JPS61223161A - Shape memory alloy - Google Patents

Abstract

PURPOSE:To improve the shape memory effect and to reduce cost by incorporating C, Cr and Ni to an Fe-base alloy having Si and Mn as principal components so that the Mn equivalent value represented in a prescribed relational expression is obtained. CONSTITUTION:The shape memory alloy consists of 0.4-2% Si, 10-28% Mn, >=1 kind among C, Cr and Ni, and the balance Fe, in which the quantity of C, Cr and Ni having a function of increasing epsilon-martensite formation is regulated so that the Mn equivalent represented in [Mn equivalent (%) = Mn(%)+9C(%)+ Cr(%)/2+Ni(%)/2] is 21-28%.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> This invention relates to an iron-based shape memory alloy that stably exhibits a good shape memory effect.

Traditionally, basic operations such as fixing, tightening, joining, or repairing one mechanical part or various structural members have been... It occupies an extremely important position regardless of the field of business, and today, concrete methods include the use of screws such as bolts and nuts, the use of rivets, keys, bottles, etc. Various techniques, such as the use of welding techniques, are employed as appropriate depending on the purpose.

However, in these basic industrial fields, with the advent of new materials and the demand for use in harsher environments and construction under adverse conditions, etc.

There is a growing demand for further technological sophistication.

For example, when fastening using screws, loosening after tightening often becomes a problem. In order to prevent such tightening from loosening later on, it is necessary to apply force in advance for considerably large tightening, or to apply special means such as using a lock nut or split bottle. Countermeasures are necessary, but highly sophisticated construction techniques are required to prevent loosening with higher precision.

By the way, in the development of underground resources, seabed resources, etc., joining and repairing pipes is considered to be an extremely important technical matter.

Connections and repairs between pipes are often carried out using welding or screw connections, but when welding joints are used, there is always a part of the pipe body that is affected by heat, so In order to achieve this goal without compromising performance, it was necessary to make special efforts in terms of materials and construction. On the other hand, when using threaded joints, in order to withstand high pressure inside the pipe, not only the shape of the thread, but also careful attention to the 1 m section during thread cutting and advanced techniques are required. Furthermore, in order to repair pipes on the ocean floor, the requirements for sealing and pressure resistance inside the pipes are quite strict, so even more advanced technology was required in this respect.

For this reason, in order to deal with the above-mentioned problems that occur when manufacturing various structures, efforts are being made to utilize shape-memory alloys in the structure materials themselves, or in their joints and joining jigs. Attempts are beginning to be made.

<Prior art and its problems> At present, a large number of alloys having shape memory properties, so-called shape memory alloys, are known, mainly Ti-Ni alloys and Cu-Zn-Ant alloys. but.

Most of them are non-ferrous alloys. Most of these alloys are more expensive to manufacture than ordinary steel, and if careful attention is not taken during manufacture, good shape memory effects cannot be obtained due to the fact that most of these alloys are internal cone. There were many problems when it came to practical use in large structures and their parts.

Among these, iron-based shape memory alloys that are expected to be applied to large structures include Fe-Mn-based alloys,
Fe-Ni alloys, Fe-Pt alloys, Fe-Pd alloys, and 18-8 austenitic stainless steels are known. Since Fe-excited alloys are the cheapest among these, reports on shape memory alloys belonging to this type have become prominent.

For example, re-Mn alloy C in which the Mn content is regulated to 15.9 to 30.0% by weight (JP-A-55-73846)
, the base metal content is 12.2 to 2 in balance with other alloying elements.
Fe-Mn-Si, N regulated to 0.59% by mass
i, Cr alloy C JP-A-55-76043),
Alternatively, Fe-
This is the C--Mn alloy (Japanese Unexamined Patent Publication No. 55-91956).

