JPWO2015199103A1 - Pinion shaft and manufacturing method thereof - Google Patents

Abstract

It is made of steel, the amount of retained austenite on the surface of the rolling surface is 20 to 50% by volume, the amount of retained austenite at the center is 0% by volume, and the surface hardness is 150 to 350 HV at the shaft end. A pinion shaft having a ferrite decarburized layer of 0.02 to 0.1 mm, and no pro-eutectoid carbides present in the ferrite decarburized layer.

Description

  The present invention relates to an alloy pinion shaft used for a planetary gear device and a method for manufacturing the same.

  In a planetary gear device such as an automobile, the planetary shaft supports a pinion gear via a needle roller. The pinion shaft corresponds to the inner ring of the rolling bearing, the inner surface of the pinion gear corresponds to the outer ring, and the shaft end of the pinion shaft is fixed to the carrier. There are two types of fixing methods: a “pinning type” that spans the locking pin and a “clamping type” that plastically deforms the shaft end, and the “clamping type” does not require a locking pin. Therefore, the number of parts can be reduced and the shaft length can be suppressed.

  However, in order to achieve a “clamping type” structure, the pinion shaft must satisfy the conflicting characteristics of softening the end part and improving the plastic workability while ensuring the strength against shear stress as a rolling bearing. is there.

  Carbon steel, carbon engineering steel, high carbon chromium bearing steel, case-hardened steel, etc. are used as the material of the pinion shaft. For example, high carbon steel is tempered (tempered) at high temperature after carbonitriding. Known are pinion shafts that have been induction hardened on the transfer surface after reducing the hardness of the caulking part, and pinion shafts that have been carbonitrided with case-hardened steel with increased chromium content to increase the structural stability. (See Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2013-228032 Japanese Unexamined Patent Publication No. 2013-227615

  When carbonitriding a steel material with a high chromium content, carbides (predetermined carbides) are selectively deposited at grain boundaries in the subsequent cooling process. And by this pro-eutectoid carbide, ductility falls and caulking property also falls. In the caulking type pinion shaft, the end of the shaft is hard enough to be caulked, but if a pro-eutectoid carbide is deposited, cracks and cracks occur in the caulking portion. However, a reduction in caulking property due to such pro-eutectoid carbide has not been studied so far, and there is room for further improvement in the caulking pinion shaft.

  This invention is made | formed in view of such a condition, and it aims at further improving the caulking property in a caulking type pinion shaft.

In order to solve the above-described problems, the present invention provides the following pinion shaft and a manufacturing method thereof.
(1) Made of steel and
The amount of retained austenite on the surface of the rolling surface is 20 to 50% by volume,
The amount of retained austenite in the core is 0% by volume,
A pinion shaft characterized by having a surface hardness of 150 to 350 HV and a ferrite decarburized layer of 0.02 to 0.1 mm on the surface layer, and no pro-eutectoid carbide in the ferrite decarburized layer at the shaft end. .
(2) The said steel materials are the mass%, C: 0.1-0.29%, Cr: 2.0-5.0%, Mo: 0.1-1.5%, Mn: 0.1 The pinion shaft according to (1), characterized in that the pinion shaft contains 1.5%, Si: 0.1 to 1.5%, and the balance is an alloy steel made of iron and inevitable impurities.
(3) A method for manufacturing a pinion shaft according to (2) above,
In mass%, C: 0.1 to 0.29%, Cr: 2.0 to 5.0%, Mo: 0.1 to 1.5%, Mn: 0.1 to 1.5%, Si: An alloy steel containing 0.1 to 1.5% and the balance being iron and inevitable impurities is processed into a predetermined shape, and then carbonitrided, and then annealed at 700 to 770 ° C. in the air or in a nitrogen atmosphere. A method for manufacturing a pinion shaft.

  In the pinion shaft of the present invention, precipitation of pro-eutectoid carbide that affects the ductility of the crimped portion is suppressed, and the crimpability is further improved. Moreover, the transfer surface has sufficient surface hardness by induction hardening, and is excellent in durability.

