JP4712603B2 - Rolling part manufacturing method, race ring and bearing - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a rolling part manufacturing method, a bearing ring, and a bearing, and in particular, a manufacturing method of a high carbon steel rolling part capable of improving production efficiency, a bearing ring manufactured by the manufacturing method, and its The present invention relates to a bearing provided with a bearing ring.

  For rolling parts constituting a rolling bearing, SUJ2 defined in JIS G4805, which is a high carbon chromium bearing steel, is widely used by taking advantage of the characteristics that it is easy to quench and has high hardness after quenching. Conventionally, when rolling parts are manufactured using a material made of high carbon steel such as SUJ2, it is hot worked, cold worked after spheroidizing annealing, and further hardened and tempered to obtain high hardness. Manufacture.

  FIG. 12 is a flowchart showing a conventional method for manufacturing a rolling part. With reference to FIG. 12, the manufacturing method of the bearing ring of a rolling bearing, ie, an inner ring and an outer ring, will be described as an example. First, in a process (S30), the round bar which is a raw material which consists of high carbon steel like SUJ2 is prepared. Next, in the step (S31), the material is cut. Next, in the step (S32), the cut material is heated and formed by hot forging to obtain a material blank ring. When cooled after hot forging, the high carbon steel becomes cementite (carbide) and pearlite structure precipitated in a network, but in this state, the hardness is high and difficult to process, which adversely affects the subsequent machining process. Therefore, in the next step (S33), the blank blank ring is subjected to spheroidizing annealing in the atmosphere to improve workability and improve the microstructure. That is, in the blank blank ring, a part of the carbide is dissolved, the pearlite layered structure is destroyed, the carbide is spheroidized, and a structure in which fine spherical carbide exists in the steel is formed. Thereby, the workability of the blank blank ring is improved. Next, in the step (S34), the blank blank ring is formed by cold forging to form an integrated stepped ring for collecting the inner ring and the outer ring. Next, in step (S35), the stepped ring is cut off and separated into a work ring that is the original shape of the inner ring and the outer ring.

  Next, in step (S36), the work ring is processed into a predetermined dimension by turning to obtain a molded part. Here, in the hot forging in the step (S32) and the atmospheric annealing in the step (S33), a decarburized layer having a thickness of 0.1 mm or more is formed on the surface layer portion of the blank blank ring. Here, the decarburized layer refers to steel by heating steel products in an atmosphere in which carbon contained in steel reacts with atmospheric gas components (for example, carbon dioxide, moisture, etc.), such as in an atmospheric furnace. The area | region where the carbon content which steel contains is lost and the carbon content which steel is formed in the surface layer part of steel products falls is shown. Therefore, after the separation in the step (S35), the decarburized layer is present except for the ring-cut portion, although it is thinned by cold forging. For this reason, in the step (S36), it is necessary to turn the entire surface of the work ring to remove the decarburized layer.

  Next, in the step (S37), quenching is performed in which the molded part is heated to a temperature not lower than the A1 point and then cooled to a temperature not higher than the Ms point. Thereby, steel becomes a martensite structure and hardens. Here, the A1 point indicates a point corresponding to a temperature at which the steel structure starts transformation from ferrite to austenite when the steel is heated. Moreover, Ms point shows the point corresponded to the temperature which the structure | tissue of steel starts martensite formation when cooling austenitized steel.

  Next, in the step (S38), tempering is performed in which the hardened molded part is heated to a temperature of A1 or lower to adjust the structure and properties of the steel. Since the steel after quenching is very hard and brittle, tempering stabilizes the structure and mechanical properties, improves toughness, reduces residual stress, or stabilizes dimensional accuracy associated with removal. Thereby, the required steel hardness is obtained. Next, in step (S39), the surface of the molded part is ground and finished. A rolling part as a finished product is manufactured by the manufacturing method as described above.

  When the decarburized layer remains on the finished rolling part, a state where the carbon of the rolling part surface layer is low occurs. In this case, problems such as inability to secure the surface hardness of the rolling component and generation of tensile stress in the surface layer portion of the rolling component occur, and the material becomes extremely dangerous as the rolling component. In the high carbon steel such as SUJ2, in the quenching in the step (S37), the quenching is not usually performed in a carburizing atmosphere. Therefore, a sufficient cutting allowance is provided for the material, and the decarburized layer is removed in the entire surface turning in the step (S36). However, turning the entire surface of the work ring has problems such as requiring a large number of man-hours and increasing costs and reducing the yield of the material.

  In order to solve such problems, a cold rolling material and a manufacturing method have been proposed in which after the hot forging, the amount of atmospheric carbon at the time of annealing is controlled to perform coal recovery (see, for example, Patent Document 1). In addition, a rolling device has been proposed which is characterized by performing post-hot forging and post coal annealing (see, for example, Patent Document 2).

  FIG. 13 is a flowchart showing another method for manufacturing a conventional rolling part, that is, a method for performing post-hot forging post-coal annealing. With reference to FIG. 13, a description will be given of an example of a method for manufacturing a bearing ring of a rolling bearing, that is, an inner ring and an outer ring. First, in a process (S30), the round bar which is a raw material which consists of high carbon steel like SUJ2 is prepared. Next, in the step (S31), the material is cut. Next, in the step (S32), the cut material is heated and formed by hot forging to obtain a material blank ring.

