JP2014055337A - Nitrided member and hydraulic rotary machine using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrided member which is superior in wear resistance and can quickly form a nitrided layer having high adhesion without providing an additional process or facility.SOLUTION: Nitriding treatment is performed on base materials of one of a cradle 9, a piston 6, a retainer 17, and a retainer guide, and of one of a retainer 17 and shoe 7, whose base materials are steel. In those nitrided members in each of which a nitrided layer is formed on the base material, the nitrided layer is composed of a γ'-Fe4 N layer formed on an outermost surface, and a ε-Fe3 N layer, formed between the γ'-Fe4 N layer and the base material, in which ranges of nitrogen concentration, hardness, and Young's modulus are between those of the γ'-Fe4 N layer and the base material.

Description

  The present invention relates to a nitride member in which a nitride layer is formed on the surface of steel as a base material.

  Conventionally, construction machines such as hydraulic excavators have been provided with hydraulic components such as pistons and rotors that are driven by hydraulic pressure. Such hydraulic parts are made of steel as a base material, and the surfaces of the parts slide on each other, so that a high load is applied. For this reason, the surface of each component wears out. To prevent this, the surface of each component is subjected to, for example, nitriding treatment or soft nitriding treatment to form a nitrided layer to improve wear resistance. Yes.

  Specifically, when nitriding is performed on the surface of the steel, which is a base material, usually, an ε-Fe3N layer is formed on the outermost surface as a nitrided layer, and γ'-Fe4N between the ε-Fe3N layer and the base material. A layer is formed. Here, the layer formed on the outermost surface of the nitride structure of the nitride layer is desired to have as high a nitrogen concentration and hardness as possible and a low Young's modulus. However, although the ε-Fe3N layer formed on the outermost surface has a relatively high hardness, there are problems such as easy formation of a porous layer and coarse crystal grains. It has been demanded.

  Therefore, as one of the prior arts for optimizing the nitride structure of the nitride layer, after nitriding the base material, the ε-Fe3N layer formed on the outermost surface of the base material is ground, and the remaining appearing on the outermost surface A method of preventing contact between base materials as bases by applying a DLC coating that forms a DLC (diamond-like carbon) layer on the γ'-Fe4N layer is proposed. (For example, refer to Patent Document 1).

  Also, as another prior art, new gas nitriding is performed in which a surface activation treatment is performed to replace the oxide film on the surface of the base material with a fluoride film before the nitriding step, and then the surface of the base material is subjected to nitriding treatment. A treatment (NV nitriding treatment) method has been proposed (see, for example, Non-Patent Document 1). By using this new gas nitriding treatment (NV nitriding treatment) method, it is conventionally possible to lower the nitriding temperature at the time of nitriding treatment and generate only a fine γ′-Fe 4 N layer as a nitride layer on the surface of the base material. Has been done.

JP 2002-31144 A

Mitsubishi Heavy Industries Technical Report Vol. 45 NO. 3: 2008

  In the prior art DLC coating method disclosed in Patent Document 1, when the base material is nitrided as described above, the ε-Fe 3 N layer formed on the outermost surface of the nitride layer is ground, and the DLC coating is performed. Since an extra process such as a process is required, the problem is that the cost increases. In addition, even if the grinding process and the DLC coating process of the ε-Fe3N layer are performed after nitriding the base material of the hydraulic component, the DLC film formed on the γ′-Fe4N layer by the DLC coating is Since the adhesion to the base material is low, there is a concern that the DLC film on the surface easily peels off from the base material together with the γ′-Fe 4 N film when the hydraulic component is used.

  In the conventional new gas nitriding (NV nitriding) method disclosed in Non-Patent Document 1, an expensive pre-cleaning facility is required, and only the γ′-Fe 4 N layer is generated on the surface of the base material. Since it is necessary to lower the nitriding treatment temperature, there is a problem that the time required for the nitriding treatment becomes long. Further, since the γ'-Fe4N layer produced at a temperature lower than the normal processing temperature tends to have a low nitrogen concentration, the surface hardness may be lowered accordingly.

  The present invention has been made based on the actual situation of the prior art, and the purpose thereof is to quickly form a nitride layer with high adhesion without providing an extra step or equipment, and to improve wear resistance. The object is to provide an excellent nitriding member.

