JPS5929082B2 - Blanks and their manufacturing methods in steel pipe manufacturing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides 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. Concerning long objects similar to.

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 can be made in a variety of ways, e.g. a) Cold compacting the powder and sintering.

b) hot compaction of the powder;

C) Fill and encapsulate the powder into capsules.

There are other methods.

This invention basically manufactures rods, pipes, etc. by the improved method of C) above.

That is, the powder is encapsulated in capsules and the capsules are subsequently extruded in one or more stages.

(Note that the term "capsule" may refer not only to the container but also to the enclosed powder.

) For economic and technical reasons, it is necessary for the encapsulant to be 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 wall thickness is 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 mechanically cold compress the capsules after encapsulating the powder therein.

However, with this technique, the results are unsatisfactory, especially when the length to diameter ratio of the capsule is greater than 1, due to the frictional forces between the capsule and the mechanical tools used for cold compaction. isn't it.

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, inter alia, to unfavorable conditions during heating prior to extrusion.

The present invention solves the aforementioned problem in a completely different way, by producing elongated objects of rods, tubes and other similar shapes, preferably of stainless steel material, having a very regular structure, in particular seamless steel tubes. can be provided.

According to the present invention, this problem is solved by starting with a powder consisting of substantially spherical particles, at least in large part, and first encapsulating this powder in a ductile metal container to form a capsule (first intermediate product). , the capsules are then compressed into blanks (
The solution is to form a second intermediate product), heat the blank thus obtained and form the object by single-stage or multi-stage extrusion.

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

To manufacture rods, tubes, etc. according to the invention, thin-walled capsules of highly ductile materials such as carbon steel, nickel, etc. are used.

According to the invention, at least a large part of the capsule is constructed of thin walls, preferably of highly ductile metal plates.

Capsule wall thickness is maximum 5% of capsule outer diameter before extrusion
, preferably 3% or less, particularly preferably 1
% or less.

A large number applies when the capsule diameter is small, and a small number applies when the capsule diameter is large.

The wall thickness of the capsule is preferably between 0.1 and 57 IL1L, more advantageously between 2.0 and 3 cages.

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

The density of the powder filled into the capsules is preferably increased to about 60 to 70% of the theoretical density (density as a solid) by a vibration method or an ultrasonic vibration method before isostatically compressing the capsules.

The powder-filled capsules have a pressure of at least 1500 bar (approximately 21800 psi), preferably at least 5
000 bar (approximately 72,500 psi) of hydrostatic pressure 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 rods, pipes, etc. according to this invention 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 possible.

To obtain satisfactory results, it is important that the powder has a low oxygen content, which is achieved by using a spherical powder atomized with 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 introduced into a high ductility capsule of a shape suitable for the required intermediate or final product and is given a density of 60-70% of the theoretical density, i.e. the density as a solid, by the vibration method.

When making compounds, various metals are used in powder form.

The powder is introduced into a capsule divided by one or more compartments.

Such partition walls may be made of plastic, steel or similar materials.

After the powder has been filled and vibrated, the walls are removed and it is encapsulated using (or without) vacuum techniques into capsules made of highly ductile material.

Thereafter, at least 15 ml of powder with encapsulated powder
00 bar, preferably 60-70% of the theoretical density by cold isostatic pressing at a pressure of e.g. 5000 bar.
The density of is 80 to the theoretical density, depending on the pressure used.
It increases to 90%.

Due to the very high initial density of the powder, the length to diameter ratio is greater than 1 (e.g. 4) and despite the fact that thin-walled capsules are used, during the cold compaction and extrusion process There are no wrinkles in the capsule.

As already mentioned, the use of thin-walled capsules 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 numerical 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, whereas 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 encapsulant material is then drawn off as a very thin film.

As the film emerges from the extrusion press, it oxidizes in the air and partially decomposes.

Residual encapsulant material is removed by subsequent annealing, nitric acid cleaning or sand blasting.

The tube etc. is then processed in the usual manner.

Since the rods, pipes, etc. of this invention are manufactured as described above, they have an extremely uniform structure 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 may be made of a material with a high quality surface finish, and the extruded tube or the like may be provided with a permanent coating of the material of the capsule.

The thickness of the surface coating or baking can be predetermined by appropriate selection of the wall thickness of the capsule.

Highly ductile materials are particularly suitable for creating such surface layers.

Hereinafter, the present invention will be described in detail with reference to examples.

