Cobalt-chromium alloy member, method for producing the same, and device using the same

Abstract

Provided is a cobalt-chromium alloy member suitable for use in medical devices, devices for gas turbines, or devices for other industrial equipment. This cobalt-chromium alloy member comprises a composition that contains, expressed in terms of mass%, 23-32% Ni, 37-48% Co, and 8-12% Mo with the balance being Cr and unavoidable impurities, wherein the composition also satisfies 20 ≤ [Cr%] + [Mo%] + [unavoidable impurities%] ≤ 40. The cobalt-chromium alloy member has a crystal structure composed of the face-centered cubic lattice (fcc), or has a crystal structure composed of the face-centered cubic lattice (fcc) and the hexagonal close-packed lattice (hcp), and has an average crystal grain size of 2-15 µm, a local crystal orientation variation (KAM value) of 0.0-1.0, both inclusive, a tensile strength of 800-1,200 MPa, and an elongation at break of 30-80%.

Description

Technical Field

[0001] The present invention relates to a cobalt-chromium alloy member suitable for medical devices such as stents, medical tubes, and medical guidewires, gas turbine devices used in high-temperature environments or corrosive environments, or other industrial equipment devices, and a method for manufacturing the same. In particular, it relates to the improvement of a cobalt-chromium alloy material that is excellent in corrosion resistance, biocompatibility, high strength, and ductility, and is suitable for implantable medical devices in the body.

Background Art

[0002] For metal members used in medical devices, especially metal members implanted in the body, metals that are excellent in corrosion resistance, biocompatibility, and have high mechanical properties are required, and stainless steel, nickel-titanium alloys, cobalt-chromium alloys, etc. have been used. As such biocompatible alloys, for example, cobalt-chromium alloys for dental casting (JIS T6115) are known, and dental stainless steel wires (JIS T6103) are known for nickel-containing alloys.

[0003] Among cobalt-chromium alloy members, a stent is a hollow tubular object intended to expand and maintain a narrowed blood vessel in the body, and is roughly classified into a self-expanding stent and a balloon-expandable stent. A self-expanding stent is fixed to the tip of a catheter, and self-expanding properties are imparted by using a superelastic alloy or a shape memory alloy from the catheter at a predetermined position. For example, a stent using a nickel-titanium alloy has been put into practical use.

[0004] A balloon-expandable stent is a stent that is fixed to a balloon catheter by diameter compression and expands the diameter by balloon expansion at a predetermined position. Mainly, stainless steel SUS316L and cobalt-chromium alloys have been put into practical use. For example, when stenosis occurs in a blood vessel, it is placed after expanding the stenotic part with a balloon catheter, supports the blood vessel inner wall from the inside, and is used to prevent restenosis. Regarding the insertion of the stent, the stent is attached to the tip of the catheter in a reduced-diameter state outside the balloon in a contracted state and inserted into the blood vessel together with the balloon part. After positioning the balloon part at the stenotic site, the stent is expanded by inflating the balloon part, the stent is placed in the expanded state of the stenotic part, and the balloon catheter is withdrawn. As alloys for balloon-expandable stents, ASTM F90-14 (Co-20Cr-15W-10Ni alloy (L605 alloy)), ASTM F562-13 (Co-20Cr-10Mo-35Ni alloy (MP35N alloy)), and SUS316L are known as surgical implant materials (see Non-Patent Documents 1, 3, and 4).

[0005] On the other hand, fractures of implanted metals in the orthopedic field and early fractures of stents in the cardiovascular medicine field have been reported, and there is a demand for metal members with more excellent fatigue characteristics. We have proposed an alloy with improved low-cycle fatigue characteristics for L605 (Co-20Cr-15W-10Ni) alloy and MP35N (Co-20Cr-10Mo-35Ni) alloy, which are most commonly used as coronary stent materials (see Patent Document 1). The composition of this alloy is in mass%, Cr is 10 to 27%, Mo is 3 to 12%, Ni is 22 to 34%, and the balance is substantially composed of Co and unavoidable impurities, but Co is preferably 37 to 48%.

[0006] A guide wire assists in inserting a diagnostic or therapeutic catheter used inside a blood vessel to a predetermined position within the blood vessel, and has a structure in which a thin wire is wound around a core wire. The guide wire requires sufficient strength and ductility so that the rotation of the tip follows the rotation at the operator's hand and does not break during the procedure. Note that Non-Patent Document 2 explains the general relationship between strength and hardness.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Non-Patent Documents

[0008]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] L605, which is a currently used Co-Cr alloy, and Ti-Ni alloys are materials that are difficult to cold-work, and their processing costs are extremely high compared to SUS316. Recently, there has been a demand for cobalt-chromium alloy members that are suitable for medical devices, gas turbine devices, and other industrial equipment devices and have high mechanical strength and ductility. In particular, there is a need to use intravascular implantable medical devices such as stents for blood vessels with fine and complex shapes such as nerve defects and blood vessels in the brain. For this purpose, it is necessary to use a thin and narrow tube to make the struts, which are the metal parts of the stent, thinner. Even so, in order to ensure sufficient blood vessel holding force, a material with as high strength as possible is required. This also leads to a reduction in the amount of metal implanted in the body. In the case of guidewires, using a wire that is as thin as possible makes it easier to insert into fine blood vessels. However, in order to achieve better torque transmission, it is necessary to have as high strength as possible. Furthermore, a ductile material is desirable to prevent breakage during use.

[0010] An object of the present invention is to provide a cobalt-chromium alloy member suitable for use in medical devices, gas turbine devices, and other industrial equipment devices. In particular, another object of the present invention is to provide a cobalt-chromium alloy member suitable for a guidewire that facilitates the insertion of an intravascular implantable medical device such as a stent into fine blood vessels.

Means for Solving the Problems

[0011] To achieve the above object, the cobalt-chromium alloy member of the present invention adopts the following configuration. [1] In terms of mass%, Ni is 23 to 32%, Co is 37 to 48%, and Mo is 8 to 12%, and the balance contains Cr and inevitable impurities, and 20 ≤ [Cr%] + [Mo%] + [inevitable impurity%] ≤ 40, and it consists of a composition that satisfies the above, has a crystal structure composed of a face-centered cubic lattice (fcc), or a crystal structure composed of a face-centered cubic lattice (fcc) and a hexagonal lattice (hcp), the average value of the crystal grain size is 2 to 15 μm, and the local crystal orientation change amount (KAM value) is 0.0 or more and 1.0 or less, and the tensile strength is 800 to 1200 MPa and the elongation at break is 30 to 80%. Cobalt-chromium alloy member.

