JPH0140081B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing iron-based alloy powder used in the production of precision parts by powder metallurgy. The powder obtained according to the present invention facilitates the manufacture of precision parts that require strong dimensional accuracy and mechanical strength. The manufacturing process begins by compacting the iron powder mixture into a rough compact approximating the shape of the final part - mixing it with a lubricant to facilitate the compaction operation. This compact is then fired to a temperature at which the components have the characteristics of the final product in terms of strength, malleability, etc. It is often necessary to obtain parts with more precise dimensions than those obtained with this method, and this is accomplished by a second compression step, or calibration, whereby the parts are produced with extremely precise dimensions. becomes. In order to obtain the often required high-strength powder metallurgy components, alloyed powders are used as starting materials, of which essentially two types are used: metal component powder mixtures and so-called spray alloyed powders. . Metal component powder mixtures are alloying elements mixed with iron powder either in elemental form or as compounds that can be decomposed in the iron powder during firing, while so-called spray alloy powders are made by spraying molten steel containing the desired alloying components. created by One of the disadvantages of metal component powder mixtures is the risk of phase separation, which occurs when powders with mutually different properties, e.g. of different particle sizes, are mixed without being mechanically bonded. arises from facts. This phase separation results in a compositional variation of the molded article produced from the metal component powder mixture, which in turn leads to dimensional changes during firing. Another disadvantage of metal component powder mixtures is their tendency to dust, especially when the alloying elements are of small particle size. This poses difficult environmental problems. On the other hand, since each powder particle of the sprayed alloy powder has the intended alloy composition, the risk of phase separation is completely eliminated. The risk of splashing is also reduced due to the absence of small particle size alloying components. However, prealloyed atomized alloy powders have another major disadvantage. That is, the compressibility is poor, and this is due to the solvent-free annealing effect on the particle powder of the alloying component. Excellent compressibility is essential to obtain high density, which is a prerequisite for high strength. In contrast, the compressibility of the metal component powder mixture is substantially the same as that of the iron powder contained therein. This fact, along with the flexibility of alloy composition that characterizes metal component powder particles, has made metal component powder particles most widely used as alloying powders. It has long been known to use copper as an alloying element in order to increase the strength in the production of sintered parts based on iron. It is also already known that parts made from iron-copper mixtures are subjected to growth or swelling during sintering. When parts are produced over long periods of time, this growth or swelling undesirably varies from part to part, and this variation is primarily due to the above-mentioned risk of phase separation of the metal component powder mixture. Japanese Patent Application No. 52-131628 concerning iron-based powder
The invention of No. 53-92306) combines the advantages of a high degree of compaction with a reduced risk of phase separation and dusting, and the powder is also known to have excellent dimensional stability of the product. Quite unexpectedly, it has also been found that calibration operations are no longer necessary in certain areas. The diffusion alloyed iron powder of Japanese Patent Application No. 52-131628 is manufactured as follows. i.e. smaller than 350 μm, preferably smaller than 175 μm, most preferably 150 μm
is mixed with copper or easily reducible copper compound powder having a particle size of less than 175 μm, preferably less than 75 μm. This powder mixture is then heated in a reducing atmosphere at 700-950°C, preferably 750-850°C for 15 minutes to 10 hours, preferably
Heat treated for 0.5-5 hours. This reduces the degree of compaction due to diffusion by 0.15 g/cm ³ (ASTM standard
B331-64) sintering copper into iron particles without causing diffusion of copper to a greater extent than B331-64). The heat treatment is carried out such that the total oxygen content of the powder is less than 1.2%, preferably less than 0.8%. The cake thus produced has a maximum particle size of less than 350 μm, preferably less than 175 μm,
Most preferably it is ground to less than 150 μm. The powder thus obtained is hereinafter referred to as diffusion alloy iron. Diffusion alloyed iron powder with copper is further mixed with pure iron powder to obtain a mixture with the desired copper content. When the powder thus obtained is used in powder metallurgy, 0 to 2%, preferably 0 to 1% of graphite, and 0 to 2%, preferably 0 to 1% of a powder solid lubricant are added in addition to the iron powder. It is desirable to add. The preferred copper content in the initial mixture to be diffusion annealed is 1-20%, preferably 5-15%, most preferably 8-12%, while the final mixture has a copper content of 1-5%. The iron powder used as the base powder needs to have a large specific surface for efficient adhesion.
