JP3005371B2 - Surface treatment method for ferritic stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention provides a high surface hardness
The present invention relates to a surface treatment method for a ferritic stainless steel material which has sufficient wear resistance, base material hardness, and base material toughness, and is suitable for components such as blades, gears, and shafts.

[0002]

2. Description of the Related Art Conventionally, attempts have been made to increase the surface hardness and abrasion resistance by forming a ceramic coating layer on the surface of a metal material having sufficient base material hardness and base material toughness. The method for forming the ceramic coating layer includes thermal spraying, PVD, and CVD.
Is mentioned. However, since a dense coating layer cannot be formed by thermal spraying, a sufficient surface hardness cannot be ensured. In the case of PVD or CVD, the thickness and adhesion strength of the coating layer are insufficient. As a result, the surface hardness and abrasion resistance are reduced. I can't raise it.

On the other hand, conventionally, gas nitriding (for example, accompanied by thermal decomposition of NH ₃ gas) or glowing (for example, N ₂ gas or NH ₃ gas) is applied to the surface of steel or Fe—Cr—Al steel. There is a method of increasing the surface hardness and abrasion resistance by generating a nitride layer by ion nitridation (with decomposition). In this method by nitriding, instead of laminating a coating layer on the surface, it is a method of changing a little from the surface of the steel to a nitride, so that there is no fear of peeling or missing, and a surface hardness of about Hv = 1000. become. However,
The base material hardness is as low as about Hv = 200, which is not enough. Even if the hardness of the base material is increased in advance by quenching, the nitriding temperature is close to the annealing temperature, so that the base material hardness of about Hv = 350 is eventually secured.

[0004]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention has a high surface hardness, a sufficient abrasion resistance, a sufficient base material hardness, and a sufficient base material toughness. It is an object of the present invention to provide a surface treatment method of a ferritic stainless steel material that can obtain a material suitable for the above-mentioned parts.

[0005]

Means for Solving the Problems In order to achieve the above object, a method for treating a surface of a ferritic stainless steel material according to the present invention uses a Fe--Cr--
A method of treating a surface of a ferritic stainless steel material in which a Ni-Al-based ferrite alloy is set to generate a glow discharge to generate a nitride layer on the surface of the ferrite alloy, wherein the composition of the ferrite alloy is Cr:
20-40 wt%, Ni: 2-30 wt%, Al: 2
15% by weight, any one or more of Zr, Y, Hf, Ce, La, Nd and Gd: 0.05 to
3.0% by weight, Ti: 0 to 0.5% by weight, balance: Fe.

According to the present invention, N ions generated by the decomposition of N _{2 or} NH ₃ by glow discharge react with the surface layer of the ferrite alloy to form a nitride layer. That is,
In the case of the present invention, the surface of the ferrite alloy is ion-nitrided. The nitride layer is mainly made of chromium nitride, but also contains aluminum nitride, iron nitride and the like. The Fe-Cr-Ni-Al-based ferrite alloy used in the present invention has NiAl-based B2-phase particles dispersed in the matrix, and has sufficient toughness as well as hardness.

[0007] Fe-Cr-N set in a reduced pressure atmosphere
The i-Al ferrite alloy is not limited to an ingot formed into an appropriate shape (for example, an alloy plate, etc.), but may be in the form of a sintered body obtained by compacting and sintering an alloy powder obtained by a water atomizing method. There are also things. In the case of the present invention, before setting in a reduced-pressure atmosphere containing nitrogen, (after molding into a predetermined shape as necessary), the mixture is placed in a non-oxidizing atmosphere at 1250 to 1350.
After heating to a temperature in the range of
Fe-Cr-Ni-Al-based ferrite alloys that have been subjected to an appropriate heat treatment for rapid cooling at a cooling rate of
This is appropriate because the iAl-based B2 phase particles are dispersed in an appropriate state in the matrix and have higher hardness. 1250-135
The holding time at a temperature in the range of 0 ° C. depends on the thickness of the material, but is usually about 30 seconds to 30 minutes.

