JP2000073156A - Production of nitrided stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a nitriding layer high in uniformity at a low cost by heating stainless steel whose ten-point average roughness Rz on the surface of the steel is controlled to a specified range in the nitriding atmosphere of a specified temp. range basically consisting of gaseous ammonia for a specified time. SOLUTION: The stainless steel whose ten-point average roughness Rz is controlled to 0.5 to 5.0 μm is heated in the nitriding atmosphere of 300 to 650 deg.C for >=30 min. Preferably, the stainless steel whose ten-point average roughness Rz is controlled to 0.5 to 5.0 μm and the total content of martensitic phases and ferritic phases in the surface layer part to a depth of 10 μm from the surface is controlled to >=80 vol.% is heated in the nitriding atmosphere of 300 to 650 deg.C basically consisting of gaseous ammonia for >=30 min. Moreover, the stainless steel contains, by mass, <=0.15% C, <=5.0% Si, <=0.5% Mn, 2.0 to 20.0% Ni, 12.0 to 50.0% Cr, 0 to 3.5% Cu, 0 to 6.0% Mo, <=0.15% N, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a nitrided stainless steel material, and particularly to a high-strength stainless steel used for mechanical parts such as a spring material, a steel belt, and a continuously variable transmission belt for an automobile engine. The present invention relates to a manufacturing method suitable for improving fatigue characteristics of a steel material.

[0002]

2. Description of the Related Art As material properties required for mechanical parts such as spring materials, steel belts, and continuously variable transmission belts for automobile engines, in addition to strength, surface hardness and fatigue properties are important. The nitriding treatment is an effective means for producing a surface hardening of the material and a surface compressive residual stress due to a supersaturated state of solid solution nitrogen and formation of a nitride, thereby improving the above-mentioned material properties. Another advantage of the nitriding treatment is that the heat treatment strain is smaller than that of induction hardening or carburizing quenching, which is the same surface hardening method.

[0003]

However, when a nitriding treatment is applied to stainless steel, a passivation film is present on the surface of the stainless steel. There is a problem that it is difficult. As a means for overcoming the nitridation resistance of stainless steel, JP-A-59-28566 discloses a method in which the dew point temperature is always lower than the temperature of the workpiece. Also, Japanese Patent Publication No. 58-2
No. 2541 discloses a method using ion nitriding. However, the former has difficulty in improving productivity in terms of speed in terms of temperature control, and the latter forms a uniform nitrided layer on the material surface due to the non-uniformity of the passive film even when ion nitriding is applied. The problem remains that it is difficult to do.

An object of the present invention is to produce a nitrided stainless steel material having a highly uniform nitrided layer at low cost by a method capable of avoiding these problems.

[0005]

In order to achieve the above object, in the present invention, nitridation hardly occurs (poor in nitridation).
A method is adopted in which the properties inherent to stainless steel are improved in advance to prepare a steel material in a state that is easy to be nitrided, and this is subjected to a nitriding treatment. As means for improving the nitriding property, a means is used in which the surface of the stainless steel material is roughened and, if necessary, the surface layer of the steel material has a metal structure rich in martensite or ferrite phase.

The invention according to claim 1 is to provide a stainless steel material having a ten-point average roughness Rz of 0.5 to 5.0 μm on a steel material surface in a nitriding atmosphere of 300 to 650 ° C. containing ammonia gas as a basic component for 30 minutes. The above is a method for producing a nitrided stainless steel material by heating. Here, the ten-point average roughness Rz is the ten-point average roughness Rz defined in JIS B0601.

According to a second aspect of the present invention, the ten-point average roughness Rz of the steel material surface is adjusted to 0.5 to 5.0 μm, and the steel surface has a depth of 10 μm from the surface.
The stainless steel material in which the total amount of the martensite phase and the ferrite phase in the surface layer is adjusted to 80% by volume or more is heated in a nitriding atmosphere of 300 to 650 ° C containing ammonia gas as a basic component for 30 minutes or more. This is a method for manufacturing stainless steel. Here, `` the surface layer from the surface to a depth of 10 μm '' is defined as the `` meaning of the terms '' in JIS B 0601. Refers to the surface layer up to a depth of 10 μm.

