EP2194154A1 - Alliage à récupération de forme bidirectionnelle - Google Patents

Alliage à récupération de forme bidirectionnelle Download PDF

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EP2194154A1
EP2194154A1 EP09015086A EP09015086A EP2194154A1 EP 2194154 A1 EP2194154 A1 EP 2194154A1 EP 09015086 A EP09015086 A EP 09015086A EP 09015086 A EP09015086 A EP 09015086A EP 2194154 A1 EP2194154 A1 EP 2194154A1
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Prior art keywords
mass
alloy
shape
recovery
temperature
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German (de)
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Kozo Ozaki
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Daido Steel Co Ltd
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Daido Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2201/00—Treatment for obtaining particular effects
    • C21D2201/01—Shape memory effect
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a two-way shape-recovery alloy. More particularly, the invention relates to a two-way shape-recovery alloy which can be caused to reversibly take a low-temperature-state shape and a high-temperature-state shape by utilizing the expansion and contraction which are accompanied phase transformations, without substantially utilizing a plastic deformation.
  • shape-memory alloys are expected to be used in applications such as
  • Ti-Ni alloys are one of the most well known classes of shape-memory alloys.
  • the Ti-Ni alloys which have undergone a shape-memory treatment at a high temperature are used in various applications.
  • the shape-memory effect of Ti-Ni alloys is attributable to the following property: when a low-temperature phase (martensite phase) which has undergone a twin deformation with external force reversely transforms to a high-temperature phase (austenite phase), this system returns to the shape formed by a shape-memory treatment.
  • the Ti-Ni alloys have a problem that it is difficult to use the alloys in a wide range of applications because the material cost is high. There also is a problem that the alloys have a transformation temperature around room temperature and, hence, are not usable in applications where a shape-recovery temperature of 100°C or higher is required.
  • iron-based shape-memory alloys represented by Fe-Mn-Si alloys are characterized by being inexpensive and having a high shape-recovery temperature.
  • the shape-memory effect of iron-based alloys is attributable to the following property: when the ⁇ phase generated by a stress-induced epsilon martensite transformation (transformation from the ⁇ (FCC) phase to ⁇ (HCP) phase induced by plastically deforming the system at a temperature not lower than M s point and not higher than M d point) reversely transforms to the ⁇ phase, this system returns to the shape of the unprocessed system.
  • the iron-based shape-memory alloys have the following and other problems:
  • JP-T-2000-501778 discloses a nitrogen-containing iron-based shape-memory alloy which contains 28.80% of Mn, 5.24% of Si, 0.20% of Cr, and 0.11% of N, with the remainder of Fe.
  • This document includes a statement to the effect that not only the shape-memory characteristics but also mechanical properties, including damping characteristics, of an Fe-Mn alloy are improved by alloying with nitrogen.
  • JP-A-10-36943 discloses a process for producing an Fe-Mn-Si shape-memory alloy.
  • an Fe-Mn-Si alloy having a given composition is shaped and then held for 15 minutes or more at a temperature higher than 1,000°C and lower than 1,200°C.
  • This document includes a statement to the effect that the process is effective in inhibiting the cracking which occurs upon stress deformation due to the intergranular precipitation of a fine intermetallic compound rich in manganese and silicon.
  • JP-A-2-221321 discloses a process for producing an iron-based shape-memory alloy.
  • an Fe-Mn-Si alloy having a given composition is processed at a temperature not lower than the M d ' point (the temperature at which neither ⁇ martensite nor ⁇ 'martensite is induced by processing) and not higher than 700°C, and is then annealed at a temperature not lower than (M d ' point + 200°C).
  • JP-A-7-292448 discloses an Fe-Mn-Si shape-memory alloy produced by subjecting an Fe-Mn-Si alloy having a given composition to a heat treatment to form the ⁇ phase having a thickness of 10 ⁇ m or larger in the surface thereof. This document includes statements to the effect that:
  • the shape-memory alloys are frequently required to have two-way working properties. Therefore, in order to apply a shape-memory alloy having a one-way shape-memory effect to a device required to have two-way working properties, it is necessary to combine this shape-memory alloy with another part to impart two-way working properties to the resultant device.
