WO2020175453A1

WO2020175453A1 - Nitriding steel member, and method and device for manufacturing nitriding steel member

Info

Publication number: WO2020175453A1
Application number: PCT/JP2020/007395
Authority: WO
Inventors: 泰平岡
Original assignee: パーカー熱処理工業株式会社
Priority date: 2019-02-26
Filing date: 2020-02-25
Publication date: 2020-09-03
Also published as: JP2022068375A; TW202100757A

Abstract

The present invention is a nitriding steel member in which a matrix phase is composed of a carbon steel or a low-alloy steel, the nitriding steel member being characterized in that a nitride compound layer is provided on the surface, a hardened layer having an austenite structure is provided below the nitride compound layer, and a diffused layer in which nitrogen is diffused in the matrix phase is provided below the hardened layer, wherein the nitride compound layer has a phase distribution in which an ε phase, a γ' phase and an ε phase are arranged in this order, the volume ratio of the γ' phase in the nitride compound layer is 20% or more, and the nitride compound layer has a thickness of 5 to 50 μm from the surface of the nitriding steel member.

Description

\¥02020/175453 1 ?€1/^2020/007395

Specification

Title of invention:

Nitride steel member and method and device for manufacturing nitrided steel member

Technical field

The present invention relates to a nitrided steel member, and a method and an apparatus for manufacturing the nitrided steel member. More specifically, the present invention relates to a nitrided steel member having excellent wear resistance, which is useful for gears for automobile transmissions, crankshafts, and the like, and a manufacturing method and a manufacturing device for the nitrided steel member.

Background technology

Among the surface hardening treatments for steel materials, the nitriding treatment, which is a low heat treatment strain treatment, is high in number, and recently, the atmosphere control technology of the gas nitriding treatment has been particularly interested.

[0003] In the basic structure constitution obtained by the gas nitriding treatment, a compound layer which is an iron nitride is formed on the surface and a hardened layer called a diffusion layer is formed inside. The hardened layer is usually made of an alloy nitride such as 3 or 0 ", which is a base material component.

[0004] In order to control the thickness (depth) of each of these two layers and/or the type of surface iron nitride, etc., in addition to the temperature and time of gas nitriding treatment, The atmosphere is also controlled appropriately. Specifically, the nitriding potential (<<) in the gas nitriding furnace is appropriately controlled.

[0005] Then, through the control, the volume fraction (iron) of the phase' (6 ₄ 1\1) and £ phase (6 _2-3 1\1) in the compound layer generated on the surface of the steel material (iron Nitride type) is controlled.

[0006] For example, it is known that the fatigue resistance is improved by forming the phase' rather than the phase (Non-Patent Document 1).

[0007] Furthermore, a nitrided steel member having improved bending fatigue strength and surface fatigue by forming a ^ phase is also provided (Patent Document 1). 〇 2020/175453 2 卩(: 170? 2020/007395

[0008] Alternatively, it has been reported that the wear resistance of the present invention is improved by increasing the s phase (Non-Patent Document 2). Then, as a nitriding method for forming a compound layer containing a large amount of s phase on the surface, a soft nitriding treatment is known, which is performed by mixing a small amount of carburizing gas into an ammonia atmosphere.

[0009] On the other hand, when the nitriding treatment is performed at a temperature higher than the eutectoid transformation point (about 590°C) of the Fe_N binary alloy, a compound layer is formed on the surface, and if it is then rapidly cooled, nitrogen is formed below it. A hardened layer containing the contained martensitic structure is formed. The nitriding treatment in this temperature range is called an nitriding treatment (A u s t e n i t i c N i t r i d i n g) in distinction from the conventional nitriding process (N i t r i d i n g).

[0010] However, in the nitriding treatment, the austenite of the structure near the surface (excluding the compound layer on the surface) is stabilized, and most of the austenite remains even if the structure is rapidly cooled thereafter. Therefore, the strain after heat treatment is almost the same as that of nitriding treatment. In addition, this stabilized talent is transformed into a hard martensitic structure by reheating it to a temperature of 250-300 ^° C.

[0011] For example, STKM- 13C (mechanical structure carbon steel pipe defined in JIS G 3445) is subjected to nitriding treatment at 640°C for 90 m in, and further nitriding treatment at 660°C for 40 min, followed by rapid cooling, Subsequent reheating at 9Om in at 280°C cures the near surface surface to 800-900 HV.

[0012] Furthermore, even if JI SS PCC (a type of cold-rolled steel sheet) was subjected to nitriding treatment at 700 ^° C, a compound layer was formed on the surface, and subsequent quenching hardened the nitrogen martensite structure underneath. A layer is formed (Non-Patent Document 3). The compound layer on the surface at this time is reported to be in the s phase. Prior art documents

Patent literature

[0013] Patent Document 1: Japanese Patent Laid-Open No. 201 3-22 1 203

Patent Document 2: JP 201 4-25 1 61 Publication

Non-Patent Document 1: Yasushi Hiraoka, Yoichi Watanabe, Akitake Ishida: Heat Treatment, Volume 55, No. 1, 1 _ 2 〇 2020/175 453 3 (: 170? 2020 /007395

Page

Non-Patent Document 2: Dietary Toke et al.: Nitriding and nitrocarburizing of iron, Agne Technology Center —, 2 0 1 3 years, page 8 4

Non-Patent Document 3: Kawai _ Ki, Toru Kidate: Summary of the 81st Spring Lecture Meeting of Japan Heat Treatment Technology Association, pp. 2 9-30

Summary of the invention

Problems to be Solved by the Invention

[0014] Friction loss in mechanical parts, such as camshafts, piston rings, crankshafts, etc., inside automobile engines is as high as 10% or more. Surface treatment such as nitriding has already been applied to some mechanical parts, but further reduction of friction loss is desired.

[0015] As one measure for reducing the wear loss of steel parts, increasing the "hardness" of steel parts can be considered. As described above, it is known that the hardness of the surface compound layer can be increased by performing the reheating treatment after the nitriding treatment and the rapid cooling.

[0016] However, in the treatment disclosed in Non-Patent Document 3, since the nitriding temperature is 700°C, which is relatively high, the hardness of the base material and the diffusion layer may be reduced.

[0017] Furthermore, a reproduction experiment was attempted on the treatment disclosed in Patent Document 2, and a hardening structure as described in the document (specifically, a mixed phase in which a phase was precipitated in the phase') Could not be reproduced (it is speculated that there is something wrong with the description in the document).

[0018] On the other hand, the compound layer formed by the soft nitriding treatment has insufficient surface hardness (see the comparative example in Fig. 11 described later) and has insufficient abrasion resistance (see Table 1 described below). See comparative example).

[0019] The inventors of the present invention have conducted sufficient studies and various experiments, and have maintained a sufficient hardness by controlling the temperature and nitriding potential of the nitriding treatment with high accuracy while limiting the configuration of the treatment furnace. Manufacturing of nitrided steel members with improved wear resistance 〇 2020/175 453 4 卩 (: 170? 2020 /007395

I knew that I could do it.

[0020] The present invention was created based on the above findings. The purpose of the present invention is

A nitride steel member having improved wear resistance in the surface layer region, and a manufacturing method and manufacturing apparatus for manufacturing such a nitrided steel member.

