JPH06308260A - Corrosion-resistant clock member - Google Patents

Abstract

PURPOSE:To provide a corrosion-resistant clock member having high corrosion resistance and surface hardness by forming part of the surface layer section of an austenitic stainless steel with a nitrified and hardened layer containing a specific quantity of N atoms and no CrN. CONSTITUTION:The surface of an austenitic stainless steel material (stainless steel product) is set to the surface state easily infiltratable by N atoms by fluoridization, and it is heated and held at about 450 deg.C or below, preferably in the range of 370-420 deg.C in particular, in the nitrifying atmosphere such as NH3 for nitrification. The surface layer of the stainless steel material is formed into a dense and uniform nitrified and hardened layer having the thickness of about 20-40mum. No CrN is practically contained in this nitrified and hardened layer, N atoms of 2-12wt.% are contained in the austenitic phase (gamma-phase) which is the parent phase, it has nearly the same corrosion resistance as that of the austenitic stainless steel material before nitrification and hardening, and the surface hardness is sharply increased by the existence of the nitrified and hardened layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion resistant timepiece member having both high corrosion resistance and high surface hardness.

[0002]

2. Description of the Related Art For a casing of a wristwatch, a ring on the outer circumference of a dial of a watch, pins for connecting a watch body and a belt, etc., a silver-colored stainless steel-like material has been conventionally used as a martensitic stainless steel material. Is used. However, since the martensitic stainless steel contains a relatively large amount of relatively expensive chromium, the stainless steel itself is expensive, and since it is necessary to perform quenching and the like, distortion occurs, Further, since it has insufficient corrosion resistance, it has a drawback that it is rusted when it is used in close contact with sweaty skin for a long time and is wetted with water.

[0003]

For this reason, recently,
It has been attempted to use an austenitic stainless steel material in place of the above-mentioned martensitic stainless steel material. Austenitic stainless steel has more corrosion resistance than the above martensitic stainless steel and is less likely to rust, but lacks surface rigidity. Therefore, hard chromium plating or chemical vapor deposition (CVD) TiN coating is required. Done. However, since the adhesion of the plating film and the coating film is low, there is a problem that the life of the timepiece member is shortened. There is also the problem that the appearance of stainless steel is lost and it does not look good. Therefore, if it is possible to improve the surface hardness of the austenitic stainless steel material, the surface hardness is high and a few things are not scratched, and moreover it is rich in corrosion resistance,
It is possible to provide a corrosion-resistant watch member that is resistant to rust. In order to improve the surface hardness of the above stainless steel material, it is usually considered that nitriding treatment is performed to form a nitriding hardened layer on the surface to increase the surface hardness. There are various methods such as salt bath nitriding, ion nitriding, and gas nitriding as methods of this type of nitriding treatment.
The nitriding temperature is usually set to about 550 to 570 ° C, and is set to about 480 ° C even at a low temperature. By nitriding the timepiece member made of the austenitic stainless steel material by such a nitriding method, although the surface hardness of the timepiece member is improved, the corrosion resistance of the austenitic stainless steel material itself is impaired and rusting occurs. I found it easier to do.

The present invention has been made in view of such circumstances, and an object thereof is to provide a corrosion resistant timepiece member having both high corrosion resistance and high surface hardness.

[0005]

In order to achieve the above object, in the corrosion-resistant timepiece member of the present invention, the base material is made of austenitic stainless steel, and at least a part of the surface layer has the following (A), It is configured by a nitride hardened layer including (B). (A) Substantially free of crystalline chromium nitride. (B) 2 to 12% by weight in the austenite phase which is the mother phase
It contains N atoms (hereinafter abbreviated as “%”).