In the present invention, for example, at least one of a mixed gas of N ₂ and H ₂ and an NH ₃ gas is used as the reduced-pressure atmosphere containing nitrogen. (N ₂ + H ₂ )
The mixed gas and NH ₃ gas is to so as to contain the required nitrogen was supplied to the reduced pressure atmosphere. The pressure of the reduced pressure atmosphere is, for example, about 65 to 1350 Pa (preferably
00 to 900 Pa). In the case of a mixed gas of (N ₂ + H ₂ ), the mixing ratio of the N ₂ gas and the H ₂ gas is usually appropriate in a range of 1: 9 to 9: 1 by volume.

In a reduced-pressure atmosphere, an anode and a cathode are arranged to face each other. Usually, a ferrite alloy is set on the cathode,
A voltage is applied between both electrodes. For example, if the size of the reduced pressure atmosphere (for example, the size of the ion nitriding furnace) is, for example,
0 cm x 30 cm x 30 cm in height, and when the distance between the cathode and the anode is 12 cm, 250-35
A glow discharge having a discharge current of 0.4 to 0.8 A is generated by applying a DC voltage of 0 V. The generation and retention time (nitridation time) of glow discharge is about 2 to 10 hours.

When the glow discharge occurs, the temperature of the ferrite alloy rises by the discharge current, and the temperature is raised in the range of 400 to 700 ° C. (preferably 550 to 600 ° C.). Conversely, the ferrite alloy temperature at the time of glow discharge occurrence is 4
The discharge current is controlled to fall within the range of 00 to 700 ° C. Thus, in the present invention, the ferrite stainless steel is subjected to the surface treatment, and a nitride film is formed on the surface. The surface hardness after the surface treatment is about Hv = 1000,
The base material hardness is about 500.

Subsequently, the raw material Fe-Cr-Ni-
The reasons for limiting the contents of the elements contained in the Al-based ferrite alloy will be described. The alloy of the present invention is an Fe-based alloy containing a large amount of Cr and Al, which are ferrite-forming elements, and Ni, which is an austenite-forming element. The reason why the alloy is mainly made into a ferrite phase is as follows. The ferrite phase alloy has NiAl-based B2 phase particles dispersed therein and has a high base material hardness. However, the base material hardness of the austenitic phase alloy is low.

[Cr: 20 to 40 weight (preferably 25
４０40% by weight)] Cr is necessary for forming a dense and uniform nitride layer on the surface of the alloy. However, in the alloy of the present invention, Ni is contained. Even when Ni is the lower limit and Al is the upper limit, 20
Cr is required in an amount of at least% by weight. Ni content is lower limit, Al
In the alloy whose amount is near the upper limit and whose Cr amount is less than 20% by weight, formation of the nitride layer is incomplete. Therefore, the lower limit of Cr is 20% by weight. Further, since the tendency of embrittlement increases as the Cr content in the alloy increases, the upper limit of Cr is 4%.
0 wt%.

[Ni: 2 to 30% by weight (preferably 10% by weight)
Ni is presumed to precipitate fine NiAl in the alloy and improve the mechanical properties (for example, hardness) of the base material. However, Ni precipitates NiAl in the presence of Al. Is an indispensable element. In order to be sufficiently effective for improving the mechanical properties, 2% by weight or more of Ni is required. If the amount of Ni increases, it is advantageous for the precipitation of NiAl. However, if the content of Ni, which is an austenite-forming element, is increased, the contents of Cr and Al must be increased accordingly. However, the Ni content is 30% by weight.
Is exceeded, the amount of Cr must be increased, which tends to cause embrittlement. Therefore, the upper limit of Ni is 30% by weight.

[Al: 2 to 15% by weight] Al is an indispensable element for precipitating fine NiAl into the alloy and ensuring sufficient base metal hardness. For that, 2% by weight
It is necessary to contain the above Al. An increase in the Al content is advantageous for the precipitation of NiAl, but if it exceeds 15% by weight, the workability of the alloy is reduced.
5% by weight.