Means for solving the problem

[0021] The present invention is a nitrided steel member having a carbon steel or low alloy steel as a mother phase, comprising a nitride compound layer on the surface, and a hardened layer having an austenite structure under the nitride compound layer. A diffusion layer in which nitrogen is diffused in the matrix is provided below the hardened layer, and the nitride compound layer has a phase distribution in the order of £ phase, a′ phase, and £ phase. The volume ratio of the phase' in the nitride compound layer is 20% or more, and the nitride compound layer is 5 to 5% from the surface of the nitrided steel member.

A nitrided steel member having a thickness of 50.

According to the present invention, the nitride compound layer on the surface has a phase distribution of the order of £ phase, ·^ phase, and £ phase, and has a thickness of 50! Since the volume ratio of the phase' in the nitride compound layer is 20% or more (such a structure was first realized by the nitriding method described later), it has sufficient hardness as a nitrided steel member. It is possible to improve wear resistance while providing

[0023] The upper limit of 50 for the thickness of the nitride compound layer is because that value is the maximum thickness confirmed by the inventor of the present application up to the time of filing of the present application (see Using the mold treatment furnace, adopt the nitrogen treatment conditions of 350 (3 steels as mother phase, treatment temperature: 640° 〇, nitriding potential: 0.6, treatment time: 2 hours). Has been confirmed to be obtained by).

[0024] Furthermore, regarding the thickness of the nitride compound layer, the lower limit of 5 is set as a condition for forming the nitride compound layer on the entire surface of the nitrided steel member (there is no case where the nitride compound layer is not locally formed). It has a value.

[0025] Further, the present invention is a nitrided steel member having a carbon steel or a low alloy steel as a parent phase, comprising a nitride compound layer on the surface, and a hardening having an austenitic structure under the nitride compound layer. A layer, and nitrogen spreads in the matrix below the hardened layer. 〇 2020/175 453 5 卩 (: 170? 2020 /007395

The nitride compound layer has a phase distribution of A′ phase and £ phase, and the volume ratio of the A′ phase in the nitride compound layer is 30% or more. The nitride compound layer is 5 to 5 from the surface of the nitrided steel member.

A nitrided steel member having a thickness of 30.

According to the present invention, the nitride compound layer on the surface has a phase distribution in the order of A′ phase and £ phase, and

Due to the volume ratio of the A'phase in the nitride compound layer being 30% or more (such a structure was first realized by the nitriding method described later), sufficient hardness as a nitrided steel member was obtained. It is possible to improve wear resistance while providing

Also in the present invention, the upper limit value of 30 is set for the thickness of the nitride compound layer, because this value is the maximum thickness confirmed by the present inventors by the time of filing of the present application. (Using the circulation type treatment furnace described later, 3 15 (with 3 as the mother phase, treatment temperature: 6500 ^° 〇, nitriding potential = 0.2, treatment time: 2 hours) It has been confirmed that it can be obtained by adopting).

Further, also in the present invention, the thickness of the nitride compound layer is set as a condition for forming the nitride compound layer on the entire surface of the nitrided steel member (the nitride compound layer may not be locally formed). , 5 are the lower limits.

[0029] In each of the above inventions, for example, carbon steel having a carbon content of not less than 0.1% in mass% can be used as the parent phase.

The present invention can also be recognized as a method for manufacturing a nitrided steel member. That is, the present invention is a method for producing a nitrided steel member having a carbon steel or a low alloy steel as a mother phase, using a circulation type processing furnace equipped with a guide cylinder and a stirring fan, wherein during the nitriding processing, The temperature range in the circulation-type treatment furnace is controlled to 610 ^{° to} 660 ^° 〇, and at the time of the nitriding treatment, the nitriding potential in the circulation-type treatment furnace is 0. The method for producing a nitrided steel member is characterized in that the nitriding treatment is controlled within the range of .6, the nitriding treatment is followed by rapid cooling, and then reheating treatment. 〇 2020/175 453 6 卩 (: 170? 2020 /007395

[0031] According to the method for manufacturing a nitrided steel member of the present invention,

A nitrided steel member having a carbon steel or low alloy steel as a matrix phase, the surface of which is provided with a nitride compound layer, the nitride compound layer having a hardened layer having an austenite structure below the hardened layer. A diffusion layer in which nitrogen is diffused in the parent phase is provided below the layer, and the nitride compound layer has a phase distribution in the order of £ phase, a′ phase, and £ phase. The volume ratio of phase in the layer is 20% or more, and the nitride compound layer has a thickness of 5 to 50 from the surface of the nitrided steel member. Steel member

Can be manufactured.

[0032] Alternatively, according to the method for manufacturing a nitrided steel member of the present invention,

A nitrided steel member having a carbon steel or low alloy steel as a matrix phase, the surface of which is provided with a nitride compound layer, the nitride compound layer having a hardened layer having an austenite structure below the hardened layer. A diffusion layer in which nitrogen is diffused in the parent phase is provided below the layer, and the nitride compound layer has a phase distribution in the order of ′′ phase and £ phase. The volume ratio of the ′′ phase is 30% or more, and the nitride compound layer has a thickness of 50° to 300°! from the surface of the nitrided steel member. Steel member

Can be manufactured.

Further, the present invention can also be recognized as an apparatus for manufacturing a nitrided steel member. That is, the present invention comprises a recycling processing furnace having a stirring fan and the guide tube, at the time of nitriding treatment, the temperature range of the recycling process furnace, controlled 6 1 0 ^° 〇_～6 6 0 ^° 〇 In the nitriding treatment, a nitrided steel member is introduced such that ammonia gas and ammonia decomposition gas are introduced into the circulation type treatment furnace in order to control the nitriding potential in the circulation type treatment furnace. The nitriding potential in the circulation-type treatment furnace is such that the amount of ammonia decomposition gas introduced into the furnace is constant and the amount of ammonia gas introduced into the furnace is changed. It is a device for manufacturing nitrided steel members, which is controlled to a target nitriding potential in the range of to 0.6. 〇 2020/175 453 7 卩(: 170? 2020/007395

[0034] According to the apparatus for manufacturing a nitrided steel member of the present invention,

Can be manufactured.

[0035] Alternatively, according to the nitrided steel member manufacturing apparatus of the present invention,

Can be manufactured.

Effect of the invention

[0036] According to the nitrided steel member of the present invention, it is possible to improve wear resistance while providing sufficient hardness as the nitrided steel member.

[0037] According to the method for manufacturing a nitrided steel member of the present invention, a nitrided steel member having sufficient hardness and wear resistance can be manufactured.

[0038] Further, according to the apparatus for manufacturing a nitrided steel member of the present invention, a nitrided steel member having sufficient hardness and wear resistance can be manufactured.

Brief description of the drawings

[0039] [Fig. 1] A cross-sectional micrograph of a nitrided steel member according to a first embodiment of the present invention.

[Fig. 2] Fig. 2 is a diagram showing an analysis result of the nitrided steel member of Fig. 1 by the Mitsumi three-port method. 〇 2020/175 453 8 卩 (: 170? 2020 /007395

FIG. 3 is a cross-sectional photomicrograph of the nitrided steel member according to the first embodiment of the present invention before being reheated.

[Fig. 4] Fig. 4 is a diagram showing the results of analysis of the nitrided steel member of Fig. 3 by the Mitsumi three-port method.

[FIG. 5] A cross-sectional micrograph of a nitrided steel member according to a second embodiment of the present invention.

[Fig. 6] Fig. 6 is a diagram showing the results of analysis of the nitrided steel member of Fig. 5 by the Mitsumi three-port method.

