JPS5850308B2 - High strength sintered steel and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-strength sintered steel that is particularly suitable for gears, cams, sprockets, etc. due to its excellent impact strength stability and mechanical properties, and a method for producing the same.

Although the static strength of machine parts manufactured by powder metallurgy is not significantly inferior to that of molten materials, the dynamic strength, that is, the impact strength, is significantly inferior to that of molten materials. This has been cited as an issue above.

Particularly in products with complex shapes such as gears, cams, and sprockets, low-density parts inevitably occur at the root of the teeth, further lowering the impact strength.

Due to these problems, it is currently difficult to use sintered parts in mechanical parts that require high strength.

Of course, efforts have been made in various places to overcome these drawbacks of sintered materials, and the representative example is the infiltration method for cold or hot forging of sintered crystals. However, all of these methods not only make the production cost extremely high, but also have the disadvantage of limiting the shape of the product, which impairs the original characteristics of powder metallurgy.

On the other hand, attempts have been made to improve the impact strength by adding a large amount of Ni to the material composition, but even if the impact strength is improved, the disadvantages of adding a large amount of Ni are an increase in retained austenite and deterioration of carburizing and quenching properties. Furthermore, it has major drawbacks such as pressure on manufacturing costs due to the use of expensive elements.

In addition to these methods, there are other methods to slow the progress of sintering, such as increasing the sintering temperature, lengthening the sintering time, or creating an atmosphere in the sintering furnace that contains a large amount of strongly reducing H2 gas. Attempts have been made to improve the strength even slightly, but these have disadvantages such as high cost, reduced productivity, reduced dimensional accuracy, and difficulty in controlling the amount of carbon.

In view of the above points, the present invention provides medium-high density (6.5 to 7.3 g/
/cC) has excellent impact strength, and is suitable for gears, cams,
The object of the present invention is to provide high-strength sintered steel having the hardenability and mechanical properties necessary for use in sprockets, etc., and to provide the same at a relatively low cost.

That is, N1-M is known as a material for high-strength sintered steel.

It is characterized by improving the impact strength after heat treatment and obtaining stable mechanical properties and excellent hardenability by adding a small amount of steel within the range described below to the system material.
It is also intended to be manufactured by the method described below.

The present invention will be explained in detail with reference to Examples below.

Table 1 shows the raw material composition and strength characteristics of the present invention and conventional materials.

After mixing and adjusting each sample to the composition listed in the table,
The specimens were press-formed into the shape of a polyurethane specimen (ASTM E-92-72), sintered at 1130° C. in a modified gas atmosphere, and subjected to the heat treatments listed in each table.

Samples 1, 2, 5.9 and 12 are conventional materials known as Ni-Mo steel compositions.

It is observed that in samples 1 to 4, the strength properties in the density region of 6.5 to 6.7 jj /cc are significantly improved by the present invention.

Samples 1 to 4 were formed by mixing iron powder containing 0.25% Mn with Ni powder, Cu powder, and Mo2C powder, and the weight percentages were Ni2% and Mn0.2.
4%, Mo0.5%, C0.5%, CuO or 0.5%
A molded body with a composition in which the remainder was essentially Fe was produced, and then sintered at 1130°C for 40 minutes in an end gas atmosphere.The sample was oil quenched at 870°C and sintered at 180°C for 2 hours. .

Furthermore, in samples 5 to 9, the effect of the amount of Cu added at a density of 7.0 fl / cc was clarified,
The effective Cu composition range in the present invention is 0.2 to 0.8
%.

Note that Samples 5 to 9 were produced using the same manufacturing method as Samples 1 to 4.

Samples 10 and 11 are related to the method of adding Mo,
Besides Mo2C and Mo, Fe-M is the cheapest.

Even when powder is used, the effect of adding Cu according to the present invention is observed, and it is clear that it has excellent performance.

In addition, samples 10 and 11 had Mn in weight percentage of 0.
Fe powder and Cu powder, Ni powder and Mn powder containing 25%,
Graphite powder (sample (10)) or Fe-M.