  Next, in the step (S43), the blank blank is subjected to spheroidizing annealing in a furnace in which the carbon potential of the atmospheric gas is controlled to improve the workability of the blank blank and improve the microstructure. At the same time, the carbon concentration in the decarburized layer formed on the surface layer portion of the blank blank ring in the hot forging in the step (S32) is improved. Here, the carbon potential indicates the carbon concentration contained in the steel when the carburization and decarburization reaction reaches equilibrium and the carbon concentration contained in the steel becomes a constant value, and indicates the carburizing ability in the atmosphere in which the steel is heated. This is the value shown. That is, the higher the carbon potential, the higher the carburizing ability. The carbon potential of the atmospheric gas should be calculated by measuring the temperature of the atmospheric gas and the composition of the atmospheric gas, that is, the concentration of carbon monoxide and oxygen, or the concentration of carbon monoxide and carbon dioxide. Can do.

  Next, in the step (S34), the blank blank ring is formed by cold forging to form an integrated stepped ring for collecting the inner ring and the outer ring. Next, in step (S35), the stepped ring is cut off and separated into a work ring that is the original shape of the inner ring and the outer ring. Next, in step (S46), the work ring is processed into a predetermined dimension by turning to obtain a molded part. Here, since carbon is supplemented to the decarburized layer of the blank blank ring by the re-coal annealing in the step (S43), it is not necessary to turn the entire surface of the work ring to remove the decarburized layer, and for dimensional finishing. In addition, a part of the surface of the work ring may be turned.

  Next, in step (S37), the molded part is quenched, and the steel becomes a martensitic structure and hardens. Next, in step (S38), the molded part is tempered to obtain the required steel hardness. Next, in step (S39), the surface of the molded part is ground and finished. A rolling part as a finished product is manufactured by the manufacturing method as described above.

In addition, as a technology for producing bearing races by eliminating annealing itself, a manufacturing method in which reheating is performed after hot rolling (see, for example, Patent Document 3), and blank blank rings after hot forging are warm. A manufacturing method (see, for example, Patent Document 4) for rolling a bearing raceway has been proposed.
JP 2002-285233 A JP 2003-194072 A JP-A-9-176740 JP-A-11-347673

  As described above, in the manufacturing method in which the entire surface of the work ring is turned to remove the decarburized layer, there are problems such as requiring a great number of man-hours and increasing the cost and reducing the yield of the material. In the manufacturing method disclosed in Patent Documents 1 and 2, in which coal removal annealing is performed after hot forging, a decarburized layer can be eliminated, but a dedicated furnace is used to perform a high-temperature and long-time treatment process such as annealing in a coal recovery atmosphere. Is required, leading to increased costs. The manufacturing method disclosed in Patent Document 3 also requires an atmosphere furnace in which an atmosphere gas is replaced with nitrogen gas or a reducing gas as a heating furnace for hot rolling processing in order to prevent decarburization. It leads to up. Further, in the manufacturing method disclosed in Patent Document 4, the decarburized layer depth is reduced, but a decarburized layer is formed on the surface layer portion, and therefore, the decarburized layer needs to be turned after the warm rolling process. Therefore, the conventional manufacturing method is not necessarily sufficient in terms of improving production efficiency and reducing manufacturing cost, and there is room for further improvement.

  Therefore, a main object of the present invention is to provide a method of manufacturing a high carbon steel rolling part capable of improving production efficiency and reducing manufacturing cost. Another object of the present invention is to provide a low-cost bearing ring and a bearing using the above-described rolling component manufacturing method.

  The manufacturing method of a rolling component according to the present invention includes a hot working process, an air annealing process, a cold working process, and a final heat treatment process. In the hot working process, a material made of high carbon steel is heated and formed. In the air annealing step, spheroidizing annealing is performed in the air to improve workability. In the cold working process, it is finished to a predetermined part size. In the final heat treatment step, quenching and tempering are performed to obtain the required hardness. In the final heat treatment step, the carbon potential of the atmospheric gas is kept at or above the carbon amount before heat treatment contained in the material before being heated in the hot working step, and carbonitriding is performed. Thereby, the carbon content which the decarburization layer which generate | occur | produces in the surface layer part of a raw material in a hot working process and an atmospheric annealing process shall be more than the carbon amount before heat processing.

  In this case, the carbon potential of the atmospheric gas is controlled in the final heat treatment step in which heating is usually performed for a long time, and the carbon decarburized in the hot working step and the atmospheric annealing step is supplemented for the decarburized layer of the material. Therefore, the decarburization layer in the surface layer portion of the raw material can be recovered without providing a special recovery process such as anthracite annealing. In addition, since a material without a decarburized layer can be provided after quenching, it is not necessary to turn the surface of the material for removing the decarburized layer. Therefore, since the process can be simplified, an improvement in production efficiency and a reduction in manufacturing cost can be achieved. Furthermore, since the amount of carbon contained in the surface layer portion of the finished rolling component is equal to or greater than the amount of carbon before heat treatment, the surface hardness of the rolling component can be improved. Therefore, the rolling fatigue strength of the rolling component can be improved.

  Preferably, a raw material contains 0.95 mass% or more and 1.1 mass% or less carbon before being heated in a hot working process. The carbon potential of the atmospheric gas in the final heat treatment step is set to 1.0% to 1.1%.