  In order to achieve the above object, the nitriding member of the present invention is a nitriding member obtained by nitriding steel as a base material, and a nitride layer is formed on the surface of the base material. A γ'-Fe4N layer formed on the outermost surface and formed between the γ'-Fe4N layer and the base material, and having a nitrogen concentration, hardness, and Young's modulus between the γ'-Fe4N layer and the base material It is characterized by comprising an ε-Fe 3 N layer in the range between.

  In the present invention configured as described above, a nitrided layer formed by nitriding a steel as a base material is composed of a γ′-Fe4N layer and an ε-Fe3N layer. Since a γ′-Fe 4 N layer having a high nitrogen concentration and hardness and a low Young's modulus appears on the outermost surface, the wear resistance can be sufficiently improved. In particular, according to the present invention, it is not necessary to generate only the γ'-Fe4N layer, and it is not necessary to perform the nitriding process by lowering the processing temperature. Therefore, the nitride layer can be rapidly formed on the base material, and the nitriding process can be performed. The nitrogen concentration and hardness of the γ′-Fe 4 N layer of the layer can be kept high.

  Furthermore, since the ε-Fe3N layer formed between the γ'-Fe4N layer and the base material has a nitrogen concentration, hardness, and Young's modulus in the range between the γ'-Fe4N layer and the base material, Rather than forming the '-Fe4N layer directly on the base material, the adhesion between the nitride layer and the base material can be improved by interposing the ε-Fe3N layer as an intermediate layer.

  In this way, by effectively utilizing the ε-Fe3N layer in addition to the γ'-Fe4N layer as the nitride layer, there is no need to provide an extra process or facility for other processing in order to optimize the nitride layer structure. Therefore, the nitrided member can be manufactured efficiently, and the manufacturing cost can be reduced.

  Further, in the nitriding member according to the present invention, in the above invention, the base material has a component composition of C: 0.25 to 0.60% by weight, Mn: 7.0 to 12.0% by weight, and the balance is Fe. And an unavoidable impurity element.

  In the present invention configured as described above, by adjusting the content of Mn contained in the base material to 7.0 to 12.0% by weight and performing nitriding treatment, the wear resistance and the nitrogen concentration in the nitrided member are reduced. In consideration of the mechanical properties and crystallographic properties of the ε-Fe3N and γ'-Fe4N layers of the nitrided layer, the desired layers are easily formed in the order of γ'-Fe4N layer and ε-Fe3N layer from the surface side. Can be formed.

  The nitride member according to the present invention is characterized in that, in the above invention, the base material contains S: 0.03% by weight or less as a component composition. If comprised in this way, toughness will fall normally as the addition amount of Mn to a base material increases, However, The content of S contained in the component of a base material is restrict | limited to 0.03 weight% or less. Thereby, even if the addition amount of Mn increases, the fall of toughness can be suppressed.

  Further, in the nitriding member according to the present invention, in the above-described invention, the composition distribution of the γ′-Fe 4 N layer and the ε-Fe 3 N layer of the nitride layer is 20% to 30% as a proportion of the ε-Fe 3 N layer. It is characterized by that.

  In the present invention configured as described above, since the ε-Fe3N layer is more easily produced as a porous layer than the γ′-Fe4N layer, the higher the proportion of the ε-Fe3N layer in the nitrided layer, the lower the hardness, The lower the proportion of the ε-Fe 3 N layer in the nitride layer, the lower the adhesion between the nitride layer and the base material. Therefore, the present invention provides a porous layer by adjusting the composition distribution of the γ′-Fe 4 N layer and the ε-Fe 3 N layer of the nitride layer so that the ratio of the ε-Fe 3 N layer is within the range of 20% to 30%. It is possible to sufficiently secure the adhesion between the nitride layer and the base material while suppressing the generation of excessively to maintain the hardness of the entire nitride layer high.

  Further, the nitriding member according to the present invention is applied to a hydraulic rotary machine including a swash plate and a cradle that supports the swash plate so as to be swingable in the invention, and the base material is composed of the cradle, The nitride layer is formed on a surface of the cradle that slides on the swash plate.

  In the present invention configured as described above, the capacity of the hydraulic rotating machine can be changed by changing the inclination of the swash plate, but the swash plate is supported by the cradle so as to be swingable. Each time the capacity of the rotary press is changed, the swash plate slides on the cradle, and a high load is applied to the sliding surface of the swash plate and the cradle. Even in such a state, a nitride layer is formed on the surface of the cradle that slides on the swash plate, so that the swash plate and the cradle are mutually connected by the function of the nitride layer as a buffer. The influence of the force exerted can be reduced. Thereby, the lifetime of a swash plate and a cradle can be improved.

