JPH0196302A - Powder metallurgical method - Google Patents

Abstract

PURPOSE:To efficiently produce a large-diameter material by sealing powder into a malleable container, heating the powder and inserting said container into a cylinder so as to provide a spacing between the container and the inside wall of the cylinder, then compressing the powder. CONSTITUTION:The metal powder or powder mixture 7 composed of a metal and nonmetal is packed into the cylindrical container 6 made of, for example, a mild steel and the container is sealed after the inside thereof is evacuated to a prescribed vacuum degree. This container is compressed by a cold isostatic press and thereafter, the container 6 is inserted into the cylinder 1 by providing the spacing 8 between the inside wall of the cylinder and the outside wall of the container. A stem 4 is then advanced to compress the container 6. The container 6 is thereby brought into tight contact with the inside surface of the cylinder 1 and the powder 7 is compressed. The pressing pressure of the stem 4 is further increased to annihilate the grain boundaries of the powder. A solid metal 9 is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for obtaining a metal material or a composite material of metal and nonmetal by a powder metallurgy method.

[Conventional technology]

The most common metal manufacturing processing technology is melting-casting-rolling-product processing (parts processing by cutting, forging, etc.).
In the case of materials that cannot be manufactured by such means, or materials for which the desired high quality cannot be obtained by such means, powders of these materials are manufactured and this is processed into one part by various processes. , powder metallurgy technology is used to process into products. The present invention also relates to powder metallurgy technology.1 The known technology closest to the present invention is the so-called hot press method in which powder is placed in a cylinder press and compressed at high temperature to produce cylindrical products or intermediate products, or the powder metallurgy is There is a method of encapsulating it in a capsule, heating it, and extruding it with a hot extrusion press to obtain a bar or tube.

[Problem that the invention seeks to solve]

In the conventional hot pressing method using a cylinder, the powder is directly filled into the cylinder and compressed, but due to the friction between the cylinder wall and the powder, sufficient pressure is not applied particularly to the center, leaving voids. easy. This central void is
Even if it is processed later using commonly used methods such as forging and rolling, the tensile stress that occurs especially in the center
The voids remain without disappearing and have an adverse effect on quality.

Hot extrusion is an excellent method for obtaining a material with true density, but because the cross-sectional area ratio of the extruded material and the billet before extrusion must be 2 to 3 or more, it is difficult to obtain a material with a large diameter. It's inconvenient though.

[Means for Solving the Problems] This invention involves sealing a metal powder or a mixed powder of metal and non-metal in a malleable container, heating it, and compressing it by pressurizing it in a cylinder. and obtain products or intermediate products. Intermediate processed products.

Further forging or rolling is performed as necessary. This invention is particularly characterized in that, when the container is inserted into the cylinder, a sufficiently large gap exists between the inner wall of the cylinder and the container.

This gap is characterized by being sufficiently large compared to a gap provided to smoothly insert the container into the cylinder or a gap that appears significantly when the container is formed based on dimensional tolerances of the container.

That is, although the usual gap as described above does not exceed 5% of the cylinder inner diameter in any case, the gap in the present invention is selected to be 6% or more of the cylinder inner diameter.

Although the upper limit value of this gap is not known, if the material and wall thickness of the container are appropriately selected, it is possible to carry out the compression process even when the gap reaches 50% of the cylinder inner diameter. but.

Choosing an unnecessarily large gap like this is not desirable in terms of work efficiency.

It is preferable to compress the container containing the powder as much as possible before heating and compressing it, from the viewpoint of heat conduction and other aspects, and cold isostatic pressing is a method for this because it can maintain a good shape. It is advantageous for

As a cylinder device for hot-compressing the powder sealed in a container, a hot extruder may be used, and the extrusion port thereof may be closed.

[For production]

In this invention, the powder raw material is housed in a container, and there is a sufficient gap between the inner wall of the cylinder and the container. Therefore, when this is pressed by the stem, the powder inside is compressed and moves in a direction parallel to the cylinder axis, causing plastic deformation and reaching true density. During this time, since there is no friction between the powder and the inner wall of the cylinder, unlike in the case of hot pressing using a conventional cylinder, the pressure from the stem is transmitted almost evenly to the center of the powder, leaving no voids inside. Then, by maintaining the compressed state at true density for a while, sintering and recrystallization progress.

The initial powder grain boundaries disappear.

The compressed material obtained in this way can be used as a material for cutting as is, but in many cases, it is further processed into smaller dimensions by hot rolling or hot forging. Used for etc. In either case, it has sufficient mechanical properties.

〔Example〕

5 US in a mild steel cylindrical container with an outer diameter of 155 fl, a length of 350 mm, a peripheral wall thickness of 1.6 mm, and an end wall thickness of 1.0 mg.
Filled with powder made by gas atomization of 304L material (average particle size iooμ, maximum particle size 150μ), and the inside was filled with 10-
It was evacuated to 1 torr and sealed. This was made into 4000 K9 f/CM by cold isostatic press. Pressurize with 1
By holding for a minute, the container dimensions are reduced to an average outer diameter of 145 mm.
．． 5 questions, the length was reduced to about 334 cods, and the packing density in the container increased from 69% to 87% of the true density.

