JP2018024919A - Machine component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a machine component having excellent durability, plastic workability or toughness.SOLUTION: A machine component is constituted by alloy steel containing chromium and has a high hardness part having a surface cured layer and a low hardness part having lower surface hardness than the surface hardness of the high hardness part. The low hardness part has a passive film containing chromium oxide on a surface and the amount of carbide existing inside of the passive film less than the amount of the carbide existing in the surface cured layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to mechanical parts.

  For example, in a planetary gear device used in an automatic transmission of an automobile, a planetary gear that meshes with a sun gear and a ring gear is freely rotatable via a needle roller on a pinion shaft whose axial end is crimped and fixed to a carrier. It is supported. Therefore, the outer peripheral surface of the pinion shaft needs to have strength against shear stress as an inner ring of a rolling bearing, and the axial end portion thereof needs to have plastic workability that can be caulked.

  As a method of manufacturing a pinion shaft having such contradictory characteristics, a high carbon chromium bearing steel is used as a material, and after nitrocarburizing, it is tempered (tempered) at a high temperature to harden the axial end portion (clamped portion). A method of induction hardening the outer peripheral surface (rolling surface) after reducing the thickness is disclosed (see Patent Documents 1 to 3). In addition, a method is disclosed in which case-hardened steel with an increased chromium content is used as a material, and the structural stability of the outer peripheral surface (rolling surface) is enhanced by carbonitriding.

  However, when an ordinary carbonitriding treatment is performed on an alloy steel having a high chromium content, pro-eutectoid carbide may be selectively deposited at grain boundaries in the subsequent cooling process. As a result, even if the hardness of the pinion shaft end portion (caulking portion) is lowered to such an extent that it can be caulked, ductility may be lowered due to the influence of pro-eutectoid carbide. In the above-mentioned prior art, it is not considered about the reduction of the caulking property (plastic workability) due to the pro-eutectoid carbide of the alloy steel having a high chromium content, and regarding the caulking property of the axial end portion of the pinion shaft, There was room for further improvement.

JP 2004-340221 A JP 2008-223104 A JP 2013-228032 A

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a mechanical component having both excellent durability and plastic workability or toughness.

  In order to solve the above problems, a mechanical component according to an aspect of the present invention is made of alloy steel containing chromium, and has a high hardness portion having a surface hardened layer and a surface hardness higher than the surface hardness of the high hardness portion. A low hardness part, and the low hardness part has a passive film containing chromium oxide on the surface, and the amount of carbide existing inside the passive film is more than the amount of carbide present in the surface hardened layer. The main point is that there are few.

In the mechanical component according to one aspect of the present invention, the amount of carbide existing inside the passive film may be 15% or less in terms of area ratio, and the surface hardness of the low hardness portion may be HV150 or more and HV350 or less.
More preferably, the amount of carbide existing inside the passive film is 1.0% to 12% by area ratio and the surface hardness of the low hardness portion is HV150 to HV350. More preferably, the amount of carbide existing inside is 1.0% or more and 12% or less in terms of area ratio, and the surface hardness of the low hardness portion is HV150 or more and HV320 or less.

Moreover, the mechanical component which concerns on 1 aspect of this invention may be provided with the medium hardness part whose surface hardness is lower than the surface hardness of a high-hardness part, and whose surface hardness is higher than the surface hardness of a low-hardness part.
In the mechanical component according to one embodiment of the present invention, the alloy steel includes carbon in an amount of 0.1 mass% to 0.29 mass%, chromium in an amount of 2.0 mass% to 5.0 mass%, and molybdenum. 0.1% to 1.5% by mass, 0.1% to 1.5% by mass of manganese, 0.1% to 1.5% by mass of silicon, and the balance being iron In addition, the surface hardness of the high hardness portion may be HV700 or more and HV850 or less, and the thickness of the passive film may be 0.1 μm or more and 30 μm or less.

  Furthermore, the mechanical component according to one aspect of the present invention can be a component of a planetary gear device. That is, the planetary gear device may include the mechanical component according to one aspect of the present invention. The mechanical component according to one embodiment of the present invention can be a component of a vehicle such as an automobile. That is, a vehicle such as an automobile may include the mechanical component according to one embodiment of the present invention. Furthermore, the mechanical component according to one embodiment of the present invention can be a component (for example, a screw shaft) constituting a ball screw. That is, the ball screw may include the mechanical component according to one embodiment of the present invention. Further, the mechanical component according to one aspect of the present invention may be a gear. Furthermore, the mechanical component according to one aspect of the present invention may be a component having serrations.

  According to the present invention, it is possible to provide a mechanical component having both excellent durability and excellent plastic workability or toughness.

