JP2022068375A - Nitride steel member and manufacturing method and manufacturing equipment for nitrided steel member - Google Patents

Abstract

A nitrided steel member having improved wear resistance in a surface layer region, and a manufacturing method and manufacturing apparatus for manufacturing such a nitrided steel member. The present invention provides a nitrided steel member having a matrix of carbon steel or low-alloy steel, comprising a nitrided compound layer on the surface, and a hardened layer having an austenitic structure below the nitrided compound layer. A diffusion layer in which nitrogen is diffused in the matrix phase is provided under the hardened layer, and the nitride compound layer has a phase distribution in the order of ε phase, γ' phase, and ε phase. , 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 μm to 50 μm from the surface of the nitride steel member. It is a nitrided steel member. [Selection drawing] Fig. 1

Description

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

Among the surface hardening treatments for steel materials, there is a strong need for nitriding treatment, which is a low heat treatment strain treatment, and in recent years, there has been increasing interest in atmosphere control technology for gas nitriding treatment.

In the basic structure obtained by the gas nitriding treatment, a compound layer which is an iron nitride is formed on the surface, and a cured layer called a diffusion layer is formed inside. The cured layer is usually made of an alloy nitride as a base material component such as Si or Cr.

In order to control the thickness (depth) of each of these two layers and / or the type of iron nitride on the surface, in addition to the temperature and time of the gas nitriding treatment, the atmosphere in the gas nitriding treatment furnace is also It is controlled appropriately. Specifically, the nitriding potential (K _N ) in the gas nitriding furnace is appropriately controlled.

Then, through the control, the volume fraction (type of iron nitride) of the γ'phase (Fe ₄ N) and the ε phase (Fe _2-3 N) in the compound layer generated on the surface of the steel material is controlled. Has been done.

For example, it is known that fatigue resistance is improved by forming a γ'phase rather than an ε phase (Non-Patent Document 1).

Further, a nitrided steel member having improved bending fatigue strength and surface fatigue by forming a γ'phase is also provided (Patent Document 1).

Alternatively, it has been reported that the wear resistance of the present invention can be improved by increasing the number of ε phases (Non-Patent Document 2). As a nitriding method for forming a compound layer containing a large amount of ε phase on the surface, a soft nitriding treatment carried out by mixing a small amount of carburizing gas with an ammonia atmosphere is known.

On the other hand, when the nitriding treatment is performed at a temperature equal to or 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 rapidly cooled thereafter, a nitrogen-containing martensite structure is formed under the compound layer. A hardened layer containing the above is formed. The nitriding treatment in the temperature range is called nitriding treatment (Austentic Nitriding) in distinction from the conventional nitriding treatment.

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

For example, STKM-13C (mechanical structure carbon steel pipe specified in JIS G 3445) is soaked at 640 ° C. for 90 min, further soaked at 660 ° C. for 40 min, then rapidly cooled, and then reheated at 280 ° C. for 90 min. By the treatment, the austenite near the surface is cured to 800 to 900 HV.

Further, even if JIS-SPCC (a type of cold-rolled steel sheet) is subjected to a nitrogen immersion treatment at 700 ° C., a compound layer is formed on the surface, and a cured layer of a nitrogen martensite structure is formed under the compound layer by subsequent quenching. (Non-Patent Document 3). It is reported that the compound layer on the surface at this time is the ε phase.

Japanese Unexamined Patent Publication No. 2013-221203 Japanese Unexamined Patent Publication No. 2014-25161 Yasushi Hiraoka, Yoichi Watanabe, Akitake Ishida: Heat Treatment, Vol. 55, No. 1, pp. 1-2 Dataly Toke et al .: Nitriding and soft nitriding of iron, Agne Technology Center, 2013, p. 84 Kazuyoshi Kawada, Toru Kidate: Japan Heat Treatment Technology Association, 81st Spring Lecture Meeting Summary, pp. 29-30

The friction loss in mechanical parts such as camshafts, piston rings, crankshafts, etc. inside engines for automobiles is as much as 10% or more. Surface treatment such as nitriding treatment has already been applied to some mechanical parts, but further reduction in friction loss is desired.

As one measure for reducing the wear loss of the steel part, it is conceivable to increase the "hardness" of the steel part. As described above, it is known that the hardness of the surface compound layer can be increased by performing the nitriding treatment and the reheating treatment after quenching.

However, in the treatment disclosed in Non-Patent Document 3, since the nitriding temperature is 700 ° C., which is relatively high, there is a concern that the hardness of the base material and the diffusion layer may decrease.

Further, a reproduction experiment was attempted for the treatment disclosed in Patent Document 2, and a cured structure as described in the document (specifically, a mixed phase in which an α "phase is precipitated in the γ'phase) is reproduced. It was not possible (it is presumed that there was some error in the description of the document).

On the other hand, the compound layer formed by the soft nitriding treatment has insufficient surface hardness (see the comparative example of FIG. 11 described later) and insufficient wear resistance (see the comparative example of Table 1 described later).

The present inventor repeated diligent studies and various experiments, and by controlling the temperature and nitriding potential of the nitriding process with high accuracy while limiting the configuration of the processing furnace, the wear resistance was maintained while maintaining sufficient hardness. It was found that it is possible to manufacture an improved nitrided steel member.

The present invention has been devised based on the above findings. An object of the present invention is to provide a nitrided 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.

The present invention is a nitrided steel member having a carbon steel or a low alloy steel as a matrix, and has a nitrided compound layer on the surface and a cured layer having an austenite structure below the nitrided compound layer. A diffusion layer in which nitrogen is diffused in the matrix is provided at the bottom of the layer, and the nitrided compound layer has a phase distribution in the order of ε phase, γ'phase, and ε phase, and the nitrided compound. The volume ratio of the γ'phase in the layer is 20% or more, and the nitrided compound layer is a nitrided steel member having a thickness of 5 μm to 50 μm from the surface of the nitrided steel member. be.

According to the present invention, the surface nitrided compound layer has a phase distribution in the order of ε phase, γ'phase, and ε phase, and has a thickness of 5 μm to 50 μm, and the γ'phase in the nitrided compound layer. By having a volume ratio of 20% or more (such a configuration is realized for the first time by the nitriding method described later), the wear resistance is improved while providing sufficient hardness as a nitrided steel member. can do.