  In this case, carbon can be reliably supplemented to the decarburized layer by keeping the carbon potential of the atmospheric gas in the final heat treatment step at or above the amount of carbon contained in the material before decarburization. Further, by defining an upper limit value of the carbon potential and not increasing the carbon potential too much, it is possible to maintain an atmosphere in which carbides do not become coarse.

  Preferably, the carbon penetration depth into the material by carbonitriding is deeper than the depth of the decarburized layer.

  In this case, the depth of the decarburized layer generated in the surface layer portion of the raw material in the hot working process and the atmospheric annealing process is measured in advance, and the time carbonitriding process is performed such that carbon penetrates deeper than that. Thereby, after carbonitriding, the amount of carbon contained in the surface layer portion of the finished rolling part can be surely made equal to or greater than the amount of carbon before heat treatment.

  The bearing ring for a rolling bearing according to the present invention is manufactured by the above-described manufacturing method. In this case, since the manufacturing process can be simplified, it is possible to improve the production efficiency and reduce the manufacturing cost of the bearing ring for the rolling bearing. Moreover, a long-life rolling bearing can be provided by providing the bearing ring which is excellent in rolling fatigue strength.

  The raceway for the tapered roller bearing according to the present invention is manufactured by the above-described manufacturing method. In this case, since the manufacturing process can be simplified, it is possible to improve the production efficiency of the races for tapered roller bearings and reduce the manufacturing cost. Moreover, a long-life tapered roller bearing can be provided by providing a bearing ring having excellent rolling fatigue strength.

  The bearing which concerns on this invention is equipped with the bearing ring manufactured by the above-mentioned manufacturing method. In this case, since the manufacturing process of the bearing ring can be simplified, it is possible to improve the production efficiency of the bearing and reduce the manufacturing cost. Moreover, a long-life bearing can be provided by providing a bearing ring having excellent rolling fatigue strength.

  As described above, in the method of manufacturing a rolling part according to the present invention, the carbon potential of the atmospheric gas is controlled in the final heat treatment process in which heating is usually performed for a long time, and the hot-working process and the atmosphere are performed on the decarburized layer of the material. Supplement the decarburized carbon in the annealing process. Therefore, the decarburization layer in the surface layer portion of the raw material can be recovered without providing a special recovery process such as anthracite annealing. In addition, since a material without a decarburized layer can be provided after quenching, it is not necessary to turn the surface of the material for removing the decarburized layer. Therefore, since the process can be simplified, an improvement in production efficiency and a reduction in manufacturing cost can be achieved. Furthermore, since the amount of carbon contained in the surface layer portion of the finished rolling component is equal to or greater than the amount of carbon before heat treatment, the surface hardness of the rolling component can be improved. Therefore, the rolling fatigue strength of the rolling component can be improved.

  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.

  FIG. 1 is a schematic cross-sectional view showing the structure of a deep groove ball bearing as a rolling bearing provided with rolling parts according to an embodiment of the present invention. With reference to FIG. 1, the structure of the deep groove ball bearing as a rolling bearing in this embodiment is demonstrated.

  In FIG. 1, this deep groove ball bearing 1 includes an annular outer ring 2 as a rolling part, an annular inner ring 3 as a rolling part disposed inside the outer ring 2, and a ball 4 as a rolling part. And an annular retainer 5. The plurality of balls 4 are in contact with the inner peripheral surface of the outer ring 2 and the outer peripheral surface of the inner ring 3, and are arranged at a predetermined pitch in the circumferential direction by the cage 5, so that they can roll on an annular track. Is retained. With the above configuration, the outer ring 2 and the inner ring 3 of the deep groove ball bearing 1 are rotatable relative to each other.

  The surface layer portion of the raceway ring (that is, the outer ring 2 and the inner ring 3) of the deep groove ball bearing 1 as the rolling part of this embodiment and the ball 4 is heat treated in the material before being heated in the hot working process. Contains carbon content greater than or equal to the previous carbon content. That is, the outer ring 2, the inner ring 3, and the balls 4 have a carbon amount in the surface layer portion that is larger than the carbon amount in the central portion. Here, the surface layer portion means, for example, a layer having a depth of 0.5 mm or less, preferably 0.2 mm or less from the surface. Thus, the rolling part has a high surface hardness. And the deep groove ball bearing 1 has a long life by providing the rolling components which are excellent in rolling fatigue strength.

  FIG. 2 is a schematic cross-sectional view showing a configuration of a cylindrical roller bearing which is a modification of the rolling bearing. With reference to FIG. 2, the structure of the cylindrical roller bearing which is a modification of a rolling bearing is demonstrated. In FIG. 2, the cylindrical roller bearing 6 includes a plurality of cylindrical rollers 7 held by a cage 5 between an outer ring 2 and an inner ring 3. The plurality of rollers 7 are in contact with the inner circumferential surface of the outer ring 2 and the outer circumferential surface of the inner ring 3, and are arranged at a predetermined pitch in the circumferential direction by the cage 5, so that they can roll on an annular track. Is retained. With the above configuration, the outer ring 2 and the inner ring 3 of the cylindrical roller bearing 6 can rotate relative to each other.