Therefore, iron powder made from sponge iron, so-called sponge powder, is desirable for producing the powder of the invention of Japanese Patent Application No. 131,628/1982. It has been found that the dimensional stability of the powder of the invention disclosed in Japanese Patent Application No. 131,628/1988 can be further improved by alloying it with phosphorus. By simply sintering the mixed powder by containing a certain amount of phosphorus, the phosphorus diffuses during heating and alloying is achieved. A surprising effect within the 1.0 weight percent range is a reduction in the distribution of this insulation value as well as a reduction in the absolute value of the dimensional change. Thus, the powder of the present invention substantially eliminates the need for calibration in the manufacture of precision parts with dimensional accuracy and high strength. In the present invention, the alloyed powder is manufactured as follows. That is, a mixture of iron powder with a maximum particle size of less than 350 μm and 1 to 20% of copper or reducible copper compound powder with a maximum particle size of less than 175 μm is made,
This mixture is annealed at a temperature of 700 to 950°C in a reducing atmosphere for 15 minutes to 10 hours, preferably 0.5 to 5 hours, and the cake thus obtained has a maximum particle size.
The degree of compaction of the annealed powder is the maximum according to ASTM standard B331-64, which is 0.15 less than the degree of compaction of the corresponding iron-copper powder mixture.
The copper alloyed iron powder thus obtained is mixed with pure iron powder to form a mixture with the desired copper content, and ^then Add phosphorus in the form of iron phosphorus to the desired phosphorus content. Phosphorus content up to 1.5% by weight,
Preferably it is 0.15-1.0%. In addition, the phosphorus content is 0.15
If the phosphorus content is less than %, the desired effect of the present application will not be obtained, and
If it exceeds 1.0%, the risk of phase separation increases rapidly;
As a result, the risk of product destruction increases. Examples of the present invention are shown below. Example 1 Three mixtures of H, I and K were made with the following compositions. Mixture H: 94.2% Sponge iron powder with a maximum particle size of 147 μm 5.0% Sponge copper powder with a maximum particle size of 147 μm 0.8% Zinc stearate powder mixture I: 49.2% Sponge iron powder with a maximum particle size of 147 μm 50.0% Copper content 10.0%, max. Particle size 147μ
m diffusion alloy iron powder 0.8% Zinc stearate powder mixture K: 46.2% Sponge iron powder 50.0% with maximum particle size 147μm Copper content 10.0%, maximum particle size 147μm
m diffusion alloy iron powder 3.0% phosphorus content 15%, maximum particle size 44μm
Iron phosphorus 0.8% and zinc stearate powder from each mixture in an automatic Dorst press.
2500 rectangular specimens measuring 10 x 10 x 30 mm were made. The parts are then heated for 1120 min in an endorgene gas atmosphere.
It was baked in a furnace for 30 minutes at °C. After sintering, a statistically sufficient number of parts were removed to measure their dimensional stability. The overall distribution value was 42 μm for mixture H, 22 μm for mixture I, and 12 μm for mixture K.
As described above, the distribution of dimensional changes was substantially smaller for K than for H and I. This means that the predetermined requirements regarding dimensional stability, ie the predetermined tolerance ranges, can be easily achieved by using material K. The dimensional accuracy obtained with the materials in the above examples corresponds to a tolerance range of IT6 class, while material H was IT9 and material I was IT7. A part with a dimensional accuracy corresponding to the tolerance range IT6 is better than a fully calibrated one, which is the tolerance range reached by repressing after sintering. Example 2 Six types of alloyed powder mixtures were made with the following compositions: Na, b; Oa, b; Pa, b. Mixture Na: 93.75% Fe 5.0% Cu (Cu powder) 0.45% P 0.8% Zn stearate mixture Oa: 93.65% Fe 5.0% Cu (Cu powder) 0.45% P 0.4% C 0.5% Zn stearate mixture Pa: 94.10% Fe 5.0% Cu (Cu powder) 4.0% C 0.5% Zn stearate mixture Nb: 93.75% Fe 5.0% Cu (diffusion alloyed iron powder containing 10% Cu) 0.45% P 0.8% Zn stearate mixture Ob: 93.65% Fe 5.0% Cu (diffusion alloyed iron powder containing 10% Cu) 0.45% P 0.4% C 0.5% Zn stearate mixture Pb: 94.10% Fe 5.0% Cu (diffusion alloyed iron powder containing 10% Cu) 0.4% C 0.5% Zn stearate A test piece was pressed from a mixture of these six types at a pressure of 590 MPa, and an endogenous
Sintered in an atmosphere at 1120℃ for 30 minutes. The measured mechanical properties of the test pieces were as shown in the table below.

【table】

[Table] From this result, it is known that the strength obtained by mixing copper powder with iron powder is not affected even if the copper powder is replaced with iron powder diffusion alloyed with copper. Components made from copper-diffusion-alloyed iron powder have excellent strength, especially when it is alloyed with carbon and phosphorus, while the tolerance ranges achieved so far are limited by post-sintering processes. It was something that could have been achieved alone.

Claims (1)

[Claims] 1. Mix the iron powder diffusion alloyed with copper with pure iron powder in an amount such that the copper content of the resulting mixture becomes the desired copper content, and further add as an alloying component.
A method for producing iron-based alloy powder for manufacturing precision parts by powder metallurgy, which has good dimensional accuracy and high strength, and is characterized by containing 0.15 to 1.0% by weight of phosphorus.