JP2000104159A - Surface hardening treating method for steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To activate the surface of steel by breaking a passive film on the surface of the steel, to maintain the activated state, to form a nitride layer free from unevenness and simultaneously to eliminate the complication of the equipment and the increase of the cost caused by the toxicity and corrosivity of atmospheric gas. SOLUTION: In a temp. rising stage to a nitriding treating temp. and also in a gaseous nitrogen atmosphere contg. hydrogen sulfide, steel having a passive film is heated, is subjected to sulfurizing treatment, is thereafter held under heating for a prescribed time in a nitriding atmosphere and is subjected to nitriding treatment. The concn. of hydrogen sulfide at the time of sulfurizing treatment is set to 30 to 300 ppm, and, on the other hand, the concn. of oxygen at the time of the sulfurizing treatment and the nitriding treatment is set to <=150 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for surface hardening a steel material, and more particularly to a method for hardening a steel material having a passive film, for example, a steel material having a passive film such as various stainless steels including austenitic stainless steel. It relates to a processing method.

[0002]

2. Description of the Related Art Conventionally, as one form of a surface hardening treatment method for improving the wear resistance and other mechanical properties of a steel material surface, a nitriding treatment for forming a nitride layer inside by heating in an atmosphere containing ammonia gas has been known. Soft nitriding treatment (hereinafter referred to as nitriding treatment) is employed. However, steel materials such as chromium steel and austenitic stainless steel containing about 15% or more of chromium are covered on the surface with a passivation film composed of a chromium oxide layer. , The nitriding treatment was difficult.

[0003] Therefore, when nitriding this kind of steel, it is necessary to remove the passivation film on the surface of the steel. A traditional way to achieve this is to pickle the steel prior to nitriding. However, although the pickling method is effective depending on the type of steel material, it is difficult to maintain the surface state after pickling, and when applied to austenitic stainless steel, etc., the passivation film is regenerated. Therefore, there is a problem that a sufficient effect cannot be obtained.

[0004]

As means for solving the above-mentioned problems, for example, Japanese Patent Publication No. 8-9766 discloses a method in which a steel material is heated and held in an atmosphere containing a fluorine compound or a fluorine gas prior to nitriding. There is proposed a nitriding method for forming a fluoride.

In the above method, the passivation film on the surface of the steel material is transformed into a fluoride film, and the nitride film is decomposed during the subsequent nitriding treatment to perform nitriding. However, the permissible concentrations of fluorine gas and nitrogen fluoride gas used for fluoridation are 1 ppm and 3 p, respectively.
Due to the extremely high toxicity of pm and the extremely high corrosiveness, there are various restrictions on the equipment, and the equipment itself is extremely complicated and expensive. Moreover, even if the passivation film is destroyed, the nitriding atmosphere at the nitriding temperature (usually 500 to 600 ° C.) is oxidizing to steel components such as chromium, silicon, manganese, and aluminum. The passivation film is re-formed in the inside, and the subsequent intrusion of nitrogen is inhibited.
It became clear that stable nitriding treatment was difficult.

Accordingly, the present invention is capable of activating the surface by destroying the passive film on the surface of the steel material, forming a uniform nitride while maintaining the state, and at the same time the toxicity and corrosion of the atmosphere gas. It is an object of the present invention to eliminate the complexity and high cost of equipment caused by the nature.

[0007]

According to the present invention, there is provided a steel material having a passivation film in a nitrogen gas atmosphere containing hydrogen sulfide during a process of raising a temperature to a nitriding treatment temperature. Is heated and sulfurized, and then heated and held in a nitriding atmosphere for a predetermined time to perform a nitriding treatment.

[0008] In a preferred embodiment, the sulfurization treatment has an oxygen concentration of 150 ppm or less and a hydrogen sulfide concentration of 3 ppm.
This is performed in a nitrogen gas atmosphere of 0 to 300 ppm. In addition, the sulfurizing treatment is usually performed for 1 to 2 hours from a room temperature to a nitriding treatment temperature (normally, 500 to 600 ° C.).
It is preferable to carry out the treatment so as to be maintained for one hour.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The method for surface hardening steel according to the present invention can be carried out in any form such as a batch nitriding furnace or a continuous nitriding furnace, but here, a two-chamber nitriding furnace shown in FIG. 1 is used. An example of the case will be described.