[0006]

In other words, the present inventors conducted a series of studies to find out the cause of deterioration of corrosion resistance due to the nitriding treatment described above. As a result, the deterioration of the corrosion resistance is caused by the precipitation of crystalline chromium nitride (CrN) in the formed nitride layer, which significantly reduces the concentration of solid solution chromium (Cr) in the matrix (austenite phase). Have found that the active Cr, which is indispensable for the formation of a passive film that should have the function of retaining the corrosion resistance inherent to stainless steel, is almost eliminated. As a result of further research, the nitriding treatment of the austenitic stainless steel was performed at a considerably low temperature (the nitriding temperature of the conventional nitriding method was 4).
When performed in a temperature range of 100 to 200 ° C. lower than a temperature range of 80 to 580 ° C.), crystalline chromium nitride (CrN) or
Nitrogen atoms permeate into the matrix phase (γ phase) of austenitic stainless steel without causing precipitation of iron nitride. Then, it was found that when the permeation amount (content) is regulated within the range of 2 to 12%, deterioration of corrosion resistance does not occur, and the permeation of the nitrogen atom forms a nitrided hard layer having high surface hardness. , Reached this invention. In this case, it is considered that the nitrogen atoms are in a state of simply penetrating into the γ phase, and thereby lattice distortion is formed, but it does not lead to precipitation of crystalline chromium nitride or the like. And when the content of the nitrogen atom exceeds the upper limit,
Crystalline chromium nitrides are generated by the penetrating nitrogen atoms and chromium, resulting in deterioration of corrosion resistance. On the other hand, if it is less than the above range, the formation of the nitriding hard layer having high surface hardness becomes insufficient.

It is noted that the corrosion-resistant timepiece member of the present invention does not substantially contain crystalline chromium nitride.
This can be confirmed by analyzing the sample by a line diffraction method, and the amount of nitrogen atoms contained in the austenite layer can be determined by Escher (Electron Spec).
troscopy for Chemical Ana
lysis) or EPMA (Electron Pr)
It can be confirmed by the Obe MicroAnalyzer). Here, in the present invention, “substantially free of crystalline chromium nitride” means that the content of crystalline chromium nitride is a trace amount (several% or less).

Next, the present invention will be described in detail.

The corrosion-resistant timepiece member of the present invention can be obtained by using austenitic stainless steel as a raw material and subjecting it to nitriding as it is, or by molding it into a predetermined shape and then nitriding the molded product. The austenitic stainless steel material is basically an 18-8 austenitic stainless steel material, and the amounts of elements and components are appropriately changed according to required characteristics such as corrosion resistance, work hardening property, heat resistance, machinability, and non-magnetic property. Austenitic stainless steel materials can be mentioned. Further, Cr-Ni-Mo based austenitic stainless steel material containing 22% or more of chromium is also targeted. Further, an austenitic stainless steel material containing 1.5% or more of molybdenum (Mo) even if chromium is less than 22% is also an object of the present invention.

The nitriding treatment applied to the above austenitic stainless steel material or its molded products (these are referred to as "stainless steel products") is performed as follows. That is, in order to facilitate permeation of N atoms during nitriding prior to the nitriding treatment,
Fluoride treatment. Fluorine-based gas used for this fluorination treatment includes NF ₃ , BF ₃ , CF ₄ , HF, SF ₆ ,
Fluorine compound gas composed of C ₂ F _6, WF ₆ , CHF ₃ , SiF _{4 and the} like can be used, and they are used alone or in combination. Other than these, other fluorine compound gas containing fluorine in the molecule can also be used as the fluorine-based gas. Although such a fluorine-based gas can be used alone, it is usually used after being diluted with an inert gas together with N ₂ gas. The concentration of the fluorine-based gas in such diluted gas is, for example, 10,000 to 100,000.
ppm, preferably 20,000 to 70,000 pp
m, more preferably 30,000 to 50,000 ppm. NF ₃ is the most practical fluorine-based gas of this type. NF ₃ is gaseous at room temperature, has high chemical stability, and is easy to handle.