It is sectional drawing which shows the structure of the pinion shaft which concerns on 1st embodiment of the machine component of this invention. It is a heat pattern figure explaining the manufacturing method of the pinion shaft of FIG. It is the front view which looked at the planetary gear apparatus using the pinion shaft of FIG. 1 from the axial direction end side. It is III-III sectional drawing of FIG. It is a typical fragmentary sectional view of the pinion shaft by which the base end part was crimped. It is a typical end view of a pinion shaft with a proximal end crimped. It is sectional drawing which shows the structure of the pinion shaft which concerns on 2nd embodiment of the machine component of this invention.

  The machine component of the present embodiment is made of alloy steel containing chromium. And the high hardness part which has a surface hardened layer, and the low hardness part whose surface hardness is lower than the surface hardness of a high hardness part are provided. This low hardness part has a passive film containing chromium oxide on the surface, and the amount of carbide present inside the passive film is more than the amount of carbide present in the hardened surface layer of the high hardness part. Few.

  The mechanical parts of this embodiment are made of alloy steel containing chromium to improve durability (for example, rolling fatigue life, wear resistance), but a passive film is formed on the surface of the low hardness part. Therefore, the carburizing amount at the time of carburizing or carbonitriding is controlled. Therefore, since the amount of carbide in the low hardness portion is suppressed, the low hardness portion has plastic workability or toughness that can be further crimped. Therefore, the mechanical component of the present embodiment has both excellent durability and more plastic workability or toughness that can be caulked.

  In such a machine part of this embodiment, the amount of carbide existing inside the passive film is preferably 15% or less in terms of area ratio and the surface hardness of the low hardness portion is HV150 or more and HV350 or less, More preferably, the amount of carbide existing inside the passive film is 1.0% or more and 12% or less in terms of area ratio, and the surface hardness of the low hardness portion is HV150 or more and HV350 or less. More preferably, the amount of carbide present is 1.0% or more and 12% or less in terms of area ratio, and the surface hardness of the low hardness portion is HV150 or more and HV320 or less. With such a configuration, the plastic workability or toughness of the low hardness part is more excellent.

  In addition, the alloy steel constituting the mechanical component of the present embodiment includes carbon in an amount of 0.1% by mass to 0.29% by mass, chromium in an amount of 2.0% by mass to 5.0% by mass, and molybdenum in an amount of 0.1%. Contains from 0.1% to 1.5% by mass of manganese, from 0.1% to 1.5% by mass of manganese, from 0.1% to 1.5% by mass of silicon, and the balance being iron and inevitable It may be an impurity. The surface hardness of the high hardness portion may be HV700 or more and HV850 or less. Further, the amount of retained austenite of the surface hardened layer is 20% by volume or more and 50% by volume or less, and the amount of retained austenite of the inner core portion of the surface hardened layer is 0% by volume (or 0% by volume exceeding 2.0% by volume or less). ). Further, the thickness of the passive film may be not less than 0.1 μm and not more than 30 μm. With such a configuration, the durability of the high hardness portion is more excellent, and the plastic workability or toughness of the low hardness portion is more excellent.

Hereinafter, a pinion shaft that rotatably supports a planetary gear in a planetary gear device used in an automatic transmission of an automobile will be described in detail with reference to the drawings as an example of a mechanical component of the present embodiment. In the drawings referred to in the description of each embodiment below, the same or corresponding parts are denoted by the same reference numerals.
[First embodiment]
The pinion shaft 4 of FIG. 1 is made of alloy steel containing chromium and has a substantially cylindrical shape (round bar shape), and includes an axial hole 15 and a plurality of (three in this example) radial holes. 16, 16, 16 and a pair of circular recesses 18a, 18b. The circular recesses 18 a and 18 b have a truncated cone shape and are formed by cutting on both end surfaces in the axial direction of the pinion shaft 4. That is, the inner surfaces of the circular recesses 18a and 18b (both axial end surfaces of the pinion shaft 4) are cutting surfaces.

The axial hole 15 extending in the axial direction of the pinion shaft 4 is formed in the radial center portion of the pinion shaft 4, and one axial end portion (the left end portion in FIG. 1) is opened at the bottom of one circular recess 18a. In addition, the other end portion in the axial direction (the right end portion in FIG. 1) is located near the other end of the intermediate portion X in the axial direction of the pinion shaft 4.
In addition, a pair of radial holes 16 and 16 are formed at substantially the center in the axial direction of the pinion shaft 4 so as to penetrate the pinion shaft 4 in the radial direction, and the other axial end of the pinion shaft 4 is formed. One radial hole 16 extending in the radial direction of the pinion shaft 4 is formed in the side portion. Each of these radial holes 16, 16, 16 has a radially inner end opening on the inner peripheral surface of the axial hole 15, and each radial outer end on the outer peripheral surface of the pinion shaft 4. It is open.