The upper limit of the thickness of the nitrided compound layer is 50 μm because the value is the maximum thickness confirmed by the present inventor by the time of filing the application of the present application (using the circulation type processing furnace described later). It has been confirmed that it can be obtained by adopting the immersion treatment conditions of a treatment temperature of 640 ° C., a nitriding potential of 0.6, and a treatment time of 2 hours using S50C steel as a parent phase).

Further, regarding the thickness of the nitrided compound layer, 5 μm is set as a lower limit as a condition for the nitrided compound layer to be formed on the entire surface of the nitrided steel member (the nitrided compound layer may not be locally formed).

Further, the present invention is a nitrided steel member having a carbon steel or a low alloy steel as a matrix, the surface of which is provided with a nitrided compound layer, and the lower portion of the nitrided compound layer is provided with a cured layer having an austenite structure. A diffusion layer in which nitrogen is diffused in the matrix is provided below the cured layer, and the nitrided compound layer has a phase distribution in the order of γ'phase and ε phase, and the nitrided compound layer has a phase distribution in that order. The volume ratio of the γ'phase in the γ'phase is 30% or more, and the nitrided compound layer is a nitrided steel member having a thickness of 5 μm to 30 μm from the surface of the nitrided steel member. ..

According to the present invention, the surface nitrided compound layer has a phase distribution in the order of γ'phase and ε phase, and has a thickness of 5 μm to 30 μm, and the volume ratio of the γ'phase in the nitrided compound layer. Is 30% or more (such a configuration is first realized by the nitriding method described later), so that it is possible to improve wear resistance while providing sufficient hardness as a nitrided steel member. can.

Also in the present invention, the upper limit of the thickness of the nitrided compound layer is 30 μm, because that value is the maximum thickness confirmed by the present inventor by the time of filing the application of the present application (circulation described later). It has been confirmed that it can be obtained by adopting the immersion treatment conditions of a treatment temperature: 650 ° C., a nitriding potential: 0.2, and a treatment time: 2 hours using S15C as a parent phase using a mold treatment furnace. ).

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

In each of the above inventions, for example, carbon steel having a carbon content of 0.1% or more 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 manufacturing a nitriding steel member having carbon steel or low alloy steel as a matrix phase by using a circulation type processing furnace equipped with a guide cylinder and a stirring fan, and at the time of nitriding treatment, the present invention is performed. The temperature range in the circulation type processing furnace is controlled to 610 ° C. to 660 ° C., and the nitriding potential in the circulation type processing furnace is controlled to the range of 0.15 to 0.6 at the time of the nitriding treatment. It is a method for manufacturing a nitrided steel member, which is characterized in that after the nitriding treatment, it is rapidly cooled and then reheated.

According to the method for manufacturing a nitrided steel member of the present invention,
A nitrided steel member having a base phase of carbon steel or low alloy steel, the surface of which is provided with a nitrided compound layer, the lower part of the nitrided compound layer is provided with a hardened layer having an austenite structure, and the lower part of the hardened layer is provided with a hardened layer. The nitrided compound layer has a phase distribution in the order of ε phase, γ'phase, and ε phase, and has a diffusion layer in which nitrogen is diffused in the matrix phase. 'It is possible to manufacture a nitrided steel member characterized in that the volume ratio of the phase is 20% or more and the nitrided compound layer has a thickness of 5 μm to 50 μm from the surface of the nitrided steel member. can.

Alternatively, according to the method for manufacturing a nitrided steel member of the present invention,
A nitrided steel member having a base phase of carbon steel or low alloy steel, the surface of which is provided with a nitrided compound layer, the lower part of the nitrided compound layer is provided with a hardened layer having an austenite structure, and the lower part of the hardened layer is provided with a hardened layer. The nitride compound layer has a phase distribution in the order of γ'phase and ε phase, and has a diffusion layer in which nitrogen is diffused in the mother phase. The volume ratio is 30% or more, and the nitrided steel member can be produced, characterized in that the nitrided compound layer has a thickness of 5 μm to 30 μm from the surface of the nitrided steel member.

The present invention can also be recognized as a manufacturing apparatus for nitrided steel members. That is, the present invention includes a circulation type processing furnace having a guide cylinder and a stirring fan, and the temperature range in the circulation type processing furnace is controlled to 610 ° C. to 660 ° C. during the nitriding process, and the nitriding process is performed. In the nitriding steel member manufacturing apparatus in which ammonia gas and ammonia decomposition gas are introduced into the circulation type processing furnace in order to control the nitriding potential in the circulation type processing furnace. The nitriding potential in the circulation type processing furnace is a target in the range of 0.15 to 0.6 by keeping the amount of the ammonia decomposition gas introduced into the furnace constant and changing the amount of the ammonia gas introduced into the furnace. It is a nitriding steel member manufacturing apparatus characterized in that it is controlled by the nitriding potential.

According to the nitrided steel member manufacturing apparatus of the present invention,
A nitrided steel member having a base phase of carbon steel or low alloy steel, the surface of which is provided with a nitrided compound layer, the lower part of the nitrided compound layer is provided with a hardened layer having an austenite structure, and the lower part of the hardened layer is provided with a hardened layer. The nitrided compound layer has a phase distribution in the order of ε phase, γ'phase, and ε phase, and has a diffusion layer in which nitrogen is diffused in the matrix phase. 'It is possible to manufacture a nitrided steel member characterized in that the volume ratio of the phase is 20% or more and the nitrided compound layer has a thickness of 5 μm to 50 μm from the surface of the nitrided steel member. can.

Alternatively, according to the apparatus for manufacturing a nitrided steel member of the present invention,
A nitrided steel member having a base phase of carbon steel or low alloy steel, the surface of which is provided with a nitrided compound layer, the lower part of the nitrided compound layer is provided with a hardened layer having an austenite structure, and the lower part of the hardened layer is provided with a hardened layer. The nitride compound layer has a phase distribution in the order of γ'phase and ε phase, and has a diffusion layer in which nitrogen is diffused in the mother phase. The volume ratio is 30% or more, and the nitrided steel member can be produced, characterized in that the nitrided compound layer has a thickness of 5 μm to 30 μm from the surface of the nitrided steel member.

According to the nitrided steel member of the present invention, wear resistance can be improved while providing sufficient hardness as the nitrided steel member.

