JPH0277554A - Iron-base shape memory alloy excellent in shape memory characteristic, corrosion resistance, and high-temperature oxidation resistance - Google Patents

Abstract

PURPOSE:To obtain an iron-base shape memory alloy excellent in shape memory characteristics, corrosion resistance, and high-temp. oxidation resistance by incorporating specific amounts of Cr and Si to Fe and also incorporating Mn, Ni, Co, Cu, and N so that they are in specific proportions to Cr and Si, respectively. CONSTITUTION:An Fe alloy having a composition which consists of, by weight, 5.0-20.0% Cr, 2.0-8.0% Si, at least one kind among 0.1-14.8% Mn, 0.1-20.0% Ni, 0.1-30.0% Co, 0.1-3.0% Cu, and 0.001-0.400% N, and the balance Fe and in which quantitative relations in Ni+0.5Mn+0.4Co+0.06Cu+0.002N>=0.67(Cr+1.2Si)-3 are satisfied among the contained components is melted and cast. By this method, the iron-base shape memory alloy having superior characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an iron-based shape memory alloy having excellent shape memory properties, corrosion resistance, and high temperature oxidation resistance.

[Prior Art] A shape memory alloy is produced by plastically deforming an alloy at a predetermined temperature near the martensitic transformation point, then heating the alloy to a predetermined temperature higher than the temperature at which it reversely transforms into its parent phase. By applying plastic deformation to a shape memory alloy at a predetermined temperature, which is an alloy that exhibits the property of recovering to its original shape before plastic deformation, the formation of marten from its matrix is possible. Transform into a site. When the alloy that has been plastically deformed in this way is then heated to a predetermined temperature that is higher than the temperature at which it reversely transforms into its parent phase.

The martensite transforms back to the original matrix and thus the alloy exhibits shape memory properties. As a result, the plastically deformed alloy recovers to its original shape before being plastically deformed.

Many non-ferrous shape memory alloys have been known as alloys having such shape memory properties. (for example,
Shape Memory Alloys (ed., Hiroyasu Funakubo, 1984, Sangyo Tosho).

Among them, Ni-Ti-based and Cu-based shape memory alloys have already been put into practical use, and these non-ferrous shape memory alloys are used in pipe fittings, clothing, medical equipment, actuators, etc. It is manufactured by In recent years, the development of technology that applies shape memory alloys to various uses has been progressing.
It is actively practiced.

However, since non-ferrous shape memory alloys are expensive, they are economically limited. Under these circumstances, iron-based shape memory alloys that are cheaper than non-ferrous shape memory alloys are being developed. As described above, it is expected that the range of application of iron-based shape memory alloys will be expanded in place of non-ferrous shape memory alloys, which are economically limited.

From the viewpoint of the crystal structure of martensite, which transforms from the thumb of an iron-based shape memory alloy through plastic deformation, iron-based shape memory alloys can be classified into fct (face-centered tetragonal) and BET (body-centered cubic) ) and heρ (dense hexagonal crystal).

Fe is an iron-based shape memory alloy that transforms from its matrix to fct martensite by applying plastic deformation.
-Pb system and Fe-Pt system are known.

(For example, “Journal of the Japan Institute of Metals, Vol.
Volume, No. 9, 1984. P881J). These iron-based shape memory alloys exhibit good shape memory properties.

As an iron-based shape memory alloy that transforms from its thumb to bet martensite (hereinafter referred to as "α'fumarunsite") by applying plastic deformation, Fe-Pt type (for example, r Acta by UMEMOTOA WAYMAN) is used.
Metalurgica, Vol 26. Per
gamon Press 1978Printed i
n Great Brj, tainJ P1529) and Fe-N1~Co-T, i system (JP-A-60-23
The alloys disclosed in Japanese Patent Application Laid-open No. 4950 and Japanese Patent Application Laid-open No. 61-106746 are known. α′ fumarunsite is a phase formed in alloys with high stacking fault energy;
As a result, the volume change during metamorphosis is large. Therefore,
During perversion.