  The nitriding member according to the present invention is a hydraulic rotating machine comprising: a rotating shaft; a cylinder block rotating with the rotation of the rotating shaft; and a piston accommodated in a cylinder of the cylinder block. The base material is composed of the piston, and the nitride layer is formed on a surface of the piston that slides with the cylinder.

  In the present invention configured as described above, since the piston repeats reciprocating movement along the rotation axis in the cylinder when the cylinder block rotates together with the rotation axis, the piston slides on the cylinder, and the piston and the cylinder slide. A high load is applied to the surface. Even in such a state, a nitrided layer is formed on the surface of the piston that slides with the cylinder. Can alleviate the effects. Thereby, the lifetime of a piston and a cylinder can be improved. In particular, according to the present invention, since the nitride layer is formed on the surface of the piston, the nitriding process can be performed more easily than the case where the nitrided layer is formed inside the cylinder of the cylinder block. .

  According to the nitride member of the present invention, the nitride layer includes two layers of γ′-Fe 4 N layer and ε-Fe 3 N layer, and the nitrogen concentration, hardness, and Young's modulus are between the γ′-Fe 4 N layer and the base material. Since the ε-Fe3N layer in the range is formed between the γ'-Fe4N layer and the base material and effectively used, a nitride layer with high adhesion can be quickly formed without providing extra steps or equipment. Can be formed. Since the γ'-Fe4N layer having a higher nitrogen concentration and hardness than the ε-Fe3N layer and having a lower Young's modulus appears on the outermost surface of the nitride layer, the wear resistance can be improved. Thereby, the practicality superior to the past can be achieved.

It is a figure which shows the structure of the variable capacity | capacitance type | mold swash plate type axial piston pump mentioned as an example of the hydraulic rotary machine with which one Embodiment of the nitriding member which concerns on this invention is applied. (A) is a figure which shows the structure of the nitriding member of a prior art, (b) The figure is a figure which shows the structure of one Embodiment of the nitriding member which concerns on this invention. It is a ternary phase diagram of Fe-Mn-N when the nitriding temperature in the nitriding treatment is 570 ° C. It is a ternary phase diagram of Fe-Mn-N when the nitriding temperature in the nitriding treatment is 400 ° C. The diagram on the left shows the relationship between each layer of the nitrided member of the prior art and the Young's modulus and hardness, and the diagram on the right shows the relationship between each layer according to this embodiment and the Young's modulus and hardness. It is a figure which shows the relationship between the stress amplitude S and the repetition frequency N of the nitriding member of a prior art, and the nitriding member which concerns on this embodiment.

  Hereinafter, the form for implementing the nitriding member concerning the present invention is explained based on figures.

  One embodiment of the nitriding member according to the present invention is applied to a hydraulic rotary machine such as a hydraulic pump and a hydraulic motor provided in a construction machine, for example. In this embodiment, this hydraulic rotating machine is composed of, for example, a variable displacement swash plate type axial piston pump (hereinafter referred to as a swash plate type pump 1 for convenience) as shown in FIG.

  The swash plate pump 1 includes, for example, a casing 2 that forms an outer shell, a rotating shaft 3 that is rotatably provided around the axis at the center of the casing 2, and a cylinder that rotates as the rotating shaft 3 rotates. The block 4, the piston 6 accommodated in the cylinder 5 of the cylinder block 4, the shoe 7 that is slidably held at the end of the piston 6, and that rotates together with the cylinder block 4, and the slant that the shoe 7 is in sliding contact with A plate 8 and a cradle 9 that supports the swash plate 8 in a swingable manner are provided.

  The casing 2 includes a cylindrical casing body 2A that covers each member such as the rotating shaft 3 and the cylinder block 4, and a front casing 2B and a rear casing 2C that close both ends of the casing body 2A. Further, the rear casing 2 </ b> C has a pair of supply / discharge passages 15 </ b> A and 15 </ b> B through which hydraulic oil is supplied to or discharged from the cylinder block 4. These supply / discharge passages 15A and 15B are connected to piping (not shown) provided on the suction side and discharge side of hydraulic oil. Between the rear casing 2 </ b> C and the cylinder block 4, a valve plate 16 that restricts the flow of hydraulic oil is interposed.

