JP2001082642A - Coupler for ferrous shape memory alloy mede pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably provide a ferrous shape memory alloy made pipe coupling having more excellent shape memory characteristics, especially having a high inside diameter shrinkage percentage. SOLUTION: This coupler for a ferrous shape memory alloy made pipe is manufactured under a centrifugal casting method, and it is favorable that prismatic crystal occupies an area of not less than 50% and the length direction of prismatic crystal occupying the area of not less than 50% matches with the direction toward a center of a cylinder within ±15 degrees.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe joint made of an iron-based shape memory alloy having a high inner diameter shrinkage.

[0002]

2. Description of the Related Art Generally, a pipe joint made of a shape memory alloy is prepared by preparing a cylinder of a shape memory alloy having an inner diameter slightly smaller than an outer diameter of a mating pipe to be fastened, and expanding the inner diameter of the cylinder at room temperature. After expanding the pipe so that it can be inserted, insert a pipe into this joint from both sides and heat it to an appropriate temperature, and the force to shrink the inner diameter of the cylinder made of shape memory alloy to return to the small diameter state before the expansion Is used to fasten the pipe. Therefore, in order to obtain high fastening strength, it is expected that the inner diameter shrinkage rate of the cylinder during heating is high.

[0003] In recent years, iron-based shape memory alloys that are advantageous in terms of cost and have good workability have been tried to be applied in various fields such as pipe joints.
Usually, when manufacturing a pipe joint made of an iron-based shape memory alloy, a steel slab of a desired component is hot-rolled into a sheet material, which is formed into a cylindrical shape, welded, and then subjected to a heat treatment to perform a cold treatment. The joints have been manufactured by expanding the diameter or by hot rolling to obtain a rod material, and through a boring process, a heat treatment, and a cold expansion step.

In the conventional manufacturing method which required such a hot working step, it was extremely difficult to obtain a fastening member of a complicated shape excellent in design, in addition to restrictions on the material. Therefore, the present inventors have developed a method of manufacturing a cast member made of an iron-based shape memory alloy that can be used as a product as cast without going through a hot working step, and have previously filed an application (Japanese Unexamined Patent Application Publication No. No. 280061). The invention of the prior application intends to improve the shape memory performance of the cylindrical member by adjusting the cooling rate after casting to be within a certain range.

[0005]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open No. 10-2 is disclosed.
The invention disclosed in Japanese Patent No. 80061 was found to reverse the concept of a method of manufacturing a cast member made of an iron-based shape memory alloy, but this invention was limited to a pipe joint made of an iron-based shape memory alloy. As a result, it has become clear from further experimental studies by the present inventors that there is still room for further improvement in shape memory properties, particularly in terms of inner diameter shrinkage.

In other words, the present inventors have demonstrated that the metal structure of the cylindrical member, which has not been known at all in the prior or prior inventions, exhibits more excellent shape memory characteristics and is industrially large. It has been found that a pipe joint made of an iron-based shape memory alloy having a meaning can be easily obtained, and the present invention has been completed. The object of the present invention is to
An object of the present invention is to easily and stably obtain a pipe joint made of an iron-based shape memory alloy having better shape memory characteristics, particularly a high inner diameter shrinkage, by specifying a macrostructure of a material.

[0007]

According to a first aspect of the present invention, there is provided a pipe joint made of an iron-based shape memory alloy manufactured by a centrifugal casting method. It is characterized by being manufactured by centrifugal casting in which the columnar crystals occupy an area of 50% or more in the structure. Also,
In the pipe joint made of an iron-based shape memory alloy according to claim 2 of the present invention, the length direction of the columnar crystal in the macrostructure in the cross section is:
Columnar crystals that coincide within ± 15 degrees with respect to the direction toward the center of the cylinder occupy an area of 50% or more. Further, it is desirable that the above-mentioned pipe joint is repeatedly subjected to diameter expansion and heating (claim 3). In order to further improve the inner diameter shrinkage, the columnar crystal is preferably 70% or more. It preferably occupies the area (claim 4).

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings. First, a description will be given from the background of finding that the inner diameter shrinkage ratio of an iron-based shape memory alloy pipe joint greatly depends on the macrostructure of an iron-based shape memory alloy cylinder.