  • Known methods for imparting two-way working properties include a method in which a one-way shape-memory alloy is combined with a spring, weight, or the like to impart two-way working properties (bias method) and a method in which two or more shape-memory parts are used (differential method).
  • bias method bias method
  • two or more shape-memory parts are used (differential method).
  • Such methods in which a one-way shape-memory alloy is combined with another part to impart two-way working properties have limitations in device miniaturization. Those methods are hence applicable to limited fields.
  • An object of the invention is to provide a two-way shape-recovery alloy which is inexpensive, has two-way working properties, has a higher shape-recovery temperature than Ti-Ni alloys, has high accuracy of shape recovery, and has strength which enables the alloy to withstand repetitions of shape recovery.
  • the present invention relates to the following items 1 to 4.
  • the Fe-Mn-Si alloy optimizing the contents of constituent elements results in volume contraction which occurs through a martensite transformation ( ⁇ ) upon cooling and in volume expansion which occurs through the reverse transformation ( ⁇ ) upon heating.
  • the shape changes accompanied by the expansion/contraction are reversible and the amounts of the shape changes are relatively large.
  • the shape-recovery temperature thereof is higher than those of Ti-Ni alloys (specifically, 90-100°C or higher), and the accuracy of shape recovery thereof is high.
  • the Fe-Mn-Si alloy having the given composition is inexpensive and has strength which enables the alloy to withstand repetitions of shape recovery.
  • the strength is further improved by adding a substitutional solid-solution strengthening element such as Mo, or a precipitation strengthening element such as Cu. Consequently, the two-way shape-recovery alloy of the invention can be used in various functional parts required to have two-way working properties.
  • the two-way shape-recovery alloy of the invention can be used as, e.g., a switch or actuator which works based on temperature changes, an expander for a piston ring, and a temperature-sensitive member for use in the oil supply mechanism of a viscous-fluid coupling.
  • the two-way shape-recovery alloy of the invention contains the elements shown below, with the remainder being iron and unavoidable impurities, and has a component balance which satisfies a given requirement.
  • the kinds of the additive elements, ranges of the contents thereof, and reasons for the limitations are as follows.
  • all the percentages defined by mass are the same as those defined by weight, respectively.
  • two-way shape recovery means that an alloy is caused to reversibly take a low-temperature-state shape and a high-temperature-state shape by mainly utilizing the expansion and contraction which are accompanied by phase transformations, without substantially utilizing a plastic deformation.
  • the alloy in order for an alloy to exert a two-way shape-recovery effect, the alloy should be prevented from generating the ⁇ ' phase upon quench-hardening. Accordingly, the alloy must have a carbon content lower than 0.20 mass%. The carbon content thereof is more preferably lower than 0.10 mass%. 13.00 ⁇ Mn ⁇ 30.00 mass %
  • Manganese is an additive element which is essential for stably attaining the two-way transformations between ⁇ and ⁇ . At high temperatures, manganese functions as an austenite-forming element. The higher the content of manganese is, the more the ⁇ martensite is apt to generate at low temperatures. From the standpoint of generating ⁇ martensite, the content of manganese must be 13.00 mass% or higher. The content of manganese is more preferably 15.00 mass% or higher. On the other hand, in case where the manganese content is excessively high, the result is a considerably lowered transformation temperature in cooling and there is a possibility that the austenite phase might be a stable phase even at -50°C. Consequently, the content of manganese must be 30.00 mass% or lower. The content of manganese is more preferably lower than 25.00 mass%. 0.10 ⁇ Si ⁇ 6.00 mass %
