Method of thermo-mechanical-treatment for fe-mn-si shape-memory alloy doped with nbc
The present invention provides a thermomechanical treatment means for a Fe—Mn—Si-based shape memory alloy having specified components with Nb, C addition with simple deformation prior to aging. Such deformation treatment prior to aging is carried out in the inventions of the prior applications in a temperature range of from 500° C. to 800° C. According to the present invention, however, the deformation treatment prior to the aging treatment can be successfully carried out not at high temperature but at room temperature, if the deformation ratio is in a specified range. The technical meaning of the present invention must be clearly understood as compared to the prior art and the inventions of the prior applications because the present invention allows the treatment at room temperature while the others require troublesome treatment at high temperature so that there is significant difference therebetween. That is, according to the present invention, the remarkable improvement in shape memory property is achieved first time by a combination of specified alloy components, specified deformation ratio at room temperature, and setting of aging condition to a certain range. With the development of the present invention, it is expected that the use of shape memory alloys will be accelerated toward the practical use in a wide variety of fields.
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The present invention relates to a thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition. More particularly, the present invention relates to a thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition which exhibits a satisfactory shape memory effect without undergoing so-called training, providing improved performance.
BACKGROUND OF THE INVENTIONIt has been a long time since the Fe—Mn—Si-based shape memory alloys had been proposed and invented. However, unfortunately, the alloys of Fe—Mn—Si system may be currently in a situation that the alloys are not sufficiently used yet and not yet put to practical use. The main cause is that the alloys can not exhibit satisfactory shape memory effect without undergoing a special thermomechanical treatment called training.
Here, the training means a process sequence of repeating the following treatment several times to improve shape memory effect. The treatment consists of deforming an alloy by 2-3% at room temperature and then heating it to around 600° C. higher than the reverse transformation temperature of the alloy.
In the face of the situation of prior art in which the aforementioned troublesome training is indispensable, inventors of this invention have earnestly studied aiming at developing a treatment with simple process, especially not requiring the training. As a result, the inventors have found a fact that if a small amount of Nb and C elements is applied to a particular shape memory alloy i.e. a Fe—Mn—Si-based shape memory alloy and a suitable aging heating treatment is subjected to the alloy to generate fine NbC carbides in structure of the alloy, a sufficiently satisfactory shape memory effect is obtained without undergoing the troublesome treatment called training, and thus previously filed a patent application (see Patent Document 1). The inventors have studied also about the thermomechanical treatments for the alloy with Nb, C addition, and they found a fact that pre-deformation in a temperature range of from 500° C. to 800° C. and a subsequent aging treatment lead to a further improved shape memory effect and thus also filed patent applications about this (see Patent Document 2, Patent Document 3).
Patent Document 1;
-
- Japanese Patent Unexamined Publication No. 2001-226747
Patent Document 2; - Japanese Patent Unexamined Publication No. 2001-296901
Patent Document 3; - Japanese Patent Unexamined Publication No. 2002-79295
- Japanese Patent Unexamined Publication No. 2001-226747
We believe that the inventions proposed in the aforementioned prior applications facilitate astonishing progress in the shape memory alloy technology, contribute to put the shape memory alloy to practical use for the future, and greatly contribute to the development of industry. However, there are still some points to be improved in proposed inventions. As for the two latter prior applications (Patent Document 2, Patent Document 3), the inventions proposed in these applications are significantly meaningful because the quite easy treatment process is achieved as well as further improved shape memory performance of alloy. In addition, it was recognized that the shape memory performance is therefore dramatically improved, thus dramatically increasing the degree of practical use That is, the works and effects of the inventions of these applications are quite noticeable. However, there still remains a problem that the treatment process requires a heating treatment in a high temperature range of from 500° C. to 800° C., which causes difficulties in most cases. It is undeniable that this point makes it difficult to put the shape memory alloys to practical use.
DISCLOSURE OF THE INVENTIONThe object of the present invention is to fundamentally solve the aforementioned problems.
The inventors of this invention has earnestly studied aiming at developing and ensuring good shape memory properties for a shape memory alloy of specified components even with deformation at low temperatures. As a result, they found that the satisfactory shape memory properties can be sufficiently ensured even with deformation at room temperature so as to achieve the aforementioned object.