  In the pinion shaft 4, cutting is performed on the outer peripheral surfaces (that is, cylindrical surfaces) of the axial end portions Y and Y, and the outer peripheral surfaces of the axial end portions Y and Y are cutting surfaces. Moreover, the outer peripheral surface (namely, cylindrical surface) of the axial direction intermediate part X except the axial both ends Y and Y among the pinion shafts 4 is ground, and the outer peripheral surface is a ground surface. The axially intermediate portion X of the pinion shaft 4 is subjected to a carbonitriding process (or carburizing process), a tempering process (annealing), an induction hardening process, and a tempering process in this order. A hardened surface layer 19 is formed on the outer circumferential surface of the intermediate portion X in the axial direction. Further, the axially opposite end portions Y and Y of the pinion shaft 4 are axially aligned with the circular concave portions 18a and 18b (the peripheral portions of the circular concave portions 18a and 18b) and remain tempered without induction hardening. It is.

The hardened surface layer 19 of the pinion shaft 4 corresponds to a “high hardness portion” that is a constituent requirement of the present invention. Moreover, the part which has the passive film 21 mentioned later among the pinion shafts 4 is corresponded to the "low-hardness part" which is the structural requirements of this invention.
Passive films 21 and 21 containing chromium oxide are formed on the bottom surfaces of the circular recesses 18a and 18b of the axially opposite ends Y and Y and the outer peripheral surfaces of the axially opposite ends Y and Y. Since the passive film 21 (having a thickness of, for example, 0.1 μm or more and 30 μm or less) is formed on the surface, the axial intermediate portion X is also formed on the outer peripheral surfaces (cylindrical surfaces) of both axial ends Y and Y. Although carbonitriding is performed at the same time, the amount of carbide existing inside the passive film 21 in both axial ends Y and Y is 15% or less in terms of area ratio, and the carbide existing in the surface hardened layer 19 Less than the amount.

  Moreover, the surface hardness of the axial direction intermediate part X (surface hardened layer 19) is HV700 or more and HV850 or less, the amount of retained austenite of the surface hardened layer 19 is 20% by volume or more and 50% by volume or less, and the surface hardened layer 19 The amount of retained austenite in the inner core portion 20 is more than 0% by volume and not more than 2.0% by volume. Furthermore, the surface hardness of both end portions Y and Y in the axial direction (particularly where the passive films 21 and 21 are formed) is HV150 or more and HV350 or less.

Since such a pinion shaft 4 has the toughness of the axial end Y, the axial end Y when crimping the axial end Y and fixing it to a member such as a carrier of a planetary gear device. Damages such as cracks and cracks are unlikely to occur. Therefore, when the pinion shaft 4 is fixed to a member such as a carrier, plastic working such as caulking can be preferably used. Further, since the strength of the axial intermediate portion X is ensured, the axial intermediate portion X (rolling surface) is hardly damaged during operation of the planetary gear device.
Here, the critical significance such as the content of alloy components contained in the alloy steel, the surface hardness, the amount of retained austenite, etc. will be described in detail.

[Carbon content]
Carbon (C) dissolves in the base and quenches, improves the hardness after tempering and improves strength, and combines with carbide-forming elements such as iron, chromium, molybdenum, vanadium to form carbides and resists carbon. It is an element that has the effect of increasing wear. If the time for carburizing treatment and carbonitriding treatment to obtain the hardness required for rolling fatigue resistance is increased, the cost increases, so the carbon content is 0.1 mass for shortening the treatment time. % Or more is preferable.

  However, if it exceeds 0.29% by mass, coarse eutectic carbides are likely to be produced during steelmaking, and the rolling fatigue life and strength may decrease. On the other hand, if it exceeds 0.29% by mass, forgeability, cold workability, and machinability may be deteriorated, resulting in an increase in processing cost. Furthermore, if it exceeds 0.29% by mass, the formability to a rod-shaped member is low, and if it is attempted to mold to a rod-shaped member having a diameter of 15 mm or less, plastic processing is difficult and cracks and cracks may occur during molding. .

[Chromium content]
Chromium (Cr) is an element having an effect of increasing the hardenability, temper softening resistance, corrosion resistance, and rolling fatigue life by dissolving in a matrix. In addition, the interstitial solid solution elements such as carbon and nitrogen are substantially prevented from moving to stabilize the base structure, and have a function of greatly suppressing a decrease in life at the time of hydrogen intrusion. Furthermore, since the carbide finely distributed in the alloy steel is composed of carbides such as (Fe, Cr) ₃ C, (Fe, Cr) ₇ C ₃ , (Fe, Cr) ₂₃ C _{6 and the} like having higher hardness, It also has the effect of increasing wear resistance. Further, the retained austenite is not easily decomposed by heat, and as a result, plastic deformation is difficult.