  The swash plate pump 1 is positioned between the shoe 7 and the end of the piston 6 on the front casing 2B side and is inserted through the rotary shaft 3 and is inserted through the shoe 7 and pressed against the sliding surface of the swash plate 8. An annular flat plate retainer 17 having an insertion hole to be inserted, and a retainer guide which is positioned between the retainer 17 and the cylinder block 4 and is inserted into the rotary shaft 3 and presses the retainer 17 toward the swash plate 8 by the outer peripheral surface. (Not shown).

  The rotary shaft 3 is rotatably supported between the front casing 2B and the rear casing 2C via bearings 20A, 20B and the like. Further, the rotating shaft 3 is formed with a protruding end 3A protruding in the axial direction from the front casing 2B, and the protruding end 3A side is rotationally driven by a prime mover (not shown) such as an engine, for example. Yes.

  The cylinder block 4 is splined to the outer peripheral side of the rotary shaft 3, and one end on the front casing 2B side of both end faces is arranged to face the swash plate 8, and the other end on the rear casing 2C side of both end faces. Is in sliding contact with the valve plate 16. Thereby, the position of the cylinder block 4 is fixed with respect to the axial direction of the rotary shaft 3, and the cylinder block 4 can rotate around the axis of the rotary shaft 3.

  The swash plate pump 1 is in a state in which the shoe 7 is pressed to the swash plate 8 side by the retainer guide and the retainer 17 as the rotating shaft 3 rotates together with the cylinder block 4 by driving a prime mover such as an engine. The piston 6 repeats reciprocating movement along the axial direction of the rotary shaft 3 in the cylinder 5 while sliding on the swash plate 8 around the axis of the rotary shaft 3, and the valve plate 16 from the supply / discharge passage 15B on the suction side. The hydraulic oil that has flowed into the cylinder block 4 via the cylinder is discharged as high-pressure oil into the supply / discharge passage 15A on the discharge side. Further, the swash plate pump 1 increases or decreases the discharge amount of hydraulic oil by changing the tilt angle of the swash plate 8 while sliding on the cradle 9.

  Therefore, the swash plate type pump 1 configured as described above has at least the surfaces of the piston 6 and the cylinder 5, the swash plate 8 and the cradle 9, the retainer 17 and the retainer guide, and the retainer 17 and the shoe 7 that slide on each other. Therefore, a high load is applied to each of the sliding surfaces.

  Therefore, in the present embodiment, before the swash plate pump 1 is incorporated into the construction machine, any one of the cradle 9, the piston 6, the retainer 17 and the retainer guide and the mother of either the retainer 17 and the shoe 7 are preliminarily provided. By nitriding the steel material, any of the surface of the cradle 9 that slides with the swash plate 8, the surface of the piston 6 that slides with the cylinder 5, the retainer 17 and the retainer guide A nitrided layer is formed on one of the sliding surfaces, one of the retainer 17 and the shoe 7.

  Hereinafter, as described above, the composition of the base material according to the present embodiment, the configuration of the nitride layer formed on the surface of the base material, and the nitriding treatment will be described in detail with reference to FIGS.

  The base material according to the present embodiment has, for example, C: 0.25 to 0.60% by weight, Mn: 7.0 to 12.0% by weight, S: 0.03% by weight or less, Si: 0 as the component composition. 0.05 to 1.0% by weight, and the balance contains Fe and inevitable impurity elements.

In addition, after the base material is placed in the furnace, the above-described nitriding process is performed under nitriding conditions in which the temperature range in the furnace, the residual NH ₃ concentration in the furnace, and the processing time are determined. In this embodiment, as the nitriding conditions, for example, the temperature range in the furnace is set to be higher than 400 ° C. and lower than 600 ° C., the residual NH ₃ concentration in the furnace is set to be higher than 40% and lower than 80%, and the processing time is set to the target effective. It is set appropriately according to the curing depth.

  The nitrided layer according to the present embodiment manufactured under the nitriding conditions set in this manner includes a γ′-Fe4N layer formed on the outermost surface, and between the γ′-Fe4N layer and the base material. And an ε-Fe3N layer having a nitrogen concentration, hardness, and Young's modulus (see FIG. 5) in the range between the γ′-Fe4N layer and the base material.