A third aspect of the present invention is to provide a stainless steel material in which the ten-point average roughness Rz of the steel material surface is adjusted to 0.5 to 5.0 μm by any one of dull roll rolling, mechanical grinding, and mechanical polishing. 300 to 650 with gas as the basic component
This is a method for producing a nitrided stainless steel material, wherein the material is heated in a nitriding atmosphere at 30 ° C. for 30 minutes or more.

According to a fourth aspect of the present invention, after any of dull roll rolling, mechanical grinding or mechanical polishing is performed, any one of barrel polishing, shot peening or shot blasting is performed. A stainless steel material in which the ten-point average roughness Rz of the steel material surface is adjusted to 0.5 to 5.0 μm, and the total amount of martensite phase and ferrite phase in the surface layer from the surface to a depth of 10 μm is adjusted to 80% by volume or more. Is heated in a nitriding atmosphere of 300 to 650 ° C. containing ammonia gas as a basic component for 30 minutes or more, to produce a nitrided stainless steel material.

[0010] The invention of claim 5 is a method for producing a nitrided stainless steel material, wherein the stainless steel material whose ten-point average roughness Rz of the steel material surface is adjusted to 0.3 to 5.0 µm is subjected to nitriding treatment. The invention according to claim 6 is characterized in that a nitriding treatment is performed on a stainless steel material whose ten-point average roughness Rz is adjusted to 0.3 to 5.0 μm by any of dull roll rolling, mechanical grinding or mechanical polishing, This is a method for producing a nitrided stainless steel material. The ten-point average roughness Rz of the steel material surface is 0.3 to 5.0.
A method for producing a nitrided stainless steel material in which a stainless steel material that has been adjusted to μm and the total amount of a martensite phase and a ferrite phase in the surface layer from the surface to a depth of 10 μm is adjusted to 60% by volume or more is nitrided. . The invention according to claim 8 is characterized in that after applying any means of dull roll rolling, mechanical grinding or mechanical polishing, further applying any means of barrel polishing, shot peening or shot blasting, the steel material surface 10-point average roughness Rz
Nitriding of stainless steel material is adjusted to 0.3-5.0 μm, and the total amount of martensite and ferrite phases in the surface layer from the surface to the depth of 10 μm is adjusted to 60% by volume or more. It is a manufacturing method.

According to a ninth aspect of the present invention, in the invention of the fifth to eighth aspects, the nitriding treatment heats the steel material to 300 to 650 ° C. in a gas obtained by mixing H ₂ S with a gas containing ammonia gas as a basic component. It specifies that it is a gas sulphonitriding method. The invention according to claim 10 is the invention according to claims 5 to 8, wherein the nitriding treatment heats the steel material to 300 to 650 ° C by plasma generated between the steel material and the furnace wall in a reduced pressure gas containing nitrogen gas as a basic component. That is, it is a plasma nitriding method. The invention according to claim 11 is the invention according to claims 5 to 8, wherein the nitriding treatment is performed by placing the steel material in a salt bath at 300 to 650 ° C containing one or more of NaCN, KCN, NaCNO and KCNO as a basic component. It is defined that the immersion is a salt bath nitriding method.

In a twelfth aspect of the present invention, in the first to eleventh aspects of the present invention, the stainless steel is, by mass%, C: 0.15% or less, Si: 5.0% or less, Mn: 5.0% or less, Ni: 2.0 to 20.0%.
%, Cr: 12.0 to 50.0%, Cu: 0 to 3.5% (including no addition), Mo: 0 to 6.0% or less (including no addition), N: 0.15%
It is specified that the balance includes Fe and inevitable impurities, including the following.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of the study of the present inventors, it has been found that the nitriding property of stainless steel is greatly improved by adjusting the surface roughness of a steel material to a specific state. It was also confirmed that the nitriding property was further improved by changing the metal structure of the surface layer to a structure mainly composed of a martensite phase or a ferrite phase. Hereinafter, matters specifying the present invention will be described.

