JP2015200022A - Manufacturing method of iron-based shape memory alloy and iron-based shape memory alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an iron-based shape memory alloy having lower cost and higher recovery strain than conventional products.SOLUTION: The manufacturing method of an iron-based shape memory alloy includes a first process of conducting plane strain compression process on a material to be proceeded containing 3 mass% to 7 mass% of Si, 15 mass% to 33 mass% of Mn and the balance Fe with inevitable impurities in a temperature range where the Si is solid dissolved in Fe to be a single phase and at strain speed where solute atom atmosphere controls movement of a transition and a crystal grain boundary can move with a strain energy of a crystal grain as a driving force and a second process for cutting the material to be proceeded on a face having 40° to 50° to an elongation direction in the plane strain compression process and parallel to a load adding direction.

Description

  The present invention relates to a method for producing an iron-base shape memory alloy and an iron-base shape memory alloy.

  Ti-Ni type shape memory alloys and iron-based shape memory alloys are known as alloys having a shape memory effect. The recovery strain of the Ti—Ni-based shape memory alloy is about 8%, which is higher than that of the iron-based shape memory alloy. However, Ti—Ni-based shape memory alloys are more expensive than iron-based shape memory alloys and are inferior in workability, so their use is limited to small precision machines and the like. On the other hand, the iron-based shape memory alloy has a low recovery strain of about 2-3%, but is inexpensive and has good workability. For this reason, in order to expand the application range of an iron-based shape memory alloy, it is required to improve the recovery strain of the iron-based shape memory alloy.

  Non-Patent Document 1 discloses that a recovery strain larger than that before the training process can be obtained by performing a training process on an Fe-Mn-Si-based shape memory alloy that is an iron-based shape memory alloy. Here, the training process is a process for improving shape memory by applying a predetermined amount of strain to a shape memory alloy imparted with shape memory and heating it to a predetermined temperature. May be repeated multiple times. In Non-Patent Document 1, the recovery strain before the training process is smaller than 3%, but after the training process, the recovery strain is higher than 3%.

  Thus, by performing the training process, the recovery strain can be increased as in Non-Patent Document 1, but the training process is costly. Moreover, higher recovery strain is required.

International Publication No. 2007/055155

Awaji Materia Co., Ltd. Development Group, "Characteristics and Applications of Fe-Mn-Si Shape Memory Alloy", [online], Awaji Materia Co., Ltd., [February 21, 2014 Search], Internet <URL: http: / /www.awaji-m.jp/r_and_d/images/sma.pdf>

  According to Non-Patent Document 1, the shape memory effect of the Fe—Mn—Si based shape memory alloy is from an austenite phase (γ phase) having a face-centered cubic structure to a martensite phase (ε phase) having a hexagonal close packed structure. It is obtained by the stress-induced transformation to (martensitic transformation) and the reverse transformation that occurs by applying recovery heat to the material that has undergone the stress-induced transformation. Since deformation due to stress-induced transformation has crystal orientation dependence, the shape memory effect is also considered to have crystal orientation dependence. For this reason, it is considered that the texture control of the shape memory alloy is effective for obtaining a larger recovery strain.

  Patent Document 1 discloses an iron-based alloy in which the presence frequency of <100> in the rolling direction is set to 2 or more by repeatedly performing cold working and heat treatment. In Patent Document 1, this existence frequency is measured by the electron backscattering pattern method, and it is assumed that the existence frequency of <100> oriented in the processing direction when the crystal orientation is completely random is 1. The presence rate at the time of occurrence is set as <100> presence frequency. The shape recovery rate in this iron-based alloy is 80% or more. However, since the strain applied to the alloy before applying the recovery heat is as small as 2%, the recovery strain applied with the recovery heat after being deformed to 5% or more as in Non-Patent Document 1 takes a practically sufficient value. This is unknown from Patent Document 1. Further, in Patent Document 1, there is room for improving the presence frequency of <100> in the rolling direction, and there is room for examining not only the crystal orientation in the rolling direction but also the crystal orientation in the plate thickness direction and the width direction. Furthermore, since cold work and heat treatment are repeated, there is a problem that the number of steps is large, resulting in an increase in manufacturing cost.

  This invention is made | formed in view of the said situation, The 1st objective is to provide the manufacturing method of the iron base shape memory alloy which has a low recovery cost and high recovery strain conventionally. A second object is to provide an iron-based shape memory alloy having a higher recovery strain than before.

