JP7262241B2 - Co-Ni-based alloy diaphragm and manufacturing method thereof - Google Patents

Description

The present invention relates to a Co--Ni based alloy diaphragm and a method for manufacturing the same.

A Co—Ni-based alloy is used as a diaphragm valve that functions as an on-off valve for corrosive gases, such as those used in semiconductor manufacturing gas processes that use highly corrosive gases, as described in Patent Documents 1 and 2 below. A metal diaphragm is used.
As an additive element contained in this Co—Ni-based alloy, Ti, which has effects such as grain refinement and deoxidation, may be used.

JP-A-09-031577 Japanese Unexamined Patent Application Publication No. 2011-202681

On the other hand, titanium compounds such as titanium oxide are known to have a catalytic action, and when the titanium compound is contained as an inclusion in the diaphragm and precipitates on the surface, it reacts with the semiconductor manufacturing gas in contact with the gas. May cause chemical reactions such as decomposition.
On the other hand, precipitation of Ti inclusions can be prevented by not adding Ti to the Co—Ni based alloy. However, in the case of a diaphragm made of a Co—Ni-based alloy that does not contain Ti at all, compared to a diaphragm made of a Co—Ni-based alloy that contains Ti, corrosion resistance is reduced and the grain size increases, resulting in mechanical problems. There is a risk of deterioration in characteristics.

In view of such problems, an object of the present invention is to provide a metal diaphragm suitable for valves and the like, and a method of manufacturing the same, which can improve the chemical stability of the semiconductor process used.

"1" In order to solve the above problems, a Co—Ni-based alloy diaphragm according to one aspect of the present invention contains Co: 30% by mass or more and 40% by mass or less, Ni: 27% by mass or more and 36% by mass or less, Cr: 12 % by mass or more and 26% by mass or less, Mo: 8% by mass or more and 13% by mass or less, Nb: 0.5% by mass or more and 3% by mass or less, Ti: 0.01% by mass or less, and the balance having a composition of unavoidable impurities, It is characterized by having a tensile strength of 1470 MPa or more, an elongation of 1.5% or more, and a hardness of 500±30 Hv.

In the present embodiment, the Co—Ni-based alloy having a composition containing specified amounts of Co, Ni, Cr, Mo, and Nb contains 0.01% by mass or less of Ti. A diaphragm made of a Co—Ni-based alloy having excellent mechanical properties such as strength of 1470 MPa or more, elongation of 1.5% or more, and hardness of 500±30 Hv can be provided.

[2] In the Co—Ni-based alloy diaphragm of the one aspect, it is preferable that the fatigue limit is 1100 MPa or more.
The Co--Ni-based alloy diaphragm of the one form described above has an excellent fatigue limit because the Ti content is kept low and the precipitation of Ti inclusions is suppressed.
[3] In the Co--Ni-based alloy diaphragm of the one embodiment, it is preferable that no Ti inclusions are present in the metal structure by observation with a measuring means capable of distinguishing fine particles having a size of 0.1 μm or more.

In the diaphragm, even if it is applied to a valve that handles gas such as used in a semiconductor process, there is no Ti inclusion in the metal structure by observation with a measuring means that can distinguish even fine particles with a size of 0.1 μm or more. , has no effect on semiconductor process gases, and has excellent chemical stability. Therefore, by applying the valve provided with the diaphragm of this embodiment to the semiconductor manufacturing process, it contributes to the improvement of the chemical stability of the semiconductor process.

[4] In the method for manufacturing a Co—Ni-based alloy diaphragm according to one aspect, Co: 30% by mass or more and 40% by mass or less, Ni: 27% by mass or more and 36% by mass or less, Cr: 12% by mass or more and 26% by mass or less , Mo: 8% by mass or more and 13% by mass or less, Nb: 0.5% by mass or more and 3% by mass or less, Ti: 0.01% by mass or less, and the balance being inevitable impurities. It is characterized by having a tensile strength of 1470 MPa or more, an elongation of 1.5% or more, and a hardness of 500±30 Hv by cold rolling and aging treatment.

According to the method of manufacturing the Co—Ni-based alloy diaphragm of the present embodiment, the alloy contains specified amounts of Co, Ni, Cr, Mo, and Nb, and contains 0.01% by mass or less of Ti. By applying aging treatment, it is possible to improve the mechanical properties, and while having good corrosion resistance, it has excellent mechanical properties such as tensile strength of 1470 MPa or more, elongation of 1.5% or more, and hardness of 500 ± 30 Hv. diaphragm can be obtained.