[FIG. 7] A cross-sectional micrograph of a nitrided steel member according to a second embodiment of the present invention before being reheated.

[Fig. 8] Fig. 8 is a diagram showing the results of analysis of the nitrided steel member of Fig. 7 by the Mitsumi three-neck method.

[FIG. 9] A cross-sectional micrograph of a nitrided steel member as a comparative example.

[Fig. 10] Fig. 10 is a diagram showing an analysis result of the nitrided steel member of Fig. 9 by the Mitsumi three-port method.

[Fig. 11] A graph showing the measurement results of hardness.

FIG. 12 is a schematic view of an apparatus for manufacturing a nitrided steel member according to an embodiment of the present invention.

FIG. 13 is a schematic cross-sectional view of a circulation type processing furnace (horizontal gas nitriding furnace).

FIG. 14 is a graph showing an example of gas introduction control.

FIG. 148 is a graph showing an example of gas introduction control.

FIG. 15 is a perspective view of a test piece used for a friction and wear test.

[Fig. 16] A perspective view of a 3 V tester used for a friction and wear test.

MODE FOR CARRYING OUT THE INVENTION

[0040] Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0041] (Structure, manufacturing method, and effect of first embodiment of nitrided steel member)

FIG. 1 is a cross-sectional micrograph of a nitrided steel member 110 according to the first embodiment of the present invention. As shown in FIG. 1, the nitrided steel member 1100 of the present embodiment has a nitride compound layer 1111 formed on the surface thereof, and will be described below below the nitride compound layer 1111. A hardened layer 1 12 having such an austenite structure is provided, and a diffusion layer 1 13 in which nitrogen is diffused in a matrix is provided below the hardened layer 1 12. The matrix phase (matrix) of this embodiment is carbon steel having a carbon content of 0.45% by mass. 〇 2020/175 453 9 卩 (: 170? 2020 /007395

[0042] In Fig. 1, the lower part of the nitride compound layer 1 11 and the hardened layer 1 12 appear black because they were strongly corroded by the corrosive liquid for observing the structure. Also visible above the surface is the polishing plate, not the constituent elements of the nitrided steel member.

[0043] The phase distribution of the nitrided steel member 110 is

It can be analyzed by using together with X-ray diffraction. Specifically, as shown in Figure 2,

By the 0 method, from the surface side, £ phase,

The crystalline phase) and the £ phase are distributed in the order. Then, by using X-ray diffraction together, the curing layer 1 1 2 is dried.

It is confirmed that the crystalline phase is the talent-stainite phase (a phase).

[0044] The nitride compound layer 1 11 has a thickness of about 30 from the surface of the nitrided steel member 1 10, which is 5

The thickness is within the range of ~50. The surface phase is several 111 thick.

[0045] Further, the volume ratio of the phase' in the nitride compound layer 1 1 1 is

Analysis range (Nitride compound layer 1 1

It can be measured based on the number of counts of'phase' and £ phase in it. Alternatively, it may be calculated by image analysis from the obtained image of FIG. In the case of the nitride compound layer 1 11 of the present embodiment, it is 41%.

[0046] The hardened layer 1 12 was expected to be transformed into a martensite structure by the reheating treatment. However, when the present inventor applied the crystal structure analysis by the X-ray diffraction method as described above, The result was that most of the stratum 1 12 was the talent-phase (phase a). Therefore, the present inventor believes that the hardened layer 1 12 is strictly a mixed structure of talent and martensite. However, depending on the steel material size after nitriding treatment, cooling conditions, and reheating conditions, the possibility that more than one type of microstructure such as a bainite structure or brownite structure may be included is not excluded.

The nitrided steel member 110 of the present embodiment was processed by using a circulation type processing furnace described later, processing temperature: 640°°, nitriding potential: 0.4, processing time: 2 hours. Nitrogen treatment was performed under the conditions, followed by rapid cooling, and further treatment temperature: 250 ^° 〇, treatment time: 〇 2020/175 453 10 卩 (: 170? 2020 /007395

It can be manufactured by being reheated under the processing condition of 2 hours.

[0048] The nitrided steel member 110 as described above has a sufficient hardness for practical use because the volume ratio of the phase' in the nitride compound layer 1 11 is 41% (20% or more). (See Example 1_30 in FIG. 11 below) and wear resistance is also improved (see Example 1_30 in Table 1 below).

[0049] For reference, a cross-sectional micrograph of the nitrided steel member 110 before reheating is shown in Fig. 3.

Further, FIG. 4 is a diagram showing an analysis result of the nitrided steel member 160 of FIG. 3 by the Mimi 30 method.

[0050] As shown in FIGS. 3 and 4, in the state before the reheating treatment, the nitride compound layer 1 1

Most of the region 1 61 corresponding to 1 is the £ phase. For this reason, sufficient hardness cannot be obtained (see Reference Example 1 in Figure 11 below).

(Structure, Manufacturing Method, and Effect of Second Embodiment of Nitrided Steel Member)

FIG. 5 is a cross-sectional photomicrograph of the nitrided steel member 120 according to the second embodiment of the present invention. As shown in FIG. 5, the nitrided steel member 120 of the present embodiment has a nitride compound layer 1 21 formed on the surface thereof, which will be described below below the nitride compound layer 1 21. The hardened layer 1 2 2 having such an austenite structure is provided, and the diffusion layer 1 2 3 in which nitrogen is diffused in the matrix is provided below the hardened layer 1 2 2. The matrix phase (matrix) of the present embodiment is carbon steel having a carbon content of 0.45% by mass.

Also in FIG. 5, the lower part of the nitride compound layer 1 2 1 and the hardened layer 1 2 2 appear black because they are strongly corroded by the corrosive liquid for observing the structure. Further, what is visible above the surface is the polishing plate, not the constituent elements of the nitrided steel member.

[0053] The phase distribution of the nitrided steel member 120 can be analyzed by using the Mimi 30 method and X-ray diffraction in combination. Specifically, as shown in Figure 6,

By the 0 method, the phase

The crystalline phase) and the £ phase are distributed in this order. Then, the X-ray diffraction is also used, so that the dried crystal phase of the hardened layer 1 2 2 is stable. 〇 2020/175 453 1 1 卩(: 170? 2020/007395

It is confirmed that it is a night phase (phase a).

[0054] The nitride compound layer 1 2 1 has a thickness of about 1 2 from the surface of the nitrided steel member 1 2 0.

The thickness is within the range. The surface phase is several 111 thick.

[0055] Further, the volume ratio of the phase' in the nitride compound layer 1 2 1 is

Analysis range by (nitride compound layer

It can be measured based on the number of counts of'phase' and £ phase in it. Alternatively, it may be calculated by image analysis from the obtained image of FIG. In the case of the nitride compound layer 1 2 1 of this embodiment, it is 5 2%.

[0056] The hardened layer 122 was expected to be transformed into a martensite structure by the reheating treatment. However, the results of Mimi 30 shown in Fig. 6 and the X-ray diffraction method described above were used. It was confirmed by crystal structure analysis that in the hardened layer 122, a large amount of talented regions partially remained. However, depending on the steel material size after nitriding treatment, cooling conditions, and reheating conditions, the possibility of including multiple types of microstructures such as a bainite structure and brownite structure cannot be ruled out.