The illustrated two-chamber nitriding furnace comprises a charging chamber 1 and a heating chamber 2, both chambers being connected via an intermediate door 3, and a charging door 4 at one end of the charging chamber 1. It is arranged. The heating chamber 2 includes a gas supply line 5a and valves 6a, 6
b and 6c, are connected to a nitrogen supply source 7, an ammonia supply source 8, and a hydrogen sulfide supply source 9, and are connected to a vacuum exhaust system and an exhaust gas treatment system via an exhaust system line 10a. On the other hand, the charging chamber 1 is connected to a nitrogen supply source 7 via a gas supply line 5b and a valve 6a ', while being connected to a vacuum exhaust system and an exhaust gas treatment system via an exhaust system line 10b. The heating chamber 2 is provided with a heating means for heating the inside thereof, while a transfer conveyor for transferring the material to be processed is provided similarly to the charging chamber 1,
These have the same configuration as the known ones.

When the material to be treated (for example, a steel material having a passivation film) is nitrided using the two-chamber type nitriding furnace, first, the material to be treated is charged into the charging chamber 1 and the exhaust system line 10 is charged.
After the inside of the charging chamber 1 and the heating chamber 2 are evacuated through the gas supply lines 5a and 5b, the atmosphere in the charging chamber 1 and the heating chamber 2 is changed to an oxygen concentration of 150 ppm. Adjust to the following nitrogen gas atmosphere,
The inside of the heating chamber 2 is heated by the heating means and maintained at a predetermined temperature in the range of 350 to 450 ° C. In this state, the material to be treated is transferred to the heating chamber 2, and the valve 6b is opened to start supplying hydrogen sulfide from the hydrogen sulfide supply source 9 into the heating chamber 2.
While the hydrogen sulfide concentration in the atmosphere is continuously supplied to be 30 to 300 ppm, the sulfurating treatment and the temperature rise of the material to be treated are performed by maintaining the temperature within the above range for a predetermined time. afterwards,
Raise the ambient temperature to the nitriding temperature.

When the temperature is raised, if the surface temperature of the steel material is effectively 350 ° C. or more, hydrogen sulfide in the atmosphere is converted into an oxide on the surface of the steel material by the following formula:

(In the formula, Me represents. A _{metal) Me x O y + yH 2} S = Me x S y + yH 2 O changed to oxides sulfides steel surface caused the reaction represented by .

The reaction of the above formula 1 is a reaction which proceeds in both forward and reverse directions. When the temperature of the reaction system is around 450 ° C., the equilibrium position is shifted to the right, and oxides on the surface of the steel material easily become sulfides. However, when the temperature of the reaction system rises, the equilibrium of the reaction deviates. When the temperature exceeds 500 ° C., the equilibrium state of Equation 1 shifts to the left, and sufficient sulfide is generated even in the presence of hydrogen sulfide in the nitriding temperature range. Not only that, the sulfide formed on the surface of the steel material due to the presence of oxygen in the atmosphere returns to the oxide. This phenomenon is more remarkable as the oxygen concentration in the atmosphere at the time of temperature rise is higher. In order to prevent this, in the present invention, the oxygen concentration in the atmosphere at the time of raising the temperature is suppressed to a certain value or less, the equilibrium position of the reaction system is shifted to the right, and 350 to 450 ° C. which is advantageous for the reaction rate. Sufficiently, sulfides are formed on the surface of the steel material at a temperature within the range described above.

When the temperature increase to the nitriding temperature is completed,
The valve 6c is opened to start supplying ammonia gas from the ammonia source to replace the atmosphere in the heating chamber 2 with a nitriding atmosphere composed of nitrogen and ammonia, and to adjust the hydrogen sulfide concentration in the atmosphere to 30 to 300 ppm. The nitriding treatment is performed by heating and maintaining for a predetermined time while continuously supplying hydrogen sulfide.

In this nitriding process, part of the ammonia in the nitriding atmosphere is decomposed to generate hydrogen, and the sulfide generated on the surface of the steel material at the time of raising the temperature by the action of the generated hydrogen is represented by the following formula 2:

## STR2 ## _{Me x S y + yH 2 =} xMe + yH 2 passivation film (oxide) in the reaction is reduced to the active metal of steel surfaces represented by S when is broken at the same time, decomposition of ammonia As a result, the nascent nitrogen generated by the gas can easily penetrate into the material, and is gradually diffused from the steel material surface to the inside while forming nitride. In this case, since sulfur has a large atomic diameter, sulfide is formed in the surface layer of the steel material at 2 to 10 μm, whereas nitrogen has a small atomic diameter and penetrates to a relatively deep portion inside the steel material to form nitride.