[0012] [2] The cobalt-chromium alloy member described in [1] is preferably obtained by heat-treating a cobalt-chromium alloy as-worked material obtained by plastically working a cobalt-chromium alloy material having the above composition into a predetermined shape at a heat treatment temperature exceeding the recrystallization temperature of the cobalt-chromium alloy material. [3] The cobalt-chromium alloy member described in [1] or [2] is preferably, in terms of mass%, Ni is 25 to 29%, Co is 37 to 48%, Mo is 9 to 11%, and the balance contains Cr and inevitable impurities, and 23 ≤ [Cr%] + [Mo%] + [inevitable impurity%] ≤ 38, and it preferably consists of a composition that satisfies the above. [4] The cobalt-chromium alloy member described in [3] is preferably heat-treated at a heat treatment temperature exceeding the recrystallization temperature of the cobalt-chromium alloy material for the cobalt-chromium alloy as-worked material obtained by plastically working the cobalt-chromium alloy material having the above composition into a predetermined shape, at 800°C or higher and 1100°C or lower, for 1 minute or more and 60 minutes or less.

[0013] [5] In the cobalt-chromium alloy member according to any one of [1] to [4], The inevitable impurities preferably have contents of Ti, Mn, Fe, Nb, W, Al, Zr, B, and C in mass %, with Ti being 1.0% or less, Mn being 1.0% or less, Fe being 1.0% or less, Nb being 1.0% or less, W being 1.0% or less, Al being 0.5% or less, Zr being 0.1% or less, B being 0.01% or less, and C being 0.1% or less.

[0014] [6] In the cobalt-chromium alloy member having the composition according to any one of [1] to [5], the predetermined shape plastically processed by cold working is tubular, the average value of the crystal grain size is 2 to 15 μm, the local crystal orientation change amount (KAM value) is 0.1 or more and 0.8 or less, and the tensile strength is 800 to 1000 MPa and the elongation at break is 30 to 80%. It is preferably a cobalt-chromium alloy member. [7] In the cobalt-chromium alloy member having the composition according to any one of [1] to [5], the predetermined shape plastically processed by cold working is wire-shaped, the average value of the crystal grain size is 4 to 15 μm, the local crystal orientation change amount (KAM value) is 0.0 or more and 1.0 or less, and the tensile strength is 1000 to 1200 MPa and the elongation at break is 30 to 60%. It is preferably a cobalt-chromium alloy member.

[0015] [8] It is preferably a device using the cobalt-chromium alloy member according to any one of [1] to [7]. Preferably, this device is a medical device, a gas turbine device, or a device for other industrial equipment.

[0016] [9] The device according to [8] is preferably any medical device such as a stent, a tube, a wire, or an implant. The device described in

[10] [9] may be a gas turbine device for any of the combustors and exhaust components of aviation and industrial gas turbine engines such as tail pipes, combustion cylinders, spray burners, frame holders, afterburners, and tail pipes. The device described in

[11] [9] may be a device for industrial equipment used in waste incinerators, boilers, high-temperature reaction vessels and rotary calcining furnaces, and petrochemical product manufacturing plants and synthesis gas plants.

[0017]

[12] By mass, Ni is 23 to 32%, Co is 37 to 48%, Mo is 8 to 12%, and the balance contains Cr and unavoidable impurities. 20 ≤ [Cr%] + [Mo%] + [unavoidable impurity%] ≤ 40 Prepare a cobalt-chromium alloy material having a composition that satisfies the above conditions. Homogenize the prepared cobalt-chromium alloy material at 1100°C to 1300°C. Plastically process the homogenized cobalt-chromium alloy material cold into a tubular or wire shape to obtain a as-processed cobalt-chromium alloy material. Perform heat treatment on the cold-plastically processed as-processed cobalt-chromium alloy material at a temperature exceeding the recrystallization temperature of the cobalt-chromium alloy material and not exceeding 1100°C for 1 minute or more and 60 minutes or less to obtain a cobalt-chromium alloy member having a crystal structure composed of a face-centered cubic lattice (fcc), or a crystal structure composed of a face-centered cubic lattice (fcc) and a hexagonal lattice (hcp), the average value of the crystal grain size being 2 to 15 μm, and the local crystal orientation change amount (KAM value) being 0.0 or more and 1.0 or less. A method for manufacturing a cobalt-chromium alloy member.

Advantages of the Invention

[0018] The cobalt-chromium alloy member of the present invention has a crystal structure composed of a face-centered cubic lattice (fcc) or a crystal structure composed of a face-centered cubic lattice (fcc) and a hexagonal lattice (hcp) by heat treatment exceeding the recrystallization temperature after cold plastic working. The average value of the crystal grain size is 2 to 15 μm, and the local crystal orientation change amount (KAM value) is 0 or more and 1.0 or less. Therefore, it has excellent mechanical properties such as improved strength and ductility, and higher reliability than existing products. From this, for example, when a medical device for internal implantation such as a stent is manufactured using the cobalt-chromium alloy member of the present invention, the reliability of the stent at the time of implantation is increased, and the implantation into the affected part becomes easier.

[0019] In the cobalt-chromium alloy member of the present invention, after cold plastic working an alloy mainly composed of Co, Ni, Cr, and Mo, heat treatment at a temperature equal to or higher than the recrystallization temperature stabilizes the face-centered cubic lattice (fcc) phase. As a result, in the formed fcc phase, during the deformation of the cobalt-chromium alloy member, fcc twin deformation and transformation from fcc to hexagonal lattice (hcp) due to deformation induction occur, showing high work hardening ability and excellent mechanical strength and ductility. In addition, in the cobalt-chromium alloy member of the present invention, when solute atoms such as Mo and Nb are further contained, they can be segregated to the dislocation core or the stacking defect of the extended dislocation to make cross slip difficult to occur, and the mechanical strength becomes even higher due to work hardening.

Brief Description of the Drawings

[0020]

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Mode for Carrying Out the Invention

[0021] [Summary of the Invention] The cobalt-chromium alloy member of the present invention is obtained by subjecting a cobalt-chromium alloy material having a specific composition to cold plastic working (hereinafter also simply referred to as "cold working") into a predetermined shape such as a tube shape or a wire shape, and then performing a specific heat treatment exceeding the recrystallization temperature. The resulting member has a crystal structure composed of a face-centered cubic lattice (fcc), or a crystal structure composed of a face-centered cubic lattice (fcc) and a hexagonal lattice (hcp). The average value of the crystal grain size is 2 to 15 μm, the local crystal orientation change amount (KAM value) is 0.0 or more and 1.0 or less, the tensile strength is 800 to 1200 MPa, and the elongation at break is 30 to 80%. In particular, the cobalt-chromium alloy member of the present invention is characterized in that a member having a local crystal orientation change amount (KAM value) of 0.0 or more and 1.0 or less can be obtained. Thereby, a cobalt-chromium alloy member exhibiting high work hardening ability and excellent mechanical strength and ductility can be obtained. Hereinafter, the details of the present invention will be described.

