JP2009235445A - Method for applying heat-treatment for steel, method for manufacturing machine part, machine part, and rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for applying a heat-treatment for a steel by which the restraint of the hardness-lowering in the semi-high temperature atmosphere and the improvements of a dimensional stability and the hardness level can be obtained; a method for manufacturing a machine part, the machine part and a rolling bearing containing this machine part. <P>SOLUTION: This method for applying the heat-treatment for the steel, is provided with; a process for preparing the steel composed of 0.7-1.2 mass% carbon, 0.1-1.1 mass% silicon, 0.25-1.5 mass% manganese and the balance iron with impurities; a process for forming a nitrogen-enriched layer in the range containing the surface of the steel by nitriding at the temperature of &ge;A<SB>1</SB>point; and a process for transforming the nitrogen-enriched layer into a bainite so that retained austenite quantity in the nitrogen-enriched layer becomes &le;5vol% by holding the temperature exceeding Ms point of the nitrogen-enriched layer and the temperature &le; 50&deg;C higher from the Ms point. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a steel heat treatment method, a machine part manufacturing method, a machine part, and a rolling bearing, and more specifically, a steel heat treatment method containing carbon of 0.7% by mass or more and 1.2% by mass or less, 0 The present invention relates to a manufacturing method of a machine part made of steel containing carbon of 7% by mass or more and 1.2% by mass or less, a machine part, and a rolling bearing including the machine part.

  In recent years, with the improvement in performance of devices using machine elements such as rolling bearings, machine elements are often used in a higher temperature environment than in the past. When the machine part which is a part which comprises a machine element consists of steel, the machine part may soften by being exposed to high temperature, and the problem that sufficient durability cannot be ensured may arise. When machine parts made of steel are used in a high temperature environment exceeding 200 ° C., the steel constituting the machine parts has a heat resistance containing a large amount of alloy elements such as chromium and molybdenum exceeding 3% by mass. Excellent steel is adopted. Thereby, even when the machine part is exposed to high temperature, softening of the machine part is suppressed, and sufficient durability is ensured.

  On the other hand, even when the machine part is used in a quasi-high temperature environment that is a temperature range of 100 ° C. or more and 200 ° C. or less, if the steel having excellent heat resistance as described above is adopted as the material of the machine part, sufficient durability is obtained. Is secured. However, mechanical parts made of steel with excellent heat resistance often have excessive characteristics compared to the characteristics required for mechanical parts used in sub-high temperature environments, but a large amount of alloying elements. Due to the inclusion, there is a problem that processing and heat treatment are difficult and the manufacturing cost is significantly increased. Furthermore, in recent years, the price of metals such as chromium has soared. In consideration of such a situation, it is preferable to employ steel in which the addition amount of the alloy element is suppressed as steel constituting the machine part used in the semi-high temperature environment.

  Further, with the improvement in performance of devices using machine elements, the machine elements are required to improve dimensional accuracy, particularly to reduce the amount of dimensional change during use. For this reason, improvement in dimensional stability is also required for machine parts constituting machine elements.

As a method for suppressing a decrease in hardness in a semi-high temperature environment of a steel in which the addition amount of the alloy element is suppressed and improving the dimensional stability, a method of bainite the steel structure is known. Since the bainite structure is stable in a quasi-high temperature environment, a mechanical part including the bainite structure is suppressed in hardness reduction in a quasi-high temperature environment and improved in dimensional stability. This bainite structure has excellent characteristics in addition to the suppression of hardness reduction and the improvement of dimensional stability in the quasi-high temperature environment, and mechanical parts using the bainite structure have been proposed (for example, Patent Document 1). reference).
JP 2001-50282 A

  However, although the bainite structure has a small decrease in hardness in a quasi-high temperature environment, it has a lower hardness level than a martensite structure formed by quench hardening, so that it is a machine part used in an environment where high stress is applied. There was a problem that it was difficult to apply.

  Accordingly, an object of the present invention is to provide a steel heat treatment method capable of achieving an improvement in hardness level as well as suppressing hardness reduction and improving dimensional stability in a quasi-high temperature environment, and suppressing dimensional stability while suppressing hardness reduction in a quasi-high temperature environment. It is providing the manufacturing method of the machine part which improved the property, and the hardness level improved, the machine part, and the rolling bearing containing the said machine part.

In one aspect of the present invention, a heat treatment method for steel includes 0.7% by mass to 1.2% by mass of carbon, 0.1% by mass to 1.1% by mass of silicon, and 0.25% by mass. A step of preparing a steel containing 1.5% by mass or less of manganese and the balance iron and impurities, and nitriding the steel at a temperature of A ₁ point or more, to a region including the surface of the steel forming a nitrogen-enriched layer the nitrogen concentration is higher layer than inside the steel, greater than the M _S point of the nitrogen-enriched layer is maintained at 50 ° C. higher temperature below the temperature than M _S point Thus, the method includes a step of transforming the nitrogen-enriched layer to bainite so that the amount of retained austenite of the nitrogen-enriched layer is 5% by volume or less.

  As described above, the bainite structure formed by transforming steel to bainite has a lower hardness level than the martensite structure formed by quench hardening. Therefore, in order to apply the bainite structure to a machine part used in an environment where a high stress is applied, it is necessary to improve the hardness level of the bainite structure.

On the other hand, as a steel surface treatment method, a nitrogen-enriched layer in which nitrogen is infiltrated near the surface by nitriding steel at a temperature of A ₁ point or more (a layer in which nitrogen is infiltrated into iron to form a solid solution) A method of forming is known. Here, when the nitriding treatment is performed on the steel, not only the hardness level is increased but also the amount of retained austenite contained in the steel structure is increased due to the penetration of nitrogen into the steel. In mechanical parts that contain residual austenite in the structure, the residual austenite may transform into martensite during use, and compressive stress may be generated on the surface of the mechanical part. In this case, the occurrence and propagation of cracks in the surface layer portion of the mechanical component are suppressed, and the durability of the mechanical component is improved. However, since the transformation of residual austenite to martensite is accompanied by a volume change, a mechanical part subjected to nitriding has a problem that the dimensional stability is lowered. Therefore, the steel surface treatment by nitriding is applied to the heat treatment of steel that constitutes mechanical parts that can actively use retained austenite, that is, mechanical parts that emphasize the effects of compressive stress generation rather than dimensional stability. Has been. As a result, nitriding was not adopted as a means for improving the hardness level for mechanical parts including a bainite structure with emphasis on dimensional stability.