Further, according to the method for manufacturing a nitrided steel member of the present invention, it is possible to manufacture a nitrided steel member having sufficient hardness and wear resistance.

Further, according to the apparatus for manufacturing a nitrided steel member of the present invention, it is possible to manufacture a nitrided steel member having sufficient hardness and wear resistance.

It is a cross-sectional micrograph of a nitrided steel member according to 1st Embodiment of this invention. It is a figure which shows the analysis result by the EBSD method of the nitrided steel member of FIG. It is a cross-sectional micrograph of the state before the reheating treatment of the nitrided steel member of the 1st Embodiment of this invention. It is a figure which shows the analysis result by the EBSD method of the nitrided steel member of FIG. It is a cross-sectional micrograph of a nitrided steel member according to the 2nd Embodiment of this invention. It is a figure which shows the analysis result by the EBSD method of the nitrided steel member of FIG. It is a cross-sectional micrograph of the state before the reheating treatment of the nitrided steel member of the 2nd Embodiment of this invention. It is a figure which shows the analysis result by the EBSD method of the nitrided steel member of FIG. It is a cross-sectional micrograph of a nitrided steel member as a comparative example. It is a figure which shows the analysis result by the EBSD method of the nitrided steel member of FIG. It is a graph which shows the measurement result of hardness. It is the schematic of the manufacturing apparatus of the nitrided steel member by one Embodiment of this invention. It is a schematic sectional drawing of a circulation type processing furnace (horizontal gas nitriding furnace). It is a graph which shows an example of a gas introduction control. It is a perspective view of the test piece used for the friction wear test. It is a perspective view of the SRV tester used for the friction wear test.

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

(Construction, manufacturing method and effect of the first embodiment of the nitrided steel member)
FIG. 1 is a cross-sectional micrograph of the nitrided steel member 110 according to the first embodiment of the present invention. As shown in FIG. 1, the nitrided steel member 110 of the present embodiment has a nitrided compound layer 111 formed on the surface thereof, and a cured layer 112 having an austenite structure as described later below the nitrided compound layer 111. A diffusion layer 113 in which nitrogen is diffused in the matrix is provided below the cured layer 112. The matrix (base material) of the present embodiment is carbon steel having a carbon content of 0.45% by mass.

In FIG. 1, the lower part of the nitrided compound layer 111 and the cured layer 112 appear black because they are strongly corroded by the corrosive liquid for observing the structure. Further above the surface is a polishing plate, not a component of the nitrided steel member.

The phase distribution of the nitrided steel member 110 can be analyzed by using the EBSD method and X-ray diffraction in combination. Specifically, as shown in FIG. 2, the EBSD method reveals the phase distribution in the order of ε phase, γ'phase (fcc crystal phase), and ε phase from the surface side. Then, by using X-ray diffraction together, it is confirmed that the fcc crystal phase of the cured layer 112 is the austenite phase (γ phase).

The nitrided compound layer 111 has a thickness of about 30 μm from the surface of the nitrided steel member 110, which is in the range of 5 μm to 50 μm. The surface ε phase is several μm thick.

Further, the volume ratio of the γ'phase in the nitride compound layer 111 is measured based on the count number of the γ'phase and the ε phase in the analysis range by the SEM / EBSD method (width of the nitride compound layer 111 is about 120 μm). obtain. Alternatively, it may be calculated by image analysis from the obtained image of FIG. In the case of the nitride compound layer 111 of this embodiment, it is 41%.

The cured layer 112 was expected to be transformed into a martensite structure by reheating treatment, but when the inventor applied the crystal structure analysis by the X-ray diffraction method as described above, most of the cured layer 112 was formed. Was the result of the austenite phase (γ phase). Therefore, the inventor of the present invention considers that the cured layer 112 is, strictly speaking, a mixed structure of austenite and martensite. However, depending on the size of the steel material after the soaking treatment, cooling conditions, and reheating conditions, the possibility of containing a plurality of types of microstructures such as bainite structure and blaublitz structure cannot be ruled out.

The nitrided steel member 110 of the present embodiment is subjected to nitriding treatment under the treatment conditions of a treatment temperature: 640 ° C., a nitriding potential: 0.4, and a treatment time: 2 hours using a circulation type treatment furnace described later. It can be produced by quenching and reheating under the treatment conditions of a treatment temperature of 250 ° C. and a treatment time of 2 hours.

The nitrided steel member 110 as described above can provide sufficient hardness for practical use because the volume ratio of the γ'phase in the nitrided compound layer 111 is 41% (20% or more) (FIG. 11 described later). 1-30 of Example 1-30), and the wear resistance is also improved (see Example 1-30 of Table 1 described later).

For reference, FIG. 3 shows a cross-sectional micrograph of the nitrided steel member 110 before the reheating treatment. Further, FIG. 4 is a diagram showing the analysis results of the nitrided steel member 160 of FIG. 3 by the EBSD method.

As shown in FIGS. 3 and 4, in the state before the reheat treatment, most of the region 161 corresponding to the nitrided compound layer 111 is the ε phase. Therefore, sufficient hardness cannot be obtained (see Reference Example 1 in FIG. 11 described later).

(Construction, manufacturing method and effect of the second embodiment of the nitrided steel member)
FIG. 5 is a cross-sectional micrograph 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 nitrided compound layer 121 formed on the surface thereof, and a cured layer 122 having an austenite structure as described later below the nitrided compound layer 121. A diffusion layer 123 in which nitrogen is diffused in the matrix is provided below the cured layer 122. The matrix (base material) 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 nitrided compound layer 121 and the cured layer 122 appear black because they are strongly corroded by the corrosive liquid for observing the structure. Further above the surface is a polishing plate, not a component of the nitrided steel member.

The phase distribution of the nitrided steel member 120 can be analyzed by using the EBSD method and X-ray diffraction in combination. Specifically, as shown in FIG. 6, the EBSD method reveals the phase distribution in the order of the γ'phase (fcc crystal phase) and the ε phase from the surface side. Then, by using X-ray diffraction together, it is confirmed that the fcc crystal phase of the cured layer 122 is the austenite phase (γ phase).

The nitrided compound layer 121 has a thickness of about 12 μm from the surface of the nitrided steel member 120, which is in the range of 5 μm to 30 μm. The γ'phase on the surface is several μm thick.

