastic deformability during warming is reduced, so that it is difficult to obtain a high-density compact. Preferably, the content is 0.006% by mass or less.

O: 0.08% by mass or less O is an element present as an oxide film on the surface of the iron-based powder and hardens the powder, and is preferably reduced as much as possible. 0.
If the content exceeds 08% by mass, the plastic deformability during warming is reduced, and it is difficult to obtain a high-density compact. For this reason, O
It was limited to 0.08% or less by mass. Preferably, the content is 0.06% by mass or less.

N: 0.002% by mass or less N is an element which forms an interstitial solid solution in the iron-based powder and hardens the powder, and is preferably reduced as much as possible. When the content exceeds 0.002% by mass, the iron-based powder is hardened, and the plastic deformability during warming is reduced, so that it is difficult to obtain a high-density compact. Preferably, the content is 0.001% by mass or less.

The balance other than the above components is substantially iron. It should be noted that there is no problem even if Si, Mn, P, and S are contained as inevitable impurities. Next, a preferred method for producing the iron-based powder having the above composition according to the present invention will be described. First, it is preferable to melt a molten metal containing iron as a main component, and to form the water atomized iron powder by a water atomizing method in which the molten metal is sprayed with high-pressure water. Water atomized powder is further dehydrated,
After being subjected to drying, classification, and the like, it is subjected to a finish reduction treatment, and is further pulverized, classified, and the like, to obtain an iron-based powder.
The finishing reduction treatment is preferably performed at a temperature in the range of 800 to 1000 ° C. in a reducing atmosphere containing hydrogen.

The iron-based powder of the present invention preferably has a hydrogen flow rate in the atmosphere of 40 to 250 l / (1 kg of iron-based powder) in the finish reduction treatment. If the flow rate of hydrogen is less than 10 l / (1 kg of iron-based powder), the reduction of C, N and O is small,
C: 0.008% by mass or less, O: 0.08% by mass or less, N: 0.00
2 mass% or less, the hardness of the iron-based powder exceeds a predetermined hardness (Hv90 or less), and it is impossible to increase the density of a green body during warming. On the other hand, if the hydrogen flow rate exceeds 250 l / (1 kg of iron-based powder), the effect is saturated and economically disadvantageous.

It goes without saying that the iron-based powder of the present invention is not limited to the above-mentioned production method. The method for producing the iron-based powder of the present invention is not particularly limited as long as the powder hardness is Hv90 or less. In the present invention, as the iron-based powder,
Ni: 4 mass% or less, M
o: 2% by mass or less, Cu: 3% by mass or less may be used as a partially alloyed iron-based powder containing one or more kinds by diffusing and adhering.

Ni, Mo, and Cu are all elements that improve the hardenability of the iron-based sintered body, and can be contained by diffusing and adhering to the surface of the iron-based powder as needed. In addition, Ni: 6 mass%, Mo: 2
% By mass and Cu: 3% by mass, the powder hardness of the iron-based powder exceeds Hv90, so that the plastic deformability during warming is reduced and a high-density compact cannot be obtained. .

The partially alloyed iron-based powder of the present invention is obtained by mixing a desired amount of an alloy element powder such as Ni or Mo or an oxide powder with the iron-based powder having the above-described composition, and forming a mixture in a predetermined atmosphere in a reducing atmosphere. It is preferable to heat-treat at a temperature (for example, 700 to 900 ° C.) to diffuse and adhere a part of the alloy element to the iron-based powder. Iron-based mixed powder of the present invention, iron-based powder of the above composition,
That is, the powder hardness is 90 or less in Vickers hardness, preferably, C: 0.008% by mass or less, O: 0.08% by mass or less,
N: a mixed powder containing 0.002% by mass or less and a balance of iron-based powder, which is substantially iron, and a predetermined amount of alloy powder and a predetermined amount of lubricant powder, or further a powder for improving machinability. is there.

Examples of the alloy powder include graphite powder and alloy element powder. Alloy powders are iron-based powders, alloy powders,
The amount is preferably 0.1 to 5.0% by mass with respect to the total amount of the machinability improving powder in view of the molding load and the strength of the sintered body. In addition, the alloy element powder may be Ni powder, Cu
Powder, powder such as Fe-P, Fe-Mo powder can be used.

Part or all of the alloying element powder is contained by pre-alloying an alloying element such as Ni, Cu, Mo, or Cr into the iron-based powder or by diffusing and adhering to the surface of the iron-based powder. can do. The mixed powder of the present invention contains, in addition to the iron-based powder and the powder for alloy, a lubricant for the purpose of improving the molding density and reducing the extraction force from the mold. As the lubricant, zinc stearate, lithium stearate, ethylenebisstearamide, calcium stearate and the like are preferable. The content of the lubricant is preferably 0.05 to 1.2 parts by weight based on 100 parts by weight of the total amount of the iron-based powder, the powder for alloy, or the powder for further improving the machinability. Further, a part or all of the lubricant may be applied to the surface of the mold to be molded.

The iron-based mixed powder may contain a machinability improving powder such as talc powder or metal sulfide powder for the purpose of improving the machinability of the sintered body, if necessary. The content of the machinability improving powder is preferably 5.0% by mass or less based on the total amount of the iron-based powder, alloy powder and machinability improving powder. Incidentally, the mixing of the iron-based mixed powder, generally known mixing method, for example, Henschel mixer, cone mixer,
A mixing method using a V-type mixer or the like is applicable.