That is, they found amazing fact that the excellent shape memory property of alloy can be developed just by applying a basic operation comprising deforming a Fe—Mn—Si-based shape memory alloy with Nb, C addition at room temperature and then subjecting the deformed alloy to aging heating treatment to precipitate NbC carbides. In brief, the aforementioned object is achieved by the present invention.
The present invention was made on the basis of the aforementioned knowledge and success. The solving means to solve the problems are the followings (1)-(7).
(1) A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition comprising: deforming a Fe—Mn—Si-based shape memory alloy with Nb, C addition by a deformation ratio of from 5% to 40% at room temperature, and subjecting the deformed alloy to aging treatment to precipitate NbC carbides.
(2) A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition according to the above (1), wherein the Fe—Mn—Si-based shape memory alloy with Nb, C addition comprises, as alloy components, Mn: 15% to 40% by weight, Si: 3% to 15% by weight, Nb: 0.1% to 1.5% by weight, C: 0.01% to 0.2% by weight, and Fe and inevitable impurities: residual amount, wherein the atomic ratio Nb/C between Nb and C is 1 or more.
(3) A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition according to the above (1), wherein the Fe—Mn—Si-based shape memory alloy with Nb, C addition comprises, as alloy components, Mn: 15% to 40% by weight, Si: 3% to 15% by weight, Cr: 1% to 20% by weight, Nb: 0.1% to 1.5% by weight, C: 0.01% to 0.2% by weight, and Fe and inevitable impurities: residual amount, wherein the atomic ratio Nb/C between Nb and C is 1 or more.
(4) A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition according to the above (1), wherein the Fe—Mn—Si-based shape memory alloy with Nb, C addition comprises, as alloy components, Mn: 15% to 40% by weight, Si: 3% to 15% by weight, Cr: 1% to 20% by weight, Ni: 0.1% to 20% by weight, Nb: 0.1% to 1.5% by weight, C: 0.01% to 0.2% by weight, and Fe and inevitable impurities: residual amount, wherein the atomic ratio Nb/C between Nb and C is 1 or more.
(5) A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition according to any one of the above (2) through (4), wherein the atomic ratio between Nb and C is set in a range of from 1.0 to 1.2.
(6) A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition according to any one of the above (2) through (5), wherein the Fe—Mn—Si-based shape memory alloy with Nb, C addition contains, as impurities, Cu: 3% by weight or less, Mo: 2% by weight or less, Al: 10% by weight or less, Co: 30% by weight or less, and/or N: 5000 ppm or less.
(7) A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition according to any one of the above (1) through (6), wherein the conditions for the aging treatment are a temperature range of 400° C. to 1000° C. and an aging time from 1 minute to 2 hours.
EFFECT OF THE INVENTIONAs a thermomechanical treatment for a Fe—Mn—Si-based shape memory alloy having specified components with Nb, C addition, conventionally, the processing treatment prior to aging is carried out by training. Alternatively, in the inventions of the prior applications, the processing treatment prior to aging is carried out in a temperature range of from 500° C. to 800° C. According to the present invention, however, the processing treatment prior to the aging treatment can be successfully carried out without high temperature, i.e. at room temperature, by setting a processing ratio in a specified range.
The technical meaning of the present invention must be clearly understood as compared to the prior art and the inventions of the prior applications on which the present invention is based because there are obvious difference therebetween. That is, according to the present invention, the remarkable improvement in shape memory property is achieved first time by a combination of specified alloy components, specified deformation ratio at room temperature, and setting of aging condition to a certain range. Amazingly by run-of-the-mill thermomechanical treatment comprising a deformation at room temperature and then aging, the shape recovery ratio equivalent to that of the sample subjected to the training can be obtained and, in addition, the shape recovery stress significantly larger than that of the sample subjected to the training can be obtained. With development of the present invention, it is expected that the use of shape memory alloys will be accelerated toward the practical use in a wide variety of fields.
BRIEF DESCRIPTION OF THE DRAWINGS
The reason why the deformation ratio at room temperature is specified to be from 5% to 40% comes from the fact that the deformation ratio lower than 5% does not effectively contribute to improvement in shape memory property while the deformation ratio over 40% makes a sample too hard so that it is extremely difficult to deform the sample after subjected to an aging treatment.
