DE3027785C2 - Process for the production of sintered iron-copper alloys of high density - Google Patents

Description

The invention relates to a method of manufacture of sintered alloys based on iron and copper, which have a greater density than conventional alloys of the same type. It consists in the fact that one is the extension of mainly pressed bodies consisting of iron and copper powder are suppressed during the sintering process

Copper stiff the most common alloy component of sintered alloys based on Elsen. These iron-copper alloys form a basic component for a wide variety of sintered materials.

The sintered alloys based on iron and copper have the serious technical Disadvantage that they expand significantly during the sintering process, which is a copper growth phenomenon referred to as. In other words, the sintered articles or Parts are made by molding powders Pressed bodies produced which have the same dimension as öie the desired objects, the Form is such that it eiw * dimensional change allows during sintering, whereupon the compacts are sintered and then post-treated, for example dimensioned or punched. Accordingly, too large a dimensional change results to a greater variation in the dimensions of the compacts. It is therefore very difficult to get through by yourself Sizing parts with the required dimensional accuracy.

As a result of the expansion during the sintering process, the strength of the compacts falls below high Pressures to such a degree that they are not used for mechanically stressed parts.

The sintered materials intended for mechanically stressed parts should therefore consist of different Reasons, including economic ones, of a dimensional change during the process of sin not subject to more than 0.4%, based on the dimension of the shape used.

Various attempts have been made to suppress the copper growth phenomenon. For example, it has been proposed to suppress this phenomenon by adding carbon, phosphorus, nickel and the like. Up to now, however, no additive has been found which gives satisfactory results. The addition of carbon has some effect when the copper content is low. With a copper content of not less than 5%, however, it is impossible to achieve the desired dimensional change. This is also the case when using phosphorus. The use of phosphorus or carbon in a large amount causes the sintered bodies to become harder, resulting in difficulty in dimensioning after sintering. Nickel is effective when used in large quantities. However, this is costly and uneconomical. .

The results obtained with other elements are summarized in Table 1.
It has also been proposed to prevent copper growth by sintering at low temperatures. But even this is "impractical because the copper growth: even at a temperature" starts from 910 ⁰ C, which is the Obefgangstemperatur vorireinem

ι ο Eisdn from the α to the JJ phase.

The invention relates to a method for producing sintered alloys based on High density iron and copper which are the above Do not have the listed disadvantages, especially the Manufacture of a sintered alloy of high density, which is composed mainly of iron and up to 50 wt .-% According to this, copper exists. Methods are used to suppress or limit the copper growth phenomenon Not less than 0.03% boron added during sintering. The sintered alloys thus produced can be used for bearings and similar parts.

In the pictures shows
F i g. 1 the influence of boron with regard to the copper content and the dimensional change during the smtering process of the alloy consisting of iron and copper;

Fig.2 shows the relationship between the boron content and the dimensional change;

F i g. 3 the relationship between the sintering temperature and the dimensional change;

F i g. 4 the relationship between carbon content and dimensional change and
F i g. 5 the relationship between copper content and the percentage of the achievable sintered density.

From FIG. 1 shows the influence of boron on the dimensional change of the pressed body consisting of a mixture of iron and copper powder during sintering, with the dimensional change during sintering on the ordinate and the copper content in the pressed body on the abscissa finely divided iron powder with a particle size of not more than 0.149 mm and a purity of not less than 99% with an amount of powdery electrolytic copper with a particle size of not more than 0.074 mm and a purity of not less than 99.6% and 0.5% zinc stearate as a lubricant good mixed. If the sample is to contain boron, a predetermined amount of iron-boron powder with a particle size of not more than 0.063 mm and a boron content of 20% is added. The mixture is deformed under a pressure of 5 t / cm ³ to give test pieces measuring 12.7-31.8-5 mm. The sintering is carried out in an atmosphere obtained by decomposing ammonia at 1130 ^° C. for 30 minutes in a sintering furnace

From FIG. 1 shows that the growth coefficient of a sample without boron increases with Copper content increases, with a copper content of 8 to 10% reaches a maximum and then drops again. So the growth coefficient is 2% with a copper content of 5% and about 2.5% with a Copper content of 8%, based on the dimensions of the mold. For the reasons stated above, should the copper content is limited to 1% so that the dimensional change does not exceed 0.4% is decreased. This imposes the characteristics of the

Alloy has severe restrictions.

However, a sample containing 025% boron will shrink regardless of the size of their copper content. The sample was also found to contain up to 8% copper contain kärin if the shrinkage on not over 0.4% is limited.

The fig. 2 graphically shows the relationship between the Boron content and dimensional change of a sample containing 8% copper with a large growth coefficientThese Representation is used to determine the lower limit of the boron content, which is used for suppression dps copper growth phenomenon is required and indicates that boron is present in an amount as low as 0.03% is already in effect.

Fig. 3 shows the relationship between sintering temperatures and dimensional change, the growth coefficient of a boron-free sample with the sintering temperature increases, while a boron-containing sample tends to shrink with increasing sintering temperature subject. For the sake of simplicity, the expression "sintering temperature 0" in this figure denotes the untreated compact before sintering.