Further, even during the nitriding treatment, sulfuration of the oxide by the hydrogen sulfide of the formula 1 and reduction of the sulfide by the hydrogen of the formula 2 occur. However, when the oxygen concentration in the nitriding atmosphere is high, the reduced metal, that is, the reduced metal,
Equation 3:

## STR3 ## By the reaction represented by (Me) _x + (1/2 O ₂ ) _y = (Me) _x O _y , the oxide film is reoxidized to regenerate the passive film, thereby inhibiting the subsequent nitridation. The problem of reoxidation of the reduced metal can be solved by increasing the concentration of hydrogen sulfide according to the oxygen concentration in the atmosphere.However, the increased concentration of hydrogen sulfide causes a high-concentration sulfide layer to be formed on the steel material surface, On the contrary, nitriding is inhibited. In order to prevent such a problem, in the present invention, the oxygen concentration is maintained at 150 ppm or less to prevent a high concentration of sulfide from being formed on the surface of the steel material.

Furthermore, in order to maintain the sulfurization of oxides and the reduction of sulfides even in a nitriding atmosphere, an appropriate amount of hydrogen sulfide needs to be present not only at the time of temperature rise but also at the time of nitriding treatment. Therefore, it is desirable to add hydrogen sulfide so that the concentration of hydrogen sulfide in the nitriding atmosphere is 30 to 300 ppm throughout the entire nitriding cycle. However, if the surface of the steel material is sufficiently sulfided at the time of heating, the sulfide formed on the surface of the steel material, the jig and the furnace material during the nitriding treatment reacts with the hydrogen in the nitriding atmosphere to generate hydrogen sulfide. Since the concentration of hydrogen sulfide in the nitriding atmosphere is 30 to 300 ppm, nitriding can be performed without adding hydrogen sulfide during the nitriding treatment. In order to form a sufficient sulfide at the time of raising the temperature, the sulfidation treatment at the time of raising the temperature is performed at 350 to 450 ° C., preferably 350 to 40 ° C.
It is preferable to carry out at 0 ° C. for 0.5 to 1 hour.

The hydrogen sulfide concentration during the sulfurizing treatment and the nitriding treatment is set to 30 to 300 ppm. If the hydrogen sulfide concentration is less than 30 ppm, uniform sulfide is not formed on the steel material surface. If the concentration of hydrogen sulfide exceeds 300 ppm, a high concentration of sulfide is formed on the surface of the steel material, the surface becomes black and easily peels off, and the intrusion of nitrogen into the steel material is inhibited, and the nitriding treatment becomes difficult. .

After the sulfuration treatment and the nitridation treatment are performed in this manner, the valves 6b and 6c are closed to stop the supply of hydrogen sulfide and ammonia, and then the intermediate door 3 is opened to remove the workpiece from the heating chamber 2. Transfer to charging room 1. The transfer to the charging chamber 1 may be performed after the heating chamber 2 is evacuated and then restored to a nitrogen atmosphere. Thereafter, the intermediate door 3 is closed and gas cooling is performed in the nitrogen gas atmosphere in the charging chamber 1 to complete the nitriding of the workpiece.

In the above description, the case where a mixed gas of ammonia and nitrogen gas is employed as the nitrogen supply source for the nitriding treatment is described as an example. However, the present invention is not necessarily limited to the mixed gas of ammonia and nitrogen gas. Instead, a gas atmosphere consisting of ammonia alone or a mixed gas of ammonia and an endothermic gas may be used.

Hereinafter, embodiments of the present invention will be described.

[0022]