Further, the volume ratio of the γ'phase in the nitride compound layer 121 is measured based on the count number of the γ'phase and the ε phase in the analysis range by the SEM / EBSD method (width of the nitride compound layer 121 of about 120 μm). obtain. Alternatively, it may be calculated by image analysis from the obtained image of FIG. In the case of the nitride compound layer 121 of this embodiment, it is 52%.

The hardened layer 122 was expected to be transformed into a martensite structure by the reheat treatment, but the hardened layer 122 was found to be in the hardened layer 122 by the result of EBSD shown in FIG. 6 and the crystal structure analysis by the X-ray diffraction method as described above. It was confirmed that a large amount of austenite remained partially. However, depending on the size of the steel material after the soaking treatment, cooling conditions, and reheating conditions, the possibility of containing a plurality of types of microstructures such as bainite structure and blaublitz structure cannot be ruled out.

The nitrided steel member 120 of the present embodiment is subjected to nitriding treatment under the treatment conditions of a treatment temperature: 640 ° C., a nitriding potential: 0.2, and a treatment time: 2 hours using a circulation type treatment furnace described later. It can be produced by quenching and reheating under the treatment conditions of a treatment temperature of 250 ° C. and a treatment time of 2 hours.

The nitrided steel member 120 as described above can provide sufficient hardness for practical use because the volume ratio of the γ'phase in the nitrided compound layer 121 is 52% (30% or more) (FIG. 11 described later). 2-12 of Example 2-12), and the wear resistance is also improved (see Example 2-12 of Table 1 described later).

For reference, FIG. 7 shows a cross-sectional micrograph of the nitrided steel member 120 before the reheating treatment. Further, FIG. 8 is a diagram showing the analysis results of the nitrided steel member 170 of FIG. 7 by the EBSD method.

As shown in FIGS. 7 and 8, in the state before the reheat treatment, most of the region 171 corresponding to the nitrided compound layer 121 is the ε phase. Therefore, sufficient hardness cannot be obtained.

(Comparative example of nitrided steel member)
FIG. 9 is a cross-sectional micrograph of the nitrided steel member 300 of the comparative example. As shown in FIG. 9, the nitrided steel member 300 of the comparative example has a nitrided compound layer 301 formed on the surface thereof, and a diffusion layer in which nitrogen is diffused in the matrix below the nitrided compound layer 301. It is equipped with 303. The matrix (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. In FIG. 9, the upper part of the nitrided compound layer 301 looks black because a large number of fine voids are present in this region. Further above the surface is a polishing plate, not a component of the nitrided steel member.

The phase distribution of the nitrided steel member 300 can also be analyzed by using the EBSD method and X-ray diffraction in combination. Specifically, as shown in FIG. 10, it can be seen by the EBSD method that most of the nitrided compound layer 301 is in the ε phase.

The nitrided compound layer 301 has a thickness of about 17 μm from the surface of the nitrided steel member 300.

The nitrided steel member 300 of the comparative example was subjected to soft nitriding treatment using a circulation type treatment furnace described later under the treatment conditions of a treatment temperature of 580 ° C., a nitriding potential of 2.5, and a treatment time of 2 hours (atmosphere). The gas can be produced by quenching (ammonia, nitrogen gas and carbon dioxide gas). It has been confirmed that the nitrided compound layer 301 of the comparative example does not cure even after being reheated (it is considered that the temperature during the soft nitriding treatment is relatively low).

In the nitrided steel member 300 as described above, most of the nitrided compound layer 301 has an ε phase, and conventionally, this hard ε phase has been used to improve wear resistance. However, the surface hardness is insufficient as compared with the ε compound layer obtained by the soaking treatment of the present invention (see the comparative example of FIG. 11 described later), which adversely affects the wear resistance and wear resistance. Is also insufficient (see the comparative example in Table 1 below).

Further, it is pointed out that the nitrided steel member 300 of the comparative example has a drawback that many voids (looks black in FIG. 9) are formed on the surface side of the nitrided compound layer 301. The presence of the void (porous) is not preferable because it can be a starting point for crack generation.

(Evaluation of hardness)
FIG. 11 is a graph showing the measurement result of hardness. The nitrided steel member 110 of the first embodiment (Example 1-30), the nitrided steel member 120 of the second embodiment (Example 2-12), the nitrided steel member 160 of the reference example (Reference Example 1-30), and , The result of measuring the hardness at a predetermined depth from the surface of each of the nitrided steel members 300 of the comparative example is plotted.

In the nitrided steel member 110 (Example 1-30) of the first embodiment, a high hardness of 1000 HV or more is obtained over the entire thickness (30 μm) of the nitrided compound layer 111. In particular, the hardness of the portion corresponding to the ε phase on the core side is increased.

On the other hand, in the nitrided steel member 160 (Reference Example 1-30) of the reference example, the hardness near the surface is slightly less than 800 HV, which is not sufficient.

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.

In addition, in the nitrided steel member 300 of the comparative example, the hardness near the surface is about 600 HV, which is not sufficient.

(Thickness of the nitrided compound layer 111 of the nitrided steel member 110 of the first embodiment)
It can be said that the thickness of the nitrided compound layer 111 of the nitrided steel member 110 of the first embodiment is generally preferable because the thicker the thickness is, the larger the wear tolerance is.

The inventor of the present invention has confirmed that the nitrided compound layer 111 tends to be thick when the carbon steel generally used for shafts has a large amount of carbon (specifically, for example, S50C steel). Then, specifically, the S50C steel was soaked at a treatment temperature of 640 ° C., a nitriding potential of 0.6, and a treatment time of 2 hours, and rapidly cooled to a treatment temperature of 250 ° C. and a treatment time of 2 hours. When reheated, the thickness of the nitrided compound layer 111 was 50 μm (see Example 1-50 in Table 1 below). Therefore, the maximum thickness of the nitrided compound layer 111 that can be recognized by those skilled in the art as being able to solve the problem of the present invention is set to 50 μm.

In addition, the inventor of the present invention has confirmed that the thickness of the nitride compound layer 111 tends to increase when the nitriding potential during the nitriding treatment is high.

(Thickness of the nitrided compound layer 121 of the nitrided steel member 120 of the second embodiment)
It can be said that it is generally preferable that the thickness of the nitrided compound layer 121 of the nitrided steel member 120 of the second embodiment is thicker because the wear tolerance is larger.

