JP2003155502A - Method for manufacturing sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing sintered compacts by which high-quality sintered compacts can be obtained in a short period of time. SOLUTION: This method comprises steps of compacting raw-material powder containing organic binders into green compacts and heating the green compacts while controlling total pressure to <=60 Pa at temperatures ranging from room temperature to <=600 deg.C. By this method, cracking and also the remaining of free-carbon can be suppressed even if the temperature-rise rate at >600 deg.C, not to speak of the temperature-rise rate at <=600 deg.C, is increased.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a sintered body such as cemented carbide or cermet. In particular, the present invention relates to a method for producing a sintered body, which enables a high quality sintered body to be obtained in a short time.

[0002]

2. Description of the Related Art Generally, sintering of cemented carbide or cermet is carried out by sufficiently mixing predetermined raw material powders to form a green compact and then introducing the green compact into a sintering furnace and heating it. Has been done. Further, pre-sintering may be performed between the green compact and the main sintering to form the pre-sintered body.

Here, the raw material powder contains an organic binder in order to impart lubricity and reduce friction between the powder and between the powder and the mold to improve dimensional accuracy. For example, paraffinic hydrocarbon is used as a binder. Such a binder is thermally decomposed and evaporated from the green compact when the green compact is heated appropriately when the green compact is heated.

[0004]

However, in the conventional sintering method, the heat treatment conditions for appropriately evaporating the binder are not clearly known, and there are the following problems.

The binder in the green compact is rapidly pyrolyzed,
The obtained sintered body may be cracked or distorted. This is because it is not clear at what stage and how the chemical reactions that affect product quality occur. Therefore, 1) the temperature rise rate becomes too high, and 2) the vacuum degree in the furnace deteriorates due to the gas components generated from the green compact, the tray on which the green compact is placed, the thermal insulator in the furnace, etc. It was a cause of producing non-defective products.

Free carbon remains in the sintered body. If the rate of temperature rise becomes too high or the degree of vacuum inside the furnace deteriorates, the binder is thermally decomposed and carbon is liberated, which remains as free carbon in the sintered body. Free carbon is weak in itself and can be the starting point of destruction.

It takes a long time to obtain a sintered body from a green compact. Since appropriate heating conditions are not known, if the temperature rising rate is too slow in order to avoid cracking or distortion of the sintered body, the cycle time of the entire sintering becomes longer than necessary.

Therefore, a main object of the present invention is to provide a method for producing a sintered body which can obtain a high quality sintered body in a shorter time.

[0009]

The present invention achieves the above object by limiting the atmospheric pressure in the heating process from room temperature to a predetermined temperature.

That is, the method for producing a sintered body of the present invention comprises a step of molding a raw material powder containing an organic binder into a green compact, and a total pressure of 60 P in the range of room temperature to 600 ° C. or less.
a Controlling the temperature to a or less and heating the green compact.

As described above, it has been conventionally practiced to remove the organic binder by heating. As a result of various examinations of suitable conditions for this removal, the temperature was 60
If the total pressure of the atmosphere is controlled to 60 Pa or less during the temperature raising process of 0 ° C or less, cracks and residual free carbon are suppressed not only when the heating rate is 600 ° C or less, but also when the heating rate is more than 600 ° C. I got the knowledge that it can be done. Therefore, it is possible to obtain a high-quality sintered body in a shorter time than ever before. A more preferable total atmospheric pressure is 50 Pa or less.

The temperature rising rate from room temperature to 600 ° C. or lower is 0.1
It is preferably ˜5.0 ° C./min. If it is less than this lower limit, the effect of shortening the sintering time is small, and if it exceeds the upper limit, cracking or strain of the sintered body or residual free carbon tends to be a problem. A more preferable temperature rising rate is 0.2 to 3.0 ° C./minute.

Further, it is preferable that the temperature rising rate from above 600 ° C. to the sintering temperature is 3.0 to 10.0 ° C./min. If it is less than this lower limit, the effect of shortening the sintering time is small, and if it exceeds the upper limit, cracking or strain of the sintered body or residual free carbon tends to be a problem. A more preferable temperature rising rate is 4.0 to 8.0 ° C.
/ Min.

