JPH0288729A - Production of sintered hard alloy - Google Patents

Abstract

PURPOSE:To obtain a sound sintered hard alloy having uniform carbon content in all range by executing the prescribed preliminary sintering treatment to a green compact for the sintered hard alloy, in which contains >=1wt.% Ni and adds powdery lubricant, and executing regular-sintering. CONSTITUTION:The powder lubricant is added to the raw material for the sintered hard alloy containing >=1wt.% Ni and compacted. Successively, to the green compact for the sintered hard alloy, the preliminary sintering treatment heating under mixed gas of hydrogen and carburizing gas atmosphere at 400-1000 deg.C is executed. Successively, the vacuum sintering is executed. Therefore, even if powdery lubricant is used, as the powdery lubricant is almost perfectly remove during the preliminary sintering and excess decarbonization is not produced, the carbon content in the finishing sintered material is uniformly contained in over the all range and the sound sintered hard alloy is obtd. without developing double carbide.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a cemented carbide containing 1% by weight or more of Ni, which has excellent wear resistance and corrosion resistance.

<Prior Art> A method for manufacturing cemented carbide starts with molding raw material powder into a predetermined shape by pressing or the like, and during the molding, a powder lubricant such as paraffin is added. The amount depends on the type of cemented carbide and the forming method, but it is approximately 1 to 10% of the total amount.
It is about 15% by weight.

This powder lubricant is not only unnecessary after molding, but also harmful, so it must be removed. This powder lubricant removal process is called a pre-sintering process, and is usually performed in a vacuum at a
A measure is being taken to heat it up to 000''C.

Note that the preliminary sintered body is then subjected to intermediate processing or sintered without being subjected to intermediate processing to obtain a sintered body.

<Problems to be Solved by the Invention> In the preliminary sintering method described as the prior art, the powder lubricant is sufficiently removed when the size of the object is small. However, when the dimensions are large, for example, the wall thickness exceeds 20 mm, the powder lubricant is not removed sufficiently and remains in the pre-sintered body as carbon, resulting in the pre-sintered body becoming carburized. Become.

When the preliminary sintered body in such a state is sintered, the amount of carbon increases by the amount of residual carbon, and harmful free carbon is generated in the sintered body. Therefore, in such cases, a method of pre-sintering in a hydrogen stream was adopted, taking advantage of the fact that hydrogen has the property of promoting evaporation of the powdered lubricant.

These methods have made it possible to almost completely remove the powder lubricant from common cemented carbide containing Co as a binder phase, such as Koshiki-CO cemented carbide.

However, with the remarkable progress of industry in recent years, there has been a demand for cemented carbide having not only high wear resistance but also high corrosion resistance, such as -C-Co-old, WC-Ni.

Alternatively, Cr(Cr3Cλ), Mo(Mo
xC) etc., or TiC-Mo2
Cemented carbide, also called cermet, based on C-Nj (Go) has also come into use. It has been found that the previously described preliminary sintering method is not sufficient for cemented carbide with such a new composition. That is, if the wall thickness is 1 oan or less, the powder lubricant can be sufficiently removed by pre-sintering in a vacuum, but if the wall thickness becomes larger than that, carbon remains in the pre-sintered body. Moreover, the concentration of residual carbon becomes different between the center and the surface layer, and even cracks may occur in the compact during preliminary sintering.

On the other hand, when cemented carbide with such a new composition is presintered in a hydrogen stream, the powder lubricant is sufficiently removed and no cracks occur in the compact, but decarburization progresses significantly. , when it is sintered, a harmful double carbide phase that occurs when the alloy is low in carbon is formed, and the degree of decarburization is different between the center and surface layers, resulting in a difference between the center and surface layers of the pre-sintered body. There is a difference in carbon concentration between the two parts.

The present invention aims to solve the above-mentioned problems and provide a method for manufacturing cemented carbide, which does not cause the molded body to crack during preliminary sintering and results in a healthy sintered body. .