[One or more of Zr, Y, Hf, Ce, La, Nd and Gd: 0.05
To 3.0% by weight (preferably 0.05 to 2.0% by weight)]
Each of these additional elements is added in order to improve the workability of the material.
It is necessary to contain at least 05% by weight.
If the content exceeds 3.0% by weight, the workability of the alloy reversely deteriorates, so the upper limit is 3.0% by weight.

[Ti: 0 to 0.5% by weight] Ti is added as needed, and improves the workability of the material. In order to cause deterioration or the like, the upper limit is set to 0.5% by weight. [Fe: balance] Fe occupies other than the above components. However, the present invention is not limited to the case where the balance is completely Fe, but is inevitably present in Fe as impurities (such as Si).
There may be.

The ferrite stainless steel surface-treated by the method of the present invention is used, for example, for components such as blades, gears, and shafts, but it goes without saying that it can be used for other purposes.

[0018]

In the surface treatment method for a ferritic stainless steel material according to the present invention, the surface of the Fe—Cr—Ni—Al ferrite alloy is covered with a dense and thick nitride layer having strong adhesion by ion nitriding. Sufficient surface hardness (Hv
= About 1000) and abrasion resistance is ensured.

Further, the composition of the Fe—Cr—Ni—Al ferrite alloy is an appropriate composition that ensures sufficient base material hardness and base material toughness, and a relatively low temperature of about 700 ° C. or less in ion nitriding. Nitriding treatment is performed, and Fe-C
The r-Ni-Al ferrite alloy has sufficient base material hardness and base material toughness, even after nitriding, even when the alloy is formed into a predetermined shape, the deformation of the alloy hardly occurs and sufficient dimensional accuracy is obtained. Become like If a Fe—Cr—Ni—Al ferrite alloy is oxidized in a high-temperature oxidizing atmosphere exceeding 1000 ° C. to form an alumina film on the surface of the alloy, sufficient surface hardness and abrasion resistance can be ensured. Since the temperature is higher than ℃, the alloy is liable to be deteriorated or deformed. In the case where a relatively low temperature of about 700 ° C. or less is required as in the present invention, it is possible to avoid the deterioration and deformation of the alloy, which is very practical.

An appropriate ferrite alloy of Fe-Cr-Ni-Al is heated to a temperature in the range of 1250 to 1350 ° C in a non-oxidizing atmosphere, held for a predetermined time, and then rapidly cooled at a cooling rate of 10 ° C / sec or more. When the heat treatment is performed in advance, the base material hardness is preferably higher.

[0021]

Embodiments of the present invention will be described below. It goes without saying that the present invention is not limited to the following embodiments. Example 1 After rolling an ingot having a composition shown in Table 1 to a sheet thickness of 0.1 mm, the temperature was raised to 1250 ° C. in a vacuum atmosphere, and the temperature was maintained for 30 minutes. Quench at a rate of
Fe-Cr-Ni to be polished, washed and ion-nitrided
-An Al-based ferrite alloy was obtained.

Subsequently, the furnace wall of the ion nitriding furnace was suspended on the sample table in the furnace with the anode as the anode and the sample table as the cathode. As shown in Table 2, the atmosphere in the furnace was set at a gas mixture ratio of nitrogen gas and hydrogen gas of 1%. :
1 (volume ratio), the atmospheric pressure was set to 800 Pa, and then a DC voltage of 300 V was applied between the anode and the cathode, and the applied power was 1
Glow discharge is performed at 50 W, and the alloy is heated to 550 ° C (nitriding temperature).
For 3 hours (nitriding time)
An Al-based ferrite alloy was ion-nitrided to form a nitride film having a thickness of about 5 μm and containing chromium nitride as a main component.

Table 3 shows the measurement results of the base material hardness and the surface hardness of the ferritic stainless steel after the surface treatment. -Example 2-The alloy composition is as shown in Table 1, the applied power, the gas mixture ratio,
Example 1 except that the nitriding temperature and the nitriding time were as shown in Table 2.
In the same manner as in the above, an ion nitriding treatment was performed to form a nitride film having a thickness of about 3 μm containing chromium nitride as a main component. Table 3 shows the measurement results of the base metal hardness and the surface hardness.

