JPS6229484B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to metal rods, metal tubes, and other materials having a structure or structure formed from metal powder or alloy powder, or a mixture thereof, or a mixture of metal powder or alloy powder and ceramic powder. The present invention relates to a capsule used for manufacturing a long product similar to the above, and a method for manufacturing the same.

Conventionally, when manufacturing rods, pipes, etc., metal powder is directly filled into the receiver of an extrusion press and extruded using a one-stage process to directly produce the desired final product, or a multi-stage process is used to pass through intermediate products and then produce the final product. A method was used to do so.

An improvement to this method is to make a blank, place it in a press receiver, and extrude it. Blanks are made in a variety of ways, including: (a) cold compaction of powder and sintering;

(b) Hot compacting the powder.

(c) Filling and enclosing the powder into capsules.

There are other methods.

This invention basically manufactures rods, pipes, etc. by the improved method described in (c) above. That is, the powder is encapsulated in capsules and the capsules are subsequently extruded in one or more stages. (Hereinafter, the term "capsule" shall be used to include not only the container but also the enclosed powder.) For economic and technical reasons, it is necessary to make the capsule container as thin as possible. However, the problem is that the capsules tend to wrinkle during the extrusion operation. In the manufacture of tubes and similar elongated objects, the ratio of length to diameter of the capsule must be greater than 1. This further increases the tendency for wrinkles to form, especially when the capsule walls are thin.

Various proposals have been made to solve this problem, but to date none of them has provided an economically or technically satisfactory solution. For example, it has been proposed to cold-compact the capsule mechanically after encapsulating the powder in the capsule container. but,
With this technique, the results are not satisfactory, especially when the length to diameter ratio of the capsule is greater than 1, due to the frictional forces between the capsule container and the mechanical tools used for cold compression. It's not a kimono. Frictional forces also reduce the total achievable reduction beyond an acceptable range and cause the reduction to vary over the length of the blank. This leads to unfavorable conditions, especially during heating prior to extrusion.

The present invention solves the aforementioned problems in a completely different way, by using the capsules of the present invention to form rods, tubes, and other similar shaped rods, preferably made of stainless steel material, having a very regular texture. Long objects, in particular seamless steel pipes, can be provided.

According to the present invention, this problem is solved by starting with a powder, at least mostly consisting of substantially spherical particles, and first encapsulating this powder in a ductile metal container to form a capsule (first intermediate product). By doing so, you can get one step towards a solution. The capsules are then compressed by applying cold isostatic pressure throughout until the density of the powder reaches at least 80% of the theoretical value (theoretical density) to form a blank (second intermediate product), thus obtained. The blank is heated and the object is formed by single or multi-stage extrusion.

This results in high quality metal rods and tubes exhibiting particularly uniform physical and chemical properties.

In the present invention, a thin-walled container made of highly ductile materials such as carbon steel, nickel, etc. is used. According to the invention, at least a large part of the capsule container is constructed of thin walls, preferably of highly ductile metal plates. The capsule wall is at most 5%, preferably 3%, of the outer diameter of the capsule before extrusion.
A capsule container is used in which the amount of carbon dioxide is not more than 1%, particularly preferably not more than 1%. If it is thicker than 5%,
This is because wrinkles occur during cold isostatic compression.
A large number applies when the capsule diameter is small, and a small number applies when the capsule diameter is large. The wall of the capsule is preferably between 0.1 and 5 mm, more advantageously between 2.0 and 3 mm. 0.1mm
It is technically difficult to manufacture a thinner one, and if one thicker than 5 mm is used, wrinkles will occur during cold isostatic compression.

As starting material for the blank, a powder is used, at least for the most part consisting essentially of spherical particles, the particle size being less than 1 mm, preferably less than 0.6 mm.

The powder density of the capsules is increased to about 60-70% of the theoretical density (density as a solid) by vibration or ultrasonic vibration methods before isostatically compressing the capsules. Capsules filled with powder are at least
A hydrostatic pressure of 1500 bar (about 21800 psi), preferably at least 5000 bar (about 72500 psi) is applied. Cold isostatic compression using hydrostatic pressure achieves compression in a much shorter time than hot isostatic compression using hot gas, and is more economical because it requires less energy.

Although the final product rods, tubes, etc. are mainly intended to be made of steel materials, it is of course possible to use other types of metal materials or mixtures thereof, such as mixtures of metal powder and ceramic powder. It is.

To obtain satisfactory results, it is important that the powder has a low oxygen content, which is achieved by using a spherical powder that has been atomized by an inert gas.