  The method for producing an iron-based shape memory alloy according to the present invention comprises a workpiece comprising 3% to 7% by mass of Si, 15% to 33% by mass of Mn, and the balance being Fe and inevitable impurities. In a temperature range in which the Si is dissolved in Fe into a single phase, the solute atom atmosphere dominates the movement of dislocations, and the strain rate at which the grain boundaries can move using the strain energy of the grains as a driving force, A first step of performing plane strain compression processing, and the workpiece subjected to the first step is formed at 40 ° to 50 ° with respect to the extension direction in the plane strain compression processing, and in the load application direction. And a second step of cutting the workpiece on a parallel surface.

Further, the method for producing an iron-based shape memory alloy of the present invention is a workpiece comprising 3% by mass or more and 7% by mass or less of Si, 15% by mass or more and 33% by mass or less of Mn, and the balance being Fe and inevitable impurities. The material is flat at a temperature of 800 ° C. or more and 1250 ° C. or less and at a strain rate of 1 × 10 ⁻⁵ s ⁻¹ or more and 1 × 10 ⁻¹ s ⁻¹ or less until the true strain amount becomes 0.5 or more. The first step of performing strain compression processing and the workpiece subjected to the first step form 40 ° to 50 ° with respect to the extension direction in the plane strain compression processing and are parallel to the load application direction. And a second step of cutting the workpiece on a smooth surface.
In the present invention, “true strain amount” means an absolute value of true strain.

In the production method of the present invention, the true strain amount is preferably 1.5 or less.
In the manufacturing method of this invention, it is preferable that the direction parallel to the said cut surface is an easy shape recovery direction.
In the manufacturing method of this invention, it is preferable that the said workpiece further contains 3 mass% or more and 7 mass% or less of Cr.
In the manufacturing method of this invention, it is preferable that the said workpiece further contains 3 mass% or more and 7 mass% or less of Ni.

  Further, the iron-based shape memory alloy of the present invention comprises 3% by mass or more and 7% by mass or less of Si, 15% by mass or more and 33% by mass or less of Mn, and the balance is Fe and unavoidable impurities. The recovery strain at is greater than 2.5%.

In the iron-based shape memory alloy of the present invention, it is preferable that the average integrated strength in the <110> orientation parallel to the direction of easy shape recovery is 2.3 times or more that of the random structure.
In the iron-based shape memory alloy of the present invention, it is preferable that the average grain size of crystal grains oriented in the <110> orientation with respect to the direction of easy shape recovery is 10 μm or less.
In the iron-based shape memory alloy of the present invention, in a phase having a face-centered cubic structure, crystal grains oriented in the <110> direction within a range of 0 ° to 15 ° with reference to the direction of easy shape recovery are volume fractions. It is preferable that the content is 22% or more.
The iron-based shape memory alloy of the present invention preferably further contains 3 mass% or more and 7 mass% or less of Cr.
The iron-based shape memory alloy of the present invention preferably further contains 3 mass% or more and 7 mass% or less of Ni.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the iron-base shape memory alloy which has low recovery cost and high recovery strain than before is provided. Also provided is an iron-based shape memory alloy having a higher recovery strain than before.

It is a schematic diagram explaining a plane strain compression process, (a) represents before deformation, (b) represents after deformation. It is a schematic diagram explaining the cut surface in a 2nd process, (a) is a perspective view, (b) is a top view. It is a schematic diagram of the apparatus for performing a plane strain compression process. It is a figure which shows the relationship between the volume rate and the strain rate of the crystal grain orientated in Cube direction, Goss direction, Brass direction, and S direction in Examples 1-3. It is a figure which shows the relationship between the volume rate of the crystal grain orientated in Example 2, 4 and the initial stage material in the Cube direction, Goss direction, Brass direction, and S direction, and the amount of true strain. It is (phi) ₂ = 0 degree cross section which shows the result of having measured the texture of Examples 1-4 using the X-ray diffractometer, (a) is Example 1, (b) is Example 2, (c ) Is Example 3 and (d) is a φ ₂ = 0 ° cross section of Example 4. It is (phi) ₂ = 20 degree cross section which shows the result of having measured the texture of Examples 1-4 using the X-ray diffractometer, (a) is Example 1, (b) is Example 2, (c ) Is Example 3, and (d) is the φ ₂ = 20 ° cross section of Example 4. It is a reverse pole figure which shows the result of having measured the texture of Example 2, 4, (a) is Example 2 and (b) is a reverse pole figure of Example 4. FIG. It is a graph which shows the relationship between the recovery strain of Examples 2-4 and an initial stage material, and the volume ratio of <110> in a tension direction. It is a graph which shows the relationship between Examples 2-4 and the recovery | restoration distortion | strain of an initial stage material, and the distortion amount in a tension test. It is a graph which shows the relationship between the recovery strain of Examples 5-8, and the strain amount in a tension test.