  The surface layer portion of the raceway ring (that is, the outer ring 2 and the inner ring 3) of the cylindrical roller bearing 6 as a rolling part and the roller 7 has a carbon amount before the heat treatment contained in the material before being heated in the hot working process. Contains carbon content. Thus, the rolling part has a high surface hardness. And the cylindrical roller bearing 6 has a long life by providing the rolling components which are excellent in rolling fatigue strength.

  FIG. 3 is a schematic cross-sectional view showing a configuration of a tapered roller bearing which is another modified example of the rolling bearing. With reference to FIG. 3, the structure of the tapered roller bearing which is another modification of a rolling bearing is demonstrated. In FIG. 3, the tapered roller bearing 8 includes a plurality of tapered rollers (conical rollers) 7 held by a cage 5 between the outer ring 2 and the inner ring 3. The tapered roller bearing 8 is designed such that the inner peripheral surface of the outer ring 2 and the outer peripheral surface of the inner ring 3, and the apex of the cone of the cone 7 meet at one point on the center line of the bearing. For this reason, the roller 7 rolls while being pressed and guided against the collar portion of the inner ring 3 by the combined force applied from the inner peripheral surface of the outer ring 2 and the outer peripheral surface of the inner ring 3. In addition, a plurality of rollers 7 are arranged at a predetermined pitch in the circumferential direction by the cage 5 so as to be freely rollable on an annular track. With the above configuration, the outer ring 2 and the inner ring 3 of the tapered roller bearing 8 are rotatable relative to each other.

  The surface layer part of the raceway ring (that is, the outer ring 2 and the inner ring 3) of the tapered roller bearing 8 as a rolling part and the roller 7 has a carbon amount before the heat treatment contained in the material before being heated in the hot working process. Contains carbon content. Thus, the rolling part has a high surface hardness. And the tapered roller bearing 8 has a long life by providing the rolling parts which are excellent in rolling fatigue strength.

  Next, the manufacturing method of the rolling component of this invention is demonstrated. FIG. 4 is a flowchart showing a method for manufacturing a rolling part. With reference to FIG. 4, the manufacturing method of the bearing ring of a rolling bearing, ie, an inner ring and an outer ring, will be described as an example.

  First, in a process (S10), the bar steel and round steel which are materials which consist of high carbon steel are prepared. As the material, for example, JIS SUJ2 or JIS SUJ3, which is a high carbon chromium bearing steel, can be used. More specifically, 0.95 mass% or more and 1.10 mass% or less of carbon, 0.15 mass% or more and 0.35 mass% or less of silicon, 0.50 mass% or less of manganese, 30% by mass or more and 1.60% by mass or less of chromium and 0.08% by mass or less of molybdenum, 0.025% by mass or less of phosphorus, 0.025% by mass or less of sulfur, and 0 It is possible to use steel which contains nickel of not more than 25% by mass and copper of not more than 0.25% by mass and consists of the remaining iron and inevitable impurities. Or 0.95 mass% or more and 1.10 mass% or less carbon, 0.40 mass% or more and 0.70 mass% or less silicon, 0.90 mass% or more and 1.15 mass% or less manganese, 0.90 mass% or more and 1.20 mass% or less of chromium, 0.08 mass% or less of molybdenum, 0.025 mass% or less of phosphorus, and 0.025 mass% or less of sulfur as impurities The steel which contains nickel of 0.25 mass% or less and copper of 0.25 mass% or less, and consists of remainder iron and unavoidable impurities can be used. Not only these but high carbon steel, that is, steel containing 0.7% by mass or more and 2.0% by mass or less of carbon can be used as a raw material.

  Next, in the step (S11), the material is cut into a predetermined length. Next, in the step (S12), the cut material is heated to a temperature of 1050 ° C. to 1100 ° C., for example, 1075 ° C., held for 30 minutes or more, for example 60 minutes, and then hot-worked, for example, upsetting A blank ring is formed by hot forging such as punching. When cooled after hot forging, the high carbon steel becomes cementite (carbide) and pearlite structure precipitated in a network, but in this state, the hardness is high and difficult to process, which adversely affects the subsequent machining process.

  Therefore, in the next step (S13), the blank blank ring is subjected to spheroidizing annealing in the atmosphere to improve workability and improve the microstructure. That is, in the blank blank ring, a part of the carbide is dissolved, the pearlite layered structure is destroyed, the carbide is spheroidized, and a structure in which fine spherical carbide exists in the steel is formed. Thereby, the workability of the blank blank ring is improved. As the spheroidizing annealing treatment, for example, a heat treatment can be performed in which the temperature is just above the A1 point, for example, 750 ° C., held for 1 to 2 hours, and then gradually cooled. Further, for example, heat treatment that repeats heating and cooling can be performed in the temperature range of 700 ° C. to 750 ° C. at 20 ° C. to 30 ° C. above and below A1 point.

  In the hot forging in the step (S12) performed in the atmosphere and the atmospheric annealing in the step (S13), a decarburized layer having a thickness of 0.1 mm or more is formed on the surface layer portion of the blank blank ring.