In view of such problems of the prior art, the present inventor has studied in detail a steel heat treatment method for improving hardness level as well as suppressing hardness reduction and improving dimensional stability in a semi-high temperature environment. As a result, in terms of the formation of the nitrogen-enriched layer by nitriding the steel, the steel is cooled to a temperature slightly higher than the M _S point of the nitrogen-enriched layer, the amount of retained austenite is 5% or less by volume By maintaining bainite for a sufficient amount of time, the hardness level of steel with a bainite structure is sufficient for machine parts used in high stress environments while ensuring dimensional stability. It has been found that it can be improved to a certain extent.

In the heat treatment method for steel in one aspect of the present invention, nitriding is performed on the steel having the above component composition in which the addition amount of the alloy element is suppressed, and after forming a nitrogen-enriched layer, exceed M _S point of the nitrogen-enriched layer, by holding the 50 ° C. higher temperature below the temperature than M _S point, the nitrogen-enriched layer as residual austenite amount of nitrogen-enriched layer is 5 vol% or less A bainite transformation process is employed. Therefore, the nitrogen-enriched layer formed in the region including the steel surface includes a bainite structure, and the amount of retained austenite is suppressed to 5% by volume or less. Therefore, according to the heat treatment method for steel in one aspect of the present invention, the hardness level is improved while the hardness reduction and the dimensional stability are improved in the semi-high temperature environment of the steel in which the addition amount of the alloy element is suppressed. A possible steel heat treatment method can be provided.

In another aspect of the present invention, the heat treatment method of steel includes 0.7% by mass or more and 1.2% by mass or less of carbon, 0.1% by mass or more and 1.1% by mass or less of silicon, and 0.25% by mass. And at least one selected from the group consisting of 2.0 mass% or less chromium, 0.5 mass% or less molybdenum, and 0.5 mass% or less nickel. A layer having a higher nitrogen concentration than the inside in a region including the surface of the steel by nitriding the steel containing the above elements and the balance iron and impurities, and nitriding the steel at a temperature of A ₁ point or higher forming a nitrogen-enriched layer is, the steel, greater than the M _S point of the nitrogen-enriched layer, by holding the 50 ° C. higher temperature below the temperature than M _S point, the nitrogen-enriched layer Nitrogen so that the amount of retained austenite is 5% by volume or less. And a step of bainite transformation to enriched layer.

  The steel heat treatment method according to another aspect of the present invention basically has the same configuration as that of the steel heat treatment method according to one aspect of the present invention, and exhibits the same effects. However, in the heat treatment method for steel according to another aspect of the present invention, the prepared steel further includes 2.0 mass% or less of chromium and 0.5 mass% or less of molybdenum in consideration of the use of the steel after the heat treatment and the like. And at least one element selected from the group consisting of nickel of 0.5% by mass or less, and differs from the steel heat treatment method according to one aspect of the present invention.

  According to the heat treatment method of steel in another aspect of the present invention, the steel to be prepared is composed of 2.0 mass% or less chromium, 0.5 mass% or less molybdenum, and 0.5 mass% or less nickel. By including at least one element selected from the above, it is possible to further improve the hardness level and further suppress a decrease in hardness in a quasi-high temperature environment while suppressing the addition amount of the alloy element. In addition, in order to ensure the improvement of the hardness level and the suppression of the hardness decrease in the semi-high temperature environment, the chromium content is 0.8 mass% or more, the molybdenum content is 0.1 mass% or more, nickel is It is desirable to set it as 0.1 mass% or more.

Here, the point A ₁ in the case of heating the steel refers to a point that the structure of the steel corresponds to the temperature to start the transformation from ferrite to austenite. Further, the M _s point means a point corresponding to a temperature at which martensite formation starts when the austenitized steel is cooled.

Further, when the temperature at which the steel is retained in the step of transforming the nitrogen-enriched layer to the bainite (hereinafter referred to as bainite transformation temperature) exceeds 50 ° C. higher than the _MS point, the hardness of the steel decreases, and the machine part As a result, the durability may be reduced. Therefore, the bainite transformation temperature is required to be 50 ° C. higher temperatures less than M _S point, it is desirable that the 30 ° C. higher temperature or lower. On the other hand, when the steel is cooled to a temperature below the _MS point, the steel undergoes martensitic transformation. Therefore, although the bainite transformation temperature needs to be higher than M _S point, considering precision of temperature control, it is preferable to 10 ° C. higher temperatures or higher than M _S point.

Furthermore, in order to transform the nitrogen-enriched layer to a bainite transformation so that the amount of retained austenite in the nitrogen-enriched layer is 5% by volume or less, A steel heated to a temperature of _one point or higher is kept at the bainite transformation temperature for a sufficient time. There is a need to. Since the holding time changes depending on conditions such as the bainite transformation temperature and the steel component composition, it is necessary to set the holding time according to the conditions. However, in the steel having the above component composition, the amount of retained austenite is 5% by volume or less. Therefore, it is preferable to set it for 60 minutes or more, and by setting it for 120 minutes or more, the amount of retained austenite can be reduced to 2 volume% or less which is a more preferable range. Further, when the steel is held at the bainite transformation temperature, the temperature of the steel may vary within the above temperature range, but it is desirable to keep the temperature constant when it is desired to easily control the amount of retained austenite. Furthermore, after the nitrogen-enriched layer is formed, the cooling rate from the _point A to the bainite transformation temperature, from the viewpoint of suppressing the generation of low strength perlite, be capable of suppressing cooling rate pearlite transformation preferably it is preferable that the 500 cooling rate of up to ° C. 200 ° C. / sec or more from _a point a in particular.