  That is, as shown in FIG. 2 (a), the nitriding member of the prior art has nitriding conditions in the order of ε-Fe3N layer (nitriding layer), γ'-Fe4N layer (nitriding layer), and base material (diffusion layer) from the surface side. Each layer is formed in a volume ratio according to the above, whereas as shown in FIG. 2B, the nitride member according to this embodiment has a γ′-Fe 4 N layer (nitride layer), ε− from the surface side. Each layer is formed in the order of the Fe3N layer (nitriding layer) and the base material (diffusion layer) in a volume ratio corresponding to the nitriding conditions.

  Further, in this embodiment, as a configuration distribution of the γ′-Fe 4 N layer and the ε-Fe 3 N layer of the nitride layer, for example, the ratio of the ε-Fe 3 N layer is 20% to 30%, and the amount of the γ′-Fe 4 N layer is It is larger than the amount of the ε-Fe 3 N layer.

  Next, as described above, the reason for defining the content range of C, Si, Mn, and S, which are the component compositions of the base material according to the present embodiment, the reason for setting the nitriding conditions, and the composition distribution of the nitride layer Explain why it was set.

[C: 0.25 to 0.60% by weight]
C is an element necessary for ensuring the strength, and from this viewpoint, the C content is set to 0.25% by weight or more. On the other hand, if the C content exceeds 0.60% by weight, the toughness decreases, so the C content is set to 0.60% by weight or less.

[Si: 0.05 to 1.0% by weight]
Si is an element necessary for deoxidation and is an element necessary for ensuring strength. Since the desired effect cannot be obtained if the Si content is less than 0.05% by weight, the Si content Is 0.05% by weight or more. On the other hand, if the Si content exceeds 1.0% by weight, the toughness decreases, so the Si content is set to 0.05 to 1.0% by weight or less.

[Mn: 7.0 to 12.0% by weight]
Mn is an element necessary for ensuring strength. By setting the content of Mn to 7.0% by weight or more, a γ′-Fe 4 N layer is formed on the outermost surface in the nitride layer according to the present embodiment, An ε-Fe 3 N layer can be formed between the γ′-Fe 4 N layer and the base material.

  Specifically, as shown in FIG. 3, under the nitriding conditions according to the present embodiment, in the Fe—Mn—N ternary phase diagram, the boundary line between the base material (parent phase) and the γ′-Fe 4 N layer, The base material (matrix) and the boundary line of the ε-Fe3N layer intersect at a point where the Mn concentration is 7.0%. When the Mn concentration is less than 7.0%, the γ'-Fe4N layer is ε-Fe3N. Although it is on the lower nitrogen concentration side than the layer, the γ′-Fe 4 N layer is on the higher nitrogen concentration side than the ε-Fe 3 N layer when the Mn concentration is 7.0% or more.

  Therefore, if the Mn content is less than 7.0% by weight, an ε-Fe 3 N layer is formed on the outermost surface having a high nitrogen concentration, and the nitride layer according to this embodiment cannot be obtained. However, the Mn content is 7. If the content is 0% by weight or more, the nitride layer according to the present embodiment can be obtained. Therefore, the Mn content is 7.0% by weight or more. On the other hand, when a large amount of Mn is added, the toughness decreases, so the Mn content is set to 12.0% or less.

[S: 0.03% by weight or less]
Along with the Mn content being 7.0% by weight or more, it is necessary to reduce the S content as much as possible, so the S content is 0.03% by weight or less.

[Temperature range in the furnace: greater than 400 ° C and less than 600 ° C]
If the temperature in the furnace is 400 ° C. or lower, the diffusion rate of nitrogen decreases rapidly. For example, as shown in FIG. 4, under the nitriding conditions when the temperature in the furnace is 400 ° C., the γ′-Fe 4 N layer and the ε-Fe 3 N layer are on the high nitrogen concentration side in the Fe—Mn—N ternary phase diagram. Even if Mn is added, the effect of promoting the formation of a nitride layer on the base material is extremely small. On the other hand, if the temperature in the furnace is 600 ° C. or higher, α to γ transformation of the base material occurs, and the formation of a nitride layer is suppressed. Therefore, under the nitriding conditions according to the present embodiment, the temperature range in the furnace is set to be greater than 400 ° C. and less than 600 ° C.