  If the content of chromium in the alloy steel is less than 2% by mass, the above-described action may not be sufficiently obtained in addition to the difficulty of forming a passive film. On the other hand, if the chromium content in the alloy steel exceeds 5% by mass, cold workability, machinability, and carbonitriding (or carburizing) may decrease, leading to an increase in cost. Furthermore, coarse eutectic carbides are likely to be generated during steelmaking, and the rolling life and strength may be reduced.

[Molybdenum content]
Molybdenum (Mo) is an element having the effect of increasing the hardenability, temper softening resistance, corrosion resistance, and rolling life by solid solution in the base like chromium. In addition, like chromium, interstitial solid solution elements such as carbon and nitrogen are substantially prevented from moving to stabilize the base structure, and have a function of greatly suppressing a decrease in life at the time of hydrogen intrusion. Furthermore, since the carbide finely distributed in the alloy steel is made of a carbide of molybdenum having a higher hardness, it also has an effect of improving wear resistance.
If the molybdenum content in the alloy steel is less than 0.1% by mass, the above-mentioned action may not be sufficiently obtained. If the content exceeds 1.5% by mass, cold workability and machinability are obtained. There is a risk of lowering and increasing costs. Furthermore, coarse eutectic carbides are likely to be generated during steelmaking, and the rolling life and strength may be reduced.

[About manganese content]
Manganese (Mn) is an element that acts as a deoxidizer during steelmaking, and is preferably added in an amount of 0.1 mass or more. Moreover, it has the effect | action which solid-dissolves to a base | substrate similarly to chromium, and lowers Ms point, ensures a large amount of retained austenite, or improves hardenability. However, if added over 1.5% by mass, not only the cold workability and machinability are lowered, but also the martensitic transformation start temperature is lowered, and a large amount of residual carbonitriding (or after carburizing) is left. Austenite may remain and sufficient hardness may not be obtained.

[About silicon content]
Silicon (Si) is an element that acts as a deoxidizing agent during steel making, like manganese, and is preferably added in an amount of 0.1 mass or more. Moreover, it is an element effective for improving the bearing life by improving the hardenability as well as chromium and manganese, and promoting the martensitic transformation of the base and the stabilization of retained austenite. Furthermore, it has the effect | action which raises temper softening resistance. However, if added over 1.5% by mass, forgeability, cold workability, machinability, and carbonitridability (or carburizability) may deteriorate.

[About surface hardness of rolling surface]
The decrease in the rolling life of the planetary gear device in the foreign matter lubrication environment is caused by stress concentration at the rising edge of the indentation formed by the biting of the foreign matter. If the surface hardness of the rolling surface of the pinion shaft 4 (surface hardness of the axial intermediate portion X (surface hardened layer 19)) is HV700 or more and HV850 or less, indentation is difficult to form, so that the planetary gear device is mixed with foreign matter. Long life even when used in. If the surface hardness of the rolling surface of the pinion shaft 4 is less than HV700, there is a risk that indentation will be formed because the hardness is insufficient, and if it exceeds HV850, it is necessary to increase the quenching temperature. The toughness may be reduced due to the coarsening of the crystal grain size.

[Residual austenite amount of the hardened surface layer 19]
When the amount of retained austenite of the surface hardened layer 19 is 20% by volume or more and 50% by volume or less, the stress concentration as described above hardly occurs. If it is less than 20% by volume, the effect of reducing the stress concentration that relieves surface fatigue is poor, and the fatigue life is reduced. On the other hand, if it exceeds 50% by volume, the surface hardness becomes insufficient and the wear resistance and surface fatigue resistance may be impaired. In order to prevent such inconvenience and to obtain an excellent fatigue life stably, the amount of retained austenite of the surface hardened layer 19 is preferably in the range of 20% by volume to 50% by volume, more preferably 30% by volume. % To 40% by volume or less.

[Residual austenite content of core 20]
By ensuring the amount of retained austenite on the surface of the rolling surface to be 20% by volume or more and 50% by volume or less, it is possible to improve the rolling fatigue life in a foreign matter lubrication environment. On the other hand, retained austenite decomposes and changes to a mixture of ferrite and cementite or martensite when stress such as a load or heat is applied, so that plastic deformation occurs in the pinion shaft. Therefore, in order to suppress the plastic bending of the pinion shaft 4 as much as possible, the amount of retained austenite of the inner core portion 20 of the surface hardened layer 19 is preferably more than 0% by volume and not more than 2.0% by volume, and 0% by volume. More preferably.

