JP5388264B2 - Manufacturing method of rolling shaft - Google Patents

Description

The present invention relates to a method for manufacturing a rolling shaft, and more particularly to a method for manufacturing a rolling shaft used in a rocker arm bearing.

The rolling shafts of rolling bearings used for rocker arms used to open and close the intake valves and exhaust valves of automobile engines are caulked to both ends of the shaft when fixed to the rocker arms. There is a case where processing to be caulked on the member is performed. In this case, the rolling surface of the rolling shaft requires high hardness, but the end must be soft so that it can be crimped. Conventionally, for example, Patent Documents 1 to 3 propose a technique in which the end of the rolling shaft is softened and the end has a hardness of 300 Hv or less in terms of Vickers hardness.
JP 2005-299914 A JP 2006-63917 A JP 2006-250294 A

  Patent Documents 1 to 3 disclose a technique in which the hardness of the end of the rolling shaft is reduced to 300 Hv or less in terms of Vickers hardness by slow cooling after carbonitriding or quenching and tempering (tempering) after carbonitriding. Has been. However, due to the heat treatment as described above, spherical and relatively hard carbide precipitates on the surface layer portion of the rolling shaft.

  When this carbide is uniformly distributed on the end face of the rolling shaft, the Vickers hardness at an arbitrary position on the same end face is stable. On the other hand, when the carbide is coarsened and unevenly distributed on the end face, the hardness is different between the location where the carbide is present and the location where the carbide is not present. As a result, the hardness at arbitrary positions on the same end face varies, which becomes an unstable factor in guaranteeing the hardness of the end face of the rolling shaft.

  Therefore, a main object of the present invention is to provide a rolling shaft capable of reducing the hardness of the end face and suppressing the variation in hardness.

Method for producing a Utatedojiku according to the present invention is a method of manufacturing a Utatedojiku used in the bearing rocker arm. The method for manufacturing a rolling shaft includes a step of processing a material formed of bearing steel to form a rough shape of a rolling shaft having an end surface intersecting the axial direction of the rolling shaft, and exposing the end surface to the atmosphere. a step of carbonitriding process at point A1 above in state, the step of cooling to less than A1 point while exposing the end surface to an atmosphere, a step of induction hardening a rolling region of the end face in the step of cooling agglomerated carbides precipitated in the surface layer portion, and a step of removing from the end surface by removing the surface layer portion of the end face.

  Here, the A1 point indicates a point corresponding to a temperature at which the steel structure starts transformation from ferrite (iron α-phase) to austenite (iron γ-phase) when the steel is heated. The A1 point corresponds to the eutectoid temperature, for example, 723 ° C. in the Fe—C system. Moreover, the A1 point of the steel material normally used for a rolling bearing is also the temperature of the vicinity.

In the manufacturing method of the rolling shaft, the cooling step may be slow cooling.
Also been rapidly cooled in step to cool and then may further comprise the step of performing the tempering is less than A1 point.

  The rolling shaft may also have a nitrogen-enriched layer in at least a part of the surface layer portion of the rolling region. Here, the nitrogen-enriched layer is a layer in which the nitrogen concentration in the steel is increased with respect to the nitrogen concentration contained in the raw steel. As will be described later, the nitrogen-enriched layer is formed by carbonitriding, but the nitrogen-enriched layer may or may not be enriched with carbon.

  Further, in at least a part of the surface layer portion of the rolling region, the austenite grain size may be 11 or more and the hardness may be 653 Hv or more in terms of Vickers hardness. Here, the austenite crystal grains are austenite crystal grains that have undergone phase transformation during quenching heating, and that remain at room temperature after transformation into martensite by cooling. In the sense that it is a grain boundary at the time of heating immediately before quenching, it may be referred to as prior austenite crystal grains.

  The austenite crystal grain may be a grain boundary that can be observed by performing a process of revealing the grain boundary, such as etching, on the gold phase sample of the target member. The measurement may be obtained by converting the average value of the JIS standard particle size number to the average particle size as described above, or while the random direction straight line superimposed on the metal phase structure by the intercept method or the like is associated with the grain boundary. An average value of the interval lengths may be taken, and a two-dimensional to three-dimensional interval length may be obtained by applying a correction coefficient.

In the rolling shaft, the end face may have a Vickers hardness of 300 Hv or less.
The rolling shaft has a solid cylindrical shape, the retained austenite occupies 10 to 50% by volume in at least a part of the surface layer portion of the rolling region, and in the central portion in the cross section of the axial central portion of the rolling region. Residual austenite may be present.