  Next, the blank blank ring is cold worked to finish a predetermined part size. In the step (S14), the blank blank ring is formed by cold forging to obtain an integrally shaped stepped ring for collecting the inner ring and the outer ring. Before performing cold forging, a metal soap as a lubricant may be applied to the blank ring after spheroidizing annealing. Next, in step (S15), the stepped ring is cut off and separated into a near-net-shaped work ring that is the original form of the inner ring and the outer ring. In some cases, shot blasting is applied to the work ring to remove dirt and burrs. Next, in a step (S16), the work ring is processed into a predetermined dimension by turning into a formed part. Here, in order to finish to a predetermined part size, a part of the surface of the cutting ring may be turned, and it is not necessary to turn the entire surface of the cutting ring to remove the decarburized layer.

  Next, final heat treatment of the molded part is performed. In the step (S17), the molded part is heated to a temperature of A1 point or higher. For example, it can be heated to a temperature of 800 ° C. or higher and 1000 ° C. or lower, for example, 850 ° C. using a batch furnace or a continuous furnace, and held for 60 minutes or longer and 150 minutes or shorter, for example 90 minutes. Then, for example, by being immersed in oil (oil cooling), quenching is performed to cool to a temperature below the Ms point. Thereby, steel becomes a martensite structure and hardens.

  At this time, the carbon potential of the atmospheric gas is maintained to be equal to or greater than the amount of carbon before heat treatment, that is, equal to or greater than the amount of carbon contained in the material before being heated in the hot forging in the step (S12). Thereby, in the hot forging in the step (S12) performed in the atmosphere and the atmospheric annealing in the step (S13), the coal is re-coalted to the decarburized layer generated in the surface layer portion of the blank blank ring, and the surface layer portion of the molded part contains. The amount of carbon is set to be equal to or greater than the amount of carbon before heat treatment. Further, by defining an upper limit value of the carbon potential and not increasing the carbon potential too much, it is possible to maintain an atmosphere in which carbides do not become coarse. For example, when SUJ2 containing 0.95 mass% or more and 1.10 mass% or less of carbon is used as a material, the carbon potential can be set to 1.0% or more and 1.1% or less. More specifically, the carbon potential is the carbon amount before heat treatment (mass%) + 0.03 or more carbon amount before heat treatment (mass%) + 0.10 or less, preferably the carbon content before heat treatment (mass%) + 0.05 or more. It can be made into the amount of pre-carbon (mass%) +0.10 or less. By slightly increasing the lower limit of the carbon potential of the atmospheric gas from the amount of carbon before heat treatment, the diffusion of carbon into the steel is accelerated, and the surface layer of the molded part has a carbon amount equivalent to or slightly higher than the amount of carbon before heat treatment as soon as possible. It can be charcoal so that it contains. On the other hand, by specifying the upper limit value of the carbon potential of the atmospheric gas, it is possible to reduce the grindability due to the formation of coarse carbides on the surface and surface layer of molded parts and the crack strength of the black skin. Can be prevented. For example, if the amount of carbon contained in the material SUJ2 is 1.00% by mass, the carbon potential can be 1.05% or more and 1.10% or less. At the same time, ammonia gas is added to RX gas, which is an atmospheric gas, and carbonitriding is performed to cure the surface of the molded part. The amount of ammonia gas added can be 3% by volume to 10% by volume, for example, 5% by volume, based on the RX gas ratio.

  Next, in the step (S18), the quenched molded part is heated to a temperature of 150 ° C. or higher and 350 ° C. or lower, which is a temperature of A1 point or lower, for example, 180 ° C. to adjust the structure and properties of the steel. Done. Since the steel after quenching is very hard and brittle, tempering stabilizes the structure and mechanical properties, improves toughness, reduces residual stress, or stabilizes dimensional accuracy associated with removal. Thereby, the required steel hardness is obtained. Next, in step (S19), the surface of the molded part is ground and finished. A rolling part as a finished product is manufactured by the manufacturing method as described above.

  As a result, in the final heat treatment step in which heating is usually performed for a long time, that is, carbonitriding and quenching in step (S17), the carbon potential is controlled, and in hot forging in step (S12) and atmospheric annealing in step (S13). Make up for decarburized carbon. Therefore, the decarburization layer of the surface part of the molded part can be recoalized without providing a special recoalization process such as recoal annealing. In addition, since a molded part without a decarburized layer can be provided after quenching, it is not necessary to turn the surface of the work ring in order to remove the decarburized layer in the turning of the step (S16). Therefore, the number of parts that need to be turned is reduced, the number of turning steps can be reduced, and the process can be simplified. Further, since the number of turning steps is small, the amount of wear of the tool used for turning can be reduced. In addition, since there are few parts to be turned, the amount of material necessary for manufacturing rolling parts can be reduced, so that the yield of the material can be improved and the amount of waste such as shavings can be reduced. Therefore, improvement in production efficiency and reduction in manufacturing cost can be achieved. Furthermore, since the amount of carbon contained in the surface layer portion of the finished rolling component is equal to or greater than the amount of carbon before heat treatment, the surface hardness of the rolling component can be improved. Therefore, the rolling fatigue strength of the rolling component can be improved.