The iron-based mixed powder using the iron-based powder of the present invention comprises:
The difference between the green density by the green density and the warm forming by cold molding, and 0.07 mg / m ³ or more, warm green density improvement amount is large by forming, excellent warm formability iron-based mixed powder It is.

[0024]

EXAMPLES (Example 1) Molten steel having the composition shown in Table 1 was melted and made into atomized iron powder by a water atomizing method. The as-atomized powder was further subjected to dehydration, drying, crushing, and classification treatments, and further subjected to a finish reduction treatment to obtain iron-based powders having the C, O, and N contents shown in Table 2. Finish reduction treatment: Dew point: 900 ℃ × 60min in hydrogen atmosphere of -30 ～ 50 ℃
, Followed by heat treatment at 900 ° C. for 15 minutes in a hydrogen atmosphere with a dew point of −30 ° C. In the finishing reduction treatment, as shown in Table 2, the hydrogen flow rate in the atmosphere was changed to a range of 10 to 200 l / (1 kg of iron-based powder).

Using the obtained iron-based powder, the hardness of the powder and the green density at room temperature and warm (130 ° C.) were measured.
The measuring method is as follows. (1) Powder Hardness Each iron-based powder was embedded in a resin and polished, and then the hardness of the cross section of the iron-based powder was measured using a Vickers microhardness tester (load: 100 g). The number of particles to be measured was 10 or more, the average value thereof was calculated, and the average value was used as the representative value of each iron-based powder. (2) Room temperature green density 0.8% by mass of graphite powder as alloy powder and 2% by mass of Cu powder with respect to the total amount of iron-based powder and alloy powder in each iron-based powder
Further, 0.75 parts by weight of zinc stearate as a lubricant was added to 100 parts by weight of the total amount of the iron-based powder and the alloy powder, and mixed with a V-type mixer to obtain a mixed powder. After charging the mixed powder into a mold, at normal temperature (25 ° C.), pressure: 686M
It was molded into a molded body having a diameter of 11 mmφ × 11 mm height at Pa.
The dimensions and weight of the obtained molded body were measured, and the green density was calculated. (3) Warm green density For each iron-based powder, graphite powder as an alloy powder is 0.8% by mass and Cu powder is 2% by mass based on the total amount of the iron-based powder and the alloy powder.
In addition, ethylene bis stearamide as a lubricant was added in an amount of 0.75 to 100 parts by weight of the total amount of iron-based powder and alloy powder.
The mixture was mixed using a V-type mixer to which a part by weight was added to obtain a mixed powder. After preheating the mold and the mixed powder to 130 ° C, the mixed powder was charged into the mold, and the pressure was 686 MPa and the diameter was 11 mm.
It was molded into a molded body having a shape of mmφ × 11 mm height. The dimensions and weight of the obtained molded body were measured, and the green density was calculated.

Table 2 shows the results.

[0027]

[Table 1]

[0028]

[Table 2]

In each of the examples of the present invention, the powder hardness is low, the amount of improvement in green density by warm compaction is large, and the green density by warm compaction is high. On the other hand, Comparative Examples outside the range of the present invention have a small amount of improvement in green density by warm forming. (Example 2) Using part of the iron-based powder (Table 3) used in Example 1 shown in Table 2, alloy element powders (Ni powder, Cu powder, MoO ₃
The powder was mixed in a predetermined amount and subjected to a heat treatment at 850 ° C. for 60 minutes to obtain a partially alloyed iron-based powder in which alloy elements were diffused and adhered to the surface of the iron-based powder by an amount shown in Table 3.

Using the obtained iron-based powders, the powder hardness and the green density at room temperature and at a warm temperature (130 ° C.) were measured in the same manner as in Example 1. Table 3 shows the results.

[0031]

[Table 3]

In each of the examples of the present invention, the powder hardness is low, the amount of green compact improvement by warm compaction is large, and the compact density by warm compaction is high. On the other hand, Comparative Examples outside the range of the present invention have a small amount of improvement in green density by warm forming.

[0033]

According to the present invention, a high-density compact can be obtained by warm compaction, and a high-density, high-strength sintered body can be provided. .

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukiko Ozaki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Inside the Technical Research Institute of Kawasaki Steel (72) Inventor Tomoyuki Kobida 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Address F-term (reference) at Kawasaki Steel Corporation Chiba Works 4K018 AA24 BA13 BB10 BC12 BC22 BC35

Claims (4)

[Claims] 1. An iron-based powder for warm compaction, wherein the powder has a Vickers hardness of 90 or less. 2. The iron-based powder has a C content of 0.008% by mass.
The iron-based powder for warm compacting according to claim 1, wherein the iron-based powder contains not more than 0.08%, not more than 0.08%, and not more than 0.002%, and the balance is substantially iron. 3. The iron-based powder further comprises, on a surface of the iron-based powder, Ni: 6% or less, Mo: 2% or less, Cu: 3% by mass%.
The iron-based powder for warm compacting according to claim 2, wherein one or two or more of the following are partially alloyed iron-based powders which are diffused and adhered. 4. An iron-based mixed powder obtained by mixing an iron-based powder, an alloy powder, a lubricant powder, and further a machinability-improving powder, wherein the iron-based powder is any one of claims 1 to 3. An iron-based mixed powder for warm forming, characterized by using the iron-based powder described in (1).