Further, the hardness of the central portion may be 550 Hv or more in terms of Vickers hardness.
The rolling shaft has a hollow cylindrical shape, and retained austenite accounts for 10 to 50% by volume in at least a part of the surface layer portion of the rolling region, and residual austenite exists in the surface layer portion on the inner peripheral side surface. May be.

According to the rolling shaft manufacturing method of the present invention, after cooling by carbonitriding, or after induction cooling in the rolling region after cooling, the end surface of the rolling shaft is ground by a method such as grinding the end surface of the rolling shaft. By removing the surface layer portion, it is possible to remove high-hardness carbides deposited on the surface layer of the end face. Therefore, it is possible to reduce the hardness of the end face of the rolling shaft and suppress the hardness variation.

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is a schematic front view showing a configuration of a rolling bearing for a rocker arm of an engine in the first embodiment. FIG. 2 is a cross-sectional view of the rocker arm rolling bearing, and FIG. 2A is a view corresponding to a cross section taken along line II-II in FIG. As shown in FIGS. 1 and 2 (a), a rocker arm 1 as a rotating member is rotatably supported by a rocker arm shaft 5 via a bearing metal or the like at the center. That is, the rocker arm 1 swings around the rocker arm shaft 5.

  An adjustment screw 7 is screwed into one end 1 b of the rocker arm 1. The adjustment screw 7 is fixed by a lock nut 8 and is in contact with the upper end of an air supply valve or exhaust valve (a valve for opening / closing an automobile engine) 9 of the internal combustion engine at the lower end thereof. The valve 9 is biased by the elastic force of the spring 10.

  The rocker arm 1 is provided with a cam follower body 50 at the other end 1a, and the cam follower body 50 integrally includes a roller support portion 14 formed in a bifurcated shape. A roller 4 constituting an outer member is supported at the center of the outer peripheral surface of the roller shaft 2 as a rolling shaft via a roller 3 as a rolling element. The axial direction of the roller 3 is arranged parallel to the axis of the roller shaft 2. The outer peripheral surface of the roller 4 is in contact with the cam surface of the cam 6 provided on the cam shaft by the urging force of the spring 10.

  As shown in FIG. 2B, which is an enlarged view of the E portion of FIG. 2A, the forked roller support portion 14 is provided with a chamfered portion 14a, and both end surfaces of the roller shaft 2 corresponding to the inner member. An end portion near 2c is caulked (plastically worked) to form a caulking fixed portion 25 and is fixed. At both ends of the roller shaft, a caulking portion 2d by plastic working is formed, and a space that is vacant is filled by forming the chamfered portion 14a. That is, at least the end surface 2c of the roller shaft 2 has a hardness suppressed to 300 Hv or less and the end portion is easily caulked, and the roller shaft 2 is caulked to be caulked to the chamfered portion 14a of the roller support portion 14. A processing fixing portion 25 is formed.

  Here, a rolling bearing constituted by a roller shaft 2, a roller 3, and a roller 4 as a rolling shaft is used as a rocker arm rolling bearing. In general, when a cage is not used, it is called a full roller bearing, but in this description, it will be described without distinction. Since the roller bearing for the rocker arm rotates while the roller 4 is in contact with the cam 6, the pressing force and impact force of the cam 6 act on the roller 4.

  In the rolling bearing according to Embodiment 1, the roller shaft 2 has a nitrogen-enriched layer because it is carbonitrided. Moreover, induction hardening is given to the surface layer part of the area | region containing the rolling surface which is a surface where a rolling element rolls. Here, the region including the rolling surface and in the vicinity of the surface of the side surface of the cylindrical rolling shaft is referred to as a rolling region. The surface layer portion of the rolling region refers to a region within a depth of 50 μm from the surface of the side surface of the rolling shaft. The nitrogen-enriched layer is formed on the surface layer portion of the rolling region. The surface layer of the rolling region is carbonitrided and induction-hardened, so the austenite grain size becomes ultra fine with No. 11 (according to JIS standards), and the hardness is 653 Hv or more in Vickers hardness. The retained austenite accounts for 10 to 50% by volume. On the other hand, the central part in the cross section of the axial center part of the rolling surface is hardened by induction heating and quenching at the time of induction hardening of the surface layer part, and there is residual austenite.

  In the surface layer portion of the rolling region and the region other than the central portion in the circular cross section of the axial center portion of the rolling shaft, the ferrite grain size or austenite crystal grain size is relatively coarse as 10th or less. Further, at the portion where the influence of induction hardening is not exerted, the hardness of the end surface 2c of the roller shaft 2 is low because it is gradually cooled after carbonitriding or tempered (tempered) after quenching. Since the surface layer portion is further removed from the end surface 2c, the hardness of the end surface 2c is in the range of 300 Hv or less.