The inventor of the present invention has confirmed that the nitrided compound layer 121 tends to become thicker when the carbon content is low (specifically, for example, S15C steel) in carbon steel generally used for gears. Then, specifically, the S15C steel was soaked at a treatment temperature of 650 ° C., a nitriding potential of 0.2, and a treatment time of 2 hours, and rapidly cooled to a treatment temperature of 250 ° C. and a treatment time of 2 hours. When reheated, the thickness of the nitrided compound layer 121 was 30 μm (see Example 2-30 in Table 1 below). Therefore, the maximum thickness of the nitrided compound layer 111 that can be recognized by those skilled in the art as being able to solve the problem of the present invention is set to 30 μm.

In addition, the inventor of the present invention has confirmed that the thickness of the nitride compound layer 121 also tends to increase when the nitriding potential during the nitriding treatment is high.

(Volume ratio of γ'phase in the nitrided compound layer 111 of the nitrided steel member 110 of the first embodiment)
The inventor of the present invention has confirmed that a larger volume ratio of the γ'phase in the nitride compound layer 111 is preferable for increasing the hardness. Specifically, for the minimum value, S50C steel was subjected to nitriding treatment at a treatment temperature: 640 ° C., nitriding potential: 0.6, treatment time: 2 hours, and rapidly cooled, and the treatment temperature: 250 ° C., treatment time: When reheated for 2 hours, the volume ratio of the γ'phase in the nitride compound layer 111 was 20% (see Example 1-50 in Table 1 below). Therefore, the minimum value of the volume ratio of the γ'phase in the nitrided compound layer 111 which can be recognized by those skilled in the art as being able to solve the problem of the present invention is set to 20%.

(Volume ratio of γ'phase in the nitrided compound layer 121 of the nitrided steel member 120 of the second embodiment)
The inventor of the present invention has confirmed that a larger volume ratio of the γ'phase in the nitride compound layer 121 is also preferable for increasing the hardness. Specifically, for the minimum value, S15C steel was subjected to nitriding treatment at a treatment temperature: 650 ° C., nitriding potential: 0.2, treatment time: 2 hours, and rapidly cooled, and the treatment temperature: 250 ° C., treatment time: When reheated for 2 hours, the volume ratio of the γ'phase in the nitride compound layer 121 was 30% (see Example 2-30 in Table 1 below). Therefore, the minimum value of the volume ratio of the γ'phase in the nitrided compound layer 121, which can be recognized by those skilled in the art as being able to solve the problem of the present invention, is set to 30%.

(Structure of manufacturing equipment for nitrided steel members)
Subsequently, a manufacturing apparatus for the nitrided steel member will be described. First, if the basic matters of the gas nitriding treatment are chemically explained, in the gas nitriding treatment, the nitriding represented by the following formula (1) is performed in the processing furnace (gas nitriding furnace) in which the object to be treated is arranged. A reaction occurs.
NH ₃ → [N] + 3 / 2H ₂・ ・ ・ (1)

At this time, the nitriding potential K _N is defined by the following equation (2).
K _N = P _NH3 / P _H2 ^3/2・ ・ ・ (2)
Here, P _{NH 3} is the partial pressure of ammonia in the furnace, and P _{H 2} is the partial pressure of hydrogen in the furnace. The nitriding potential K _N is well 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 the formula (3).
NH ₃ → 1 / 2N ₂ + 3 / 2H ₂・ ・ ・ (3)

In the furnace, the reaction of the formula (3) mainly occurs, and the nitriding reaction of the formula (1) can be almost ignored quantitatively. Therefore, if the concentration of ammonia in the furnace consumed in the reaction of the formula (3) or the concentration of the hydrogen gas generated in the reaction of the formula (3) is known, the nitriding potential can be calculated. That is, since the generated hydrogen and nitrogen are 1.5 mol and 0.5 mol, respectively, from 1 mol of ammonia, the hydrogen concentration in the furnace can be known by measuring the ammonia concentration in the furnace, and the nitriding potential can be calculated. Can be done. 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.

The ammonia gas flowing 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, fresh (new) ammonia gas is continuously inflowed into the furnace with respect to the existing gas in the furnace, so that the existing gas is continuously discharged to the outside of the furnace (extruded by the supply pressure). ..

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 ammonia gas decomposed increases and the nitrogen gas generated by the decomposition reaction is generated. + The amount of hydrogen gas increases. On the other hand, if the flow rate of ammonia gas introduced into the furnace is large, the amount of ammonia gas discharged to the outside of the furnace without being decomposed increases, and the amount of nitrogen gas + hydrogen gas generated in the furnace decreases. do.

By the way, FIG. 12 is a schematic view 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 includes a circulation type processing furnace 2, and uses only two types of gases, ammonia and ammonia decomposition gas, as the gas to be introduced into the circulation type processing furnace 2. ing. The ammonia decomposition gas is a gas also called AX gas, which is a mixed gas composed 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. Only three types of nitrogen gas can be selected.

An example of the cross-sectional structure of the circulation type processing furnace 2 is shown in FIG. In FIG. 13, a cylinder 202 called a retort is arranged in the furnace wall (also called a bell) 201, and a cylinder 204 called an internal retort is further arranged inside the cylinder 202. As shown by the arrow in the figure, the introduced gas supplied from the gas introduction pipe 205 passes around the object to be treated and then passes through the space between the two cylinders 202 and 204 by the action of the stirring fan 203. And circulate. Reference numeral 206 is a flared gas hood, reference numeral 207 is a thermocouple, reference numeral 208 is a lid for cooling work, and reference numeral 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 product S to be treated 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 detecting device 3. , A nitride potential adjuster 4, a programmable logic controller 30, and an in-core introduction 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 that can detect the hydrogen concentration or the ammonia concentration in the processing furnace 2 as the atmosphere gas concentration in the furnace. The detection main body of the sensor communicates with the inside of the processing furnace 2 via the atmospheric gas pipe 12. In the present embodiment, the atmosphere gas pipe 12 is formed by a path that directly connects the sensor main body of the atmosphere gas concentration detection device 3 and the processing furnace 2, and is connected to the exhaust gas combustion decomposition device 41 on the way. 40 is connected. As a result, the atmospheric gas is distributed into the discarded gas and the gas supplied to the atmospheric gas concentration detecting device 3.