In the manufacturing method of the present invention, not only a method of forming the raw material powder into a green compact and then performing main sintering, but also forming the raw material powder into a green compact and pre-sintering this pre-sintered body It can be applied to any of the methods in which the main sintering is performed after the forming process. Pressing or extrusion can be used for forming the raw material powder into a green compact.

The sintered body obtained by this manufacturing method includes cemented carbide containing WC as a hard phase, TiC, TiN or Ti.
Examples include cermet having CN as a hard phase, and ceramics containing alumina as a main component.

When obtaining a cemented carbide and a cermet, the raw material powder is at least one selected from the group consisting of carbides, nitrides, carbonitrides and borides of the periodic table 4a, 5a and 6a elements. A hard phase powder and a binder phase powder made of an iron group metal are included.

For example, when obtaining a cemented carbide having excellent special wear resistance, the raw material powders include a hard phase powder made of WC and a binder phase powder made of an iron group metal. In that case, the content of the binder phase powder is preferably 1% by weight or less. By using the cemented carbide that does not substantially contain the binder phase powder, it is possible to obtain a sintered body having extremely excellent hardness.
Examples of iron group metals include Co, Ni and Fe.

Paraffin hydrocarbons, waxes and the like can be used as the organic binder. Paraffinic hydrocarbons are saturated chain hydrocarbon having the general formula C _n H _{2n + 2.} Usually, as the paraffinic hydrocarbon mixed with the raw material powder of the sintered body, a material of n = 10 to 40 is used. Especially, n = 10 ~
A mixture of multiple species is used rather than the 40 individual substances alone.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. (Preliminary test example 1) First, before obtaining a sintered body, paraffin wax (mp 130 °) used as a binder was used.
F), microwax (mp200 ° F) and EVA (ethylene vinyl acetate copolymer) were examined by a thermobalance to determine how much weight loss occurs when heated at a heating rate of 10 ° C / h.

As a result, as shown in the graph of FIG. 1, a drastic weight loss occurs in the range of 200 to 300 ° C. for paraffin wax, 300 to 450 ° C. for microwax, and 400 to 450 ° C. for EVA. It was found that thermal decomposition proceeded rapidly in the temperature range. It is considered that the pyrolysis gas of the binder is generated from the green compact during heating from room temperature to 450 ° C. or lower, and it is expected that suitable sintering can be performed if the degree of vacuum in the furnace at that time can be appropriately maintained.

(Test Example 1) Next, a sintered body was prepared, and the effect of the temperature rise-atmosphere conditions on the product size was confirmed by experiments. 3% by weight of paraffin wax is added to a raw material powder consisting of WC having an average particle size of 2.0 μm and Co having an average particle size of 1.3 μm: 10% by weight and inevitable impurities, and thoroughly mixed. The mixed raw material is compressed and pressed into a green compact. Here, the product dimensions after sintering are width 10 mm, depth 10 mm, height 2 mm, width 10 mm,
10 mm depth, 5 mm height, 10 mm width, 10 mm depth, 10 m height
Three types of green compacts were prepared so as to have m.

The green compact thus obtained is sintered using a sintering furnace described in Japanese Patent Publication No. 58-9806. This sintering furnace is equipped with a furnace body capable of maintaining a predetermined degree of vacuum inside, a heating chamber provided in the furnace body, a conveyor for loading and unloading compacts into and from the heating chamber, and a furnace provided outside the furnace body. Cooling means for cooling the inside.

The furnace body has an exhaust system capable of reaching a vacuum of 10 ^-3 Pa inside. The heating chamber is surrounded by heat insulating material and has an openable door. In addition, a heater is provided in the heating chamber and a thermocouple is installed to control the heating chamber to a predetermined temperature. The lower surface of the heating chamber is open, and the moving table can be fitted into the lower surface of the heating chamber by driving the conveyor. The cooling means for cooling the sintered body after sintering includes a blower and a heat exchanger.