[Surface hardness of axial end Y]
In the pinion shaft 4, a high hardness is required for the rolling surface in order to ensure a rolling fatigue life. However, since the axial end Y is fixed by caulking, the hardness should be plastically deformable. There must be. The surface hardness of the axial end Y (particularly where the passive films 21 and 21 are formed) is preferably HV350 or less, more preferably HV150 or more and HV350 or less, and HV150 or more and HV320 or less. More preferably. If the surface hardness of the axial end Y exceeds HV350, cracking may occur during caulking, and if it is less than HV150, rigidity after caulking may not be maintained. Moreover, if the surface hardness of the axial direction end Y is HV320 or less, the generation of cracks during caulking can be further suppressed, so that the caulking process conditions can be set more freely.

[About the thickness of the passive film 21]
By providing the passivation film 21 containing chromium oxide on the surface of the axial end Y of the pinion shaft 4 (the bottom and outer peripheral surfaces of the circular recesses 18a and 18b), the axial end during carburizing and carbonitriding It is possible to limit the penetration of carbon into Y, and to suppress the surface hardness of axial end Y and the generation of proeutectoid carbide. The thickness of the passive film 21 is preferably 0.1 μm or more and 30 μm or less. If the thickness of the passive film 21 is less than 0.1 μm, carbon intrusion may not be sufficiently suppressed. If the thickness is more than 30 μm, it may be peeled off during use in an actual machine as a harmful scale, resulting in adverse effects. There is a risk of getting out.

[About the amount of carbide at the axial end Y]
For example, when normal carbonitriding is performed on case-hardened steel with increased chromium content, pro-eutectoid carbides are likely to selectively precipitate at the grain boundaries in the subsequent cooling process, and the surface of the end Y in the axial direction Even when the hardness is low, the precipitated carbide may be a starting point of cracking during caulking. Therefore, the amount of carbide at the axial end Y, that is, the amount of carbide existing inside the passive film 21 is preferably 15% or less in terms of area ratio, and is 1.0% or more and 12% or less. It is more preferable.

  If the amount of carbide at the axial end Y is more than 15%, the carbides are easily bonded to each other, and caulking cracks are likely to occur when caulking. On the other hand, if the amount of carbide at the axial end Y is 1.0% or more, sufficient strength can be obtained, so that crimping and fixing can be performed more reliably. In addition, if the amount of carbide at the axial end Y is 12% or less, the occurrence of cracking during caulking can be further suppressed, so that the caulking process conditions can be set more freely.

  Next, a method for manufacturing such a pinion shaft 4 will be described with reference to FIG. First, a material made of alloy steel containing chromium (for example, high-carbon chromium bearing steel, case-hardened steel) is processed into a substantially cylindrical shape (round bar shape) to form a pinion shaft-shaped member (processing step). At the time of this processing, the outer peripheral surface (cylindrical surface) of the axially intermediate portion of the substantially cylindrical material is ground, and a work-affected layer is formed on at least both axial end surfaces of the substantially cylindrical material. In addition, the material is cut so as to be accompanied by plastic flow, and a work-affected layer is formed on the surface of both end portions in the axial direction of the member (bottom portions of the circular recesses 18a and 18b). The outer peripheral surface of the end portion in the axial direction of the substantially cylindrical material may also be cut to generate a work-affected layer on the outer peripheral surface.

The work-affected layer is formed thicker as it becomes harder, and is difficult to form by grinding. The thickness of the work-affected layer may be controlled to 3 μm or more and 40 μm or less, for example, by adjusting conditions such as the processing speed.
The cutting conditions are not particularly limited as long as the work-affected layer can be formed and cutting can be performed with plastic flow. For example, in the case of manufacturing a pinion shaft from a bearing steel material, If so, the following conditions can be exemplified. Both end surfaces in the axial direction of the material while moving the material made of bearing steel processed into a substantially cylindrical shape with a diameter of 16 mm in the axial direction at a feed rate of 0.02 mm / rotation while rotating at a rotational speed of 1000 rpm to 3000 rpm. And cutting the outer peripheral surface. Then, cutting is performed so as to be accompanied by plastic flow, and a work-affected layer is formed.

  Subsequently, the member having the work-affected layer is subjected to heat treatment including carburizing or carbonitriding at 850 ° C. or more and 950 ° C. or less (heat treatment step). At that time, since the heat treatment is performed on the member having the work-affected layer in the heat-up process of the heat treatment process, the end surfaces in the axial direction where the work-affected layer is formed and the outer peripheral surface of the end portion in the axial direction are made of chromium. A passive film 21 containing an oxide is formed (passive film forming step). On the other hand, a surface hardening by a carburizing process or a carbonitriding process is performed on the axially intermediate part (that is, the ground part) where the work-affected layer is not formed after the temperature raising process. That is, formation of the passive film 21 and surface hardening by carburizing or carbonitriding are achieved by a single treatment.