Further, the atmosphere gas concentration detecting device 3 detects the atmosphere gas concentration in the furnace, and then outputs an information signal including the detected concentration to the nitride potential regulator 4.

The nitriding potential regulator 4 includes an in-core nitriding potential arithmetic unit 13 and a gas flow rate output adjusting device 30. Further, the programmable logic controller 31 has a gas introduction amount control device 14 and a parameter setting device 15.

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

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

Then, the gas flow rate output adjusting device 30 sets the nitriding potential calculated by the in-core nitriding potential calculation device 13 as the output value, sets the target nitriding potential (set nitriding potential) as the target value, and sets the ammonia gas and the ammonia decomposition gas. Control is carried out with each introduction amount as an input value. More specifically, it is possible to control the amount of ammonia gas to be introduced into the furnace to be constant and the amount of ammonia gas to be introduced into the furnace to be changed. The output value of the gas flow rate output adjusting device 30 is transmitted to the gas introduction amount control device 14.

The gas introduction amount control device 14 sends a control signal to the first supply amount control device 22 for ammonia gas and the second supply amount control device 26 for ammonia decomposition gas, respectively, in order to realize the introduction amount of each gas. It has become.

The in-firer introduction gas supply unit 20 of the present embodiment includes a first in-firet introduction gas supply unit 21 for ammonia gas, a first supply amount control device 22, a first supply valve 23, and a first flow meter 24. ,have. Further, the in-firer introduction gas supply unit 20 of the present embodiment includes a second in-core introduction gas supply unit 25 for ammonia decomposition gas (AX gas), a second supply amount control device 26, and a second supply valve 27. , A second flow meter 28.

In the present embodiment, the ammonia gas and the ammonia decomposition gas are mixed in the furnace introduction gas introduction pipe 29 before entering the processing furnace 2.

The first furnace introduction gas supply unit 21 is formed of, for example, a tank filled with the first furnace introduction gas (ammonia gas in this example).

The first supply amount control device 22 is formed by a mass flow controller, and is interposed between the first furnace introduction gas supply unit 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 furnace introduction gas supply unit 21 to the first supply valve 23, and sends an information signal including the detected supply amount to the gas introduction amount control device 14. It is designed to output to. The control signal can be used for correction of control by the gas introduction amount control device 14.

The first supply valve 23 is formed by an electromagnetic valve that switches an open / closed state according to a control signal output by the gas introduction amount control device 14, and is formed between the first supply amount control device 22 and the first flow meter 24. Being intervened.

The second furnace introduction gas supply unit 25 is formed of, for example, a tank filled with the second furnace introduction gas (ammonia decomposition gas in this example).

The second supply amount control device 26 is formed by a mass flow controller, and is interposed between the second furnace introduction gas supply unit 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 furnace introduction gas supply unit 25 to the second supply valve 27, and sends an information signal including the detected supply amount to the gas introduction amount control device 14. It is designed to output to. The control signal can be used for correction of control by the gas introduction amount control device 14.

The second supply valve 27 is formed by an electromagnetic valve that switches the open / closed state according to the control signal output by the gas introduction amount control device 14, and is formed between the second supply amount control device 26 and the second flow meter 28. Being intervened.

(Operation of manufacturing equipment for nitrided steel members (manufacturing method))
Next, the operation of the manufacturing apparatus 1 of the present embodiment will be described. First, the product S to be processed 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, only the mixed gas of ammonia gas and the ammonia decomposition gas or only the ammonia gas is introduced into the processing furnace 2 from the furnace introduction gas supply unit 20 at the 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 22 and the second supply amount control device 26 (both are 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.

The in-core nitriding potential calculation device 13 of the nitriding potential regulator 4 calculates the nitriding potential in the furnace (at first, the value is extremely high (because there is no hydrogen in the furnace), but the decomposition of ammonia gas (hydrogen generation)). Decreases as it progresses), and it is determined whether or not the sum of the target nitriding potential and the reference deviation value has been exceeded. This reference deviation value can also be set and input in the parameter setting device 15.

When it is determined that the calculated value of the nitriding potential in the furnace is less than the sum of the target nitriding potential and the reference deviation value, the nitriding potential regulator 4 introduces the gas introduced into the furnace via the gas introduction amount control device 14. Starts control of.

The in-core nitriding potential calculation device 13 of the nitriding potential regulator 4 calculates the in-core 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-core nitriding potential calculation device 13 as the output value, sets the target nitriding potential (set nitriding potential) as the target value, and introduces the gas into the furnace. PID control is performed with the input value of. Specifically, in the PID control, control is performed so 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. In the PID control, each setting parameter value set and input by the parameter setting device 15 is used. As the setting parameter value, for example, different values are prepared depending on the value of the target nitriding potential.

Then, the gas flow rate output adjusting device 30 controls the amount of each introduced gas in the furnace as a result of the PID 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.

The gas introduction amount control device 14 sends a control signal to the first supply amount control device 22 for ammonia gas and the second supply amount control device 26 for ammonia decomposition gas, respectively, in order to realize the introduction amount of each gas.

With the above control, the nitriding potential in the furnace can be stably controlled in the vicinity of the target nitriding potential. As a result, the soaking treatment of the product S to be treated can be performed with extremely high quality.

An example of the above control is shown in FIG. The amount of ammonia decomposition gas introduced into the furnace is constant, and the amount of ammonia gas introduced into the furnace is feedback-controlled in small steps in the vicinity of 40 (l / min). As a result, the nitriding potential is controlled to 0.17 with high accuracy.

Further, depending on the material type and shape of the product S to be treated, it is possible to carry out a cooling step after the soaking treatment in the manufacturing apparatus 1. However, if sufficient hardness cannot be obtained after the treatment at the cooling rate of the manufacturing apparatus 1, the product S to be treated is placed outside the furnace while maintaining the heating temperature after the immersion treatment in the manufacturing apparatus 1. It is necessary to transport it to a quenching device (for example, an oil tank) and then quench it. Alternatively, it is necessary to take out the product S to be processed after being cooled 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 device, and then quench the product S.

According to the study of the present inventor, the austenite structure stabilized with 1.0% or more nitrogen becomes brownite (layered structure of ferrite phase and γ'phase) when the cooling rate is slow, and the hardness and fatigue strength decrease. There is a concern that it will lead to. Therefore, when gas cooling or air cooling is adopted, it is important to optimize the cooling rate for each component. On the other hand, when oil cooling is adopted, it is sufficiently possible to retain the austenite structure if it is a general component.