<Means for Solving the Problems> The means for achieving the above object of the present invention are as follows. That is, a pre-sintering process is performed in which a compact obtained by compacting cemented carbide raw material powder to which a powder lubricant has been added is heated to 400 to 1000°C in a mixed gas atmosphere of hydrogen and carburizing gas. This is a method in which a sintering treatment is performed.

Note that carburizing gases include, for example, methane and ethane.

Any gas may be used as long as it has a carburizing effect, including a hydrogen ashing gas such as propane, but as described later, methane is most preferred, and in the case of methane, the concentration relative to hydrogen gas is preferably 4 to 30% by volume.

In addition to the above method, a preliminarily heated compact obtained by compacting a cemented carbide raw material powder containing 100% by weight or more of a binder phase metal to 400 to 1000°C in a vacuum or an inert atmosphere is used. A molded body obtained by performing sintering treatment and then regular sintering treatment, or by molding raw material powder of cemented carbide containing 100% by weight or more of binder phase metal, in a vacuum or inert There is also a method of performing a sintering treatment in which the material is heated to 1300 to 1500°C in an atmosphere.

The reason for the above limitation will be explained below.

■ Regarding the composition of the target cemented carbide As mentioned above, in the case of cemented carbide that does not contain old and has normal Co as a binder phase, it can be sufficiently manufactured using conventional technology, so 1% by weight of old Limited to cemented carbide containing the above. In addition,
Here, cemented carbide refers to IVa, Va, 'A of the periodic table.
Group a metal carbide, nitride, boride, or two of them
one or more of the group of hard substances consisting of a solid solution consisting of more than one species, and 0.1 to 30% by weight of one of the iron group metals.
Refers to an alloy consisting of a species or two or more species.

■For molded bodies containing powdered lubricant 2-1 Mixed gas composition In order to facilitate the removal of powdered lubricant, hydrogen gas is used as the basis, but using only this gas has problems such as excessive decarburization during preliminary sintering. Therefore, in order to suppress this, an appropriate amount of carburizing gas is included. Here, the carburizing gas includes, for example, hydrocarbon gases such as methane, ethane, and propane.
Any gas may be used as long as it has a carburizing effect. However, in the case of high-order hydrocarbon gases, a slight change in the concentration significantly changes the carburizing properties, making it difficult to perform pre-sintering stably. Therefore, the carburizing gas is preferably a low-order hydrocarbon gas, and methane gas is particularly preferred.

2-2 Concentration of methane gas If the concentration of methane gas is too low, specifically less than 4% by volume, decarburization cannot be sufficiently suppressed during preliminary sintering, and on the contrary, it is too high, specifically less than 30% by volume. If it exceeds the volume percentage, decarburization will not occur but carburization will occur. Therefore, the concentration of methane gas in hydrogen gas is set to 4 to 30% by volume.

2-3 Concerning the concentration of oxygen in the mixed gas Cemented carbide may also contain elements that are easily oxidized, such as Cr and Ti. At this time, if oxygen or oxidizing gas (H2O, CO2, etc.) is more than 20 ppm by weight in the hydrogen-carburizing gas mixture, these elements will be oxidized and the amount of oxidation will increase, resulting in It becomes impossible to obtain a sound cemented carbide. Therefore, the concentration of oxygen or oxidizing gas in the mixed gas was set to 20 ppm by weight or less.

■About the case of compacts that do not contain powder lubricant 3-1
Cemented Carbide Composition In this case, press forming is performed without using a powder lubricant, so pressability is important. The pressability improves as the amount of iron group metal increases, and there is virtually no problem at 10% by weight or more. Therefore, in addition to the limitation (2), the amount of iron group metal serving as the binder phase is limited to 10% by weight or more.