  As a result, in the surface layer portion of the rolling region, it is difficult to generate both surface damage such as surface origin separation due to metal contact caused by slipping or oil film breakage, and load-dependent internal origin type separation. Further, at least in the axial center portion of the rolling region, the strength is increased from the center portion of the cross section to the surface layer portion, or high crack fatigue strength is provided. On the other hand, other parts such as the end portions are low in hardness, and thus are easily caulked in a mass production process.

  Next, a method for manufacturing the roller shaft 2 as a rolling shaft will be described. FIG. 3 is a flowchart showing an outline of a method for manufacturing a roller shaft. As shown in FIG. 3, first, in a step (S10), a material is prepared. For example, a round bar or a round pipe, which is a material made of high carbon steel, can be prepared. As the material, JIS SUJ2 or JIS SUJ3, which is a high carbon chromium bearing steel, can be used. If necessary, processing such as cutting, forging, and turning of the material into a predetermined length is performed. As a result, a molded part molded into a schematic shape of the rolling shaft (that is, a solid or hollow cylindrical shape) is produced.

  Next, in step (S20), carbonitriding of the molded part is performed. FIG. 4 is a diagram for explaining the heat treatment method in the first embodiment. FIG. 5 is a diagram in which specific conditions are added to the heat pattern in the first embodiment. As shown in FIGS. 4 and 5, the carbonitriding process is performed by heating to a temperature of A1 point or higher, for example, 850 ° C., and holding for 90 minutes, for example. At this time, the carbon potential of the atmospheric gas is maintained at or above the amount of carbon contained in the surface layer portion of the molded part, and further, heating is performed in an atmosphere in which ammonia gas is added to RX gas that is the atmospheric gas.

  Thus, carbonitriding is performed in which the carbon concentration and nitrogen concentration of the surface layer portion of the molded part are adjusted to desired concentrations. By the carbonitriding treatment, a nitrogen-enriched layer that is a “carbonitriding treatment layer” is formed on the surface layer portion of the molded part. Since the carbon concentration of steel used as a material in the carbonitriding process is high, carbon may not easily enter the steel surface from the normal carbonitriding process atmosphere. For example, in the case of steel having a high carbon concentration, a carburized layer having a higher carbon concentration may be generated, and a carburized layer having a higher carbon concentration may be difficult to generate. Therefore, the carbon concentration in the steel can be increased by keeping the carbon potential of the atmosphere gas at or above the amount of carbon contained in the surface layer portion of the material.

  Here, the carbon potential indicates the carbon concentration contained in the surface layer of the steel when the carburization and decarburization reaction reaches equilibrium and the carbon concentration contained in the steel becomes a constant value, and in the atmosphere where the steel is heated. It is a value indicating the carburizing ability. That is, the higher the carbon potential, the higher the carburizing ability. The carbon potential of the atmosphere gas can be calculated by measuring the temperature of the atmosphere gas and the composition of the atmosphere gas, that is, the concentration of carbon monoxide and oxygen, or the concentration of carbon monoxide and carbon dioxide. .

  On the other hand, the nitrogen concentration in the steel depends on the Cr concentration in the steel, etc., but it is as low as about 0.025% by weight or less in normal steel, so it does not depend on the carbon concentration in the steel. A nitrogen-enriched layer is clearly produced. The nitrogen concentration in the nitrogen-enriched layer can be adjusted so that, for example, the nitrogen concentration at a depth of 50 μm from the surface of the molded part is 0.1% by mass or more and 0.7% by mass or less. This is because if the nitrogen concentration is less than 0.1% by mass, there is no effect of nitrogen enrichment, and in particular the surface damage life is reduced. On the other hand, if the nitrogen concentration is greater than 0.7% by mass, voids called voids are formed, or the amount of retained austenite increases so that the hardness does not come out, resulting in a short life. The nitrogen concentration of the nitrogen-enriched layer can be measured by, for example, EPMA (wavelength dispersion type X-ray microanalyzer).

  Returning to FIG. 3, next, in the step (S30), the molded part is gradually cooled to a temperature lower than the A1 point. In this case, the cooling rate may be 1.1 ° C./min or less. For example, after furnace cooling from the carbonitriding temperature to 650 ° C., the furnace is cooled from 650 ° C. to 500 ° C. Next, in step (S40), the molded part is air-cooled outside the furnace to room temperature. As shown in FIG. 4, spherical and relatively hard agglomerated carbides are deposited on the surface layer of the molded part by the slow cooling process after the carbonitriding process. The ratio of the agglomerated carbide is larger in the surface layer portion than in the molded part.