The fluorination treatment is carried out by creating a fluorine-containing gas atmosphere having the above concentration and placing the above stainless steel product in this atmosphere and holding it in a heated state. The heating in this case is performed by raising the temperature of the stainless steel product itself to 300 to 550 ° C. An appropriate time is selected for the holding time of the stainless steel product in such a fluorine-based gas atmosphere depending on its shape and dimensions. Usually, it is set within the range of ten minutes to several tens of minutes. This fluorination treatment facilitates the penetration of N atoms into the surface layer of the stainless steel product. The reason for this is not clear at this stage, but it can be considered as follows. That is, a passivation film that inhibits the permeation and diffusion of N atoms that have a nitriding effect is formed on the surface of the stainless steel product. For this reason, in the past, due to the presence of a passive film (oxide film), nitrogen atoms did not penetrate unless the temperature during the nitriding treatment was raised considerably. As a result, crystalline chromium nitride was not formed in the surface hardened layer. Precipitation was generated. However, in this invention, prior to the nitriding treatment, the fluorine treatment is performed in a fluorine-based gas atmosphere. When the stainless steel product having the passivation film formed on the surface is held in a heated state in the above-mentioned fluorine-based gas atmosphere, the passivation film is converted into a fluoride film. Since this fluorinated film allows N atoms to penetrate more easily than the passive film, the surface of the stainless steel product is formed into a surface state in which N atoms easily penetrate by the fluorination treatment. Therefore, when a stainless steel product having such a surface state in which N atoms easily penetrate is held in a heated state in a nitriding atmosphere as shown below, N atoms in the nitriding gas form a surface layer of the stainless steel product. Since it penetrates uniformly at a constant depth, it is considered that a deep and uniform nitride hardened layer is formed.

As described above, the nitriding treatment is performed by holding the stainless steel product in which N atoms are easily permeated by the fluorine treatment in a heated state in a nitriding atmosphere and performing the nitriding treatment. In this case, as the nitriding gas for creating the nitriding atmosphere, a single gas consisting of only NH ₃ or a mixed gas of a gas having a carbon source (for example, RX gas) and NH ₃ (for example, NH ₃ , CO, and CO ₂₎ is used. Mixed gas) is used. Usually, an inert gas such as N ₂ is mixed with the above single gas or mixed gas before use. In some cases, H ₂ gas may be mixed with these gases and used. In such a nitriding atmosphere, the fluorinated stainless steel product is maintained in a heated state. In this case, the heating temperature is 450 ° C. or lower, which is a temperature significantly lower than that of the conventional nitriding treatment. Is set.
Particularly preferred is in the range of 370 to 420 ° C. That is, if the temperature exceeds 450 ° C., crystalline CrN is generated in the nitrided hardened layer, the active Cr concentration in the matrix decreases, and the corrosion resistance of stainless steel itself is impaired. In particular, by nitriding at a temperature of 420 ° C. or lower, a corrosion resistance comparable to that of the austenitic stainless steel itself, which is the base material, can be maintained, and a nitriding hardened layer with high hardness is formed on the surface of the stainless steel product. Therefore, it is preferable to set in such a temperature range. At a nitriding treatment temperature of 370 ° C. or less, even if the nitriding treatment is performed for 24 hours, the nitriding hard layer is formed only to a depth of 10 μm or less, which is not practical because it has poor industrial value. The nitriding treatment time is usually 10 to 20.
Set in time.

By such a nitriding treatment, the surface layer of the above-mentioned stainless steel product is formed into a dense and uniform nitriding hardened layer having a thickness of about 20 to 40 μm (the whole is a single layer). According to the above nitriding treatment, the austenitic stainless steel product hardly causes dimensional deformation and surface roughness after the nitriding treatment. That is, in the conventional nitriding treatment, the outer shape of the stainless steel product expands due to the precipitation and formation of crystalline chromium nitride, which causes a dimensional change, and the surface roughness deteriorates. In addition to the enormous cost of finishing, it is difficult to apply the technology to precision parts. On the other hand, the nitriding hard layer of the present invention does not substantially contain crystalline chromium nitride and has a dense structure, so that dimensional change and deterioration of surface roughness do not occur,
Eliminates the need for final finishing.