(About the importance of the guide tube (internal retort))
Further, according to the experiment of the present inventor, when the guide tube 5 (internal retort) is removed from the manufacturing apparatus 1 and the nitriding treatment is performed, the uniformity of the nitriding potential in the furnace is lowered and the uniformity of the treatment is reduced. Was confirmed to decrease.

(Verification of hardness and fatigue strength)
A friction and wear tester as shown in FIG. 16 (test piece) having a shape (φ25 × 8 mm size) as shown in FIG. 15 is treated under each condition shown in Table 1 to be described later. Abrasion resistance was evaluated using a vibration friction wear tester SRV4) manufactured by Optimole, Germany.

As a slider, a ball of φ10 silicon nitride (hardness: about 1600 HV) is used, and it reciprocates under dry conditions (room temperature 25 ° C., humidity 30%, no lubricating oil) while applying a load of 10 N. Sliding was repeated (amplitude 1 mm, 50 Hz, 10 minutes), and the maximum amount of wear (measured in a cross section perpendicular to the sliding direction) was measured.

In FIG. 16, 401 is an oscillation block head plate, 402a is a twist sensor, 402b is a test piece fixative, 403a is an upper test piece holder, and 404 is a vertical load axis. be.

(Example 1-30)
Examples 1-30 in Table 1 correspond to the nitrided steel member 110 of the first embodiment described with reference to FIGS. 1 and 2. Example 1-30 is subjected to nitriding treatment using the above-mentioned circulation type treatment furnace 2 under the treatment conditions of a treatment temperature: 640 ° C., a nitriding potential: 0.4, and a treatment time: 2 hours, and then quenched. Then, it was manufactured by reheating under the treatment conditions of a treatment temperature of 250 ° C. and a treatment time of 2 hours (the parent phase is S45C steel).

The phase distribution of the nitrided compound layer is in the order of ε phase, γ'phase, and ε phase, and the thickness of the nitrided compound layer is about 30 μm from the surface of the nitrided steel member. The volume ratio was 41%.

Such a nitrided steel member of Example 1-30 provides a sufficient hardness distribution as shown by the black triangulation points in FIG. 11 and has a low maximum wear amount (sufficient) as shown in Table 1. It has been confirmed that it provides excellent friction and wear characteristics).

(Example 1-36)
Example 1-36 is a nitrided steel member manufactured by changing the nitriding potential at the time of nitriding treatment to 0.5 with respect to Example 1-30.

The phase distribution of the nitrided compound layer is in the order of ε phase, γ'phase, and ε phase, and the thickness of the nitrided compound layer is about 36 μm from the surface of the nitrided steel member. The volume ratio was 33%.

Such a nitrided steel member of Example 1-36 also provides a sufficient hardness distribution as shown by the black triangulation points in FIG. 11, and has a low maximum wear amount as shown in Table 1. It was confirmed that it provides sufficient friction and wear characteristics).

(Example 1-40)
Example 1-40 is a nitrided steel member manufactured by changing the nitriding potential at the time of nitriding treatment to 0.6 with respect to Example 1-30.

The phase distribution of the nitrided compound layer is in the order of ε phase, γ'phase, and ε phase, and the thickness of the nitrided compound layer is about 40 μm from the surface of the nitrided steel member. The volume ratio was 24%.

Such a nitrided steel member of Example 1-40 also provides a sufficient hardness distribution as shown by the black triangulation points in FIG. 11, and has a low maximum wear amount as shown in Table 1. It was confirmed that it provides sufficient friction and wear characteristics).

(Example 1-50)
Example 1-50 is a nitrided steel member manufactured by changing the matrix phase to S50C steel and further changing the nitriding potential at the time of nitriding treatment to 0.6 with respect to Example 1-30. ..

The phase distribution of the nitrided compound layer is in the order of ε phase, γ'phase, and ε phase, and the thickness of the nitrided compound layer is about 50 μm from the surface of the nitrided steel member. The volume ratio was 20%.

Such a nitrided steel member of Example 1-50 also provides a sufficient hardness distribution as shown by the black triangulation points in FIG. 11, and has a low maximum wear amount as shown in Table 1. It was confirmed that it provides sufficient friction and wear characteristics).

(Example 1-15)
Example 1-15 is a nitriding steel member manufactured by changing the nitriding temperature at the time of nitriding treatment to 620 ° C. with respect to Example 1-30.

The phase distribution of the nitrided compound layer is in the order of γ'phase and ε'phase, the thickness of the nitrided compound layer is about 15 μm from the surface of the nitrided steel member, and the volume ratio of the γ'phase in the nitrided compound layer is. , 37%.

Such a nitrided steel member of Example 1-15 also provides a sufficient hardness distribution as shown by the white circles in FIG. 11, and has a low maximum wear amount (sufficient) as shown in Table 1. It has been confirmed that it provides excellent friction and wear characteristics).

(Reference Example 1-30, Reference Example 1-36, Reference Example 1-40)
For Examples 1-30, 1-36, and 1-40, the states before the reheat treatment are referred to as Reference Example 1-30, Reference Example 1-36, and Reference Example 1-40, respectively, in terms of hardness and maximum. The amount of wear was evaluated.

As a result, it was found that the hardness was an insufficient hardness distribution as shown by the white triangulation points in FIG. 11, and the frictional wear characteristics were also relatively high maximum wear amount as shown in Table 1. Met.

(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. Example 2-12 was subjected to nitriding treatment using the above-mentioned circulation type treatment furnace 2 under the treatment conditions of a treatment temperature of 640 ° C., a nitriding potential of 0.2, and a treatment time of 2 hours, and then rapidly cooled. Then, it was manufactured by reheating under the treatment conditions of a treatment temperature of 250 ° C. and a treatment time of 2 hours (the parent phase is S45C steel).

The phase distribution of the nitrided compound layer is in the order of γ'phase and ε phase, the thickness of the nitrided compound layer is about 12 μm from the surface of the nitrided steel member, and the volume ratio of the γ'phase in the nitrided compound layer is. , 52%.

Such a nitrided steel member of Example 2-12 provides a sufficient hardness distribution as shown by the white circles in FIG. 11 and has a low maximum wear amount (sufficient) as shown in Table 1. It was confirmed to provide frictional wear characteristics).