  Further, the nitriding performed on the steel in the step of forming the nitrogen-enriched layer may be a nitrogen-enriching treatment in which nitrogen enters while suppressing the detachment (decarburization) of carbon from the steel. Further, carbonitriding treatment may be performed in which carbon is introduced into the steel together with nitrogen. More specifically, when the carbon content of the untreated steel is sufficient to ensure the desired surface hardness, for example, when the carbon content of the steel is 1% by mass or more, decarburization is suppressed. However, when the nitrogen content is made to infiltrate nitrogen and the carbon content of the steel is less than 1% by mass, a carbonitriding process in which carburizing is performed simultaneously with nitrogen enrichment can be employed. Hereinafter, the reason which limited the component range of steel to said range is demonstrated.

Carbon: 0.7% by mass or more and 1.2% by mass or less In the steel constituting the machine part, if the carbon is less than 0.7% by mass, the hardness and rigidity of the machine part may be insufficient. On the other hand, if the carbon content exceeds 1.2% by mass, a large iron carbide is formed in the steel, which may adversely affect the durability of the machine part. Therefore, carbon needs to be 0.7 mass% or more and 1.2 mass% or less.

Silicon: 0.1 mass% or more and 1.1 mass% or less In the steel which comprises a machine part, when silicon is less than 0.1 mass%, there exists a possibility that durability of a machine part may fall. On the other hand, when silicon exceeds 1.1 mass%, the hardness of a raw material will rise and the problem that cold workability may fall may generate | occur | produce. Therefore, silicon needs to be 0.1 mass% or more and 1.1 mass% or less.

Manganese: 0.25% by mass or more and 1.5% by mass or less In the steel constituting the machine part, if the manganese content is less than 0.25% by mass, the durability of the machine part may be lowered. On the other hand, when manganese exceeds 1.5 mass%, the problem that the hardness of a raw material will rise and cold workability will fall may generate | occur | produce. Therefore, manganese needs to be 0.25 mass% or more and 1.5 mass% or less.

  The method of manufacturing a machine part according to the present invention includes a step of preparing a steel member made of steel and formed into a schematic shape of the machine part, and a step of performing a heat treatment on the steel member. And the said heat processing is implemented using the heat processing method of the said steel.

  According to the method for manufacturing a machine part of the present invention, the steel member formed into the general shape of the machine part achieves a reduction in hardness and an improvement in dimensional stability in a semi-high temperature environment, and an improvement in the hardness level. Since the heat treatment method for steel according to the present invention that can be performed is carried out, it is possible to manufacture a machine part that suppresses a decrease in hardness in a semi-high temperature environment, improves dimensional stability, and has an improved hardness level. it can.

  The mechanical component in one aspect of the present invention is manufactured by the above-described method for manufacturing a mechanical component. According to the machine component in one aspect of the present invention, by being manufactured by the method for manufacturing a machine component of the present invention, a decrease in hardness in a quasi-high temperature environment is suppressed and dimensional stability is improved, and hardness is increased. It is possible to provide a machine part having an improved level.

  The mechanical component according to another aspect of the present invention includes carbon of 0.7% by mass to 1.2% by mass, silicon of 0.1% by mass to 1.1% by mass, and 0.25% by mass to 1%. .5% by mass or less of manganese and the balance iron and impurities. In the region including the surface, a nitrogen-enriched layer that is a layer having a higher nitrogen concentration than the inside is formed. The nitrogen-enriched layer includes a bainite structure, and the amount of retained austenite is suppressed to 5% by volume or less.

  In the machine part according to another aspect of the present invention, a nitrogen-enriched layer is formed in a region including the surface of the machine part having the above-mentioned appropriate component composition, and the nitrogen-enriched layer contains a bainite structure. That is, in the mechanical component, the nitrogen concentration of the bainite structure formed in the surface layer portion is increased. As described above, since the bainite structure is stable in a quasi-high temperature environment, a decrease in hardness in the quasi-high temperature environment is suppressed in the machine component according to another aspect of the present invention. Further, the hardness level of the bainite structure is improved by increasing the nitrogen concentration of the bainite structure. Furthermore, dimensional stability is improved by suppressing the amount of retained austenite of the nitrogen-enriched layer to 5% by volume or less. As a result, according to the mechanical component in another aspect of the present invention, it is possible to provide a mechanical component in which a decrease in hardness in a semi-high temperature environment is suppressed, dimensional stability is improved, and a hardness level is improved.

  In still another aspect of the present invention, the mechanical component includes 0.7% by mass or more and 1.2% by mass or less of carbon, 0.1% by mass or more and 1.1% by mass or less of silicon, and 0.25% by mass or more. At least one selected from the group consisting of 1.5 mass% or less manganese, 2.0 mass% or less chromium, 0.5 mass% or less molybdenum, and 0.5 mass% or less nickel. It is comprised from the steel which consists of these elements and which consists of remainder iron and an impurity. In the region including the surface, a nitrogen-enriched layer that is a layer having a higher nitrogen concentration than the inside is formed. The nitrogen-enriched layer includes a bainite structure, and the amount of retained austenite is suppressed to 5% by volume or less.

  The mechanical component according to still another aspect of the present invention basically has the same configuration as the mechanical component according to the other aspect of the present invention, and exhibits the same operational effects. However, in the machine part according to still another aspect of the present invention, in consideration of the use of the machine part and the like, the steel constituting the machine part is further 2.0% by mass or less of chromium and 0.5% by mass or less of molybdenum. And at least one element selected from the group consisting of nickel of 0.5% by mass or less, and differs from the machine component according to another aspect of the present invention.

  According to the mechanical component in still another aspect of the present invention, the steel constituting the mechanical component is composed of 2.0 mass% or less of chromium, 0.5 mass% or less of molybdenum, and 0.5 mass% or less of nickel. By including at least one element selected from the group, it is possible to further improve the hardness level and further suppress a decrease in hardness in a quasi-high temperature environment while suppressing the addition amount of the alloy element. In addition, in order to ensure the improvement of the hardness level and the suppression of the hardness reduction in the semi-high temperature environment, the chromium content is 0.8% by mass or more, the molybdenum content is 0.1% by mass or more, and nickel is contained. The amount is desirably 0.1% by mass or more.