It is sectional drawing which shows an example of the pinion shaft of this invention. It is a graph which shows the relationship between a ferrite decarburization layer depth and the surface hardness of a shaft end part. With the value of Equation 1. It is a graph which shows the relationship with the presence or absence of a crack. It is a graph which shows the relationship between the value of Formula 2, and the presence or absence of damage. It is a graph which shows the relationship between the value of Formula 3, and the bending amount after an endurance test.

  Hereinafter, the present invention will be described in detail.

  In the present invention, the pinion shaft is a caulking type and has, for example, the structure shown in FIG. In the illustrated pinion shaft 10, the outer peripheral surface of the columnar support shaft 11 becomes a rolling surface 13, and the shaft end portions 18 a and 18 b function as caulking portions. A center hole 15 and branch holes 16a and 16b are provided as oil supply holes for supplying lubricating oil to the rolling surface 13. The center hole 15 has an opening in the radial center of one of the shaft end portions 18a and 18b (here 18a) of the support shaft 11 and extends in the axial direction therefrom. Further, two branch holes 16a and 16b are formed by branching from the center hole 15 and extending outward in the radial direction so as to open to the rolling surface 13. Further, a hardened surface layer 19 is formed on the rolling surface 13 of the support shaft 11.

  In the present invention, the pinion shaft 10 is made of SUJ2-5 high carbon chrome bearing steel, ISO683 bearing steel such as 100CrMnSi6-4, or mass%, C: 0.1 to 0.29%, Cr: 2.0. -5.0%, Mo: 0.1-1.5%, Mn: 0.1-1.5%, Si: 0.1-1.5%, with the balance consisting of iron and inevitable impurities It is preferable to form with alloy steel. Below, alloy components, such as C and Cr, are demonstrated.

[C: 0.1-0.29%]
C (carbon) dissolves in the base of the alloy steel to improve the hardness after quenching and tempering, and also forms carbide by combining with carbide forming elements such as Fe, Cr, Mo, etc. It is an element that has an enhancing effect. In order to obtain the hardness required for rolling fatigue resistance, carbonitriding is performed. However, if the processing time is increased, the cost is increased, so that the C content is 0.1% or more in order to shorten the processing time. It is necessary to. However, if the C content exceeds 0.29%, forgeability, cold workability, and machinability may be reduced, resulting in an increase in processing cost. In addition, the rod formability is poor, and particularly when the shaft diameter is 15 mm or less, plastic working is difficult, and cracks and cracks are likely to occur during molding. Furthermore, if it exceeds 0.29%, coarse eutectic carbides are likely to be produced during steelmaking, and the rolling fatigue life and strength may be reduced. A preferable C content is 0.15 to 0.24%.

[Cr: 2.0-5.0%]
Cr (chromium) is an element having a function of improving the hardenability, temper softening resistance, corrosion resistance, and rolling fatigue life by dissolving in a matrix. It also has the effect of substantially preventing the movement of interstitial solid-solution elements such as carbon and nitrogen, making the base structure stable, and greatly reducing the lifespan at the time of hydrogen intrusion. Furthermore, since the carbides finely distributed in the alloy steel are 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. In addition, the retained austenite is not easily decomposed by heat, and as a result, it is difficult to plastically deform. Therefore, if the Cr content is less than 2.0%, these effects may not be sufficiently obtained. However, if the Cr content exceeds 5.0%, cold workability, machinability, and carbonitriding may decrease, leading to an increase in cost. Furthermore, coarse eutectic carbides are likely to be produced during steel making, and the rolling fatigue life and strength may be reduced. A preferable Cr content is 2.5 to 3.5%.

[Mo: 0.1 to 1.5%]
Mo (molybdenum) is an element having a function of increasing the hardenability, temper softening resistance, corrosion resistance, and rolling fatigue life by dissolving in a matrix as in Cr. Moreover, like Cr, it has the effect | action which suppresses the lifetime fall at the time of hydrogen penetration | invasion substantially by making the penetration | invasion type solid solution elements, such as carbon and nitrogen, substantially difficult to move, stabilizing a base organization. Furthermore, since the carbide finely distributed in the alloy steel is made of molybdenum carbide having a higher hardness, it also has an effect of improving the wear resistance. Therefore, if the Mo content is less than 0.1%, these effects may not be sufficiently obtained. However, if the Mo content exceeds 1.5%, cold workability and machinability may be reduced, leading to an increase in cost. Furthermore, coarse eutectic carbides are likely to be produced during steel making, and the rolling fatigue life and strength may be reduced. A preferable Mo content is 0.2 to 0.5%.