[5] In the method for producing a Co--Ni-based alloy diaphragm according to one aspect, it is preferable to obtain a metal structure free from Ti inclusions by observation using a measuring means capable of distinguishing fine particles having a size of 0.1 μm or more.

By obtaining a diaphragm without Ti inclusions by observation with a measuring means capable of distinguishing even fine particles of 0.1 μm or more in the metal structure, even if it is applied to a valve that handles gas such as used in a semiconductor process, It is possible to provide a diaphragm that has no influence on semiconductor process gases and can improve chemical stability. Therefore, by applying the valve provided with the diaphragm according to this embodiment to the semiconductor manufacturing process, it contributes to improving the chemical stability of the semiconductor process.

According to the present embodiment, the Co—Ni-based alloy having a composition containing specified amounts of Co, Ni, Cr, Mo, and Nb contains Ti in an amount of 0.01% by mass or less. , tensile strength of 1470 MPa or more, elongation of 1.5% or more, and hardness of 500±30 Hv. Further, the Co—Ni-based alloy of the present embodiment is excellent in fatigue properties.

Sectional drawing which shows the diaphragm of 1st Embodiment. The block diagram which shows embodiment which applied the said diaphragm to the pressure sensor. The block diagram which shows embodiment which applied the said diaphragm to the diaphragm valve. Graph showing an SN curve of a Co—Ni-based alloy sample according to an example. Graph showing an SN curve of a Co—Ni-based alloy sample according to a comparative example. 5 is a graph showing the results of a corrosion test in which a weight loss rate was obtained using 36% HCl for an example sample and a comparative example sample; 5 is a graph showing the results of a corrosion test in which the weight loss rate was determined using 10% HCl for an example sample and a comparative example sample. 5 is a graph showing the results of a corrosion test in which the weight loss rate was determined using 48% HBr for the example sample and the comparative example sample. 5 is a graph showing the results of a corrosion test in which the weight reduction rate was determined using 14% HBr for the example sample and the comparative example sample.

An embodiment of a Co—Ni based alloy diaphragm according to the present invention will be described below with reference to the drawings.
A diaphragm 1 according to the present embodiment shown in FIG. As one form, a structure having a collar portion 4 continuously formed through a hole can be employed. The diaphragm 1 of this form is housed in a casing (not shown) or the like, attached to a pipe or the like, deformed by the pressure of the fluid flowing inside the pipe, and used to measure the fluid pressure or the like.
An example of applying such a diaphragm to a pressure sensor is shown in FIG.
The diaphragm is housed in a casing (not shown) or the like and used for a diaphragm valve or the like that opens and closes a flow path inside the casing. An example of applying the diaphragm to a diaphragm valve is shown in FIG.

The Co—Ni-based alloy forming the diaphragm 1 of the present embodiment contains Co: 30% by mass or more and 40% by mass or less, Ni: 27% by mass or more and 36% by mass or less, Cr: 12% by mass or more and 26% by mass or less, Mo: It has a composition of 8% by mass or more and 13% by mass or less, Nb: 0.5% by mass or more and 3% by mass or less, Ti: 0.01% by mass or less, and the balance being unavoidable impurities.
Co (cobalt) itself has a large work hardening ability, and has the effect of reducing notch brittleness, increasing fatigue strength, and increasing high-temperature strength. , the matrix becomes too hard to process, and the face-centered cubic lattice phase becomes unstable with respect to the close-packed hexagonal lattice phase.

Ni stabilizes the face-centered cubic lattice phase, maintains workability, and has the effect of improving corrosion resistance. It is difficult to obtain a face-centered cubic lattice phase, and if it exceeds 36% by mass, the mechanical strength decreases.
Cr is an essential component for ensuring corrosion resistance and has the effect of strengthening the matrix. Therefore, the content is made 12% by mass or more and 26% by mass or less.
Mo has the effect of solid-solving into the matrix to strengthen it, the effect of increasing work hardening ability, and the effect of improving corrosion resistance when coexisting with Cr. When the content exceeds 8% by mass, workability is lowered and a brittle σ phase is likely to be generated.