However, the shape memory effect of the above alloy system (Fe-Mn system) is extremely small (the amount of expansion and contraction due to heating and cooling is at most twice that of normal steel), making it extremely unsatisfactory for use as a shape memory alloy. There was only one. Because F
The shape memory effect of e-Mn alloys is similar to that of Ni-Ti alloys and C
Unlike thermoelastic martensitic alloys such as U-based alloys, e-
It is said that this is caused by the formation of martensite, and therefore it is difficult to obtain the so-called "complete shape memory effect" in which the shape is completely restored to the shape before plastic deformation.Therefore, there is no other choice than C: Therefore.

At present, there has been a long-awaited expectation for the appearance of an iron alloy having an even more refined shape memory effect, backed by means for stably obtaining a good shape memory effect.

However, the mechanism of the shape memory effect in Fe-Mn alloys as described above is not necessarily clear, but it is interpreted in detail as follows.

That is, when cold processing is performed, e
- Martensite is generated and processing strain is stored as C-martensite. Next, what about the alloy in this state? When heated above the A01 point, the plastic strain during cold working is reversibly released during reverse transformation from C-martensite to austenite, and as a result, a shape memory effect is exhibited. Therefore, ε-martensite is likely to be generated during cold working, and the lattice distortion due to working is C.
It is expected that an alloy that suppresses the generation of dislocations will have a better shape memory effect, but in conventional alloys, the formation of ε-martensite during this processing is not sufficient, and most of the plastic strain It is thought that a good shape memory effect could not be obtained because these were introduced as dislocations.

Means for Solving the Problems> From the above-mentioned viewpoints, the present inventors solved the above-mentioned problems found in conventionally known iron-based shape memory alloys, and created a shape memory alloy with even better shape memory. We have conducted repeated research to create an alloy that is both effective and inexpensive.

Fe-Mn-based shape memory alloy (C, Cr and N
i, is also an element that exerts the effect of promoting the formation of 6-martensite, and by comprehensively considering these effects, the Mn equivalent expressed by the formula % formula % ( ) can be calculated as Fe-Mn
When a small amount of Sl is added to an iron alloy whose Mn content has been adjusted to a specific range higher than the Mn content of the shape memory alloy, the e-
The formation of martensite becomes extremely easy, and the shape memory effect at room temperature is significantly improved compared to conventional iron alloys.

This led us to the following knowledge.

This invention was made based on the above findings, iron alloy.

Contains Si: 0.4 to 2.0% (hereinafter, component proportions are shown on a weight basis), Mn: 10-2896, and further contains one of C, Cr, and Ni.
By configuring the chemical composition to include more than 100% of the total weight, the remainder being Fe and unavoidable impurities, and having a Mn equivalent expressed by 1 formula of 21 to 2896, it is possible to stably maintain an excellent shape memory effect. It is characterized by the fact that it can be made to perform effectively.

The shape memory effect referred to here means that plastic deformation strain applied below the rMs point completely returns to the shape before plastic deformation when it is heated above the Ac point and then cooled to room temperature.
1. This does not refer to the shape memory effect that is usually referred to (i.e., only a portion of the plastic deformation strain applied below the rMs point returns to the shape before plastic deformation). Yes, therefore.

It goes without saying that the shape memory alloy of the present invention makes use of the restoring force and amount of restoration due to the so-called "incomplete shape memory effect".

Next, the reason why the composition ratio of the alloy is numerically limited as described above in this invention will be explained.

+ (a) 3i Si component I: facilitates the formation of ε-martensite during cold working of Fe-Mn alloy and has the effect of greatly improving the shape memory effect, but when its content is 0.4 If it is less than 2.0%, the desired effect cannot be obtained in the above action;
The Sl content was set at 0.4-2.0% since the hot workability of the alloy would be significantly degraded if it was contained in excess of 0.4% to 2.0%.

(b) Mn The Mn element is an element that has a very large influence on the production of 8-martensite, which is effective in expressing the shape memory effect, but if its content is less than 10%, even if the Mn equivalent is Even if C-martensite is within the appropriate range, C-martensite formation at room temperature C: is insufficient;
* Even if the content exceeds v, the generation of C-martensite will not be sufficient, and in any case, a good shape memory effect will not be obtained, so the Mtl content is 10
~2896.