[0022] [Details of the Present Invention] (Cobalt-Chromium Alloy Material) The cobalt-chromium alloy material of the present invention has a composition in which Ni is 23 to 32%, Co is 37 to 48%, Mo is 8 to 12%, and the balance contains Cr and inevitable impurities and satisfies 20 ≦ [Cr%] + [Mo%] + [inevitable impurity%] ≦ 40. Inevitable impurities refer to components that are not intentionally added but are inevitably mixed due to the material or the process. The components of the inevitable impurities are not particularly limited, and examples include Ti, Mn, Fe, Nb, W, Al, Zr, B, or C, etc., and they may not be contained. Further, the cobalt-chromium alloy material of the present invention is not particularly limited as long as it has a specific composition range. As described later, it may be homogenized, may be hot-worked such as hot rolling or hot forging, or may be processed into a specific shape by cutting or the like.

[0023] The reason for limiting the composition range of the cobalt-chromium alloy material of the present invention will be described below. The content of each component of the cobalt-chromium alloy material is the content (mass %, hereinafter simply referred to as “%”) when the entire cobalt-chromium alloy material is 100 mass %. In addition, the numerical range of the present invention includes the upper limit value and the lower limit value. The same applies not only to the composition ranges shown below, but also to the temperature treatment range, the tensile strength range, and the ranges of elongation at break and uniform elongation. However, this is not the case when it is clearly stated that the numerical range does not include the upper limit value or the lower limit value, such as “exceeding” or “less than”.

[0024] Ni (nickel) stabilizes the face-centered cubic lattice phase, maintains workability, enhances corrosion resistance, improves low-cycle fatigue life, and has the effect of improving strength and ductility by heat treatment exceeding the recrystallization temperature after cold working. However, in the composition ranges of Co, Cr, and Mo of the cobalt-chromium alloy material of the present invention, when the content of Ni is less than 23%, it is difficult to obtain the effect of improving strength and ductility by the heat treatment, and when it exceeds 32%, it is also difficult to obtain the effect of improving strength and ductility by the heat treatment. Therefore, the Ni content of the present invention is 23 to 32%, preferably 25 to 29%. Thereby, the effect of improving strength and ductility can be further obtained.

[0025] Co (cobalt) itself has a large work hardening ability, reduces notch brittleness, increases fatigue strength, increases high-temperature strength, improves low-cycle fatigue life, and has the effect of improving strength and ductility by heat treatment exceeding the recrystallization temperature after cold working. When the content of Co is less than 37%, the effect is weak. In this composition, when it exceeds 48%, the matrix becomes too hard and processing becomes difficult, and the effect of improving strength and ductility by heat treatment exceeding the recrystallization temperature after cold working is lost. Therefore, the Co content of the present invention is 37 to 48%, preferably 40 to 45%. Thereby, the effect of improving strength and ductility can be further obtained.

[0026] Molybdenum (Mo) has the effects of solid-solubilizing in the matrix to strengthen it, increasing work hardening ability, and enhancing corrosion resistance when coexisting with Cr. However, if the Mo content is less than 8%, the desired effects cannot be obtained. If it exceeds 12%, the workability will rapidly decrease, and brittle σ-phase is likely to be generated. Therefore, the Mo content of the present invention is 8 - 12%, preferably 9 - 11%. Thereby, the improvement effects of strength and ductility can be further obtained.

[0027] When the total content of Cr, Mo, and inevitable impurities is less than 20% with the total cobalt-chromium alloy material being 100%, the hexagonal lattice (hcp) phase becomes stable. When it exceeds 40%, the face-centered cubic lattice (fcc) phase becomes unstable and the body-centered cubic lattice (bcc) layer is likely to appear. That is, when the total content of Cr, Mo, and inevitable impurities is not 20 - 40%, the fcc phase is difficult to be stabilized. When the cobalt-chromium alloy member obtained thereby is deformed, fcc twin deformation or transformation from fcc to hcp due to deformation induction is less likely to occur, and excellent ductility and low-cycle fatigue life cannot be obtained. Therefore, the total content of Cr, Mo, and inevitable impurities of the present invention is 20 - 40%, preferably 23 - 38%. Thereby, excellent ductility and low-cycle fatigue life can be obtained. In addition, the content of inevitable impurities may be 0%. When it exceeds 0%, the composition ratio of inevitable impurities is adjusted so that the total is 100% based on the composition ratios of Co, Ni, Cr, and Mo.

[0028] Chromium (Cr) is an essential component for ensuring corrosion resistance and also has the effect of strengthening the matrix. When the inevitable impurities are 0%, the Cr content of the present invention is preferably 12 - 28%, more preferably 14 - 27%, and still more preferably 18 - 22%. When it is 12% or more, excellent corrosion resistance is easily obtained. When it is 28% or less, the workability and toughness are less likely to rapidly decrease. Thereby, more excellent corrosion resistance can be obtained while ensuring workability and toughness.

[0029] Ti (titanium) has a strong deoxidizing, denitrifying, and desulfurizing effect. However, if there is too much, inclusions in the alloy will increase, or the η phase (Ni 3 Ti) will precipitate and the toughness will decrease. Therefore, the content of Ti in the present invention is desirably 1.0% or less as an unavoidable impurity.

[0030] Mn (manganese) has a deoxidizing and desulfurizing effect and an effect of stabilizing the face-centered cubic lattice phase. However, if there is too much, the corrosion resistance and oxidation resistance will deteriorate. Therefore, the content of Mn in the present invention is desirably 1.5% or less. More desirably, the upper limit as an unavoidable impurity is 1.0% or less.

[0031] Fe (iron) has a function of stabilizing the face-centered cubic lattice phase and improving workability. However, if there is too much, the oxidation resistance will decrease. Therefore, the content of Fe in the present invention is desirably 1.0% or less as an unavoidable impurity.

[0032] C (carbon) not only dissolves in the matrix but also forms carbides with Cr, Mo, etc., and has an effect of preventing the coarsening of crystal grains. However, if there is too much, a decrease in toughness, deterioration of corrosion resistance, etc. will occur. Therefore, the content of C in the present invention is desirably 0.1% or less.