  Here, in the mechanical component in the other aspect described above and still another aspect, the amount of retained austenite of the nitrogen-enriched layer is preferably 2% by volume or less. This further improves the dimensional stability of the machine part. In general, in a mechanical component such as a rolling bearing, the strength of the surface layer portion of the mechanical component, specifically, the region having a thickness of about 0.15 mm including the surface is often important. Therefore, in the mechanical component in the other aspect described above and still another aspect, the thickness of the nitrogen-enriched layer is preferably 0.15 mm or more. Furthermore, from the viewpoint of improving the hardness level, the nitrogen-enriched layer is preferably composed of a bainite structure, a martensite structure, and 5% by volume or less of retained austenite, from the viewpoint of improving dimensional stability. The bainite structure preferably occupies 80% volume or more.

  Preferably, in the mechanical component according to the other aspect described above and still another aspect, the nitrogen-enriched layer has a carbon content of 0.8% by mass or more and 1.2% by mass or less, and 0.1% by mass or more and 0.8% by mass or less. Contains nitrogen.

  The carbon content has a great influence on the hardness of the steel. And the hardness of the steel which comprises a machine part is one of the important factors which dominate the durability of the said machine part. If the carbon content in the steel is less than 0.8% by mass, the hardness of the surface layer may be insufficient depending on the application of the machine part. Therefore, the carbon content in the nitrogen-enriched layer is preferably 0.8% by mass or more. On the other hand, if the carbon content in the steel exceeds 1.2% by mass, a large iron carbide is formed in the steel, which may adversely affect the durability of the machine part. Therefore, the carbon content in the nitrogen-enriched layer is preferably 1.2% by mass or less.

  On the other hand, when the nitrogen content in the nitrogen-enriched layer is less than 0.1% by mass, the effect of improving the hardness level of the bainite structure becomes small. Therefore, the nitrogen content in the nitrogen-enriched layer is preferably 0.1% by mass or more. Moreover, when the nitrogen content in steel exceeds 0.8 mass%, a void is formed in steel and there exists a possibility of reducing the durability of the machine component which consists of the said steel. Therefore, the nitrogen content in the nitrogen-enriched layer is preferably 0.8% by mass or less.

  The mechanical part may be used as a part constituting a bearing. The mechanical component of the present invention, in which the decrease in hardness in a quasi-high temperature environment is suppressed, the dimensional stability is improved, and the hardness level is improved, is suitable as a component constituting a bearing.

  The rolling bearing according to the present invention includes a race member and a plurality of rolling elements that are in contact with the race member and disposed on an annular raceway. And at least any one of a track member and a rolling element is the above-mentioned machine part. Thereby, it is possible to provide a rolling bearing with improved durability and dimensional stability in a semi-high temperature environment.

  As is apparent from the above description, according to the steel heat treatment method of the present invention, a steel heat treatment method capable of achieving an increase in hardness level as well as suppressing a decrease in hardness and improving dimensional stability in a semi-high temperature environment is provided. can do. Further, according to the method of manufacturing a machine part, the machine part and the rolling bearing of the present invention, a decrease in hardness in a quasi-high temperature environment is suppressed, dimensional stability is improved, and a machine part manufacturing method with improved hardness level, A mechanical component and a rolling bearing including the mechanical component can be provided.

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

  FIG. 1 is a schematic cross-sectional view showing a configuration of a deep groove ball bearing as a rolling bearing provided with mechanical parts according to an embodiment of the present invention. FIG. 2 is a schematic partial cross-sectional view showing an enlarged main part of FIG. With reference to FIG. 1 and FIG. 2, the deep groove ball bearing as a rolling bearing in one embodiment of this invention is demonstrated.

  Referring to FIG. 1, a deep groove ball bearing 1 includes an annular outer ring 11 as a race member, an annular inner ring 12 as a race member disposed inside the outer ring 11, and an outer ring 11 and an inner ring 12. And a plurality of balls 13 as rolling elements that are arranged and held by an annular cage 14. An outer ring rolling surface 11 </ b> A is formed on the inner circumferential surface of the outer ring 11, and an inner ring rolling surface 12 </ b> A is formed on the outer circumferential surface of the inner ring 12. And the outer ring | wheel 11 and the inner ring | wheel 12 are arrange | positioned so that 12A of inner ring | wheel rolling surfaces and 11A of outer ring | wheels may mutually oppose. Further, the balls 13 are in contact with the inner ring rolling surface 12A and the outer ring rolling surface 11A on the ball rolling surface 13A which is the surface thereof, and are arranged at a predetermined pitch in the circumferential direction by the cage 14. It is held on an annular track so as to be freely rollable. With the above configuration, the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1 are rotatable relative to each other.

  Here, the outer ring 11, the inner ring 12 and the ball 13, which are mechanical parts, are 0.7 mass% to 1.2 mass% carbon, 0.1 mass% to 1.1 mass% silicon, 0% It is comprised from the steel which contains 25 mass% or more and 1.5 mass% or less manganese, and consists of remainder iron and an impurity. Then, referring to FIG. 2, areas including outer ring rolling surface 11 </ b> A, inner ring rolling surface 12 </ b> A, and ball rolling surface 13 </ b> A that are the surfaces of outer ring 11, inner ring 12, and ball 13 include inner portions 11 </ b> C, 12 </ b> C, 13 </ b> C. The outer ring nitrogen-enriched layer 11B, the inner ring nitrogen-enriched layer 12B, and the ball nitrogen-enriched layer 13B, which are layers having a higher nitrogen concentration, are formed. Furthermore, the outer ring nitrogen-enriched layer 11B, the inner ring nitrogen-enriched layer 12B, and the ball nitrogen-enriched layer 13B include a bainite structure, and the amount of retained austenite is suppressed to 5% by volume or less. Here, the impurities include inevitable impurities such as those derived from steel raw materials or those mixed in the manufacturing process.