Hereinafter, a method for producing an iron-based shape memory alloy and an iron-based shape memory alloy according to an embodiment of the present invention will be described.
The manufacturing method of the iron-based shape memory alloy according to the present embodiment is a work piece comprising 3% by mass or more and 7% by mass or less of Si, 15% by mass or more and 33% by mass or less of Mn, the balance being Fe and inevitable impurities. The strain rate at which the grain boundary can move in the temperature range where the Si is dissolved in Fe into a single phase and the solute atomic atmosphere governs the movement of dislocations and the strain energy of the grains as a driving force. Thus, the first step of performing plane strain compression processing and the workpiece subjected to the first step form a load of 40 ° to 50 ° with respect to the extension direction in the plane strain compression processing, and a load is applied. And a second step of cutting the workpiece on a plane parallel to the direction.
According to this manufacturing method, an iron-based shape memory alloy having a high recovery strain can be obtained. Hereinafter, this mechanism will be described.

  In the first step, a workpiece which is an iron-based shape memory alloy in which Si is solid-solved in iron having a face-centered cubic structure, in a temperature range where Si is solid-solved in Fe and becomes a single phase, and The plane strain compression processing is performed at a strain rate at which the crystal grain boundary can move with the solute atomic atmosphere governing the dislocation motion and the strain energy of the crystal grains as a driving force. As shown in FIG. 1, the plane strain compression process is a compression process performed in a state where a workpiece is constrained in a direction orthogonal to the load application direction. An example of the plane strain compression process is rolling. In the following description, with respect to the orientation in which crystal grains are oriented by plane strain compression processing, the orientation of the plane (compression plane) perpendicular to the load application direction is represented by {hkl} as the plane index, and plane strain compression processing is performed. The orientation in the extending direction in which the workpiece 4 extends is represented by <uvw>, which is a direction index.

  In the first step, in the initial stage of processing, along with an increase in strain due to plane strain compression processing, due to slip deformation, Cube orientation {001} <100>, Goss orientation {011} <100>, Brass orientation {011} The volume ratio of crystal grains oriented in <211>, S orientation {123} <634> increases. Thereafter, as the amount of strain increases, the volume ratio of crystal grains oriented in the Cube orientation increases, and a sharp Cube texture ({001} <100> texture) develops. The development mechanism of such a Cube texture is as follows.

  In plane strain compression of a metal having a face-centered cubic structure, the Cube orientation has a smaller Taylor factor than other orientations. The Taylor factor is a value that represents the total slip amount of the slip surface generated when a unit strain amount is given, and is a value that depends on the deformation mode and the crystal orientation. The lower the Taylor factor, the smaller the amount of deformation applied to the crystal grains oriented in the direction with respect to the unit strain amount, and the smaller the amount of dislocations that are lattice defects caused by the deformation accumulated inside. That is, since the Cube orientation has a relatively small Taylor factor, the amount of dislocations accumulated therein is small, and the strain energy is also small. Also, since the Cube orientation is a stable orientation with respect to plane strain compression, it is difficult to rotate even when deformation progresses. For this reason, when plane strain compression processing is performed in the temperature range in which the Fe-Si alloy becomes a single-phase solid solution, the volume fraction of crystal grains oriented in the Cube orientation, Goss orientation, Brass orientation, and S orientation increases due to slip deformation. At the same time, the crystal grain boundaries of the crystal grains oriented in the Cube orientation having a low strain energy move by consuming the strain energy of the other crystal grains such as the S orientation, and the crystal grains oriented in the Cube orientation grow. growing. That is, in the temperature range in which a single-phase solid solution is formed, dislocation movement is limited by the solute atmosphere, so that dislocations are randomly arranged in the crystal grains. For this reason, dislocations are aligned to form subgrains, and it is difficult to reduce strain energy. As a result, the strain energy of all crystal grains increases as the amount of strain increases, and crystal grains oriented in the Cube orientation that are stable against deformation and have low strain energy are crystals of other orientations such as the S orientation. Consume grains.

  Here, in order to express such behavior in the formation process of the texture, it is necessary to appropriately set the temperature and strain rate for performing the plane strain compression processing. Under processing conditions in which dislocations can move freely within crystal grains, subgrains are formed by dislocations gathering, and strain energy of crystal grains is reduced. For this reason, the difference in strain energy between crystal grains becomes small, and the crystal grains oriented in the Cube orientation as described above cannot grow while consuming the other crystal grains.