[0033] Nb (niobium) dissolves in the matrix and strengthens it, and has an effect of increasing the work hardening ability. However, if it exceeds 3.0%, the σ phase or δ phase (Ni 3 Nb) will precipitate and the toughness will decrease. Therefore, the content of Nb in the present invention is desirably 3.0% or less. More desirably, the upper limit as an unavoidable impurity is 1.0% or less.

[0034] W (tungsten) dissolves in the matrix and strengthens it, and has an effect of significantly increasing the work hardening ability. However, if it exceeds 5.0%, the σ phase will precipitate and the toughness will decrease. Therefore, the content of W in the present invention is desirably 5.0% or less. More desirably, the upper limit as an unavoidable impurity is 1.0% or less.

[0035] Aluminum has the effect of deoxidizing and improving oxidation resistance. However, if it is too much, deterioration of corrosion resistance and the like will occur. Therefore, the content of Al in the present invention is desirably 0.5% or less.

[0036] Zirconium has the effect of increasing the grain boundary strength at high temperatures and improving hot workability. However, if it is too much, the workability will conversely deteriorate. Therefore, the content of Zr in the present invention is desirably 0.1% or less.

[0037] Boron has the effect of improving hot workability. However, if it is too much, the hot workability will conversely decrease and it will be prone to cracking. Therefore, the content of B in the present invention is desirably 0.01% or less.

[0038] (As-received cobalt-chromium alloy processed material) The as-received cobalt-chromium alloy processed material of the present invention is obtained by cold working the above cobalt-chromium alloy material into a predetermined shape. In the present invention, due to the occurrence of twin deformation and induced transformation during cold working, fcc deformation twins and hcp phase (ε phase) are introduced, and a high-density banded deformation band structure is formed. Thereby, very high strength can be obtained. In addition, in the present invention, by cold working, the crystal grains are refined, and higher strength is more easily obtained.

[0039] The predetermined shape is not particularly limited, but for example, it is preferably tube-shaped or wire-shaped. Thereby, it can be used for medical or aerospace devices in the shape of tubes or wires.

[0040] (Cobalt-chromium alloy member) The cobalt-chromium alloy member of the present invention is obtained by subjecting the above as-received cobalt-chromium alloy processed material to a specific heat treatment at a temperature above the crystallization temperature. The cobalt-chromium alloy member of the present invention has the same composition as the above cobalt-chromium alloy material. By mass, Ni is 23 to 32%, Co is 37 to 48%, and Mo is 8 to 12%. The balance contains Cr and unavoidable impurities, and has a composition satisfying 20 ≤ [Cr%] + [Mo%] + [unavoidable impurity%] ≤ 40. Preferably, by mass, Ni is 25 to 29%, Co is 37 to 48%, and Mo is 9 to 11%. The balance contains Cr and unavoidable impurities, and preferably has a composition satisfying 23 ≤ [Cr%] + [Mo%] + [unavoidable impurity%] ≤ 38.

[0041] The unavoidable impurities preferably have a content of Ti, Mn, Fe, Nb, W, Al, Zr, B, and C by mass, where Ti is 1.0% or less, Mn is 1.0% or less, Fe is 1.0% or less, Nb is 1.0% or less, W is 1.0% or less, Al is 0.5% or less, Zr is 0.1% or less, B is 0.01% or less, and C is 0.1% or less. Thereby, high work hardening ability and excellent mechanical strength and ductility can be easily obtained.

[0042] The cobalt-chromium alloy member of the present invention has a crystal structure composed of a face-centered cubic lattice (fcc), or a crystal structure composed of a face-centered cubic lattice (fcc) and a hexagonal lattice (hcp). That is, in the present invention, by heat treatment, the fcc deformation twin or hcp phase in the as-worked cobalt-chromium alloy material changes to the fcc phase. When the cobalt-chromium alloy member is deformed by the formation of the fcc phase, fcc twin deformation or transformation from fcc to hcp due to deformation induction occurs again. The cobalt-chromium alloy member of the present invention in which such deformation and transformation occur is excellent in mechanical strength and ductility.

[0043] The cobalt-chromium alloy member of the present invention has a local crystal orientation change amount (KAM value) of 0.0 or more and 1.0 or less. The KAM value is, for example, a local change in crystal orientation obtained by electron backscatter diffraction (EBSD) measurement, and can be represented by the local orientation difference (Kernel Average Misorientation: KAM) defined by the following formula (1).

Number

[0044] The average value of the crystal grain size of the cobalt - chromium alloy member of the present invention is 2 μm or more and 15 μm or less, preferably 4 μm or more and 15 μm or less, and more preferably 4 μm or more and 10 μm or less. Thereby, it is easy to ensure high mechanical strength. The average value of the crystal grain size is calculated by the area fraction method using EBSD. Specifically, the average value of the crystal grain size can be calculated in accordance with JIS G0551 "Steel - Microscopic Test Method for Crystal Grain Size" or AS TM E112 - 13 "Standard Test Methods for Determining Average Grain Size".

[0045] In the cobalt - chromium alloy member of the present invention, the tensile strength is 800 - 1200 MPa. In the cobalt - chromium alloy member, the elongation at break is 30 - 80%, preferably 30 - 60%, and more preferably 50 - 60%. The tensile strength and elongation at break are measured, for example, by a tensile test using an autograph manufactured by Shimadzu Corporation. The cobalt - chromium alloy member having the above physical properties is excellent in mechanical strength and ductility.

[0046] In the cobalt-chromium alloy member, the uniform elongation is preferably 25 to 60%, more preferably 30 to 60%, and still more preferably 50 to 60%. The uniform elongation is measured, for example, by a tensile test using an autograph manufactured by Shimadzu Corporation. The cobalt-chromium alloy member having the above physical properties is excellent in mechanical strength and ductility.

[0047] In particular, when the cobalt-chromium alloy member of the present invention is in a tubular shape with a hollow interior and a circumferential surface surrounded by a cobalt-chromium alloy, the average value of the crystal grain size is 2 to 15 μm, the local crystal orientation change amount (KAM value) is 0.1 or more and 0.8 or less, the tensile strength is 800 to 1000 MPa, and the elongation at break is preferably 30 to 80%. When the cobalt-chromium alloy member of the present invention is in a wire shape with a cross-sectional shape such as a circular cross-section, an elliptical cross-section, a flat cross-section, or a non-circular cross-section such as a concave or convex shape, the average value of the crystal grain size is 4 to 15 μm, the local crystal orientation change amount (KAM value) is 0.0 or more and 1.0 or less, the tensile strength is 1000 to 1200 MPa, and the elongation at break is preferably 30 to 60%. Thereby, higher strength and excellent ductility can be obtained.