Embodiment 1 Using a two-chamber nitriding furnace shown in FIG. 1, a material to be treated is charged into a charging chamber 1, and the atmosphere in the charging chamber 1 and the heating chamber 2 is changed to a nitrogen gas having an oxygen concentration of about 50 ppm. The atmosphere is adjusted and the inside of the heating chamber 2 is maintained at about 400 ° C. In this state, the material to be processed is transferred to the heating chamber 2 and the supply of hydrogen sulfide into the heating chamber 2 is started to continuously supply hydrogen sulfide so that the concentration of hydrogen sulfide in the atmosphere becomes 100 ppm. While maintaining the temperature at about 350 ° C. for 30 minutes, the sulfurating treatment is performed. Then, it takes about 30 minutes for nitriding temperature (about 570 ° C)
Heat up to 2. When the temperature increase is completed, the atmosphere in the heating chamber 2 is replaced with a nitriding atmosphere composed of ammonia gas, and hydrogen sulfide is continuously supplied so that the hydrogen sulfide concentration in the atmosphere becomes 130 ppm. Heating and holding for 5 hours are performed for nitriding. Note that the oxygen concentration is maintained at about 50 ppm even during this nitriding treatment. After the elapse of the time, the material to be treated was transferred to the charging chamber 1 and gas-cooled in a nitrogen gas atmosphere to obtain a sample. The material to be treated is a SUS304 pipe (100 mmφ × 3 mmφ × 10 mm).
0 mm) and SUS304, SUS410 and S45C round bars (diameter 30 mmφ × 100 mm).

[0023]

Example 2 In Example 1, the oxygen concentration in the atmosphere during the sulfurizing treatment and the nitriding treatment was set to 150 ppm, respectively.
Except that the sulfuration treatment and the nitridation treatment were performed in the same manner as in Example 1 to obtain a sample.

[0024]

[Comparative Example 1] In Example 1, the oxygen concentration in the atmosphere during the sulfurizing treatment and the nitriding treatment was 260 ppm, respectively.
Except that the sulfuration treatment and the nitridation treatment were performed in the same manner as in Example 1 to obtain a sample.

[0025]

Comparative Example 2 In Example 1, the oxygen concentration in the atmosphere at the time of the sulfurizing treatment and the nitriding treatment was 750 ppm, respectively.
Except that the sulfuration treatment and the nitridation treatment were performed in the same manner as in Example 1 to obtain a sample.

The thickness of the nitride layer was measured for each of the samples obtained in Examples 1 and 2 and Comparative Examples 1 and 2. Table 1 shows the results. In the table, the polished surface means the surface obtained by polishing the surface of the pipe, the rolled surface means the surface of the as-rolled round bar, and the cut surface means the surface obtained by cutting the round bar.

[0027]

[Table 1]

From the results shown in Table 1, when the concentration of hydrogen sulfide and the temperature of the sulfurizing treatment are predetermined, the oxygen concentration in each atmosphere during the sulfurizing treatment and the nitriding treatment is a factor in forming the nitride layer. I understand. That is, when the oxygen concentration is 150 ppm or less, stainless steel (SUS304 and SUS410)
Can be nitrided, but as shown in Comparative Examples 1 and 2, when the oxygen concentration exceeds 150 ppm, the stainless steel cannot be nitrided. Note that a sulfide layer of several microns was observed on the surface of the nitride layer.

[0029]

Example 3 In Example 1, the sulfurating treatment and nitriding were performed in the same manner as in Example 1 except that the oxygen concentration during the sulfurizing treatment and the nitriding treatment were each set to 100 ppm, and the maintenance temperature during the sulfurizing treatment was 450 ° C. Processing was performed to obtain a sample.

[0030]

Comparative Example 3 Sulfidation and nitriding were carried out in the same manner as in Example 1 except that the oxygen concentration during the sulfidation treatment and the nitridation treatment were each 100 ppm, and the maintenance temperature during the sulfurization treatment was 500 ° C. Processing was performed to obtain a sample.

[0031]

Comparative Example 4 Sulfidation treatment and nitridation were carried out in the same manner as in Example 1 except that the oxygen concentration during the sulfurization treatment and the nitridation treatment were each set to 100 ppm, and the maintenance temperature during the sulfurization treatment was set to 550 ° C. Processing was performed to obtain a sample.

While observing the surface condition of each of the obtained samples, the thickness of the nitride layer was measured. Table 2 shows the results.

[0033]

[Table 2]

From the results shown in Table 2, it can be seen that under a predetermined condition of the concentration of hydrogen sulfide and the concentration of oxygen, the sulfidation temperature is a factor in forming a nitride layer. That is, when the sulfidation temperature is in the range of 350 to 450 ° C., a substantially uniform nitride layer can be formed. However, as shown in Comparative Examples 3 and 4, when the sulfidation temperature exceeds 450 ° C. A non-uniform nitride layer is formed.