An alloy as to be subjected to the thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition of the present invention has the following chemical compositions, just as specified in the prior applications, 1) Mn: 15% to 40% by weight, Si: 3% to 15% by weight, Nb: 0.1% to 1.5% by weight, C: 0.01% to 0.2% by weight, and Fe and inevitable impurities: residual amount, wherein the atomic ratio Nb/C between Nb and C is 1 or more;
2) The Fe—Mn—Si-based shape memory alloy with Nb, C addition has the following compositions Mn: 15% to 40% by weight, Si: 3% to 15% by weight, Cr: 1% to 20% by weight, Nb: 0.1% to 1.5% by weight, C: 0.01% to 0.2% by weight, and Fe and inevitable impurities: residual amount, wherein the atomic ratio Nb/C between Nb and C is 1 or more; has the following compositions Mn: 15% to 40% by weight, Si: 3% to 15% by weight, Cr: 1% to 20% by weight, Ni: 0.1% to 20% by weight, Nb: 0.1% to 1.5% by weight, C: 0.01% to 0.2% by weight, and Fe and inevitable impurities: residual amount, wherein the atomic ratio Nb/C between Nb and C is 1 or more.
In either of the Fe—Mn—Si-based shape memory alloys with Nb, C addition, the atomic ratio Nb/C between Nb and C in the alloy is preferably from 1.0 to 1.2.
Further, the alloy as to be subjected to a thermomechanical treatment method for the Fe—Mn—Si-based shape memory alloy of the present invention is permitted to contain, as impurities, one or more of a group consisting of Cu of 3% by weight or less, Mo of 2% by weight or less, Al of 10% by weight or less, Co of 30% by weight or less, and N of 5000 ppm or less.
EMBODIMENTS OF THE INVENTION Hereinafter, the invention will be specifically described on the basis of
First, a Fe-28Mn-6Si-5Cr-0.53Nb-0.06C alloy (% by weight) with Nb, C addition of the present invention was prepared by melting. How the shape memory property is improved by rolling at room temperature and then subjecting it to an aging treatment in a temperature range of 400° C. to 1000° C. for a time period from 1 minute to 2 hours, is shown below.
As is known from this figure, the sample rolled by 10% has shape memory recovery ratios nearly equivalent to or slightly lower than those of the alloy with no Nb, C addition which was subjected to training five times. Practically the necessary initial strain is believed to be about 4%. A shape memory recovery ratio of about 90% shown at this strain strongly suggests that it is used as a practically applicable alloy. Training of at least five times is necessary for obtaining the same shape recovery ratio as this sample, with a conventional Fe—Mn—Si-based shape memory alloy with no Nb, C addition. As is understood from this, the present invention exhibits shape memory properties with a simple method.
The sample with a higher rolling ratio of 20% has shape memory recovery ratios nearly equivalent to or slightly higher than those of the case without rolling (only aged). However, the sample with a further higher rolling ratio of 30% has shape memory recovery ratios lower than those of the case which was only aged in a range with large initial strain.
On the other hand, as for shape recovery stress which is one of the important shape memory properties for practical use, the shape recovery stresses of samples aged after rolling by 20% and 30% are remarkably improved.
The test pieces used were the same as those used for obtaining the results shown in
That is, as is known from the results of this figure (
As described above, the present invention was made by finding that the deformation treatment prior to the aging treatment to a Fe—Mn—Si-based shape memory alloy having specified components with Nb, C addition can be successfully carried out at room temperature if the deformation ratio is in a specified range. The technical meaning of the present invention must be clearly understood because there are obvious advantages as compared to a conventional one which requires the training accompanied by troublesome operation and the inventions of the prior applications which still require high-temperature deformation in a range of from 500° C. to 800° C.
That is, according to the present invention, the remarkable improvement in shape memory property is achieved first time by a combination of specified alloy components, specified deformation ratio at room temperature, and setting of aging condition to a certain range. Amazingly by run-of-the-mill thermomechanical treatment comprising a deformation at room temperature and then aging, the shape recovery ratio equivalent to that of the sample subjected to the training can be obtained and, in addition, the shape recovery stress significantly larger than that of the sample subjected to the training can be obtained. Anyway, the meaning of the present invention is significant. The shape memory alloy according to the present invention can be used as tightening materials for various applications, for example, for tightening water pipes, tightening oil pipes, etc., which will produce great economic effects.
It should be noted that the applications as tightening materials mentioned above are just examples and the present invention is not limited to such applications. With the development of the present invention, it is expected that the shape memory alloy will be put to practical use for various applications in a wide variety of fields.