The nitrided steel member 120 of the present embodiment was treated by using a circulation type treatment furnace described later, treatment temperature: 640°°, nitriding potential: 0.2, treatment time: 2 hours. After being subjected to the nitriding treatment under the conditions, it is rapidly cooled, and then it is reheated under the treatment conditions of the treatment temperature: 250 ^° C. and the treatment time: 2 hours, whereby it can be produced.

[0058] The nitrided steel member 120 as described above has sufficient hardness for practical use because the volume ratio of the ^ phase in the nitride compound layer 1 21 is 52% (30% or more). (See Example 2 _ 12 in Figure 11 below) and wear resistance is also improved (see Example 2-12 in Table 1 below).

[0059] For reference, a cross-sectional micrograph of the nitrided steel member 120 before reheating is shown in Fig. 7.

Further, FIG. 8 is a diagram showing an analysis result of the nitrided steel member 170 shown in FIG. 7 by the Mimi 30 method.

[0060] As shown in Figs. 7 and 8, in the state before the reheating treatment, the nitride compound layer 1 2 〇 2020/175 453 12 boxes (: 170? 2020 /007395

Most of the region 1 71 corresponding to 1 is the £ phase. Therefore, sufficient hardness cannot be obtained.

[0061] (Comparative example of nitrided steel members)

FIG. 9 is a cross-sectional micrograph of a nitrided steel member 300 of Comparative Example. As shown in FIG. 9, the nitrided steel member 300 of the comparative example has a nitride compound layer 3001 formed on the surface thereof, and nitrogen is present in the matrix below the nitride compound layer 301. It has a diffusion layer 303 that is diffused. The parent phase (base material) of the comparative example is also carbon steel having a carbon content of 0.45% by mass.

The surface side of the compound layer obtained by the conventional general nitriding treatment is porous. Figure

In Fig. 9, the upper part of the nitride compound layer 301 appears black because there are many fine voids in this region. Further, what is seen above the surface is the polishing plate, not the constituent elements of the nitrided steel member.

[0063] The phase distribution of the nitrided steel member 300 can also be analyzed by using the Mimi 30 method and X-ray diffraction in combination. Specifically, as shown in FIG.

By the 0 method, it can be seen that most of the nitride compound layer 301 is in the phase.

The nitride compound layer 3001 has a thickness of about 17 from the surface of the nitrided steel member 300.

[0065] The nitrided steel member 300 of the comparative example was processed using a circulation type processing furnace described below, with a processing temperature of 5800°, a nitriding potential of 2.5, and a processing time of 2 hours. After the soft nitriding process is performed (atmosphere gas is ammonia, nitrogen gas and carbon dioxide gas), it can be rapidly cooled to be manufactured. It has been confirmed that the nitride compound layer 301 of the comparative example does not cure even if it is subjected to the reheating treatment (probably because the temperature during the soft nitriding treatment is relatively low).

In the nitrided steel member 300 as described above, most of the nitride compound layer 3001 is the ^ phase, and conventionally, this hard phase was used to improve the wear resistance. However, the surface hardness was insufficient as compared with the compound layer formed by the nitriding treatment of the present invention (see the comparative example in Fig. 11 described later), which adversely affects the wear resistance and the wear resistance. Abrasion is also insufficient (see Comparative Example in Table 1 below). 〇 2020/175 453 13 卩 (: 170? 2020 /007395

[0067] Furthermore, regarding the nitrided steel member 300 of the comparative example, it was pointed out that a lot of voids (which appear black in Fig. 9) are formed on the surface side of the nitride compound layer 3001. To be done. Since the void (porous) can be the starting point of crack initiation, its presence is not preferable.

(Evaluation of hardness)

Figure 11 is a graph showing the results of hardness measurement. Nitrided steel part 1 1 〇 (Example 1 _ 30) of the first embodiment, Nitrided steel member 1 2 0 of the second embodiment (Example 2-1 2), Nitrided steel member 1 60 of the reference example (Reference Example 1_30), and for each of the nitrided steel members 300 of Comparative Example, the results obtained by measuring the hardness at a predetermined depth from the surface are plotted.

[0069] In the nitrided steel member 110 (Example 1_30) of the first embodiment, the nitride compound layer was used.

Throughout the entire thickness of 1 1 (3 0 ), a high hardness of 1 0 0 0 1! V or higher is obtained. In particular, the hardness of the portion corresponding to the phase on the core side is large.

[0070] On the other hand, in the nitrided steel member 160 of the reference example (Reference example 1_30), the hardness in the vicinity of the surface is slightly lower than 8 0 0 1 ^to 1 V, which is not sufficient. ..

[0071] In the nitrided steel member 120 (Example 2_12) of the second embodiment, the hardness decreases toward the inside, but the hardness near the surface is sufficiently high.

[0072] More, in the nitride steel member 3 0 0 Comparative Example, the hardness in the vicinity of the surface has a 6 0 0 1 ^- about 1 V, not sufficient.

(Thickness of Nitride Compound Layer 1 11 of Nitride Steel Member 110 of First Embodiment)

It can be said that, as for the thickness of the nitride compound layer 1 11 of the nitrided steel member 110 according to the first embodiment, generally, the thicker the thickness, the larger the allowable wear amount, and therefore the more preferable.

The inventor of the present invention has found that the nitride compound layer 1 11 tends to be thick when the carbon steel generally used for shafts has a large amount of carbon (specifically, for example, 3500 steel). I confirmed the tendency. Then, specifically, 350 (3 steels, treatment temperature = 640 ° 〇, nitriding potential: 0.6, treatment time: 2 hours, nitrification treatment, quenching, treatment temperature: 25 0 ^° 〇, Treatment time: When reheated for 2 hours, nitride compound layer 1 〇 2020/175 453 14 卩 (: 170? 2020 /007395

The thickness of 11 was 50 (see Example 1_50 in Table 1 below). Therefore, the maximum value of the thickness of the nitride compound layer 1 11 which can be recognized by those skilled in the art as solving the problem of the present invention is set to 50 |^|.

[0075] In addition, the inventors of the present invention have confirmed that the thickness of the nitride compound layer 1 11 tends to increase when the nitriding potential during the nitriding treatment is high.

(Thickness of Nitride Compound Layer 1 21 of Nitride Steel Member 120 of Second Embodiment)

Regarding the thickness of the nitride compound layer 1 21 of the nitrided steel member 120 of the second embodiment, generally, it can be said that the thicker the thickness, the larger the allowable wear amount, which is preferable.

[0077] The present inventor has a tendency that the carbon compound steel generally used for gears has a low carbon content (specifically, for example, 3 15 (3 steel), the nitride compound layer 1 2 1 tends to be thick. . confirmed direction and, specifically, 3 1 5 (3 steel processing temperature: 6 5 0 ^° 〇, nitriding potential:. 0 2, treatment time: to nitriding treatment for 2 hours, and quenched When the treatment temperature was 250° C. and the treatment time was 2 hours, the nitride compound layer 1 21 had a thickness of 30 (see Examples 2 to 30 in Table 1 below). Therefore, the maximum value of the thickness of the nitride compound layer 1 11 which can be recognized by those skilled in the art as solving the problem of the present invention is set to 30 |^|.

In addition, the present inventor has confirmed that the thickness of the nitride compound layer 1 2 1 also tends to increase when the nitriding potential during the nitriding treatment is high.