The shrinkage of the inner diameter of the iron-based shape memory alloy cylinder is
The type of material (chemical composition, etc.) and the degree of diameter expansion performed in advance,
It changes to some extent depending on the heating temperature, the presence or absence of the diameter expansion and the repeated heating (called training), and the like.
Therefore, in order to obtain a joint having a large inner diameter shrinkage ratio and good performance, it is natural that the material, the diameter expansion ratio, and the heating temperature must be selected so as to be optimal. However, in the case of an iron-based pipe joint made of a shape memory alloy, it is a fact that the inner diameter shrinkage rate (shape recovery performance of the shape memory alloy) is not always constant only by optimizing these conditions. This is shown in FIG.

FIG. 1 shows that the components of the material are constant (28% Mn-
6% Si-5% Cr-Fe), and form a cylindrical shape directly by centrifugal casting or rolled and hot-rolled sheet material to form a cylindrical solution at an appropriate temperature. After heat treatment (the shape at this stage is memorized), the inner diameter is expanded at various expansion ratios (horizontal axis), and then the degree of the shape memory effect obtained by heating to 600 ° C. It is indicated by an index called rate (vertical axis).

[0011] The results show that within the range of the same dimensions and manufactured in the same process, although there is a tendency that the inner diameter contraction rate on the vertical axis is influenced by the inner diameter expansion rate on the horizontal axis, for example, 10%.
It is clear that, for a centrifugally cast material of 0A, etc., a considerable difference occurs in the inner diameter shrinkage rate even when the diameter expansion rate is almost the same. The same can be said for the 200A, 250A, and 300A centrifugally cast materials. It is natural that a pipe joint using such a material having a variation has unstable performance such as joint strength and lacks reliability. Therefore, it is needless to say that a clear understanding of the conditions under which a high inner diameter shrinkage ratio can be stably obtained is a precondition for putting this material into practical use as a pipe joint.
Then, the inventors examined what conditions caused the variation in FIG. 1. As a result, it was found that the degree of inner diameter shrinkage depends largely on the macrostructure of the iron-based shape memory alloy cylinder.

Here, the macro structure means mainly information on "crystal shape" which can be grasped by direct visual observation or observation with a microscope at a low magnification of several times at most, out of the crystal structure constituting the material. . Needless to say, the crystal structure of the metal can be changed from an extremely fine level of structure that can be identified only with a high-magnification electron microscope to a level that can be distinguished by high-magnification observation with an optical microscope. It has a multi-layered structure such as an organizational structure to be identified. Of these, the macroscopic structure seen with the naked eye or an extremely low magnification optical microscope is determined by polishing the cross section of the material to a certain extent and then applying an appropriate etchant to observe the crystal shape. . Although it may be visible only by polishing, proper corrosion makes identification easier. Usually, in the case of an iron-based shape memory alloy, a commonly used solution such as “2-4% nitric acid + methanol” or “nitric acid + hydrochloric acid (2-5% in total) + water” can be used as a corrosive liquid. is there.

The important crystalline form among the factors identified as the macrostructure is not limited to the shape but also has the following viewpoint. Generally, a solid metal solidified from a molten state is composed of small crystal grains, and the crystals formed at that time are classified into two different types, "free crystals" and "columnar crystals" depending on the conditions at the time of solidification. A free crystal refers to a crystal having a polygonal shape that is almost spherical (FIG. 2 (a)), and a columnar crystal having a crystal elongated in a specific direction (FIG. 2 (b)). The former base material composed of free crystals is relatively isotropic in various properties in any direction, whereas the latter base material mainly composed of columnar crystals has a columnar shape. In many cases, it has a property (anisotropic) that shows different performance depending on the direction of the characteristic evaluation with respect to the crystal direction. That is,
The difference in crystal shape has a considerable effect on the properties of the base material.

The distinction between these two types of crystals can be easily made by observing the macrostructure. It seems natural that crystals are free crystals because they basically tend to have a shape close to a sphere in order to minimize the surface area. However, during the process of solidification starting from the actual molten state, it is usual that free crystals and columnar crystals are mixed at a certain ratio due to the influence of temperature gradient in a specific direction and uneven cooling. Among the causes for the formation of columnar crystals, crystal growth is not completely isotropic, and in particular, a preferential orientation with a high growth rate (in the case of the material targeted by the present invention, metallurgy <1
00> direction), and the characteristic characteristic of the crystal, which tends to elongate in that direction, greatly contributes.
Furthermore, when crystal nuclei occur at certain positions during solidification,
It is normal for a large number of crystal nuclei to be generated at the same time around them, so that each of these crystal nuclei interferes with each other when they grow, resulting in suppression of mutual growth in a specific direction. I do. The tendency to grow in this specific direction and the tendency of the co-generated crystal nuclei to mutually restrain the growth of each other act to form columnar crystals having a unique shape.