(Example 2-7)
Example 2-7 is a nitrided steel member manufactured by changing the nitriding potential at the time of nitriding treatment to 0.18 with respect to Example 2-12.

The phase distribution of the nitrided compound layer is in the order of γ'phase and ε phase, the thickness of the nitrided compound layer is about 7 μm from the surface of the nitrided steel member, and the volume ratio of the γ'phase in the nitrided compound layer is. , 60%.

Such a nitrided steel member of Example 2-7 also provides a sufficient hardness distribution as shown by the white circles in FIG. 11, and has a low maximum wear amount (sufficient) as shown in Table 1. It has been confirmed that it provides excellent friction and wear characteristics).

(Example 2-16)
Example 2-16 is a nitrided steel member manufactured by changing the nitriding temperature at the time of nitriding treatment to 630 ° C. and the nitriding potential to 0.25 with respect to Example 2-12.

The phase distribution of the nitrided compound layer is in the order of γ'phase and ε phase, the thickness of the nitrided compound layer is about 16 μm from the surface of the nitrided steel member, and the volume ratio of the γ'phase in the nitrided compound layer is. , 45%.

Such a nitrided steel member of Example 2-16 also provides a sufficient hardness distribution as shown by the white circles in FIG. 11, and has a low maximum wear amount (sufficient) as shown in Table 1. It has been confirmed that it provides excellent friction and wear characteristics).

(Example 2-30)
Example 2-30 is manufactured by changing the matrix phase to S15C steel, further changing the nitriding temperature during the nitriding treatment to 650 ° C., and changing the nitriding potential to 0.2 with respect to Example 2-12. It is a nitrided steel member.

The phase distribution of the nitrided compound layer is in the order of γ'phase and ε phase, the thickness of the nitrided compound layer is about 30 μm from the surface of the nitrided steel member, and the volume ratio of the γ'phase in the nitrided compound layer is. , 30%.

Such a nitrided steel member of Example 2-30 also provides a sufficient hardness distribution as shown by the white circles in FIG. 11, and has a low maximum wear amount (sufficient) as shown in Table 1. It has been confirmed that it provides excellent friction and wear characteristics).

1 Nitriding steel member manufacturing equipment (surface hardening equipment)
2 Circulation type processing furnace 3 Atmospheric gas concentration detector 4 Nitrating potential regulator 5 Internal retort 6 Retort 7 Furnace opening / closing lid 8 Stirring fan 9 Stirring fan drive motor 12 Atmospheric gas piping 13 In-combustion nitriding potential arithmetic unit 14 Gas introduction amount control device 15 Parameter setting device (touch panel)
20 In-core gas supply unit 21 1st in-core gas supply unit 22 1st in-core gas supply control device 23 1st supply valve 25 2nd in-core introduction gas supply unit 26 2nd in-core gas supply control device 27 2nd Supply valve 29 Gas introduction pipe in the furnace 30 Gas flow rate output regulator 31 Programmable logic controller 40 Gas waste pipe in the furnace 41 Exhaust gas combustion decomposition device 110 Steel nitride member (first embodiment)
111 Nitride compound layer 112 Hardened layer 113 Diffusion layer 120 Nitride steel member (second embodiment)
121 Nitride compound layer 122 Hardened layer 123 Diffusion layer 160 Nitride steel member (Reference Example 1)
161 Region corresponding to the nitrided compound layer 170 Nitride steel member (Reference Example 2)
171 Region corresponding to the nitrided compound layer 300 Nitride steel member (comparative example)
301 Nitriding compound layer 303 Diffusion layer 201 Furnace wall or bell 202 Retort 203 Stirring fan 204 Guide tube (internal retort)
205 Gas inlet pipe 206 Flared gas exhaust or gas hood 207 Thermocouple 208 Cooling work lid 209 Cooling work blower

Claims (5)

A nitrided steel member whose parent phase is carbon steel or low alloy steel.
A nitride compound layer is provided on the surface,
A cured layer having an austenite structure is provided below the nitrided compound layer.
A diffusion layer in which nitrogen is diffused in the matrix is provided below the cured layer.
The nitrided compound layer has a phase distribution in the order of ε phase, γ'phase, and ε phase.
The volume ratio of the γ'phase in the nitrided compound layer is 20% or more, and the volume ratio is 20% or more.
The nitrided compound layer is a nitrided steel member having a thickness of 5 μm to 50 μm from the surface of the nitrided steel member. A nitrided steel member whose parent phase is carbon steel or low alloy steel.
A nitride compound layer is provided on the surface,
A cured layer having an austenite structure is provided below the nitrided compound layer.
A diffusion layer in which nitrogen is diffused in the matrix is provided below the cured layer.
The nitrided compound layer has a phase distribution in the order of γ'phase and ε phase.
The volume ratio of the γ'phase in the nitrided compound layer is 30% or more, and the volume ratio is 30% or more.
The nitrided compound layer is a nitrided steel member having a thickness of 5 μm to 30 μm from the surface of the nitrided steel member. The nitrided steel member according to claim 1 or 2, wherein the base phase is carbon steel having a carbon content of 0.1% or more in mass%. It is a method of manufacturing a nitrided steel member having a carbon steel or a low alloy steel as a parent phase by using a circulation type processing furnace equipped with a guide cylinder and a stirring fan.
During the nitriding process, the temperature range in the circulation type processing furnace is controlled to 610 ° C to 660 ° C.
At the time of the nitriding process, the nitriding potential in the circulation type processing furnace is controlled in the range of 0.15 to 0.6.
A method for manufacturing a nitrided steel member, which comprises quenching after the nitriding treatment and further performing a reheating treatment. Equipped with a circulation type processing furnace with a guide tube and a stirring fan,
During the nitriding process, the temperature range in the circulation type processing furnace is controlled to 610 ° C to 660 ° C.
At the time of the nitriding process, in order to control the nitriding potential in the circulation type processing furnace, ammonia gas and ammonia decomposition gas are introduced into the circulation type processing furnace. And,
The nitriding potential in the circulation type processing furnace is a target in the range of 0.15 to 0.6 by keeping the amount of the ammonia decomposition gas introduced into the furnace constant and changing the amount of the ammonia gas introduced into the furnace. A nitriding steel member manufacturing apparatus characterized in that it is controlled by the nitriding potential.

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