JPS60245701A - Production of sintered metallic body - Google Patents

Abstract

PURPOSE:To obtain a sintered metallic body which has no defects such as corrosion and cracks and has excellent sintering strength, shape maintainability, etc. by decomposing thermally and removing a synthetic resin binder from the molding of a kneaded plastic mixture composed of self-fluxing alloy powder, high melting metallic powder and said binder. CONSTITUTION:The kneaded matter composed of, for example, the Ni self- fluxing alloy powder, pulverized Mo powder and synthetic resin binder is subjected to a heating treatment and is molded to a sheet-shaped plastic material P. The plastic material P is adhered to the base surface 2 of a cast iron die body I0 and thereafter the plastic material P is pressed by a pattern M to form a work forming part Ia. The body I0 is then installed in a vacuum sintering furnace 5 and is subjected to decomposition of the synthetic resin binder and sintering of the metallic powder under heating-cooling conditions consisting of the regions (A-C)D1-D3 shown in the figure. The sintered body S to be obtd. as a result thereof has good weldability with the body I0, has uniform porosity, obviates generation of cracks, corrosion, etc. and has good dimensional accuracy.

Description

[Detailed description of the invention] A0 Purpose of invention (1) Industrial application fields The present invention relates to a method for manufacturing a metal sintered body.

(2) Conventional technology.

When producing a metal sintered body, a molded body is obtained from a plastic material obtained by kneading a self-fusing alloy powder and a synthetic resin binder, and then the synthetic resin binder in the molded body is thermally decomposed and the self-fusing alloy powder is sintered. tying is done.

(3) Problems to be solved by the invention In the above manufacturing method, since a molded body is formed from a plastic material, a molded body with a predetermined shape can be easily obtained. If the resin binder is not removed by thermal decomposition, the decomposed gas will corrode the sintered body and adversely affect the quality of the sintered body. Furthermore, if the temperature of the powder body is suddenly raised to the sintering temperature, the porosity will vary greatly, making it impossible to obtain a sintered body having a uniform porosity.

In order to further improve the sintering strength, it is necessary to sinter the powder at a temperature from just below the in-phase line of the self-fusing alloy to above the liquidus line. flows, reducing the shape retention and dimensional accuracy of the sintered body. Furthermore, defects such as cracks may occur in the sintered body depending on the cooling conditions of the sintered body after sintering.

In view of the above, the present invention is free from defects such as corrosion and cracks, and
Another object of the present invention is to provide the above-mentioned manufacturing method, which makes it possible to obtain a sintered body having high sintering strength, good shape retention and dimensional accuracy, and uniform porosity.

B0 Structure of the Invention (1) Means for Solving Problems The present invention comprises a step of obtaining a molded body from a plastic material obtained by kneading a self-fusing alloy powder, a high melting point metal powder, and a synthetic resin binder; a step of thermally decomposing the synthetic resin binder by holding the synthetic resin binder at 600 to 650°C to leave a powder consisting of the self-fusing alloy powder and high melting point metal powder; and holding the powder at 900 to 1000°C. a step of obtaining a pre-sintered compact by holding the pre-sintered compact at 1000-1200°C to obtain a sintered compact;
The sintered body is cooled at a maximum cooling rate of 2°C/min to 00°C.
a second cooling step of the sintered body from about 800°C to about 400°C at a maximum cooling rate of 3°C/min; and a step of cooling the sintered body from about 400°C to room temperature for 3 seconds. The method is characterized by using a second step of cooling.

(2) Function Most of the synthetic resin binder can be removed by thermal decomposition by maintaining the molded body at the above temperature before sintering. Further, by temporarily sintering the powder body while maintaining the above-mentioned temperature, it is possible to prevent variations in porosity and obtain a sintered body having a uniform porosity and free of defects such as cranks.