The material after solidification is generally heated to a high temperature or subjected to a process such as rolling in a heated state to finish the product. During heating or processing to a high temperature, the crystal is altered, and both free crystals and columnar crystals are reorganized into new isotropic crystals. In other words, columnar crystals are most often found in products after they have solidified from the molten state and have gone through a process such as high-temperature and long-time heating and hot working. Generally, there are not so many columnar crystals remaining after passing through.

When the result of FIG. 1 was examined in detail based on such metallurgical findings, it was found that the difference in the inner diameter shrinkage ratio corresponds to each macrostructure.
First, the area ratio occupied by columnar crystals was measured by developing a macrostructure at the cross section (cylinder end face) of an iron-based shape memory alloy cylinder giving each measurement point (in practice, these measurements were performed by solution heat treatment of the cylinder). (Ie, before the diameter expansion). When the results were made to correspond to the diameter expansion and the inner diameter shrinkage rate after heating at 600 ° C., it was found that the cylinder having a higher columnar crystal ratio was located in a portion having a higher inner diameter shrinkage rate as a whole. Conversely, a cylinder having a columnar crystal ratio of 0%, such as a cylinder obtained by rolling and welding a sheet material, has a significantly lower inner diameter shrinkage ratio.

FIG. 3 clearly shows this tendency.
In this figure, only those having a diameter expansion ratio within a certain range (7.35 to 7.5%) are picked up from the results shown in FIG. 1 and the relationship between the columnar crystal ratio and the inner diameter shrinkage ratio is obtained. It is shown. From this figure, it can be seen that the inner diameter shrinkage ratio increases as the columnar crystal ratio increases. Assuming that the inner diameter shrinkage rate of 2.5% or more is practically desirable, a columnar crystal ratio of 50% or more is required. It is more preferable that high performance can be stably ensured even if the influence of other conditions is adversely affected.
It is considered effective to have a columnar crystal ratio of 0% or more.

Incidentally, the shape memory alloy cylinder used for this investigation is manufactured by the following method. The group using the cylinder obtained by rolling and welding a sheet material obtained by hot rolling an ingot and further performing a heat treatment is a group indicated by "sheet winding / welding material" in the figure. In addition, a group obtained by directly solidifying into a cylindrical shape by centrifugal casting, manufacturing a cylindrical shape without going through a hot working process, and cutting the inner surface by an appropriate thickness to obtain a heat-treated cylinder ("Centrifugal Casting "). In the former, the columnar crystal ratio is basically zero. On the other hand, the columnar crystal ratio of the latter, along with how much columnar crystals were present in the as-cast state and how it changed due to subsequent heat treatment, was taken from which part of the entire casting thickness of the cylinder. It depends on what you have. This is because, in the crystal of the centrifugally cast material, free crystals generally tend to appear in the outermost layer and the inner layer, and columnar crystals tend to be formed in the middle. The specific distribution of free crystals and columnar crystals depends on the inner surface properties of the mold used for centrifugal casting, the type of coating material, the coating thickness and uniformity, the preheating temperature of the mold, the injection temperature of molten steel. In the solidification process, the rotational speed of the metal mold and the rotational center misalignment, the presence or absence of uneven rotation,
It is thought that it is determined by the influence of casting conditions such as forced cooling of the mold.

In the course of the above examination, the lower structure in the columnar crystal on the cross section of the cylinder made by centrifugal casting was also investigated. When the above-mentioned corrosion is performed, it is possible to confirm a lower structure in the columnar crystal, which shows a trace of the crystal growing in a dendritic manner. Among them, running in the longitudinal direction in the central part of the crystal is the main trunk formed at the earliest stage of solidification (an example is indicated by [P] in an enlarged view of FIG. 2B). Also called). Since the direction of the main trunk substantially coincides with the length direction of the columnar crystal, the direction of the main trunk is hereinafter referred to as the length direction of the columnar crystal. It was confirmed that the length direction of the columnar crystals examined in the centrifugally cast material was approximately within ± 15 degrees from the circumferential position where the crystals exist to the direction toward the center of the cylinder. did it.