Slipping deformation easily occurs within α′ martensite.

These iron-based shape memory alloys do not exhibit good shape memory characteristics in their original state.

However, by making the parent phase of these iron-based shape memory alloys into the thumb that has the Invar effect (i.e., the coefficient of thermal expansion becomes extremely small in a certain temperature range), the α' It is known that the sliding deformation of fumarunsite is suppressed and, as a result, these alloys exhibit good shape memory properties.

High manganese steel and 5US304 austenitic stainless steel specified in the JIS standard are used as iron-based shape memory alloys that transform from their parent phase to hcρ martensite (hereinafter referred to as "ε martensite") by applying plastic deformation. Steel is known. , ε martensite is a phase formed in alloys with low stacking fault energy, resulting in small volume changes during transformation. Therefore, during transformation, slip deformation is difficult to occur in ε martensite, and these iron-based shape memory alloys.

Shows good shape memory properties. (For example, Zenji Nishiyama, “
Martensitic Metamorphosis - Basic Edition J December 1971 Maruzen).

The following alloys have been proposed as iron-based shape memory alloys that transform from their thumb to ε-martensite by applying plastic deformation.

Iron-based shape memory alloy disclosed in Japanese Patent Publication No. 49-10409: ■ Ni: 10-18wt, %, Cr: 10
~25tyt,% at.

If necessary, the system contains Co: 20iit, % or less.

■ Cr: 10-2 (ht,%), Ni:
17.5wt, % or less, Mn: 30.5wt, %
Hereinafter, a system containing Co: 15wt% or less, a system containing 6% of Mn: 15 to 35%, (■
Mn: 12.5-30tgt, %Ni
: A system containing 15vt, % or less (hereinafter referred to as "prior art 1").

In Prior Art 1, as seen in the examples as shape memory characteristics, when a tensile strain of about 4% is applied and then heated to a predetermined temperature, a recovery strain of about 1% can be obtained.

Iron-based shape memory alloy disclosed in Japanese Patent Publication No. 59-83744: ■ C: O, 1-0, 35wt, %+ Sl: 0
．． 5wt0% or less, Mn: 8, 0-15.0wt. %,
So Q A Q: System containing 0.01 to 0.06 wtJ, ('2) C: 0.1 to 0.35 wt, %, Si
: 0.5wt, x or less, Mn: 8.0~I5.0w
t. "l, 5oil An: 0.01~0.06
In wt, %, Ni: 1. (ht, % or less, C
r: A system containing 1.0wt0% or less. (below,
(referred to as "Prior Art 2").

In Prior Art 2, as seen in the Examples, the shape memory property can be recovered by about 30% by applying a tensile strain of 10% or less and then heating to a predetermined temperature.

The iron-based shape memory alloys disclosed in Prior Art 1 and 2 are:
The shape recovery is only partial, and the amount of recovery is only about 30% of the added strain.

Iron-based shape memory alloy disclosed in Japanese Patent Publication No. 6], -54859: Mn: 20-4 (ht, %, Si: 3.5-
8. (A system containing ht, %.

(Hereinafter referred to as "prior art 3").

Iron-based shape memory alloy disclosed in JP-A-61-201761: Mn: 20-40wt, %, Si: 3.5-
8.0wt. %, Ni: 10wt, % or less, C
r: 10wt, % or less, Co: 1ovt, % or less, MO: 2wt, % or less, C: 1wt, % or less,
AQ: 1wt% or less, Cu: 1tit0% or less.

(Hereinafter referred to as "prior art 4").

The iron-based shape memory alloys disclosed in Prior Art 3 and 4 have excellent shape memory properties. That is.

The shape memory properties obtained in Prior Art 3 and 4 are as follows.

It is as follows.