Furthermore, by mixing high melting point metal powder with self-fusing alloy powder, the shape retention and dimensional accuracy of the sintered body can be maintained even when the powder is sintered at temperatures from just below the in-phase line to above the liquidus line of the self-fusing alloy. Moreover, a sintered body with high sintering strength can be obtained. Furthermore, the occurrence of defects such as cracks can be prevented under the above cooling conditions.

(3) Example FIG. 1 shows a press mold 1, which consists of a mold body 1o and a workpiece molding section 1a integrated with the mold body 1o.The workpiece molding section 1a is as follows. It is composed of a metal sintered body S obtained by the method described below.

i. Production of plastic material 80 parts of Ni self-melting alloy powder as self-melting alloy powder and 20 parts of Mo pulverized powder as high melting point metal powder are sufficiently mixed in a V-blender to obtain a mixed powder.

A synthetic resin binder is obtained by mixing a tetrafluoroethylene resin emulsion and an acrylic resin emulsion in a ratio of 1:14.

Add 3 parts of synthetic resin binder to 100 parts of the above mixed powder and thoroughly knead with a table and kneader.
The water in the synthetic resin binder is evaporated by heating to 00 to 150°C. The obtained kneaded product has a shape of numerous nodules due to being caked by the synthetic resin binder.

The kneaded product is heated to 80 to 100°C and passed through a roll machine multiple times to obtain a sheet-like plastic material. In this case, if the rolls of the roll machine are heated to the same degree as the kneaded material, the sheet forming operation can be easily performed. The obtained sheet-like plastic material has appropriate flexibility and tear strength at room temperature.

ii. Manufacture of the mold As shown in Fig. 2(a), the mold body 1o is made of cast iron (JI
The base surface 2 forming the workpiece molding part 1a is casted from S Fe12 material) and is molded so that the base surface 2 forming the workpiece molding part 1a is 5 to 30 mm lower than the outer surface of the workpiece molding part 1a (dashed line water) in the completed mold 1. has been done. The mold body 1o is used as-cast, and an acrylic resin adhesive is applied to the base surface 2 having a black crust after cleaning.

As shown in FIG. 2(b), a sheet-like plastic material P is attached to the base surface 2. In this case, in order to obtain a predetermined thickness, sheet-like plastic materials P are laminated. Also, the mold body 10 is 80
When heated to ~100°C, the sheet-like plastic material P
The pasting work can be done easily.

As shown in FIG. 2(C), the plastic material P is pressed by the model M to form the workpiece forming portion 1a.

As shown in FIG. 2(d), an enclosure 3 is attached to the mold body 10 to surround the plastic material P, the surface of the plastic material P is covered with ceramic powder, and a 0.75 m diameter steel ball 4
and perform a backup.

This hack-up suppresses the dimensional change, that is, expansion, of the sintered body S during sintering of Ni self-fusing alloy-Mo powder, which will be described later, due to the weight of the steel ball 4.

Next, the mold body 10 is placed in a vacuum sintering furnace 5, and the synthetic resin binder is decomposed and the metal powder is sintered under the heating-cooling conditions shown in the third step. As the carrier gas, nitrogen gas or highly reducing hydrogen gas is used.

(A) First heating zone (Fig. 3 A) This heating zone A is from room temperature to 650°C, and the temperature increase rate is 10~b. In the heating zone A, water first evaporates, and then the temperature in the synthetic resin binder evaporates. The tetrafluoroethylene resin and acrylic resin decompose and gasify. These synthetic resins are 300 to 400
It gasifies at °C, but considering heat conduction, the temperature is 600-650 °C.
℃ for 90 minutes to remove most of the synthetic resin, and
i. Leave the self-fusing alloy-Mo powder body. Explaining the gasification of this synthetic resin by the change in the degree of vacuum inside the vacuum sintering furnace 5, it is 1 Torr at room temperature, but 90 Torr at 650°C.
When the temperature is soaked for a minute, the degree of vacuum decreases to a maximum of 2 Torr. This is mainly due to the generation of decomposed gas from synthetic resins. After 90 minutes, the degree of vacuum will return to 1"I.
This means that the cracked gas has been removed from the vacuum sintering furnace 5.