The reason that the higher the columnar crystal ratio obtained in FIG. 3 is, the more excellent the shape recovery performance is, is considered as follows. It is natural that the appearance of the shape memory effect is related to the crystal orientation, considering the mechanism of the appearance of this effect. That is, after the shape memory processing, the crystal is deformed in a specific direction (<110> direction, more precisely <11
0> direction, it is shifted by about 4 degrees.
10> direction), there is a remarkable anisotropy that a greater shape recovery is obtained than deformation in other directions. The crystal direction which is advantageous for exhibiting the shape memory effect is orthogonal to the preferential growth direction (<100> direction) of the columnar crystal.
Therefore, if the columnar crystal grows uniformly in the thickness direction of the joint cylinder, it deforms in the crystal direction, which is advantageous for the shape memory effect, during the process of expanding the cylinder in the circumferential direction, which is called expanding the diameter. Will be realized inevitably. This is considered to be a cause of obtaining a shape memory performance higher than the average value in a cylinder having many columnar crystals. On the other hand, a free crystal shows only an average performance because the direction of the crystal is random, so it is considered that the columnar crystal shows superior performance when both are compared.

The centrifugal casting method is a casting method in which a molten iron material is injected into a metal mold and solidified while being rotated at a high speed with a metal mold as described above. In this case, since the solidification proceeds inward from the contact surface with the mold, the columnar crystal also grows in this direction. If the casting conditions are appropriate, the ratio of columnar crystals will increase and the direction will be correctly aligned with the center of the cylinder. Therefore, if the joint cylinder manufactured by centrifugal casting is manufactured so as to have a high columnar crystal ratio, it can have excellent shape memory performance.

On the other hand, casting methods that do not rely on centrifugal casting include, for example, sand casting and lost wax. In the centrifugal casting method, molten steel is rapidly cooled only from the outside where it comes into contact with the mold.In the sand casting method and lost wax method, however, the molten steel is only the outer surface in the low heat conduction type of sand or wax. However, the inner surface is also cooled relatively slowly in contact with the mold. For this reason, the direction of the columnar crystals at the time of solidification tends to be difficult to become a uniform shape from the outside to the inside with a uniform wall thickness as in the case of centrifugal casting.

It is obvious from the above that the effect of improving the shape memory performance cannot be expected if the direction of the columnar crystal deviates from the desired direction even if it is a columnar crystal. Therefore, in the case of such a casting method, only columnar crystals grown toward the center of the cylinder need to be considered.
In this case, focusing on the columnar crystal whose length direction coincides with the direction toward the center of the cylinder within ± 15 degrees, it is confirmed that the relationship with the shape recovery amount is established as in the case of centrifugal casting. Was done. FIG. 4 schematically shows a macrostructure of a part of the cross section of the cylinder. Of the individual crystals surrounded by a thick line in the figure, an arrow indicating the direction of the columnar crystal (actually, the growth direction of the main trunk) is attached. The number of inclinations of the direction of the arrow with respect to the direction from the point where each crystal is located toward the center of the cylinder was measured, and the portion that matched within ± 15 degrees was indicated by oblique lines. In this case, the ratio of the area of the columnar crystals in the hatched portion on the average in the cross section is an index having meaning.

The direction of the columnar crystal is determined by the direction in which the macrostructure is observed in the cross section of the cylinder, and there is no particular restriction on the vertical section. A columnar crystal inclined at an angle of 15 degrees or more in a cross section also warps from the circumferential direction in a direction advantageous for the shape memory effect manifested in a direction perpendicular to the length direction. On the other hand, in the case of the columnar crystals which are inclined in the longitudinal section, the perpendicular direction does not deviate from the circumferential direction, so that there is no particular problem.

After the solution heat treatment, including the sand casting material and the lost wax casting material, the first diameter expansion (7.5%) → 600
The performance as a pipe joint was evaluated through a process including a training process of heating at 200 ° C. → second diameter expansion (5%) → heating at 300 ° C. At any time after the first diameter expansion and after the second diameter expansion, the cylinder undergoes inner diameter shrinkage due to heating. Therefore, the cylinder at any stage can be used as a pipe joint. However, in order to increase the inner diameter shrinkage ratio even slightly, the shape is once recovered by heating at 600 ° C. immediately after the first diameter expansion. By going through this process,
The principle of the training process is that the shape memory effect after the second diameter expansion can be enhanced.