[Residual NH ₃ concentration in the furnace: greater than 40% and less than 80%]
If the residual NH ₃ concentration in the furnace is 40% or less, a nitride layer is not formed on the phase diagram, and if the residual NH ₃ concentration in the furnace is 80% or more, a porous layer is easily generated. The residual NH ₃ concentration in the furnace is greater than 40% and less than 80%.

[Compositional distribution of nitride layer: Ratio of ε-Fe3N layer is 20% to 30%]
Among the nitrided layers according to this embodiment, the ε-Fe3N layer is more easily formed with a porous layer than the γ′-Fe4N layer. It is necessary to. In addition, since the ε-Fe3N layer of the nitride layer according to the present embodiment is formed between the γ′-Fe4N layer and the base material, the adhesion between the nitride layer and the base material is improved as will be described later. In order to improve the ratio, the ratio of the ε-Fe3N layer needs to be 20% or more. Accordingly, the proportion of the ε-Fe 3 N layer is set to 20% to 30% as the constituent distribution of the nitride layer.

  Here, there is generally a linear relationship between hardness and wear resistance, and there is a tendency for wear resistance to improve as the hardness increases. Therefore, the inclination of construction machinery used under heavy loads is high. As for the outermost surface of the nitride layer formed in the plate pump 1, it is desirable that a layer having the highest possible hardness appears on the outermost surface. In general, the lower the Young's modulus, the easier it is to absorb the impact received by the surface and the better the wear resistance. Therefore, the outermost surface of the nitride layer formed on the swash plate pump 1 of a construction machine can be formed. It is desirable that a layer having a low Young's modulus appears.

  The γ'-Fe4N layer formed on the outermost surface of the nitride layer of the present embodiment has finer crystal grains than those of the ε-Fe3N layer, and the generation of a porous layer is suppressed. As shown, the hardness of the outermost γ'-Fe4N layer is higher than the hardness of the ε-Fe3N layer formed on the outermost surface in the nitride layer of the conventional nitride member shown in the left diagram of FIG.

  Further, as shown in the right side of FIG. 5, the γ′-Fe 4 N layer formed on the outermost surface of the nitride layer of the present embodiment is formed on the outermost surface of the nitride layer of the conventional nitride member shown in the left side of FIG. It is lower than the Young's modulus of the ε-Fe 3 N layer. Therefore, it can be seen that the nitriding member according to the present embodiment is more wear resistant than the nitriding member of the prior art and is suitable for use in a state where a high load is applied.

  Moreover, as shown in FIG. 6, the S (stress amplitude) -N (number of repetitions) curve of the nitrided member according to the present embodiment is on the higher stress amplitude side than the SN curve of the nitrided member according to the prior art, The fatigue limit is also increasing. Therefore, it can be seen that the nitrided member according to the present embodiment is more excellent in fatigue resistance than the nitrided member of the prior art and is suitable for use under a high load condition.

  According to the present embodiment configured as described above, any one of the piston 6, the cradle 9, the retainer 17 and the retainer guide in the swash plate pump 1 of the construction machine, and the mother of either the retainer 17 and the shoe 7. By subjecting the steel material to nitriding under the nitriding conditions set as described above, the surface of the cradle 9 that slides with the swash plate 8 and the surface of the piston 6 that has the cylinder 5 A nitrided layer comprising a γ'-Fe4N layer and an ε-Fe3N layer on a sliding surface, one sliding surface of the retainer 17 and the retainer guide, and one sliding surface of the retainer 17 and the shoe 7 Can be formed.

  A γ'-Fe4N layer is formed on the outermost surface of the nitride layer, and an ε-Fe3N layer is formed between the γ'-Fe4N layer and the base material. The γ'-Fe4N layer formed on the outermost surface has a higher nitrogen concentration and hardness than the ε-Fe3N layer formed therebelow and a lower Young's modulus. Therefore, the swash plate 8 and the cradle 9, the cylinder 5 and the piston 6 Even if the retainer 17 and the retainer guide and the retainer 17 and the shoe 7 slide relative to each other, the influence on the surface can be reduced. Thereby, abrasion resistance can fully be improved.

  Further, the present embodiment does not generate only the γ′-Fe 4 N layer as the nitride layer, but maintains the temperature range in the furnace at a temperature higher than 400 ° C. and lower than 600 ° C., and the γ′-Fe 4 N layer and the ε-Fe 3 N layer. Therefore, one of the surface of the cradle 9 that slides with the swash plate 8, the surface of the piston 6 that slides with the cylinder 5, and the retainer 17 and the retainer guide. And a nitride layer can be quickly formed on any one of the retainer 17 and the shoe 7, and as shown in the right figure of FIG. Nitrogen concentration and hardness can be kept high.