When the surface roughness of the steel material becomes rough, the surface irregularities become large, and the surface area of the interface between the gas and the molten salt and the metal at the time of nitriding increases, thereby promoting the nitriding. In addition, a passivation film imperfect region is generated in the concave portion of the surface unevenness, and the effect of accelerating nitridation also appears. Various indicators can be considered as an index of the surface roughness. For example, JIS B 0601 defines a center line average roughness Ra, a maximum height Rmax, and a ten-point average roughness Rz. As a result of detailed studies by the inventors, it was found that the nitriding property of the stainless steel material depends on the ten-point average roughness Rz.

On the roughened steel surface, it is considered that nitrogen stays in the concave portions of the surface irregularities and the nitriding reaction is accelerated. If so, the information of the “average” height difference between the concave portions and the convex portions becomes important when considering the roughened form in which a uniform nitride layer is formed. The ten-point average roughness Rz is considered to be an index that well reflects such an average height difference.

When the ten-point average roughness Rz is 0.3 μm or more, the effect of improving the nitriding property due to the unevenness appears, and as a result, the surface hardness and the fatigue properties of the steel material after the nitriding treatment are improved. When Rz is 0.5 μm or more, the effect becomes more remarkable. However, when Rz was larger than 5.0 μm, a phenomenon in which the fatigue characteristics deteriorated was observed. This reduction in fatigue properties
This is considered to be due to the notch effect at the concave and convex portions becoming apparent and the breakage being likely to occur. Therefore, in the present invention, the surface roughness of the stainless steel material to be subjected to the nitriding treatment is specified so that the ten-point average roughness Rz is in the range of 0.3 to 5.0 μm. Heating in a nitriding atmosphere containing ammonia gas as a basic component, when applying a so-called general gas nitriding method, Rz is 0.5 to
It is preferable to make the unevenness in the range of 5.0 μm.

Such surface irregularities are caused by dull roll rolling,
Preferably, it is formed by either mechanical grinding or mechanical polishing. According to these mechanical means, an optimum roughened form can be obtained relatively easily, and an effect of improving the nitridation property due to the generation of microscopic cracks in the passive film on the surface can be expected.

The metal structure of the surface layer is preferably mainly composed of a martensite phase or a ferrite phase. This is because these phases have a crystal structure in which the diffusion rate of nitrogen is high.
However, since the effect of improving the nitriding property can be obtained only by adjusting the surface roughness as described above, the austenite phase may be present in the surface layer. As a result of the investigation, when the total amount of the martensite phase and the ferrite phase in the surface layer from the surface to a depth of 10 μm was 60% by volume or more, a high nitriding property improving effect was recognized. When the total amount is 80% by volume or more, a more remarkable nitriding property improving effect is exhibited. Note that the martensite phase and the ferrite phase do not necessarily have to be mixed, and the nitriding property improving effect is exhibited if any one phase is present at 60% by volume or more. In using various nitriding methods, it is sufficient to consider the metallographic structure in the surface layer up to a depth of 10 μm. Rather, if the martensitic phase is formed into a metal structure that is too deep inside the steel material, ductility may be reduced. Depth 10
The total amount of the martensite phase and the ferrite phase in the surface layer up to μm can be quantified by, for example, a thin film X-ray diffraction method.

In order to make the surface layer of a high-strength steel such as a metastable austenitic steel have a metal structure in which the total amount of the martensite phase and the ferrite phase is 60% by volume or more,
It is desirable to use any means of barrel polishing, shot peening or shot blasting.

For a stainless steel material whose “surface roughness” or “metal structure of the surface layer” is adjusted as described above, a “nitriding method” or a “gas softening method” which is a general nitriding treatment of a steel material is applied. Nitriding method ”,“ Gas sulfur nitriding method ”,
Effective nitriding is possible by applying the "plasma nitriding method" and the "salt bath nitriding method". In addition, the application of the "ion nitriding method", the "salt bath nitrocarburizing method", and the "salt bath oxynitriding method" is also effective.