That is, in this case, it is assumed that the pipe is used as a pipe joint in a state where heating up to 600 ° C. and subsequent to the second diameter expansion are performed. In order to confirm whether or not the cylinder has a pipe, the cylinder is heated independently without fastening the pipe, and the inner diameter shrinkage is measured. The columnar crystal whose longitudinal direction is within ± 15 degrees with respect to the direction toward the center of the cylinder in the cross section of the cylinder and the inner diameter shrinkage rate at the last heating at 300 ° C. FIG. 5 shows the relationship with the “area ratio”. The area ratio of columnar crystals within ± 15 degrees is determined by the method shown in FIG. 4, but by adopting this factor, the columnar crystal ratio and the shape memory effect can be expanded over a wider range than in FIG. And the relationship was confirmed. It has been shown that in order to obtain an iron-based shape memory alloy joint having excellent shape memory performance, it is effective that the columnar crystal ratio having such a direction accounts for 50% or more, preferably 70% or more. ing.

The present invention has been made based on the results of such studies. Further, the present invention contains, for example, 5% or less of C, 20 to 40% of Mn, 3.5 to 8% of Si, and if necessary, 20% or less of Cr or / and 10% or less of Ni. It can be most effectively applied to an iron-based shape memory alloy material such as Fe.

[0028]

(Example 1) Fe-Mn-Si based shape memory alloy (0.02%
C-5.92% Si-27.8% Mn-5.07% C
r) was formed into a cylindrical shape having an outer diameter of 123 mmφ, an inner diameter of 95 mmφ, and a length of 2650 mm by centrifugal casting, which was divided into lengths of 80 mm each, and then annealed at 1150 ° C. From these short cylinders, two short cylinders (the former is referred to as cylinder A and the latter as cylinder B) which are located at the farthest part from the part closest to the nozzle side during casting are selected, and the inner and outer surfaces are machined. Outside diameter 11
Finished to 7.8 mmφ and 7.5 mm thick. In this state, the end faces on both sides of the cylinder were corroded with a 3% nital solution (a mixed solution of 3% nitric acid and methanol) to reveal a macrostructure.

As a result, the columnar crystal ratio in the cylinder A was 90% and 93% on the both end faces, respectively, an average of 92%, and in the cylinder B, 43% and 37% on the both end faces, the average was 40%. Next, the inner diameter of each cylinder was increased by 7.45% at room temperature using a collet type mold, and then heated to 300 ° C. to recover the shape. The cylinder having a high columnar crystal ratio of 92% was obtained. In A, an inner diameter shrinkage rate of 3.4% was obtained,
In the cylinder B having a low columnar crystal ratio, the inner diameter shrinkage ratio was only 2.7%.

If these short cylinders made of a shape memory alloy are inserted into a pipe before being heated to 300 ° C., they function as pipe joints for fastening the pipe by contraction of the inner diameter by heating. In this case, how strongly the pipe can be fastened depends on the shrinkage ability of the joint at the time of heating, and it has been confirmed that the important shrinkage rate is controlled by the columnar crystal rate. It was also confirmed that a high columnar crystal ratio increased the shrinkage ratio.

Example 2 Fe--Mn--Si based shape memory alloy (0.02% C-6.05% Si-32.1% M
n) was obtained by the lost wax method with an outer diameter of 64.7 mmφ and an inner diameter of 5
It was manufactured in a cylindrical shape of 6.0 mmφ and 75 mm in length. After heat-treating this at 1150 ° C., the first diameter expansion of 7.6% was first performed using a mandrel, and then the shape recovery rate when heated to 600 ° C. was examined. was gotten. Next, a second diameter expansion of 5.2% was performed on the same by the mandrel diameter expansion method. In this state, a macrostructure was developed in the same manner as in Example 1, and the length direction of the columnar crystals on both end surfaces of the cylinder was ± 1 with respect to the direction toward the center of the cylinder.
When the columnar crystal ratio of those within 5 degrees was examined,
The average was 60%. In order to confirm how much the inner diameter of the obtained cylinder as a pipe joint has the ability to shrink,
When heated to 300 ° C. without being inserted into the pipe, a high inner diameter shrinkage of 3.8% was obtained, and it was recognized that the joint had sufficient performance.