  Furthermore, since the ε-Fe3N layer formed between the γ'-Fe4N layer and the base material has a nitrogen concentration, hardness, and Young's modulus in the range between the γ'-Fe4N layer and the base material, Rather than forming the '-Fe4N layer directly on the base material, the adhesion between the nitride layer and the base material can be improved by interposing the ε-Fe3N layer as an intermediate layer. Thereby, even if the swash plate 8 and the cradle 9, the cylinder 5 and the piston 6, the retainer 17 and the retainer guide, and the retainer 17 and the shoe 7 slide relative to each other, the coating of the nitride layer is prevented from peeling from the base material. can do.

  As described above, by effectively using the ε-Fe3N layer in addition to the γ′-Fe4N layer as the nitride layer, this embodiment is suitable for use under a high load condition. For example, DLC (diamond It is not necessary to provide an extra process such as a grinding process of the ε-Fe 3 N layer and a DLC coating process for forming a (like carbon) layer, and equipment for pre-cleaning the base material. Therefore, the nitride member according to this embodiment can be efficiently manufactured, and the manufacturing cost can be suppressed. Accordingly, excellent practicality can be achieved.

  In addition, the present embodiment focuses on the Mn concentration and the state of each layer in the ternary phase diagram of Fe—Mn—N under nitriding conditions in which the temperature range in the furnace is greater than 400 ° C. and less than 600 ° C. By setting the amount to 7.0% by weight or more, any one of the piston 6, the cradle 9, the retainer 17 and the retainer guide, and the base material of either the retainer 17 or the shoe 7 from the surface side. A nitride layer can be successfully formed in the order of the γ′-Fe 4 N layer and the ε-Fe 3 N layer. Furthermore, by adjusting the content of Mn as a component of these base materials to 12.0% by weight or less, it is possible to suppress a decrease in toughness due to the addition of a large amount of Mn. Thereby, the nitride member excellent in abrasion resistance and fatigue resistance can be obtained easily.

  In the present embodiment, as described above, the content of Mn as a component of the base material of any one of the piston 6, the cradle 9, the retainer 17 and the retainer guide, and any one of the retainer 17 and the shoe 7 is set. 7.0 to 12.0% by weight, and even if the Mn content is increased in this way, by limiting the content of S contained in the base material component to 0.03% by weight or less, the toughness is reduced. It can suppress effectively that it falls. Thereby, the lifetime of the swash plate 8, the cradle 9, the cylinder 5, the piston 6, the retainer 17, the retainer guide, and the shoe 7 can be increased, and the frequency of replacement work of these components can be reduced.

  In the present embodiment, the surface of the cradle 9 that slides with the swash plate 8, the surface of the piston 6 that slides with the cylinder 5, and the sliding surface of either the retainer 17 or the retainer guide. , And the ratio of the ε-Fe3N layer of the nitride layer formed on one of the sliding surfaces of the retainer 17 and the shoe 7 is limited to 30% or less, thereby making the ε-Fe3N layer a γ'-Fe4N layer. Even if formed between the base material and the base material, it is possible to prevent the porous layer from being generated excessively, and the hardness of the entire nitrided layer can be kept high.

  Further, in the present embodiment, the surface of the cradle 9 that slides with the swash plate 8, the surface of the piston 6 that slides with the cylinder 5, and the sliding surface of any one of the retainer 17 and the retainer guide. Even if the proportion of the γ′-Fe 4 N layer is increased by increasing the proportion of the ε-Fe 3 N layer of the nitride layer formed on one of the sliding surfaces of the retainer 17 and the shoe 7 to 20% or more, ε Since the formation amount of the -Fe3N layer is secured to some extent, the ε-Fe3N layer can exhibit a sufficient adhesion between the γ'-Fe4N layer and the base material.