In the gas nitriding method, a gas having a component mainly composed of ammonia gas can be used. For example, an ammonia gas alone or an ammonia gas and an RX gas (endothermic modified gas;
Carbon monoxide + hydrogen + nitrogen, NX gas (a modified gas obtained by completely burning butane or the like; nitrogen as a main component), propane, butane, (CO ₂ + CO) mixed gas, and the like may be used. In the gas sulphonitriding method, ammonia gas is CO ₂ + N ₂ + H
Gas mixed with ₂ S can be used. In the plasma nitriding method,
N ₂ + H ₂ mixed gas can be used. In the salt bath nitriding method, NaCN,
A molten salt obtained by using one or more of KCN, NaCNO and KCNO as a basic component and adding one or two of Na ₂ CO ₃ and K ₂ CO ₃ thereto can be used.

Considering application to high-strength steel such as metastable austenitic stainless steel, it is efficient to perform nitriding treatment also serving as aging treatment, so that the nitriding treatment temperature is in the range of 300 to 650 ° C. It is desirable to do. If the temperature is lower than 300 ° C., nitriding does not proceed sufficiently, and an increase in strength due to aging cannot be expected. If the temperature exceeds 650 ° C., when a martensite phase is formed on the surface of the steel material, part of the martensite phase is reversely transformed into an austenite phase, resulting in a decrease in strength and a stagnation of the nitriding reaction. If the heating time of the nitriding treatment is less than 20 minutes, there is a high possibility that sufficient nitriding cannot be achieved. Desirable heating time for the nitriding treatment is 20 minutes to 5 hours, more preferably 30 minutes to 5 hours.

The nitriding method of the present invention is particularly applied to a high-strength steel made of a metastable austenitic stainless steel or a stainless steel having a component composition capable of positively forming a martensite phase and a ferrite phase on the surface layer of a steel material. It is effective to do. In order to obtain such stainless steel, C: 0.15% or less, Si: 5.0% or less, Mn: 5.0% or less, Ni: 2.0 to 20.0%, Cr: 12.0 to 50.0%, Cu: 0 to 3.5
% (Including no additive), Mo: 0 to 6.0% (including no additive),
N: It is desirable to have a chemical composition containing 0.15% or less, with the balance being Fe and unavoidable impurities.

[0024]

EXAMPLES Example 1 As a test material, stainless steel having a chemical composition shown in Table 1 was used.

[0025]

[Table 1]

This steel was melted in a vacuum melting furnace and subjected to forging → hot rolling → intermediate annealing → cold rolling, followed by a solution heat treatment of “holding at 1050 ° C. × 1 minute → water cooling”, and thereafter, Cold rolling was performed at a rolling rate of 0.15 mm to a sheet thickness of 0.15 mm. This cold-rolled material is subjected to emery polishing of various counts 50 times in order to adjust the surface roughness of the sample, and is further subjected to shot peening (pressure 1 kgf / mm ² , bead diameter 0.25 to 0.60 mmφ)
At different treatment times.

These samples were subjected to a nitriding treatment by a gas nitriding method, a gas nitriding method, a gas nitriding method, or a plasma nitriding method. Gas nitriding is performed using 50% by volume of ammonia + RX50
The heating was performed by heating at 500 ° C. for 3 hours in a mixed gas of volume%. The gas sulphonitriding was carried out by heating at 560 ° C. for 3 hours in a mixed gas of 80% by volume of ammonia and 0.1% by volume of H ₂ S and the balance being CO ₂ . In plasma nitriding, a sample is placed in a closed furnace into which a mixed gas of N ₂ 80% by volume + H ₂ 20% by volume is injected at 5 Torr, and a DC voltage of about 1000 V is applied to the furnace wall to generate plasma.
The sample was brought into contact with the plasma and heated at 540 ° C. for 3 hours. Salt bath nitriding is performed using NaCN 40% by mass + Na ₂ CO ₃ 40
The sample was immersed for 1 hour in a salt bath at 520 ° C. of which the main component was mass% and the balance was (NaK) ₄ Fe (CN) ₆ .