A mixture of powder (containing 60% Mo) and graphite powder (sample 0υ) was molded, and the weight percentage was 2% Ni, Mn.
0.24%, Mo 0.5%, CuO, 8%, C0,
A molded body consisting essentially of Fe with the remaining 5% is then sintered at 1130°C for 40 minutes in an end gas atmosphere and then sintered at 870°C.
It was quenched in oil and then tempered at 180'C for 2 hours.

Samples 12 and 13 demonstrate the effects of the present invention when alloyed steel powder is used.

Note that samples 12 and 13 contain N i , Mo , Mn
The weight percentages are 1.85%, 0.5%, and 0.3, respectively.
%, and the balance is substantially Fe in alloy steel powder containing 0.5%
Graphite powder (sample 12) or 0.5% Cu powder and 0.5% graphite powder (sample 13) were mixed, molded, sintered in an end gas atmosphere for 11308040 minutes, and then oil quenched at 870°C.
It was tempered at 180°C for 2 hours.

Furthermore, Samples 14 and 15 showed excellent properties after carburizing and carbonitriding in a case-hardened steel composition, and Sample 16 showed excellent properties after high-frequency heat treatment in a tempered steel composition.

Samples 14 to 16 were sintered using the same manufacturing method as sample 7. Sample 14 was carburized at 900°C for 1 hour, sample 15 was carbonitrided at 900°C, and sample 16 was carbonitrided at 900°C for 1 hour.
These samples were oil-quenched after high-frequency heating at 00KH2 and then tempered for 1800G for 2 hours.

As mentioned above, the alloy according to the present invention has excellent toughness even when sintered in a neutral or carburizing sintering atmosphere, and in order to reduce powder surface oxides, hydrogen or decomposition Needless to say, even better strength properties are exhibited when sintered in ammonia gas.

As is clear from the above examples, the present invention improves the strength properties of Fe Ni Mo-Mn C sintered steel with a trace amount of Cu added after heat treatment in the medium density range (6.5 to 7, Oβ/cc). This is what I did.

The lower limit of the amount of Cu added at which the effect is recognized is 0.2%, and the upper limit is 0.8%.

That is, Cu added from the outside melts during the sintering process to form a liquid phase, which spreads between powder particles to form a thin film.
Cu is dispersed over a wide range, substantially forming an extremely wide diffusion interface, and rapidly diffusing into the Fe matrix.

Cu in the diffused Fe matrix has a concentration gradient in the powder particles, but it also has a slightly higher concentration inside the parts closer to the diffusion interface, that is, in the neck parts and grain boundaries caused by sintering between particles. have

Therefore, the strengthening due to alloying becomes large in the neck portion where the fracture stress is substantially concentrated the most, and the strength characteristics from a macroscopic perspective are improved.

Such an effect cannot be observed if the amount of Cu added is too small because a sufficient diffusion interface cannot be formed, and if too much Cu is added, undiffused Cu may remain or more than necessary Cu may be added. However, since the portion with high Cu concentration in Fe increases, the toughness is adversely affected, and especially after heat treatment, Cu
Due to precipitation hardening, the hardness becomes too high in some areas and the original effect is lost.

For the above reasons, the range of the amount of Cu added is 0.2 to 0.7
% is desirable.

Further, the effect of the present invention is remarkable in the medium density region, particularly in the density region of 6.5 to 6.7 g/CC.

In this way, the effect of adding Cu in the present invention can be seen from the effect of adding Cu in the present invention.
Unlike the alloy strengthening effect of base (ma) IJ lux in -Cu-C steel, Fe-Ni-Cu-C steel, etc., Fe-Ni-Mn-Mo-C-based sintered steel diffuses a small amount of copper liquid phase. This method is characterized by strengthening the sintered steel.