The iron-based shape memory alloys of Prior Art 3 and 4 are melted in a high-frequency heating atmospheric furnace, the melted alloy is then cast into an ingot, and the ingot thus cast is then
By holding at a temperature in the range of 1,050-1,250 °C for 1 hour and then hot rolling the thus heated ingot,
Test specimens with dimensions of n x 30 mm were prepared. Next, the test piece prepared in this way was incubated at room temperature for 4 hours.
Plastic deformation was applied to the test piece by bending it at an angle of 5°, and the test piece was heated to a predetermined temperature above the austenite transformation point. When the shape recovery rate of the alloy was investigated in this way, it was found that the alloy showed a shape recovery rate of 75 to 90%.6 [Problems to be Solved by the Invention] However, the problems disclosed in Prior Art 3 Although iron-based shape memory alloys have excellent shape memory properties, they are insufficient in corrosion resistance and high temperature oxidation resistance.

The iron-based shape memory alloy disclosed in Prior Art 4 contains Cr, Ni, Co and M for the purpose of improving corrosion resistance.

At least one element of the above is added to the alloy. However, prior art 4.

I have the following problem. That is, as mentioned above, in order to improve the corrosion resistance of the alloy, at least one element among Cr, Ni, Co, and MO is added, and in particular, manganese is added in a large amount of 20 to 4 (ht, %). Since the corrosion resistance is added, the effect of improving corrosion resistance is not necessarily sufficient.Furthermore, in Prior Art 4, after applying plastic deformation, it is necessary to heat the alloy for the purpose of recovering the original shape. , cannot impart sufficient high-temperature oxidation resistance to the alloy.More than 15wt, Z, 20-40w7, M of 2
The alloy of prior art 4 containing n and further containing Cr is
Due to the presence of Cr, very brittle intermetallic compounds (
(hereinafter referred to as "σ phase"). The formation and presence of this σ phase significantly deteriorates the shape memory properties, workability, and toughness of iron-based shape memory alloys.

For these reasons, there is a strong desire to develop an iron-based shape memory alloy with excellent shape memory properties, corrosion resistance, and high-temperature oxidation resistance, but such an iron-based shape memory alloy has not yet been proposed.

Therefore, an object of the present invention is to provide an iron-based shape memory alloy having excellent shape memory properties, corrosion resistance, and high temperature oxidation resistance.

[Means for Solving the Problems] When plastic deformation is applied to an HCP-type ferrous shape memory alloy at a predetermined temperature, the phase of the alloy transforms from its parent phase, that is, austenite, to ε-martensite. The above alloy in which the parent phase of the matrix has been transformed into ε-martensite in this way,
Thereafter, when heated to a temperature above the austenite transformation point (hereinafter referred to as rAf point) and near the Af point, ε-martensite undergoes reverse transformation into its parent phase, that is, austenite, and as a result, undergoes plastic deformation. The alloy recovers to its original shape before plastic deformation.

In order to exhibit the shape memory properties of the above-mentioned HCP type iron shape memory alloy, it is necessary to satisfy the following conditions.

(1) Before plastic deformation is applied to the alloy at a predetermined temperature, the parent phase of the alloy needs to mainly consist of austenite. The above-mentioned predetermined temperature refers to a temperature at which the parent phase can transform into ε-martensite when plastic deformation is applied to the alloy at that temperature.

(2) The stacking fault energy of austenite must be low. Furthermore, by applying plastic deformation to the alloy, it is necessary that the parent phase transforms only into ε martensite, and not into α' fumarunsite.

(3) The yield strength of austenite l- must be high. Furthermore, when plastic deformation is applied to the alloy, no sliding deformation should occur in the crystal structure of the alloy.

This invention solves the problems of the prior art described above while satisfying the above conditions.Cr: 5.0 to 2
0.0wt. %, Si: 2.0-8.0wt. %.

At least one element selected from the group consisting of:

Mn: 0.1-14.8wt, %, Ni: O,
1-20.0wt. %.

Co: 0,1~30. (ht,%.