  In the first step, the temperature is set to a temperature range where a single-phase solid solution is formed. The strain rate is a strain rate at which the crystal grain boundary can move with the solute atomic atmosphere governing the dislocation motion and the crystal strain energy as the driving force. Under such conditions, the movement of dislocations is hindered by solute atoms, and dislocations exist disorderly in the crystal grains. Therefore, the crystal grains oriented in the Cube orientation as described above are in the other position such as the S orientation. As a result, a highly textured Cube texture is formed.

  In the second step, as shown in FIG. 2, the workpiece 4 subjected to the first step has an angle of 40 ° to 50 ° with respect to the extension direction in the plane strain compression processing, and the load application direction. The workpiece 4 is cut along a plurality of surfaces 5 parallel to the surface. Thereby, a bar or a plate (hereinafter referred to as a shape memory alloy material) can be obtained. Since the Cube texture is formed in the workpiece subjected to the first step, <110 near the longitudinal direction of the shape memory alloy material, that is, near the cutting direction parallel to the cutting surface 5 and the compression surface 4A. There are many crystal grains in which> is oriented. In addition, the angle θ between the extending direction and the cutting direction is preferably 43 ° to 47 °, and more preferably 44.5 ° to 45.5 °.

  Here, the shape memory effect in the iron-based shape memory alloy utilizes the martensitic transformation from the austenite phase to the martensite phase as described above. The martensitic transformation occurs when {111}, which is the close-packed surface of the face-centered cubic structure, shifts in the <112> direction. That is, it is caused by the motion of Shockley partial dislocation (a / 6) <112> on {111}. The maximum orientation of the Schmid factor in this {111} <112> shear system is <144>. The Schmid factor is a value indicating the ratio of the stress generated in the shearing system when an external force is applied to the external force. It can be said that the higher the Schmid factor, the easier the shear system is to act. If <144> having the maximum Schmid factor in the {111} <112> shear system is oriented in the tensile direction, which is the direction in which the shape is memorized (the direction in which shape recovery is easy), martensitic transformation is likely to occur, resulting in shape memory. It is thought that the effect can be enhanced.

  As described above, the shape memory alloy material obtained by the second step has a high volume ratio of crystal grains in which <110> is oriented in the longitudinal direction. Since <110> is only about 10 ° away from <144>, according to this shape memory alloy material, a high recovery strain can be obtained.

  Thus, according to the manufacturing method according to the present embodiment, an iron-based shape memory alloy having a high recovery strain can be obtained without performing a training process. Furthermore, since an iron-based shape memory alloy having a high recovery strain can be obtained by two steps, the manufacturing cost can be reduced.

In the above manufacturing method, the temperature of the first step was 800 ° C. or higher 1250 ° C. or less, strain rate and a 1 × ¹⁰ -5 ^{s -1} or 1 × ^{10 -1 s} -1 or less, the true strain amount 0. 5 or more is preferable.

If the temperature in the first step is 800 ° C. or higher and 1250 ° C. or lower, the Fe—Si solid solution alloy can be made into a single-phase solid solution, and therefore the movement of dislocations is hindered by the solute atoms. This temperature is preferably 850 ° C. or higher and 1100 ° C. or lower. In addition, by setting the strain rate in the first step to 1 × 10 ⁻⁵ s ⁻¹ or more and 1 × 10 ⁻¹ s ⁻¹ or less, the plane strain compression processing is prevented from moving dislocations by solute atoms, and crystal It can be performed in a state where the grain boundary can be moved. The strain rate is preferably 5 × 10 ⁻⁵ s ⁻¹ or more and 5 × 10 ⁻³ s ⁻¹ or less. Further, by setting the true strain amount to 0.5 or more, it is possible to form a Cube texture with high orientation in the first step due to the above-described behavior. The true strain amount is preferably 1.5 or less.

  According to the above method, a shape memory alloy material having a high recovery strain can be obtained. Moreover, it is preferable that the direction parallel to the cut surface in the second step is the shape recovery easy direction (tensile direction). As a result, a higher shape recovery effect can be obtained, and a larger recovery strain can be obtained.

  In the above method, the workpiece may include 3% by mass or more and 7% by mass or less of Cr. In addition to this, the workpiece may further contain 3 mass% or more and 7 mass% or less of Ni. Even in such an Fe—Mn—Si—Cr alloy or an Fe—Mn—Si—Cr—Ni alloy, a shape memory alloy having a high recovery strain can be produced by the above-described method.

  Moreover, you may give a training process about the shape memory alloy raw material manufactured by the said method. Thereby, the recovery strain can be further increased.