As described above, the nitrided hard layer contains substantially no crystalline chromium nitride, and the austenite phase (γ phase) as the mother phase contains 2 to 12% of N atoms. ing. Therefore, the nitriding-treated stainless steel product has substantially the same level of corrosion resistance as the austenitic stainless steel material before nitriding and hardening, and the presence of the nitriding and hardening layer significantly improves the surface hardness. The corrosion resistance of such a nitrided stainless steel product is higher as the surface condition before nitriding is more precisely polished. In terms of material, S
The higher the chromium content, such as US310 (25% chromium, 20% nickel), the better the corrosion resistance. Also, 18-8
Regarding the austenitic stainless steel, the better the molybdenum content, the better. The nitrided stainless steel product obtained as described above has excellent corrosion resistance comparable to that of the austenitic stainless steel material before nitriding, and the surface hardness is significantly improved, and, It is non-magnetic. That is, according to the conventional nitriding treatment,
By the precipitation of crystalline chromium nitride, the non-magnetic property of the austenitic stainless steel itself is impaired, and the nitrided hardened layer becomes magnetic.
In the corrosion-resistant timepiece member of the present invention, since the nitrided hardened layer does not substantially contain crystalline chromium nitride, it remains non-magnetic. The surface of the nitrided stainless steel product does not lose its stainless-like texture unlike conventional plated products and TiN-coated products and has a good appearance.

A strong mixed acid treatment containing HNO ₃ may be applied to the stainless steel product (stainless steel nitride product) which has been subjected to the above nitriding treatment. By this treatment, oxide scale adhering to the surface of the stainless steel product that has been nitrided is removed, and at the same time, by the action of nitric acid, the passivation film (oxide film) caused by the solid solution chromium is formed on the surface of the stainless steel nitride product. ) Becomes thicker at an early stage, and the oxide film can be strengthened. More specifically, in some cases, the nitriding treatment may cause oxide scale on the surface portion of the stainless nitride product, and since this oxide scale easily rusts, the corrosion resistance of the nitride hardened layer depends on the presence of the oxide scale. descend. Therefore, the oxide scale can be removed by performing the strong mixed acid treatment as described above, and the deterioration of the corrosion resistance can be prevented. The corrosion resistance of austenitic stainless steel is due to the formation of a passive film (oxide film) based on the solid solution chromium in the matrix phase. And strengthening will be carried out, and improvement of corrosion resistance will be seen. Such strong mixed acid, mixed acid consisting of HNO ₃ -HF, HNO mixed acid such as consisting of HNO _3-HCl
Acids containing ₃ are used. HNO in these strongly mixed acids
The concentration of ₃ is 10-20%, HF is 1-10%, HCl
Is set in the range of 5 to 25%. The balance of the strong mixed acid is water. And the said process WHEREIN: The liquid temperature of strong mixed acid is 20-5.
The temperature is controlled to 0 ° C., and the stainless nitride product is immersed in the strong mixed acid solution for 20 to 60 minutes. When such a strong mixed acid treatment is carried out, the outermost surface layer that occupies 20 to 30% of the total nitriding hardened layer is removed, but the surface hardness of the remaining portion is high, so sufficient rigidity is maintained. ing. In this case, the remaining hardened nitride layer becomes completely non-magnetic due to the removal of the outermost surface phase. That is, although the outermost surface layer of the nitriding hardened layer may be somewhat magnetic depending on the case, even in such a case, the magnetically outermost surface layer is removed by the strong mixed acid treatment. The strong-acid-treated stainless nitride product exhibits magnetic permeability equivalent to that of the austenitic stainless steel material (base material). Further, the outermost surface layer portion has a large amount of permeation of nitrogen atoms, and based on the large amount of permeation amount of this nitrogen atom, the outermost surface layer portion is slightly more rusty than other portions, so the outermost surface portion By the removal of the layer portion, the layer below which the amount of permeation of nitrogen atoms is relatively small (2 to 5% of N atoms) forms the surface layer. Although the hardness of this layer is somewhat lower than that of the outermost surface portion, it still has sufficient hardness and has the property of being less likely to rust. Therefore, the product treated in this manner is most suitable as a timepiece member that requires high rust prevention.