Example 3 The alloy composition is as shown in Table 1, and the applied power, gas mixture ratio,
Example 1 except that the nitriding temperature and the nitriding time were as shown in Table 2.
In the same manner as in the above, an ion nitriding treatment was performed to form a nitride film having a thickness of about 10 μm and containing chromium nitride as a main component. Table 3 shows the measurement results of the base metal hardness and the surface hardness.

Example 4 The alloy composition is as shown in Table 1, and the applied power, gas mixture ratio,
Example 1 except that the nitriding temperature and the nitriding time were as shown in Table 2.
In the same manner as in the above, an ion nitriding treatment was performed to form a nitride film having a thickness of about 10 μm and containing chromium nitride as a main component. Table 3 shows the measurement results of the base metal hardness and the surface hardness.

Example 5 The alloy composition is as shown in Table 1 and the plate thickness is 1.4 m.
m, and the applied power, the gas mixture ratio, the nitriding temperature, and the nitriding time are as shown in Table 2.
A μm nitride film was formed. Table 3 shows the measurement results of the base metal hardness and the surface hardness.

Example 6 An alloy powder having the composition shown in Table 1 was obtained by a water atomizing method, and the powder was compacted into a disk having a diameter of 30 mm and a height of 5 mm, and heated to 1350 ° C. in a vacuum atmosphere. After sintering at a temperature of 3 hours, the temperature was raised to 1250 ° C. in a vacuum atmosphere, and the temperature was maintained for 30 minutes.
It was rapidly cooled at a speed of seconds, polished and washed to obtain an Fe-Cr-Ni-Al-based ferrite alloy to be ion-nitrided.

Thereafter, ion nitriding was performed in the same manner as in Example 1 except that the applied power, the gas mixture ratio, the nitriding temperature, and the nitriding time were as shown in Table 2. A 30 μm nitride film was formed. Table 3 shows the measurement results of the base metal hardness and the surface hardness. -Example 7-After obtaining an alloy powder having a composition shown in Table 1 by a water atomizing method, F to be ion-nitrided in the same manner as in Example 6.
An e-Cr-Ni-Al ferrite alloy was obtained.

Thereafter, ion nitriding was performed in the same manner as in Example 1 except that the applied power, the gas mixture ratio, the nitriding temperature, and the nitriding time were as shown in Table 2. A 15 μm nitride film was formed. Table 3 shows the measurement results of the base metal hardness and the surface hardness. -Example 8-The alloy composition is as shown in Table 1, and the applied power, gas mixture ratio,
Example 1 except that the nitriding temperature and the nitriding time were as shown in Table 2.
In the same manner as in the above, an ion nitriding treatment was performed to form a nitride film having a thickness of about 5 μm containing chromium nitride as a main component. Table 3 shows the measurement results of the base metal hardness and the surface hardness.

Example 9 The alloy composition is as shown in Table 1, and the applied power, gas mixture ratio,
Example 1 except that the nitriding temperature and the nitriding time were as shown in Table 2.
In the same manner as in the above, an ion nitriding treatment was performed to form a nitride film having a thickness of about 5 μm containing chromium nitride as a main component. Table 3 shows the measurement results of the base metal hardness and the surface hardness.

Example 10 The alloy composition is as shown in Table 1, and the applied power, gas mixture ratio,
Example 1 except that the nitriding temperature and the nitriding time were as shown in Table 2.
In the same manner as in the above, an ion nitriding treatment was performed to form a nitride film having a thickness of about 5 μm containing chromium nitride as a main component. Table 3 shows the measurement results of the base metal hardness and the surface hardness.

Comparative Example 1 An ingot having the composition shown in Table 1 was rolled to a thickness of 0.1 mm and then washed to obtain an Fe-Cr-Al-based ferrite alloy to be ion-nitrided. The alloy composition is as shown in Table 1,
Except that the applied power, the gas mixture ratio, the nitriding temperature, and the nitriding time are as shown in Table 2, an ion nitriding treatment was performed in the same manner as in Example 1 to form a nitride film having a thickness of about 10 μm and containing chromium nitride as a main component. Formed. Table 3 shows the measurement results of base metal hardness and surface hardness.
It is as follows.