  Next, in a process (S50), the surface layer part of the end surface of a cylindrical molded part is removed. For example, the surface layer portion of the end face can be removed by mechanical processing such as grinding. By removing the surface layer portion of the end surface, the high-hardness carbides precipitated on the surface layer of the end surface are also removed.

  Next, in the step (S60), the portion corresponding to the rolling region in the molded part, that is, the surface layer portion on the side surface side of the columnar shape is induction-hardened. Induction hardening is performed, for example, by rapid heating to a temperature of 800 to 1000 ° C. and then water cooling. The frequency used for induction hardening can be 50 kHz-150 kHz, for example.

  Next, in step (S70), tempering is performed. For example, it can be tempered at a low temperature, heated to 180 ° C., held for 120 minutes, and then air-cooled. Next, in step (S80), a finishing step is performed. Specifically, a finish process such as a grinding process is performed and finished on the molded part subjected to the heat treatment step, and the roller shaft 2 as the rolling shaft according to the present embodiment is completed.

  Next, in the heat treatment (referred to as heat pattern H1) shown in FIGS. 4 and 5, how the microstructure is generated for each process will be described. First, for example, carbonitriding is performed at point A1 or higher. By this carbonitriding process, a nitrogen-enriched layer is formed in the surface layer portion of the rolling region of the rolling shaft. In this nitrogen-enriched layer, C and N, which are interstitial elements for iron atom Fe, invade hypereutectoid, for example, carbide is precipitated in austenite (two-phase coexistence). That is, the nitrogen-enriched layer is hypereutectoid steel. Moreover, since carbonitriding is not performed inside the rolling shaft, an austenite phase is formed due to the composition of the original steel material. Alternatively, the carbonitriding treatment may be performed at a temperature where two phases of ferrite and austenite or two phases of austenite and cementite coexist in the rolling shaft.

  Subsequently, when cooling, it is gradually cooled from the carbonitriding temperature. The purpose of this slow cooling is to soften the tissue and improve workability. During this slow cooling, pearlite composed of ferrite and cementite is generated from the above-mentioned austenite, and softening is promoted by agglomerating and coarsening the cementite in the pearlite without layering. Therefore, the temperature range for slow cooling may be from the carbonitriding temperature to about (A1 point-100 ° C.). Even if it is gradually cooled to a temperature lower than this, agglomeration and coarsening of cementite cannot be expected, and it takes time and efficiency is lowered. As a guide, it may be up to about 620 ° C. Thereafter, air cooling may be performed to shorten the time, or water cooling or oil cooling may be performed.

  In the nitrogen-enriched layer, pearlite is generated from austenite having a (carbide + austenite) structure, and the carbides therein are aggregated and coarsened. Note that the explanation of the microstructure described above gives priority to easy understanding, so that secondary factors in nitrogen and more complicated actual microstructure are ignored.

  Next, induction hardening is performed. In the previous stage of induction hardening, the nitrogen-enriched layer has a structure in which agglomerated carbides (large ratio) and ferrite are mixed. In the induction hardening, rapid heating is performed, and at this time, austenite is nucleated while the carbide is dissolved. Since the density of the dispersed carbide is very high, the austenite nucleus generation density is very high, and the crystal grains of the austenite structure formed by associating the generated austenite with each other are ultrafine. In addition, since the nitrogen-enriched layer is a hypereutectoid steel, carbides coexist, and the carbides are just formed, preventing the growth of ultrafine austenite grains. For this reason, ultrafine austenite grains can be obtained in the nitrogen-enriched layer. As the temperature of rapid heating increases, the carbides are dissolved, and a large amount of carbon is dissolved in the ultrafine austenite. In addition, the central portion in the cross section of the rolling shaft is affected by the fact that it is not a nitrogen-enriched layer, but basically changes in the same manner as the change in the surface layer portion.

  Next, when induction hardening is performed, that is, quenching is performed after rapid heating, austenite is transformed into martensite. At this time, since a large amount of carbon is dissolved, austenite is stabilized, and untransformed austenite is left behind in a fine region between martensites. This is retained austenite. This retained austenite is very fine because it is formed between martensite. The volume ratio of retained austenite is set to 10 to 50% by volume, which can suppress crack propagation in surface-origination peeling and internal origin peeling.

  Thereafter, tempering is performed at a temperature of about 180 ° C. so as not to significantly reduce the hardness. In this low-temperature tempering at about 180 ° C., high-density dislocations are maintained with almost no loss. This tempering is performed to stabilize the structure. In this tempering, cementite does not aggregate and hardly softens. Depending on the steel material, this tempering may be omitted. The induction-hardened structure containing the above retained austenite is tough and can realize a long life under severe use conditions.