Nb dissolves in the matrix and strengthens it, _and has the effect of increasing the work hardening ability. , and Nb, the content is set to 0.5% by mass or more and 3% by mass or less.
Ti has strong deoxidizing, denitrifying, and desulfurizing effects, as well as the effect of refining the ingot structure. may have an impact.
Therefore, the Ti content is preferably 0.01% by mass or less, and more preferably in the range of 0.001% by mass to 0.01% by mass. Also, by suppressing Ti inclusions, excellent fatigue characteristics can be obtained, for example, a fatigue limit of 1100 MPa or more.

"Production method"
A Co—Ni-based alloy having the above composition is melted by vacuum melting, forged, hot-rolled, and then rolled at a final rolling reduction rate of 20 to 90% at room temperature to obtain a thin sheet material having a thickness of about 0.13 mm. can do. A basic shape of the diaphragm 1 having the dome-shaped dome portion 2 and the flange portion 4 can be obtained by punching out the thin plate material to a required diameter by press working.
Since the concave side of the diaphragm 1 is the gas-contacting side, it is desirable to mirror-finish it by polishing or the like. For example, it is preferable to process the concave side to have a surface roughness Ra of 0.03 μm or less.
Next, the mirror-finished diaphragm 1 is subjected to aging treatment at 300° C. to 650° C., eg, 520° C. for 0.5 to 5 hours, eg, about 2 hours.
By this aging treatment, it is possible to obtain the diaphragm 1 having improved tensile strength, excellent elongation, increased hardness, and excellent fatigue limit for the Co—Ni-based alloy having the above composition.

A Co—Ni based alloy diaphragm having a tensile strength of 1470 MPa or more, an elongation of 1.5% or more, and a hardness of 500±30 Hv if the diaphragm is made of the Co—Ni based alloy having the composition described above after the aging treatment. can be obtained. That is, for example, a Co—Ni based alloy diaphragm having a tensile strength of 1800 MPa level, an elongation of 3.8% level and a hardness of 660 Hv level can be obtained. In addition, the diaphragm made of the Co—Ni-based alloy having the above composition has excellent resistance to hydrochloric acid, hydrogen bromide, etc., exhibits excellent chemical resistance such that there is little reaction even when it comes in contact with these, and there is little weight loss even when it comes in contact with these. have.

The Ti contained in this Co—Ni-based alloy diaphragm is 0.01% by mass or less, and since the Ti content is adjusted to be small, a metal structure in which Ti inclusions are not precipitated can be obtained. .
The metal structure in which Ti inclusions are not precipitated as described here means that the surface of the metal structure is observed at a magnification of 1000 to 10000 times using a surface magnifying observation device such as a digital microscope. It means that Ti inclusions with a grain size of 0.1 μm or more cannot be confirmed in a state where inclusions and precipitates with a diameter of 1 μm or more can be observed. More specifically, the surface of the metal structure is observed at a magnification of 1000 times or the like, and if particulate precipitates can be confirmed, the precipitates are further checked at a magnification of 10000 times or the like to see if they are particulate precipitates. Whether or not the particulate precipitates are Ti inclusions can be determined by identifying the particulate precipitates at a magnification of 6000 to 8000 using an EDS (energy dispersive X-ray spectrometer).

It should be noted that if a Co-Ni-based alloy containing about 0.3 mass% to 0.7 mass% of Ti is used for the above-mentioned Co-Ni-based alloy, and a diaphragm is manufactured by the same means as described above, it will be described later. As shown in the comparative example, a metal structure is obtained in which Ti inclusions having a grain size of about 0.7 μm to 3.2 μm are precipitated in the metal structure at an average of about 1.3×10 ⁻⁴ pieces/μm.
A diaphragm having such a large number of Ti inclusions may cause a chemical reaction such as decomposition of the process gas when it comes into contact with the process gas used in semiconductor manufacturing or the like.
In this respect, if the diaphragm has the composition described above, Ti inclusions with a grain size of 0.1 μm or more do not exist in the metal structure. Therefore, it is possible to provide a diaphragm that contributes to chemical stability in the semiconductor process. Also, by suppressing the Ti inclusions having the above grain size, excellent fatigue characteristics can be obtained, for example, a fatigue limit of 1100 MPa or more.