INDUSTRIAL APPLICABILITYThe present invention provides a thermomechanical treatment means for a Fe—Mn—Si-based shape memory alloy having specified components with Nb, C addition with simple processing treatment prior to aging. Conventionally, the processing treatment prior to aging is carried out by training. Alternatively, in the inventions of the prior applications, the processing treatment prior to aging is carried out in a temperature range of from 500° C. to 800° C. According to the present invention, however, the processing treatment prior to the aging treatment can be successfully carried out without high temperature, i.e. at room temperature, if using a processing ratio in a specified range.
The technical meaning of the present invention must be clearly understood as compared to the prior art and the inventions of the prior applications because there are obvious difference therebetween. That is, according to the present invention, the remarkable improvement in shape memory property is achieved first time by a combination of specified alloy components, specified processing ratio at room temperature, and setting of aging condition into a certain range.
The technical meaning of the present invention must be clearly understood as compared to the prior art and the inventions of the prior applications because there are obvious difference therebetween. That is, according to the present invention, the remarkable improvement in shape memory property is achieved first time by a combination of specified alloy components, specified deformation ratio at room temperature, and setting of aging condition to a certain range. Amazingly by run-of-the-mill thermomechanical treatment comprising a deformation at room temperature and then aging, the shape recovery ratio equivalent to that of the sample subjected to the training can be obtained and, in addition, the shape recovery stress significantly larger than that of the sample subjected to the training can be obtained. With development of the present invention, it is expected that the use of shape memory alloys will be accelerated toward the practical use in a wide variety of fields.
Claims
1. A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition comprising:
- deforming a Fe—Mn—Si-based shape memory alloy with Nb, C addition by a deformation ratio of from 5% to 40% at room temperature, and
- subjecting the deformed alloy to aging heating treatment to precipitate NbC carbides.
2. A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition as claimed in claim 1, wherein the Fe—Mn—Si-based shape memory alloy with Nb, C addition comprises, as alloy components, Mn: 15% to 40% by weight, Si: 3% to 15% by weight, Nb: 0.1% to 1.5% by weight, C: 0.01% to 0.2% by weight, and Fe and inevitable impurities: residual amount, wherein the atomic ratio Nb/C between Nb and C is 1 or more.
3. A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition as claimed in claim 1, wherein the Fe—Mn—Si-based shape memory alloy with Nb, C addition comprises, as alloy components, Mn: 15% to 40% by weight, Si: 3% to 15% by weight, Cr: 1% to 20% by weight, Nb: 0.1% to 1.5% by weight, C: 0.01% to 0.2% by weight, and Fe and inevitable impurities: residual amount, wherein the atomic ratio Nb/C between Nb and C is 1 or more.
4. A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition as claimed in claim 1, wherein the Fe—Mn—Si-based shape memory alloy with Nb, C addition comprises, as alloy components, Mn: 15% to 40% by weight, Si: 3% to 15% by weight, Cr: 1% to 20% by weight, Ni: 0.1% to 20% by weight, Nb: 0.1% to 1.5% by weight, C: 0.01% to 0.2% by weight, and Fe and inevitable impurities: residual amount, wherein the atomic ratio Nb/C between Nb and C is 1 or more.
5. A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition as claimed in any one of claims 2 through 4, wherein the atomic ratio between Nb and C is set in a range of from 1.0 to 1.2.
6. A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition as claimed in any one of claims 2 through 4, wherein the Fe—Mn—Si-based shape memory alloy with Nb, C addition contains, as impurities, Cu: 3% by weight or less, Mo: 2% by weight or less, Al: 10% by weight or less, Co: 30% by weight or less, and/or N: 5000 ppm or less.
7. A thermomechanical treatment method for a Fe—Mn—Si-based shape memory alloy with Nb, C addition as claimed in any one of claims 1 through 4, wherein the conditions for the aging heating treatment are a temperature range of 400° C. to 1000° C. and a time period from 1 minute to 2 hours.
Type: Application
Filed: Dec 17, 2003
Publication Date: Oct 27, 2005
Applicant: National Institute for Materials Science (Tsukuba-shi, Ibaraki)
Inventors: Takehiko Kikuchi (Ibaraki), Setsuo Kajiwara (Ibaraki), Alberto Baruj (Ibaraki), Kazuyuki Ogawa (Ibaraki), Norio Shinya (Ibaraki)
Application Number: 10/519,255