  An example of an apparatus for performing plane strain compression processing is an apparatus shown in FIG. FIG. 3 is a schematic diagram showing a compression processing machine 1 used for plane strain compression processing. The compression processing machine 1 includes a compression jig 2 and a heating furnace 3 as a heat source. The compression jig 2 includes a lower jig 21 and an upper jig 22. The lower jig 21 has a rectangular parallelepiped shape including a U-shaped groove 21 </ b> A extending in the extending direction in the plane strain compression processing. The upper jig 22 is a rectangular parallelepiped provided with a convex portion 22 </ b> A corresponding to the groove 21 </ b> A of the lower jig 21. A rectangular parallelepiped workpiece 4 is disposed between the groove 21 </ b> A of the lower jig 21 and the protrusion 22 </ b> A of the upper jig 22. The heating furnace 3 is disposed so as to surround the compression jig 2. Using such a compression processing machine 1, the first step is performed according to the following procedure. First, the temperature of the workpiece 4 is raised by the heating furnace 3, and after the workpiece 4 reaches a predetermined temperature, the upper jig 22 is reduced at a constant speed to compress the plane strain until a predetermined true strain amount is reached. Processing. After the true strain amount reaches a predetermined value, the movement of the upper jig 22 is stopped. By cutting the workpiece subjected to such processing in the second step, it is possible to obtain a shape memory alloy material in which a large number of <110> oriented crystal grains exist in the vicinity of the longitudinal direction.

  According to the above-described method, an iron-based shape memory alloy having a recovery strain exceeding 2.5% in the shape recovery easy direction can be obtained without performing a training process. Moreover, depending on the conditions of plane strain compression processing, the recovery strain can be 3.5% or more. Furthermore, the recovery strain can also be improved by setting the tensile strain applied to the iron-based shape memory alloy obtained by the above method to an appropriate value. That is, when performing the third step of applying tensile strain to the iron-based shape memory alloy obtained in the second step in the direction parallel to the cut surface (longitudinal direction), the tensile strain is set to 9% or less. It is preferably 5% or more and 9% or less.

  In such an iron-based shape memory alloy, it is preferable that the average integrated strength in the <110> orientation oriented parallel to the direction of easy shape recovery is 2.3 times or more the average integrated strength of the random structure. In this iron-based shape memory alloy, it is preferable that the average grain size of the crystal grains oriented in the <110> direction with respect to the direction of easy shape recovery is 10 μm or less. Furthermore, in the phase having a face-centered cubic structure, the crystal grains oriented in the <110> direction within the range of 0 ° to 15 ° with reference to the direction of easy shape recovery include 22% or more by volume fraction. It is more preferable that it is contained in an amount of 26% or more. According to such an iron-based shape memory alloy, a higher recovery strain can be obtained. Here, in addition to the phase having a face-centered cubic structure (γ phase) in the iron-based shape memory alloy, a phase having a hexagonal close-packed structure (ε phase) may be included. By setting the volume ratio of the phase to 7% or less, preferably 2% or less, the above-described effects can be obtained. In this case, it is preferable that 26% or more of the crystal grains in which the <110> direction is oriented within a range of 0 ° to 15 ° with respect to the easy recovery direction are contained in the γ phase.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

[Work material]
The solid solution alloy to be processed is an alloy of 28 mass% Mn (manganese), 6 mass% Si (silicon), 5 mass% Cr (chromium), and Fe (iron) containing inevitable impurities. In this example, a rectangular parallelepiped sample cut out from the bar material of this alloy and having dimensions of 10 mm in the load application direction, 7 mm in the extension direction, and 20 mm in the restraining direction was used as the workpiece. In addition, annealing was performed in the air at a temperature of 900 ° C. for 24 hours before the plane strain compression processing. In the following description, the sample after annealing is referred to as an initial material.

[Plane strain compression processing (first step)]
Using the compression processing machine 1 shown in FIG. 3, plane strain compression processing was performed on the initial material at a temperature of 900 ° C. After reaching a predetermined true strain amount, air cooling was performed.

[Cutting (second step)]
As shown in FIG. 2, the sample subjected to plane strain compression processing was cut at two angles parallel to the load application direction at an angle of 45 ° with respect to the extension direction, to obtain a sample of shape memory alloy material.