"pressure sensor"
FIG. 2 shows the structure of one embodiment in which the diaphragm made of the Co—Ni-based alloy having the composition described above is applied to a pressure sensor.
A pressure sensor 10 shown in FIG. 2 includes a cap member 5 having an introduction passage for introducing a fluid to be measured and a diaphragm 6 integrated inside the cap member 5 . The diaphragm 6 is composed of a thin pressure-receiving portion 6A, a cylindrical portion 6B extending so as to surround the outer peripheral edge of the pressure receiving portion 6A, and a collar portion 6C formed on the outer periphery of the cylindrical portion 6B. A pressure chamber 6D is provided.
The cap member 5 has a cup shape with an opening 5a, and has a flange portion 5b on the outer peripheral side of the opening 5a. The cap member 5 is made of, for example, metal or a composite material of metal and resin. A reference pressure chamber 8 is formed inside the cap member 5 so as to be partitioned by the cap member 5 and the diaphragm 6 . An introduction port (not shown) for introducing a reference gas is formed in the cap member 5 , and the reference gas is introduced through this introduction port to control the internal pressure of the reference pressure chamber 8 .

As shown in FIG. 2, the pressure sensor 10 is attached around the opening 12a formed in the peripheral wall of the pipe 12 forming the flow path 11 of the object to be measured, and the fluid in the pipe 12 is introduced into the pressure chamber 6D of the diaphragm 6. Then, the pressure receiving portion 6A can be deformed by receiving the pressure of the fluid.
The reference pressure chamber 8 side of the pressure receiving portion 6A of the diaphragm 6 is processed to have a smooth surface, for example, a mirror surface, and an insulating film 13 such as a silicon oxide film and a bridge circuit 15 are formed. The bridge circuit 15 is composed of four strain gauges (not shown), and wires 16 such as connector wires 16a, 16b, 16c and 16d are connected to each strain gauge.

When the reference gas is introduced into the reference pressure chamber 8 and the fluid pressure of the pipe 12 is applied to the pressure chamber 6D, the pressure receiving portion 6A of the diaphragm 6 is deformed, and this deformation changes the resistance of the four strain gauges. A change in resistance can be measured by 15, and the pressure in the pressure chamber 6D can be detected by calculating this measurement result. However, since the pressure-receiving portion 6A is thin and directly receives the pressure of the fluid, the Co—Ni-based alloy forming the pressure-receiving portion 6A of the diaphragm 6 must have high strength and excellent corrosion resistance.

As described above, the Co—Ni-based alloy constituting the pressure receiving portion 6A of the diaphragm 6, which is required to have high strength and excellent corrosion resistance even in a corrosive environment, has the above-described composition, has high strength and high It is made of a Co—Ni base alloy that is corrosion resistant.
Since the diaphragm 6 is made of the Co—Ni-based alloy described above, it has excellent mechanical strength, high corrosion resistance, and excellent chemical resistance. Also, there is little possibility of being affected by the fluid.

"diaphragm valve"
FIG. 3 shows an embodiment in which the diaphragm according to the present invention is applied to a diaphragm valve. The diaphragm valve 20 of this embodiment is a flat plate-shaped valve in which a first channel 21 and a second channel 22 are formed. It comprises a main body 23, a diaphragm 26 placed on the main body 23, and a lid body 25 sandwiching the diaphragm 26 together with the main body 23. - 特許庁Inside the main body 23, there are a first flow path 21 extending from one side surface 23a of the main body 23 to the center of the upper surface 23b of the main body 23, A second flow path 22 is formed. A portion of the main body 23 where the first flow path 21 is opened on one side surface 23a serves as an inflow port 27, and a portion of the main body 23 where the second flow path 22 opens on the other side surface 23c serves as an outflow port 28A. there is

A peripheral stepped portion 28 is formed in a portion where the first flow path 21 communicates with the central side of the upper surface of the main body 23 , and a valve seat 29 is attached to the peripheral stepped portion 28 . Diaphragm 26 is made of a Co--Ni base alloy equivalent to diaphragm 1 described above, and is formed in a disk-dome shape comprising dome portion 26A, boundary portion 26B, and flange portion 26C, like diaphragm 1 described above.
The diaphragm 26 is sandwiched between the main body 23 and the lid 25 so that a pressure chamber 26a is formed between the diaphragm 26 and the upper surface 23b of the main body 23 with the protruding side of the dome portion 26A facing up.
A through-hole 25 a for inserting the stem 24 is formed in the center of the upper surface of the lid 25 , and the stem 24 is arranged so as to contact the center of the upper surface of the diaphragm 26 .