[0016]

As described above, in the corrosion-resistant timepiece member of the present invention, since the nitrided hardened layer constituting the surface layer does not contain the crystalline chromium nitride, the stainless steel containing the crystalline chromium nitride in the nitrided hardened layer. Compared with nitride products, solid solution chromium in the austenite phase (matrix) is not consumed by the precipitation formation of crystalline chromium nitride. Therefore, a passivation film (oxide film) generated by the action of the crystalline chromium of the mother phase is sufficiently formed on the surface of the nitrided hardened layer, and thereby it has excellent corrosion resistance equivalent to that of the mother phase. Further, since the crystalline chromium nitride is not precipitated and formed in the nitride hardened layer, the dimensional change and the deterioration of the surface roughness of the stainless nitride product due to the precipitation and production of the crystalline chromium nitride do not occur. As a result, it is not necessary to perform final finishing after the nitriding treatment. That is, the corrosion-resistant watch member of the present invention has a high surface hardness due to 2 to 12% of N atoms permeatingly contained in the mother phase of the surface layer, and is formed by the nitrided hardened layer made of crystalline chromium nitride. It has a high surface hardness almost equal to that. The stainless steel texture is maintained and looks good for a long time.

Next, examples will be described together with comparative examples.

[0018]

Example 1 A wristwatch casing made of SUS304 (hereinafter abbreviated as "casing"), a casing made of SUS316 (chrome 18%, nickel 12%, molybdenum 2%, core hardness Hv = 310), and SUS310.
(Chromium 25%, Nickel 20%, Core hardness Hv = 37
Three types of test products of casing 0) were prepared.
Then, these were placed in a muffle furnace, the inside of the furnace was sufficiently vacuum-purged, and then the temperature was raised to 400 ° C. Then, in that state, a fluorine-based gas (NF ₃ 10 vol% + N ₂ 90 vo)
1%) to bring the inside of the furnace to the atmospheric pressure state, and in that state 1
It was held for 5 minutes and fluorinated. Next, after discharging the fluorine-based gas from the furnace, the nitriding gas (NH ₃ 25 vol%
+ N ₂ 60vol% + CO 5vol% + CO ₂ 5vol
%) Was introduced, and the inside of the furnace was kept at 400 ° C. for 24 hours to carry out nitriding treatment and taken out.

The surface hardness of each of the above-mentioned test products (SUS304 casing, SUS316 casing, SUS310 casing) that had been subjected to nitriding treatment was measured, and Hv =
880, Hv = 1050 with SUS316 casing,
The casing made of SUS310 had Hv = 1120.
The depth of the hardened layer is 18 μm for the SUS304 casing and 20 μm for the SUS316 casing.
It was 18 μm in a SUS310 casing.

[0020]

Second Embodiment In the first embodiment, the nitriding temperature is set to 44.
The processing time was changed to 12 hours while changing to 0 ° C. Other than that was performed like Example 1. The same measurement was performed on the obtained three types of nitriding-treated casings, and the surface hardness was Hv = 1100 or more for all three cases, and the thickness of the nitriding hardened layer was 23 μm for the SUS304 casing and 25 μm for the SUS316 casing, S
The US310 casing had a thickness of 20 μm.

[0021]

Third Embodiment In the first embodiment, the nitriding temperature is set to 38.
The treatment time was changed to 15 hours while changing to 0 ° C. Other than that was performed like Example 1. When the same measurement was performed on the obtained three types of nitriding-treated casings, the surface hardness of all three was Hv = 950 or more, and the thickness of the nitriding hardened layer was 15 μm for the SUS304 casing and 15 μm for the SUS316 casing. , S
The US310 casing had a thickness of 12 μm.