For each sample, the total amount (volume%) of the martensite phase and the ferrite phase in the surface layer before nitriding and the ten-point average roughness Rz were examined. Further, the surface hardness (Hv0.5) and the fatigue limit (N / mm ² ) after the nitriding treatment were examined. The total amount (volume%) of the martensite phase and the ferrite phase in the surface layer portion was determined by a thin film X-ray diffraction method.
In addition, in the test material of the present invention, the ferrite phase was not present in the surface layer portion, and a double phase structure of a martensite phase and a retained austenite phase was exhibited. The ten-point average roughness is JI
It was measured by a contact-type diamond surface roughness meter based on the method specified in SB 1061. The surface hardness was measured by a Vickers hardness tester with a load of 500 g. The fatigue limit was determined by performing a bending-tensile fatigue test. That is, the length of the parallel part is 10
Fatigue tests were conducted at various tensile stress levels, with a test specimen having a width of 0 mm and a width of 3 mm placed on a pulley, with a surface bending tensile stress applied and removed as one cycle, at various tensile stress levels. Stress exceeding 1 × 10 ⁷ cycles was defined as the fatigue limit. The results are shown in Tables 2 and 3.

[0029]

[Table 2]

[0030]

[Table 3]

Focusing on the surface hardness after nitriding, Table 2
According to the gas nitriding method, a high value of Hv 650 or more is obtained when the ten-point average roughness Rz before the nitriding treatment is 0.5 μm or more. Since the hardness of the center of each of these samples after nitriding was about Hv600, it was clear that nitriding had occurred when the ten-point average roughness Rz was adjusted to 0.5 μm or more. is there. On the other hand, ten point average roughness
The surface hardness of Nos. 11 and 16 in which Rz was less than 0.5 μm was Hv6.
It is about 00, which indicates that almost no nitriding has occurred. As the value of the ten-point average roughness Rz increases, the surface hardness also increases. However, as seen in Nos. 12-15, R
When z exceeds 5.0 μm, the rise is hardly observed. It should be noted that No. 1 has a lower level of surface hardness as compared with other examples having the same surface roughness (Nos. 2, 3 etc.).
This is because the amount of martensite in the surface layer was a low value of less than 80% by volume.

In Table 3, the gas sulphidizing method, the plasma nitriding method,
In the case of salt bath nitriding method, ten point average roughness before nitriding treatment
When Rz is 0.3 μm or more, a high value of Hv650 or more is obtained. Since the hardness of the center of each sample after nitriding was about Hv580, the ten-point average roughness R
When z is adjusted to 0.3 μm or more, it is clear that nitriding has occurred. On the other hand, the ten-point average roughness Rz
The surface hardness of No. 33, 38 and 40, which was less than 0.3 μm, was H
It is v630 or less, indicating that nitriding is not sufficiently occurring. As the value of the ten-point average roughness Rz increases, the surface hardness also increases. However, as seen in Nos. 34 to 37 and 39, when Rz exceeds 5.0 μm, the increase is hardly observed. In addition, No. 21 has a lower level of surface hardness as compared with other examples having the same surface roughness (No. 22, 23, etc.). This is because the amount of martensite in the surface layer was a low value of less than 60% by volume.

Next, focusing on the fatigue limit after the nitriding treatment,
According to the gas nitriding method in Table 2, a high value of 1500 N / mm ² or more was obtained only in the present invention example in which the ten-point average roughness Rz before the nitriding treatment was 0.5 to 5.0 μm. Rz is 0.5
Rz is not less than 5.0μm (No.11,16)
It can be seen that even when the value exceeds m (Nos. 12 to 15), high values cannot be obtained for the fatigue characteristics.