[Mn: 0.1 to 1.5%]
Mn (manganese) is an element that acts as a deoxidizer during steel making, and its content needs to be 0.1% or more. Moreover, like Mn, it has the effect | action which solid-dissolves in a base | substrate and lowers Ms point and ensures a large amount of retained austenite, or improves hardenability. However, if added in a large amount, not only cold workability and machinability are lowered, but also the martensitic transformation disclosure temperature is lowered, and a large amount of retained austenite remains after carbonitriding, and sufficient hardness cannot be obtained. There is a case. Therefore, the Mn content is 1.5% or less. A preferable Mn content is 0.5 to 1.2%.

[Si: 0.1 to 1.5%]
Si (silicon) is an element that acts as a deoxidizing agent during steelmaking, like Mn. Further, like Cr and Mn, it is an element effective in improving the bearing life by improving the hardenability 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. Therefore, the Si content needs to be 0.1%. However, if added in a large amount, the forgeability, cold workability, and carbonitriding properties may deteriorate, so the Si content needs to be 1.5% or less. A preferable Si content is 0.3 to 0.5%.

  Others are Fe and unavoidable impurities, but an appropriate amount of Ni, Cu or the like may be added if necessary.

And it adjusts so that the following may be satisfied with the manufacturing method mentioned later.
(A) The amount of retained austenite on the rolling surface 13 of the support shaft 11 is 20 to 50% by volume.
(B) The amount of retained austenite at the core 20 of the support shaft 11 is 0% by volume.
(C) The surface hardness of the shaft end portions 18a and 18b is 150 to 350 HV.
(D) The surface layer of the shaft end portions 18a and 18b has a ferrite decarburized layer of 0.02 to 0.1 mm, and no proeutectoid carbide exists in the ferrite decarburized layer. The hardness is preferably 700 to 850 HV, and more preferably 760 to 790 HV, in order to improve the rolling life.

  In order to obtain the pinion shaft 10 of the present invention, it is preferable that the wire material made of the above alloy steel is turned into a predetermined shape and carbonitrided at 830 to 960 ° C. After the carbonitriding process, the cooling rate is adjusted to cool, and annealing is performed at 700 to 830 ° C., preferably 700 to 770 ° C. in the air or nitrogen atmosphere. The rolling surface 13 is subjected to induction hardening / tempering treatment.

  The rolling surface 13 is made to have a surface retained austenite amount of 20 to 50% by volume and a retained austenite amount of the core 20 of 0% by volume by the carbonitriding and induction quenching and tempering processes. By setting the surface retained austenite amount of the rolling surface 13 to 20 to 50% by volume, preferably 30 to 50% by volume, good durability can be imparted to the rolling surface 13. In addition, the pinion shaft 10 may be subjected to a load at a high temperature. By setting the amount of retained austenite of the core 20 to 0% by volume, it is possible to prevent the pinion shaft 10 from being bent due to thermal decomposition of the retained austenite.

  Further, the surface hardness of the shaft end portions 18a and 18b is set to 150 to 350 HV, preferably 200 to 300 HV, by carbonitriding.

  In the carbonitriding process, the processing temperature and the composition of the processing gas (RX gas, enriched gas, ammonia gas) are set so that the rolling surface 13, the core part 20, and the shaft end parts 18a and 18b have the above-mentioned retained austenite amount and hardness. And adjust the flow rate.

  In the induction hardening / tempering treatment, the high frequency output conditions are set as appropriate. Since the surface is heated by quenching by causing electromagnetic induction by high frequency electromagnetic waves, only the rolling surface 13 is cured to increase the hardness, and the inside can be kept in toughness. Further, the shaft end portions 18a and 18b can be made into a state that can be caulked.

  In the treatment of the shaft end portions 18a and 18b, the cooling after the carbonitriding treatment is preferably 1.6 ° C./sec or more, more preferably 10 ° C./sec or more up to 550 ° C. Although there is no restriction | limiting in the upper limit of a cooling rate, 100 degrees C / sec or less is preferable. If the cooling rate is slower than 1.6 ° C./sec and the annealing temperature in the air or nitrogen atmosphere deviates from 700 to 770 ° C., the intended ferrite decarburized layer may not be formed. Moreover, as an annealing time in air | atmosphere or nitrogen atmosphere, 2 to 5 hours are preferable.