[Texture measurement]
The sample was cut at a center position in the height direction (load application direction) of the workpiece subjected to the first step and a plane perpendicular to the load application direction. The cut surface was subjected to mechanical polishing and electrolytic polishing to give a mirror surface, which was used as an observation surface.
With respect to the observation surface, the crystal orientation was measured for a 450 × 450 μm ² region in the center of the observation surface by an EBSD (Electron Backscatter Diffractin) method. The interval between the measurement points was 1 μm. For the EBSD method, a system in which JSM-5600 manufactured by JEOL was equipped with OIM manufactured by TSL was used. Based on this measurement result, the abundance (volume ratio) of crystal grains oriented in the Cube orientation, Goss orientation, Brass orientation, and S orientation in the measurement region was calculated. More specifically, the abundance (volume ratio) of crystal grains oriented in the Cube orientation, Goss orientation, Brass orientation, and S orientation in the γ phase in the measurement region was calculated. A crystal having a {011} surface normal in the range of 0 ° to 15 ° with respect to the direction of load and <100> in the range of 0 ° to 15 ° with respect to the extension direction. The grains were calculated as being grains oriented in the Goss orientation. The same applies to the Cube orientation, the Brass orientation, and the S orientation.
Further, based on the abundance of crystal grains oriented in the Cube orientation calculated as described above, <110> is oriented in the longitudinal direction (cutting direction) in the γ phase for the sample cut in the second step. The abundance (volume ratio) of the obtained crystal grains was calculated. Further, the volume fraction of the ε phase was calculated.
In addition, the {001}, {110}, {211}, and {310} pole figures of the observation surface were experimentally measured by the Schulz reflection method using CuKα rays using an X-ray diffractometer. . The crystal orientation distribution function was determined based on these pole figures, the average integrated strength in each orientation was determined, and the texture was evaluated. The texture of the initial material was also evaluated in the same manner.

[Measurement of recovery strain]
On the cut surface of the sample cut in the second step, indentations were made at two points along the longitudinal direction with a Vickers indenter. The distance L ₀ between the indentations was 6 mm. Using samples marked with indentations, subjected to tensile tests and tensile direction in the longitudinal direction of the sample at room temperature and measure the distance L ₁ between the indentations. Further, the strain amount (L ₁ -L ₀ ) / L ₀ at this time was calculated as the tensile strain. Thereafter, heat treatment was performed at 400 ° C. for 10 minutes to give heat to the sample, and the distance L ₂ between the indentations after the heat treatment was measured. The recovery strain (L ₁ -L ₂ ) / L ₀ was calculated from the distances L ₀ , L ₁ , L ₂ between the indentations.

[Examples 1 to 4]
Samples of Examples 1 to 4 subjected to plane strain compression processing under the conditions shown in Table 1 were prepared, and texture measurement was performed. As shown in Table 1, in Examples 1-3, plane strain compression processing is performed by changing the strain rate, and in Example 4, plane strain compression processing is performed to a higher true strain at the same strain rate as Example 2. went.

  Texture measurement was performed on the observation surface of the sample subjected to plane strain compression processing under such conditions. The volume ratio and average integration frequency of the crystal grains oriented in the Cube orientation, Goss orientation, Brass orientation, and S orientation were determined. The results are shown in FIGS. Further, the average crystal grain size of the crystal grains oriented in the Cube orientation and the S orientation was obtained from the crystal orientation map obtained by the crystal orientation measurement by the EBSD method for the observation surface. The results were obtained in Table 1. The crystal grain size is a diameter when each crystal grain is approximated to a circle.

  FIG. 4 shows the relationship between the volume ratio and strain rate of crystal grains oriented in the Cube orientation, Goss orientation, Brass orientation, and S orientation on the observation surfaces of Examples 1 to 3. According to FIG. 4, the smaller the strain rate, the larger the volume ratio of the crystal grains oriented in the Cube orientation. This is presumably because the effect of hindering the movement of dislocations due to Si as a solute atom has increased. In Table 1, the average grain size of the crystal grains oriented in the Cube orientation of Example 3 is the largest among Examples 1 to 3, and the average grain of the crystal grains oriented in the S orientation of Example 3 The diameter is the smallest among Examples 1-3. This also shows that since the strain rate is low in Example 3, the effect of hindering the dislocation movement due to Si is increased, and the crystal grain boundaries are easily moved. That is, in Example 3, since the grain boundary of the crystal grains oriented in the Cube orientation with a low Taylor factor (accumulated strain energy is small) is easy to move, it is oriented in the S orientation with a high Taylor factor. It is considered that crystal grains oriented in the Cube orientation are likely to grow while consuming the crystal grains.

  FIG. 5 shows the relationship between the volume ratio of crystal grains oriented in the Cube orientation, Goss orientation, Brass orientation, and S orientation and the true strain amount in Examples 2 and 4 and the initial material. According to FIG. 5, the larger the amount of true strain, the larger the volume ratio of crystal grains oriented in the Cube orientation. The larger the true strain amount, the greater the difference in strain energy due to the difference in orientation. As a result, the driving force for growing crystal grains oriented in the Cube orientation increased, and it is considered that such a result was obtained. It is done.