Cu: 0.1-3.0tst,%, N: 0.0
01-0.400 t0%, however, Ni + 0.5Mn
+ 0.4Co+ 0.06Cu+ 0.002N≧0
．． 67 (Cr+1.2SL) -3, and the remainder consists of Fe and inevitable impurities.

Next, the chemical composition of the iron-based shape memory alloy of this invention is as follows:
The reason for limiting the range to the above-mentioned range will be described below.

(1) Cr (Chromium): Cr has the effect of lowering the stacking fault energy of austenite and improving the corrosion resistance and high temperature oxidation resistance of the alloy. Furthermore, Cr has the effect of increasing the yield strength of austenite.

However, the Cr content is 5.0wt. If the amount is less than %, the desired effects described above cannot be obtained. On the other hand, Cr
It is not allowed for the content to exceed 20.0tgt,% for the following reasons. That is, since Cr is a ferrite-forming element, when the Cr content increases, the formation of austenite is inhibited. Therefore, in this invention, in order to form austenite, Mn, Ni, Co, which are austenite forming elements, are used as described below.
, adding at least one element of Cu and N to one alloy. As the Cr content increases, it is also necessary to add larger amounts of the austenite-forming elements mentioned above.

However, adding a large amount of austenite-forming elements is economically disadvantageous. Furthermore, when the Cr content increases.

σ phase tends to form in the alloy. For this reason,
Cr content is 20.0wt. %, it is necessary to increase the content of austenite-forming elements, which impairs economic efficiency, and furthermore, due to the formation of σ phase, the shape memory properties 9 of the alloy deteriorate in workability and toughness. do. Therefore, the Cr content is 5.0 to 20.0wt. It should be limited within the range of %.

(2) Si (Silicon): Si has the effect of lowering the stacking fault energy of austenite and improving the high temperature oxidation resistance of the alloy. Furthermore, Si has the effect of increasing the yield strength of austenite. However, the Si content is 2.0w.
t. If the amount is less than %, the desired effects described above cannot be obtained. On the other hand, the Si content is 8. Owt.

%, the ductility of the alloy decreases significantly, and the hot workability and cold workability of the alloy deteriorate significantly. Therefore, the Si content is 2.0 to 8.0wt. It should be limited within the range of %.

We investigated the effects of the Cr and Si contents on high-temperature oxidation resistance in iron-based shape memory alloys by the tests described below. That is, it is an austenite-forming element. While varying the contents of Cr and Si, which are ferrite-forming elements, in an alloy steel containing 9% Mn of 0.1 to 14.8 st, one variety was prepared according to the method described in the "Example" below. A sample was prepared. Similarly,
1 content of 16,3wt,%.

6.(ht,% Cr content and 6.(ht,% S)
"Specimen A" was prepared from an alloy steel having an i content. Next, each of the specimens thus prepared was heated to a temperature of 600° C. in an air atmosphere.

Then, the oxidation state of each specimen was visually observed to evaluate the high temperature oxidation resistance of the specimen. The test results are shown in FIG.

In FIG. 1, the horizontal axis shows the Cr content (wt, %), and the vertical axis shows the Si content (wt, %). 1st
In the figure, the area surrounded by dotted lines indicates the Cr content and S
This shows that the i content is within the scope of this invention. In addition, in Figure 1, the "◎" mark indicates that no oxidation was observed, the "OJ" mark indicates that oxidation was slightly observed, and the "x" mark indicates that oxidation was noticeable. Indicates that it has been recognized. As is clear from Figure 1, 0.1 to 14
．． lht, Mn content within the range of 5.0-20.
0wt. Cr content within the range of 2.0-8.0
wt. Specimens with Si content within the range of % show excellent high temperature oxidation resistance. Specimen r with a high 1 content of 16.3tit,%, which is outside the scope of this invention.
AJ exhibits extremely low high temperature oxidation resistance.