Also in the diaphragm valve 20 having the above configuration, the diaphragm 26 is made of the above-described Co—Ni-based alloy. There is an effect that the valve 20 can be provided.
Moreover, the fluid in contact with the diaphragm 6 is not affected, and even if the fluid is highly corrosive, there is little possibility of being affected.

Co—Ni-based alloys having the compositions shown in Tables 1 to 5 below were melted by vacuum melting, forged, hot-rolled, and then rolled at room temperature to obtain thin plates with a thickness of 0.13 mm. . A diaphragm having a structure equivalent to that of the diaphragm shown in FIG. 1, which has a dome-shaped dome portion and a flange portion, was obtained by punching this thin plate material into a diameter of 20 mm.
Since the concave side of this diaphragm is the gas-contacting side, it was mirror-finished by polishing to have a surface roughness Ra of 0.03 μm or less.
Then, the mirror-finished diaphragm was subjected to an aging treatment at 520° C. for 2 hours to obtain a desired diaphragm.
The Co—Ni-based alloys having compositions shown in Tables 1 to 5 below are the alloys of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively.

"Measurement of Tensile Strength, Elongation, Hardness and Fatigue Limit"
Diaphragms were produced from the alloys of Examples 1 and 2 and Comparative Examples 1 to 3 by the steps described above. In addition, the tensile strength, elongation, hardness, and fatigue limit were determined using thin plate materials made of the alloys of Examples 1 and 2 and Comparative Examples 1 to 3, and a part of the concave side of the diaphragm was cut out to observe the surface. gone.
The results are summarized in Table 6 below.

As the results shown in Table 6 show, the Co—Ni-based alloys of Comparative Examples 1 to 3 containing 0.47 to 0.53% by mass of Ti contain 0.002 to 0.01% by mass of Ti. The alloys of Examples 1-2 have comparable or better performance in tensile strength, elongation, hardness and fatigue limit.
That is, the tensile strength is equivalent at a level of 1800 MPa, the elongation is equivalent at about 3.8 to 4.6%, the hardness before aging is equivalent at 500 to 520 Hv, and the hardness after aging is equivalent at a level of 660 to 670 Hv. be. On the other hand, the alloys of Examples 1 and 2 have a fatigue limit of about 1100 MPa and have better properties (increased from 50 to 125 MPa).
The alloys of Comparative Examples 1 to 3 are Co—Ni-based alloys that are excellent in tensile strength, elongation, hardness, and fatigue limit. It was found to be equally good in hardness and better in fatigue limit.
In the alloy of Comparative Example 3, precipitation of Ti inclusions was observed at a rate of 0.71% as shown in the cleanliness column, and inclusions were observed and analyzed in detail as described below.
Here, cleanliness was measured as follows.
First, 30 points on the polished surfaces of the alloys of Examples 1 and 2 and Comparative Example 3 were individually observed by magnifying them 500 times using a metallurgical microscope. Observation was made by 19 squares×19 squares with 10 μm per square. The total number of inclusions observed at this time was divided by the total number of lattice points (19 squares x 19 squares) x 30 points (10830 pieces), and the value expressed as a percentage was taken as the cleanliness level.

"Observation of inclusions"
The concave surfaces of the diaphragms of Examples 1 and 2 and the diaphragm of Comparative Example 3 were individually observed at 10 locations with a digital microscope at a magnification of 1000 times. Observation was made by 19 squares×19 squares with 10 μm per square. The observation area corresponds to 36100 μm ² .
In addition, regarding Comparative Example 3 in which a large number of inclusions were confirmed by observation, the observation magnification was increased to 10,000 times, and the grain size of the inclusions was measured. In addition, each inclusion was magnified 6000 to 8000 times using an EDS (energy dispersive X-ray spectrometer) to identify the substance, and the inclusion was identified and selected by element to determine whether it was a Ti inclusion. . The results are set forth in Table 7 below.

A large number of inclusions were confirmed in the diaphragm of Comparative Example 3, and when the elements were identified by EDS, it was confirmed to be Ti inclusions. According to the observation method described above, the presence of Ti inclusions having a grain size of 0.1 μm or more can be confirmed.
As a result of observation, as shown in Table 7, the diaphragm of Comparative Example 3 was confirmed to have precipitated numerous fine Ti inclusions. However, in the diaphragms of Examples 1 and 2, no observable Ti inclusions with a grain size of 0.1 μm or more could be confirmed. That is, in the diaphragms of Examples 1 and 2, it can be considered that Ti inclusions having a particle size of 0.1 μm or more are not precipitated.
For this reason, even if the diaphragm of this embodiment is used in an environment of corrosive gas such as semiconductor manufacturing process gas or in the presence of corrosive fluid, there is no influence on the process gas. It can be seen that there is no problem in terms of influence on the semiconductor manufacturing process.