  The shaft end portions 18a and 18b are caulking portions that receive a large strain. By forming a ferrite decarburized layer having no pro-eutectoid carbide in this portion at a depth of 0.02 to 0.1 mm, harmful pre-deposition It is possible to eliminate the carbide, and to make the ferrite soft and have ductility that can withstand caulking. If the ferrite decarburized layer is shallower than 0.02 mm, the ductile ferrite region is too narrow and it becomes difficult to obtain good caulking properties. On the other hand, when the ferrite decarburized layer is formed to be thicker than 0.1 mm, it becomes difficult to perform caulking and fixing, and the ferrite decarburized layer appears on the rolling surface 13, and the surface hardness of the rolling surface 13 satisfies the above. As a result, the durability of the pinion shaft 10 decreases.

  Thus, in the pinion shaft 10 of the present invention, precipitation of pro-eutectoid carbides affecting the ductility of the caulking portion at the shaft end portions 18a and 18b is suppressed, and the pinion shaft 10 has excellent caulking properties and rolling. The surface hardening layer 19 of the surface 13 has sufficient hardness and is excellent in durability.

  Hereinafter, the present invention will be further described with reference to examples, but the present invention is not limited thereto.

(Examples 1-12, Comparative Examples 1-6)
A wire rod made of alloy steels A to I shown in Table 1 was subjected to turning, heat treatment, outer diameter rough grinding, and outer diameter finish grinding to produce a pinion shaft. Alloy steels A to I are all within the composition range of the present invention. The heat treatment conditions were carbonitriding for 3 hours at 830 to 930 ° C., cooling by adjusting the cooling rate, and annealing in air or nitrogen atmosphere at 650 to 830 ° C. for 2 to 10 hours. The transfer surface was subjected to induction hardening and tempering at 200 kHz. The alloy steel H is SUJ2 steel, and the alloy steel I is 100CrMnSi6-4 steel.

  About the produced pinion shaft, the test piece was extract | collected from the axial end part, while measuring the depth of the ferrite decarburization layer with the electron microscope, the presence or absence of the pro-eutectoid carbide in a ferrite decarbonization layer was confirmed by chemical analysis. Further, the amount of retained austenite on the surface or center of the support shaft, the surface hardness of the rolling surface, and the surface hardness of the shaft end were measured. The results are shown in Table 2.

Furthermore, the following tests were conducted in order to evaluate caulking properties and durability. The results are shown in Table 2.
(1) Crimpability test After the end of the produced pinion shaft was caulked and fixed to the carrier, it was confirmed whether cracks or cracks were generated due to insufficient ductility. Specifically, using a caulking press tester manufactured by NSK Ltd., a caulking portion is formed at the axial end of each pinion shaft at a caulking load of 23.5 kN and a caulking speed of 40 mm / sec. Then, the presence or absence of breakage (cracking) of the caulking portion was confirmed.
(2) Durability test It was operated in a state where the shaft end portion of the produced pinion shaft was caulked and fixed to the carrier, and the presence or absence of damage due to insufficient strength was confirmed. Specifically, using a hydraulic fluctuation excitation tester manufactured by NSK Ltd., operation is performed with a pull-out load of 4.7 kN, an excitation frequency of 35 Hz, and a test cycle of 1 million times. The presence or absence of damage was confirmed. In addition, this test was not implemented about the thing whose surface hardness of the shaft end part was high and could not be caulked.

  As shown in Table 2, when the ferrite decarburized layer at the shaft end is within the range of the present invention, there is no crack in the caulking test, and the durability is high. On the other hand, as in Comparative Examples 1 to 3, when the ferrite decarburized layer is not formed as specified, cracks and breakage occur. Moreover, also when the amount of retained austenite of a rolling surface or a core part is outside the scope of the present invention as in Comparative Examples 4 to 6, cracks and breakage occur.