(B) Second heating zone (Fig. 3B) This heating zone B is in the range of 900 to 1000°C,
The Ni self-fusing alloy-Mo powder body is heated at a temperature below the solidus line (1010 to 1020°C) of the Ni self-fusing alloy, for example 950°.
C is soaked for 30 minutes and subjected to solid phase sintering treatment, and then pre-sintered. The temperature increase rate from the first heating zone A is 10~
b Ru.

Since the Ni self-fusing alloy-Mo powder body in the vacuum sintering furnace 5 is heated from its surface and increases in temperature, a predetermined heating time is required until the entire powder body reaches a uniform temperature. If it is suddenly heated to the sintering temperature of 1000 to 1200°C, the surface part of the Ni self-fusing alloy-Mo powder body and the base surface 2
There is a temperature difference between the part in contact with the core and the core, which increases the variation in porosity, making it impossible to obtain a sintered body with uniform porosity, and also making it more likely to produce defects such as cranks after sintering.

In the second heating zone B, a small amount of undecomposed synthetic resin is completely gasified and removed. Due to this gasification etc., the vacuum sintering furnace 5
The degree of vacuum inside the chamber temporarily drops to 47 orr, but returns to I Torr after 30 minutes.

(C) Third heating zone (Fig. 3C) This heating zone C is located at the solidus line (1(l) of the Ni self-fusing alloy.
l O~1020'c) from just below the liquidus line (1075~
1085℃), i.e. 1000-1200℃
The Ni self-fusing alloy-MO pre-sintered body is maintained at a constant temperature of 1100 to 1180°C, preferably 1120°C, which is a temperature exceeding the liquidus line, for 120 minutes to melt the Ni self-fusing alloy. A liquid phase sintering process is performed to form a sintered body S. In this case, the flow of the Ni self-fusing alloy is hindered by the presence of MO, and therefore shape retention is good.

The temperature increase rate from the second heating zone B is 15 to 20°C/min, and since the Ni self-fusing alloy-MO pre-sintered body has already been heated to a high temperature in the second heating zone B, the third heating zone C
It takes only a short time to raise the temperature.

If the holding time in the third heating zone C is insufficient, sintering will not be completed completely and defects will occur in the sintered body S.

The reason why the sintering temperature is selected to be 1120°C as described above is that this temperature is lower than the eutectic temperature of the mold body 1o made of cast iron. If the mold body 1o is made of steel thread such as cast steel, the sintering temperature is preferably 1160°C. The reason for this is that when the sintering temperature is around 1200°C, there are problems such as large dimensional changes in the sintered body S, it is not easy to control the furnace temperature, and the temperature inside the furnace fluctuates. This is because 1160° C. is appropriate as the working temperature for removal.

(D) Cooling zone (Figure 3 D) This cooling zone D includes a primary cooling zone D from the sintering temperature to about 800°C, and a cooling zone D from about 800°C to about 400°C.
It is divided into a secondary cooling zone D2 from approximately 400° C. to room temperature and a tertiary cooling zone D3 from approximately 400° C. to room temperature.

The primary cooling zone DI is a stable region of the sintered body S at high temperatures, and in this cooling zone DI, thermal stimulation is avoided as much as possible, and at the same time, the cooling rate is slow at a maximum of about 2°C/min in consideration of cooling efficiency. Cool it down. When rapid cooling is performed in this cooling zone D, cranks occur frequently in the sintered body S.

In the secondary cooling zone D2, linear expansion (12
, 5x 10-6/℃) and a maximum of 3° to absorb the dimensional change during Ar1 transformation and to avoid rapid cooling of the sintered body S.
Cool at a slow rate on the order of C/min. In this case, the linear shrinkage of the sintered body S is 14.6 x 10-"7°C, but since it is porous, it follows the shrinkage of the mold body 10. When rapidly cooled in this cooling zone D2, sintering There are many cranks on body S.