[0035]

Embodiment 4 In a nitrogen gas atmosphere having an oxygen concentration of 50 ppm, hydrogen sulfide was changed to a hydrogen sulfide concentration of 13 ppm in the nitrogen gas atmosphere.
After performing sulfurization treatment at about 350 ° C. for 30 minutes while adding so that the concentration becomes 0 ppm, the oxygen concentration is 50 ppm,
In addition, nitrogen gas (40% by volume) and ammonia gas (60
% By volume) while maintaining the nitriding temperature (about 570 ° C.) for 3.5 hours while adding hydrogen sulfide so that the hydrogen sulfide concentration in the nitriding atmosphere becomes 130 ppm. Thereafter, the sample was cooled in a nitrogen gas atmosphere to obtain a sample.

[0036]

Example 5 In Example 4, except that hydrogen sulfide was not added at the time of nitriding, a sulfurating treatment and a nitriding treatment were performed in the same manner as in Example 4 to obtain a sample.

The thickness of the nitride layer of the obtained sample was measured. Table 3 shows the results.

[0038]

[Table 3]

From the results shown in Table 3, it can be seen that even when hydrogen sulfide was not added to the nitriding atmosphere during the nitriding treatment, the result was almost the same as that of Example 4 in which hydrogen sulfide was added throughout the entire cycle of the sulfurizing treatment and the nitriding treatment. Is obtained. Although hydrogen sulfide was detected from the exhaust gas during the nitriding treatment, it is considered that this was generated by the reaction of the sulfide formed during the temperature rise with the hydrogen generated by the decomposition of ammonia.

[0040]

Embodiment 6 A sulfuration treatment and a nitridation treatment were carried out in the same manner as in the embodiment 4 except that the concentration of hydrogen sulfide in the atmosphere during the sulfuration treatment and the nitridation treatment was changed to 300 ppm. Was.

[0041]

Comparative Example 5 A sample was obtained in the same manner as in Example 4 except that a nitrogen gas containing no hydrogen sulfide was used when the temperature was raised to the nitriding temperature.

[0042]

Comparative Example 6 Example 4 was repeated except that a nitrogen gas atmosphere without hydrogen sulfide was used when the temperature was raised to the nitriding temperature, while an ammonia gas atmosphere without hydrogen sulfide was used during the nitriding process. A nitriding treatment was performed in the same manner as described above to obtain a sample.

The thickness of the nitride layer was measured for each of the samples obtained in Example 6, Comparative Example 5, and Comparative Example 6.
Table 4 shows the results.

[0044]

[Table 4]

From the results shown in Table 4, the samples of Comparative Example 5 in which no hydrogen sulfide was present at the time of raising the temperature to the nitriding temperature and Comparative Example 6 in which no hydrogen sulfide was present at the time of raising the temperature and the nitriding were almost completely nitrided. It can be seen that no is formed.

[0046]

As is apparent from the above description, according to the present invention, the passive film of steel, such as austenitic stainless steel, which is hardly nitrided by the conventional method, is surely destroyed to activate the surface and to form a uniform surface. A nitride layer can be formed.
Also, regardless of the type of steel, it is possible to prevent non-uniformity in nitriding due to seizure during machining of low alloy steel. In addition, hydrogen sulfide used to remove the passive film on the steel surface has an allowable concentration of 10 ppm, which is higher than the allowable concentration of nitrogen fluoride, 3 ppm, and the allowable concentration of fluorine, 1 ppm. , The equipment can be simplified. Furthermore, when compared in a temperature range around the nitriding temperature, excellent effects are obtained, such as hydrogen sulfide being extremely advantageous in terms of the corrosion resistance of the furnace material as compared with the fluorine-based gas, and the production cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a nitriding apparatus used for carrying out the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Loading room 2 ... Heating room 3 ... Intermediate door 4 ... Loading door 5 ... Gas supply line 6a, 6b, 6c, 6a '... Valve 7 ... Nitrogen supply source 8 ... Ammonia supply source 9 ... Hydrogen sulfide supply source 10a ， 10b… Exhaust system line

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[Procedure amendment]

[Submission date] July 14, 1999 (1999.7.1)
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

According to the present invention, as a means for solving the above-mentioned problems, an oxygen concentration of 150 ppm or less and a hydrogen sulfide concentration of 3
A steel material having a passivation film in a nitrogen gas atmosphere containing 0 to 300 ppm is heated in a temperature range of 350 to 450 ° C. to perform a sulfurating treatment, and then is heated and held in a nitriding atmosphere for a predetermined time to perform a nitriding treatment. It is.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