[0079] (Volume ratio of ^ phase in nitride compound layer 1 11 of nitrided steel member 110 of the first embodiment)

The inventor of the present invention has confirmed that a larger volume ratio of phases in the nitride compound layer 1 1 1 is preferable for increasing hardness. Regarding the minimum value, concretely, 3500 steel is treated at a treatment temperature of 6400°, a nitriding potential of 0.6, and a treatment time of 2 hours. When reheated at a temperature of 250° C. for a treatment time of 2 hours, the volume ratio of the ^ phase in the nitride compound layer 11 was 20% (Example 1_ in Table 1 below). See 50). Therefore, the minimum value of the volume ratio of the phase in the nitride compound layer 1 11 which can be recognized by those skilled in the art as solving the problem of the present invention is set to 20%. 〇 2020/175 453 15 卩(: 170? 2020/007395

[0080] (Volume ratio of ^ phase in nitride compound layer 1 21 of nitrided steel member 120 of Second Embodiment)

The present inventor has confirmed that the larger the volume ratio of the ^ phase in the nitride compound layer 1 21 is, the better it is to increase the hardness. As for the minimum value, concretely, 3150 steel is treated at a treatment temperature of 6500°, a nitriding potential of 0.2, a treatment time of 2 hours, and subjected to nitrification treatment, followed by rapid cooling, and treatment temperature. = 2500° 〇, treatment time: When reheated for 2 hours, the volume fraction of · ^ phase in the nitride compound layer 1 21 was 30% (Example 2 _ in Table 1 below). See 30). Therefore, the minimum value of the volume ratio of the ^ phase in the nitride compound layer 1 21 which can be recognized by those skilled in the art as solving the problem of the present invention was set to 30%.

(Configuration of Nitriding Steel Member Manufacturing Apparatus)

Next, an apparatus for manufacturing a nitrided steel member will be described. First, the basic items of the gas nitriding process will be described chemically. In the gas nitriding process, the following equation (1) is used in the processing furnace (gas nitriding furnace) where the article to be processed is placed. Nitriding reaction occurs.

3 ® [1\1]+3/2¾-(1)

At this time, the nitriding potential% is defined by the following equation (2).

% = ^3/2 ⑵

Here, is the partial pressure of ammonia in the furnace, and is the partial pressure of hydrogen in the furnace. The nitriding potential is known as an index showing the nitriding ability of the atmosphere in the gas nitriding furnace.

On the other hand, in the furnace during the gas nitriding treatment, a part of the ammonia gas introduced into the furnace is thermally decomposed into hydrogen gas and nitrogen gas according to the reaction of equation (3). \1 ₂ +3/2¾-(3)

[0084] The reaction of the formula (3) mainly occurs in the furnace, and the nitriding reaction of the formula (1) can be almost neglected quantitatively. Therefore, if the concentration of ammonia in the furnace consumed in the reaction of equation (3) or the concentration of hydrogen gas generated in the reaction of equation (3) is known, 〇 2020/175 453 16 卩(: 170? 2020/007395

The nitriding potential can be calculated. That is, the hydrogen and nitrogen generated are 1.5 mol and 0.5 mol, respectively, from 1 mol of ammonia. Therefore, measuring the ammonia concentration in the furnace also reveals the hydrogen concentration in the furnace, and It can be calculated. Alternatively, if the hydrogen concentration in the furnace is measured, the ammonia concentration in the furnace can be known, and the nitriding potential can also be calculated.

[0085] The ammonia gas flown in the gas nitriding furnace is circulated in the furnace and then discharged to the outside of the furnace. That is, in the gas nitriding process, the fresh (new) ammonia gas constantly flows into the furnace with respect to the existing gas in the furnace, so that the existing gas is continuously discharged outside the furnace (pushed out by the supply pressure). ..

[0086] Here, if the flow rate of the ammonia gas introduced into the furnace is small, the gas residence time in the furnace becomes long, so that the amount of decomposed ammonia gas increases and the decomposition reaction is generated. The amount of nitrogen gas and deuterium gas is increased. On the other hand, if the flow rate of ammonia gas introduced into the furnace is large, the amount of ammonia gas that is not decomposed and is discharged to the outside of the furnace increases, and the amount of nitrogen gas and deuterium gas generated in the furnace increases. Decrease.

[0087] Now, Fig. 12 is a schematic diagram showing a manufacturing apparatus for manufacturing a nitrided steel member according to an embodiment of the present invention. As shown in FIG. 12, the manufacturing apparatus 1 of the present embodiment is provided with a circulation type treatment furnace 2, and only two types of gas, ammonia and ammonia decomposition gas, are introduced into the circulation type treatment furnace 2. I am using. Ammonia decomposition gas, also called 8X gas, is a mixed gas consisting of nitrogen and hydrogen in a ratio of 1:3. However, as the introduced gas, (1) only ammonia gas, (2) only two types of ammonia and ammonia decomposition gas, (3) only two types of ammonia and nitrogen gas, or (4) ammonia and ammonia decomposition gas And only three types of nitrogen gas can be selected from.

FIG. 13 shows an example of a cross-sectional structure of the circulation type processing furnace 2. In Fig. 13, a cylinder 20 2 called a retort is arranged in a furnace wall (also called a bell) 201, and a cylinder 20 4 called an inner retort is arranged inside the cylinder. 〇 2020/175 453 17 卩(: 170? 2020/007395

The introduction gas supplied from the gas introduction pipe 205 passes through the periphery of the object to be treated as shown by the arrow in the figure, and then the two stirring cylinders 2 0 2 and 2 2 are operated by the stirring fan 2 0 3. It circulates through the space between 0 and 4. Reference numeral 206 is a gas hood with flare, 207 is a thermocouple, 208 is a lid for cooling work, and 209 is a fan for cooling work. The circulation type processing furnace 2 is also called a horizontal gas nitriding furnace, and its structure itself is known.

The object to be treated 3 is carbon steel or low alloy steel, and is, for example, a crankshaft, a gear or the like which is an automobile part.

Further, as shown in FIG. 12, the processing furnace 2 of the surface hardening processing apparatus 1 of the present embodiment includes a furnace opening/closing lid 7, a stirring fan 8, a stirring fan drive motor 9, and an atmosphere gas concentration. A detector 3, a nitriding potential controller 4, a programmable logic controller 31 and an in-furnace introduced gas supply unit 20 are provided.

The stirring fan 8 is arranged in the processing furnace 2 and rotates in the processing furnace 2 to stir the atmosphere in the processing furnace 2. The stirring fan drive motor 9 is connected to the stirring fan 8 so as to rotate the stirring fan 8 at an arbitrary rotation speed.

The atmosphere gas concentration detecting device 3 is composed of a sensor capable of detecting the hydrogen concentration or the ammonia concentration in the processing furnace 2 as the atmosphere gas concentration in the furnace. The main body of detection of the sensor communicates with the inside of the processing furnace 2 through an atmospheric gas pipe 12. In the present embodiment, the atmospheric gas pipe 12 is formed in a path that directly connects the sensor main body of the atmospheric gas concentration detection device 3 and the processing furnace 2, and is connected to the exhaust gas combustion decomposition device 41 on the way. Furnace gas disposal pipe 40 is connected. As a result, the atmospheric gas is distributed between the discarded gas and the gas supplied to the atmospheric gas concentration detection device 3.

Further, the atmospheric gas concentration detecting device 3 is configured to detect the atmospheric gas concentration in the furnace and then output an information signal including the detected concentration to the nitriding potential controller 4.