[0048] The cobalt-chromium alloy member of the present invention is preferably obtained by heat treatment under the following conditions. The heat treatment temperature of the present invention is preferably higher than the recrystallization temperature of the cobalt-chromium alloy material and 1100 °C or lower, more preferably 800 °C or higher and 1100 °C or lower, and still more preferably 900 °C or higher and 1100 °C or lower. The recrystallization temperature of the cobalt-chromium alloy material is, for example, in the range of 780 °C to 820 °C for a Co-20Cr-10Mo-26Ni alloy having the composition of this example, but may be in the range of 750 °C to 1000 °C depending on the alloy composition of the cobalt-chromium alloy material. By setting the temperature above the recrystallization temperature, recrystallization occurs and the fcc phase is stabilized. By setting the temperature at 1100 °C or lower, coarsening of the crystal grain size can be suppressed. As a result, a cobalt alloy member having the tensile strength, uniform elongation, and elongation at break within the above ranges and having high mechanical strength and ductility can be obtained.

[0049] The heat treatment time of the present invention is preferably 1 minute or more and 60 minutes or less. By setting it to 1 minute or more, recrystallization is sufficiently carried out and the fcc phase is stabilized. By setting it to 60 minutes or less, coarsening of the crystal grain size is suppressed. As a result, a cobalt alloy member having the tensile strength, uniform elongation, and elongation at break within the above ranges and having high mechanical strength and ductility can be easily obtained.

[0050] In particular, the cobalt-chromium alloy member is preferably obtained by heat-treating a cobalt-chromium alloy as-processed material at a heat treatment temperature exceeding the recrystallization temperature of the cobalt-chromium alloy material at 800°C or higher and 1100°C or lower for 1 minute or more and 60 minutes or less.

[0051] The cobalt-chromium alloy member of the present invention may have a banded deformed zone structure. The banded deformed zone structure of the present invention is an aggregate structure of dislocation cells in which a large number of dislocations generated by cold working are concentrated, and is a structure in the vicinity of fcc deformation twins and hcp phase (ε phase) introduced during cold working.

[0052] The cobalt-chromium alloy member of the present invention has a low stacking fault energy, and when deformed, partial dislocations move to form plate-like fine fcc twins and hcp phases, thereby obtaining high work hardening ability. In addition, solute atoms such as Mo and Nb, which have a larger or approximate atomic radius compared to Co, Ni, and Cr with an atomic radius of 1.25 Å, are strongly attracted to the stacking faults of the dislocation core or extended dislocation and segregate, making it difficult for cross slip to occur, so high work hardening ability is exhibited.

[0053] In addition, since the high work hardening ability of the cobalt-chromium alloy member of the present invention is exhibited not only near body temperature but also at high temperatures, it has the characteristic of high high-temperature strength properties. Therefore, the use of the cobalt-chromium alloy member is not limited to medical use, and the cobalt-chromium alloy member of the present invention can withstand use under more severe conditions for industrial equipment such as aerospace and steam turbines.

[0054] (Method for manufacturing a cobalt-chromium alloy member) The method for manufacturing a cobalt-chromium alloy member includes a step of preparing a cobalt-chromium alloy material, a step of homogenizing the prepared cobalt-chromium alloy material at 1100°C to 1300°C, and subjecting the homogenized cobalt-chromium alloy material to cold plastic working into a tubular or wire shape to obtain a cobalt-chromium alloy as-worked material, and a step of heat-treating the cold-plastically worked cobalt-chromium alloy as-worked material at a temperature exceeding the recrystallization temperature of the cobalt-chromium alloy material and not exceeding 1100°C for 1 minute or more and 60 minutes or less. The recrystallization temperature of the cobalt-chromium alloy material is, for example, 800°C. Thereby, a cobalt-chromium alloy member having high mechanical strength and ductility can be obtained.

[0055] In the step of preparing the cobalt-chromium alloy material, the cobalt alloy material is used. In the step of performing cold plastic working, a cobalt-chromium alloy as-worked material cold-worked into a tubular or wire shape is obtained. In the step of heat-treating the cobalt-chromium alloy as-worked material, the cobalt-chromium alloy member is obtained.

[0056] In the homogenization treatment, by performing a heat treatment on the cobalt-chromium alloy material at 1100°C to 1300°C, each composition is uniformly dispersed. Thereby, the uniformity of mechanical properties is ensured in the subsequent cold working process. By setting the homogenization treatment temperature to 1100 °C or higher, the material can be efficiently homogenized. By setting it to 1300 °C or lower, excessive coarsening of crystal grains can be prevented, and significant oxidation of the material surface can be prevented. Other conditions for the homogenization treatment can be appropriately set within a range that does not impair the physical properties of the obtained cobalt-chromium alloy member. The cobalt-chromium alloy material to be homogenized may be any cobalt-chromium alloy material having the above specific composition. For example, it may be an alloy ingot produced by high-frequency melting. Further, the cobalt-chromium alloy material after the homogenization treatment may be hot-worked into a shape that is easy to cold-work, such as a round bar shape.

[0057] Also, in the method for manufacturing a cobalt-chromium alloy member of the present invention, a cobalt-chromium alloy material that has been cold-worked into a plate material for a stent may be heat-treated at a temperature of 1100 °C or lower and above the recrystallization temperature, and then aged at a temperature of 200 °C or higher and below the recrystallization temperature. Thereby, solute atoms such as Mo are attracted to the dislocation cores or stacking defects of the extended dislocations to fix the dislocations, and a higher strength characteristic can be obtained by so-called static strain aging.

[0058] The cobalt-chromium alloy material of the present invention is obtained by producing an alloy ingot having the same composition as the above cobalt-chromium alloy material by high-frequency melting, performing hot forging and homogenization treatment at 1100 °C to 1300 °C, and creating a round bar with a diameter of 8 mm and a length of 270 mm by hot rolling and cutting.

[0059] By the above manufacturing method of the present invention, a cobalt-chromium alloy member having a crystal structure composed of a face-centered cubic lattice (fcc) or a crystal structure composed of a face-centered cubic lattice (fcc) and a hexagonal lattice (hcp) is obtained, the average value of the crystal grain size is 2 to 15 μm, and the local crystal orientation change amount (KAM value) is 0.0 or more and 1.0 or less.

Example

[0060] The first embodiment of the present invention is a tubular member made of the cobalt-chromium alloy material of the present invention. That is, by cold working the above cobalt-chromium alloy material, a tube material with a diameter of 1.6 mm, a thickness of 0.1 mm, and a length of 1 m was obtained. This tube material corresponds to the as-processed cobalt-chromium alloy material. Furthermore, by subjecting this tube material to a predetermined heat treatment, ductility was imparted to obtain a cobalt-chromium alloy member as a tube material.