  In outer ring 11, inner ring 12 and ball 13 which are machine parts in the present embodiment, outer ring rolling surface 11A, inner ring rolling surface 12A and ball made of steel having the above-mentioned appropriate component composition are formed. An outer ring nitrogen-enriched layer 11B, an inner ring nitrogen-enriched layer 12B, and a ball nitrogen-enriched layer 13B are formed in regions including the rolling contact surface 13A, respectively. The outer ring nitrogen-enriched layer 11B, the inner ring nitrogen-enriched layer 12B, and the ball nitrogen-enriched layer 13B include a bainite structure. That is, in the outer ring 11, the inner ring 12 and the ball 13, the nitrogen concentration of the bainite structure formed in the surface layer portion is increased by the outer ring nitrogen-enriched layer 11B, the inner ring nitrogen-enriched layer 12B and the ball nitrogen-enriched layer 13B. Yes. Therefore, in the outer ring 11, the inner ring 12 and the ball 13, a decrease in the hardness of the surface layer portion in the semi-high temperature environment is suppressed, and the hardness level is improved. In addition, the amount of retained austenite in the outer ring nitrogen-enriched layer 11B, the inner ring nitrogen-enriched layer 12B, and the ball nitrogen-enriched layer 13B is suppressed to 5% by volume or less, thereby improving the dimensional stability. As a result, the outer ring 11, the inner ring 12 and the ball 13 are mechanical parts in which a decrease in hardness in a semi-high temperature environment is suppressed, dimensional stability is improved, and a hardness level is improved. Further, the deep groove ball bearing 1 which is a rolling bearing provided with the outer ring 11, the inner ring 12 and the ball 13 is a rolling bearing having improved durability and dimensional stability in a quasi-high temperature environment.

  Here, the outer ring 11, the inner ring 12 and the ball 13 are replaced with the steel by 0.7 to 1.2% by mass of carbon and 0.1 to 1.1% by mass of silicon. And 0.25 mass% or more and 1.5 mass% or less of manganese, and further comprising 2.0 mass% or less of chromium, 0.5 mass% or less of molybdenum, and 0.5 mass% or less of nickel. It may comprise at least one element selected from the group, and may be composed of steel consisting of the remaining iron and impurities. Thereby, while suppressing the addition amount of an alloy element, while further improving a hardness level, the hardness fall in a semi-high temperature environment can be suppressed further.

  Furthermore, the outer ring nitrogen-enriched layer 11B, the inner ring nitrogen-enriched layer 12B, and the ball nitrogen-enriched layer 13B are 0.8 mass% or more and 1.2 mass% or less of carbon, and 0.1 mass% or more and 0.8 mass% or less. % Or less of nitrogen is preferable. Thereby, formation of large carbides by excess carbon and formation of voids by excess nitrogen while ensuring sufficient hardness in the surface layer portion, particularly the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A. And the durability of the outer ring 11, the inner ring 12 and the ball 13 can be improved.

  FIG. 3 is a schematic cross-sectional view showing a configuration of a thrust needle roller bearing as a rolling bearing provided with a mechanical component that is a first modification of the present embodiment. FIG. 4 is a schematic partial cross-sectional view showing an enlarged main part of the race ring in FIG. FIG. 5 is an enlarged schematic cross-sectional view showing the needle roller in FIG. With reference to FIGS. 3-5, the thrust needle roller bearing which is a 1st modification is demonstrated.

  Referring to FIG. 3, the thrust needle roller bearing 2 has a disk-like shape, and a pair of race rings 21 as race members arranged so that one main surface faces each other, and as a rolling element, A plurality of needle rollers 23 and an annular retainer 24 are provided. The plurality of needle rollers 23 are in contact with the raceway rolling surface 21 </ b> A formed on the main surfaces of the pair of raceways 21 facing each other at the roller raceway 23 </ b> A that is the outer circumferential surface thereof, and are circumferentially moved by the cage 24. Are held at a predetermined pitch so as to be able to roll on an annular track. With the above configuration, the pair of race rings 21 of the thrust needle roller bearing 2 can rotate relative to each other.

  Here, referring to FIGS. 3 to 5, the bearing ring 21 of the thrust needle roller bearing 2 in this modification corresponds to the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1, and the needle roller 23 corresponds to the ball 13. , Have the same configuration and have the same effect. That is, the race ring 21 and the needle roller 23 are made of the same steel as the outer ring 11, the inner ring 12 and the ball 13. In the region including the raceway rolling surface 21A, the raceway nitrogen-enriched layer 21B (layer having a higher nitrogen concentration than the interior 21C) corresponding to the outer-ring nitrogen-enriched layer 11B and the inner-ring nitrogen-enriched layer 12B is rolled. A roller-enriched layer 23B (layer having a higher nitrogen concentration than the interior 23C) corresponding to the ball nitrogen-enriched layer 13B is formed in the region including the running surface 23A. As a result, the bearing ring 21 and the needle roller 23 are mechanical parts in which a decrease in hardness in a semi-high temperature environment is suppressed, dimensional stability is improved, and a hardness level is improved. Further, the thrust needle roller bearing 2 which is a rolling bearing provided with the bearing ring 21 and the needle roller 23 is a rolling bearing with improved durability and dimensional stability in a semi-high temperature environment.

  FIG. 6 is a schematic cross-sectional view illustrating a configuration of a constant velocity joint including a mechanical component which is a second modification example of the present embodiment. FIG. 7 is a schematic cross-sectional view taken along line VII-VII in FIG. FIG. 8 is a schematic cross-sectional view showing a state where the constant velocity joint of FIG. 6 forms an angle. FIG. 9 is a schematic partial cross-sectional view showing an enlarged main part of FIG. FIG. 10 is a schematic partial cross-sectional view showing an enlarged main part of FIG. 6 corresponds to a schematic cross-sectional view taken along line VI-VI in FIG. With reference to FIGS. 6-10, the constant velocity joint which is a 2nd modification is demonstrated.

  Referring to FIGS. 6 and 7, constant velocity joint 3 includes inner race 31 connected to shaft 35, and outer race 32 arranged to surround the outer peripheral side of inner race 31 and connected to shaft 36. A torque transmitting ball 33 disposed between the inner race 31 and the outer race 32 and a cage 34 for holding the ball 33 are provided. The ball 33 is disposed in contact with the inner race ball groove 31A formed on the outer peripheral surface of the inner race 31 and the outer race ball groove 32A formed on the inner peripheral surface of the outer race 32 on the ball rolling surface 33A. The cage 34 is held so as not to fall off.