  Here, in the step (S17), the time for the carbonitriding process can be controlled as the time for making the carbon penetration depth into the molded part by the carbonitriding process deeper than the depth of the decarburized layer. That is, the depth of the decarburized layer is measured in advance, and a time carbonitriding process in which carbon penetrates deeper than that can be performed. The depth of the decarburized layer is determined by measuring the carbon concentration distribution in the surface layer portion with EPMA (Electron Probe Micro Analysis) after cutting and polishing the surface layer portion of the molded part before carbonitriding, for example, and the carbon concentration is reduced. It can be estimated from the depth. In addition, the time required for the carbonitriding process is determined from the depth of the region where the carbon concentration is higher than the center part of the molded part by measuring the carbon concentration distribution in the surface part of the molded part after the carbonitriding process with EPMA. The carbon penetration depth can be estimated, the relationship between the carbon penetration depth and the carbonitriding time can be obtained, and can be defined using the obtained relational expression. For example, when carbonitriding at 850 ° C., there is a relationship of D = 0.35 to 0.4√H between the carbon penetration depth D (mm) and the carbonitriding time H (hours).

  FIG. 9 is a schematic diagram illustrating the amount of carbon contained in steel in each manufacturing process. In FIG. 9, when a rolling part is manufactured using steel containing 1.0% by mass of carbon, a decarburized layer is formed in the surface layer portion after atmospheric annealing. For example, a decarburized layer containing 0.7% by mass of carbon is formed in the surface layer portion, and the depth of the decarburized layer is L1. And the time for carbonitriding is controlled, and the carbon penetration depth into the steel by carbonitriding is made deeper than the depth of the decarburized layer. For example, when carbon enters the steel surface layer portion, a carbon intrusion layer containing 1.1% by mass of carbon is formed, and the depth of the carbon intrusion layer is L2. In this case, a relationship of L1 <L2 is established between L1 and L2. Thereby, after carbonitriding, the amount of carbon contained in the surface layer portion of the steel can be surely made equal to or greater than the amount of carbon before heat treatment.

  Next, a modification of the method for manufacturing a rolling part according to the present invention will be described. FIG. 5 is a flowchart showing a modification of the rolling part manufacturing method. The rolling part manufacturing method shown in FIG. 5 and the rolling part manufacturing method shown in FIG. 4 described above basically include the same steps. However, in the rolling part manufacturing method shown in FIG. 5, the steps corresponding to steps (S13) to (S15) in FIG. 4 are changed from steps (S23) to (S24) as shown in FIG. This is different from the rolling component manufacturing method shown in FIG.

  Specifically, after forming the material blank ring by hot forging in step (S12), the material blank ring is subjected to warm ring rolling as it is in step (S23) without performing the usual spheroidizing annealing. Formed and rolled into a work ring that becomes the original shape of the inner ring and the outer ring. This warm working advances the spheroidization of the carbide, and at the same time a strong work is applied, so that the carbide spheroidizes while being refined.

  The heating conditions for warm working can be set as follows. That is, in order not to leave undissolved pearlite, it is necessary to perform warm processing at 600 ° C. or higher. On the other hand, in order to prevent a situation in which the austenite transformation amount increases too much due to excessively high temperature and pearlite is regenerated, it is necessary to perform warm processing at 820 ° C. or less. In order to soften better, the processing temperature is preferably 680 ° C. or lower and 800 ° C. or higher where the spheroidization rate of the carbide is high.

  Next, softening cooling is performed in step (S24). Thereby, after cooling, the carbide can be made fine and spheroidized. Here, in order to lower the hardness after cooling, it is necessary to gradually cool the cooling rate after warm working. The cooling rate is preferably as low as possible, and it is necessary to set the cooling rate to 5 ° C./second or less in order to sufficiently soften. However, in consideration of productivity and cost, it is necessary to set it to 1 ° C./second or more. In order to soften better, a cooling rate of 3 ° C./second or less is preferable.

  Thereby, when performing warm processing as it is after hot processing of a raw material, the structure | tissue which the carbide | carbonized_material became fine spheroid after cooling can be made by carrying out slow cooling control of heating conditions and the subsequent cooling rate. Therefore, since the spheroidizing annealing after hot working can be omitted, the process can be further simplified, and further improvement in production efficiency and reduction in manufacturing cost can be achieved.

  Next, the heat treatment method in the final heat treatment step, that is, the carbonitriding and quenching step and the tempering step will be described in detail. FIG. 6 is a diagram for explaining a heat treatment method in a final heat treatment step, that is, a carbonitriding and quenching step and a tempering step included in the method for manufacturing a rolling part. In FIG. 6, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 6, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature. Details of the heat treatment method will be described with reference to FIG.

  Referring to FIG. 6, a molded part finished to a predetermined dimension by cold working is heated to a temperature of 800 ° C. or higher and 1000 ° C. or lower, which is a temperature of A1 point or higher, for example, 850 ° C., and is 60 minutes or longer and 150 minutes. Hold for the following time, for example 90 minutes. At this time, the carbon potential of the atmospheric gas is maintained to be equal to or higher than the carbon amount before the heat treatment, and further, heating is performed in an atmosphere in which ammonia gas is added to RX gas that is atmospheric gas. Thereby, the carbonitriding process in which the carbon concentration and the nitrogen concentration in the surface layer portion of the molded part are adjusted to desired concentrations is performed. Thereafter, the molded part is immersed, for example, in oil (oil cooling), so that the molded part is cooled from a temperature of A1 point or higher to a temperature of Ms point or lower. Thereby, the carbonitriding and quenching process is completed, and the molded part is quenched and hardened.

