JPH0483812A - Iron series sintered machine parts having high bearing pressure fatigue strength and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture an iron series sintered machine parts having high bearing pressure fatigue strength by packing fine particle diameter of iron series powder on surface layer part receiving the bearing pressure and the specific particle diameter or more of the iron series powder on the other part, respectively and sintering after pressurize-compacting to the prescribed shape at the time of manufacturing the iron series sintered machine parts. CONSTITUTION:To >=0.5mm depth from a surface loaded with the bearing pressure, the sintered density ratio is necessary to be >=97%. In the case of being <97% of this, the sufficient bearing pressure fatigue strength is not obtd. and further, in the case of being <0.5mm of thickness having >=97% the sintered density ratio, the sufficient fatigue strength to the bearing pressure is not obtd., too. To a position except the part having >=97% sintered density ratio of the face loaded with the bearing pressure, by forming <=93% sintered density ratio to >=85% of this volume, lightening in weight. is obtd. By constituting this in such way, the iron series sintered machine parts is light in weight. and have >=360kgf/mm<2> of durable bearing pressure fatigue strength.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a ferrous sintered mechanical component having high surface pressure fatigue strength suitable for use in automobile gears, etc., and a method for manufacturing the same.

<Prior art> In general, increasing the sintered density and surface hardening treatment are considered effective in improving the contact fatigue strength of sintered materials, as disclosed in JP-A No. 63-62801. .

However, the sintered density of iron-based sintered materials produced by the current compression molding-sintering process is at most 92%, and even when using the recompression process, the sintered density is at most 97%. .

On the other hand, automobile parts are becoming smaller and lighter in order to improve fuel efficiency. One way to reduce size and weight is to increase the strength of sintered materials, but conventionally, Japanese Patent Application Laid-Open No. 61-231102
As disclosed in the above publication, a large amount of expensive alloying elements were added to deal with the problem.

<Problem to be solved by the invention> As described above, with conventional iron-based sintered materials, sufficient durable surface pressure fatigue strength of 360 kgf/am'' or more could not be obtained due to the low sintered density. contained large amounts of expensive alloying elements.

The present invention solves these conventional problems and provides three inexpensive
It has a durable high surface pressure fatigue strength of 60 kgf/mm” or more,
Moreover, it is an object of the present invention to provide a relatively lightweight iron-based sintered mechanical component and a method for manufacturing the same.

<Means for Solving the Problems> The present invention provides a sintered density ratio of 97% or more for the surface layer of iron-based sintered machine parts that receives surface pressure of 0-15 mm or more, and 85% for other volume ratios. The sintered density ratio of the part that accounts for more than 93%
or less, and has a durable surface pressure fatigue strength of 360 kgf/W" or more. , Fill the surface layer that receives surface pressure with a thickness of 5 mm or more with iron-based powder with an average particle size of 15 μm or less, and fill the other parts that account for 85% or more of the volume with iron-based powder with an average particle size of 60 μm or more. , a method for producing iron-based sintered mechanical parts having high surface pressure fatigue strength, characterized in that the parts are pressure-formed into a predetermined shape and then sintered.

It goes without saying that the present invention includes alloying or using alloyed steel powder in accordance with the required strength of the sintered body, thereby further reducing the weight of the parts.

<Function> In the present invention, it is necessary that the sintered density ratio of 0.5 or more groups from the surface to which surface pressure is applied is 97% or more.

If it is less than 97%, sufficient surface pressure fatigue strength cannot be obtained, and even if the thickness of the sintered density ratio of 97% or more is less than 0.5 mm, sufficient surface pressure fatigue strength cannot be obtained.

For areas other than areas where the sintered density ratio of the surface to which surface pressure is applied is 97% or more, weight reduction can be achieved by setting the sintered density ratio of 85% or more of the volume to 93% or less.

In addition, setting the sintered density ratio of 85% or more to 93% or less is as follows:
This is because it was taken into consideration that the density changes continuously from the surface of the sintered body to the center.