As Example 1, particle size 0.6 micronized with argon
Copper powder, which is spherical and has a low total oxygen content, was filled into a tubular capsule and vibrated.

The capsule is a ring with an external diameter of approximately 140 mm, made of steel with a low carbon content, a wall thickness of 3 m and a length of 550 m7IL.
Met.

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 was evacuated and sealed in a known manner, after which the capsule was submerged in a liquid (water in this example) and cold isostatically compressed by applying a pressure of 5000 bar over the capsule.

The capsules shrunk and the powder density increased from about 68% to about 90% without wrinkles in the capsule 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 Example 1 was required.

Now, the blank made by the previous cold isostatic pressing was then heated to 900°C in a preheating furnace, and finally heated to 1240°C by an induction coil, and then the blank was extruded and formed into a seamless steel pipe. .

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 encapsulant was removed, but the tube was unusable.

Wrinkles created during compression can cause cracks and other material defects,
This made the tube useless.

As Example 2, a compound tube was manufactured as follows.

In a capsule made of sheet metal corresponding to Example 1 having a continuous inner tube in the center, a thin-walled tube was placed midway between the outer and inner walls of the capsule.

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 0.6 mm or less. 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.

Chromium nickel steel (Cr18
%.

The inner intermediate space was filled with spherical steel powder containing Ni (8%) while being vibrated.

After removing the intermediate wall, evacuating and sealing, the capsule was
Cold isostatic pressing was carried out at 000 bar.

The blank was then heated and formed into a seamless steel tube as described in Example 1.

The capsule material was also removed in a nitric acid bath. Histological examination of the compound tube revealed that the tissue was completely dense and 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 order to examine the necessity of compression before extrusion, the same powder and capsule material as in Example 1 were immediately heated to 1200° C. without isostatic compression and extruded into a tube as the final product.

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. be.

Meanwhile, the same powder and 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 a defect-free product.

Furthermore, in order to examine the effect of the shape of the material powder on the compressed density, four of the eight capsules were filled with irregularly shaped stainless steel powder (pulverized with water), and the remaining Four capsules were filled with regular spherical stainless steel powder (pulverized with argon or other active gas) and then the capsules were heated to 2000 bar.
000psi), 4000 bar (approx. 58000psi)
), 6000 bar (approximately 87000 psi) and 80
Cold isostatic pressing was carried out at 00 bar (approximately 116,000 psi).

Wrinkles appeared on the surface of the four capsules filled with irregularly shaped powder.

In contrast, capsules filled with spherical powder did not show any defects.

Tests have therefore 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; It gives high apparent density.

Figure 1 shows the ratio of the density when compressing inert gas fine powder (solid line) and the density when compressing this machine fine powder (dotted line) to cold isostatic hydrostatic compression force. , using powder that has been atomized by inert gas,
It can be seen that densities of over 80% are achieved at considerably lower pressures.

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

[Brief explanation of drawings]

Fig. 1 shows the relationship between compression force and compaction density when inert gas fine powder and this machine-pulverized powder are compressed by cold isostatic hydrostatic compression force, and Fig. 2 shows one embodiment of the present invention. FIG. 3 is an example cross-sectional view. 1... tube, 2... capsule wall.

Claims (1)

[Scope of Claims] 1. An annular metal container made of a ductile thin metal plate and having a wall thickness of 0.1 to 5 mm and 5% or less of the outer diameter before extrusion is filled with at least a large portion of an inert gas. Stainless steel powder processed into spherical particles with a diameter of 1 mm or less by atomization, with a theoretical density of 60 to 70
% density, and the container containing this powder is compressed as a whole by cold isostatic pressure until the powder density reaches at least 80% of the theoretical density.
Blanks used in steel pipe manufacturing using the extrusion method. 2. An annular metal container made of a ductile metal sheet and having a wall thickness of 0.1 to 5 mm and 5% or less of the outer diameter before extrusion, at least a large part of which is substantially atomized by spraying with an inert gas. is filled with stainless steel powder processed into spherical particles with a diameter of 1 mrIL or less, and the powder is vibrated to bring the density of the powder to 60 to 70 of the theoretical density.
%, the container is sealed, and the container containing the powder is then subjected to cold isostatic pressure to compress the powder in its entirety until the density of the powder in the container reaches at least 80% of the theoretical density. Blank manufacturing method in steel pipe manufacturing using the method.