[0061] The composition of the cobalt-chromium alloy material used in this example is shown in Table 1. The unit is mass%.

Table 1

[0062] In Examples 1 to 4, the content of Cr at 20 mass% and Mo at 10 mass% was kept constant, and the content of Co was varied with respect to the content of Ni. The content of Ni was varied in the range of 23 to 32 mass%. In Comparative Examples 1 to 4, as comparative materials, commercially available Co-20Cr-10Mo-35Ni alloy (hereinafter simply referred to as "MP35N alloy"), Co-20Cr-10Mo-20Ni alloy, Co-20Cr-15W-10Ni alloy (hereinafter simply referred to as "L605 alloy"), and SUS316L (manufactured by Hayes) were used respectively. In Examples 1 to 4, it has been confirmed that they have a crystal structure composed of a face-centered cubic lattice (fcc), or a crystal structure composed of a face-centered cubic lattice (fcc) and a hexagonal lattice (hcp).

[0063] Regarding the cobalt-chromium alloy materials with the compositions of Examples 1 to 4 and the alloys with the compositions of Comparative Examples 1 to 4 that were hot-worked into a rod shape and then heat-treated at 1200°C for 1 minute, a low-cycle fatigue test was conducted at a strain amplitude of 0.01.

[0064] The test results are shown in Fig. 1. In Examples 1 to 4, the fatigue life was good in all cases, being 3000 cycles or more. In particular, the cobalt-chromium alloy materials with 23% by mass of Ni (Example 4), 26% by mass of Ni (Example 3), and 29% by mass of Ni (Example 2) showed an improvement in low-cycle fatigue life compared to any of the off-the-shelf products of Comparative Examples 1 to 4.

[0065] Also, for the cobalt-chromium alloy materials of the compositions of Examples 1 to 4 and the alloys of the compositions of Comparative Examples 1 to 4 that were hot-worked into a bar shape and then heat-treated at 1200°C for 1 minute, using a Tensilon tensile testing machine manufactured by Instron, the strain rate was 2.5×10 -4 s -1 and a tensile test was carried out, and the results are shown in Table 2. The cobalt-chromium alloy materials according to Examples 1 to 4 showed a tensile strength of 848 to 886 MPa, indicating a high tensile strength characteristic of cobalt-chromium alloys equivalent to that of the MP35N alloy (Comparative Example 1).

Table 2

[0066] Fig. 2 is an external photograph of a cobalt-chromium alloy as-processed material (upper) and a cobalt-chromium alloy member (lower) heat-treated at 1050°C for 5 minutes, which were produced by cold working of the Co-20Cr-10Mo-26Ni alloy material according to Example 3, which has the best fatigue life among cobalt-chromium alloy materials. Fig. 2A is an overall photograph, and Fig. 2B is an enlarged photograph of the main part. The size is an outer diameter of 1.6 mm, a thickness of 0.1 mm, and a length of 980 to 1280 mm, and it has good surface properties.

[0067] Figure 3 shows the tensile strength measurement results of tubes made of the fabricated Co-20Cr-10Mo-26Ni alloy, including the as-cold-worked cobalt-chromium alloy as-fabricated material (hereinafter, also simply referred to as the "as-fabricated material") and cobalt-chromium alloy members (hereinafter, also simply referred to as the "heat-treated materials") heat-treated at 650 °C, 750 °C, 850 °C, 950 °C, and 1050 °C for 5 minutes. The horizontal axis represents strain [%], and the vertical axis represents stress [MPa]. The tensile test was conducted using an autograph manufactured by Shimadzu Corporation at a test speed of 1.2 mm / s and a gauge length of 110 mm.

[0068] Table 3 also shows the 0.2% proof stress [MPa], tensile strength [MPa], and elongation at break [%] obtained from Figure 3. Those heat-treated at 650 °C and 750 °C (also simply referred to as "650 °C and 750 °C heat-treated materials", etc.) showed higher tensile strength and lower ductility compared to the as-fabricated material. The tensile strength decreases with heat treatment at temperatures above 850 °C, but the ductility increases. The material heat-treated at 1050 °C for 5 minutes had an elongation at break of 63.7%, a yield stress of 561.1 MPa, and a tensile strength of 1040.6 MPa.

Table 3

[0069] Figure 4 shows the relationship between the yield stress (YS), tensile strength (UTS), elongation at break (Total elongation: total elongation), and heat treatment temperature (Annealing temperature) for the tube material of the Co-20Cr-10Mo-26Ni alloy. The yield stress is shown as the 0.2% proof stress (σ 0.2 ). When the heat treatment temperature is 850 °C or higher, the yield stress and tensile strength decrease, and the elongation at break increases significantly. Figure 5 shows the yield stress (σ 0.2 ) and tensile strength (σ UTS) This is a drawing comparing the value of the elongation at break (Total elongation: total elongation) with the literature value of the L605 alloy (see Non-Patent Document 2). The vertical axis represents the yield stress and tensile strength [MPa], and the horizontal axis represents the elongation at break strain [%]. The solid line indicates the tube as the cobalt-chromium alloy member according to this example, and the dotted line indicates the L605 alloy tube. When compared with the literature value of the tensile strength, the yield stress of the tube of the present invention is higher than that of the L605 alloy tube showing the same degree of elongation. Also, it shows a greater elongation than that of L605 showing the same degree of yield stress. Moreover, the material heat-treated at a temperature of 850 °C or higher for 5 minutes has the same strength as the L605 material and shows a greater elongation at break.

[0070] Figure 6 is an IQ map obtained by the electron backscatter diffraction (EBSD) method for the as-worked material obtained by cold-working a Co-20Cr-10Mo-26Ni alloy material into a tube shape, and the heat-treated materials obtained by heat-treating this at temperatures of 650 °C, 750 °C, 850 °C, 950 °C, and 1050 °C for 5 minutes. The IQ map, also called the image quality map, is a map indicating the quality of crystallinity. It is a plot of the intensity of the peak indicating the band in the Hough space when the EBSD pattern is subjected to the Hough transform (a method of converting a straight line into a point). The clearer the band, the better the crystallinity of the pattern generation region and the higher the IQ value. What appears linear in Figure 6 are regions with poor crystallinity such as grain boundaries, dislocations, and stacking faults. The as-worked material and the heat-treated materials at 650 °C and 750 °C have a high dislocation density and the worked structure remains, but the heat-treated materials heat-treated at a temperature of 850 °C or higher have a recrystallized structure. Also, as the heat treatment temperature increases, the crystal grain size increases.