3-2 Preliminary sintering or sintering method Since the compact does not contain powder lubricant, it will naturally not be carburized or cracked even if pre-sintered in a vacuum or inert gas. do not have. Therefore, sintering is limited to a vacuum or inert gas core. Note that if intermediate processing after preliminary sintering is not necessary, direct sintering may be performed without preliminary sintering or intermediate processing. In this case as well, the atmosphere is vacuum or inert gas.

<Examples> The present invention will be described in more detail below with reference to Examples and Comparative Examples.

41 Actual Examples 2 First, a mixed powder containing 2.5% by weight of paraffin as a powder lubricant was added to cemented carbide raw material powders having the three compositions shown in Table 1 below at a pressure of 1t/c1il. Press molding was performed to obtain a molded body. The dimensions of this molded body are 38X 38X
It was made into a square with 30 prints.

Table 1 Composition of Samples The molded bodies were charged into a pre-sintering furnace which was capable of simultaneously flowing CI and λ gases, and pre-sintered with various gas compositions. There are two gas compositions for the method of the present invention: Hλ-5, 6 volume% CH, +fλ-10.
, 0 volume% CH≠ and only one type, ie, Hλ, as a comparative example (
In this case, the carbon content of the raw material powder before adding paraffin is approximately 0.
．． There were three types (7% more by weight). In addition, the temperature raising conditions are 20 hours up to 700°C in both cases, and 700°C
It was cooled when it reached . Further, the concentration of oxygen or oxide gas in the mixed gas was set to 20 ppa+ or less by weight. Preliminary sintering was performed with varying CHy concentrations as needed, vacuum sintering was performed as needed, and microstructural observations were also performed.

No cracks were observed in the pre-sintered body obtained by pre-sintering in such a gas atmosphere. Therefore, next, the carbon content of these pre-sintered bodies and the carbon content before pre-sintering were measured. Figure 1 shows an example of the results.

First, a comparative example indicated by a dashed line △ will be described.

This is an example of sample 2 pre-sintered in H2, but the surface part has less carbon (hereinafter abbreviated as C) than the center part, and the difference is 0.4% by weight. Even in the center before pre-sintering (this amount of C is measured before adding paraffin)
It can be seen that the amount of C is reduced by 0.5% by weight compared to the above. Therefore, this pre-sintered body is sintered as it is (in vacuum, 1
Even at 350° (:X1 hr), a significant difference in structure occurs between the surface and the inside, making it impossible to put it to practical use. Although detailed data will be omitted, vacuum pre-sintering produced a difference in the amount of H and C between the surface and the center, which was the same as that of pre-sintering, and also caused cracks, so this method is also not suitable for practical use. On the other hand, an example of preliminary sintering in an H-nee CL atmosphere, which is the method of the present invention, is as follows. First, Sample 2 will be described as in the comparative example. In the case of Hλ-5,6 volume% CH,
The case of F12-10.0 volume % CH is shown in mu, and it can be seen that in both cases, the amount of C is almost constant from the surface to the center. It can also be seen that although the amount of C is reduced compared to before preliminary sintering, the extent is smaller than that of the comparative example.

It can also be seen that the higher the CI and gas concentration, the higher the amount of C.

In this way, by this Hλ-CHq atmosphere pre-sintering,
It has become clear that the two problems of Hλ pre-sintering, namely, significant decarburization and the occurrence of a significant difference in C content between the surface and the interior, can be suppressed or solved. However, this amount of C is lower than the amount of C required to obtain a sound structure, so even if sintered, a sound alloy cannot be obtained. However, this problem can be solved by appropriately controlling the amount of C before pre-sintering, and the CI and concentration of pre-sintering. For example, the amount of C before pre-sintering may be kept as it is, and the C concentration before pre-sintering may be increased to approximately 25% by volume, or the amount of C before pre-sintering may be reduced to 0.
It was confirmed that the problem could be solved by increasing the CI concentration by about 5% by weight and pre-sintering the concentration of CI from 5.6 to 10.0% by volume.