[0094] The nitriding potential controller 4 includes an in-furnace nitriding potential computing device 13 〇 2020/175 453 18 卩 (: 170? 2020 /007395

And a flow rate output adjusting device 30. In addition, the programmable logic controller 31 has a gas introduction amount control device 14 and a parameter setting device 15.

[0095] The in-furnace nitriding potential calculation device 13 is configured to calculate the nitriding potential in the processing furnace 2 based on the hydrogen concentration or the ammonia concentration detected by the in-furnace atmosphere gas concentration detection device 3. .. Specifically, a formula for calculating the nitriding potential programmed according to the actual gas introduced in the furnace is incorporated, and the nitriding potential is calculated from the value of the atmospheric gas concentration in the furnace.

[0096] The parameter setting device 15 is composed of, for example, a touch panel, and can set and input the total flow rate of gas introduced into the furnace, the gas type, the processing temperature, the target nitriding potential, and the like. Each setting parameter value input by setting is transmitted to the gas flow rate output adjusting device 30.

[0097] Then, the gas flow rate output adjusting device 30 is connected to the in-reactor nitriding potential calculating device 1

Control is performed with the nitriding potential calculated in step 3 as the output value, the target nitriding potential (set nitriding potential) as the target value, and the input amounts of ammonia gas and ammonia decomposition gas as input values. It has become. More specifically, it is possible to control the amount of ammonia decomposition gas introduced into the furnace to be constant and to change the amount of ammonia gas introduced into the furnace. The output value of the gas flow rate output adjusting device 30 is transmitted to the gas introduction amount control device 14.

[0098] The gas introduction amount control device 14 includes a first supply amount control device 2 2 for ammonia gas and a second supply amount control device 26 for ammonia decomposition gas so as to realize the introduction amount of each gas. Each is designed to send a control signal.

The in-furnace introduced gas supply unit 20 of the present embodiment includes a first in-reactor introduced gas supply unit 21 for ammonia gas, a first supply amount control device 2 2 and a first supply valve 2 3 And a first flow meter. In addition, the in-reactor introduction gas supply unit 20 of the present embodiment includes a second in-reactor introduction gas supply unit 25 for ammonia decomposition gas (eight gas), 〇 2020/175 453 19 卩 (: 170? 2020 /007395

It has a supply amount control device 26, a second supply valve 27, and a second flow meter.

[0100] In the present embodiment, the ammonia gas and the ammonia decomposition gas are adapted to be mixed in the furnace introduction gas introduction pipe 29 before entering the processing furnace 2.

[0101] The first-reactor-introduced-gas supply unit 21 is formed of, for example, a tank filled with the first-reactor-introduced gas (in this example, ammonia gas).

[0102] The first supply amount control device 22 is formed by a mass flow controller and is interposed between the first in-reactor introduced gas supply part 21 and the first supply valve 23. The opening degree of the first supply amount control device 22 changes according to the control signal output from the gas introduction amount control device 14. Further, the first supply amount control device 22 detects the supply amount from the first in-furnace introduced gas supply part 21 to the first supply valve 23, and outputs an information signal including the detected supply amount to the gas introduction amount. It is designed to output to the control unit 14. The control signal can be used for correction of the control by the gas introduction amount control device 14 or the like.

[0103] The first supply valve 23 is formed by a solenoid valve that switches between open and closed states in accordance with a control signal output from the gas introduction amount control device 14 and is connected to the first supply amount control device 2 2 and the first flow rate. It is installed between the instrument and the instrument.

[0104] The second-reactor-introduced-gas supply unit 25 is formed by, for example, a tank filled with the second-reactor-introduced gas (in the present example, an ammonia decomposition gas).

[0105] The second supply amount control device 26 is formed by a mass flow controller and is interposed between the second in-furnace introduced gas supply part 25 and the second supply valve 27. The opening degree of the second supply amount control device 26 changes according to the control signal output from the gas introduction amount control device 14. Further, the second supply amount control device 26 detects the supply amount from the second in-furnace introduced gas supply unit 25 to the second supply valve 27, and outputs an information signal including the detected supply amount to the gas introduction amount. It is designed to output to the control unit 14. The control signal can be used for correction of the control by the gas introduction amount control device 14 or the like.

[0106] The second supply valve 27 is formed by a solenoid valve that switches between open and closed states in accordance with a control signal output by the gas introduction amount control device 14 and the second supply amount control device 2 \\0 2020/175453 20 ?01/1?2020/007395

It is installed between 6 and the second flow meter.

[Operation of Nitride Steel Member Manufacturing Apparatus (Manufacturing Method)]

Next, the operation of the manufacturing apparatus 1 of this embodiment will be described. First, the article to be treated 3 is put into the circulation type processing furnace 2 and the circulation type processing furnace 2 is heated to a desired processing temperature. After that, a mixed gas of ammonia gas and ammonia decomposition gas or only ammonia gas is introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at a set initial flow rate. This set initial flow rate can also be set and input in the parameter setting device 15 and is controlled by the first supply amount control device 2 2 and the second supply amount control device 2 6 (both mass flow controllers). Further, the stirring fan drive motor 9 is driven to rotate the stirring fan 8 to stir the atmosphere in the processing furnace 2.

[0108] The in-reactor nitriding potential calculator 13 of the nitriding potential controller 4 calculates the in-reactor nitriding potential (it is an extremely high value at the beginning (because there is no hydrogen in the furnace), the Decrease as the decomposition (hydrogen generation) progresses), and determine whether it is below the sum of the target nitriding potential and the standard deviation value. This reference deviation value can also be set and input in the parameter setting device 15.

[0109] When it is determined that the calculated value of the in-reactor nitriding potential is less than the sum of the target nitriding potential and the standard deviation value, the nitriding potential controller 4 causes the in-reactor amount control device 1 Control of the amount of introduced gas is started.

The in-furnace nitriding potential calculator 13 of the nitriding potential controller 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal. Then, the gas flow rate output adjusting device 30 sets the nitriding potential calculated by the in-furnace nitriding potential calculating device 13 as an output value, sets the target nitriding potential (set nitriding potential) as the target value, and introduces it into the furnace. Perform I 0 control with the input amount of gas. Specifically, in the I port control, control is performed so that the amount of ammonia decomposition gas introduced into the reactor is constant and the amount of ammonia gas introduced into the reactor is changed. Concerned 〇 2020/175 453 21 卩 (: 170? 2020 /007395

In the I port control, each set parameter value set and input by the parameter setting device 15 is used. For this setting parameter value, for example, different values are prepared depending on the value of the target nitriding potential.

Then, the gas flow rate output control device 30 controls the introduction amount of each of the in-reactor introduced gas as a result of the I port control. Specifically, the gas flow rate output adjusting device 30 determines the flow rate of each gas, and the output value is transmitted to the gas introduction amount control device 14.

[01 12] The gas introduction amount control device 14 includes a first supply amount control device 2 2 for ammonia gas and a second supply amount control device 26 for ammonia decomposition gas in order to realize the introduction amount of each gas. To each of the control signals.

[0113] By the control as described above, the in-furnace nitriding potential can be stably controlled in the vicinity of the target nitriding potential. As a result, it is possible to perform the nitrification treatment of the article to be treated 3 with extremely high quality.

An example of the above-described control is shown in FIGS. The amount of ammonia decomposed gas introduced into the furnace is constant, and feedback control is performed in small increments in the vicinity of the amount of ammonia gas introduced into the furnace of 40 (丨/〇!丨11). As a result, the nitriding potential is controlled to 0.17 with high accuracy.