[0071] Figure 7 is a KAM map showing the KAM values obtained by EBSD for the as-worked material obtained by cold-working a Co-20Cr-10Mo-26Ni alloy material into a tube shape and the heat-treated materials obtained by heat-treating this at temperatures of 650 °C, 750 °C, 850 °C, 950 °C, and 1050 °C for 5 minutes. The KAM value is calculated from the above formula (1), and the numerical values in the figure are the average KAM values within the field of view. The as-machined material, the heat-treated materials at 650 °C and 750 °C have a high dislocation density, with the worked structure remaining and the average KAM value being as high as 1 or more. However, the heat-treated materials heat-treated at temperatures of 850 °C or higher have a low KAM value of 1 or less and a recrystallized structure with a low defect density. Also, as the heat treatment temperature increases, the crystal grain size becomes larger. That is, the KAM value of the as-machined material is 1.32 ± 0.74, while the 650 °C heat-treated material, which is at a temperature lower than the recrystallization temperature, is 1.26 ± 0.71, and the 750 °C heat-treated material is 1.25 ± 0.69. On the other hand, the 850 °C heat-treated material, which is at a temperature higher than the recrystallization temperature, is 0.48 ± 0.30, the 950 °C heat-treated material is 0.47 ± 0.30, and the 1050 °C heat-treated material is 0.32 ± 0.15.

[0072] Figure 8 shows the crystal grain sizes of the as-machined material obtained by cold-working a Co-20Cr-10Mo-26Ni alloy material into a tube shape, and the heat-treated materials obtained by heat-treating this at temperatures of 650 °C, 750 °C, 850 °C, 950 °C, and 1050 °C for 5 minutes. The crystal grain size was calculated from the crystal orientation map (a map showing the distribution of the specified crystal orientation) measured by EBSD. The average crystal grain size of the as-machined material is 5.1 μm, while the 650 °C heat-treated material, which is at a temperature lower than the recrystallization temperature, is 5.3 μm, and the 750 °C heat-treated material is 4.3 μm. On the other hand, the 850 °C heat-treated material, which is at a temperature higher than the recrystallization temperature, is 2.3 μm, the 950 °C heat-treated material is 3.2 μm, and the 1050 °C heat-treated material is 7.6 μm. In the heat treatment at 850 °C, fine crystal grains of 2.3 μm are obtained by recrystallization.

[0073] The second embodiment of the present invention is a wire-shaped member using the cobalt-chromium alloy material of Example 3 of the present invention. That is, for the cobalt-chromium alloy material, a wire material with a diameter of 0.5 mm and a length of 1 m was obtained by cold working. This wire material corresponds to the as-machined cobalt-chromium alloy material. Further, by subjecting this wire material to a predetermined heat treatment to impart ductility, a cobalt-chromium alloy member as a wire material was obtained. Figure 9 is a photograph of the appearance of a wire-shaped as-fabricated cobalt-chromium material produced by cold working. Figure 9A is an overall photograph, and Figure 9B is an enlarged photograph of the main part. It has a diameter of 0.5 mm and a length of 1000 mm, presenting a good appearance.

[0074] Figure 10 is a drawing showing the tensile strength measurement results for heat-treated materials obtained by heat-treating a wire-shaped as-fabricated cobalt-chromium material produced by cold working the fabricated Co-20Cr-10Mo-26Ni alloy material at 650 °C, 850 °C, and 1050 °C for 5 minutes. The horizontal axis represents strain [%], and the vertical axis represents stress [MPa]. The tensile test was conducted using an autograph manufactured by Shimadzu Corporation at a test speed of 1.2 mm / s and a gauge length of 110 mm. Similar results were obtained for No. 1 and 2 fabricated under the same conditions.

[0075] Table 4 shows the tensile strength [MPa] and elongation at break [%] of the wire-shaped as-fabricated cobalt-chromium alloy material cold-worked in the present invention, the wire as a cobalt-chromium alloy member obtained by heat-treating this wire-shaped as-fabricated material at 450 °C, 650 °C, 850 °C, and 1050 °C for 5 minutes, and a comparative material wire.

Table 4

[0076] Table 5 shows a comparison of the tensile strength and elongation at break of the wire as a cobalt-chromium alloy member according to an embodiment of the present invention with SUS316L, L605 alloy, and MP35N alloy. The cobalt-chromium alloy member fabricated in Table 5 was fabricated under the same conditions as the cobalt-chromium alloy member fabricated in Table 4, and similar results were obtained.

Table 5

[0077] The wire as a cobalt-chromium alloy member according to an embodiment of the present invention exhibits strength superior to that of SUS316L, which is most widely used as a guide wire, and shows tensile strength and elongation at break comparable to those of wires of L605 alloy and MP35N (FIG. 10, Table 5).

[0078] FIG. 11 shows the relationship between the yield stress, tensile strength, elongation at break and heat treatment temperature for Co-20Cr-10Mo-26Ni alloy wire. When the heat treatment temperature is 850 °C or higher, the yield stress and tensile strength decrease, and the elongation at break increases significantly.

[0079] FIG. 12 is an IQ map obtained by EBSD for as-worked material obtained by cold working a Co-20Cr-10Mo-26Ni alloy material into wire form, and heat-treated materials obtained by heat-treating this at 450 °C, 650 °C, 850 °C, and 1050 °C for 5 minutes. The as-worked material, 450 °C, and 650 °C heat-treated materials have a high dislocation density and the worked structure remains, but the heat-treated materials heat-treated at a temperature of 850 °C or higher have a recrystallized structure. Also, as the heat treatment temperature increases, the crystal grain size increases.

[0080] FIG. 13 is a KAM map obtained by EBSD for as-worked material obtained by cold working a Co-20Cr-10Mo-26Ni alloy material into wire form, and heat-treated materials obtained by heat-treating this at 450 °C, 650 °C, 850 °C, and 1050 °C for 5 minutes. That is, the KAM value of the as-worked material is 1.76 ± 0.93, whereas the 450 °C heat-treated material, which is at a temperature lower than the recrystallization temperature, is 2.34 ± 1.07, and the 650 °C heat-treated material is 2.04 ± 1.05. On the other hand, the 850 °C heat-treated material, which is at a temperature higher than the recrystallization temperature, is 0.33 ± 0.43, and the 1050 °C heat-treated material is 0.96 ± 0.61. The as-worked material, 450 °C, and 650 °C heat-treated materials have a high KAM value of 1.76 to 2.01, a high dislocation density, and the worked structure remains, but the samples heat-treated at a temperature of 850 °C or higher, which is higher than the recrystallization temperature, have a KAM value reduced to 1 or less, and the density of defects such as dislocations has decreased.