In the case of sample 1 (marked C2), HλCHQ is the same as sample 2.
It can be seen that the remarkable effect of pre-sintering is recognized. Then, this preliminary sintered body was sintered (in vacuum at 1400°C
hr) It was confirmed that a sound alloy could be obtained.

In the case of sample 3 (l, ■ mark), no effect was observed in sample 1.2, and it can be seen that there remains a C lid difference of about 0.2% between the surface and the inside. However, since the width of the healthy structure of this alloy is about 0.4%C, this level is sufficient. However, since this amount of C is lower than the amount of C that would result in a sound phase region, a sound alloy cannot be obtained even by sintering (in vacuum, at 1350° C. for 1 hr). This problem can be solved by appropriately controlling the amount of C before pre-sintering and the CH% concentration during pre-sintering, as in Sample 2. For example, the amount of C before pre-sintering can be left as is and the concentration of CI is about 25% by volume and pre-sintered, or the amount of C before pre-sintering can be increased by about 0.7% by weight and H2- 6-10) Sintering (in vacuum, 1350℃
After X 1 hr), it was confirmed that a sound alloy was obtained.

1 Cermet (a type of cemented carbide, hereinafter referred to as sample 4) whose composition is 45% by weight Tic - 10% by weight TiN 5% by weight TaC - 25% by weight Mo:LC 15% by weight Ni
A mixed powder made by blending 4% by weight of paraffin as a powder lubricant with the raw material powder is press-molded into 38X 38X 3
A molded body of 0.0 % was obtained.

This compact was charged into the same preliminary sintering furnace as in Example 1, and
Pre-sintered with a different gas composition. The gas composition is 12-10.0% by volume CH (as the method of the present invention), H as a comparative example,
There are two types, L only. The temperature raising conditions were the same as in Example 1 (in both cases, the temperature was raised to 700°C for 20 hr, and when it reached 700°C, it was cooled. Also, the concentration of oxygen or oxide gas in the mixed gas was set to 20% by weight or less than 1). .

No cracks were observed in the pre-sintered body thus obtained. Therefore, next, the amount of C in these preliminary sintered bodies and the amount of C before preliminary sintering were measured.

Figure 2 shows an example of the results.

First, a comparative example indicated by a broken line marked with a circle will be described.

This is an example of sample 4 pre-sintered in R2, but the surface is more markedly detached than the center, and the difference is as much as 1.3%. It can be seen that the amount of C was decarburized by 0.8% compared to the amount of C (measured before adding paraffin).

Therefore, this pre-sintered body was sintered (in vacuum, for 14 hours).
Even if the temperature is 00°C x Ihr), a significant difference in structure occurs between the surface and the inside, making it impossible to put it to practical use. Although detailed data will be omitted, when vacuum preliminary sintering was performed, many cracks were generated from the surface of the compact to near the center, which also made it impossible to put it to practical use.

On the other hand, an example in which R2-CB, which is the method of the present invention, is pre-sintered in an atmosphere is shown by a solid line marked with . Compared to the results of the comparative example,
It can be seen that the amount of decarburization decreases significantly from the surface to the center, and the difference between the surface and the center is as small as 0.3%C. This preliminary sintered body is sintered (in vacuum, 1400℃ x 1h
r) It was found that a sound alloy was obtained from the surface to the center.

That is, as described in Example 1, the HLCH-
It can be said that the conventional problems have been solved by atmosphere pre-sintering.

Regarding sample 2 shown in Table 1 of Example 1, Example 1
A molded article similar to that was obtained. This is R1-1,6 volume%C,
H, atmosphere pre-sintering. The temperature raising conditions were the same as in Example 1.

The results are as follows: R21000 shown in FIG. 1 of Example 1
In terms of volume, decarburization was suppressed compared to Hλ pre-sintering, and there was no difference in the amount of C between the surface and center. That is, it was found that the effect was similar to that of (2CH) and atmosphere preliminary sintering.