In this invention, Cr and Si, which are ferrite-forming elements, are added to the alloy, and at least one element among Mn, Ni, Co, Cu, and N, which are austenite-forming elements, is added to the alloy. , the parent phase of the alloy is primarily austenite before plastic deformation is applied to the alloy.

<3) Mn (manganese): Mn is a strong element that forms austenite.
Mn has the effect of making the parent phase of the alloy mainly austenite before plastic deformation is applied to the alloy. However, the Mn content is 0.1wt.

If it is less than 2, the desired effects described above cannot be obtained. On the other hand, when the Mn content exceeds 14.8111t.%, the corrosion resistance and high temperature oxidation resistance of the alloy deteriorate. Therefore, the Mn content should be limited within the range of 0.1 to 14.8 wt.

We investigated the effect of Mn content on elongation at break in iron-based shape memory alloys by the tensile test described below. That is, 11. (ht, %Cr, 6.Owt.

% Si and 12.0 wt. Various specimens were prepared according to the method described in the "Example" section below, while varying the Mn content in alloy steel containing %Ni.

Next, for each of the specimens thus prepared, the relationship between Mn content and elongation at break was investigated by a tensile test. The test results are shown in FIG.

In FIG. 2, the horizontal axis shows Mn content (t, It, %), and the vertical axis shows elongation at break (%). In FIG. 2, the area indicated by a solid line indicates that the Mn content is within the range of the present invention. As is clear from FIG. 2, when the 1 content exceeds 14.8% and 6%, the elongation at break of the alloy decreases due to the formation of the σ phase.

(4) Ni (nickel): Ni is a strong element that forms austenite,
Further, Ni has the effect of mainly changing the parent phase of the alloy to austenite 1 to 1 before plastic deformation is applied to the alloy. However, if the Ni content is less than 0.1 wt, 1, the desired effects described above cannot be obtained. On the other hand, N
i content is 20. (ht,%), the transformation point of E-martensite (hereinafter referred to as "rMs point") shifts significantly to a lower temperature range, and the temperature at which plastic deformation is applied to one alloy becomes significantly lower. Therefore, the Ni content , 0.1-20.
(ht, should be limited within the range of %.

(5) Co (cobalt): Co is an austenite-forming element, and Co
has the effect of converting the parent phase of an alloy into mainly austenite before plastic deformation is applied to the alloy.

Furthermore, Mn, Ni, Cu, and N have the effect of lowering the Ms point, whereas Co has the effect of hardly lowering the Ms point. Therefore, Co is an extremely effective element for adjusting the Ms point within a desired temperature range. However, if the Co content is 0.
If the Co content is less than 1 wt.%, the desired effects described above cannot be obtained.On the other hand, even if the Co content exceeds 30.0% (htJ), no particular improvement in the above-mentioned effects can be obtained. The content should be limited within the range of 0.1-30.0 wt.%.

(6) Cu (@): Cu is an austenite forming element, and Cu
has the effect of making the parent phase of the alloy mainly austenite before plastic deformation is applied to the alloy.

Furthermore, Cu has the effect of improving the corrosion resistance of the alloy. However, if the Cu content is less than 0.1 wt.%, the desired effects described above cannot be obtained. - way,
Cu content is 3.0wt. %, the formation of ε-martensite is inhibited. The reason for this is that Cu has the effect of increasing the stacking fault energy of austenite. Therefore, the Cu content is 0.1 to 3.0w
t. It should be limited within the range of %.

(7) N (Nitrogen): N is an austenite-forming element, and N has the effect of mainly converting the parent phase of the alloy into austenite before plastic deformation is applied to the alloy.

Furthermore, N has the effect of improving the corrosion resistance of the alloy and increasing the yield strength of austenite.

However, if the N content is less than 0.001, the desired effects described above cannot be obtained. On the other hand, when the N content is 0
．． If it exceeds 400 wt.%, Cr and Si nitrides tend to form, and the shape memory properties of the alloy deteriorate. Therefore, the N content is 0.001 to 0.400w
It is limited to a range of t and %.