The figure shows a hot extrusion device, in which 1 is a container, that is, a cylinder, 2 is a die, 3 is an extrusion port, and 4 is a stem. 3
is blocked. The inner diameter of the container 1 is 155 mm.

The container 6 subjected to the cold isostatic pressing described above is shown in FIG.
7 is the powder inside the container, and 8 is the gap created between the inner wall of the container and the outer wall of the container. The size of the gap 8 at this time is 9.5 wings on average, which corresponds to 6.1% of the inner diameter of the container.

Next, when the stem 4 is moved forward and the container 6 is compressed, the container 6 comes into close contact with the inner surface of the container 1, and the powder 7 is compressed, as shown in FIG. 2(b). Furthermore, the pressing force of stem 4 was increased to 200
When raised to 0 t Ic and held for 10 seconds, the same figure (c
), the grain boundaries of the powder disappear and the powder changes to a solid metal 9.

The metal 9 described above was taken out along with the container 6, and the container 6 was removed by machining, and microscopic examination revealed that it was a completely solid metal with no voids at all. This metal 9 is forged at 1150°C into a round bar with a diameter of 30 mm, and has a specific gravity of 7.901 to 7.902 and a tensile strength of 6.
97 scraps TM21 elongation is 0.7-64.6 53.2-6
0.0% and 1 There was no change in the same type of material made by the normal manufacturing method.

In addition, a first test was conducted to find out the relationship between the inner diameter of the container 1 and the gap 8.

Length 350mm, solid wall thickness 1.6mm, end wall thickness 1.0f
Using fll+, cylindrical containers with various outer diameters were made from mild steel, filled with the aforementioned 5US304L material powder, and the insides were evacuated and sealed in the same manner, then 4oooKgt7tyr
? It was compressed by cold isostatic pressing (CIP). These were hot-pressed at 2000 t in containers with four different inner diameters to obtain products, and the structures of the center, middle and outer layers of the products were observed using a microscope to check for the presence of voids.

Table 1 shows the case when a container with an inside diameter of 155H is used, Table 2 shows the case when a container with an inside diameter of 175H is used, Table 3 shows the case when a container with an inside diameter of 190H is used, and Table 4 shows the case when a container with an inside diameter of 215H is used.
Each case using an ffll container is shown below. Table 6 shows the average container outer diameter (a) before and after cold isostatic pressing (CIP) and the gap size (X) relative to the container inner diameter.
and the results of microscopic examination of the metal part of the product (○ mark: no voids, × mark: voids) are shown.

Table 1 Container inner diameter 155fl Table 2 Container inner diameter 175 fl Table 3 Container inner diameter 190 m Table 4 Container inner diameter 215 fl From the test results in Table 6 above, a container filled with raw material powder was cold isostatically pressed. When inserting into a container (cylinder), the gap that occurs between the inner surface of the container and the container,
It has been found that if the inner diameter of the container is selected to be 6% or more, the product obtained by hot compression becomes a completely solid body with no internal voids.

As shown in FIG. 2(a), if the outer diameter d of the container 6 after cold isostatic pressing is significantly smaller than the inner diameter of the container, the container 6 will be Deform as shown in b). That is, although the bottom plate 6b and the lid 6c, which are welded to the peripheral wall 6a at portions 6d% and 6e, hardly deform,
The peripheral wall 6a is deformed into a U-shape in cross section, thereby reducing its volume. In order for the container 6 to deform smoothly in this way,
It was also found from the test results in Table 6 above that even if the gap 8 is large, hot compression of the powder is performed without any problem, and even when the gap is close to 50% of the inner diameter of the container, compression is performed well.

〔Effect of the invention〕

As described above, according to the present invention, metals having a dense structure or composite materials of metals and non-metals can be produced more efficiently and inexpensively than the conventional hot isostatic pressing method, and can be heated using conventional cylinders. Unlike the hot extrusion method, the product can be manufactured without leaving any voids inside the product, and it is also easier to manufacture products with larger diameters than products using the hot extrusion method.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the operation process of the hot compression process in an embodiment of the present invention, and FIG. 2 is a sectional view of the container before and after the hot compression process. 1...Cylinder, 4...Stem, 6...Container. 7...Powder, 8...Gap. Patent applicant Sanyo Special Steel Co., Ltd.

Claims (4)

[Claims] (1) A process of filling a malleable metal container with metal powder or a mixed powder of metals and non-metals and sealing it, heating the powder sealed in this container, and converting the heated container into a cylinder. The powder particles are inserted into the cylinder and pressed and compressed by the stem, and when the container is inserted into the cylinder, the powder particles move to a state where no voids are left between the container and the inner wall of the cylinder. A powder metallurgy method characterized by the existence of a gap large enough to (2) The powder metallurgy method according to claim 1, characterized in that, prior to heating, the container containing the powder is pre-compression molded to 75% or more of the theoretical density by cold isostatic pressing. . (3) The powder metallurgy method according to claim 1, wherein the outer diameter of the container is 94% or less of the inner diameter of the cylinder into which it is inserted. (4) The powder metallurgy method according to claim 1, wherein the cylinder is a container of a hot extruder with a closed extrusion port.