Just to be sure, the concentration of CJH was increased to 127.6 volume%C.
Preliminary sintering in a jHg atmosphere was also carried out, but in this case significant carburization occurred and carbon precipitation was observed on the surface of the presintered body.

Therefore, in the case of CB Hsr gas, it has been found that when the concentration changes in the Hλ gas, the carburizing property or decarburizing property of the gas tends to change. Therefore, as carburizing gases, C, H
．． Although it is also possible to use CH Yagas, it was found that CH Yagas shown in Example 1 is more preferable.

Branch ■1 For Samples 2 and 3 shown in Table 1 of Example 1, the mixed powders to which no powder lubricant was added were press-molded at 1 t/c4 to obtain compacts of 38 x 38 x 30 mm.

These were pre-sintered in vacuum (temperature raised to 700°C over 8 hours) and further sintered (in vacuum at 1350°C for 1 hour).

As a result, it was found that in both Samples 2 and 3, although 0.1-0.2% C was decarburized by these steps, sound alloys were obtained.

Further, the same result was obtained when direct sintering was performed without undergoing the above-mentioned preliminary sintering. That is, it has been found that if a compact is made by a novel method in which no powder lubricant is added to the mixed powder, a sound alloy can be obtained by sintering as described above (preliminary sintering→).

<Effects of the Invention> As described above, according to the method of the present invention, even if a powder lubricant is used, the powder lubricant is almost completely removed during preliminary sintering, and excessive decarburization is also prevented. Therefore, the amount of carbon in the final sintered body is uniform over the entire area, and a sound cemented carbide is obtained without the formation of double carbide phases.

Moreover, there is no possibility that the molded body will crack during preliminary sintering.

On the other hand, for those containing 10% by weight or more of bonded metals,
400~ in vacuum or non-oxide atmosphere
Pre-sintered by heating to 1000℃ or 1300℃
By heating and sintering to ~1500''C, a sound cemented carbide can be easily obtained because there is no variation in carbon content caused by powder lubricant, no decarburization, and no carburization.

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes in carbon content due to preliminary sintering performed in Example 1 of the present invention, and FIG. 2 is a graph showing changes in carbon content due to preliminary sintering performed in Example 1. Diagram: Depth from sample surface/″JrLγζ Depth from sample surface/jaw claw

Claims (1)

[Claims] 1. A compact obtained by compacting cemented carbide raw material powder to which a powder lubricant has been added is heated to 400 to 1000°C in a mixed gas atmosphere of hydrogen and carburizing gas. Ni, characterized in that it undergoes a preliminary sintering treatment and then a sintering treatment.
A method for manufacturing cemented carbide containing 1% by weight or more of 2. The method for manufacturing cemented carbide according to claim 1, wherein the carburizing gas is methane, and its concentration with respect to hydrogen gas is 4 to 30% by volume. 3. The concentration of oxygen or oxidizing gas (H_2O, CO_2, etc.) in the mixed gas of hydrogen and carburizing gas is 20 parts by weight.
3. The method for manufacturing a cemented carbide according to claim 1 or 2, characterized in that the content of the cemented carbide is pm or less. 4. A compact obtained by compacting a cemented carbide raw material powder containing 10% by weight or more of a binder phase metal consisting of one or more iron group metals is placed in a vacuum or an inert atmosphere. 1. A method for producing a cemented carbide containing 1% by weight or more of Ni, the method comprising performing a preliminary sintering treatment of heating to 400 to 1000° C. and then performing a sintering treatment. 5. A compact obtained by compacting a cemented carbide raw material powder containing 10% by weight or more of a binder phase metal consisting of one or more iron group metals is placed in a vacuum or an inert atmosphere. 1. A method for producing a cemented carbide containing 1% by weight or more of Ni, the method comprising performing a sintering treatment of heating to 1300 to 1500°C.