JPH04350101A - Mixed powder for powder metallurgy and sintered body thereof - Google Patents

Abstract

PURPOSE:To offer a mixed powder for a powder metallurgy from which a sintered body of high density and high strength less in variation of dimentional accuracy and characteristic is obtd. when sintering by premix method, and to offer the sintered body having characteristic above mentioned. CONSTITUTION:In the mixed powder for powder metallurgy to obtain an iron based sintered member, Ni, Cu and Mo are used as an essential component of a powder mixed with iron powder which effectively exerts an effect of the added elements by preliminary alloying an easily oxidable elements such as Cr, Mn, Si to avoid trouble by oxidation of an easily oxidable elements.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a powder metallurgy method that can produce a sintered body based on iron powder and alloy powder, which has high density and high strength, and has less dimensional accuracy and less variation in properties during sintering. The present invention relates to a mixed powder for use in the manufacturing process, and a sintered body as described above.

0002

BACKGROUND OF THE INVENTION Powder metallurgy is a method that significantly rewrites the conventional production process consisting of rolling, forging, casting, etc., and produces a product by compression molding metal powder as a raw material and then sintering it. Therefore, powder metallurgy can produce materials that are difficult to manufacture using conventional melting methods, such as high-melting metal materials such as W and Mo, porous materials such as oil-impregnated bearings and filters, and cemented carbide and cermet. It becomes possible to manufacture In addition, there are manufacturing advantages such as improved material yield due to non-cutting, high dimensional accuracy, and material advantages such as less segregation and anisotropy that tend to occur in melted materials. Since it has various advantages that cannot be obtained by the powder metallurgy method, various parts that were conventionally manufactured by the melting method are now being manufactured by the powder metallurgy method.

[0003] Most of the sintered bodies currently produced by powder metallurgy are used as automobile parts;
In particular, iron-based sintered members are widely used. Various types of iron-based sintered parts are known. For example, in order to improve strength, weather resistance, wear resistance, etc., graphite or copper is added to the main component of iron powder. It is known to mix and sinter fine powders such as: In addition, from the perspective of expanding the range of application of sintered parts, higher toughness and strength are required of sintered parts, and as a means to achieve this, alloying is performed by adding alloying elements such as Ni and Mo. There are also known methods.

By the way, the premix method and the prealloy method are known as representative methods for obtaining a high-strength iron-based sintered body by powder metallurgy.

[0005] The premix method is a method in which iron powder and other alloying fine powders are uniformly mixed, compacted, and then heated and sintered to dissolve additional elements. This method has the advantage that the forming process is relatively simple, but the iron powder and fine alloy powder may separate and segregate due to the difference in specific gravity during the stage up to compaction, or the alloy powder may separate and segregate during sintering. There is a problem in that the fine powder does not diffuse sufficiently, and there is a quality problem in that the strength and dimensions of the sintered body vary.

On the other hand, the pre-alloy method uses Ni, Mo,
This method uses alloyed steel powder in which alloying elements such as Cr are dissolved in iron in advance, and the problems pointed out in the premix method do not occur. However, with this method, the alloy steel powder obtained by pre-alloying is much harder than iron, so it is not possible to sufficiently increase the compaction during powder compaction.
It is difficult to obtain a high-density sintered body. Therefore, the physical properties of the alloy steel cannot be fully utilized.

Each of the above methods has its own merits and demerits, but if the above-mentioned problems such as occurrence of segregation and insufficient diffusion can be overcome, the premix method is better than the prealloy method to achieve the desired sintering. It is considered to be advantageous in obtaining solids.

By the way, as a means for preventing segregation, a method has been proposed in which graphite powder is attached to iron or steel powder using an organic binder, as disclosed in, for example, Japanese Patent Laid-Open Nos. 56-136901 and 63-103001. has been done. For example, Japanese Patent Publication No. 45-9649 and Japanese Patent Publication No. 63-297
As disclosed in No. 502, a so-called diffusion attachment method has also been developed in which other metal powder is diffused and attached to iron powder by heat treatment. In particular, the diffusion adhesion method hardly reduces compressibility and also prevents problems of uneven strength and dimensional accuracy due to segregation to some extent. In other words, the diffusion adhesion type alloy steel powder is one in which fine alloying powder such as Ni, Cu, Mo, etc. is added to iron powder, mixed uniformly, and then subjected to a diffusion treatment to diffuse and adhere the alloying powder to the surface of the iron powder. Therefore, once it is diffused and attached, no segregation occurs.