By vibrating the packed powder consisting of spherical particles, a very high apparent density is achieved. This point is an extremely important feature of the present invention, and is based on the difference between irregularly shaped powder and spherical powder.

The spherical powder is encapsulated in a highly ductile capsule container of a shape suitable for the required intermediate or final product, and is given a density of 60 to 70% of the theoretical density, ie, the density as a solid, by the vibration method. When making compounds, various metals are used in powder form. powder is 1
or into a capsule container divided by more than one wall. Such partition walls may be made of plastic, steel or similar materials. After filling and vibrating the powder, the walls are removed and the powder is placed in a capsule container made of highly ductile material using (or without) a vacuum method.
Encapsulate. The capsules are then subjected to cold isostatic isostatic compression at a pressure of at least 1500 bar, preferably for example 5000 bar, resulting in
The 70% density increases to 80-90% of the theoretical density, depending on the pressure used. The initial density of the powder is so high that the length to diameter ratio is 1.
Despite the fact that larger (for example 4) and thin-walled capsule containers are used, the capsules do not wrinkle during the cold compression and extrusion process. As mentioned above, the use of thin-walled capsule containers is very important from an economic point of view.

The ratio between the outer diameter of the capsule and the wall thickness is important. According to the invention, the ratio is at most 5%, preferably less than 3%, particularly advantageously less than 1%. On the other hand, the capsule wall thickness is preferably about 0.1 to 5
mm, particularly preferably between 0.2 and 2 mm. For the above ratios, larger ratio values are used for smaller capsule diameters, and conversely smaller ratio values are used for larger capsule diameters.

Global compaction in cold isostatic pressing imparts a substantially uniform density to the blank over its entire length. Due to the significant increase in density, the blank can be heated in a short time by means of induction furnaces or similar methods.

After heating, the capsules are extruded using a single-stage or multi-stage process. The capsule material is then drawn off as a very thin film. When the film comes out of the extrusion press, it oxidizes in the air and partially peels off. The remainder of the capsule container material is then annealed,
Removed by nitric acid cleaning or sand blasting. The tube etc. is then processed in the usual manner.

Since the final products such as rods and pipes are manufactured in the above manner, they have extremely uniform structures and extremely harmonious physical and chemical properties, especially in terms of hardness and chemical resistance. The fluctuations are substantially small.
This point also applies to compound products. These properties in tubes or the like are based on the fact that segregation, which always occurs in conventional production methods, especially segregation appearing as lines, cannot occur.

If desired, the capsule can be made of a material with a high quality surface finish and the extruded tube or the like can be provided with a permanent coating of the capsule material. The thickness of the surface coating or baking can be predetermined by suitably selecting the wall thickness of the capsule container. Highly ductile materials are particularly suitable for creating such surface layers.

In the following, the invention will be explained in detail with reference to examples.

As Example 1, a tubular capsule container was filled with steel powder, which was pulverized with argon and had a spherical particle size of 0.6 mm or less and a low total oxygen content, and was vibrated. The capsule container was a ring with an external diameter of approximately 140 mm, made of low carbon steel, with a wall thickness of 3 mm and a length of 550 mm. The annular capsule had at its inner center a continuous tubular section of the same quality carbon steel with approximately the same wall thickness as the outer casing of the capsule. The carbon content of the capsule material needed to be low to prevent carburization of the powder during heating and extrusion. The capsule container was evacuated and sealed in a known manner.

As Reference Example 1, the capsule produced in Example 1 was submerged in a liquid (water in this Reference Example), and cold isostatic compression was performed by applying a pressure of 5000 bar to the entire capsule. The capsules shrunk and the powder density increased from about 68% to about 90% without wrinkles in the capsule container material.

For ease of explanation, capsules identical to those of Example 1 were subjected to conventional cold compression, ie, mechanical compression, instead of cold isostatic compression. In this case, a powder density of 75% of the theoretical density was obtained, but twice the pressure in Reference Example 1 was required.

Now, the blank made by the above cold isostatic compression is then heated to 900℃ in a preheating furnace, and finally heated to 1240℃ by an induction coil, and then extruded into a seamless steel pipe. Molded. The tube was cooled in a water bath and the capsule material was removed in a nitric acid bath. There were no defects in the tube.

For comparison, blanks made by mechanical compaction were heated and extruded in the same manner. The capsule material was removed, but the tube was unusable. The wrinkles created during compression caused cracks and other material defects that rendered the tube unusable.

As Example 2, a capsule for a compound pipe was manufactured as follows.