6 and 7 are φ ₂ cross sections showing the results of measuring the texture of the observation surfaces of Examples 1 to 4 using an X-ray diffractometer. These figures represent the crystal distribution function obtained by the measurement in an orthogonal coordinate system with Euler angles (φ ₁ , Φ, φ ₂ ) as axes. FIG. 6 shows a φ ₂ cross section where φ ₂ = 0 ° and FIG. 7 shows φ ₂ = 20 °. The upper left vertex, the upper right vertex, the lower left vertex, and the lower right vertex of the quadrangle in each figure are (φ ₁ , Φ) = (0 °, 0 °), (90 °, 0 °), (0 °, 90 °) in this order. ), (90 °, 90 °). Contour lines in the quadrangle represent the integrated strength of crystal orientation. The value of the contour line in the figure is the average integrated intensity expressed as a multiple of the average value, where the average value is 1. Moreover, Fig.6 (a)-(d) represents the result of Examples 1-4 in order, FIG.7 (a)-(d) also represents the result of Examples 1-4 in order. In FIG. 6A and FIG. 7A, the positions of the Cube orientation, Goss orientation, Brass orientation, and S orientation existing on each cross-sectional view are written in C, G, B, and S, respectively. According to FIGS. 6 and 7, it can be seen that, in any of the examples, the average integrated strength in the Cube orientation is high and a Cube texture is formed. It can be seen that the smaller the strain rate and the greater the true strain amount, the higher the average integrated strength in the Cube orientation.

  FIG. 8 is an inverted pole figure showing the axial density in the 45 ° direction, which is the cutting direction in the second step, calculated based on the result of measuring the texture of the observation surface using an X-ray diffractometer. FIG. 8A shows the results of Example 2, and FIG. 8B shows the results of Example 4. The contour lines in this inverse pole figure represent the integrated strength of the crystal orientation in the longitudinal direction. The value of the contour line is an average accumulation intensity expressed as a multiple of the average value, where the average value is 1. According to FIG. 8, it can be seen that there are many crystal grains in which <110> is oriented in the longitudinal direction.

  FIG. 9 shows the relationship between the recovery strain of Examples 2 to 4 and the initial material and the volume ratio of <110> in the tensile direction (the volume ratio of crystal grains in which <110> is oriented in the tensile direction in the γ phase). It is a graph to show. In Examples 2 to 4, recovery strain higher than that of the initial material was obtained. In Example 4, the recovery strain exceeded 2.5%, and in Examples 2 and 3, recovery strain exceeding 3.5% was obtained.

  FIG. 10 is a graph showing the relationship between the recovery strains of Examples 2 to 4 and the initial material and the strain amount (tensile strain) in the tensile test. For comparison, data of a shape memory alloy not subjected to the training process described in Non-Patent Document 1 is also described. According to Examples 2 to 4, recovery strain higher than that of Non-Patent Document 1 was obtained.

  9 and 10, Example 3 showed higher recovery strain than Example 4 despite the fact that the volume fraction of the crystal grains in which <110> was oriented in the tensile direction was the same. Such a difference in the magnitude of the recovery strain is considered to be due to the size of the crystal grains in which <110> is oriented in the tensile direction. From Table 1, the average crystal grain size of the crystal grains oriented in the Cube orientation is smaller in Example 3 than in Example 4. For this reason, it can be said that the average crystal grain size of the crystal grains in which the <110> orientation is oriented in the tensile direction is smaller in Example 3 than in Example 4. The <110> orientation is an orientation close to <144> that easily undergoes martensitic transformation during deformation, but when the crystal grain size increases, a shear system other than the {111} <112> shear system that causes martensitic transformation also works. It is considered that slip deformation (deformation mode in which the shape does not recover) is likely to occur. For this reason, in Example 4, the frequency of occurrence of slip deformation is greater than that in Example 3, and as a result, the recovery strain is considered to be reduced.

  Moreover, although the volume fraction of the crystal grains in which <110> is oriented in the tensile direction is lower than that of Example 4, Example 2 showed higher recovery strain than that of Example 4. Such a difference in the magnitude of the recovery strain is considered to be because the amount of true strain applied in the first step is smaller in Example 2 than in Example 4. That is, in Example 4, since the true strain amount was relatively large, deformation due to the activity of the crystal slip system increased, and as a result, shape memory characteristics were considered to be lower than in Example 2.

[Examples 5 to 8]
Samples of Examples 5 to 8 subjected to plane strain compression processing under the conditions shown in Table 2 were prepared, and texture measurement and recovery strain measurement were performed. As shown in Table 2, in Examples 5 and 6, the true strain amount was 0.8, in Examples 7 and 8, the true strain amount was 1.3, and in each example, the strain rate and temperature were the same value. .