However, the formation of the passive film 21 and the surface hardening by the carburizing process or the carbonitriding process may be performed separately (two processes may be performed). That is, after heat-treating the member having a work-affected layer and forming the passive film 21 on the both axial end surfaces and the outer peripheral surface of the axial end portion where the work-affected layer is formed (passive film forming step) The member on which the passive film 21 is formed may be subjected to heat treatment including carburizing or carbonitriding.
Note that the temperature increase during the heat treatment including the carburizing process or the carbonitriding process is preferably performed gradually so that the passive film 21 is easily formed, and the temperature increasing rate is, for example, 5 ° C./min to 25 ° C./min. It is preferable to control.

  After heat treatment including carburizing treatment or carbonitriding treatment, after annealing treatment (refining treatment) at 650 ° C. or higher and 780 ° C. or lower in air or nitrogen atmosphere, the axial intermediate portion (heat treatment in heat treatment step) The surface hardening layer 19 is formed by subjecting only the surface of the material subjected to the induction hardening to induction hardening only on the portion different from the portion where the work-affected layer is formed (induction hardening step). Then, a tempering process is further performed. By such a treatment, the surface hardness layer 19 having a surface hardness of HV700 or more and HV850 or less is provided in the axial intermediate portion X, the surface hardness of both axial ends Y and Y is HV150 or more and HV350 or less, and the axial direction The pinion shaft 4 having the passive film 21 on the outer peripheral surfaces of both end surfaces and the axial end portion Y is obtained. Further, the amount of carbide existing inside the passive film 21 is set to 15% or less by area ratio. Furthermore, the amount of retained austenite of the surface hardened layer 19 is set to 20% by volume or more and 50% by volume or less, and the amount of retained austenite of the core 20 inside the surface hardened layer 19 is set to 0% by volume.

  Thus, the passive film 21 is formed by defining the thickness of the work-affected layer and the temperature increase rate during the heat treatment including the carburizing process or the carbonitriding process, and the axial end Y (the passive film 21 of the passive film 21) is formed. Since the amount of carbides present on the inner side is suppressed, niobium (Nb), which is an element for preventing the formation of coarse grains, is used in spite of using alloy steel with an increased chromium content for improving rolling fatigue life. ) Is not required.

Here, the work-affected layer at the axial end Y and the heating rate during carburizing or carbonitriding will be described in detail.
The formation of the passive film 21 is related to the work-affected layer on the surface and the rate of temperature increase at the time of temperature increase. The presence of a work-affected layer on the surface promotes the diffusion of chromium to the surface, so that no chromium oxide is contained before the start of carburizing or carbonitriding (ie, at the elevated temperature of carburizing or carbonitriding). A dynamic film 21 is formed.

If the thickness of the work-affected layer is less than 3 μm, the generation of the passive film 21 may be insufficient. On the other hand, in order to obtain a work-affected layer deeper than 40 μm (that is, when the work-affected layer has a thickness exceeding 40 μm), processing under severe cutting conditions is required. It is not realistic considering the load.
In addition, the passive film 21 is not formed when processing is performed at room temperature, but is formed under a certain temperature environment during temperature rise. Therefore, when the temperature is increased at a rate faster than 25 ° C./min, there is a possibility that the passive film 21 having a sufficient thickness cannot be formed. On the other hand, at a speed slower than 5 ° C./min, it takes too much time to raise the temperature to the carburizing temperature or the carbonitriding temperature, which is not realistic from the viewpoint of productivity.

  The pinion shaft 4 of FIG. 1 includes a passive film 21, but the passive film 21 is intended to limit carbon intrusion into the axial end Y during carburizing and carbonitriding. It is unnecessary after carburizing and carbonitriding. Therefore, after the carburizing and carbonitriding, the passive film 21 may be removed by a process of removing the passive film by cutting or the like. If the passive film 21 is removed, the end Y in the axial direction is composed of only a layer having a lower hardness, so that the caulking process becomes easier.

  Next, a planetary gear device using the pinion shaft 4 will be described with reference to FIGS. The planetary gear device includes a sun gear 1 having teeth 1a formed on the outer peripheral surface, a ring gear 2 disposed concentrically with the sun gear 1 and having teeth 2a formed on the inner peripheral surface, the sun gear 1 and the ring gear 2 And a plurality (generally 3 to 4) of planetary gears 3, 3, and 3 arranged at equal intervals in the circumferential direction. The teeth 3a formed on the outer peripheral surfaces of the plurality of planetary gears 3, 3 and 3 mesh with both teeth 1a and 2a.