[0009]

[Problems to be Solved by the Invention] The present invention has been made against this technical background, and focuses on the premix method, and aims to achieve high density, high strength, and dimensional accuracy during sintering by this method. The object of the present invention is to provide a mixed powder for powder metallurgy that can produce a sintered body with little variation, a sintered body having such characteristics, and a heat-treated product obtained by heat-treating the sintered body.

0010

[Means for Solving the Problems] The structure of the present invention that has solved the above problems is a mixed powder for powder metallurgy which is made by mixing iron powder and alloy powder, wherein the alloy powder is Ni,
The gist is that in addition to containing Cu and Mo as essential components, it also contains one or more selected from the group consisting of Cr, Mn, and Si.

[0011] By sintering a mixed powder consisting of the above-mentioned components, a sintered body having high density and high strength and less variation in dimensional accuracy during sintering can be obtained. It is also effective to heat-treat the sintered body, which can make the sintered body higher in density and strength.

0012

[Function] The present inventors conducted research from various angles with a view to improving the diffusibility of additive powder to iron powder. As a result, by alloying one or more elements selected from the group consisting of Cr, Mn, and Si into the Ni-Cu-Mo system and mixing the alloyed additive powder with iron powder, The present invention was completed based on the discovery that the diffusibility of the added powder is promoted.

Elements such as Cr, Mn, and Si are known as reinforcing components, but they are easily oxidized during sintering. These elements are generally added as single powders during sintering, but they are oxidized during sintering, thinning the surface of the iron powder and reducing the strength of the sintered body. The sufficient effect as an ingredient was not exhibited. So Cr,M
By alloying n, Si, etc. with oxidation-resistant Ni, Cu, Mo, etc., oxidation of Cr, Mn, Si, etc. was suppressed, and this facilitated the diffusibility of the additive powder into the iron powder. . Furthermore, the reinforcing effect, which is the original effect of Cr, Mn, Si, etc., was also achieved.

In the present invention, elements such as Ni, Cu, and Mo must also be in the form of an alloy rather than in the form of individual metal powder. In other words, alloying elements such as Ni, Cu, and Mo each have a high melting point and a slow diffusion rate into iron powder when used alone, but by pre-alloying these elements, the melting point can be lowered than when they are single powders. This contributes to improving the strength of the sintered body by improving its diffusibility into iron powder.

The use of alloy powder is also effective from the viewpoint of obtaining a sintered body having uniform properties. That is, the procedure for obtaining a sintered body using the mixed powder of the present invention is: (1) mixing it as it is with other auxiliary raw materials and sintering, (2) attaching iron powder and alloy powder in advance using a binder or diffusion treatment. It is possible to adopt any of the following procedures, such as mixing and sintering with other auxiliary raw materials, but whichever procedure is adopted, uniform adhesion can be achieved by using alloy powder. A sintering powder with a fairly uniform particle size distribution is obtained. Therefore, the properties of the powder are constant,
The characteristics of the obtained sintered body are also uniform.

As mentioned above, the mixed powder of the present invention can be used in the form of either a binder-attached sintering powder or a diffusion-attached sintering powder; It is particularly preferable to do so, and the subsequent sintering treatment results in the same effect as that of two-stage annealing treatment, which is also preferable from the viewpoint of improving strength.

By the way, the present applicant has discovered that when manufacturing raw material powder for manufacturing sintered bodies by diffusing and adhering Ni and Cu to iron powder, N
When i and Cu are added as separate metal powders,
It is known that when Ni-Cu alloy powder is added, the dimensional change as a sintered part is significantly different even if Ni and Cu are mixed at the same weight ratio ( JP-A No. 2-217401). That is, especially when the amount of Cu added increases, Cu-Growth
An abnormal expansion phenomenon called "abnormal expansion phenomenon" occurs, which appears as a large dimensional change, but it has been found that the dimensional change can be reduced by adding Cu as a Cu-Ni alloy powder. Therefore, in the present invention, it is effective to pre-alloy the additive element to iron, especially from the viewpoint of preventing dimensional changes in the sintered body containing Cu as the additive element. Next, the components of the alloy powder used in the present invention will be explained.