In the tertiary cooling zone D3, the temperature of the sintered body S and the mold body 10 is cooled to room temperature by gas cooling (including air cooling) other than liquid cooling such as water or oil.

In this way, a mold 1 is obtained in which the workpiece molding portion 1a is formed of the sintered body S made of Ni self-fusing alloy-MO.

The sintered body S has good weldability with the mold body 10, has a uniform porosity, is free from defects such as cracks and corrosion, and has a precision of dimensional change within ±0 to +2i1. well,
It has good shape retention and high sintering strength. Therefore, it can be used for press work immediately after simple finishing.

The surface hardness of the sintered body S is about 20 on the Rockwell hardness B scale, and if it has this hardness, it will not cause any problems in normal press work, but depending on the work, the sintered body S may be subjected to high pressure. In this case, since the sintered body S is porous, there is a risk of buckling.

In order to deal with such problems, it is possible to infiltrate the high-pressure working part of the sintered body S with a low melting point metal such as a self-fusing alloy of Cu or Ni, or to impregnate and harden a synthetic resin such as an epoxy resin to close the pores. It is necessary to significantly increase the hardness of the sintered body S and improve its buckling strength.

As the self-fusing alloy powder, in addition to the above-mentioned Ni self-fusing alloy powder, C
O self-fusing alloy, Fe self-fusing alloy, etc. can be used. Further, the high melting point metal powder should preferably be one to which a self-fluxing alloy can be easily welded, and W, WC, stainless steel, etc. can be used in addition to the above-mentioned MO.

Note that the present invention is not limited to the case where the mold body is used as a base material and a sintered body is laminated thereon as in the above embodiment, but also applies to the case where only a sintered body is manufactured without using a base material. It is possible.

C6 Effect of the invention According to the invention, the molded body is heated at 600°C to 650° before sintering.
By maintaining the temperature at C, most of the synthetic resin binder can be removed by thermal decomposition and problems such as corrosion of the sintered body due to decomposition gas can be avoided.

In addition, by holding the powder body at 900 to 1000°C and pre-sintering it, it is possible to prevent variations in porosity and obtain a sintered body that has uniform porosity and is free from defects such as cracks and cracks. .

Furthermore, by mixing high melting point metal powder with self-fusing alloy powder, it is possible to
Even when sintered at a temperature of 0 to 1200°C, the shape retention and dimensional accuracy of the sintered body can be improved, and a sintered body with high sintering strength can be obtained.

Furthermore, by dividing the cooling process into the primary to tertiary stages as described above, it is possible to prevent defects such as cranks from occurring in the sintered body.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a cross-sectional view of a press mold, FIG. 2 is an explanatory diagram of the manufacturing process of the mold, and FIG. It is a graph showing the relationship between time and P... plastic material, S... sintered compact, 1... press mold, 10... mold body, 1a...
・Workpiece forming section patent applicant Honda Motor Co., Ltd.

Claims (1)

[Claims] A step of obtaining a molded body from a plastic material obtained by kneading a self-fusing alloy powder, a high melting point metal powder, and a synthetic resin binder, and a step of thermally decomposing the synthetic resin binder by maintaining the molded body at a temperature of 600 to 650°C. A step of leaving a powder body consisting of a self-fusing alloy powder and a high melting point metal powder, and
A step of holding the temporary sintered body at 1000-1200°C to obtain a sintered body, and a step of holding the temporary sintered body at 1000-1200°C to obtain a sintered body, and heating from 1000-1200°C to approximately 800°C at a maximum of 2
A step of primarily cooling the sintered body at a cooling rate of °C/min;
A metal comprising: secondarily cooling the sintered body from approximately 800°C to approximately 400°C at a maximum cooling rate of 3°C/min; and tertiary cooling the sintered body from approximately 400°C to room temperature. A method for producing a sintered body.