Next, the effect of Ni is based on the case of the known Fe-N1-C material, and the upper limit is set as the amount of Ni exceeding 4.0% lowers the toughness and makes the raw material expensive. is 4.
It was set to 0%.

If the amount of Ni added is 1% or less, there is virtually no effect on the strength, so the lower limit was set at 1%.

The same goes for Mo, if it is less than 0.2%, it has no effect on strength, hardenability or wear resistance, and if it is more than 4%, the toughness is reduced and becomes expensive.

Mn is an element that has a great effect on improving hardenability, as is also known in ingot lumber, and it may cause a decrease in hardenability especially when high-purity iron powder is used in powder metallurgy. The minimum amount of Mn required for heat-treated steel was 0.05%.

On the other hand, as the amount of Mn increases, the powder itself gradually hardens or becomes more easily oxidized, so the maximum amount is limited to 0.5%.

The various effects and addition amount of carbon have already become commonplace, and 0.2% is the minimum amount necessary for strength in this sintered steel.

On the other hand, sliding materials, wear-resistant materials, etc. require a large amount of carbon in the form of residual graphite, which is undesirable because it impairs mechanical strength and toughness, so it is limited to less than 2%.

As described above, the present invention has excellent mechanical strength of 6.5 to 7.3.
This article relates to high-strength sintered steel with medium-high density β/cc and its manufacturing method, especially heat treatment (carburizing, carburizing,
It is suitable for parts that require shock and wear resistance, such as various gears, cams, and sprockets that are used after carbonitriding, bright hardening, induction hardening, etc.).

Claims (1)

[Claims] 1 By weight percentage, Ni1-4%9Mn 0.05-0
．． 5% 1M00.2-4%, CuO, 2-0.8%,
A high-strength sintered steel characterized by comprising 12 to 2.0% CO and the remainder substantially Fe. 2. The high-strength sintered steel according to claim 1, which has a medium density (6.5 to 7.0 g/'CC). 3 Containing at least 0.05 to 0.5% Mn and Fe in weight percentage 0) A mixture of powder and at least Cu powder and C powder is molded to form N11 to 4 in weight percentage.
%, Mn 0.05-0.5%2M00.2-4%,
A molded body having a composition of 0.2 to 0.8% Cu, 0.2 to 2.0% C, and the balance substantially Fe is prepared, and then heated at 1100 to 1200'C in a neutral or carburizing atmosphere.
A method for producing high-strength sintered steel, which is characterized by sintering the steel. 4 A mixture of dust powder containing at least 0.05 to 0.5% Mn and Fe in weight percentage and at least Cu powder and C powder is Mn005 to 0.5 in weight percentage.
Fe powder and Ni powder containing %M. The method for producing high-strength sintered steel according to claim 3, which uses powder, Cu powder, and C powder. 5 The powder containing at least 0.05 to 0.5% Mn and Fe in weight percentage is Ni1 to 4 in weight percentage.
%, Mn 0.05-0.5%, Mo0.2-0.
4. The method for producing high-strength sintered steel according to claim 3, wherein the alloy steel powder is made of iron with the balance being substantially 4%. 6. The method for producing high-strength sintered steel according to claim 4, wherein the Mn powder to be mixed is Fe-Mn powder. 7. The method for producing high-strength sintered steel according to claim 4, wherein the Mn powder to be mixed is Mo2C. 8. A method for producing high-strength sintered steel according to claim 4, in which the Mn powder to be mixed is powder of Mo itself. 7.9 Claims 3 and 4, in which heat treatment is performed after sintering. Section 5;
The method for producing high-strength sintered steel according to item 6, 7, or 8. 10. The method for producing high-strength sintered steel according to claim 9, wherein the heat treatment is carburizing. 11. The method for producing high-strength sintered steel according to claim 9, wherein the heat treatment is carbonitriding. 12. The method for producing high-strength sintered steel according to claim 9, wherein the heat treatment is bright. 13. The method for producing high-strength sintered steel according to claim 9, wherein the heat treatment is high frequency.