  • Silicon is an element which reduces stacking-fault energy to accelerate the transformation from the ⁇ phase to the ⁇ phase. From this standpoint, the content of silicon must be 0.10 mass% or higher. The content of silicon is more preferably 0.30 mass% or higher. On the other hand, in case where the silicon content is excessively high, the strengthening by solid-solution formation is significant and this leads to a decrease in material ductility. Consequently, the content of silicon must be 6.00 mass% or lower. The content of silicon is more preferably 4.00 mass% or lower. 0.05 ⁇ Cr ⁇ 12.00 mass %
  • Chromium has the function of controlling the temperature at which the transformation from the ⁇ phase to the ⁇ phase occurs, and further has the function of improving the corrosion resistance of the material. From the standpoint of obtaining such effects, the content of chromium must be 0.05 mass% or higher. On the other hand, chromium functions as an ⁇ -stabilizing element at high temperatures. Therefore, an excessively high chromium content tends to convert a heat-treated structure into an ⁇ ' martensite structure. Consequently, the content of chromium must be 12.00 mass% or lower. 0.01 ⁇ Ni ⁇ 3.00 mass %
  • Nickel has the function of regulating transformation temperatures without causing a structural change in a heat treatment. From the standpoint of obtaining this effect, the content of nickel must be 0.01 mass% or higher. On the other hand, nickel is a potent austenite-forming element. Therefore, an excessively high nickel content results in a structural change. Consequently, the content of nickel must be 3.00 mass% or lower. N ⁇ 0.100 mass %
  • Nitrogen combines with aluminum and other elements to form nitrogen compounds and thereby adversely-influences hot workability or cold workability. Furthermore, nitrogen functions as an interstitial element to form a solid solution in the iron and serves as a potent austenite-forming element. As in the case of carbon, an excessively high nitrogen content changes transformation behavior and results in the formation of the ⁇ ' (BCT) phase in quench-hardening. Consequently, in order for exerting a two-way shape-recovery effect, it is necessary to prevent the alloy from generating the ⁇ ' phase upon quench-hardening. From this standpoint, the content of nitrogen must be lower than 0.100 mass%. The content of nitrogen is more preferably lower than 0.050 mass%.
  • the unavoidable impurities specifically include the followings.
  • P ⁇ 0.050 mass % Phosphorus unavoidably comes into the alloy from raw materials.
  • Phosphorus is an element which segregates at grain boundaries to reduce the hot workability of the material. It is therefore preferred to reduce the content of phosphorus to be lower than 0.050 mass%.
  • the content of phosphorus is more preferably lower than 0.010 mass%.
  • Sulfur unavoidably comes into the alloy from raw materials. Sulfur segregates at grain boundaries to impair hot workability.
  • the sulfur which has come into the alloy forms MnS and hence exerts a limited influence on hot workability.
  • the content of sulfur is more preferably lower than 0.050 mass%. O ⁇ 0.050 mass %
  • Oxygen unavoidably comes into the steel. Oxygen combines with aluminum and silicon to form oxides and thereby adversely influences hot workability or cold workability. It is therefore preferred to reduce the content of oxygen to be lower than 0.050 mass%. The content of oxygen is more preferably lower than 0.020 mass%. Mo ⁇ 0.10 mass % W ⁇ 0.10 mass % V ⁇ 0.05 mass % Co ⁇ 0.10 mass %
  • Molybdenum, tungsten, vanadium, and cobalt each may unavoidably come into the steel. Although these elements do not exert a considerable influence on transformation temperatures or the type of structure, it is preferred to reduce the contents thereof to be lower than the values shown above. Incidentally, these elements each function as a substitutional solid-solution strengthening element. In such a case, the elements may be added in amounts not smaller than the values shown above. This respect will be described later. Cu ⁇ 0.10 mass %
  • Copper is an element which unavoidably comes into the alloy from raw materials. Excessively high copper contents cause the alloy to show red shortness, and considerably impair the processability thereof. From the standpoint of maintaining processability, it is preferred to reduce the content of copper to be lower than 0.10 mass%.
  • the content of copper is more preferably lower than 0.05 mass%.
  • Aluminum unavoidably comes into the alloy because it is used as a deoxidizer like silicon. Aluminum combines with oxygen to form an oxide and thereby adversely influences hot workability or cold workability. It is therefore preferred to reduce the content of aluminum to be lower than 0.10 mass%. Incidentally, it is possible to positively add aluminum, on condition that a given amount of nickel should be added, to thereby improve strength based on the secondary precipitation of an Al-Ni intermetallic compound. In such a case, an aluminum content of up to 1.00 mass% is allowable. This respect will be described later.
  • the two-way shape-recovery alloy of the invention must satisfy the following expression (1) besides the requirement that the contents of component elements should be the respective ranges shown above. 600 ⁇ 33 ⁇ Mn + 11 ⁇ Si + 28 ⁇ Cr + 17 ⁇ Ni ⁇ 1050
  • the value determined from expression (1) correlates with the transformation temperatures of the alloy, and is an experiential value.
  • the ⁇ phase can be stably ensured at a high temperature (300°C or higher) and the ⁇ phase can be stably ensured at a low temperature (-50°C or lower), respectively.
  • manganese mainly serves as an austenite-forming element and also functions as an element which forms the ⁇ phase upon cooling. Silicon accelerates the conversion of the ⁇ phase to the ⁇ phase at low temperatures but functions as an ⁇ -stabilizing element at high temperatures.
  • chromium functions as an ⁇ -stabilizing element at high temperatures, it is an element effective in controlling the temperatures at which the ⁇ phase transforms to the ⁇ phase.
  • Nickel is an element effective in controlling the temperatures at which the ⁇ phase transforms to the ⁇ phase.
  • the value of expression (1) becomes too large, the A s point becomes room temperature or lower and it becomes difficult to cause this alloy to undergo shape recovery at a temperature higher than the shape-recovery temperatures of Ti-Ni alloys. From the standpoints of attaining an A s point which is higher than the shape-recovery temperatures of Ti-Ni alloys and thereby enabling the alloy of the invention to undergo shape recovery at a temperature of 90-100°C or higher, the value of expression (1) must be 1,050 or smaller.
  • the value of expression (1) is more preferably 900 or smaller.
  • a martensite transformation starts at a transformation start temperature in cooling (M s point) and is finished at a transformation finish temperature is cooling (M f point).
  • the reverse transformation starts at a transformation start temperature in heating (A s point) and is finished at a transformation finish temperature in heating (A f point).
  • the A s point can be elevated to 90°C or higher, or 100°C or higher, by optimizing the value of expression (1).
  • the value of A f - M s can be reduced to 200-300°C or smaller by optimizing the contents of the component elements, such as Mn and Si, which influence the transformation temperature.
  • the value of A f - M s is preferably 150°C or smaller.
  • the value of A f - M s is more preferably 100°C or smaller.
  • each transformation temperature can be determined by drawing a tangent to an expansion-contraction curve at each of points respectively located before and after the area where the inclination of the curve changes and taking the temperature corresponding to the point of intersection of these tangents as the transformation temperature.
  • the two-way shape-recovery alloy of the invention may further contain one or more of the following elements besides the elements described above.
  • substitutional solid-solution strengthening element can be added thereto so long as this exerts no influence on the transformation behavior exhibited by the alloy upon heating/cooling.
  • substitutional solid-solution strengthening element include molybdenum, tungsten, vanadium, and cobalt. Any one of these elements may be added, or two or more thereof may be added.
  • the contents of molybdenum, tungsten, vanadium, and cobalt should be not lower than the respective lower limits shown above, respectively.
  • the contents of these elements are excessively high, not only the effect is not enhanced any more or an increased cost results but also there are cases where such high contents thereof influence transformation behavior. It is therefore preferred that the contents of these elements should be not higher than the respective upper limits shown above, respectively.
  • the copper precipitates at grain boundaries to reduce hot workability.
  • the nickel inhibits the copper from precipitating at grain boundaries.
  • the copper undergoes secondary precipitation within the grains to improve strength.
  • it is preferred to regulate the content of copper to 0.10 mass% or higher.
  • an excessively high copper content results in a decrease in hot workability. It is therefore preferred to regulate the content of copper to 1.00 mass% or lower.
  • an oxide generates in a large amount to reduce hot workability or cold workability.
  • nickel when a given amount of nickel is added simultaneously with the addition of aluminum, the secondary precipitation of an Ni-Al intermetallic compound occurs to improve strength. From the standpoint of obtaining this effect, it is preferred to regulate the content of aluminum to 0.10 mass% or higher. On the other hand, an excessively high aluminum content results in a decrease in hot workability on cold workability. It is therefore preferred to regulate the content of aluminum to 1.00 mass% or lower. From the standpoint of attaining precipitation strengthening without reducing hot workability or cold workability, it is preferred to add nickel in an amount equal to or larger than the aluminum amount. More preferably, the nickel amount is at least two times the aluminum amount.
  • the minimal amount thereof present in the alloy is the smallest non-zero amount used in the Examples of the developed alloys as summarized in Tables 1 and 2.
  • the maximum amount thereof present in the alloy is the maximum amount used in the Examples of the developed alloys as summarized in Tables 1 and 2.
  • the two-way shape-recovery alloy of the invention has the function of reversibly taking a low-temperature-state shape and a high-temperature-state shape based on the expansion/contraction which are accompanied by the transformation between ⁇ and ⁇ , without substantially using a plastic deformation.
  • the two-way shape-recovery alloy having such function can be applied to functional parts such as:
  • the alloy may be used after the surface thereof is subjected to any of various surface treatments.
  • the surface treatments include nitriding, PVD, and CVD.
  • oxidation resistance and wearing resistance can be imparted.
  • the two-way shape-recovery alloy to which wearing resistance has been imparted by a surface treatment can be applied to a mechanical part (e.g., a coil spring, piston ring, or the like) which is used in the state of being in contact with a mating material.
  • the two-way shape-recovery alloy of the invention can be produced by melting raw materials which have been mixed together in a given proportion and then casting the melt. It is preferred that, after the cast is forged to impart a given shape thereto, the forged alloy is subjected to a solution heat treatment (ST treatment) and subsequent air cooling in order to eliminate the influence of the forging.
  • the temperature for the solution heat treatment is preferably 700-1,200°C.
  • Fig. 1 is shown the changes in length of a eutectoid steel (0.77 mass% carbon) with changing temperature and with phase transformations.
  • the eutectoid steel has a ferrite ( ⁇ ) phase structure.
  • this eutectoid steel undergoes expansion ⁇ contraction ⁇ expansion along the curve A ⁇ B ⁇ C ⁇ D as shown in Fig. 1 .
  • this eutectoid steel is gradually cooled from the ⁇ -phase region to room temperature, the eutectoid steel undergoes contraction ⁇ expansion ⁇ contraction along the curve D ⁇ E ⁇ F ⁇ A and returns to the shape which the steel possessed before the heating.
  • the reason why the eutectoid steel contracts along the curve B ⁇ C during heating is that an ⁇ transformation occurs.
  • the martensite transformation which is caused by such a heat treatment and the reverse transformation are positively used for structure control.
  • the ⁇ ' transformation which occurs upon cooling, accompanies volume expansion
  • general iron-based alloys cannot be used as shape-recovery alloys required to contract upon cooling.
  • the ⁇ ' transformation highly depends on the cooling rate of the material. Therefore, a change in cooling rate may result in the formation of a bainite structure or ferrite structure and stable volume expansion (i.e., reproducibility of shape recovery) cannot be obtained.
  • the ⁇ transformation finish temperature in heating (A f point) is as high as 700°C or above.
  • the difference between the A f point and the ⁇ ' transformation start temperature in cooling (M s point) is as large as 200-300°C or more. Namely, the hysteresis loop accompanying heating/cooling is large.
  • the two-way shape-recovery alloy of the invention comprises an Fe-Mn-Si alloy as the base, and the contents of the component elements therein are optimized. Therefore, when this alloy is cooled from a high temperature (300°C or higher) to a low temperature (-50°C or lower), a transformation occurs from the ⁇ (FCC) phase to the ⁇ (HCP) phase and neither the ⁇ (BCC) phase nor the ⁇ ' (BCT) phase generates. Since the ⁇ transformation causes volume contraction, the cooling results in contraction to a degree higher than the shape change accompanied by thermal contraction. On the other hand, when this alloy is heated, the ⁇ transformation occurs. The heating hence results in expansion to a degree higher than the shape change accompanied by thermal expansion. In addition, the changes in shape accompanied by the expansion/contraction are reversible. No plastic deformation is hence necessary for shape recovery.
  • the two-way shape-recovery alloy of the invention shows a relatively large shape change amount. Specifically, by optimizing the component elements, the degree of change in length ( ⁇ L/L 0 ⁇ 100) in heating becomes 0.3% or higher, preferably 0.5% or higher, more preferably 0.7% or higher. By optimizing the shape of this two-way shape-recovery alloy (e.g., shaping the alloy into a spring), that shape change amount can be further increased.
  • the degree of change in length in cooling is the same as the degree of change in length in heating. Specifically, the degree of change in length per heating/cooling cycle is 0.1 % or lower, and the degree of shape recovery is exceedingly high. Even when a heating/cooling cycle is repeated several hundred times, the rate of shape recovery hardly deteriorates with the lapse of time.
  • the two-way shape-recovery alloy of the invention comprises an Fe-Mn-Si alloy as the base
  • the shape-recovery temperature (A s point) is higher than those of conventional Ti-Ni alloys.
  • the hysteresis loop accompanying heating/cooling (A f - M s ) is smaller than those of general iron-based alloy.
  • the A s point becomes 90°C or higher, preferably 100°C or higher.
  • the value of A f - M s becomes 200°C or smaller, preferably 150°C or smaller, more preferably 100°C or smaller.
  • the two-way shape-recovery alloy of the invention comprises an Fe-Mn-Si alloy as the base, it is inexpensive and has strength which enables the alloy to withstand repetitions of shape recovery.
  • the strength is further improved by adding a substitutional solid-solution strengthening element such as Mo or a precipitation strengthening element such as Cu. Consequently, the two-way shape-recovery alloy of the invention can be used in various functional parts required to have two-way working properties. Examples
  • Each of the materials respectively having the chemical compositions shown in Table 1 and Table 2 (50 kg each) was melted in a high-frequency-heating melting furnace, followed by casting.
  • the casts obtained were respectively subjected to soaking at 1,200°C for 24 hours, subsequently forged to ⁇ 30 mm at a temperature of 800°C or higher, and then gradually cooled.
  • the resultant forged alloys were respectively subjected to a solution heat treatment at 800°C for 30 minutes and then air-cooled.
  • an aging treatment was conducted after the solution heat treatment and the air cooling. The aging treatment was conducted at a temperature of 500°C for a period of 1.5 hours.
  • Example 1 0.10 1.24 19.12 0.011 0.042 0.06 0.01 1.45 0.08 0.10 0.02 0.07 0.039 0.028 0.092
  • Example 2 0.08 5.24 15.37 0.034 0.033 0.02 1.34 11.81 0.07 0.01 0.05 0.08 0.064 0.010 0.063
  • Example 3 0.11 0.72 19.55 0.023 0.004 0.03 0.64 3.11 0.04 0.06 0.00 0.04 0.021 0.027 0.090
  • Example 4 0.01 0.32 15.99 0.044 0.010 0.03 1.98 6.33 0.05 0.00 0.00 0.06 0.090 0.019 0.013
  • Example 5 0.04 5.24 22.12 0.031 0.017 0.09 1.66 5.81 0.05 0.03 0.05 0.02 0.078 0.044 0.060
  • Example 6 0.05 4.01 19.02 0.024 0.042 0.05 0.77 3.42 0.06 0.06 0.01 0.01 0.018 0.041 0.036
  • Example 7 0.15 5.09 14.42
  • a differential dilatometer was used to determine transformation - temperatures in heating/cooling (As, A f , M s , and M f ) and the degree of the change in length occurring with the transformation in heating (coefficient of expansion).
  • the size of each test piece was ⁇ 5 mm ⁇ 20 mm, the rate of heating was 10 °C/min, and the rate of cooling was 10 °C/min.
  • a test piece having a parallel-part length of 40 mm was subjected to a thermal fatigue test.
  • a strain measurement part (region having a length of 15 mm) in the parallel part of the test piece was heated and, at the time when a maximum temperature was reached, both ends of the test piece was fixed.
  • the test piece in this state was subjected to 300 repetitions of a cooling/heating cycle to examine the relationship between the temperature change and the stress generated in the test piece.
  • the maximum temperature and minimum temperature were set at 300°C and 50°C, respectively.
  • the rate of heating was 250 °C/min on average, and the rate of cooling was 83 °C/min on average.
  • Tensile test was carried out using a JIS 14A (M18) sample. Conditions of the tensile test were in accordance with JIS Z2241.
  • Example 1 0.88 168 234 685 ⁇ Example 2 0.55 145 154 918 ⁇ Example 3 0.79 180 234 751 ⁇ Example 4 0.80 132 233 742 ⁇ Example 5 0.47 103 121 979 ⁇ + ⁇ Example 6 0.75 189 198 781 ⁇ Example 7 0.70 195 207 815 ⁇ Example 8 0.52 134 145 943 ⁇ + ⁇ Example 9 0.91 230 251 666 ⁇ Example 10 0.70 141 195 818 ⁇ Example 11 0.50 127 138 956 ⁇ + ⁇ Example 12 0.57 152 161 906 ⁇ + ⁇ Example 13 0.70 149 193 815 ⁇ Example 14 0.44 92 98 1000 ⁇ + ⁇ Example 15 0.81 189 232 734 ⁇ Example 16 0.66 166 185 865 ⁇ Example 17 0.42 98 104 1028 ⁇ + ⁇ Example
  • Comparative Example 1 JST and Comparative Example 2 (NSC) were low in A s because the values of expression (1) exceeded 1,050.
  • Comparative Example 3 JST-2
  • Comparative Example 4 (corresponding to SUS304) contained only the ⁇ phase even at -50°C because the nickel content was excessively high.
  • Comparative Example 5 (SUS420), Comparative Example 6, and Comparative Example 7 generated the ⁇ phase because each alloy had an improper component balance.
  • Comparative Example 8 was low in A s because the value of expression (1) exceeded 1,050.
  • Comparative Example 9 generated the ⁇ ' phase because the chromium content was excessively high.
  • Comparative Example 10 contained only the ⁇ phase even at -50°C because the nitrogen content was excessively high.
  • Examples 1 to 28 at -50°C each contained the ⁇ phase and contained neither the ⁇ phase nor the ⁇ ' phase, because the components had been optimized.
  • the degree of change in length during heating was 0.3% or higher in each Example.
  • the value of A f - M s was 300°C or smaller in each Example, and A s was 90°C or higher in each Example.
  • Fig. 2 is shown a heating-cooling transformation curve for the alloy of Example 7. It can be seen from Fig. 2 that transformations between ⁇ and ⁇ occur during heating/cooling and this results in reversible changes in shape.
  • Fig. 3 is shown the relationship between A f - M s and A s in the alloys of the Examples and Comparative Examples.
  • the A s is on the relatively low-temperature side and the A f - M s is relatively small.
  • the alloys of the Comparative Examples including the ⁇ phase or ⁇ ' phase tend to have an A s of 600°C or higher and a large value of A f - M s .
  • Fig. 4 is shown the relationship between the temperature change and the stress generated in the test piece in the first cycle, 100th cycle, and 300th cycle in the alloy obtained in Example 2.
  • Table 4 shows the results of the tensile test. As shown in Table 4, the followings can be seen.
  • Example 1 Example 2 873 Example 3 855 Example 4 863 Example 5 903 Example 6 835 Example 7 842 Example 863 Example 9 837 Example 10 867 Example 11 887 Example 12 989 Example 13 997 Example 14 1065 Example 15 1013 Example 16 899 Example 17 964 Example 18 997 Example 19 1124 Example 20 946 Example 21 955 Example 22 997 Example 23 948 Example 24 1015 Example 25 976 Example 26 996 Example 27 1004 Example 28 896 Comparative Example 1 834 Comparative Example 2 842 Comparative Example 3 863 Comparative Example 4 630 Comparative Example 5 753 Comparative Example 673 Comparative Example 8 621 Comparative Example 9 1134 Comparative Example 10 593

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DE102012113053A1 (de) * 2012-12-21 2014-06-26 Thyssenkrupp Steel Europe Ag Verbindungsmittel mit Formgedächtnis
WO2014135530A1 (fr) * 2013-03-08 2014-09-12 Thyssenkrupp Steel Europe Ag Moyen de déviation à température contrôlée
WO2014146733A1 (fr) 2013-03-22 2014-09-25 Thyssenkrupp Steel Europe Ag Alliage à mémoire de forme à base de fer
WO2020108754A1 (fr) * 2018-11-29 2020-06-04 Thyssenkrupp Steel Europe Ag Produit plat constitué d'un matériau à mémoire de forme à base de fer

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JP6182725B2 (ja) * 2012-12-28 2017-08-23 国立研究開発法人物質・材料研究機構 制振合金
US10450624B2 (en) 2013-07-10 2019-10-22 Thyssenkrupp Steel Europe Ag Method for producing a flat product from an iron-based shape memory alloy
CN104388829B (zh) * 2014-12-05 2016-05-25 哈尔滨理工大学 一种取向铁基形状记忆合金的制备方法
KR101665803B1 (ko) * 2014-12-23 2016-10-13 주식회사 포스코 풀림방지 볼트용 선재, 풀림방지 볼트 및 그들의 제조방법
WO2018047787A1 (fr) * 2016-09-06 2018-03-15 国立大学法人東北大学 MATÉRIAU D'ALLIAGE À MÉMOIRE DE FORME À BASE DE Fe ET SON PROCÉDÉ DE PRODUCTION

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EP0430754A1 (fr) * 1989-11-22 1991-06-05 Ugine S.A. Alliage inoxydable à mémoire de forme et procédé d'élaboration d'un tel alliage
JPH04365837A (ja) * 1991-09-07 1992-12-17 Nippon Steel Corp 形状記憶合金
WO1997003215A1 (fr) * 1995-07-11 1997-01-30 Kari Martti Ullakko Alliages ferreux a memoire de forme et amortissement de vibrations, contenant de l'azote
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DE102012113053A1 (de) * 2012-12-21 2014-06-26 Thyssenkrupp Steel Europe Ag Verbindungsmittel mit Formgedächtnis
WO2014135530A1 (fr) * 2013-03-08 2014-09-12 Thyssenkrupp Steel Europe Ag Moyen de déviation à température contrôlée
WO2014146733A1 (fr) 2013-03-22 2014-09-25 Thyssenkrupp Steel Europe Ag Alliage à mémoire de forme à base de fer
WO2020108754A1 (fr) * 2018-11-29 2020-06-04 Thyssenkrupp Steel Europe Ag Produit plat constitué d'un matériau à mémoire de forme à base de fer

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