When performing the sintering, first, the green compact is set outside the heating chamber in the furnace. The green compact is placed on a moving table on a tray and set. Next, the door of the heating chamber is opened and the moving table is transferred to the lower surface of the heating chamber by the conveyor. After that, the door is closed, the inside of the furnace main body is kept in vacuum, and heated by the heater. When the green compact is heated to a predetermined temperature, a part of the paraffin inside becomes liquid and flows out, and a part of it evaporates.
The paraffin that has flown out is collected in a tank connected to the furnace body.

After the removal of paraffin is completed, the temperature is continuously raised to the sintering temperature to obtain a sintered body. When the sintering is completed, the door of the heating chamber is opened and the sintered body is transferred to the outside of the heating chamber. Then, a blower circulates the gas in the furnace to cool the sintered body.

[0026] Using such a sintering furnace, from room temperature to 600
Sintering was performed by controlling the total pressure in the furnace at a temperature rise of ℃ or less to various conditions. The sintering conditions are as follows.

Maximum total pressure in the furnace: Condition A: 20 Pa Condition B: 50 Pa Condition C: 65 Pa Heating rate up to 600 ° C: 600 ° C heating in about 2 hours (4.8 ° C /
Min) Temperature rising rate from 600 ° C to sintering temperature (1450 ° C) Condition 1: 850 ° C temperature rise in about 2 hours (7 ° C / min) Condition 2: 850 ° C temperature rise in about 2 hours and 30 minutes (5.7 ° C) / Min) Condition 3: 850 ° C temperature rise in approximately 4 hours (3.5 ° C / min) Holding time at sintering temperature: 30 minutes Heating chamber dimensions: 300 mm x 300 mm x 300 mm

As a result, in the sintering under the conditions A and B and the combination of the conditions 1 to 3, the size was good in all the samples in any case. On the other hand, in the combination of condition C and condition 1, microcracks were generated in the test piece having a thickness of 10 mm, which was defective. Also, in the combination of condition C and condition 2,
Although no cracks occurred, 3 out of 100 were defective due to carburization.

(Test Example 2) Next, the effect of the temperature rise-atmosphere conditions on the size of the extruded product was confirmed by experiments. WC with an average particle size of 0.5 μm, Co with an average particle size of 1.0 μm: 8% by weight, TaC with an average particle size of 1.2 μm: 2% by weight, and 10% by weight of paraffin wax are added to the raw material powder consisting of inevitable impurities. Mix. This mixed raw material is extruded to obtain a rod-shaped green compact. Here, the product dimensions after sintering are 4 mm in diameter and 4 mm in length.
The green compact was prepared so that it would be 00. This green compact was introduced into the same sintering furnace as in Test Example 1 and sintered. The dimensions of the heating chamber
It is 500 mm × 1000 mm × 500 mm. The sintering conditions were as follows.

Maximum total pressure in the furnace: the same condition A to condition C as in Test Example 1 Heating rate up to 600 ° C .: 600 ° C. heating in about 20 hours (0.48 ° C. /
Min) Temperature rising rate from 600 ℃ to sintering temperature (1400 ℃) Condition 4: 800 ℃ increase in about 2 hours (6.7 ℃ / min) Condition 5: 800 ℃ increase in about 2 hours and 30 minutes (5.3 ℃) / Min) Condition 6: 800 ° C temperature rise in approximately 4 hours (3.3 ° C / min) Holding time at sintering temperature: 30 minutes

As a result, in the sintering under the combination of the conditions A and B and the conditions 4 to 6, the size was good in all the samples in any case. On the other hand, under the heating condition in which the condition C was selected, carburization was observed in the sintered body, which was not good.