In a preferred embodiment, the sulfurization treatment has an oxygen concentration of 150 ppm or less and a hydrogen sulfide concentration of 30 ppm or less.
In a nitrogen gas atmosphere of up to 300 ppm, it is usually carried out for 1 to 2 hours from room temperature to a nitriding treatment temperature (normally 500 to 600 ° C.).
At a temperature of 0.5 to 1 hour.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

When the material to be treated (for example, a steel material having a passivation film) is nitrided using the two-chamber type nitriding furnace, first, the material to be treated is charged into the charging chamber 1 and the exhaust system line 10 is charged.
After the inside of the charging chamber 1 and the heating chamber 2 are evacuated through the gas supply lines 5a and 5b, the atmosphere in the charging chamber 1 and the heating chamber 2 is changed to an oxygen concentration of 150 ppm. Adjust to the following nitrogen gas atmosphere,
The inside of the heating chamber 2 is heated by the heating means and maintained at a predetermined temperature in the range of 350 to 450 ° C. In this state, the material to be treated is transferred to the heating chamber 2, and the valve 6c is opened to start supplying hydrogen sulfide from the hydrogen sulfide supply source 9 into the heating chamber 2.
While the hydrogen sulfide concentration in the atmosphere is continuously supplied to be 30 to 300 ppm, the sulfurating treatment and the temperature rise of the material to be treated are performed by maintaining the temperature within the above range for a predetermined time. afterwards,
Raise the ambient temperature to the nitriding temperature.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

When the temperature increase to the nitriding temperature is completed,
The valve 6b is opened to start supplying ammonia gas from the ammonia source to replace the atmosphere in the heating chamber 2 with a nitriding atmosphere composed of nitrogen and ammonia, and to adjust the hydrogen sulfide concentration in the atmosphere to 30 to 300 ppm. The nitriding treatment is performed by heating and maintaining for a predetermined time while continuously supplying hydrogen sulfide.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

[0022]

Embodiment 1 Using a two-chamber nitriding furnace shown in FIG. 1, a material to be treated is charged into a charging chamber 1, and the atmosphere in the charging chamber 1 and the heating chamber 2 is changed to a nitrogen gas having an oxygen concentration of about 50 ppm. The atmosphere is adjusted and the inside of the heating chamber 2 is maintained at about 400 ° C. In this state, the material to be processed is transferred to the heating chamber 2 and the supply of hydrogen sulfide into the heating chamber 2 is started to continuously supply hydrogen sulfide so that the concentration of hydrogen sulfide in the atmosphere becomes 100 ppm. While maintaining the temperature at about 350 ° C. for 30 minutes, the sulfurating treatment is performed. Then, it takes about 30 minutes for nitriding temperature (about 570 ° C)
Heat up to 2. When the heating is completed, the atmosphere in the heating chamber 2 is replaced with a nitriding atmosphere made of ammonia gas, and hydrogen sulfide is continuously supplied so that the concentration of hydrogen sulfide in the atmosphere becomes 130 ppm. Heating and holding for 5 hours are performed for nitriding. The oxygen concentration is maintained at about 50 ppm during the nitriding process. After the elapse of the time, the material to be processed was transferred to the charging chamber 1 and gas-cooled in a nitrogen gas atmosphere to obtain a sample. The material to be treated is a SUS304 pipe (100 mmφ × 3 mmφ × 10 mm).
0 mm) and SUS304 and SUS410 round bars (diameter 30 mmφ × 100 mm).

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

[0027]

[Table 1]

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction contents]

[0033]

[Table 2]

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction contents]

[0038]

[Table 3]

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction contents]

[0044]

[Table 4]

Claims (3)

[Claims] 1. A steel material having a passivation film is heated and nitrided in a nitrogen gas atmosphere containing hydrogen sulfide during a process of raising the temperature to a nitriding temperature, and then heated and held in a nitriding atmosphere for a predetermined time. A surface hardening treatment method for a steel material, characterized by performing a nitriding treatment by a nitriding treatment. 2. The method according to claim 1, wherein the nitrogen gas atmosphere for performing the sulfidation treatment has an oxygen concentration of 150 ppm or less and a hydrogen sulfide concentration of 30 to 300 ppm.
The method of claim 1, wherein 3. The method according to claim 1, wherein the steel material is heated in a temperature range of 350 to 450 ° C. for 0.5 to 1 hour to perform a sulfurating treatment.