-Comparative Example 2- An ingot having the composition shown in Table 1 was rolled to a thickness of 0.1 mm, heated to 800 ° C in nitrogen gas, held for 30 minutes, and then annealed by slow cooling. Then, in nitrogen gas, 10
The temperature was raised to 50 ° C. for 5 minutes, followed by cooling by air cooling, followed by quenching. Then, the temperature was raised to 100 ° C., held for 10 minutes, and then tempered by air cooling to obtain an Fe—Cr ferrite alloy.

Subsequently, the furnace wall of the ion nitriding furnace was suspended on the furnace sample table with the anode as the anode and the sample table as the cathode. As shown in Table 2, the atmosphere in the furnace was set at a gas mixture ratio of nitrogen gas and hydrogen gas of 1%. :
After the atmospheric pressure was set to 800 Pa, a DC voltage of 280 V was applied between the anode and the cathode, glow discharge was performed at an applied power of 160 W, and the alloy was heated to 550 ° C. (nitriding temperature).
Holding time (nitriding time), ion-nitriding of Fe-Cr ferrite alloy, thickness of about 3μ mainly composed of chromium nitride
m of nitride film was formed.

The relationship between the distance from the surface toward the inside and the hardness of the ferritic stainless steel material after the surface treatment in Examples 1 to 4 is shown in a graph in FIG.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

As can be seen from the hardness measurement results of the example and the comparative example, it is clear that the surface treatment method for ferritic stainless steel of the present invention can secure a sufficient base material hardness.

[0040]

According to the surface treatment method for a ferritic stainless steel material according to the present invention, the surface of the Fe-Cr-Ni-Al ferrite alloy is covered with a dense and thick nitride layer having strong adhesion by ion nitriding. In addition, sufficient surface hardness and abrasion resistance are ensured, and in the case of ion nitriding, sufficient base material hardness and base material toughness of the alloy are maintained. The properties, base material hardness, and base material toughness are all sufficient, so that what is suitable for components such as blades, gears, shafts, and the like can be obtained. Therefore, it can be said that the present invention is very useful.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the distance taken from the surface to the inside and the hardness of the ferritic stainless steel material after surface treatment of Examples 1 to 4.

Continuation of the front page (72) Inventor Kazuhiro Nakada 2-12-8 Hannan-cho, Abeno-ku, Osaka-shi (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 8/38 C21D 6/00

Claims (4)

(57) [Claims] 1. The method of claim 1, wherein Fe-Cr-
A ferrite-based stainless steel surface treatment method comprising: setting a Ni-Al-based ferrite alloy, generating glow discharge, and performing nitriding treatment to form a nitride layer on the ferrite alloy surface. But Cr: 20 to 40% by weight, Ni: 2 to 30% by weight, Al: 2 to 15% by weight, Zr, Y, Hf, Ce, L
one or more of a, Nd and Gd: 0.05 to 3.0% by weight, Ti: 0 to 0.5% by weight, and balance: Fe Surface treatment method for materials. 2. An Fe—Cr—Ni—Al-based ferrite alloy is set in a non-oxidizing atmosphere at 1250 to 13
After heating to a temperature in the range of 50 ° C. and holding for a predetermined time, 10
The surface treatment method for a ferritic stainless steel material according to claim 1, wherein a heat treatment for quenching at a cooling rate of at least C / sec is performed. 3. Fe-Cr-Ni- during glow discharge occurrence
The surface treatment method for a ferritic stainless steel material according to claim 1 or 2, wherein the temperature of the Al-based ferrite alloy is 400 to 700 ° C. 4. The ferrite system according to claim 1, wherein the nitrogen in the reduced pressure atmosphere is nitrogen obtained by introducing at least one of a mixed gas of N ₂ and H ₂ and an NH ₃ gas. Surface treatment method for stainless steel.