JPS5983744A - Shape memory alloy - Google Patents

Abstract

PURPOSE:To provide an Fe-Mn type shape memory alloy improved in shape memory effect with a reduced Mn-amount, by compounding specific amounts of C, Si, Mn and sol Al as base components. CONSTITUTION:A shape memory alloy comprises, on the wt. basis 0.1-0.35% C, 0.5% or less Si, 8.0-15.0% Mn, 0.01-0.06% sol Al, according to necessity, further one or more of 1.0% or less Ni and 1.0% or less Cr and the remainder Fe and inevitable impurities. By this alloy composition, excellent shape memory effect is obtained with a reduced Mn-amount. The shape memory effect of this alloy means that only a part of plastic deformation stress applied at an Ms point or less returns to the shape prior to plastic deformation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to shape memory alloys, ie alloys having a shape memory effect.

As is already well known, the operations of fixing, tightening, joining and repairing mechanical elements and structural members are important basic operations in industrial technology. The use of various welding techniques has been put into practical use.

In response to various demands such as the appearance of new materials and use under more severe conditions, technological sophistication is required even in the field of such basic industrial operations.

By the way, when tightening using conventional screws, bolts, etc., loosening after tightening may become a problem, and in order to prevent such loosening after tightening, it is necessary to apply a large tightening force in advance. Unless you add it or use other special methods, you will not be able to fully prevent loosening. In order to prevent loosening to a high degree, highly advanced construction techniques are required.

Furthermore, joining and repairing pipes together is often accomplished by welding or screwing. However, when welding is used, there are always parts that are affected by heat, so in order to join and repair pipes without degrading the performance of those parts, various ingenuity is required in terms of materials and construction. On the other hand, in order to withstand high pressure inside the pipe, threaded joints require a variety of attention to detail, such as the shape of the thread and the thread cutting process, as well as a high level of skill.

Furthermore, regarding repairs on the seabed, 'ts
In order to deal with the above-mentioned problems in manufacturing the structure, even more advanced technology is required because the requirements for internal sealability and Ili, I correctness are quite strict. Conventionally, attempts have been proposed to utilize the shape memory properties of composite materials themselves.

However, most of the conventional shape memory alloys are non-ferrous alloys. Especially Ti-Ni, Cu-Zn-Al
However, all of these alloys are more expensive to manufacture than ordinary steel, and it is difficult to obtain a good shape memory effect unless careful attention is paid to the manufacturing method. Therefore, it cannot be said to be practical.

On the other hand, Fe-Δb is an iron-based shape memory alloy.

The Fe-Ni, Fe-Pt, Fe-Pd series and type 304 stainless steel are well known.

Among these, the Fe-Mn system is the cheapest, so
Several shape memory alloys using this system have been reported.
9-9 (1975), 941-948, JP-A-1987-
76043, and JP-A-55-73846).

However, in these cases, the Mn content is too high to obtain the required shape memory effect, and they cannot be said to be cheaper than ordinary steel. From the viewpoint of manufacturing cost, it is preferable that the amount of Mn be lower.

In order to solve the above-mentioned problems of the conventional technology, the present inventors have developed a screw,
? In order to utilize shape memory alloys for tightening and fixing bolts, joining and repairing pipes, we have been researching for many years on the development of shape memory alloys that have a lower Mn content than conventional shape memory steels and are actually closer to common steel types. We have discovered a practical shape memory alloy with a low Mn content that is suitable for the above-mentioned uses, and completed the present invention.

Here, the present invention has a weight ratio of C: 0.1 to 0.35.
φ or less, Si: o, s% or less, Mn: 8.0 to 1
5.0%, Sol, AI: 0.0 i ~ 0.06
%, further necessary Nj: 1.0% or less and Cr
: It is a shape memory alloy characterized by consisting of 1.0% v or less of 1st or 2nd type, balance Fe and unavoidable impurities.

Note that the shape memory alloy according to the present invention refers to an alloy that exhibits shape memory power, and the shape memory effect of the invention herein refers to the following:
This does not refer to the conventional general shape memory effect in which the plastic deformation strain that has increased by 7711 below the Ms point completely returns to the shape before plastic deformation when it is heated to the Ac1 point or higher and then cooled to room temperature, but below the Ms point. This means that only a portion of the plastic deformation strain applied returns to the shape before plastic deformation, and does not mean that the plastic deformation strain completely returns to the shape before plastic deformation. In the present invention, this amount of restoration and restoring force due to the so-called incomplete shape memory effect are utilized.

The reason why the alloy composition is limited as described above in the present invention is as follows.