  Moreover, the relationship between a ferrite decarburization layer depth and an end surface hardness is shown in FIG. 2 based on Examples 1-4, 10 and Comparative Examples 1-4. The plot “●” in the figure is an example, and the plot “▲” is a comparative example, but the examples are all within the scope of the present invention indicated by the dotted line in the figure, and no cracks or breakage occurs. On the other hand, in the comparative example deviating from the scope of the present invention indicated by the dotted line, cracks or breakage occurs. In Comparative Example 1, the ferrite decarburized layer depth and end surface hardness are within the dotted line, but as shown in Table 2, pro-eutectoid carbide is present in the ferrite decarburized layer, and cracking occurs in the caulking test. Occurred.

In addition to the above, from the results of Examples 1 to 12 and Comparative Examples 2 to 4, there is a correlation between the value of the following formula 1 regarding end hardness and ferrite decarburized layer depth and the presence or absence of cracks in the caulking test. I found out. And it turned out that a crack does not generate | occur | produce, if the value of Formula 1 is the range of 0.8-39.6. In particular, the value of Formula 1 is preferably in the range of 0.8 to 25.2. Table 2 shows the value of Equation 1 together, and FIG. 3 shows the relationship between the value of Equation 1 and the presence or absence of cracks in a graph.
Formula 1 = (430-end surface hardness) × ferrite decarburized layer depth

In addition, from the results of Examples 1 to 12 and Comparative Examples 3, 5, and 6, between the value of the following formula 2 regarding the rolling surface surface hardness and the amount of rolling surface retained austenite, and the presence or absence of breakage in the durability test We found that there is a correlation. And it turned out that it will not be damaged if the value of Formula 2 is in the range of 1175-7910. In particular, the value of Formula 2 is preferably in the range of 2640 to 4410. Table 2 shows the value of Equation 2 together, and FIG. 4 shows the relationship between the value of Equation 2 and the presence or absence of breakage in a graph.
Formula 2 = (Rolling surface surface hardness−550) × (55−Rolling surface residual austenite amount)

Further, from the results of Examples 1 to 12, there is a correlation between the value of the following formula 3 regarding the Cr amount of the material, the amount of rolling surface retained austenite, and the surface hardness of the rolling surface, and the amount of bending after the durability test. Found that there is. It has been found that if the value of Equation 3 is 54 or more, the amount of bending can be reduced. In particular, the value of Formula 3 is preferably 60 or more. Table 2 shows the value of Equation 3 together, and FIG. 5 is a graph showing the relationship between the value of Equation 3 and the amount of bending.
Formula 3 = (Cr amount / Rolling surface residual austenite amount) × (Rolling surface surface hardness−677) × (60−Rolling surface residual austenite amount)

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on June 24, 2014 (Japanese Patent Application No. 2014-129501), the contents of which are incorporated herein by reference.

  According to the present invention, the caulking property of the caulking pinion shaft can be further improved.

DESCRIPTION OF SYMBOLS 10 Pinion shaft 11 Support shaft 13 Rolling surface 15 Center hole 16a, 16b Branch hole 18a, 18b Shaft end part 19 Surface hardening layer 20 Core part

Claims (3)

Made of steel, and
The amount of retained austenite on the surface of the rolling surface is 20-50% by volume,
The amount of retained austenite in the core is 0% by volume,
A pinion shaft characterized by having a surface hardness of 150 to 350 HV and a ferrite decarburized layer of 0.02 to 0.1 mm on the surface layer, and no pro-eutectoid carbide present in the ferrite decarburized layer at the shaft end. .   The said steel materials are the mass%, C: 0.1-0.29%, Cr: 2.0-5.0%, Mo: 0.1-1.5%, Mn: 0.1-1.5 The pinion shaft according to claim 1, wherein the pinion shaft is made of an alloy steel composed of iron and unavoidable impurities. A method of manufacturing a pinion shaft according to claim 2,
In mass%, C: 0.1 to 0.29%, Cr: 2.0 to 5.0%, Mo: 0.1 to 1.5%, Mn: 0.1 to 1.5%, Si: An alloy steel containing 0.1 to 1.5% and the balance being iron and inevitable impurities is processed into a predetermined shape, and then carbonitrided, and then annealed at 700 to 770 ° C. in the air or in a nitrogen atmosphere. A method for manufacturing a pinion shaft.

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