In a capsule container made of a thin sheet metal corresponding to Example 1 and having a continuous inner tube in the center, a thin wall tube was placed between the outer wall and the inner wall of the capsule container. The outer intermediate space was filled with spherical powder of 25% chromium steel with high silicon and aluminum content while being vibrated. The particle size was less than 0.6 mm. It is extremely difficult to produce blanks of this quality by conventional methods, ie, by refined alloys. It is known that this material is particularly suitable for powder metallurgy and that its products are of great industrial importance.

Chrome nickel steel (Cr18%,
Spherical steel powder containing 8% Ni was filled into the inner intermediate space while being vibrated. The intermediate wall was removed, evacuated, and sealed to form a capsule.

As Reference Example 2, the capsules produced in Example 2 were subjected to cold isostatic compression at 5000 bar.
The blank was then heated and formed into a seamless steel tube as described in Reference Example 1. The capsule material was also removed in a nitric acid bath. Histological examination of the compound tube shows that the tissue is completely dense;
It was also uniform. There was a perfect bond and no flaws in the bonded area of the two materials. It should be emphasized that it has been practically impossible to produce defect-free compound tubes using previously known methods.

In addition, in order to examine the necessity of compression before extrusion, the same powder and capsule container material as in Example 1 were immediately heated to 1200 ° C. without isostatic compression.
The final product was extruded into tubes. The tube shows surface flaws due to wrinkles in the capsule, which is due to the low initial density of the powder. Therefore, this test result indicates that it is necessary to compress the blank before extrusion in order to prevent the already known phenomenon of capsule wrinkling and suppress the occurrence of surface defects. It is.

Meanwhile, the same capsules as in Example 1 were isostatically compressed to 2000 bar (approximately 29000 psi). The capsules shrunk without wrinkles and the density of the powder increased to 82% of the theoretical value. The blank was heated and extruded in the same manner as above. The resulting tube was defect-free and free of any wrinkles. Tests have shown that up to 80% cold isostatic pressing is sufficient to produce defect-free products.

Furthermore, in order to examine the effect of the shape of the material powder on the compressed density, four of the eight capsule containers were filled with irregularly shaped stainless steel powder (pulverized with water), and the remaining 4 were filled with regular spherical stainless steel powder (pulverized with argon or other inert gas). The capsules are then heated to 2000 bar (approximately
29000psi), 4000 bar (approx. 58000psi), 6000 bar (approx. 87000psi) and 8000 bar (approx.
Cold isostatic compression was performed at 116,000 psi).

Wrinkles appeared on the surface of the four capsules filled with irregularly shaped powder. On the other hand, in contrast, capsules filled with spherical powder did not show any defects. Therefore, tests have shown that when performing cold isostatic pressing to achieve a density of 80% or more, the use of spherical powder is an essential requirement if wrinkling is to be avoided. This gives it a high apparent density.

Figure 1 shows the ratio of the density when compressing inert gas fine powder (solid line) and the density when compressing water fine powder (dotted line) to cold isostatic hydrostatic compression force, respectively. 80°C at considerably lower pressures using powders atomized by inert gas.
% or more can be achieved.

FIG. 2 is a cross-sectional view of one embodiment of the final product, showing a tube 1 surrounded by a thin wall 2 of nickel.

[Brief explanation of the drawing]

Figure 1 shows the relationship between compression force and compaction density when inert gas fine powder and water fine powder are compressed by cold isostatic hydrostatic compression force, and Figure 2 shows an example of the final product. FIG. 1...tube, 2...capsule wall.

Claims (1)

[Claims] 1. A capsule filled with stainless steel powder, wherein a blank is manufactured by applying cold isostatic pressure to the capsule, and a stainless steel pipe is manufactured from this blank by an extrusion method. In this method, an annular metal container made of a ductile metal sheet and having a wall thickness of 0.1 to 5 mm and not more than 5% of the outer diameter before extrusion is substantially atomized by at least a large part of the inert gas atomization. Diameter is 1mm
A capsule for manufacturing steel pipes, which is obtained by filling and enclosing stainless steel powder processed into spherical particles as shown below at a density of 60 to 70% of the theoretical density. 2. A method for manufacturing a capsule filled with stainless steel powder, which comprises applying cold isostatic pressure to the capsule to manufacture a blank, and manufacturing a stainless steel pipe from this blank by an extrusion method. In this method, an annular metal container made of a ductile metal sheet and having a wall thickness of 0.1 to 5 mm and not more than 5% of the outer diameter before extrusion is substantially atomized by at least a large part of the inert gas atomization. Fill the container with stainless steel powder processed into spherical particles with a diameter of 1 mm or less, apply vibration to the powder, increase the density of the powder to 60 to 70% of the theoretical density, and then seal the container. A method for manufacturing capsules in steel pipe manufacturing, characterized by: