Method for producing foil member for air bearings, and austenitic alloy of γ-prime precipitation strengthening type

Abstract

Provided is a method for producing a foil member for air bearings which is able to combine room-temperature strength with nonmagnetic properties and which is expected to have high high-temperature strength when exposed to high temperatures.　The method for producing a foil member for air bearings at least includes an aging treatment step in which an austenitic Fe-based alloy material of the γ-prime precipitation strengthening type containing Ni in an amount of 60.0 mass% or less is subjected to an aging treatment at 600-860°C, the foil member for air bearings having a thickness of 0.01-1.0 mm and a magnetic permeability of 1.01 or less. Also provided is the austenitic Fe-based alloy material of the γ-prime precipitation strengthening type.

Description

Method for manufacturing foil member for air bearing, and gamma prime precipitation strengthened austenitic alloy

[0001] The present invention relates to a method for manufacturing an air bearing foil member that has high strength at room temperature and also provides high high-temperature strength when exposed to high temperatures, and to a gamma prime precipitation-strengthened austenitic alloy.

[0002] In high-speed rotating machines, such as turbomachinery, bearings must support the shaft with as low a coefficient of friction as possible and with minimal vibration. Conventionally, many bearings for high-speed rotating machines use lubricating oil as the working fluid. However, for applications requiring even higher rotational speeds or where lubricating oil contamination is undesirable, hydrodynamic air bearings, which use air as the working fluid, have been considered. Hydrodynamic air bearings use foils made of thin metal plates. As the rotation speed of the shaft increases, the air inside the bearing is compressed. The compressed air elastically deforms the foil like a spring, lifting the shaft via the compressed air, allowing it to rotate with a low coefficient of friction. Furthermore, when used as bearings in turbochargers, for example, because the bearings are located near high-temperature components such as the turbine, the foil components for the air bearings may be exposed to high temperatures. Regarding the thin metal plates used for air bearing foil components, a nickel alloy sold under the trade name Inconel (Inconel is a registered trademark of HUNTINGTON ALLOYS CORPORATION) has been disclosed (Patent Document 1). It is also disclosed that examples of materials for the top foil include phosphor bronze, stainless steel, and Inconel (registered trademark) (Patent Document 2). It is also disclosed that the top foil, porous foil, and shim foil are preferably manufactured from beryllium copper, stainless steel, or Inconel (registered trademark), and it is particularly disclosed that Alloy 718 is processed into a tip and then crimped and molded for use as the tip of the tip foil (Patent Document 3). It is also disclosed that, when the Ni-based alloy Alloy X-750 is used as a foil member for an air bearing, aging treatment under various conditions is performed after solution treatment (Non-Patent Document 1).

[0003] JP 2017-15254 A JP 2019-15322 A JP 2008-517238 A

[0004] DellaCorte, C. , Radil, K. , Bruckner, R.J. , and Howard, S. A. , NASA TM 2007-214691, National Aeronautics and Space Administration, Cleveland, OH

[0005] The Ni alloys sold under the trade name Inconel (registered trademark) shown in Patent Document 1 are difficult to identify due to the wide variety of alloys. However, they are generally broadly divided into solid-solution strengthened and precipitation strengthened alloys. While solid-solution strengthened alloys are easy to process, such as plastic working and welding, they have low strength and are difficult to obtain sufficient strength. Precipitation strengthened alloys offer high strength, but are difficult to process, such as plastic working and welding, and require many labor hours. Since there is no detailed description of alloys with a high content of Ni, a valuable resource, there is no disclosure of the required strength of thin metal sheets used in air bearing foil components. Among the top foil materials shown in Patent Document 2, phosphor bronze, stainless steel, and Inconel (registered trademark), phosphor bronze does not provide sufficient strength, while stainless steel and Inconel (registered trademark) have many varieties and are not particularly detailed, and the required strength, workability, heat treatment, etc. are not disclosed at all. The beryllium copper shown in Patent Document 3 has insufficient heat resistance, stainless steel is not described in detail, and Inconel (registered trademark) has strength and workability issues similar to those in Patent Document 1. Although Alloy 718 is a high-strength alloy, because it is a gamma double prime precipitation-strengthened alloy, its heat resistance is insufficient when used near high-temperature parts, such as those of a turbocharger. Furthermore, while non-patent document 1 describes the heat treatment conditions for the Ni-based alloy Alloy X-750, this alloy contains a high Ni content of 70% or more, and alloys containing 70% or more of this precious resource are undesirable from the perspective of protecting the global environment. As described above, the types of thin metal sheets suitable for air bearing foil members, manufacturing methods such as heat treatment, etc., have not been fully investigated, including from the perspective of effective resource utilization, and there have been issues such as insufficient heat resistance.

[0006] Furthermore, with the recent advancement in electrification, magnetic materials are sometimes used in high-speed rotating machinery such as turbochargers and compressors, and in these cases, air bearing foils are required to be non-magnetic, as magnetization could interfere with normal operation. However, to achieve non-magnetic properties, the metal material must have an austenitic structure, but austenitic structures generally have the problem of being weaker than martensite structures.

[0007] The object of the present invention is to provide a method for manufacturing an air bearing foil member suitable for use near high-temperature parts such as turbochargers, which is made by aging a gamma prime precipitation strengthened austenitic Fe-based alloy material with a low Ni content, thereby maintaining non-magnetic properties and achieving high strength from room temperature to high temperatures.

[0008] In order to solve these problems, the present inventors have conducted extensive research into manufacturing methods for obtaining the desired properties in air bearing foil members, and as a result have newly discovered that by performing an appropriate aging treatment on a gamma prime precipitation strengthened austenitic Fe-based alloy material with a Ni content limited to 60.0% or less, which can be manufactured into thin plate material by plastic working such as rolling, it is possible to achieve both the non-magnetic properties and high strength required for air bearing foils, thereby arriving at the present invention.

[0009] That is, one aspect of the present invention is a method for manufacturing an air bearing foil member, which includes at least an aging treatment step of performing aging treatment at 600 to 860°C on a gamma prime precipitation strengthened austenitic Fe-based alloy material containing 60.0% or less of Ni by mass, to obtain an air bearing foil member having a thickness of 0.01 to 1.0 mm and a magnetic permeability of 1.01 or less. Preferably, the method further contains more than 0.05% but not more than 3.0% of Al, 1.5 to 3.0% of Ti, and 2.5% or less (including 0%) of Nb. Preferably, the gamma prime precipitation strengthened austenitic Fe-based alloy material contains, in mass %, C: 0.10% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less (including 0%), S: 0.01% or less (including 0%), Ni: 25.0 to 60.0%, Cr: 10.0 to 20.0%, and one or both of Mo and W: Mo+W / 2: 0.05 to 4.0%. The aluminum alloy foil for an air bearing preferably comprises more than 0.05% and not more than 3.0%, titanium (Ti) from 1.5 to 3.0%, niobium (Nb) from 2.5% or less (including 0%), vanadium (V) from 1.0% or less (including 0%), boron (B) from 0.001 to 0.015%, magnesium (Mg) from 0.0005 to 0.01%, magnesium (Mg / S) ratio from 1.0 or more, nitrogen (N) from 0.01% or less (including 0%), oxygen (O) from 0.005% or less (including 0%), the balance being iron and unavoidable impurities. The aluminum alloy foil for an air bearing preferably comprises an aging temperature of 690 to 860°C, an aging time of 1 to 10 hours, and a particle size of the spherical gamma prime phase particles from 10 to 60 nm.

[0010] Another aspect of the present invention is a gamma prime precipitation-hardened austenitic Fe-based alloy material containing 60.0% or less Ni by mass, which has a gamma prime phase and is adapted for use as an air bearing foil member by at least solution treatment and aging treatment, and which has a heat sag of 2.5 mm or less. Here, the heat sag is defined as the amount of deflection deformation that occurs after the following steps: 1) solution treatment is performed on the gamma prime precipitation-hardened austenitic Fe-based alloy material at 1,050°C for 5 minutes, followed by aging treatment at 850°C for 4 hours; 2) specimens having a thickness of 0.2 mm, a width of 10 mm, and a length of 100 mm are cut from the aging-treated alloy material; 3) 10 mm portions at both longitudinal ends of the 100 mm-long plate-shaped specimens are fixed; 4) the central portion of the specimen is bent 5 mm in the depth direction and fixed; 5) heating and holding the specimen at 600°C for 50 hours; and 600°C for 50 hours; 600°C for 50 hours; and 7) cooling. In addition, in the present invention, the amount of thermal sag when heated and held at a temperature of 600°C for 100 hours is 2.5 mm or less. In addition, in the present invention, the amount of thermal sag when heated and held at a temperature of 700°C for 4 hours is 0.5 mm or less. In addition, in the present invention, the amount of thermal sag when heated and held at a temperature of 700°C for 50 hours is 0.5 mm or less. In addition, in the present invention, the amount of thermal sag when heated and held at a temperature of 800°C for 4 hours is 2.5 mm or less. Preferably, the steel further contains Al: more than 0.05% but not more than 3.0%, Ti: 1.5 to 3.0%, and Nb: 2.5% or less (including 0%). Preferably, the gamma prime precipitation strengthened austenitic Fe-based alloy material contains, in mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less (including 0%), S: 0.01% or less (including 0%), Ni: 25.0 to 60.0%, Cr: 10.0 to 20.0%, and one or both of Mo and W: Mo+W / 2: 0.05 to 4.0%. , Al: more than 0.05% and not more than 3.0%, Ti: 1.5 to 3.0%, Nb: 2.5% or less (including 0%), V: 1.0% or less (including 0%), B: 0.001 to 0.015%, Mg: 0.0005 to 0.01%, Mg / S: 1.0 or more, N: 0.01% or less (including 0%), O: 0.005% or less (including 0%), the balance being Fe and unavoidable impurities.

[0011] According to the present invention, even when an air bearing is used near a high temperature area using a gamma prime precipitation strengthened austenitic Fe-based alloy material with a low Ni content that has been subjected to appropriate aging treatment, it is expected that the foil member will maintain high strength, thereby achieving both high strength and non-magnetic properties and achieving greater reliability.

[0012] 1 is a graph showing a comparison of the amount of thermal settling between an example of the present invention and a comparative example, and FIG. 2 is a scanning electron microscope photograph showing γ prime phase particles in an example of the present invention and a comparative example.

[0013] First, the "γ prime precipitation strengthened austenitic Fe-based alloy" referred to in the present invention will be explained. The "Fe-based alloy" referred to in the present invention is one in which the balance of added alloy components is Fe. Therefore, for example, even if the Ni content is greater than the remaining Fe content, it is still an Fe-based alloy. Note that an alloy with an excessively low Fe content may no longer be considered an Fe-based alloy. As will be described later, an alloy containing at least 20 mass% Fe is defined as an "Fe-based alloy" in the present invention. Furthermore, γ prime precipitation strengthened alloys do not include γ double prime precipitation strengthened alloys such as Alloy 718. This definition is made for clarity, and the present invention targets γ prime precipitation strengthened alloys among the aforementioned Fe-based alloys.

[0014] The foil member for an air bearing of the present invention (hereinafter simply referred to as the foil member) includes at least an aging treatment step in which a gamma prime precipitation-strengthened austenitic Fe-based alloy (hereinafter simply referred to as the alloy material) containing 60.0% or less Ni by mass is aged at 600 to 860°C. From the perspective of protecting the global environment, it is preferable that the amount of Ni used in the alloy material of the present invention be as low as possible. Therefore, the alloy material of the present invention is an Fe-based alloy material with a reduced amount of Ni added, instead of a Ni-based alloy material containing a large amount of Ni, such as Alloy-X750, which corresponds to Inconel®-X750 as shown in the aforementioned Patent Document 3. Furthermore, the alloy material of the present invention exhibits precipitation of a gamma prime phase in the austenitic structure by the aging treatment described below. This gamma prime phase is an intermetallic compound containing Ni, Al, Ti, Nb, and other constituent elements. Precipitation of the gamma prime phase by appropriate aging treatment can improve strength. Ni is an element necessary for maintaining a stable nonmagnetic austenite matrix structure and for the precipitation of the γ prime phase. However, excessive Ni addition leads to resource depletion and an increase in cost, so the Ni content is set to 60.0% or less. The preferred upper limit of Ni is 57.0%, and the more preferred upper limit is 49.0%. The preferred lower limit of Ni content for obtaining the effects of Ni is described above.

[0015] Next, the elements that may be contained in the alloy material specified in the present invention and their preferred contents will be described. Unless otherwise specified, the contents are expressed in mass percent. <C: 0.10% or Less> C needs to be added in small amounts because it forms MC-type carbides together with V, Ti, and Nb, refining crystal grains and improving strength and ductility in a balanced manner. However, adding more than 0.1% disperses coarse MC-type carbides, resulting in a decrease in ductility, and reduces the amount of Ti and Nb required for the gamma prime phase formed by aging, thereby reducing the strength improvement effect. Therefore, C is preferably set to 0.10% or less. More preferably, C is set to 0.08% or less, and even more preferably, 0.05% or less. Furthermore, to ensure the above-mentioned effects of C, the lower limit of C is preferably 0.01%.

[0016] <Si: 1.0% or less, Mn: 2.0% or less> Si and Mn are added as deoxidizing elements, but excessive addition can increase oxide-based inclusions and impair formability into thin plate, so it is preferable to limit Si to 1.0% or less and Mn to 2.0% or less. A more preferable upper limit for Si is 0.5%, and a more preferable upper limit for Mn is 1.0%. If the deoxidizing effect can be compensated for by other elements, the lower limits for Si and Mn may be zero% (below the no-addition level).

[0017] <P: 0.04% or less (including 0%), S: 0.01% or less (including 0%)> P and S are impurity elements that are not intentionally added but are mixed in from raw materials, etc., and low amounts are preferable, with each being 0%. If mixed in, P of 0.04% or less and S of 0.01% or less do not adversely affect the manufacturing method and characteristics of the air bearing foil member, so P is preferably 0.04% or less and S is preferably 0.01% or less. A more preferable upper limit for P is 0.03%, and an even more preferable upper limit for P is 0.02%. A more preferable upper limit for S is 0.005%, and an even more preferable upper limit is 0.003%.

[0018] <Ni: 25.0 to 60.0%> Ni is an essential element for not only stabilizing the austenite matrix structure and making it nonmagnetic, but also forming a finely dispersed and precipitated gamma prime phase upon aging treatment, thereby increasing strength at room temperature and high temperatures. Ni content less than 25.0% not only destabilizes the austenite structure, but also leads to an insufficient amount of gamma prime phase precipitation, potentially preventing the air bearing foil member from achieving the strength required at room temperature and high temperatures. Therefore, the lower limit of Ni is preferably set to 25.0%. As described above, the upper limit of Ni content is set to 60.0% or less because excessive Ni addition leads to resource depletion and price increases. The Ni content can be appropriately selected within the range of 25.0 to 60.0%, taking into account the properties and price. For example, if economic efficiency is prioritized, maintaining necessary properties while suppressing price, the upper limit of Ni content is preferably set to 30.0%. On the other hand, when it is desired to give priority to high strength and obtain even higher strength, the lower limit of the Ni content is preferably set to 30.0% and the upper limit to 49.0%. Furthermore, when it is desired to obtain high strength at high temperatures, the lower limit of the Ni content is preferably set to 49.0% and the upper limit to 60.0%.

[0019] <Cr: 10.0 to 20.0%> Cr is an element effective for maintaining the corrosion resistance and oxidation resistance of air bearing foil members. If the Cr content is less than 10.0%, sufficient corrosion resistance and oxidation resistance cannot be obtained. On the other hand, if the Cr content exceeds 20.0%, the austenite matrix structure becomes unstable, and harmful brittle phases such as σ phase and α dash phase may form, causing embrittlement. Therefore, the Cr content is preferably set to 10.0 to 20.0%. The lower limit of Cr is more preferably 12.0%, the upper limit of Cr is more preferably 18.0%, the lower limit of Cr is even more preferably 13.0%, and the upper limit of Cr is even more preferably 17.0%.

[0020] <One or Both of Mo and W: Mo+W / 2: 0.05-4.0%> Mo and W are congener elements and are effective in increasing strength at room temperature and high temperatures through solid solution strengthening by dissolving in the austenite structure of air bearing foil components. In the present invention, precipitation strengthening is achieved by precipitation of the gamma prime phase through aging treatment. While alloying elements such as Ni, Al, Ti, and Nb, which constitute the gamma prime phase, are reduced in the austenite structure after aging treatment, reducing the solid solution strengthening effect, Mo and W, which are not gamma prime phase constituents, remain in solid solution in the austenite structure after aging treatment, maintaining their solid solution strengthening effect. Therefore, they provide solid solution strengthening in addition to the precipitation strengthening due to gamma prime phase precipitation. Mo and W may be added alone or in combination. When added in combination, the amount can be expressed as Mo+W / 2, calculated as the atomic weight ratio of the two elements (this can also be applied to the case of single addition by setting either element to 0%). When Mo and W are added in an amount of Mo+W / 2 less than 0.05%, the effect of improving high-temperature strength is small. On the other hand, when added in an amount exceeding 5.0%, embrittling phases such as Laves phases may form. Therefore, it is preferable to use one or both of Mo and W, with Mo+W / 2 being 0.05 to 4.0%. The upper limits of Mo and W are preferably within the range of 0.1 to 5.0%, taking into account the balance between cost and properties. Specifically, for example, to suppress cost while maintaining necessary properties, Mo+W / 2 is preferably 1.5% or less, and more preferably 1.0% or less. Furthermore, to obtain higher strength while maintaining necessary properties, Mo+W / 2 is preferably greater than 1.5% and less than 4.0%. When cost reduction is important, Mo, which is less expensive than W, may be added alone.

[0021] <Al: More than 0.05% and Not More than 3.0%> Al, along with Ni, Ti, and Nb, is one of the main constituent elements of the γ prime phase, which is an intermetallic compound particle that is finely dispersed and precipitated by aging treatment. It is an element necessary for increasing strength at room temperature and high temperatures. To contribute to strengthening by precipitating the γ prime phase, an addition of more than 0.05% is necessary. On the other hand, adding more than 3.0% Al may reduce workability during foil member manufacturing. Therefore, the Al content is preferably more than 0.05% and not more than 3.0%. The preferred range of Al content within the above range can be appropriately selected in consideration of the amounts of Ti and Nb, which are the other main elements constituting the γ' phase. For example, a more preferred lower limit is 0.2%. A more preferred upper limit is 2.5%, and an even more preferred upper limit is 2.2%.

[0022] <Ti: 1.5 to 3.0%> Ti, along with Ni, Al, and Nb, is one of the main constituent elements of the gamma prime phase, which is an intermetallic compound particle that is finely dispersed and precipitated by aging treatment. It is an element necessary for increasing strength at room temperature and high temperatures. To contribute to strengthening by precipitating the gamma prime phase, an addition of 1.5% or more is necessary. On the other hand, adding more than 3.0% Ti tends to generate a coarse intermetallic compound, the eta (η) phase, during high-temperature heating, resulting in reduced strength and ductility at high temperatures. Therefore, the Ti content is preferably 1.5 to 3.0%. The Ti content can be appropriately selected within the above range, taking into account the amounts of Al and Nb, the other main elements that constitute the gamma prime phase. For example, a preferred lower limit is 1.7%, and a more preferred lower limit is 1.8%.

[0023] <Nb: 2.5% or Less (Including 0%)> Nb, together with Ni, Al, and Ti, is one of the constituent elements of the gamma prime phase, which is an intermetallic compound particle that is finely dispersed and precipitated by aging treatment. Nb is an effective element for increasing strength at room temperature and high temperatures. Nb does not necessarily need to be added in balance with the amounts of Al and Ti. However, if added, Nb content exceeding 2.5% generates a coarse Laves phase composed of FeNb, resulting in reduced strength and ductility at high temperatures. Therefore, Nb content is preferably 2.5% or less. The preferred range of Nb can be appropriately selected within the above range, taking into account the balance with Al and Ti. When Nb is added, a more preferred lower limit is 0.15%, and an even more preferred lower limit of Nb is 0.4%. Furthermore, a preferred upper limit of Nb is 2.0%. Ta, which is a related element to Nb, is an expensive element and does not need to be actively added in the present invention. However, since Ta has the same effect as Nb in terms of strength, when considering the addition of Ta, it can be substituted for Nb so as to satisfy the relationship Nb=Ta / 2.

[0024] <V: 1.0% or less (including 0%)> V is added as needed because it has the effect of refining austenite grains by forming MC-type carbides and improving strength at room temperature and high temperatures. When added, V content exceeding 1.0% may form coarse carbides, reducing ductility, or may form an unstable oxide film at high temperatures, impairing oxidation resistance. Therefore, V content is preferably 1.0% or less (including 0%). When added, a more preferred range is 0.10 to 1.0%, and a more preferred upper limit of V is 0.5% or less.

[0025] <B: 0.001 to 0.015%> When added in small amounts, B is an effective element for increasing strength and ductility at high temperatures through its grain boundary strengthening effect. However, if added in amounts less than 0.001%, the amount of segregation to grain boundaries is small and the effect is insufficient. On the other hand, if added in amounts exceeding 0.015%, the initial melting temperature during heating decreases, resulting in a decrease in hot workability. Therefore, B is preferably set to 0.001 to 0.015%. A more preferred range is 0.001 to 0.010%.

[0026] <Mg: 0.0005 to 0.01%> Mg not only acts as a deoxidizer to reduce oxygen but also bonds with grain boundary segregated S to fix it, improving hot workability. If the Mg content is less than 0.0005%, the effect is insufficient. On the other hand, if the Mg content exceeds 0.01%, the amount of oxides and sulfides increases, reducing cleanliness as inclusions and increasing the amount of compounds with low-melting-point Ni, reducing hot workability. Therefore, the Mg content is preferably limited to 0.0005 to 0.01%. A more preferable lower limit for Mg is 0.001%, and a more preferable upper limit for Mg is 0.007%. An even more preferable upper limit for Mg is 0.005%. Note that a portion of Mg may be replaced with Ca, in which case (Mg + 0.6 × Ca) may be limited to the range of Mg alone.

[0027] <Mg / S: 1.0 or More> As mentioned above, the purpose of adding Mg is to improve hot workability by fixing S that segregates at grain boundaries, so it is preferable to adjust the amount of Mg added within a specific range depending on the amount of S. In order to suppress the adverse effects of S on hot workability, it is effective to limit the Mg / S value to 1.0 or more, and preferably to 2.0 or more. Note that the same effect can be obtained by substituting part or all of the Mg with Ca. When part or all of the Mg is substituted with Ca, it is preferable to limit (Mg + 0.6 × Ca) / S to 1.0 or more. The relationship (Mg + 0.6 × Ca) / S is also preferably 2.0 or more.

[0028] <N: 0.01% or less (including 0%), O: 0.005% or less (including 0%)> O and N combine with Al, Ti, Nb, etc. to form oxide-based and nitride-based inclusions, which reduce cleanliness and fatigue strength. Furthermore, reducing the amounts of Al, Ti, and Nb that form the γ prime phase reduces the amount of γ prime phase particles due to dispersed precipitation during aging, which may inhibit the increase in strength due to aging precipitation. Therefore, it is preferable to keep the contents as low as possible, even to 0%. Preferably, O is 0.005% or less and N is 0.01% or less. More preferably, O is 0.004% or less and N is 0.005% or less.

[0029] <Balance: Fe and Inevitable Impurities> In order to obtain the air bearing foil member of the present invention, Fe is necessary as an inexpensive major element of the austenite phase that constitutes the matrix, and the balance is essentially Fe. The Fe content is preferably 20% or more, more preferably 30% or more, and even more preferably 35% or more. In addition to unavoidable impurities, the balance includes the following elements, which have little substantial effect as long as they are within the following ranges, and therefore can be tolerated within the following ranges: Co: 0.5% or less, Cu: 0.2% or less, Zr: 0.4% or less, REM: 0.1% or less. Furthermore, Ag, Sn, Pb, As, and Bi are also impurity elements that segregate at austenite grain boundaries and reduce high-temperature strength. Therefore, it is preferable to limit each of Ag, Sn, Pb, As, and Bi to 0.01% or less.

[0030] Next, the manufacturing method of the present invention will be described. In the manufacturing method of the present invention, an alloy material having the above-described composition is subjected to aging treatment at 600 to 860°C (aging treatment step). To improve the strength of a precipitation-hardened alloy, it is necessary to finely disperse and precipitate the gamma prime phase within the austenite matrix. The aging treatment step is an important step for obtaining the properties required for an air bearing foil member. The foil is processed into a thin plate shape by rolling or other methods until it reaches or approaches the final thickness for the air bearing foil member. It is sufficient to include this step in the manufacturing process, including both before and after processing the thin metal plate into an air bearing foil. If the aging treatment temperature is lower than 600°C, precipitation of the gamma prime phase hardly occurs. On the other hand, if the aging treatment temperature is higher than 860°C, coarse gamma prime phase precipitation or other coarse intermetallic compounds precipitate, preventing any improvement in strength. Therefore, the aging treatment temperature is set to 600 to 860°C. A more preferred aging temperature is 690 to 860°C, and a preferred aging time is 1 to 10 hours. Aging under these conditions allows for the dispersion and precipitation of spherical gamma prime phase particles of a preferred size in a relatively short time, thereby achieving the preferred 0.2% proof stress at room temperature and at high temperatures. A more preferred upper limit of the aging time is 5 hours. In the present invention, it is also preferred to subject the alloy material to a high-temperature solution treatment prior to the aging treatment in order to homogenize the alloy components within the material. By performing the solution treatment, gamma prime phase is appropriately precipitated in the subsequent aging precipitation step, which tends to make it easier to obtain the characteristics described in the present invention. The solution treatment temperature is preferably 850 to 1100°C. Here, the term "alloy material" as used herein refers to a hot-worked material obtained by subjecting a hot-worked material having the aforementioned composition to hot forging, hot rolling, or other hot-worked material, or a cold-worked material obtained by subjecting a hot-worked material to cold rolling, cold forging, or other cold-worked material.

[0031] Air bearings work by compressing the air inside the bearing due to the high-speed rotation of the shaft. This compressed air elastically deforms the air bearing foil (hereinafter simply referred to as foil), like a spring, and levitates the shaft via the compressed air. Therefore, the foil member is manufactured from a thin metal plate to allow elastic deformation due to air pressure. Thinner foil members are more susceptible to elastic deformation, but if they are too thin, they lack strength. On the other hand, if they are too thick, they are strong enough but require high air pressure for elastic deformation. Therefore, the thickness is set to 0.01 to 1.0 mm. The preferred lower limit is 0.05 mm, and the preferred upper limit is 0.5 mm. Furthermore, if the foil member for an air bearing is magnetized due to the influence of an external magnetic field, such as from motorization, the desired amount of elastic deformation due to compressed air may become uncontrollable. Furthermore, the member must be nonmagnetic because deformation during shaft rotation can cause wobble or distortion in the rotor. The permeability, an indicator of nonmagnetic properties, is set to 1.01 or less to ensure that the foil member's operation is not affected.

[0032] The air bearing foil member after the above-described aging treatment can be expected to have the following mechanical properties. Air bearing foil members must be able to elastically deform like a spring under the pressure of compressed air. Therefore, a wide stress range over which they can be elastically deformed is preferable. Because the stress range over which they can be elastically deformed is the stress range up to the yield stress, a high 0.2% proof stress, which is an index of yield stress, is preferable. However, the 0.2% proof stress is affected by factors such as the pressure of the compressed air used and the thickness of the air bearing foil member. While a high 0.2% proof stress at room temperature is desirable, the aging treatment used in the manufacturing method of the air bearing foil member of the present invention can increase the 0.2% proof stress of a gamma prime precipitation-strengthened austenitic Fe-based alloy material to 650 MPa or more. Furthermore, while the 0.2% proof stress of thin metal sheets generally decreases with increasing temperature, it is preferable for the 0.2% proof stress to decrease as little as possible even with increasing temperature. The aging treatment, which is a manufacturing method of an air bearing foil member according to the present invention, enables the gamma prime precipitation strengthened austenitic Fe-based alloy material to maintain a 0.2% yield strength at high temperatures, for example, a 0.2% yield strength of 550 MPa or more at 700°C, due to aging precipitation. Therefore, it is preferable that the 0.2% yield strength be 650 MPa or more at room temperature and 550 MPa or more at 700°C. It is also preferable that the 0.2% yield strength does not decrease much even when exposed to high temperatures for a long period of time, and it is preferable that the 0.2% yield strength be 450 MPa or more at room temperature and 450 MPa or more at 700°C after heating the air bearing foil member after aging treatment at 800°C for 400 hours.

[0033] The Young's modulus of the air bearing foil member of the present invention at room temperature is preferably 180 GPa or more. As mentioned above, since the air foil elastically deforms like a spring due to the pressure of compressed air, it is preferable to reduce the energy loss of the rotating shaft, and increasing the Young's modulus is effective for this purpose. Having the above-mentioned Young's modulus further suppresses deformation of the air bearing foil member, suppressing shaft wobble and distortion caused by member deformation, and more reliably achieving the effects of reducing output energy loss and suppressing shortening of the structure's lifespan due to shaft vibration. Furthermore, the Young's modulus of metal materials is temperature-dependent, and tends to decrease significantly as the temperature increases. Therefore, it is preferable that the air bearing foil member of the present invention also have a high Young's modulus in high-temperature environments. Specifically, the Young's modulus of the air bearing foil member of the present invention is preferably 170 GPa or more at 200°C, preferably 160 GPa or more at 400°C, preferably 145 GPa or more at 600°C, and preferably 130 GPa or more at 600°C. These Young's moduli can be obtained by applying an appropriate aging treatment to the alloy material processed into a thin metal plate in addition to the alloy composition specified in the present invention.

[0034] Next, we will discuss the reasons for limiting the preferred structure of the air bearing foil component. <Spherical γ prime phase particle size: 10 to 60 nm> First, the primary precipitation-strengthening phase of the alloy material specified in the present invention is spherical γ prime phase particles, which significantly contribute to the strength of the alloy material in the present invention. Essentially, the composition specified in the present invention and appropriate aging conditions are used to preferentially precipitate the spherical γ prime particles that contribute to the aforementioned strength, while preventing the precipitation of γ double prime phase particles. Spherical γ prime phase particles do not necessarily have a perfect spherical shape; for example, they do not have angular shapes such as cubes or rectangular parallelepipeds, nor shapes with slightly rounded corners. Because the γ prime phase is stable up to higher temperatures than the γ double prime phase, if strength at high temperatures, such as 600°C or higher, is required, a composition in which the γ prime phase is the precipitation-strengthening phase is selected. When the γ double prime phase becomes the primary precipitation strengthening phase, strength significantly decreases at temperatures above 600°C. Therefore, the present invention specifies a preferred size of spherical γ prime phase particles as the precipitation strengthening phase. The "particle size" of the precipitated γ prime phase specified in the present invention refers to the circle-equivalent diameter when observed with a scanning electron microscope. Here, the circle-equivalent diameter is the average value measured by image processing of several dozen γ prime phase particles with distinguishable sizes observed within an area of ​​approximately 0.8 μm × 1.0 μm in any observation image of the scanning electron microscope. To obtain a preferred 0.2% proof stress of an air bearing foil member, the particle size of the spherical γ prime phase particles is preferably 10 nm or more through appropriate aging treatment. However, coarsening beyond 60 nm makes it difficult to obtain a preferred 0.2% proof stress. Therefore, the particle size of the spherical γ prime phase particles is preferably 10 to 60 nm. The composition and particle size of the γ prime phase particles precipitated by aging vary depending on the composition of the alloy material for the air bearing foil component, but within these ranges, a desirable 0.2% proof stress can be achieved. The spherical γ prime phase particles dispersed and precipitated by aging treatment will grow further if the air bearing is used at a high temperature and exposed to high temperatures for a long period of time. If the spherical γ prime phase particles grow and become coarse, the 0.2% proof stress will decrease if the material is used at high temperatures for a long period of time. Therefore, it is preferable to minimize the decrease in particle number and prevent excessive growth.To avoid a significant decrease in strength even when exposed to high temperatures for a long period of time, it is preferable that the gamma prime phase particles maintain their spherical shape and have a particle size of 200 nm or less after being held at 800°C for 400 hours.

[0035] The gamma prime precipitation-strengthened austenitic Fe-based alloy material of the present invention, which can be used as an air bearing foil member by at least undergoing a solution treatment and an aging treatment, has a thermal sag of 2.5 mm or less. A method for measuring the thermal sag of the present invention is described below. First, a test piece 0.2 mm thick, 10 mm wide, and 100 mm long is taken from a gamma prime precipitation-strengthened austenitic Fe-based alloy material that has been solution-treated at 1,050°C for 5 minutes and aging-treated at 850°C for 4 hours. Both longitudinal ends of the 100 mm-long plate-shaped test piece are fixed at 10 mm positions. The longitudinal center of the test piece is then bent 5 mm in the depth direction and fixed in a deflected state due to elastic deformation. The test piece is then heated and held at 600°C for 50 hours. The amount of deflection after cooling is taken as the thermal sag of the present invention. A preferred thermal sag is 2.2 mm or less. Air bearing foil members obtained from the gamma prime precipitation strengthened austenitic Fe-based alloy material of the present invention having these characteristics have a wide elastic deformation range even in high temperature environments, making them suitable for use as air bearing foils.

[0036] In the gamma prime precipitation hardened austenitic Fe-based alloy material of the present invention, when the heating conditions are changed to 600°C for 100 hours in the above-mentioned measurement of the thermal sag, the thermal sag is 2.5 mm or less (preferably 2.3 mm or less). Furthermore, in the gamma prime precipitation hardened austenitic Fe-based alloy material of the present invention, when the heating conditions are changed to 700°C for 4 hours in the above-mentioned measurement of the thermal sag, the thermal sag is 1.0 mm or less (preferably 0.5 mm or less, more preferably 0.3 mm or less). Furthermore, in the gamma prime precipitation hardened austenitic Fe-based alloy material of the present invention, when the heating conditions are changed to 700°C for 50 hours in the above-mentioned measurement of the thermal sag, the thermal sag is 1.0 mm or less (preferably 0.5 mm or less). Furthermore, in the measurement of the above-mentioned thermal sag of the gamma prime precipitation strengthened austenitic Fe-based alloy material of the present invention, when the heating holding conditions are changed to a temperature of 800°C for 4 hours, the thermal sag is 2.5 mm or less (preferably 2.3 mm or less).

[0037] Example 1 Table 1 shows example compositions of alloy materials according to an embodiment and a comparative example that serve as foil members for air bearings to which the manufacturing method of the present invention is applied. Alloy materials 1 and 2 have a Ni content of 60% or less, and alloy material 10 has a composition with a Ni content of 70% or more. A 2-mm-thick cold-rolled material was extracted from hot-worked materials having these alloy compositions, and cold-rolled materials (thin metal sheets) with a thickness of 0.2 mm were produced by repeatedly cold-rolling and annealing. The thin metal sheets of alloy material 1 and alloy material 2 were subjected to a solution treatment at 1050°C for 5 minutes, followed by an aging treatment at 750°C for 4 hours. Alloy material 10 was subjected to a solution treatment at 1070°C for 5 minutes, followed by an aging treatment at 700°C for 16 hours. Test pieces measuring 0.2 mm thick, 10 mm wide, and 100 mm long were taken from the aged material, and both ends of the 100 mm long plate-shaped test pieces were fixed at 10 mm positions in the longitudinal direction. The test pieces were then bent 5 mm in the depth direction at the center of the longitudinal direction, and fixed in a state where they were deflected by elastic deformation. They were then heated at 700°C for 4 hours and 50 hours, cooled, and removed, and the amount of plastic deformation (hereinafter referred to as thermal settling) was measured and evaluated.

[0038]

[0039] Figure 1 shows the thermal settling of aged materials after heating and cooling at 700°C for 4 and 50 hours. Under all conditions, the thermal settling of Alloy Materials 1 and 2, which are examples of the present invention, was 0.4 mm or less, which was smaller than the thermal settling of Comparative Alloy Material 100, indicating that thermal settling at high temperatures is unlikely to occur.

[0040] Figure 2 shows scanning electron microscope (SEM) images of γ prime phase particles in hot-worked alloy materials 1 and 2 (aged materials) that were aged at 750°C for 4 hours, and in hot-worked alloy material 100 that was aged at 700°C for 16 hours, labeled "Aged Materials." Also shown is a representative example of an SEM image of γ prime phase particles in alloy materials 1, 2, and 100 after aging and subsequent heating and holding at 800°C for 400 hours, labeled "Aged Materials → After 800°C x 400h Holding." The scale bar in the SEM image indicates 0.5 μm, or 500 nm, indicating that the particle size of the γ prime phase particles in the aged materials is in the range of 10 to 60 nm. Furthermore, it can be seen that the γ prime phase particles have grown, but are less than 200 nm, after heating and holding at 800°C for 400 hours. However, while the gamma prime particles of Alloy Materials 1 and 2, which were aged at 800°C for 400 hours, were spherical, the gamma prime particles of Alloy Material 100, which was aged at 800°C for 400 hours, were changed to a rectangular parallelepiped shape with rounded corners. Furthermore, the number of particles was small, suggesting that the long-term high-temperature holding time caused the particles to coarsen and soften. Furthermore, Alloy Material 1 was aged at 750°C for 4 hours, and its magnetic permeability was measured to be 1.01 or less, confirming its nonmagnetic nature. The SEM used for observation was a JIB-4700 (manufactured by JEOL Ltd.) with a resolution of 12 nm, and observations were performed under conditions of an accelerating voltage of 20 kV and a working distance (WD) of 6.0 mm.

[0041] (Example 2) Subsequently, the room temperature and high temperature Young's moduli were measured. Table 2 shows the alloy compositions of alloy materials 3 to 7, which have a Ni content of 60% or less, and alloy material 101, which has a Ni content of 70% or more. Hot-rolled materials with a thickness of 2 mm were produced from hot-worked materials having the compositions of alloy materials 3 to 7 and 11 described above, and these hot-rolled materials were subjected to solution treatment and aging treatment to obtain aged materials. Alloy materials 3 to 6 were subjected to solution treatment at 1050°C for 30 minutes, followed by aging treatment at 850°C for 4 hours. Alloy material 7 was subjected to solution treatment at 980°C for 30 minutes, followed by aging treatment at 800°C for 4 hours. Alloy material 101 was subjected to solution treatment at 980°C for 30 minutes, followed by aging treatment at 700°C for 20 hours. Test pieces measuring 1.5 mm thick, 60 mm long, and 10 mm wide were prepared from these aged materials. Young's modulus was measured by the cantilever resonance method in accordance with JIS Z 2280-1993. Tests at room temperature (25°C) were conducted in air, and tests at high temperatures from 100°C to 800°C were conducted in an Ar gas atmosphere. The results of Young's modulus measurements from 25°C to 800°C are shown in Table 3. It was confirmed through prior observation that the grain size of the gamma prime phase particles in the aged materials of the present invention examples was in the range of 10 to 60 nm.

[0042]

[0043]

[0044] As shown in Table 3, although the Young's moduli of the aged materials 3 to 7, which are examples of the present invention, were all slightly lower than that of Alloy Material 101, which contains a large amount of Ni, they were still able to exhibit sufficient Young's modulus characteristics for air bearing applications with an extremely short aging treatment time, less than one-quarter that of Alloy Material 101. Specifically, the Young's moduli of the examples of the present invention at room temperature (25°C) were 190 GPa or more, the Young's moduli of the examples of the present invention at 200°C were 180 GPa or more, the Young's moduli of the examples of the present invention at 400°C were 170 GPa or more, the Young's moduli of the examples of the present invention at 600°C were 155 GPa or more, and the Young's moduli of the examples of the present invention at 800°C were 140 GPa or more. In particular, Alloy Material 3 showed no decrease in Young's modulus between 300°C and 400°C, Alloy Material 6 showed no decrease in Young's modulus between 500°C and 600°C, and Alloy Material 7 showed no decrease in Young's modulus between 300°C and 500°C, confirming that they have excellent high-temperature Young's modulus characteristics.

[0045] (Example 3) Next, the relative magnetic permeability of alloy materials 3 to 7 and 101 was also measured. Samples of φ20 × 10 mm were taken from the aged alloy materials 3 to 7 and 101 produced under the same conditions as in Example 2, and the samples were measured using a low magnetic permeability measuring device "μ meter" manufactured by Denshijiki Kogyo Co., Ltd. The measurement results are shown in Table 4. The relative magnetic permeability is the average of measurements obtained by measuring the front and back surfaces of the sample once each. As a result of the measurement, it was confirmed that all of the aged alloy materials were non-magnetic, with a relative magnetic permeability of 1.01 or less.

[0046]

[0047] Example 4: Test conditions were changed from those of Example 1, and heat setting properties were measured. 2-mm-thick cold-rolled materials were extracted from hot-worked materials having the alloy compositions shown in Table 5. Cold-rolled materials (thin metal plates) with a thickness of 0.2 mm were produced by repeatedly cold-rolling and annealing. Alloy 8 to Alloy 11 were subjected to a solution treatment at 1050°C for 5 minutes, followed by aging treatment at 850°C for 4 hours. Alloy 102 was subjected to a solution treatment at 980°C for 5 minutes, followed by aging treatment at 700°C for 20 hours. Alloy 103 was subjected to a solution treatment at 980°C for 30 minutes, followed by aging treatment at 700°C for 20 hours. Test specimens with a thickness of 0.2 mm, width of 10 mm, and length of 100 mm were extracted from these aged specimens, and both longitudinal ends of the 100-mm-long plate-shaped test specimens were fixed at 10 mm positions. The test specimen was then bent 5 mm in the depth direction at the center of its length and fixed in a state where it was bent elastically, and heated and held at 400°C for 50 hours, 400°C for 100 hours, 600°C for 50 hours, and 600°C for 100 hours. After cooling, the specimen was removed and the amount of plastic deformation (amount of thermal settling) was measured for evaluation. Alloy material 102 is a material equivalent to Alloy 718, whose main precipitation strengthening phase is γ double prime.

[0048]

[0049]

[0050] As can be seen from Table 6, under the test conditions of 400°C, all samples had similar amounts of thermal sag, regardless of the heating time. On the other hand, under the heating holding condition of 600°C for 50 hours, the amounts of thermal sag for Inventive Examples 8 to 11 were 2.0 mm or less, and under the heating holding condition of 600°C for 100 hours, the amounts of thermal sag for Inventive Examples 8 to 11 were 2.2 mm or less. Both of these amounts were smaller than the amounts of thermal sag for alloy materials 102 and 103, which were subjected to aging treatment as comparative examples, indicating that thermal sag at high temperatures is less likely to occur.

[0051] (Example 5) Further, the test conditions were changed to measure the thermal sag characteristics. In addition to Alloy Materials Nos. 1, 2, and 100 used in Example 1, 2 mm thick cold-rolled materials were collected from hot-worked materials having the alloy compositions shown in Table 6. Cold-rolled materials (thin metal plates) with a thickness of 0.2 mm were produced by repeatedly cold-rolling and annealing. Alloy Materials 1, 2, and 101 were subjected to the same solution treatment and aging treatment as in Example 1. Alloy Material 104 was subjected to a solution treatment at 980°C for 5 minutes, followed by aging at 720°C for 8 hours and then aging at 620°C for 8 hours. Test specimens with a thickness of 0.2 mm, width of 10 mm, and length of 100 mm were collected from these aged specimens, and both longitudinal ends of the 100 mm long plate-shaped test specimens were fixed at 10 mm positions. The test specimen was then bent 5 mm in the depth direction at the center of its length, and fixed in a state where it was bent by elastic deformation, and heated at 800°C for 4 hours and 50 hours, and after cooling, it was removed and evaluated by measuring the amount of plastic deformation (amount of thermal settling). In addition, the alloy material 104 alone was also measured for the amount of thermal settling when heated at 700°C for 4 hours and 50 hours, which was the same condition as in Example 1.

[0052]

[0053]

[0054] From Table 8, it was confirmed that under the test conditions of 800°C for 4 hours, the thermal sag of alloy materials Nos. 1 and 2, which are examples of the present invention and which were subjected to aging treatment, was 2.3 mm or less, which was smaller than that of alloy materials 100 and 104, which were comparative examples and which were subjected to aging treatment. Furthermore, when compared with invention examples 1 and 2 in Figure 1, it was found that sample No. 104 had a large thermal sag even under the test conditions of 700°C.

[0055] From the above, it can be seen that the alloy material that has undergone the aging treatment of the present invention has a low content of Ni, a valuable resource, but also has little thermal settling, and is therefore thought to have a wider elastic deformation range than the comparative Ni-based alloy, from room temperature to high temperatures of around 800°C.It also has excellent Young's modulus characteristics, making it suitable for use as an air bearing foil component used in an elastic deformation range.

Claims

1. A method for manufacturing a foil member for an air bearing, comprising at least an aging treatment step of performing aging treatment at 600 to 860°C on a gamma prime precipitation strengthened austenitic Fe-based alloy material containing 60.0% or less Ni by mass%, to obtain a foil member for an air bearing having a thickness of 0.01 to 1.0 mm and a magnetic permeability of 1.01 or less.

2. A method for manufacturing an air bearing foil member as set forth in claim 1, wherein the gamma prime precipitation strengthened austenitic Fe-based alloy further contains Al: more than 0.05% and not more than 3.0%, Ti: 1.5 to 3.0%, and Nb: not more than 2.5% (including 0%).

3. The gamma prime precipitation strengthened austenitic Fe-based alloy material contains, by mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less (including 0%), S: 0.01% or less (including 0%), Ni: 25.0 to 60.0%, Cr: 10.0 to 20.0%, one or both of Mo and W: Mo+W / 2: 0.05 to 4.0%, Al: more than 0.05% and 3.0% or less, 2. A method for manufacturing an air bearing foil member according to claim 1, characterized in that the alloy consists of Ti: 1.5 to 3.0%, Nb: 2.5% or less (including 0%), V: 1.0% or less (including 0%), B: 0.001 to 0.015%, Mg: 0.0005 to 0.01%, Mg / S: 1.0 or more, N: 0.01% or less (including 0%), O: 0.005% or less (including 0%), the balance being Fe and unavoidable impurities.

4. A method for manufacturing an air bearing foil member according to any one of claims 1 to 3, characterized in that the aging treatment temperature is 690 to 860°C, the aging treatment time is 1 to 10 hours, and the particle size of the spherical gamma prime phase particles is 10 to 60 nm.

5. A gamma prime precipitation strengthened austenitic Fe-based alloy material containing 60.0% or less Ni by mass, having a gamma prime phase when subjected to at least aging treatment, and usable as a foil member for an air bearing, wherein the gamma prime precipitation strengthened austenitic Fe-based alloy material has a heat sag of 2.5 mm or less, wherein the heat sag is defined as follows: the gamma prime precipitation strengthened austenitic Fe-based alloy material is subjected to a solution treatment at 1050°C for 5 minutes and an aging treatment at 850°C for 4 hours, and a test piece having a thickness of 0.2 mm, a width of 10 mm, and a length of 100 mm is taken from the alloy material after the aging treatment; the 100 mm long plate-shaped test piece is fixed at both longitudinal ends 10 mm apart, and then the longitudinal center of the test piece is bent by 5 mm in the depth direction and fixed in a deflected state; the test piece is heated and held at 600°C for 50 hours; and the deflection deformation amount is measured after cooling.

6. A gamma prime precipitation hardened austenitic Fe-based alloy material containing 60.0% or less Ni by mass, having a gamma prime phase when subjected to at least aging treatment, and usable as a foil member for an air bearing, wherein the gamma prime precipitation hardened austenitic Fe-based alloy material has a heat sag of 2.5 mm or less, wherein the heat sag is defined as follows: the gamma prime precipitation hardened austenitic Fe-based alloy material is solution treated at 1050°C for 5 minutes and aged at 850°C for 4 hours, a test piece having a thickness of 0.2 mm, a width of 10 mm, and a length of 100 mm is taken from the aging-treated alloy material, and the 100 mm long plate-shaped test piece is fixed at both longitudinal ends 10 mm apart, and then the longitudinal center of the test piece is bent 5 mm in the depth direction and fixed in this deflected state, and the test piece is heated and held at 600°C for 100 hours, followed by cooling, and the amount of deflection is defined as the amount of deflection deformation occurring after cooling.

7. A gamma prime precipitation hardened austenitic Fe-based alloy material containing 60.0% or less Ni by mass, having a gamma prime phase after at least aging treatment, and usable as a foil member for an air bearing, wherein the gamma prime precipitation hardened austenitic Fe-based alloy material has a heat sag of 0.5 mm or less, wherein the heat sag is defined as follows: the gamma prime precipitation hardened austenitic Fe-based alloy material is solution treated at 1050°C for 5 minutes and aged at 850°C for 4 hours, a test piece having a thickness of 0.2 mm, a width of 10 mm, and a length of 100 mm is taken from the aging-treated alloy material, both ends of the 100 mm-long plate-shaped test piece are fixed at 10 mm in the longitudinal direction, and the central portion of the test piece is bent 5 mm in the depth direction and fixed in a deflected state, and the test piece is heated and held at 700°C for 4 hours, followed by cooling, and the amount of deflection is defined as the amount of deflection deformation occurring after cooling.

8. A gamma prime precipitation hardened austenitic Fe-based alloy material containing 60.0% or less Ni by mass, having a gamma prime phase when subjected to at least aging treatment, and usable as a foil member for an air bearing, wherein the gamma prime precipitation hardened austenitic Fe-based alloy material has a heat sag of 0.5 mm or less, wherein the heat sag is defined as follows: the gamma prime precipitation hardened austenitic Fe-based alloy material is solution treated at 1050°C for 5 minutes and aged at 850°C for 4 hours, a test piece having a thickness of 0.2 mm, a width of 10 mm, and a length of 100 mm is taken from the aging-treated alloy material, both ends of the 100 mm-long plate-shaped test piece are fixed at 10 mm in the longitudinal direction, and the central portion of the test piece is bent 5 mm in the depth direction and fixed in a deflected state, and the test piece is heated and held at 700°C for 50 hours, followed by cooling, and the amount of deflection is defined as the amount of deflection deformation occurring after cooling.

9. A gamma prime precipitation hardened austenitic Fe-based alloy material containing 60.0% or less Ni by mass, having a gamma prime phase after at least aging treatment, and usable as a foil member for an air bearing, wherein the gamma prime precipitation hardened austenitic Fe-based alloy material has a heat sag of 2.5 mm or less, wherein the heat sag is defined as follows: the gamma prime precipitation hardened austenitic Fe-based alloy material is solution treated at 1050°C for 5 minutes and aged at 850°C for 4 hours, a test piece having a thickness of 0.2 mm, a width of 10 mm, and a length of 100 mm is taken from the aging-treated alloy material, and the 100 mm long plate-shaped test piece is fixed at both longitudinal ends 10 mm apart, and then the longitudinal center of the test piece is bent 5 mm in the depth direction and fixed in a deflected state, and the test piece is heated and held at 800°C for 4 hours, followed by cooling, and the amount of deflection is defined as the amount of deflection deformation occurring after cooling.

10. A method for manufacturing an air bearing foil member according to any one of claims 5 to 9, wherein the gamma prime precipitation strengthened austenitic Fe-based alloy further contains Al: more than 0.05% and not more than 3.0%, Ti: 1.5 to 3.0%, and Nb: not more than 2.5% (including 0%).

11. By mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less (including 0%), S: 0.01% or less (including 0%), Ni: 25.0 to 60.0%, Cr: 10.0 to 20.0%, one or both of Mo and W: Mo+W / 2: 0.05 to 4.0%, Al: more than 0.05% and 3.0% or less, Ti: 1.5 to 3.0%, Nb: 2.5% 10. The gamma prime precipitation strengthened austenitic Fe-based alloy material according to any one of claims 5 to 9, characterized in that it consists of 0.0% or less (inclusive of 0%), V: 1.0% or less (inclusive of 0%), B: 0.001 to 0.015%, Mg: 0.0005 to 0.01%, Mg / S: 1.0 or more, N: 0.01% or less (inclusive of 0%), O: 0.005% or less (inclusive of 0%), the balance being Fe and unavoidable impurities.

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