Carbon: If carbon exceeds 0.35%, Ms A will be below room temperature, and sufficient shape memory effect will not be obtained even if cold worked at room temperature. In the present invention, carbon is 0.3%.
5% or less. Or, if it is less than 0.10, a sufficient shape memory effect cannot be obtained.

Silicon (Si): If the silicon content exceeds 0.005%, the Ms point will be below room temperature, and even if cold working is applied at room temperature, a sufficient effect will not be obtained. Therefore, in the present invention, the silicon content is 0.5% or less. do.

Manganese (Ivin): If manganese is less than 8.0φ, the formation of ε martensite, which is effective for expressing the shape memory effect, is insufficient, and a sufficient effect cannot be obtained. If it exceeds the Ms point, it will be below room temperature.
Even if the blade is cold worked at room temperature, a sufficient shape memory effect cannot be obtained.

Preferably 9-11% 2. Soluble aluminum (Sol, A1): Sol, A1
If it is less than 0.01%, the deoxidizing effect will be insufficient, but if it exceeds 0.06%, the toughness will deteriorate,
Since the required mechanical properties cannot be obtained, in the present invention, Sol,
AI OJ shall be 1 to 0.06%.

Nickel (Ni) and Chromium (Cr): In the present invention, if desired, at least one of nickel and chromium may be added in an amount of 1.0% or less each to further improve mechanical properties. However, each 1.0%
If it exceeds 1.0%, the Ms point will be below room temperature, and even if cold working is applied at room temperature, a sufficient effect will not be obtained, so the upper limit for each is set at 1.0%.

As is clear from what has already been said, for a practical shape memory alloy, the Ms point must first be above room temperature, so that plastic deformation below the Ms point can be applied at room temperature. This makes manufacturing extremely simple. Furthermore, it is also required that the Ac1 point is not too high. This is because it becomes possible to change the shape without requiring large-scale heating equipment.

Hereinafter, the present invention will be further explained by examples.

It should be noted that these Examples are shown merely for illustrative purposes and are not intended to limit the present invention.

Example: For 13 types of steel having each steel composition shown in Table 1, a steel ingot obtained by high-frequency melting was heated to 1150°C and rolled into a steel plate with a ridge thickness of 5 mm, and then air-cooled to room temperature. , again 100
It was heated to 0°C and subjected to a hardening treatment by water cooling.

A plate-shaped tensile test piece with a thickness of 3 mm x width of 20 mm x length of 160 mm was machined from the steel plate obtained in this way, and after being subjected to tensile deformation of 10% or less at room temperature, an Ac1 point was obtained. After reheating as above, it was cooled to room temperature.

Furthermore, the recovery rate of the length of the test piece was measured by measuring the length of the test piece before and after reheating.

These results are also shown in Table 1. The alloy of the present invention clearly has a greater shape memory effect than the comparative alloys, with a recovery rate of 2φ or more. It can be seen that it can be applied to tightening delts, joining pipes, repairing pipes, etc.

Such excellent shape memory effect (restorability) in the present invention
Although the mechanism by which this is obtained is not necessarily clear, it can be explained as follows. That is, in the alloy of the present invention, Fe-C-St-Mn-AI
In the system, it is considered that by adding C, ε martensite can be sufficiently generated below the Ms point, even without adding as much Mn as in conventional alloys. On the other hand, during cold working below the Ms point, part of the plastic deformation strain is caused by the ε martensite t formed as described above.
Or, it is thought that deformation is caused by fine twins generated during quenching, which are not dependent on the lattice.

Therefore, when reheating, this deformation is reversely transformed into the matrix lattice at the Ac4 point or higher, and the shape of the material is restored to its original shape before plastic deformation! be.

As described above, according to the present invention, the Mn
An excellent shape memory effect of, for example, 2% or more can be obtained with a low n content and a composition close to that of general steel materials, and the effects of the present invention from a practical standpoint are remarkable. I understand.

Table 1 Note-1) *: Outside the scope of the present invention However, Ll: Gauge distance before heating t2: Distance between animal points after heating

Claims (2)

[Claims] (1) In weight%, c: o, i~0.35%, Si:
0.5% or less, Mn: 8.0-15.0%, S
ol, Al: 0. (11~0.06%, balance Fe
and unavoidable impurities. (2) Overlapping chip, C: 0.1-0.35%, Si: 0
．． 5% or less, Mn: 8.0%-15.0%, So
l. AI: 0.01 to 0.06, Ni: 1.0 or less, and Cr: 1. ．． A shape memory alloy comprising 0% or less of type 1 or type 2, the balance being Fe and unavoidable impurities.