(Test Example 3) Further, regarding the cermet, the influence of the temperature rising-atmosphere conditions on the product was examined. TiCN with an average particle size of 1.0 μm: 50% by weight, WC with an average particle size of 1.0 μm: 20
% By weight, Ni with an average particle size of 1.5 μm: 8% by weight, average particle size 1.0 μ
Paraffin wax as a raw material powder consisting of Co: 12% by weight, Mo ₂ C with an average particle size of 1.2 μm: 10% by weight, and inevitable impurities.
Add 4% by weight and mix well. 1 of the obtained mixed powder
It was molded into a green compact with a compression press of ton / cm ² . This green compact was introduced into the same sintering furnace and heating chamber as in Test Example 1 and sintered. The sintering conditions were as follows.

Maximum total pressure in the furnace: the same condition A to condition C as in Test Example 1 Heating rate up to 600 ° C .: 600 ° C. heating in about 2.5 hours (3.8 ° C. /
Min) Temperature rising rate from 600 ℃ to sintering temperature (1400 ℃) Condition 7: Temperature rise at 800 ℃ for more than 2 hours (6.5 ℃ / min) Condition 8: Temperature rise at 800 ℃ for about 2 hours and 40 minutes (5.0 (° C / min) Condition 9: 800 ° C temperature rise in approximately 4 hours and 20 minutes (3.1 ° C / min) Holding time at sintering temperature: 30 minutes

As a result, in the sintering under the combination of the conditions A and B and the conditions 7 to 9, the size was good in all the samples in any case. On the other hand, under the heating condition in which condition C was selected, defects were observed due to carburization.

(Test Example 4) Using the green compact of Test Example 1, the vacuum degree in the furnace was changed to 400 ° C, 600 ° C, 80 ° C for about 2 hours from room temperature.
The temperature was raised to 0 ° C., and thereafter, sintering was performed under the condition 2 of Test Example 1 to examine the amount of free carbon produced in the obtained sintered body. The results are shown in the graph of FIG.

As is clear from this graph, the free carbon amount remarkably increases when the degree of vacuum in the furnace exceeds 60 Pa when the temperature is raised to 400 ° C.

[0037]

As described above, according to the method of the present invention, if the total pressure of the atmosphere is controlled to 60 Pa or less during the temperature rising process from room temperature to 600 ° C. or less, the heating rate particularly above 600 ° C. is increased. Even if this happens, cracking and residual free carbon can be suppressed. Therefore, it is possible to obtain a high-quality sintered body in a shorter time than ever before.

[Brief description of drawings]

FIG. 1 is a graph showing a thermal loss of an organic binder.

FIG. 2 is a graph showing the amount of free carbon produced when the furnace pressure is changed.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22C 29/16 C22C 29/16 H (72) Inventor Yoshinori Matsumoto 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Issue Sumitomo Electric Industries, Ltd. Itami Factory F-term (reference) 4K018 AD03 AD04 AD06 AD07 AD10 AD12 DA03 KA14

Claims (7)

[Claims] 1. A step of molding a raw material powder containing an organic binder into a green compact, and a step of heating the green compact by controlling the total pressure to 60 Pa or less in the range of room temperature to 600 ° C. or less. A method for manufacturing a sintered body, comprising: 2. The temperature rising rate from room temperature to 600 ° C. or lower
The method for producing a sintered body according to claim 1, wherein the temperature is 0.1 to 5.0 ° C / min. 3. The temperature rising rate from above 600 ° C. to the sintering temperature is
The method for producing a sintered body according to claim 1, wherein the temperature is 3.0 to 10.0 ° C / min. 4. The method for producing a sintered body according to claim 1, wherein the raw material powder includes a hard phase powder made of WC and a binder phase powder made of an iron group metal. 5. The method for producing a sintered body according to claim 4, wherein the content of the binder phase powder is 1% by weight or less. 6. The raw material powder includes at least one hard phase powder selected from the group consisting of carbides, nitrides, carbonitrides and borides of elements of Groups 4a, 5a and 6a of the periodic table, and an iron group. 2. The method for producing a sintered body according to claim 1, further comprising a binder phase powder made of metal. 7. The method for producing a sintered body according to claim 1, wherein the organic binder contains paraffin hydrocarbon.