  Further, the hardened and molded part is heated to a temperature of 150 ° C. or higher and 350 ° C. or lower, which is a temperature of A1 or lower, for example, 180 ° C., held for 30 minutes to 240 minutes, for example, 120 minutes, and then It is cooled in air at room temperature (air cooling). Thereby, the tempering process is completed. With the above procedure, the final heat treatment process for the rolling parts is completed.

  As a result, in the carbonitriding and quenching process in which heating is usually performed for a long time, the carbon potential is controlled and carbon decarburized in the surface layer portion of the steel is compensated. Therefore, decarburization of the product can be recoalized without providing a special recoal treatment process such as recoal annealing.

  FIG. 7 is a diagram for explaining a modification of the heat treatment method in the final heat treatment step, that is, the carbonitriding and quenching step and the tempering step, included in the method for manufacturing a rolling part. In FIG. 7, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 7, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature. With reference to FIG. 7, the detail of the modification of the heat processing method is demonstrated.

  Referring to FIG. 7, a molded part finished to a predetermined size by cold working is heated to a temperature of 800 ° C. or higher and 1000 ° C. or lower, which is a temperature of A1 point or higher, for example, 850 ° C., and is 60 minutes or longer and 150 minutes. Hold for the following time, for example 90 minutes. At this time, the carbon potential of the atmospheric gas is maintained to be equal to or higher than the carbon amount before the heat treatment, and further, heating is performed in an atmosphere in which ammonia gas is added to RX gas that is atmospheric gas. Thereby, the carbonitriding process in which the carbon concentration and the nitrogen concentration in the surface layer portion of the molded part are adjusted to desired concentrations is performed. Thereafter, the molded part is immersed, for example, in oil (oil cooling), so that the molded part is cooled from a temperature of A1 point or higher to a temperature of Ms point or lower. Thereby, primary hardening is completed.

  Further, the re-heating in which the molded part subjected to the primary quenching is reheated to a temperature of 730 ° C. or higher and 830 ° C. or lower, which is a temperature of A1 point or higher, for example, 800 ° C. is performed, and then 30 minutes or longer and 120 minutes or shorter. For example, 50 minutes. At this time, for example, in order to prevent decarburization, heating is performed in an atmosphere containing RX gas so that the carbon concentration and the nitrogen concentration adjusted in the carbonitriding process become the desired concentrations. Furthermore, when the molded part is cooled with oil, for example, the molded part is rapidly cooled from a temperature not lower than the A1 point to a temperature not higher than the Ms point and hardened by hardening. Thereby, the secondary quenching is completed.

  Further, the molded part that has been subjected to the secondary quenching is heated to a temperature of 150 ° C. or higher and 350 ° C. or lower, which is a temperature of A1 or lower, for example, 180 ° C. and held for 30 minutes or longer and 240 minutes or shorter, for example 120 minutes. Then, it is cooled in air at room temperature (air cooling). Thereby, the tempering process is completed. With the above procedure, the final heat treatment process for the rolling parts is completed.

  The above heat treatment improves the cracking strength while carbonitriding the surface layer portion, compared to the heat treatment method described in FIG. 6, that is, the heat treatment method (normal quenching), which is followed by carbonitriding once as it is, The aging rate of dimensional change can be reduced. Further, it is possible to obtain a microstructure in which the grain size of the austenite crystal grains is less than or equal to half that in the case of performing normal quenching. Therefore, the rolling parts manufactured by the above heat treatment have a longer rolling fatigue characteristic, can further improve the crack strength, and can further reduce the aging rate of dimensional change. The austenite crystal grains are austenite crystal grains that have undergone phase transformation during quenching heating, and remain at room temperature even after transformation to martensite by cooling.

  FIG. 8 is a diagram for explaining another modification of the heat treatment method in the final heat treatment step, that is, the carbonitriding and quenching step and the tempering step, included in the method of manufacturing a rolling part. In FIG. 8, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 8, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature. With reference to FIG. 8, the detail of the other modification of the heat processing method is demonstrated.

  The heat treatment method shown in FIG. 8 and the heat treatment method shown in FIG. 7 described above are basically the same steps including the temperature and time conditions. However, in the heat treatment method shown in FIG. 8, oil quenching is not performed after carbonitriding to complete primary quenching, but first cooling to a temperature below A1 point and then cooling to room temperature (room temperature). This is different from the heat treatment method shown in FIG.

  This makes it possible to reduce the time and energy required for reheating as compared with the case of reheating after quenching and cooling to room temperature, which is advantageous in that the manufacturing cost can be reduced. . The cooling temperature that continues after carbonitriding may be a temperature lower than the A1 point, that is, a temperature not higher than the transformation point from iron austenite to ferrite, and may be, for example, 650 ° C. or higher and 700 ° C. or lower.

  Examples of the present invention will be described below. Samples were manufactured by a conventional method of manufacturing a rolling part, that is, a method in which the final heat treatment is performed in an atmosphere in which the entire surface of the ring to be cut is not ground before the final heat treatment step and is not recoalized. Moreover, the other sample was manufactured with the manufacturing method of the rolling components of this invention shown in FIG. 4 using the same raw material. And the microstructure of the surface layer part of the sample after completion of quenching and tempering was observed with a microscope, and the carbon concentration distribution was further measured by EPMA.