(8) Ratio of the total content of austenite-forming elements to the total content of ferrite-forming elements: In this invention, as described above, before plastic deformation is applied to the alloy at a predetermined temperature, the parent phase of the alloy is: It consists mainly of austenite.

Absolutely necessary. Therefore, in this invention, in addition to the above-mentioned limitations on the chemical composition of the alloy of this invention, it is necessary to satisfy the following formula.

Ni+0.5Mn+0.4Co+0.06Cu+0.0
02N≧0.67(Cr+1.2Si) −3° The austenite-forming power of the austenite-forming elements contained in the alloy of the present invention can be expressed as follows from the viewpoint of Nj equivalent.

Ni equivalent = Ni+ 0.5Mn+ 0.4Co+ 0
．． 06Cu+ 0.002NNi equivalent is an indicator of austenite forming ability.

The ferrite-forming power of the ferrite-forming elements contained in the alloy of this invention can be expressed as follows from the viewpoint of Cr equivalent.

Cr equivalent=Cr+1.2Si Cr equivalent is an index of ferrite forming ability.

By satisfying the above-mentioned formula, the parent phase of Alloy No. 9 can be made primarily of austenite before Alloy No. 1 is subjected to plastic deformation at a predetermined temperature.

(9) Impurities: The content of C2P and S, which are impurities, is 1 tst, % or less for C, and 0.1 wt, % for P.
It is desirable that S is 0.1vt% or less.

Next, the iron-based shape memory alloy of the present invention will be explained in more detail by way of examples, while comparing it with comparative alloys outside the scope of the present invention.

[Example] As shown in Table 1, the alloy steel of the present invention has a chemical composition within the scope of the present invention, and as also shown in Table 1, the alloy steel of the present invention has a chemical composition outside the scope of the present invention. Comparative alloy steels having the following properties were melted in a melting furnace under atmospheric pressure or vacuum and then cast into ingots. The obtained ingot was then heated to a temperature within the range of 1000 to 1250°C and then hot rolled to a thickness of 12 nn to obtain the alloy steel specimen of the present invention (hereinafter referred to as
Samples Nα1 to 15 (referred to as "specimens of the present invention") and Nα1 to Nα9 of comparative alloy steels outside the scope of the present invention (hereinafter referred to as "comparative specimens J") were prepared.

Next, 5 test specimens of the present invention N1kl~15. The shape memory properties, corrosion resistance, and high temperature oxidation resistance of each of the comparative specimens Nc 1 to 9 were examined by the tests described below. The results of these tests are also shown in Table 1.

(1) Shape memory properties Shape memory properties were investigated by a tensile test consisting of the following. Specimen Nα1 of the present invention prepared as described above
~15, and from each of comparative specimens Na 1 to 9,
A test piece on a round bar with a diameter of 6 m and a gauge ratio R of 30 rm was cut out, and each of the test pieces cut out in this way was
At the deformation temperature shown in the table, a 4% tensile strain is applied, and then each test piece is heated to a predetermined temperature above and near the Af point, and then, after the tensile strain is applied and heated, The gauge distance of each specimen is measured, and the shape recovery rate is calculated based on the measurement result between the gauges to evaluate the shape memory characteristics of each specimen.

The results of the above-mentioned tensile test are also shown in the "shape memory properties" column of Table 1.

The evaluation criteria for shape memory properties were as follows.

O: Shape recovery rate is 70% or more.

○: Shape recovery rate is 30 to less than 70%.

X: Shape recovery rate is less than 30%.

The shape recovery rate was calculated according to the formula below.

However, Lo: initial gauge length of the test piece, Ll: gauge length of the test piece after adding tensile strain, L2: gauge length of the test piece after heating.

Since the Ms point differs for each specimen, the optimum temperature for applying plastic deformation was set for each specimen. This temperature is shown in Table 1, column "Deformation temperature".