The gas sulphonitriding method, the plasma nitriding method,
In the case of salt bath nitriding method, ten point average roughness before nitriding treatment
Only in the present invention example in which Rz is 0.3 to 5.0 μm, 1
A high value of 500 N / mm ² or more has been obtained. Not only when Rz is less than 0.3 μm (No. 33, 38, 40), but when Rz exceeds 5.0 μm (No. 34 to 37, 39), high values cannot be obtained for fatigue properties. Understand.

FIGS. 1 and 2 show No. 3 of Table 2, respectively.
Optical microscope photographs (oxalic acid electrolytically etched structure) of sample cross sections after nitriding (Example of the present invention) and No. 11 (Comparative example) are shown. In the example of the present invention shown in FIG.
A nitride layer (portion that looks black) of about μm is formed. On the other hand, in the case of the comparative example shown in FIG. 2, formation of a nitride layer is hardly recognized.

FIGS. 3 and 4 show No. 2 of Table 3, respectively.
4 shows optical microscope photographs (oxalic acid electrolytically etched structure) of sample cross sections after nitriding treatment of No. 4 (Example of the present invention) and No. 33 (Comparative example). In the example of the present invention shown in FIG. 3, the surface layer has a depth of 30 μm.
A degree of nitride layer (a portion that looks black) is formed. On the other hand, in the case of the comparative example shown in FIG. 4, the formation of a nitride layer is hardly recognized.

Example 2 A 60% cold rolling was performed on a solution heat-treated material of “holding at 1050 ° C. × 1 minute → water cooling” of the steel in Table 1, and then subjected to # 400 emery polishing and shot peening. (pressure 1 kgf / mm ^2, the bead diameter 0.25～0.60Mmfai, processing time
2 minutes), nitriding by gas nitriding at various temperatures and times (gas composition: the same as in Example 1),
Alternatively, nitriding treatment by a salt bath nitriding method (salt bath composition: Example 1)
And the surface hardness after the nitriding treatment was measured. Tables 4 and 5 show the results.

[0038]

[Table 4]

[0039]

[Table 5] According to the gas nitriding method shown in Table 4, the samples of the present invention all had high surface hardness of Hv 740 or higher, and the nitriding occurred sufficiently, whereas the sample of the comparative example had Hv 640.
Stopped below. In the case of the salt bath nitriding method in Table 5, all of the examples of the present invention have a high surface hardness of Hv750 or more, and the nitriding has sufficiently occurred. It is stopped at. In any of these nitriding methods, nitriding does not proceed sufficiently at a temperature of less than 300 ° C or for a short time of less than 30 minutes, and at a temperature of more than 650 ° C, part of the martensitic phase in the surface layer becomes an austenite phase. Reverse transformation leads to stagnation of nitriding.

[0040]

As described above, according to the present invention, the nitriding property of a stainless steel material originally having poor nitriding property due to the presence of the passivation film could be improved. The method for producing a nitrided stainless steel material of the present invention is inexpensive and relatively easy to implement industrially, and thus contributes to the spread of nitriding products using stainless steel materials.

[Brief description of the drawings]

FIG. 1 is an optical microscope photograph of a cross section of a stainless steel material after nitriding by the method of the present invention using a gas nitriding method.

FIG. 2 is an optical microscope photograph of a cross section of a stainless steel material after nitriding by a comparative method using a gas nitriding method.

FIG. 3 is an optical microscope photograph of a cross section of a stainless steel material after nitriding by the method of the present invention using a gas sulphonitriding method.

FIG. 4 is an optical microscope photograph of a cross section of a stainless steel material after nitriding by a comparative method using a gas sulphonitriding method.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Morimoto 4976 Nomura Minami-cho, Shinnanyo-shi, Yamaguchi Prefecture Inside Nisshin Steel Research Institute (72) Inventor Naoto Hiramatsu 4976 Nomura-minami-cho, Shinnanyo-shi, Yamaguchi Nisshin Steel Technology Co., Ltd.