"Fatigue strength"
4 and 5 show the results of obtaining SN curves using the thin plate materials made of the Co--Ni based alloys of Example 1 and Comparative Example 3. FIG. The alloy of Example 1 is indicated as alloy A in FIG.
From the comparison between FIGS. 4 and 5, it can be seen that the alloy of Example 1 and the alloy of Comparative Example 3 exhibit substantially the same SN curves and have the same fatigue strength.

"Corrosion test"
The diaphragms of Example 1 and Comparative Example 3 were tested for corrosion resistance to hydrochloric acid (HCl) and hydrogen bromide (HBr).
A plurality of diaphragms of Example 1 and Comparative Example 3 were prepared and their weight loss rates were measured when immersed in 36% hydrochloric acid, 10% hydrochloric acid, 48% HBr, and 14% HBr.
When the immersion time was 9, 24, and 48 hours, the number of samples was n=1, and when the immersion time was 72 hours, the number of samples was set to n=5.

FIG. 6 shows the weight loss rate when immersed in 36% hydrochloric acid, FIG. 7 shows the weight loss rate when immersed in 10% hydrochloric acid, and FIG. 8 shows the weight loss rate when immersed in 48% HBr. , and FIG. 9 shows the weight reduction rate when immersed in 14% HBr.
From the results shown in FIGS. 6 to 9, the diaphragm made of the Co—Ni-based alloy of Example 1 exhibits the same corrosion resistance against hydrochloric acid and hydrogen bromide as the diaphragm made of the Co—Ni-based alloy of Comparative Example 3. rice field. Therefore, it can be seen that the diaphragm made of the Co--Ni based alloy of Example 1 is excellent in corrosion resistance. Although the results shown in FIG. 9 show some differences in the weight reduction rate, the difference in the actual weight reduction rate is as small as about 1%, and both can be considered to have excellent corrosion resistance.

From the results described above, it is clear that the diaphragm made of the Co—Ni-based alloy of Example 1 has corrosion resistance equivalent to that of the Co—Ni-based alloy of Comparative Example, which has a reputation for corrosion resistance, in other words, has chemical resistance. is.

DESCRIPTION OF SYMBOLS 1... Diaphragm 2... Dome part 3... Boundary part 4... Flange part 6... Diaphragm 6A... Pressure receiving part 6B... Cylindrical part 6C... Flange part 6D... Pressure chamber 10... Pressure sensor 11... Flow path 12 Piping 12a Opening 20 Diaphragm valve 21 First flow path 22 Second flow path 24 Stem 25 Cover 26 Diaphragm.

Claims (5)

Co: 30% by mass or more and 40% by mass or less, Ni: 27% by mass or more and 36% by mass or less, Cr: 12% by mass or more and 26% by mass or less, Mo: 8% by mass or more and 13% by mass or less, Nb: 0.5% by mass % or more and 3% by mass or less, Ti: 0.01% by mass or less, and the balance being inevitable impurities,
A Co—Ni-based alloy diaphragm having a tensile strength of 1470 MPa or more, an elongation of 1.5% or more, and a hardness of 500±30 Hv. The Co—Ni-based alloy diaphragm according to claim 1, having a fatigue limit of 1100 MPa or more. 3. The Co--Ni-based alloy diaphragm according to claim 1, wherein no Ti inclusions are present in the metal structure when observed by a measuring means capable of distinguishing even fine particles of 0.1 μm or more in size. Co: 30% by mass or more and 40% by mass or less, Ni: 27% by mass or more and 36% by mass or less, Cr: 12% by mass or more and 26% by mass or less, Mo: 8% by mass or more and 13% by mass or less, Nb: 0.5% by mass % or more and 3% by mass or less, Ti: 0.01% by mass or less, and the balance inevitable impurities. A method for producing a Co--Ni-based alloy diaphragm characterized by having a hardness of 1.5% or more and a hardness of 500±30Hv. 5. The method for producing a Co--Ni-based alloy diaphragm according to claim 4, wherein a metal structure in which no Ti inclusions are present is obtained by observation using a measuring means capable of distinguishing even fine particles having a size of 0.1 μm or more.

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