  FIG. 6 is a perspective view of the rolling shaft manufactured by the manufacturing method of the rolling shaft of the first embodiment. FIG. 7 is a schematic cross-sectional view of the rolling shaft taken along line VII-VII shown in FIG. FIG. 8 is a schematic cross-sectional view of the rolling shaft taken along line VIII-VIII shown in FIG. A hardened layer 2a is formed because induction hardening is performed on the surface layer portion of the solid cylindrical roller shaft 2 shown in FIGS. 6 to 8 on the side surface that is not the end surface 2c. As shown in FIGS. 7 and 8, the hardened layer 2a is formed from the surface layer portion of the rolling surface to the central portion 2e in the cross section of the axial central portion of the rolling surface.

  Thus, by performing the above heat treatment, the austenite crystal grain size of the hardened layer 2a can be made into ultrafine grains of No. 11 or more, so that the load-dependent rolling fatigue life can be extended. When the austenite grain size number is 10 or less, crack fatigue strength and rolling fatigue life under severe use conditions are not greatly improved. The finer austenite grains (that is, the larger the particle size number) is desirable, but it is usually difficult to obtain a particle size number exceeding # 13.

  Further, the hardness of the surface layer portion of the rolling surface can be set to 653 Hv or more, so that surface damage and internal origin peeling in the surface layer portion can be reliably suppressed, and the rolling fatigue life can be greatly improved. When the hardness is less than 653 Hv, the rolling fatigue life is not greatly improved and may be deteriorated. Usually, the range of the hardness of the surface layer portion is 720 Hv or more.

  Moreover, a retained austenite can be made into the range of 15-35 volume% which is 10-50 volume% and a more preferable range. When the amount of retained austenite is less than 15% by volume, the surface damage life is reduced, and when it is less than 10% by volume, it further decreases, and a long life under severe use conditions cannot be obtained. On the other hand, when the amount of retained austenite exceeds 50% by volume, it does not become fine retained austenite, the hardness of the surface layer portion is lowered, and the rolling fatigue life is shortened. The amount of retained austenite can be based on, for example, the amount of austenite at a depth of 50 μm from the surface of the rolling shaft.

  The amount of retained austenite is measured, for example, by comparing the diffraction intensities of martensite α (211) and retained austenite γ (220) by X-ray diffraction, X-ray diffractometry or transmission electron microscope observation (TEM: Transmission). Electron Microscopy) can be used. Austenite can be measured using a magnetic measuring device such as a magnetic balance by utilizing the fact that austenite is not a ferromagnetic material unlike ferrite and cementite.

  In the central portion 2e, since it is hardened by induction hardening, residual austenite is present although not as much as the surface layer portion. Therefore, the hardness of center part 2e can be improved, for example, can be set to 550 Hv or more. Therefore, it is possible to increase the strength of the center portion 2e and to obtain high crack fatigue strength of the rolling shaft. If the hardness of the center portion 2e is less than 550 Hv, it is not possible to obtain a high crack fatigue strength that can meet the demand for higher speed and higher load of the automobile engine.

  On the other hand, as described with reference to FIG. 3, by removing the surface layer portion of the end surface that is a portion other than the region of the rolling surface, the high-hardness carbides precipitated on the surface layer of the end surface are also removed. As a result, the hardness of the end face of the rolling shaft can be reduced and the hardness of the end can be reduced to 300 Hv or less, so that the end can be easily crimped. An intermediate layer (hardness of 300 Hv or more and 653 Hv or less) exists between the hardened layer 2a and the end surface 2c.

  In summary, the rolling shaft according to the present embodiment is subjected to carbonitriding and induction hardening to the rolling region, so that the strength is increased or the crack fatigue strength is increased. Good fatigue properties, ie long life.

  Further, the rolling shaft of the present embodiment is softened by performing a slow cooling process after the carbonitriding process, and the hardened carbide on the surface layer part of the end surface is removed, so that the end part is caulked. Easy to process. Further, the wear of the caulking tool is reduced, which is advantageous in terms of the tool life. In addition, since it is possible to remove high-hardness carbides that are unevenly distributed on the end face, it is possible to suppress variations in measured values of hardness, which is an unstable factor in guaranteeing end face hardness. it can.