[0022]

COMPARATIVE EXAMPLE 1 The three types of casings used in Example 1 were subjected to fluorination treatment at 400 ° C., and the same nitriding gas as that used in Example 1 was used. It was put in the same furnace and subjected to nitriding treatment at 550 ° C. for 5 hours and taken out. The surface hardness of the obtained three types of nitriding-treated casings is Hv = 1280 and Hv =
1280, Hv = 1300, and the cured layer depth is 30 to
It was 35 μm.

Next, the test products obtained in Examples 1 to ₃ were immersed in a strong mixed acid solution of 5% HF-18% HNO ₃ at 40 ° C. for 60 minutes and then taken out and examined. The outermost surface layer (3 to 6 μm) of the nitriding hard layer was removed. Further, also in Comparative Example 1, when the same treatment was carried out, the entire nitrided hard layer was removed and removed.

Next, the surface hardness and the content of N atoms on the outermost surface of the nitride hardened layer of the test pieces obtained in Examples 1 to 3 and Comparative Example 1 and those treated with a strong mixed acid solution were determined. The results are summarized in Table 1 below. In Table 1, “with acid treatment” means that a strong mixed acid treatment has been carried out, and “without acid treatment” means that after nitriding is completed. Further, the content of N atom was determined from the chart obtained by subjecting each of the above samples to EPMA line analysis. For the corrosion resistance, a salt spray test (SST test) based on JIS2371 was performed and the time until rusting was determined. Further, the presence or absence of crystalline chromium was judged from the chart obtained by subjecting each sample to an X-ray diffraction test.

[0025]

[Table 1]

The following can be seen from the above table. Casing made of SUS310 of Example 2 (with acid treatment)
And a casing made of SUS316 of Comparative Example 1 (without acid treatment)
As is clear from the comparison with, if there is no crystalline chromium nitride in the nitrided hardened layer and the N atom concentration is within 12%, corrosion resistance can be obtained to a practical level, but at the boundary of 12%, If it exceeds this, precipitation of crystalline chromium nitride will be observed and the corrosion resistance will be significantly reduced. On the contrary, as is clear from the SUS316 casing of Example 3 (with acid treatment), when the N atom concentration is less than 2%, the surface hardness is usually Hv 700 or less and the surface rigidity becomes insufficient. As is clear from the comparison between Examples 1 to 3 and Comparative Example 1, the higher the nitriding temperature, the higher the concentration (content) of N atoms in the nitride hardened layer. When treated with a strong mixed acid, the outermost surface layer portion (N
The maximum atomic concentration) is dissolved and removed, and the layer underneath appears, so that the N atomic concentration and the surface hardness decrease. Since the N atom concentration in the nitriding hardened layer is higher in the SUS310 casing than in the SUS316 casing, at the time of nitriding, in proportion to the Cr concentration in the base material,
The concentration of N atoms becomes high. In the comparative example, since the crystalline chromium nitride is deposited over the entire nitride hardened layer and lacks the corrosion resistance, the strong mixed acid treatment causes the entire nitrided hard layer lacking the corrosion resistance to disappear, exposing the base material.

The results of the EPMA line analysis are shown in FIG. 1 (Example 1), showing the results of Example 1 (SUS316 casing, no acid treatment) and Comparative Example 1 (SUS316 casing, no acid treatment). 2 and (Comparative Example 1). As is clear from the N atom concentration curves in FIGS. 1 and 2, in Example 1, the N atom concentration (content) in the outermost surface layer of the nitrided hard layer is 7.6%. Comparative Example 1
Then, it is remarkably high at 12.8%. The N atom concentration of the EPMA is measured using a standard calibration curve.