  The inner race ball groove 31A and the outer race ball groove 32A formed on the outer peripheral surface of the inner race 31 and the inner peripheral surface of the outer race 32 pass through the centers of the shaft 35 and the shaft 36 as shown in FIG. In a state where the axes are in a straight line, each of them is formed in a curve (arc) shape having a curvature center at points A and B that are equidistant from the joint center O on the axis to the left and right on the axis. That is, the trajectory of the center P of the ball 33 that rolls in contact with the inner race ball groove 31A and the outer race ball groove 32A is centered on the point A (inner race center A) and point B (outer race center B). Each of the inner race ball groove 31A and the outer race ball groove 32A is formed so as to have a curved line (arc). As a result, even when the constant velocity joint makes an angle (when the constant velocity joint operates so that the axes passing through the centers of the shaft 35 and the shaft 36 intersect), the ball 33 always has the shaft 35 and the shaft 36. Located on the bisector of the angle (∠AOB) formed by the axis passing through the center.

  Next, the operation of the constant velocity joint 3 will be described. 6 and 7, in constant velocity joint 3, when rotation about the shaft is transmitted to one of shafts 35 and 36, the ball fitted in inner race ball groove 31A and outer race ball groove 32A. The rotation is transmitted to the other of the shafts 35 and 36 via 33. Here, as shown in FIG. 8, when the shafts 35 and 36 form an angle θ, the ball 33 includes the inner race ball groove 31 </ b> A and the outer race ball having the centers of curvature at the inner race center A and the outer race center B described above. Guided by the groove 32A, the center P is held at a position on the bisector of ∠AOB. Here, since the inner race ball groove 31A and the outer race ball groove 32A are formed so that the distance from the joint center O to the inner race center A is equal to the distance from the outer race center B, the ball 33 The distances from the center P to the inner race center A and the outer race center B are equal, and the triangle OAP and the triangle OBP are congruent. As a result, the distances L from the center P of the ball 33 to the shafts 35 and 36 are equal to each other, and when one of the shafts 35 and 36 rotates around the axis, the other also rotates at a constant speed. Thus, the constant velocity joint 3 can ensure constant velocity even when the shafts 35 and 36 form an angle. The cage 34, together with the inner race ball groove 31A and the outer race ball groove 32A, prevents the balls 33 from jumping out from the inner race ball groove 31A and the outer race ball groove 32A when the shafts 35 and 36 rotate. It performs the function of determining the joint center O of the constant velocity joint 3.

  Here, referring to FIGS. 6 to 10, the inner race 31, the outer race 32, and the ball 33 of the constant velocity joint 3 in this modification correspond to the inner ring 12, the outer ring 11, and the ball 13 of the deep groove ball bearing 1, respectively. However, it has the same configuration and has the same effect. That is, the inner race 31, the outer race 32, and the ball 33 are made of the same steel as the outer ring 11, the inner ring 12, and the ball 13. The inner race 31, the outer race 32, and the surface of the inner race ball groove 31 </ b> A formed on the surface of the ball 33, the outer race ball groove 32 </ b> A, and the region including the ball rolling surface 33 </ b> A are each enriched with inner ring nitrogen. Inner race nitrogen-enriched layer 31B, outer race nitrogen-enriched layer 32B and ball nitrogen-enriched layer 33B corresponding to layer 12B, outer ring nitrogen-enriched layer 11B and ball nitrogen-enriched layer 13B (more than internal 31C, 32C, 33C) A layer having a high nitrogen concentration) is formed. As a result, the inner race 31, the outer race 32, and the ball 33 are mechanical parts that are suppressed in hardness reduction in a semi-high temperature environment, improved in dimensional stability, and improved in hardness level. The constant velocity joint 3 including the inner race 31, the outer race 32, and the ball 33 is a constant velocity joint with improved durability and dimensional stability in a quasi-high temperature environment.

  Next, a description will be given of a method for manufacturing machine components in one embodiment of the present invention, and machine elements such as rolling bearings and constant velocity joints equipped with the machine components. FIG. 11 is a diagram illustrating an outline of a machine component and a method of manufacturing a machine element including the machine component according to an embodiment of the present invention.

  Referring to FIG. 11, in the method of manufacturing machine parts and machine elements in the present embodiment, first, a steel material preparation process is performed as a process (S100). Specifically, in this step (S100), 0.7% by mass or more and 1.2% by mass or less of carbon, 0.1% by mass or more and 1.1% by mass or less of silicon, and 0.25% by mass or more. At least one selected from the group consisting of 1.5 mass% or less manganese, 2.0 mass% or less chromium, 0.5 mass% or less molybdenum, and 0.5 mass% or less nickel. A steel made of the remaining iron and impurities, for example, a steel bar made of high carbon chrome bearing steel such as JIS standards SUJ2, SUJ3, SUJ5, and a steel wire are prepared. In the step (S100), 0.7 mass% or more and 1.2 mass% or less of carbon, 0.1 mass% or more and 1.1 mass% or less of silicon, and 0.25 mass% or more and 1.5 mass% or less. A steel bar, a steel wire, or the like may be prepared, which contains manganese in an amount of not more than% by mass and is made of steel made of the remaining iron and impurities.

  Next, a forming step is performed as a step (S200). Specifically, in the step (S200), the steel material prepared in the step (S100) is subjected to processing such as cutting, forging, and turning, so that the steel material becomes the outer ring 11, the track as a machine part. It is formed into a schematic shape such as a ring 21 and an inner race 31. This process (S100) and (S200) comprises the steel member preparation process which consists of steel and prepares the steel member shape | molded by the general shape of the machine part.

  Next, a heat treatment step including a nitriding step performed as step (S300) and a bainite transformation step performed as step (S400) is performed. Details of this heat treatment step will be described later.

  Next, as a process (S500), a finishing process in which a finishing process or the like is performed on the steel member that has been subjected to the heat treatment process is performed. Specifically, for example, polishing is performed on the inner ring rolling surface 12A, the raceway rolling surface 21A, the outer race ball groove 32A, and the like of the steel member that has been subjected to the heat treatment process. Thereby, the machine part in this Embodiment is completed and the manufacturing method of the machine part in this Embodiment is completed.