  The plurality of planetary gears 3, 3, and 3 are rotatably supported around the pinion shaft 4 via a plurality of needle rollers 5 and 5, respectively. That is, the planetary gear 3, the pinion shaft 4, and the needle rollers 5, 5 constitute a rolling bearing (radial needle bearing), and the pinion shaft 4 of these corresponds to the inner ring of the rolling bearing.

  A base end portion (right end portion in FIG. 4) of each pinion shaft 4 is fixed to a substrate 7 of a carrier 6 that is rotatable around the sun gear 1. More specifically, the base end portion of each pinion shaft 4 is crimped and fitted into a through hole 8a formed in the substrate 7 by an interference fit. The pinion shaft 4 with the proximal end crimped is shown in FIGS. A part of the base end portion of the pinion shaft 4 or the entire circumferential direction is fixed to the substrate 7 of the carrier 6 by being caulked and spread radially outward. When the base end portion of the pinion shaft 4 is caulked and spread outward in the radial direction, the inner peripheral side portion of the base end portion of the pinion shaft 4 is deformed and deformed by tensile stress, and the outer peripheral side portion is contracted and deformed by compressive stress. . Therefore, cracks are unlikely to occur during caulking.

  In the illustrated example, the sun gear 1 is formed in a cylindrical shape, and the substrate 7 is formed in an annular shape with an L-shaped cross section. As shown in FIG. 4, the cylindrical portion 10 formed on the inner peripheral edge of the substrate 7 is spline-engaged with the outer peripheral surface of the rotating shaft 11. The sun gear 1 is supported around the rotary shaft 11 so as to be rotatable relative to the rotary shaft 11. The ring gear 2 is supported around the sun gear 1, the carrier 6, and the rotation shaft 11 so as to be rotatable relative to the sun gear 1, the carrier 6, and the rotation shaft 11.

  Further, the tip end portion (left end portion in FIG. 4) of each pinion shaft 4 is fitted into a through-hole 8b formed in a connecting plate 12 formed in an annular shape that constitutes the carrier 6 together with the substrate 7, and is fixed by crimping. The tip portions of the pinion shafts 4 are connected to each other. The caulking of the tip end portion of the pinion shaft 4 is also the same as in the case of the base end portion of the pinion shaft 4 described above. As shown in FIGS. The whole is fixed to the connecting plate 12 by being caulked and spread outward in the radial direction.

  An outer peripheral surface (a portion between the substrate 7 and the connecting plate 12) of the axially intermediate portion of the plurality of pinion shafts 4 is a cylindrical surface-shaped inner ring raceway 13. On the other hand, the inner peripheral surface of the planetary gear 3 is a cylindrical outer ring raceway 14. The needle rollers 5, 5 are arranged between the inner ring raceway 13 and the outer ring raceway 14, and the planetary gear 3 is rotatably supported around the axial intermediate portion of the pinion shaft 4.

  In such a planetary gear device including the planetary gear 3 and the pinion shaft 4, for example, the rotation shaft 11 is used as a drive shaft or a driven shaft, and the center of the sun gear 1 or the ring gear 2 is coupled to the driven shaft or the drive shaft. ing. Then, any one of the sun gear 1, the ring gear 2, and the planetary gear 3 is rotatable, and the drive shaft is switched by switching whether the sun gear 1, the ring gear 2, or the planetary gear 3 is non-rotatable. Speed change and rotation direction conversion between the motor and the driven shaft.

[Second Embodiment]
Next, the pinion shaft 4 of the second embodiment will be described with reference to FIG. In addition, since the structure and manufacturing method of the pinion shaft 4 of 2nd embodiment are substantially the same as the structure and manufacturing method of the pinion shaft 4 of 1st embodiment, only a different part is demonstrated and description of the same part is abbreviate | omitted. To do.

  In the case of the pinion shaft 4 of the first embodiment, the passive films 21 and 21 are formed on the inner surfaces of the circular recesses 18a and 18b and the outer peripheral surface of the axial end Y. On the other hand, in the case of the pinion shaft 4 of the second embodiment, both end surfaces in the axial direction are recessed by cutting to form circular recesses 18a and 18b, and corners on the outer periphery of the axial end portions Y and Y are formed. Since chamfering is performed by cutting (thus, the inner surfaces of the circular concave portions 18a and 18b, the outer peripheral side portions of both axial end surfaces, and the chamfered portions are cutting surfaces), as shown in FIG. 7, the circular concave portions 18a and 18b Passive films 21 and 21 are also formed on the outer peripheral side portion and the chamfered portion of both axial end surfaces along with the inner surface. The shape of the chamfered portion may be flat (so-called C chamfering) as shown in FIG. 7, or may be curved (so-called R chamfering (round chamfering)).