  Next, a case where the rolling shaft has a hollow cylindrical shape will be described. FIG. 9 is a schematic diagram showing a cross section of a hollow cylindrical rolling shaft. In the case of the hardened layer 2a shown in FIG. 9, the entire radial direction from the rolling surface surface layer portion of the outer peripheral side surface 2b of the roller shaft 2 to the inner peripheral side surface 2f is the hardened layer 2a, and the uncured layer portion is the surface layer portion of the end surface 2c. Only near. That is, the hardened layer 2a (hardness 653Hv or more) is formed over the entire radial direction from the outer peripheral side surface 2b to the inner peripheral side surface 2f of the roller shaft 2. Such a hardened layer 2a is preferably formed over the entire circumference of the roller shaft 2 in the circumferential direction.

  In the hollow cylindrical roller shaft 2 shown in FIG. 9, the region of the hardened layer 2 a occupying the entire volume of the roller shaft 2 is larger than the solid roller shaft shown in FIG. 7. Therefore, the static crack strength of the roller shaft 2 is increased, and the roller shaft 2 is not easily deformed. Moreover, even if a load is repeatedly applied, since the center part in the axial direction of the inner peripheral side surface 2f is the hardened layer 2a, the crack fatigue strength is high. Therefore, the occurrence of cracks can be prevented, and the possibility of leading to breakage of the roller shaft 2 is reduced.

  Desirably, the hardened layer pattern in FIG. 9B is more advantageous in strength than the hardened layer pattern in FIG. 9A because the region of the hardened layer 2a on the inner peripheral side surface 2f is wider. Further, the one that prevents the generation of cracks over a wide area of the inner peripheral side surface 2f against the tensile stress generated by the repeated loading of the load is less than the one that prevents only the central portion of the inner peripheral side surface 2f. This is also advantageous when receiving an unbalanced load due to the unstable behavior of the rocker arm 1.

  By making the rolling shaft into a hollow cylindrical shape, weight reduction of the rolling shaft can be achieved. Therefore, by using a rolling bearing having a hollow cylindrical rolling shaft for a rocker arm and using the rocker arm for an automobile engine, the fuel efficiency of the automobile can be improved. Since the rolling shaft is subjected to the heat treatment shown in FIGS. 4 and 5 and the surface layer portion of the end surface is removed, the rolling shaft has a nitrogen-enriched layer in the surface layer portion of the rolling region, and the surface layer of the rolling region. The austenite crystal of the part is refined with a grain size number of 11 or more, and has an appropriate hardness in the surface layer part and the end face of the rolling region. In the rolling shaft, the retained austenite occupies 10 to 50% by volume in the surface layer portion of the rolling region, and the retained austenite exists in the surface layer portion on the inner peripheral side surface. Therefore, the hollow cylindrical rolling shaft has high strength or high crack fatigue strength, good rolling fatigue characteristics, easy caulking of the end, and reduced hardness variation of the end face. Is done.

(Embodiment 2)
FIG. 10 is a flowchart showing an outline of the method of manufacturing the roller shaft according to the second embodiment. The roller shaft manufacturing method of the second embodiment and the manufacturing method of the first embodiment described above based on the flowchart shown in FIG. 3 basically have the same steps. However, the second embodiment is different from the first embodiment in that the step of removing the end surface layer portion is performed after induction hardening.

  Specifically, as shown in FIG. 10, after the molded part is air-cooled to room temperature in step (S40), the surface layer portion of the cylindrical outer peripheral side surface of the molded part is subsequently induction-hardened in step (S51). . In the subsequent step (S71), the surface layer portion of the end surface of the cylindrical molded part is removed by mechanical processing such as grinding. Other steps are as described in the first embodiment.

  Also by the manufacturing method shown in FIG. 10, a rolling shaft having the same properties as the rolling shaft described in the first embodiment can be obtained. Therefore, the rolling shaft manufactured by the manufacturing method of the second embodiment has high strength or high crack fatigue strength, good rolling fatigue characteristics, and easy caulking of the end portion. Variations in hardness are suppressed.

(Embodiment 3)
FIG. 11 is a flowchart showing an outline of the method of manufacturing the roller shaft according to the third embodiment. FIG. 12 is a diagram for explaining a heat treatment method according to the third embodiment. FIG. 13 is a diagram in which specific conditions are added to the heat pattern in the third embodiment. The roller shaft manufacturing method of the third embodiment and the manufacturing method of the first embodiment described above based on the flowchart shown in FIG. 3 basically have the same steps. However, the third embodiment is different from the first embodiment in the cooling method after carbonitriding.

  Specifically, as shown in FIG. 11, after carbonitriding the molded part at the point A1 or higher in step (S20), it is rapidly cooled to 100 ° C., for example, by oil cooling in step (S32). In this case, the cooling rate may be 150 ° C./second or more. Next, in the step (S42), a tempering process, that is, a tempering process is performed at a point less than A1. The slow cooling process in the heat treatment method of the first embodiment shown in FIGS. 4 and 5 and the tempering process shown in FIGS. 12 and 13 correspond to each other, and a part other than the surface layer part, for example, the rolling shaft This contributes to reducing the hardness of the end. The subsequent steps (S50) of the end face surface layer removal step and subsequent steps are as described in the first embodiment.