[0115] Furthermore, depending on the material type and shape of the article to be treated 3, the manufacturing apparatus 1 can also perform the cooling step after the nitrification treatment. However, if sufficient hardness cannot be obtained after the treatment at the cooling rate of the manufacturing apparatus 1, the workpiece 3 is removed from the furnace while the heating temperature is maintained after the nitrification treatment in the manufacturing apparatus 1. It is necessary to transfer to a rapid cooling device (eg oil tank) and then to quench. Alternatively, it is necessary to take out the article to be treated 3 after cooling in the manufacturing apparatus 1 from the manufacturing apparatus 1, raise the temperature again to the heating temperature in another heating furnace equipped with a quenching apparatus, and then quench the material.

[01 16] According to the study by the present inventor, a talented structure stabilized with 1.0% or more of nitrogen is a brownite (a layered structure of a ferrite phase and a'phase) when the cooling rate is slow. Therefore, there is a concern that hardness and fatigue strength may be reduced. Therefore, gas cooling 〇 2020/175 453 22 卩 (: 170? 2020 /007395

When adopting air cooling or air cooling, it is important to optimize the cooling rate for each component. On the other hand, when oil cooling is adopted, it is possible to maintain the talented tissue with ordinary parts.

[0117] (About the importance of the guide tube (internal retort))

Further, according to the experiments conducted by the inventors of the present invention, when the guide tube 5 (internal retort) was removed from the manufacturing apparatus 1 to carry out the nitriding treatment, the in-furnace uniformity of the nitriding potential was lowered and the treatment It was confirmed that the uniformity was reduced.

[0118] (Verification of hardness and fatigue strength)

Friction and wear as shown in Fig. 16 was carried out on 345 〇 steel (test piece) having the shape (¢ 25 X80101 size) as shown in Fig. 15 under the conditions shown in Table 1 below. The abrasion resistance was evaluated using a tester (Ovitimol, Germany: vibration friction wear tester 3 V 4).

[0119] As a slider, a ball of silicon nitride of ¢10 (hardness: about 16001 ^to 1) is used, and it is used under the condition of dry type (room temperature 25 ^° (:, humidity 30%, no lubricant)). Then, reciprocal sliding is repeated while applying a load of 10 (amplitude 1, 501 ^to 12,

10 minutes), and the maximum wear amount (measured in a cross section perpendicular to the sliding direction) was measured.

[0120] In Fig. 16, 401 is an oscillation block head plate, 4023 is a torsion sensor, 402 is a test piece fixture,

4033 is the upper specimen holder and 404 is the vertical load axis.

[0121] [Table 1]

[0122] (Example 1_30) 〇 2020/175 453 23 卩 (: 170? 2020 /007395

Example 1_30 in Table 1 corresponds to the nitrided steel member 110 of the first embodiment described with reference to FIGS. 1 and 2. In Example 1_30, the circulation treatment furnace 2 was used to perform the nitriding treatment under the treatment conditions of treatment temperature: 640°, nitriding potential: 0.4, treatment time: 2 hours. After that, it was rapidly cooled, and then it was reheated under the treatment conditions of treatment temperature: 250 ^° 〇, treatment time: 2 hours (manufacturing phase: 3 4 5 (3 steel)).

[0123] The phase distribution of the nitride compound layer is in the order of £ phase, ^ phase, and £ phase, and the thickness of the nitride compound layer is about 300! From the surface of the nitrided steel member. ^* ^

The volume ratio of the' phase was 41%.

[0124] The nitrided steel members of Examples 1 _ 30 as described above provided a sufficient hardness distribution as shown by the black triangle points in Fig. 11 and had a low hardness as shown in Table 1. It was confirmed to provide maximum wear (sufficient friction wear characteristics).

[0125] (Examples 1 to 36)

Example 1_36 is a nitrided steel member manufactured by changing the nitriding potential during nitrification treatment to 0.5 in comparison with Example 1_30.

[0126] The phase distribution of the nitride compound layer is in the order of £ phase, ·^ phase, and £ phase, and the thickness of the nitride compound layer is approximately 360° from the surface of the nitrided steel member. ^* ^

The volume ratio of the' phase was 33%.

[0127] The nitrided steel members of Examples 1 to 36 as described above also provided a sufficient hardness distribution as generally indicated by the black triangle points in Fig. 11 and, as shown in Table 1, It was confirmed to provide low maximum wear (sufficient friction wear properties).

[0128] (Examples 1 to 40)

Example 1_40 is a nitrided steel member produced by changing the nitriding potential at the time of nitrification treatment to 0.6 in comparison with Example 1_30.

[0129] The phase distribution of the nitride compound layer is in the order of £ phase, ·^ phase, £ phase, and the thickness of the nitride compound layer is about 4001 from the surface of the nitrided steel member. ^* ^

The volume ratio of the' phase was 24%.

[0130] The nitrided steel members of Examples 1 to 40 as described above are also generally shown in Fig. 11 by black triangle points. 〇 2020/175 453 24 卩 (: 170? 2020 /007395

It was confirmed that it provides a sufficient hardness distribution as described above and also provides a low maximum wear amount (sufficient friction and wear characteristics) as shown in Table 1.

[0131] (Examples 1 to 50)

Example 1-50 was produced by changing the matrix phase to 350 (3 steel) and the nitriding potential during nitrification treatment to 0.6 compared to Example 1-30. It is a nitrided steel member.

[0132] The phase distribution of the nitride compound layer is in the order of £ phase, ^ phase, and £ phase, and the thickness of the nitride compound layer is about 500! From the surface of the nitrided steel member. ^* ^

The volume ratio of the ‘phase’ was 20%.

[0133] The nitrided steel members of Examples 1 to 50 described above also provided a sufficient hardness distribution as generally indicated by the black triangle points in Fig. 11 and, as shown in Table 1, It was confirmed to provide low maximum wear (sufficient friction wear properties).

[0134] (Examples 1 to 15)

Example 1_15 is a nitrided steel member produced by changing the nitriding temperature during the nitriding treatment to 6200° as compared with Example 1_30.

[0135] The phase distribution of the nitride compound layer is in the order of'phase' and £ phase, and the thickness of the nitride compound layer is about 15 from the surface of the nitrided steel member. The volume ratio was 37%.

[0136] The nitrided steel members of Examples 1 to 15 like this also provided a sufficient hardness distribution as indicated by the white circles in Fig. 11 and had a low hardness as shown in Table 1. It was confirmed to provide maximum wear (sufficient friction wear characteristics).

[0137] (Reference example 1 _ 30, Reference example 1 _ 36, Reference example 1 _ 40)

Regarding Example 1 — 30, Example 1 — 36, and Example 1 — 40, the state before the reheating treatment was respectively Reference Example 1 _ 3 0, Reference Example 1 _ 3 6, Reference Example 1 _ 4 The hardness and the maximum wear amount were evaluated as 0.