The results of the X-ray diffraction test are shown in FIG. 3 (Example 1) and FIG. 4 (Comparative Example 1), representing the results of Example 1 and Comparative Example 1 (both made of SUS316, without acid treatment). )Pointing out toungue. In these figures, the curve (a) is the X-ray diffraction curve of Example 1, the curve (b) is the X-ray diffraction curve of SUS316 (SUS316 raw material) not subjected to nitriding treatment, and the curve (c) is Comparative Example 1. 2 is an X-ray diffraction curve of Figure 3
In, γn represents a γ phase (mother phase) containing nitrogen atoms by nitriding. From the comparison between the curve (a) and the curve (b), γn (mother phase) of the curve (b) is left (lower angle side) than the corresponding γ-Fe phase (mother phase) of the curve (b). As a result, the lattice constant is increased, and lattice strain is observed. This is the cause of the improvement in the surface hardness of the example product. On the other hand, in the curve (c) of the comparative example, CrN
There are many peaks of the crystalline chrome nitride such as, which indicates that the corrosion resistance of the nitride hardened layer is reduced.

Further, Example 1 obtained as described above
And the casing of Comparative Example 1 (both SUS316
In order to examine the electrochemical corrosivity, the anodic polarization test (according to JIS G 0579) was performed. The result is shown in FIG. From FIG. 5, comparing the order of the passivation holding current density level in the vicinity of the passivation region (broken line X), Example 1 (curve A) is much less than the SUS316 base material without nitriding treatment (curve B). It can be seen that it has not deteriorated. On the other hand, Comparative Example 1
(Curve C) is 3 compared to the SUS316 base material (Curve B).
It can be seen that there is a difference of several digits or more, and the corrosion resistance is significantly deteriorated by the nitriding treatment.

[0030]

[Example 4] Furthermore, the three types of nitriding-treated casings obtained in Example 1 were subjected to shot blasting to remove oxide scale adhering to the surface, and subjected to an SST test. Rusting occurred within 72 hours.

Next, these test products were treated with 20% HCl.
It was immersed in a strong mixed acid solution of -13% HNO ₃ for 60 minutes at a liquid temperature of 45 ° C., and then the hardness was measured. As a result, the surface hardness was Hv = 850 to 900, and the thickness of the nitriding hard layer was strong. It is soaked with mixed acid and reduced by 5-8 μm 12-15
It was μm. Then, add the acid-treated test product to S
As a result of having been subjected to the ST test, the corrosion resistance is improved.
No rust occurred at all even after 00 hours.

[0032]

Example 5 A non-magnetic stainless steel plate piece (Cr 18%, Ni 12%, Mn 1.
5%) and SUS316 plate pieces were subjected to fluorination treatment and nitriding treatment in the same procedure and conditions as in Example 1 to obtain three types of nitriding treated casings. And these
It was taken out by immersing it in a strong mixed acid solution of 0% HF-15% HNO ₃ at a liquid temperature of 40 ° C. for 30 minutes.

Next, when the magnetic permeability (μ) of each of these was measured, it is as shown in Table 2 below, and it can be seen that none of them is magnetized by nitriding.

[0034]

[Table 2]

[Brief description of drawings]

FIG. 1 is an EPMA line analysis curve diagram for an example product.

FIG. 2 is an EPMA line analysis curve diagram for a comparative example product.

FIG. 3 is an X-ray diffraction curve diagram for an example product.

FIG. 4 is an X-ray diffraction curve diagram for a comparative example product.

FIG. 5 is a current density-voltage curve diagram for an example product and a comparative example product.

Claims (5)

[Claims] 1. A base material is made of an austenitic stainless steel material, and at least a part of the surface layer portion has the following (A),
A corrosion-resistant timepiece member comprising a nitrided hardened layer including (B). (A) Substantially free of crystalline chromium nitride. (B) 2 to 12% by weight in the austenite phase which is the mother phase
N atoms of are contained. 2. The corrosion resistant timepiece member according to claim 1, wherein the austenitic stainless steel contains 22% by weight or more of chromium. 3. The austenitic stainless steel containing molybdenum in an amount of 1.5% by weight or more.
Corrosion resistant watch member described. 4. The corrosion resistant timepiece member according to claim 1, wherein only the component (B) is restricted as follows. (B) The austenite phase, which is the mother phase, contains 2 to 5% by weight of N atoms. 5. The corrosion resistant timepiece member according to claim 1, wherein the thickness of the nitriding hardened layer is set to 14 to 40 μm.