  In the case of the pinion shaft 4 of the second embodiment, as described above, the axial length of the material is shortened by cutting when the pinion shaft 4 is manufactured. decide. That is, if a material having a larger axial length than the pinion shaft 4 of the finished product is prepared and both end portions in the axial direction of the material are cut as described above to obtain the normal axial length of the pinion shaft 4, Even when such a manufacturing method is employed, the pinion shaft 4 having a desired axial length can be manufactured. In addition, when the passive film 21 is removed by cutting or the like after carburizing or carbonitriding, the axial length of the material may be determined in consideration of the fact that the axial length is shortened accordingly. .

  In the case of the pinion shaft 4 of the first embodiment, the axial intermediate portion X having the hardened surface layer 19 and the axial end portion Y having the passive film 21 are in contact with each other and aligned in the axial direction. On the other hand, in the case of the pinion shaft 4 of the second embodiment, as shown in FIG. 7, the passive film 21 and the surface hardened layer 19 are interposed between the axial intermediate portion X and the axial end portion Y. A medium hardness portion Z of medium hardness that is not present is interposed. Since neither the passive film 21 nor the surface hardened layer 19 is formed on the surface of the medium hardness portion Z, the surface hardness of the medium hardness portion Z is lower than that of the surface hardened layer 19 and the passive film 21. (That is, the hardness between the surface hardness of the passive film 21 and the surface hardness of the surface hardened layer 19).

In addition, said 1st and 2nd embodiment showed an example of this invention, Comprising: This invention is not limited to 1st and 2nd embodiment. Various changes or improvements can be added to the first and second embodiments, and forms to which such changes or improvements are added can also be included in the present invention.
For example, in the first and second embodiments, a pinion shaft as a part used in a planetary gear device or the like is given as an example of a mechanical part. However, the mechanical part of the present invention is not limited to a pinion shaft. Absent. Other examples of mechanical parts to which the present invention can be applied include shaft parts such as tappet roller shafts, parts constituting ball screws, gears, and parts having serrations.

  For example, the screw shaft of a ball screw is processed when the end is processed into various shapes (post-processing) at the time of manufacture by the manufacturer, or the end is processed into various shapes at the time of use by the user if desired ( May be post-processed). Therefore, if the end portion of the screw shaft is a low hardness portion in the present invention, the end portion is easily processed in the post-processing as described above. Therefore, the machine part of the present invention is suitable for a part to be post-processed like a screw shaft of a ball screw.

Further, for example, if the tooth base of a gear has a high hardness, cracks may easily occur due to stress concentration. If the sliding portion of the gear is the high hardness portion in the present invention and the tooth root is the low hardness portion in the present invention to increase toughness, the gear can be miniaturized. Therefore, the mechanical component of the present invention is suitable for a component that should be prevented from breaking due to stress concentration, such as a gear.
Furthermore, for example, a part having serrations can increase the joining force by plastically deforming the serration part during serration joining. Therefore, if at least a part of the serration portion is a low hardness portion in the present invention, the joining force tends to be high during serration joining. Therefore, the mechanical component of the present invention is suitable for a component that is plastically deformed during use, such as a component having serrations.

4 Pinion shaft 13 Inner ring raceway 19 Surface hardened layer 20 Core portion 21 Passive coating X Axial intermediate portion Y Axial end portion

Claims (3)

  A high-hardness portion made of alloy steel containing chromium and having a surface hardened layer, and a low-hardness portion having a surface hardness lower than the surface hardness of the high-hardness portion, the low-hardness portion being a chromium oxide A mechanical component having a passivated film containing bismuth on the surface, wherein the amount of carbide existing inside the passivated film is less than the amount of carbide present in the hardened surface layer.   The machine part according to claim 1, further comprising a medium hardness portion having a surface hardness lower than that of the high hardness portion and higher than that of the low hardness portion. The alloy steel includes carbon in an amount of 0.1 mass% to 0.29 mass%, chromium in an amount of 2.0 mass% to 5.0 mass%, molybdenum in an amount of 0.1 mass% to 1.5 mass%, Containing 0.1 mass% or more and 1.5 mass% or less of manganese, 0.1 mass% or more and 1.5 mass% or less of silicon, and the balance is iron and inevitable impurities,
The surface hardness of the high hardness portion is HV700 or more and HV850 or less,
The mechanical part according to claim 1 or 2, wherein the thickness of the passive film is 0.1 µm or more and 30 µm or less.

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