(2) Corrosion resistance Specimens of the present invention Nα1 to 15. and comparative specimen Nα1
A two-year atmospheric exposure test was conducted for each of the items 9 to 9, and
Its corrosion resistance was investigated. After the above test was completed, each specimen was visually inspected to evaluate the occurrence of rust. The results of the above test are also shown in the "Corrosion Resistance" column of Table 1.

The evaluation criteria for the occurrence of rust were as follows.

O: No rust formation observed. 0: Some occurrence of rust is observed.

×: Significant occurrence of rust is observed.

(3) High-temperature oxidation resistance The high-temperature oxidation resistance was investigated by the following high-temperature oxidation resistance test. Each of comparative specimens NQ1 to NQ9 was heated to a temperature of 600°C in the atmosphere, and the oxidation status of the surface of each specimen after heating was visually inspected. Evaluate high temperature oxidation. The results of the above test are also shown in the "High temperature oxidation resistance" column of Table 1.

The evaluation criteria for oxidation status were as follows.

◎No carbon dioxide is observed. ○ Some amount of carbon dioxide is observed. X: Oxidation is significantly observed.

As is clear from Table 1, the comparative specimen Nα1 is.

Since the Cr content is so low that it is outside the scope of the present invention, it is inferior in corrosion resistance and high temperature oxidation resistance.

Comparative specimen NQ2 has a high Cr content that is outside the range of the present invention, and therefore is inferior in shape memory properties.

Comparative specimen Nα3 has a low Si content that is outside the range of the present invention, and therefore is inferior in shape memory properties and high temperature oxidation resistance.

Comparative specimen Nn4 has a high Si content that is outside the range of the present invention, and therefore is inferior in shape memory properties. Furthermore, cracking was observed in comparative specimen Nα4.6 Comparative specimen Nα5 had a high Mn content outside the range of the present invention, and therefore was inferior in corrosion resistance and high-temperature oxidation resistance.

Comparative specimen Nα6 has a high Ni content that is outside the range of the present invention, and therefore is inferior in shape memory properties.

Comparative specimen Na 7 has a high Cu content that is outside the range of the present invention, and therefore is inferior in shape memory properties.

Comparative specimen Na 8 has a high N content that is outside the range of the present invention, and therefore is inferior in shape memory properties.

Comparison test leave 9 is 1 set r Ni+0.5Mn+0.4G
o+0.06Cu 100.002N≧0.67 (Cr
+1.2Si) -34 is not added by 't+N, so the shape memory properties are inferior.

On the other hand, the present invention specimens Nα1 to 15 all had
Excellent shape memory properties, corrosion resistance and high temperature oxidation resistance.

[Effects of the Invention] As explained above, the iron-based shape memory alloy of the present invention has the following properties:
It has excellent shape memory properties, corrosion resistance and high temperature oxidation resistance, and is suitable for use as pipe fittings, various fastening devices, etc. materials, and biomaterials, and its manufacturing cost is low. can be reduced, thus providing an industrially useful effect.

[Brief explanation of the drawing]

Figure 1 is a graph showing the effects of the contents of Cr, Si, and Mn on high-temperature oxidation resistance in iron-based shape memory alloys, and Figure 2 is a graph showing the effects of Mn content and elongation at break in iron-based shape memory alloys. It is a graph showing the relationship between.

Claims (1)

[Claims] 1 Cr: 5.0 to 20.0wt. %, Si: 2.0-8.0wt. %, at least one element selected from the group consisting of: Mn: 0.1-14.8wt. %, Ni: 0.1-20.0wt. %, Co: 0.1-30.0wt. %, Cu: 0.1-3.0wt. %, N: 0.001-0.400wt. %, however, Ni+0.5Mn+0.4Co+0.06Cu+
0.002N≧0.67(Cr+1.2Si)-3, and the remainder: Fe and inevitable impurities. An iron-based shape memory alloy with excellent shape memory properties, corrosion resistance, and high temperature oxidation resistance. .