Ni has the effect of improving toughness and hardenability, and Mo improves hardenability and prevents softening during hardening and tempering treatments. Further, Cu has the effect of improving the strength or hardness of the sintered body.

By the way, in the case of the Ni-Cu system, a completely solid solution type alloy powder can be obtained, and as the Cu content increases, the melting point can be lowered. Alloying becomes easy. However, if the amount of Cu increases too much, the dimensions after sintering will expand, making it ineffective in terms of practicality. On the other hand, in the Ni-Mo system, 50% (
(meaning of weight %, the same applies hereinafter) There is a eutectic point near Mo, and N
By alloying with the i-Mo system, the melting point of Mo can be lowered, which facilitates the diffusibility into iron powder, that is, uniform alloying. However, if the proportion of Mo is too large, the liquidus temperature will rise rapidly, so that the effect of lowering the melting point will be almost eliminated. From the above points of view, Ni
-Cu-Mo3 element composition ratio is Ni: 45-80%
, Cu: 5 to 50%, and Mo: 50 to 5%.

[0020] The present invention uses C as an essential element of the alloy powder.
It contains one or more selected from the group consisting of r, Mn, and Si, and these are effective from the viewpoint of improving strength, but if too much is used, the effects of the basic components such as Ni, Cu, and Mo mentioned above are reduced. This could lead to a reduction in For these reasons, elements such as Cr, Mn, and Si,
5 parts per 100 parts by weight of the total amount of Ni, Cu and Mo
It should be about 100 parts by weight.

[0021] The ratio of alloy powder to iron powder is 1 to 1.
It is preferable to set it to about 12%, and if it is more than this, the amount of iron powder becomes relatively small, and the basic sinterability as an iron powder-based sintered body cannot be obtained.

The particle size of the alloy powder used in the present invention is not particularly limited, but the average particle size is 2.
It is desirable that the thickness be about 0 μm or less. This is because if the average particle size becomes too large, the alloying of the alloy powder into the iron powder during the sintering process will deteriorate, making it difficult to obtain a uniform structure, which will reduce the strength and
This is because variations in hardness occur.

[0023]

[Example] Iron powder - 6% Alloy powder - 0.6% Graphite - 0.
6 tons/cm2 of 75% zinc stearate mixed powder
After powder compaction, it was sintered at 1250°C in a hydrogen atmosphere. Then, the tensile strength of the sintered body was investigated using various alloy powders. The alloy powder was manufactured using a water spray method and had an average particle size of approximately 1.
2μm, 60%Ni-15%Cu-15
%Mo system, and contains Cr, Mn, Si, etc.

FIG. 1 shows the relationship between the composition of the alloy powder used and the tensile strength. In addition, FIG. 1 also shows the tensile strength when basic components such as Ni, Cu, and Mo are added as individual powders without being alloyed.

As is clear from FIG. 1, the strength of the mixed powder of the present invention is improved compared to the one in which the basic components are added in the form of single powder, and the strength of the mixed powder of the present invention is improved, and Cr, Si, Mn
It can be seen that the effects of strengthening elements such as these are also effectively exhibited.

[0026]

Effects of the Invention The present invention is constructed as described above, and the powder to be mixed with iron powder contains Ni, Cu, and Mo as basic components, and these are pre-alloyed with easily oxidizable elements such as Cr, Mn, and Si. By making it into a solid form, it is possible to effectively utilize the effects of the added elements while avoiding the disadvantages caused by the oxidation of easily oxidizable elements. I was able to get the body together.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the tensile strength of various sintered bodies and alloy powder composition.

Claims (2)

[Claims] 1. A mixed powder for powder metallurgy made by mixing iron powder and alloy powder, wherein the alloy powder contains Ni, Cu and Mo as essential components, and also contains Cr, Mn and Si.
A mixed powder for powder metallurgy, characterized in that it contains one or more selected from the group consisting of: 2. A sintered body obtained by sintering the mixed powder according to claim 1.