[0138] As a result, it was found that the hardness had an insufficient hardness distribution as shown by the white triangles in Fig. 11, and the friction and wear characteristics were relatively high as shown in Table 1. It was the maximum amount of wear. 〇 2020/175 453 25 卩 (: 170? 2020 /007395

[0139] (Example 2-12)

Example 2-12 in Table 1 corresponds to the nitrided steel member 120 of the second embodiment described with reference to FIGS. 5 and 6. The Example 2 _ 1 2 was subjected to a nitriding treatment using the above-mentioned circulation type treatment furnace 2 under the treatment conditions of treatment temperature: 640° 〇, nitriding potential: 0.2, treatment time: 2 hours. After that, it was rapidly cooled, and then it was reheated under the treatment conditions of treatment temperature: 250 ^° 〇, treatment time: 2 hours (manufacturing phase: 3 4 5 (3 steel)).

[0140] The phase distribution of the nitride compound layer is in the order of'phase' and £ phase, and the thickness of the nitride compound layer is about 12 from the surface of the nitrided steel member. The volume ratio of was 52%.

[0141] The nitrided steel members of Examples 2-12 as described above provided a sufficient hardness distribution as indicated by white circles in Fig. 11 and had a low maximum wear as shown in Table 1. It was confirmed to provide a quantity (sufficient friction and wear properties).

[0142] (Examples 2-7)

Example 2_7 is a nitrided steel member manufactured by changing the nitriding potential at the time of nitrification treatment to 0.18 as compared with Example 2-12.

[0143] The phase distribution of the nitride compound layer is in the order of'phase' and £ phase, and the thickness of the nitride compound layer is about 7 from the surface of the nitrided steel member. The volume ratio was 60%.

[0144] The nitrided steel members of Examples 2 to 7 also provided a sufficient hardness distribution as generally indicated by the white circles in Fig. 11 and had a low maximum maximum as shown in Table 1. It was confirmed to provide the amount of wear (sufficient friction and wear characteristics).

[0145] (Examples 2-16)

Example 2 _ 16 is a nitrided steel member manufactured by changing the nitriding temperature at the time of nitrification treatment to 6 3 〇 ^° 〇 and the nitriding potential to 0.25 in comparison with Example 2 _ 1 2. is there.

[0146] The phase distribution of the nitride compound layer is in the order of'phase' and £ phase, and the thickness of the nitride compound layer is about 16 from the surface of the nitrided steel member. of 〇 2020/175 453 26 卩(: 170? 2020/007395

The volume ratio was 45%.

[0147] Such a nitrided steel member of Example 2 _ 16 also provided a sufficient hardness distribution as generally indicated by the white circles in Fig. 11 and had a low hardness as shown in Table 1. It was confirmed to provide maximum wear (sufficient friction wear characteristics).

[0148] (Examples 2 to 30)

Example 2-30 is different from Example 2-12 in that the matrix phase is changed to 3 15 (3 steel, and the nitriding temperature at the time of the nitriding treatment is 650°° and the nitriding potential is 0°. It is a nitrided steel member manufactured by changing to .2.

[0149] The phase distribution of the nitride compound layer is in the order of A'phase and £ phase, and the thickness of the nitride compound layer is about 30 from the surface of the nitrided steel member. The volume ratio of was 30%.

[0150] The nitrided steel members of Examples 2-30 also provided a sufficient hardness distribution as indicated by the white circles in Fig. 11 and had a low hardness as shown in Table 1. It was confirmed to provide maximum wear (sufficient friction wear characteristics).

Explanation of symbols

[0151] 1 Nitriding steel member manufacturing equipment (surface hardening equipment)

2 Circulation type processing furnace

3 Atmosphere gas concentration detector

4 Nitriding potential controller

5 Internal retort

6 Retort

7 furnace lid

8 stirring fan

9 Stirring fan drive motor

1 2 Atmosphere gas piping

1 3 In-furnace nitriding potential calculator

1 4 Gas introduction amount control device

1 5 Parameter setting device (touch panel) /175453 27 卩 (: 170? 2020 /007395 0 Reactor gas introduction part

1 Introduced gas supply unit in the 1st reactor

2 First supply control device

3 First supply valve

5 Introduced gas supply part in No. 2 reactor

6 Second supply control device

7 Second supply valve

9 Furnace gas introduction piping

0 Gas flow rate output adjustment device

1 Programmable logic controller

0 Furnace gas waste piping

1 Exhaust gas combustion decomposition device

10 Nitride steel member (first embodiment)

1 1 Nitride compound layer

1 2 Hardened layer

1 3 diffusion layer

20 Nitride steel member (second embodiment)

2 1 Nitride compound layer

22 Hardened layer

23 Diffusion layer

60 Nitride steel member (Reference example 1)

6 1 Area corresponding to nitride compound layer

70 Nitride steel member (Reference example 2)

7 1 Area corresponding to nitride compound layer

00 Nitride steel member (comparative example)

01 Nitride compound layer

03 Diffusion layer

01 Furnace wall or bell /175453 28 卩 (: 170? 2020 /007395 02 Retort

03 Stirring fan

04 Guide tube (internal retort)

05 Gas introduction pipe

06 Gas hood with flare

07 Thermocouple

08 Lid for cooling work

09 Blower for cooling work

Claims

\¥0 2020/175 453 29 卩(: 17 2020/007395 Claims

[Claim 1] A nitrided steel member having a matrix phase of carbon steel or low alloy steel,

Provided with a nitride compound layer on the surface,

A hardened layer having an austenite structure is provided below the nitride compound layer,

A diffusion layer in which nitrogen is diffused in the matrix is provided below the hardened layer,

The nitride compound layer has a phase distribution in the order of £ phase, A′ phase, and £ phase.

The volume ratio of the a'phase in the nitride compound layer is 20% or more, and the nitride compound layer is 5 0 1 to 5 from the surface of the nitrided steel member.

A nitrided steel member having the following thickness.

[Claim 2] A nitrided steel member having carbon steel or a low alloy steel as a matrix phase,

Provided with a nitride compound layer on the surface,

The nitride compound layer has a phase distribution of A′ phase and £ phase in this order, the volume ratio of the A′ phase in the nitride compound layer is 30% or more, and the nitride compound layer is A nitrided steel member having a thickness of 511 to 301 from the surface of the nitrided steel member.

[Claim 3] The nitrided steel member according to claim 1 or 2, wherein a carbon steel having a carbon content of 0.1% by mass or more is used as a matrix phase.

[Claim 4] A method for producing a nitrided steel member having a carbon steel or a low alloy steel as a matrix phase by using a circulation type processing furnace equipped with a guide cylinder and a stirring fan, the method comprising: The temperature range in the circulation type processing furnace is 610 ^°

Controlled to ~660°0, 〇 2020/175 453 30 boxes (: 170? 2020 /007395

At the time of the nitriding treatment, the nitriding potential in the circulation type treatment furnace is controlled in the range of 0.15 to 0.6.

After the nitriding treatment, it is quenched and then reheated.

A method for manufacturing a nitrided steel member, comprising:

[Claim 5] A circulation type processing furnace having a guide cylinder and a stirring fan is provided,

During nitriding, the temperature range of the recycling treatment furnace is controlled to 6 1 0 ^° 〇 ~ 6 6 0 ° 〇,

Manufacture of a nitrided steel member in which ammonia gas and ammonia decomposition gas are introduced into the circulating treatment furnace in order to control the nitriding potential in the circulating treatment furnace during the nitriding treatment. A device,

The nitriding potential in the circulation type treatment furnace is in the range of 0.15 to 0.6 when the amount of ammonia decomposition gas introduced into the furnace is constant and the amount of ammonia gas introduced into the furnace is changed. Is controlled to the target nitriding potential of

An apparatus for manufacturing a nitrided steel member characterized by the above.