  FIG. 11 is a graph showing the relationship between recovery strain and tensile strain in Examples 5 to 8. For comparison, data of a shape memory alloy not subjected to the training process described in Non-Patent Document 1 is also described. According to Examples 5 to 8, a higher recovery strain than that of Non-Patent Document 1 was obtained.

  In Example 5, since the amount of tensile strain applied in the tensile test was 9% or less, plane strain compression was performed under the same conditions to obtain a higher recovery strain than Example 6 in which the tensile strain amount exceeded 9%. I was able to. Similarly, in Example 7, since the amount of tensile strain applied in the tensile test was 9% or less, plane strain compression was performed under the same conditions, and the recovery strain higher than that in Example 8 in which the tensile strain amount exceeded 9%. Could get. Moreover, as shown in Table 2, the ε phase was present in the samples of Examples 5 to 8. However, since the volume fraction of the ε phase was 7% or less, a high recovery strain could be obtained. did it. Further, in Examples 5 to 7 in which the volume fraction of the ε phase was 2% or less, a higher recovery strain could be obtained than in Example 8 in which the volume fraction of the ε phase was more than 2%.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit of the present invention. The present invention is not limited by the above description, but only by the scope of the appended claims.

  The iron-base shape memory alloy manufactured by the manufacturing method of the present invention and the iron-base shape memory alloy according to the present invention have a higher recovery strain than before. For this reason, it can utilize suitably for the joint for pipes for connecting two pipes, the joint board for rails, and the member for damping structures.

DESCRIPTION OF SYMBOLS 1 Plane strain compression processing machine 2 Compression jig 3 Heating furnace 4 Work material C Cube direction ({001} <100>)
G Goss orientation ({011} <100>)
B Brass direction ({011} <211>)
SS orientation ({123} <634>)

Claims (12)

3 to 7 mass% Si, 15 to 33 mass% Mn, the work piece consisting of Fe and inevitable impurities in the balance,
In the temperature range where the Si is dissolved in Fe into a single phase, the solute atom atmosphere dominates the movement of dislocations, and the strain rate at which the grain boundaries can move using the strain energy of the grains as a driving force, A first step of strain compression processing;
The work material which performed said 1st process makes 40 degrees-50 degrees with respect to the expansion | extension direction in the said plane strain compression process, and cuts a work material in the surface parallel to a load addition direction. And a process for producing an iron-based shape memory alloy. 3 to 7 mass% Si, 15 to 33 mass% Mn, the work piece consisting of Fe and inevitable impurities in the balance,
Plane strain compression processing at a temperature of 800 ° C. to 1250 ° C. and a strain rate of 1 × 10 ⁻⁵ s ^{−1 to} 1 × 10 ⁻¹ s ⁻¹ until the true strain amount is 0.5 or more. A first step of performing
The work material which performed said 1st process makes 40 degrees-50 degrees with respect to the expansion | extension direction in the said plane strain compression process, and cuts a work material in the surface parallel to a load addition direction. And a process for producing an iron-based shape memory alloy.   The method for producing an iron-based shape memory alloy according to claim 2, wherein the true strain amount is 1.5 or less.   The method for producing an iron-based shape memory alloy according to any one of claims 1 to 3, wherein a direction parallel to the cut surface is a shape recovery easy direction.   The method for producing an iron-based shape memory alloy according to any one of claims 1 to 4, wherein the workpiece further contains 3 mass% or more and 7 mass% or less of Cr.   The method for producing an iron-based shape memory alloy according to claim 5, wherein the workpiece further contains 3 mass% or more and 7 mass% or less of Ni. 3 mass% or more and 7 mass% or less of Si, 15 mass% or more and 33 mass% or less of Mn, and the balance consists of Fe and inevitable impurities,
An iron-based shape memory alloy having a recovery strain in the direction of easy shape recovery of greater than 2.5%.   The iron-based shape memory alloy according to claim 7, wherein an average integrated strength in a <110> orientation parallel to the shape recovery easy direction is 2.3 times or more that of a random structure.   The iron-based shape memory alloy according to claim 7 or 8, wherein the average grain size of the crystal grains oriented in the <110> orientation with respect to the direction of easy shape recovery is 10 µm or less.   The phase having a face-centered cubic structure includes 22% or more of a volume fraction of crystal grains oriented in the <110> direction within a range of 0 ° to 15 ° with respect to the shape recovery easy direction. The iron-base shape memory alloy according to any one of?   The iron-based shape memory alloy according to any one of claims 7 to 10, further comprising 3 mass% or more and 7 mass% or less of Cr.   The iron-based shape memory alloy according to claim 11, further comprising 3 mass% or more and 7 mass% or less of Ni.

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