  Furthermore, as a process (S600), an assembly process is performed in which completed machine parts are combined to assemble machine elements. Specifically, the deep groove ball bearing 1 is assembled by combining, for example, the outer ring 11, the inner ring 12, the ball 13, and the cage 14, which are mechanical parts in the present embodiment manufactured by the above-described process. Thereby, the machine element provided with the machine part of the present invention is manufactured.

  Next, details of the heat treatment step will be described. FIG. 12 is a diagram for explaining the details of the heat treatment step included in the method of manufacturing a mechanical component in the present embodiment. In FIG. 12, the horizontal direction indicates time, and the time has passed as it goes to the right. In FIG. 12, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature.

Referring to FIG. 11, in the heat treatment step in the present embodiment, first, a nitriding step (step (S300)) in which a steel member as an object to be processed is nitrided is performed. Specifically, referring to FIG. 12, for example, a steel member is heated to a temperature T ₁ that is a temperature equal to or higher than the A ₁ transformation point in a mixed atmosphere of a carburizing gas containing ammonia and carbon monoxide and hydrogen gas. , by being held for a time t _1, while decarburization is suppressed in the surface layer of the steel member, or while entering the carbon in the surface layer portion of the steel member, nitrogen penetrates into the surface layer portion of the steel member. Thereby, a nitride layer having a higher nitrogen concentration is formed in the region including the surface of the steel member than in the internal region which is a region other than the region including the surface. This nitride layer corresponds to the outer ring nitrogen-enriched layer 11B, the raceway nitrogen-enriched layer 21B, the inner race nitrogen-enriched layer 31B, and the like in the present embodiment.

Next, referring to FIG. 12, the steel member nitriding process is completed, a 50 ° C. temperature higher temperatures below than M _S point above M _S point of the nitrogen-enriched layer from _one or more points A temperature Temperature cooling step to be cooled is conducted to T _2. Specifically, the steel member nitriding process is implemented, for example, is immersed in salt bath, is cooled to a temperature T _2. The cooling of the steel member in this cooling step is performed at a cooling rate at which the steel member does not undergo pearlite transformation. The cooling rate at which the steel member does not undergo pearlite transformation can be determined in consideration of, for example, the CCT (Continuous Cooling Transformation) diagram of the steel constituting the steel member.

Next, referring to FIG. 12, the bainite transformation step of the steel member is maintained at a temperature _{T 2} (step (S400)) is performed. Specifically, in step (S400), steel members which are cooled to a temperature T ₂ in the cooling step, by being held for the time t ₂ to temperature T _2, nitrogen-enriched formed on the steel member The layers (outer ring nitrogen-enriched layer 11B, raceway ring nitrogen-enriched layer 21B, inner race nitrogen-enriched layer 31B, etc.) undergo bainite transformation, and a bainite structure is formed. Thereafter, the M _S point below the temperature of the steel member is a nitrogen-enriched layer, for example by being air-cooled, the heat treatment step in the present embodiment is completed. Here, the temperatures T ₁ and T ₂ and the times t ₁ and t ₂ can be determined in accordance with the composition of the steel member, the use of the machine part to which the heat treatment step is applied, etc. For example, the temperature T ₁ is 800 ° C. or more and 950 ° C. or less, T ₂ can be 180 ° C. or more and 250 ° C. or less, time t ₁ can be 0.5 hours or more and 6 hours or less, and time t ₂ can be 0.5 hours or more and 6 hours or less.

  According to the manufacturing method of machine parts and machine elements including the heat treatment process described above, the machine elements such as the deep groove ball bearing 1, the thrust needle roller bearing 2 and the constant velocity joint 3 in the above-described embodiment and the above-described embodiment constituting the machine element are described. Machine parts in form can be manufactured.

  In the present embodiment, as an example of the mechanical component of the present invention, a deep groove ball bearing, a thrust needle roller bearing, and a mechanical component constituting a constant velocity joint have been described. However, the mechanical component of the present invention is not limited to this. It may be a mechanical part that can be used in a semi-high temperature environment, for example, a mechanical part constituting a hub, a gear, a shaft, or the like. Further, as steel applicable to the steel heat treatment method, machine part manufacturing method, machine part and rolling bearing of the present invention, specifically, high carbon chromium bearing steels such as JIS standards SUJ2, SUJ3, SUJ5, JIS Carbon tool steels such as standards SK95 and SK85, steels such as alloy tool steels such as JIS standards SKS81 and SKS94, or nickel added to these steels in a range of 0.5 mass% or less, from these steels Examples include those from which chromium has been removed.

  Embodiment 1 of the present invention will be described below. A sample subjected to heat treatment by the heat treatment step in the above embodiment was produced, and an experiment was conducted to investigate the material characteristics and durability of the sample. The experimental procedure is as follows.

  First, a method for manufacturing a sample is described. In the preparation of the sample, first, 0.7% by mass to 1.2% by mass of carbon, 0.1% by mass to 1.1% by mass of silicon, and 0.25% by mass to 1.5% by mass. % Of manganese and further 2.0% by mass or less of chromium, and a steel material made of JIS standard SUJ2, which is a steel made of the balance iron and impurities, is prepared. The steel member corresponding to the shape was formed. Then, after performing the following four types of heat processing with respect to the said steel member, the sample was produced by implementing finishing. For the heat treatment, the heat treatment of an example for producing a sample having the same configuration as the mechanical component of the present invention and the heat treatment of Comparative Examples A to C for producing a sample outside the scope of the present invention were performed.

(Example)
The steel member was heat-treated by the heat treatment step in the embodiment described above based on FIG. Here, referring to FIG. 12, in the nitriding step, a mixed gas atmosphere of RX gas and ammonia in which the carbon potential (C _P ) value of the atmosphere is controlled to 1.05 and the concentration of undecomposed ammonia is controlled to 0.25% by volume. A steel member was inserted into the furnace and heated. Here, the temperature T ₁ was 850 ° C., and the time t ₁ was 90 minutes. Thereafter, the bainite transformation step was performed by immersing the steel member subjected to the nitriding treatment in a quenching salt bath and maintaining the steel member at a constant temperature. At this time, temperature _{T 2} is 250 ° C., the time _{t 2} was set to 4 hours. As a result, the nitrogen concentration on the surface of the steel member was about 0.4 mass%, the penetration depth of nitrogen was about 0.4 mm, and the surface layer portion into which nitrogen had entered had a bainite structure. The steel member was finished to complete a sample (nitriding + bainite transformation; Examples).