F i g. 3 also shows that the copper growth ^{begins at about 800 °} C. and is moderate at a temperature which exceeds the transition temperature of pure iron from the "- to the /? - phase, and is drastic at a temperature which is above the melting point of copper at 1083 ⁰ C goes This phenomenon is caused by the alloying. The iron framework expands through diffusion of the copper atoms into the crystal lattice of the iron, furthermore through the interruption of the intergranular iron area as a result of the penetration of the remaining liquid copper phase into this area.

On the other hand, the addition of boron to the Fe-Cu system causes the boron to co-precipitate as a ternary phase of Fe-Cu-B within the crystalline iron particles. This phase is formed rapidly at a temperature not below 1050 ^° C. and reduces the concentration of the copper that has diffused into the crystal lattice of iron. As a result, there is no expansion of the iron lattice. In the Fe-B system, boron prevents copper from diffusing in the same way as carbon does. It appears that these effects synergistically suppress the copper growth phenomenon.

The influence of the carbon content on the dimensional change was then determined using sintered Fe-Cu steel which contained 8% copper and had a large growth coefficient. The tests were carried out with boron-containing and boron-free samples F i g. 4 shows the results. the added carbon consisted of graphite, and the test pieces were prepared under the same conditions as in the compound ^{5 g>} with F i. said first

From Figure 4 it can be seen that in the boron-free Control sample, the copper growth phenomenon is still insufficiently suppressed. Also lies the surface hardness of the sintered body in the order of magnitude of over 70 according to the Rockwell B scale and is so high that machining does not make it economical reasonable improvements in dimensional accuracy can be achieved.

On the other hand, "a suitable amount of boron-containing sample IGT ^b5 * that their shrinkage is moderated by interaction with the carbon so that the Dimensioni variation during

4 ") Sintering essentially reached 0 In addition, the surface hardness of the sintered body is not more than 70 on the Rockwell B scale, regardless of the amount of carbon content: the dimensioning does not cause any problems.

Table 1 shows a TeQ of the results obtained with elements that essentially appear to behave the same as boron. The reason for choosing these elements is that they belong to the same group as boron and have similar chemical properties and alloy-forming properties Possess properties like this. However, all elements other than boron were not found to be satisfactory.

Table Γ

Comparison of different elements

JO

j>

Added Type of Dimensions elements Powder addition modification None 2.5% aluminum metallic 6.1 sulfur Fe-S 3.3 Schwefer MoS ₂ 2.0 lithium Stearate 2.8 zinc metallic 2.4 titanium metallic 2.4 lead metallic 2.3 Silicon Fe-Si 2.0 tin metallic 1.8 phosphorus Fe-P 1.2 phosphorus red phosphorus 1.0 carbon graphite 1.0 boron B ₄ C -0.1 boron Fe-B -0.2 boron Cu-B -0.6

Amount added: 0.5%; Matrix: Fe + 0.8% Cu

Table 2 shows the results from a number of sintered alloys based on Fe-Cu, which are still contained other alloying elements. From these values it can be seen that the teaching according to the invention can be used on all alloys based on Fe-Cu, as the addition of boron changes the dimensions is reduced or restricted.

Table 2

Alloys with the Ni Cr specified iron Dimensions Components except 1.4 - 8% copper and modification, % as remaining% 1.4 - B. C. 1.4 - Mon Mn _ - - 2.0 _ _ 0.15 + 2.00 - - 2.0 - 0.15 -0.09 0.30 - 0.7 - - -0.06 0.30 - - - 0.15 + 1,4.5 0.30 - - - 0.15 -0.02 0.10 - - - - -0.25 0.05 i, 5 0.15 + 1.87 0.05 1.5 0.15 0 0.20 1.5 + 0.20

continuation

Alloys with the specified Components except 8% copper and iron as the remainder,%

Ni

Cr

Mon Mn B

3.0 3.0 -

1.0

ι, ο

0.5 0.5 0.2 0.2

0.6
0.6

Dimensional change,%

+ 1.57 0.15 +0.18

+ 1.46 0.15 +0.39

As a result of investigations into what influence boron has on Fe-Cu materials with high copper content, it has been found that the addition of a suitable amount of boron increases the density to the same value can be, as by the enamel impregnation with copper.

The in the F i g. Results shown in Figure 5 are of interest. That is, the density of the alloy without boron drops sharply with a copper content between about 10 to 20% and increases with increasing copper content gradually on. The value of pure iron is finally reached with a copper content of 40%. On the on the other hand, the density of an alloy with a boron content of 0.1% increases uniformly with the Copper content and reaches a value of not less than 92% of the theoretical density at 15% Cu.

So far, such a result has only been achieved by copper melt impregnation. The invention thus enables the production of high-density sintered bodies in a quality that one through Melt impregnation obtained with copper is equivalent or even superior.

So the addition of boron prevents the copper growth phenomenon in Fe-Cu sintered steel, what is of great importance from a technical point of view.

For this purpose 3 sheets of drawings

Claims (1)

1
Claim: Process for the production of sintered alloys from iron and up to 50% by weight of copper with high density, characterized in that to suppress or limit the Copper growth phenomenon during sintering, at least 0.03% boron can be added.