(c) C, Or, and N1 These elements have the effect of promoting the formation of C-martensite by coexisting with the Mn component, so one or more of these elements are added. The total amount is limited to a range of 21 to 28% by the normal Ni value according to the formula.

This means that the corresponding amount is less than 2196 or 2
This is because if it exceeds 896, e-martensite will not be sufficiently produced in any case, making it impossible to achieve a sufficiently satisfactory shape memory effect. Note that the C component is extremely effective in improving the strength properties of alloy 1, but
Considering the point of ensuring workability, it is desirable to suppress the content to 0.5* or less.

Now, Figure 181 shows the restoration rate (
This is a graph showing the influence of Mn equivalent value and Si content on α value), and from FIG.
96 and containing 0.4 to 2.0% Si (=
It is clear that only this material has an extremely excellent recovery rate (α value), that is, a good shape memory effect.

Note that the restoration rate (α value) was measured in a first-order manner.

First, strip-shaped specimens with a thickness of 1 snow, whose front view is shown in Figure 2 (IL), were prepared from iron alloys of various compositions. As shown, bending is performed until an angle of 90 degrees is formed with a radius of curvature of 10+w, and each test piece after core bending is heated and maintained in a heating furnace at a temperature of Aa1 or higher, and then heated to room temperature. Changes in the bending angle of the specimen due to heating and cooling (
1$2Refer to Figure (e)). Next, from the values obtained in this study.

The restoration rate (α value) is calculated using

Here, if the recovery rate (Cα value) is greater than 0, it means that a shape memory effect is being expressed, and the larger the α value, the better the shape memory effect is judged to be. be.

Next, the present invention will be explained using examples and comparing with comparative examples.

<Example> An iron alloy having the chemical composition shown in Table 1 was melted by high-frequency melting.

Next, the ingot of the alloy was heated to 1200°C, rolled to a thickness of 5 snow plates, air cooled to room temperature, then heated again to 1100°C and water-cooled, which was a quenching treatment.

From the board material obtained in this way, thickness 1s + width 5sw
Cut out strip-shaped test pieces of snow with a length of 100 mm, and bend each test piece at room temperature as shown in Figure 182 above.
Heating to Ae 1 point or higher and air cooling to room temperature were performed, and the recovery rate (Cα value) was measured.

These results are also shown in Table V.

As is clear from the results shown in Table 1.

All iron alloys that meet the conditions of the present invention have a recovery rate of 0.3.
The above-mentioned large values indicate that the material is sufficient to meet requirements such as improving the reliability of energy resource development equipment, or ensuring reliability in pipe joints and repairs, etc. It is clear that comparative alloys in which the Bt acid component content is outside the range defined by the present invention do not have a sufficiently satisfactory shape memory effect.

As explained above, according to the present invention, it is possible to obtain a low-cost iron alloy that has a significantly superior shape memory effect than conventionally known Fe-Mn alloys, and can be used for fastening and fixing various structural members. This not only improves the reliability of the system, but also brings extremely useful industrial effects, such as bringing the possibility of developing new industrial technology closer to home.

[Brief explanation of the drawing]

Figure 1 shows the effect of Mn equivalent value and Si on recovery rate (α value).
Graph showing the influence of content. Figure 2 is an explanatory diagram of the method for measuring the shape memory effect (recovery rate).
) is the test piece after bending, and Fig. 2 (el is Ae) is the test piece after bending.
, respectively, show the state of the test piece after heating and cooling to above a point. Applicant Sumitomo Metal Industries Co., Ltd. Agent Tomi 1) Kazuo Haka 2 people OIQ
20 30 40 50Mn amount (weight%)
λ

Claims (1)

[Claims] Contains Si: 0.4 to 2.0% and Mn: 10 to 28% by weight, and further contains one of C, Cr and Ni.
The remainder is Fe and unavoidable impurities, and the formula Mn equivalent (%) = Mn (%) + 9C (%) + Cr (%)
Mn equivalent expressed as /2+Ni (%)/2 is 21 to 2
A shape memory alloy having a chemical composition of 8%.