With this configuration, the iron-based sintered mechanical component of the present invention is lightweight and can have a durable surface pressure fatigue strength of 360 kgf/mm2 or more.

Next, a method for manufacturing iron-based sintered parts according to the present invention will be described.

In order to make the sintered density ratio of the surface layer part 97% or more, it is necessary to use iron-based powder with an average particle size of 15 μm or less.

If the average particle size exceeds 15 μm, it is difficult to achieve a sintered density ratio of 97% or more in the subsequent normal pressure forming and sintering steps.

In addition, in order to make the sintered density ratio 93% or less, the average grain size is 6.
It is necessary to use iron-based powder with a diameter of 0 μm or more.

As the powder particle size decreases, the sintered density increases.
This is because if the average particle diameter is less than 60 μm, it is difficult to achieve a sintered density ratio of 93% or less.

Incidentally, as the particle size of iron-based powder becomes smaller, the manufacturing cost increases, so the product of the present invention, which uses a large amount of iron-based powder with an average particle size of 60μ or more, is lighter and at the same time costs less. It's advantageous.

Next, the present invention will be explained in more detail based on Examples.

<Example> Example 1 Fe-1,1%Cr-0,7%Mn with average particle size of 78 μm
14. The component copper powder was filled into a ring-shaped mold with an outer diameter of 60M and an inner diameter of 20mm to a thickness of 7 mm, and the average particle size was 1B.
10. Steel powder of similar composition classified to 6μ mark is 0.71
After filling to a thickness of 11m, molding at a pressure of 6t/cd, 1
Sintering and sizing in AX gas at 250°C and 60ml, followed by sizing at 920°C.
A contact fatigue test piece was prepared by carburizing at 50Wlin and carbon potential of 0.9% and tempering at 160°C and 60ml.

Using these test pieces, a 6-ball Mori test was conducted to determine the durable contact fatigue strength (
σ−) was calculated. Table 1 shows the sintered density ratio of the surface to which surface pressure was applied (high-density surface) and the density ratio of the center of the plate thickness, as determined by an optical microscope. Moreover, the relationship between σ and the particle size of the copper powder used is shown in FIG.

It can be seen that extremely high fatigue strength is exhibited within the scope of the present invention.

Example 2 Fe-1,1%Cr-0,7%Mn with average particle size of 78 μm
A ring-shaped mold with an outer diameter of 60mm and an inner diameter of 20++nn was filled with steel powder to a thickness of 7mm, and then copper powder of the same composition with an average particle size of 10μm was filled with 0.3.0.6.0.9mm. .1.2mm
A sintered body was produced under the same conditions as in Example 1, and 6
Tamamori fatigue test was conducted. The relationship between σ- and the filling thickness of fine powder is shown in FIG. 2, and it can be seen that high fatigue strength can be obtained within the range of the present invention.

Table 1 Density of test piece By setting the compaction density ratio, it became possible to economically achieve high fatigue density and weight reduction.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the particle size of the powder placed on the bearing surface and the durable bearing fatigue strength.
It is a graph showing the relationship between the thickness of a portion of 7% or more and the durable surface pressure fatigue strength. <Effect of the invention>

Claims (2)

[Claims] 1. The thickness of the surface layer of iron-based sintered machine parts that receives surface pressure is 0.
The sintered density ratio of 5 mm or more is 97% or more, the sintered density ratio of other parts that account for 85% or more of the volume is 93% or less, and has a durable surface pressure fatigue strength of 360 kgf/mm^2 or more. Iron-based sintered machine parts with high surface pressure fatigue strength. 2. When manufacturing iron-based sintered machine parts, iron-based powder with an average particle size of 15 μm or less is applied to the surface layer that receives surface pressure with a thickness of 5 mm or more, and an average particle size of 60 μm is applied to other areas that account for 85% or more of the volume. A method for producing iron-based sintered mechanical parts having high surface pressure fatigue strength, which comprises filling each of the above-mentioned iron-based powders, press-forming them into a predetermined shape, and then sintering them.