Claims (12)

[Claims] The ten-point average roughness Rz of a steel material surface is 0.5 to 5.0 μm.
A method for producing a nitrided stainless steel material, comprising heating a stainless steel material adjusted to m in a nitriding atmosphere of 300 to 650 ° C. containing ammonia gas as a basic component for 30 minutes or more. 2. The ten-point average roughness Rz of a steel material surface is 0.5 to 5.0 μm.
m, and a stainless steel material in which the total amount of martensite phase and ferrite phase in the surface layer from the surface to a depth of 10 μm has been adjusted to 80% by volume or more, at a temperature of 300 to 650 ° C with ammonia gas as a basic component. A method for producing a nitrided stainless steel material that is heated in a nitriding atmosphere for at least 30 minutes. 3. The ten-point average roughness of a steel material surface by any of dull roll rolling, mechanical grinding or mechanical polishing.
A method for producing a nitrided stainless steel material, comprising heating a stainless steel material having a Rz adjusted to 0.5 to 5.0 μm in a nitriding atmosphere of 300 to 650 ° C. containing ammonia gas as a basic component for 30 minutes or more. 4. After performing any of dull roll rolling, mechanical grinding or mechanical polishing, barrel polishing,
By applying any means of shot peening or shot blasting, the ten-point average roughness Rz of the steel material surface is adjusted to 0.5 to 5.0 μm, and the depth from the surface is 10 μm.
Heat the stainless steel material in which the total amount of the martensite phase and the ferrite phase in the surface layer up to μm is adjusted to 80% by volume or more in a nitriding atmosphere of 300 to 650 ° C. containing ammonia gas as a basic component for 30 minutes or more, Manufacturing method of nitrided stainless steel. 5. The ten-point average roughness Rz of a steel material surface is 0.3 to 5.0 μm.
A method for producing a nitrided stainless steel material, wherein the stainless steel material adjusted to m is subjected to nitriding treatment. 6. The ten-point average roughness of a steel material surface by any of dull roll rolling, mechanical grinding or mechanical polishing.
A method for producing a nitrided stainless steel material, wherein a nitriding treatment is performed on a stainless steel material whose Rz is adjusted to 0.3 to 5.0 μm. 7. Ten-point average roughness Rz of a steel material surface is 0.3 to 5.0 μm.
m, and a nitriding treatment is performed on the stainless steel material in which the total amount of the martensite phase and the ferrite phase in the surface layer from the surface to a depth of 10 μm is adjusted to 60% by volume or more,
Manufacturing method of nitrided stainless steel. 8. After any of dull roll rolling, mechanical grinding or mechanical polishing is performed, barrel polishing,
By applying either means of shot peening or shot blasting, the ten-point average roughness Rz of the steel material surface is adjusted to 0.3 to 5.0 μm, and the depth from the surface is 10 μm.
A method for producing a nitrided stainless steel material in which a stainless steel material in which the total amount of a martensite phase and a ferrite phase in a surface layer up to μm is adjusted to 60% by volume or more is nitrided. 9. A nitriding treatment is performed by heating a steel material at a temperature of 300 to 650 ° C. in a gas obtained by mixing H ₂ S with a gas containing ammonia gas as a basic component.
The production method according to any one of claims 5 to 8, wherein the method is a gas sulphonitriding method in which heating is performed at a low temperature. 10. The method according to claim 5, wherein the nitriding treatment is a plasma nitriding method in which the steel is heated to 300 to 650 ° C. by plasma generated between the steel and the furnace wall in a reduced pressure gas containing nitrogen gas as a basic component. 9. The production method according to 8. 11. The nitriding treatment is performed by using NaCN, KCN, NaCNO and
300-650 ℃ with one or more KCNO as basic components
6. A salt bath nitriding method in which a steel material is immersed in a salt bath.
9. The production method according to any one of items 1 to 8. 12. The stainless steel contains 0.15% by mass of C: 0.15% by mass.
% Or less, Si: 5.0% or less, Mn: 5.0% or less, Ni: 2.0 to 20.
0%, Cr: 12.0 to 50.0%, Cu: 0 to 3.5% (including no addition), Mo: 0 to 6.0% or less (including no addition), N: 0.15%
Including the following, the balance consists of Fe and inevitable impurities,
The manufacturing method according to claim 1.