  In the heat treatment (referred to as heat pattern H2) shown in FIG. 12 and FIG. 13, quenching is performed from the carbonitriding temperature by, for example, oil cooling. In this case, martensite and the like are generated from austenite inside due to the composition of the original steel material. This martensite structure is hard. Since the caulking process is difficult as it is, the tempering process (tempering process) is performed. Tempering proceeds rapidly at a temperature as close as possible to the A1 point just below the A1 point. That is, high temperature tempering is performed. Therefore, tempering is desirably performed in the range of A1 point to 650 ° C, more preferably in the range of A1 point to 680 ° C. By this tempering, the high dislocation density in the martensite structure disappears, and a structure of ferrite having a low dislocation density and aggregated and coarsened cementite is obtained.

  In the nitrogen-enriched layer, martensite is generated from austenite having a (carbide + austenite) structure generated during heating by quenching such as oil cooling. Martensite is softened in the same manner as martensite generated inside by the above-described high-temperature tempering. The original carbides agglomerate. In the description of the microstructure described above, as in the first embodiment, secondary factors in nitrogen and a more complicated actual microstructure are ignored.

  Thus, since carbonitriding and induction hardening are performed on the rolling region, the austenite grain size of the surface layer portion of the rolling region is 11 or more ultrafine grains, and the surface layer portion of the rolling region is The hardness can be 653 Hv or more. On the other hand, the region of the rolling surface is subjected to quenching after carbonitriding, then subjected to tempering (tempering) to be softened, and high-hardness carbide is removed from the surface layer portion of the end surface. The hardness of other parts, for example, the end face, can be 300 Hv or less. Therefore, the rolling shaft subjected to the above heat treatment has high strength or high crack fatigue strength, good rolling fatigue characteristics, easy caulking of the end portion, and variation in end surface hardness. It is suppressed.

(Embodiment 4)
FIG. 14 is a flowchart showing an outline of the method of manufacturing the roller shaft according to the fourth embodiment. The roller shaft manufacturing method of the fourth embodiment and the manufacturing method of the third embodiment described above based on the flowchart shown in FIG. 11 basically have the same steps. However, the fourth embodiment is different from the third embodiment in that the step of removing the end surface layer portion is performed after induction hardening.

  Specifically, as shown in FIG. 14, after the tempering treatment of the molded part in the step (S42), the surface layer portion of the cylindrical outer peripheral side surface of the molded part is subsequently induction hardened in the step (S51). . In the subsequent step (S71), the surface layer portion of the end surface of the cylindrical molded part is removed by mechanical processing such as grinding. Other steps are as described in the first embodiment.

  Also by the manufacturing method shown in FIG. 14, a rolling shaft having the same properties as the rolling shaft of Embodiment 3 can be obtained. Therefore, the rolling shaft manufactured by the manufacturing method of Embodiment 4 has high strength or high cracking fatigue strength, good rolling fatigue characteristics, easy caulking of the end, and end surface. Variations in hardness are suppressed.

  Examples of the present invention will be described below. An experiment was conducted to determine the Vickers hardness distribution at the end face when the surface layer portion of the end face was not removed with respect to the rolling shaft that was gradually cooled after the carbonitriding process described in the first embodiment. Vickers hardness was measured at any 8 points on the same end face. The results are shown in Table 1.

  From Table 1, the hardness variation at the same end face is Hv28, and the hardness at the measurement position 2 is higher than the others. This is presumably because the agglomerated carbide is precipitated at the measurement position 2 and the hardness is higher than the other measurement positions. On the other hand, Vickers hardness was measured at eight locations on the same end face after removing the surface layer portion of the end face and removing carbides deposited on the surface layer for the same rolling shaft. The results are shown in Table 2.

  From Table 2, the variation in hardness at the same end face was reduced to Hv7. That is, it was shown that by removing the surface layer portion of the end surface, the high-hardness carbides deposited on the surface layer of the end surface are also removed, and an effect of suppressing variation in the hardness of the end surface can be obtained.

  Further, the relationship between the distance from the end face and the hardness was determined for the rolling shaft that was gradually cooled after carbonitriding. FIG. 15 is a graph showing the relationship between the depth from the end face (unit: mm) and the Vickers hardness (unit: Hv). From FIG. 15, the Vickers hardness on the surface of the end face was 275 Hv, but the inside of 0.5 mm was 242 Hv. For example, it can be seen that if about 0.3 mm is removed from the end surface, an end surface having a Vickers hardness of about 250 Hv, which is easy to be plastically worked (caulked), can be obtained.