[0081] Figure 14 shows the crystal grain sizes calculated from the crystal orientation maps measured by EBSD for the as-worked material obtained by cold working a Co-20Cr-10Mo-26Ni alloy material into a tube shape and the heat-treated materials obtained by heat-treating this material at 450 °C, 650 °C, 850 °C, and 1050 °C for 5 minutes. That is, the average crystal grain size of the as-worked material is 9.04 μm, while the 450 °C heat-treated material, which is at a temperature lower than the recrystallization temperature, is 10.3 μm, and the 650 °C heat-treated material is 7.78 μm. On the other hand, the 850 °C heat-treated material, which is at a temperature higher than the recrystallization temperature, is 4.43 μm, and the 1050 °C heat-treated material is 12.1 μm. In the heat treatment at 850 °C, which is at a temperature higher than the recrystallization temperature, fine crystal grains of 4.4 μm are obtained by recrystallization.

Industrial Applicability

[0082] As described in detail above, a cobalt-chromium alloy member having high strength and high ductility can be obtained by cold working a cobalt-chromium alloy material having the alloy composition of the present invention into a predetermined shape such as a tube or wire and then performing a heat treatment exceeding the recrystallization temperature of the cobalt alloy material. Such a cobalt-chromium alloy member is suitable for use in medical devices, gas turbine devices, or other industrial equipment devices because it uses a cobalt-chromium alloy member with a long fatigue life.

[0083] Examples of medical devices include in-vivo implantable medical devices such as stents, catheters, fastening cables, guide rods, orthopedic cables, heart valves, and implants. Other medical devices can also be used as bone drill bits or wires for removing gallstones. Examples of gas turbine devices include combustion chambers and exhaust components of aviation and industrial gas turbine engines such as tail pipes, combustion cylinders, spray bars, frame holders, afterburners, and tail pipes. Examples of industrial equipment devices include those used in waste incinerators, boilers, high-temperature reaction vessels, rotary kilns, and manufacturing plants for petrochemical products and synthesis gas plants.

Claims

1. By mass percentage, consisting of Ni: 23 - 32%, Co: 37 - 48%, Mo: 8 - 12%, Cr: 12 - 28%, and inevitable impurities: the balance, 20 ≤ [Cr%] + [Mo%] + [inevitable impurities%] ≤ 40, which is a composition satisfying the above, wherein the inevitable impurities are at least one or more of Ti, Mn, Fe, Nb, W, Al, Zr, B, and C, and by mass percentage, Ti is 1.0% or less, Mn is 1.0% or less, Fe is 1.0% or less, Nb is 1.0% or less, W is 1.0% or less, Al is 0.5% or less, Zr is 0.1% or less, B is 0.01% or less, and C is 0.1% or less, having a crystal structure composed of a face - centered cubic lattice (fcc), or a crystal structure composed of a face - centered cubic lattice (fcc) and a hexagonal lattice (hcp), the average value of the crystal grain size is 2 - 15 μm, and the local crystal orientation change amount (KAM value) is 0.0 or more and 1.0 or less, showing a tensile strength of 800 - 1200 MPa and an elongation at break of 30 - 80% Cobalt - chromium alloy member.

2. For a cobalt - chromium alloy as - processed material obtained by cold - plastic working a cobalt - chromium alloy material having the above composition into a predetermined shape, it is obtained by heat - treating at a heat - treatment temperature exceeding the recrystallization temperature of the cobalt - chromium alloy material The cobalt - chromium alloy member according to Claim 1.

3. By mass percentage, consisting of Ni: 25 - 29%, Co: 37 - 48%, Mo: 9 - 11%, Cr: 14 - 27%, and inevitable impurities: the balance, 23 ≤ [Cr%] + [Mo%] + [inevitable impurities%] ≤ 38, which is a composition satisfying the above The cobalt - chromium alloy member according to Claim 1 or 2.

4. For a cobalt - chromium alloy as - processed material obtained by cold - plastic working a cobalt - chromium alloy material having the above composition into a predetermined shape, as a heat - treatment at a heat - treatment temperature exceeding the recrystallization temperature of the cobalt - chromium alloy material, heat - treated at 800°C or more and 1100°C or less for 1 minute or more and 60 minutes or less The cobalt - chromium alloy member according to Claim 3.

5. The predetermined shape plastically worked cold is tube - shaped, the average value of the crystal grain size is 2 - 15 μm, and the local crystal orientation change amount (KAM value) is 0.1 or more and 0.8 or less, showing a tensile strength of 1000 - 1200 MPa and an elongation at break of 30 - 80% The cobalt - chromium alloy member according to any one of Claims 1 to 4.

6. The predetermined shape plastically worked cold is wire - shaped, The average value of the crystal grain size is 4 to 15 μm, the local crystal orientation change amount (KAM value) is 0.0 or more and 1.0 or less, and the tensile strength is 1000 to 1200 MPa and the elongation at break is 30 to 60%. The cobalt-chromium alloy member according to any one of claims 1 to 4.

7. A device using the cobalt-chromium alloy member according to any one of claims 1 to 6.

8. The device is any one of a stent, a tube, a wire, and an implant, a medical device. The device according to claim 7.

9. The device is any one of a combustion chamber and an exhaust component of an aircraft and industrial gas turbine engine, such as a tail pipe, a combustion cylinder, a spray bar, a flame holder, an afterburner, and a tail pipe, a gas turbine device. The device according to claim 7.

10. The device is a device for industrial equipment used in waste incinerators, boilers, high-temperature reaction vessels and rotary kilns, and in the production plants of petrochemical products and synthesis gas plants. The device according to claim 7.

11. By mass%, Ni: 23 to 32%, Co: 37 to 48%, Mo: 8 to 12%, Cr: 12 to 28%, unavoidable impurities: the balance, 20 ≦ [Cr%] + [Mo%] + [unavoidable impurity%] ≦ 40, Prepare a cobalt-chromium alloy material having a composition that satisfies homogenize the prepared cobalt-chromium alloy material at 1100 ° C to 1300 ° C, subject the homogenized cobalt-chromium alloy material to cold plastic working into a tube shape or a wire shape to obtain a cobalt-chromium alloy as-worked material, perform heat treatment on the cold-plastically worked cobalt-chromium alloy as-worked material at a temperature exceeding the recrystallization temperature of the cobalt-chromium alloy material and 1100 ° C or lower for 1 minute or more and 60 minutes or less to obtain the cobalt-chromium alloy member according to any one of claims 1 to 10 A method for manufacturing a cobalt-chromium alloy member.

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