Example 3 Fe--Mn--Si Shape Memory Alloy (0.01% C-6.41% Si-27.8% Mn)
-4.93% Cr) by centrifugal casting method with an outer diameter of 271.0 mm
A cylinder with an inner diameter of 217.0 mmφ was manufactured and this was
Cut to 40mm, outer diameter 241.6mmφ, inner diameter 23
Machined to 5.6 mmφ, first expanded by 7.4% by hydraulic expansion, heated to 600 ° C, and then expanded by 5.2% by hydraulic expansion. Diameter applied. The macrostructure of both end surfaces of the obtained cylinder was revealed, and the columnar crystal ratio was examined. Each of the end faces had a high columnar crystal ratio of 87% and 92% with an average of 90%. As a result of examining the inner diameter shrinkage rate by heating this to 300 ° C. without inserting it into a pipe, 3.5
% Shrinkage was confirmed.

(Comparative Example 1) Fe-Mn-Si based shape memory alloy (0.01% C-6.35% Si-27.9% Mn
-5.07% Cr) 8 mm thick hot rolled sheet at room temperature with an outer diameter of 24 mm.
It was bent into a 1.6 mmφ cylindrical shape, and a 140 mm long shape memory alloy cylinder was manufactured by TIG welding. This cylinder was expanded in the same manner as in Example 3 to a first enlarged diameter (7.5%),
Heating was performed at 600 ° C. and a second diameter expansion (5.2%) was performed to reveal macrostructures on both end surfaces of the obtained cylinder. However, since the material was a hot-rolled thick plate, no columnar crystals that would have been produced at the time of casting remained, and the columnar crystal ratio was 0%. The cylinder after the second diameter expansion can be used as a joint for a pipe of 250 A size.
When the inner diameter shrinkage ratio was examined by heating to, only a shrinkage ratio of 2.7% was obtained.

[0034]

In order to be able to use the iron-based shape memory alloy stably as a pipe joint, it is required that the inner diameter shrinkage ability by heating is large. The joint is designed to provide a stable supply of high-performance pipe joints that are practically advantageous by setting a certain limit on the columnar crystal ratio in the macrostructure. Is extremely large.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between an inner diameter expansion ratio and an inner diameter shrinkage ratio in centrifugally cast materials and sheet-winding / welding materials of iron-based shape memory alloy cylinders of various sizes.

FIGS. 2A and 2B are schematic diagrams showing a morphology of a crystal in a cross-sectional macrostructure of a cylinder made of an iron-based shape memory alloy, where FIG.
(B) shows a columnar crystal.

FIG. 3 is a view showing the relationship between the area ratio of columnar crystals and the shrinkage ratio of the inner diameter, which are taken out of FIG.

FIG. 4 is a diagram schematically showing a part of a macrostructure of a cross section of a cylinder made of an iron-based shape memory alloy, particularly focusing on an angle formed between a columnar crystal and a direction toward a cylinder center.

FIG. 5 shows the relationship between the inner diameter shrinkage rate and the area ratio of columnar crystals (the length direction of which is within ± 15 degrees with respect to the direction toward the center of the cylinder) of various cast cylindrical materials subjected to training processing. FIG.

Continuing on the front page (72) Inventor Hiroshi Kubo 35-120 Kawachi Moto-Hasekura, Aoba-ku, Sendai-shi, Miyagi 11-204 Kawauchi Housing (72) Inventor Hiroaki Otsuka 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development In the headquarters (72) Inventor Tadakatsu Maruyama 2-3-13 M & C Building, Kanda Ogawacho, Chiyoda-ku, Tokyo F-term in Awaji Sangyo Co., Ltd. Tokyo Branch 3H013 AA02 FA01

Claims (4)

[Claims] An iron-based shape memory alloy pipe joint manufactured by a centrifugal casting method, wherein columnar crystals occupy an area of 50% or more in a macrostructure in a cross section. For pipes made of iron-based shape memory alloy. 2. In the macrostructure in the cross section, the length direction of the columnar crystal is ± 15 with respect to the direction toward the center of the cylinder.
A pipe joint made of an iron-based shape memory alloy, characterized in that the columnar crystals that coincide within a degree occupy an area of 50% or more. 3. The joint for a pipe made of an iron-based shape memory alloy according to claim 1, wherein the diameter expansion and the heating are repeatedly performed. 4. The iron-based shape memory alloy according to claim 1, wherein the columnar crystals occupy an area of 70% or more in the macrostructure in the cross section. Pipe fittings.