  From the end surface (0 mm depth) to the vicinity of 0.5 mm depth, the hardness decreases substantially linearly. However, the hardness is substantially constant inside the depth of 0.5 mm. The depth at which the hardness becomes substantially constant is considered to vary depending on the steel material and heat treatment conditions. However, within a range up to a certain depth, removing the surface layer portion of the end surface regardless of the depth to be removed also removes the hard carbides precipitated on the surface layer of the end surface, resulting in rolling. It has been shown that the effect of reducing the hardness of the end face of the shaft can be obtained.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic front view which shows the structure of the rolling bearing for rocker arms. It is sectional drawing of the rolling bearing for rocker arms. It is a flowchart which shows the outline of the manufacturing method of a roller shaft. 5 is a diagram for describing a heat treatment method in Embodiment 1. FIG. FIG. 3 is a diagram in which specific conditions are added to the heat pattern in the first embodiment. 2 is a perspective view of a solid cylindrical rolling shaft manufactured by the rolling shaft manufacturing method of Embodiment 1. FIG. It is a cross-sectional schematic diagram of the rolling shaft by the VII-VII line shown in FIG. It is a cross-sectional schematic diagram of the rolling shaft by the VIII-VIII line shown in FIG. It is a schematic diagram which shows the cross section of a hollow cylindrical shape rolling shaft. 6 is a flowchart showing an outline of a method of manufacturing a roller shaft according to a second embodiment. 10 is a flowchart showing an outline of a method of manufacturing a roller shaft according to a third embodiment. 10 is a diagram for explaining a heat treatment method in Embodiment 3. FIG. It is the figure which added specific conditions to the heat pattern in Embodiment 3. FIG. 10 is a flowchart showing an outline of a method of manufacturing a roller shaft according to a fourth embodiment. It is a graph which shows the relationship between the depth from an end surface, and Vickers hardness.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Rocker arm, 1a, 1b end part, 2 roller shaft, 2a Hardened layer, 2b Outer side surface, 2c End surface, 2d Caulking part, 2e Center part, 2f Inner side surface, 3 Roller, 4 Roller, 5 Rocker arm axis, 6 cams, 7 adjustment screws, 8 lock nuts, 9 valves, 10 springs, 14 roller support parts, 14a chamfered parts, 25 caulking fixed parts, 50 cam follower body.

Claims (9)

In a method for manufacturing a rolling shaft used for a rocker arm bearing,
By processing the material formed by bearing steel, a step of forming the outline shape of the rolling shaft having an end face which intersects the axial direction of the rolling axis,
A step of carbonitrided at point A1 above while exposing the end surface to an atmosphere,
A step of cooling to less than A1 point while exposing the end surface to an atmosphere,
A process of induction hardening the rolling region;
The agglomerated carbides precipitated in the surface layer portion of the end surface in the step of cooling, Ru and a step of removing from said end surface by removing the surface layer portion of said end face, Utatedojiku method of manufacturing. The method for manufacturing a rolling shaft according to claim 1, wherein in the cooling step , cooling is performed gradually. In step wherein cooling, and quenched, then, Ru further comprising a step of performing a tempering below the point A1, the manufacturing method of the rolling shaft according to claim 1. The manufacturing method of the rolling shaft in any one of Claims 1-3 which has a nitrogen enriched layer in at least one part of the surface layer part of the said rolling region. The rolling shaft according to any one of claims 1 to 4, wherein the austenite grain size is 11 or more and the hardness is 653 Hv or more in terms of Vickers hardness in at least a part of a surface layer portion of the rolling region. Manufacturing method . The rolling shaft manufacturing method according to claim 1, wherein the end face has a Vickers hardness of 300 Hv or less. It has a solid cylindrical shape,
The residual austenite occupies 10 to 50% by volume in at least a part of the surface layer portion of the rolling region, and the residual austenite exists in the central portion in the cross section of the axial central portion of the rolling region. Item 7. A method for manufacturing a rolling shaft according to any one of Items 6 to 7. The method for manufacturing a rolling shaft according to claim 7, wherein the hardness of the central portion is 550 Hv or more in terms of Vickers hardness. Having a hollow cylindrical shape,
The residual austenite occupies 10 to 50% by volume in at least a part of the surface layer portion of the rolling region, and the residual austenite exists in the surface layer portion on the inner peripheral side surface. Manufacturing method of rolling shaft.

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