  Thus, the surface of the cradle 9 that slides with the swash plate 8, the surface of the piston 6 that slides with the cylinder 5, the sliding surface of one of the retainer 17 and the retainer guide, and the retainer By appropriately setting the distribution of the γ′-Fe4N layer and the ε-Fe3N layer of the nitride layer formed on one of the sliding surfaces of the shoe 17 and the shoe 7, both the hardness and adhesion of the nitride layer are set. Therefore, a balanced member can be realized. Therefore, even if the swash plate 8 and the cradle 9, the cylinder 5 and the piston 6, the retainer 17 and the retainer guide, and the retainer 17 and the shoe 7 slide relative to each other, the nitrided layer is stable. Reliability can be obtained.

  In this embodiment, the swash plate 8 and the cradle 9, the cylinder 5 and the piston 6, the retainer 17 and the retainer guide, and the retainer 17 and the shoe 7 slide relative to each other. Since the nitride layer is formed by nitriding only, the wear of the nitride layer is not promoted, and the nitride layer can function as a buffer for a long time. In particular, in the present embodiment, by selecting the piston 6 as the surface on which the nitrided layer is to be formed among the cylinder 5 and the piston 6, the outer surface of the piston 6 is subjected to nitriding treatment, so that the nitriding treatment work is facilitated. It can be advanced, and excellent work efficiency can be realized.

The above-described embodiment is applied to a hydraulic rotating machine of a construction machine. The mother of either one of the cradle 9, the piston 6, the retainer 17 and the retainer guide, and either the retainer 17 and the shoe 7 is used. When the material is formed by nitriding under a nitriding condition in which the temperature range in the furnace is set to be higher than 400 ° C. and lower than 600 ° C., and the residual NH ₃ concentration in the furnace is set to be higher than 40% and lower than 80%. However, the present invention is not limited to this case, and if steel is used as a base material, for example, parts other than construction machinery may be formed by nitriding under appropriately set nitriding conditions. .

  In the present embodiment, the case where the hydraulic rotating machine is composed of a variable displacement swash plate type axial piston pump has been described. However, the present invention is not limited to this, and the hydraulic rotating machine is, for example, a variable displacement swash plate type axial piston motor or A variable displacement oblique axis type axial piston pump / motor may be used, and the hydraulic rotating machine is not limited to the variable displacement type, but may be a fixed displacement type.

  Moreover, in this embodiment, as a component composition of a base material, C: 0.25-0.60 weight%, Mn: 7.0-12.0 weight%, S: 0.03 weight% or less, Si: 0 0.05 to 1.0% by weight and the balance containing Fe and inevitable impurity elements have been described. However, the present invention is not limited to this case. For example, elements other than C, Mn, S, and Si are added to the base material. If the content of Mn is 7% or more, the range of the content of C, S, and Si may not be limited.

1 Swash plate pump (hydraulic rotating machine)
3 Rotating shaft 4 Cylinder block 5 Cylinder 6 Piston 7 Shoe 8 Swash plate 9 Cradle 17 Retainer

Claims (6)

In a nitriding member in which a nitriding treatment is performed on steel as a base material, and a nitride layer is formed on the surface of the base material,
The nitride layer is
A γ'-Fe4N layer formed on the outermost surface;
It is formed between this γ'-Fe4N layer and the base material, and consists of an ε-Fe3N layer having a nitrogen concentration, hardness, and Young's modulus in the range between the γ'-Fe4N layer and the base material. A nitride member characterized by the above. The nitride member according to claim 1,
The base material has a component composition of C: 0.25 to 0.60% by weight, Mn: 7.0 to 12.0% by weight, and the balance contains Fe and inevitable impurity elements. . The nitride member according to claim 2,
The base material contains S: 0.03% by weight or less as a component composition. The nitriding member according to any one of claims 1 to 3,
A nitriding member characterized in that a ratio of the ε-Fe3N layer is 20% to 30% as a constituent distribution of the γ'-Fe4N layer and the ε-Fe3N layer of the nitride layer. In the nitriding member according to any one of claims 1 to 4,
It is applied to a hydraulic rotating machine that includes a swash plate and a cradle that supports the swash plate in a swingable manner,
The nitriding member, wherein the base material is made of the cradle, and the nitriding layer is formed on a surface of the cradle that slides on the swash plate. In the nitriding member according to any one of claims 1 to 4,
It is applied to a hydraulic rotating machine comprising a rotating shaft, a cylinder block that rotates as the rotating shaft rotates, and a piston that is housed in a cylinder of the cylinder block.
The base material is made of the piston, and the nitrided layer is formed on a surface of the piston that slides on the cylinder.

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