  FIG. 10 is a diagram illustrating a surface layer portion of a rolling component according to a conventional manufacturing method. FIG. 11 is a view showing a surface layer portion of a rolling part according to the manufacturing method of the present invention. 10 and 11, (A) is an optical micrograph (magnification 400 times) of the microstructure of the surface part of the rolling part that has been corroded and observed using picral (picric acid alcohol solution). (B) is a graph showing the relationship between the depth from the surface of the rolling component and the carbon concentration, the horizontal axis indicates the depth (unit: mm) from the surface of the rolling component, and the vertical axis indicates EPMA. It shows the carbon concentration (unit: mass%) measured by.

  Referring to FIG. 10B, the carbon concentration from the surface of the rolling part to the depth of 0.1 mm is 0.6 to 0.8 mass%, compared with the inside of the depth of 0.1 mm or more from the surface. As a result, the carbon concentration is low. That is, it can be seen that a decarburized layer is generated in the surface layer portion. In FIG. 10A, the white background indicates the observation surface of the rolling part, and the black dots indicate carbon. It is observed that there are few black spots near the surface of the rolling part, and the carbon concentration is low in the decarburized layer generated in the surface layer portion.

  On the other hand, referring to FIG. 11 (B), the carbon concentration from the surface of the rolling component to a depth of 0.06 mm is higher than that inside the depth of 0.06 mm or more from the surface. That is, it can be seen that the surface layer portion of the rolling component is recovered by the carbonitriding process, and the amount of carbon contained before the material is further heated is increased. In FIG. 11 (A), the upper part of the photograph shows the surface part of the rolling part, black spots are increasing near the surface of the rolling part, and the carbon concentration near the surface of the rolling part is high. Observed.

  From the above, in the rolling component that has been carbonitrided in the final heat treatment step, the carbon content of the surface layer portion is greater than or equal to the carbon content that is contained before the material is heated. Thereby, it can be said that the surface hardness of the rolling parts is improved and the rolling fatigue strength is also improved. Furthermore, a rolling bearing having a long service life can be provided by using a rolling component having excellent rolling fatigue strength for the rolling bearing.

  In the above description, a rolling bearing provided with race rings (inner and outer rings) as rolling parts and rolling elements (balls or rollers) has been described as an example. However, the present invention is applied to various rolling parts. can do. For example, the present invention can be applied to screw shafts and nuts in ball screws, guide rails and sliders in linear guide devices, shafts and outer cylinders in linear motion bearings, and the like.

  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 cross-sectional schematic diagram which shows the structure of the deep groove ball bearing as a rolling bearing provided with the rolling components of one embodiment of this invention. It is a cross-sectional schematic diagram which shows the structure of the cylindrical roller bearing which is a modification of a rolling bearing. It is a cross-sectional schematic diagram which shows the structure of the tapered roller bearing which is the other modification of a rolling bearing. It is a flowchart which shows the manufacturing method of rolling components. It is a flowchart which shows the modification of the manufacturing method of rolling components. It is a figure explaining the heat processing method in the last heat treatment process included in the manufacturing method of rolling components. It is a figure explaining the modification of the heat processing method. It is a figure explaining the other modification of the heat processing method. It is a schematic diagram explaining the carbon content which the steel in each manufacturing process contains. It is a figure which shows the surface layer part of rolling components by the conventional manufacturing method. (A) is an optical micrograph of the microstructure, and (B) is a graph showing the relationship between the depth from the surface of the rolling component and the carbon concentration. It is a figure which shows the surface layer part of rolling components by the manufacturing method of this invention. (A) is an optical micrograph of the microstructure, and (B) is a graph showing the relationship between the depth from the surface of the rolling component and the carbon concentration. It is a flowchart which shows the manufacturing method of the conventional rolling component. It is a flowchart which shows the other manufacturing method of the conventional rolling component.

Explanation of symbols

  1 deep groove ball bearing, 2 outer ring, 3 inner ring, 4 balls, 5 cage, 6 cylindrical roller bearing, 7 roller, 8 tapered roller bearing.

Claims (6)

A hot working process of heating and forming a material made of high carbon steel;
An atmospheric annealing process that improves the workability by performing spheroidizing annealing in the atmosphere;
A cold working process for finishing to a predetermined part size;
A final heat treatment step for quenching and tempering to obtain a required hardness, and a rolling part manufacturing method comprising:
In the final heat treatment step, the carbon potential of the atmospheric gas is kept above the amount of carbon before heat treatment contained in the material before being heated in the hot working step, and carbonitriding is performed, thereby performing the hot working step and The method for manufacturing a rolling part, wherein the amount of carbon contained in the decarburized layer generated in the surface layer portion of the material in the atmospheric annealing step is equal to or greater than the amount of carbon before the heat treatment. The raw material contains 0.95% by mass or more and 1.1% by mass or less carbon before being heated in the hot working step,
The method for manufacturing a rolling part according to claim 1, wherein the carbon potential is 1.0% to 1.1%.   The rolling part manufacturing method according to claim 1 or 2, wherein a carbon penetration depth into the material by the carbonitriding process is made deeper than a depth of the decarburized layer.   A bearing ring for a rolling bearing manufactured by the method for manufacturing a rolling part according to any one of claims 1 to 3.   A race for a tapered roller bearing manufactured by the method for manufacturing a rolling part according to any one of claims 1 to 3.   A bearing comprising the bearing ring according to claim 4 or 5.