(Comparative Example A)
A steel member was prepared from a steel material of JIS standard SUJ2 in the same manner as in the above example, and a nitriding step was performed under the same conditions. Then, by immersing the steel member during tempering Nyuabura held at 100 ° C., by cooling from a temperature of more than ₁ point A to M _S point below the temperature was carried out quenching. Further, the steel member was tempered by heating to 180 ° C. and holding for 120 minutes, and then high-temperature tempering by heating to 250 ° C. and holding for 120 minutes. Thereby, like the said Example, the nitrogen concentration in the surface of a steel member was about 0.4 mass%, and the penetration depth of nitrogen was about 0.4 mm. The steel member was finished to complete a sample (nitriding + quenching + high temperature tempering; Comparative Example A).

(Comparative Example B)
The steel member was produced from the steel material of JIS specification SUJ2 similarly to the said Example. Then, C _P value inserts the steel member in a furnace of RX gas atmosphere is adjusted to 0.85 was heated to 850 ° C., and held for 30 minutes. At this time, since ammonia gas was not added to the RX gas, nitrogen did not enter the steel member. Then, the surface layer part of the steel member was bainite transformed by being immersed in a quenching salt bath maintained at 250 ° C. and holding for 4 hours as in the example. The steel member was finished to complete a sample (bainite transformation; Comparative Example B).

(Comparative Example C)
The steel member was produced from the steel material of JIS specification SUJ2 similarly to the said Example. Then, C _P value inserts the steel member in a furnace of RX gas atmosphere is adjusted to 0.85 was heated to 850 ° C., and held for 30 minutes. Then, by immersing the steel member during tempering Nyuabura held at 100 ° C., by cooling from a temperature of more than ₁ point A to M _S point below the temperature was carried out quenching. Further, the steel member was tempered by heating to 180 ° C. and holding for 120 minutes, and then high-temperature tempering by heating to 250 ° C. and holding for 120 minutes. The steel member was finished to complete a sample (quenching + high temperature tempering; Comparative Example C).

Next, a method for investigating material characteristics and durability will be described. The investigation of material properties and durability is as follows: (1) hardness, (2) retained austenite amount, (3) dimensional stability, (4) crack strength, (5) crack fatigue strength, (6) rolling fatigue of the specimen. Life, (7) Rolling fatigue life of ball bearings (clean oil), (8) Rolling fatigue life of ball bearings (foreign oil mixed), (9) Rolling fatigue life of ball bearings (sub-high temperature clean oil), The test was carried out for 11 items of (10) Charpy impact value and (11) fracture toughness value (K _IC ). Hereinafter, the investigation method for each item will be described.

(1) Hardness A cylindrical test piece (hereinafter referred to as a φ12 test piece) having a diameter of φ12 mm and a length of L22 mm and an inner ring and an outer ring of a JIS standard 6206 model ball bearing were prepared, and the hardness was measured. The measurement position was the end face of both the φ12 test piece and the inner and outer rings of the ball bearing, and the measurement position was measured with a Rockwell hardness meter.

(2) Amount of retained austenite In the production of the inner ring and outer ring of φ12 test piece and 6206 model ball bearing similar to (1), the finishing process is omitted, and the position 0.15 mm deep from the end face (surface after finishing process) The amount of retained austenite at a position corresponding to) was measured. The amount of retained austenite was calculated based on the X-ray diffraction intensity corresponding to the martensite (211) plane and the X-ray diffraction intensity corresponding to the austenite (200) plane.

(3) Dimensional stability An outer ring of a JIS standard 6206 model ball bearing was prepared and evaluated by calculating the ratio between the initial outer diameter and the outer diameter after being heated to 230 ° C. and held for 2 hours.

(4) Crack strength A ring-shaped test piece having an outer diameter of φ24 mm, an inner diameter of φ18.5 mm, and a thickness of t7 mm was prepared, and the test piece was compressed in the radial direction with an Amsler type tester. As recorded. And the ratio of the intensity | strength with respect to the comparative example A was evaluated as a crack strength ratio.

(5) Crack fatigue strength A ring-shaped test piece having an outer diameter of φ24 mm, an inner diameter of φ18.5 mm, and a thickness of t7 mm similar to (4) was prepared, and 50 Hz in the radial direction by a hydraulic shaker (Shimadzu servo pulsar). The test piece was repeatedly stressed under the condition that a stress of 800 to 1500 MPa was applied to the inner peripheral surface at a repetition rate of. Then, the number of repeated stresses and the load at which the test piece broke was recorded, and this was repeated multiple times. Then, the test results were statistically processed, and the test piece was broken by repeated 10 ⁸ stress loads. The expected stress value (10 ⁸ times strength) was calculated. Then, to evaluate the ratio of the 10 ⁸ times the intensity of Comparative Example C it.

(6) Rolling fatigue life of test piece The rolling fatigue life test of φ12 test piece was performed using a point contact rolling life tester. FIG. 13 is a schematic front view showing the configuration of the main part of the point contact rolling life tester. FIG. 14 is a schematic side view showing the configuration of the main part of the point contact rolling life tester. A point contact rolling life tester will be described with reference to FIGS. 13 and 14.

With reference to FIGS. 13 and 14, the point contact rolling life tester 90 includes a drive roller 92, a guide roller 93, and a steel ball 94. The φ12 test piece 91 is driven by the drive roller 92 and rotates in contact with the steel ball 94. The steel ball 94 is guided by the guide roller 93 and rolls while exerting a high surface pressure with the φ12 test piece 91. The point contact rolling life tester 90 is operated as described above, and the test is performed 10 times by performing two tests on each φ12 test piece 91 using the five φ12 test pieces 91. The load number (life) of the load until peeling occurred on the test piece 91 was investigated. The diameter of the steel ball 94 was 19.05 mm, the contact stress P _max between the steel ball 94 and the φ12 test piece 91 was 5.88 GPa, the stress load rate was 46240 times / minute, and the lubricating oil was turbine oil VG68. The obtained life was statistically analyzed, and the rolling fatigue life (L ₁₀ life) at which the cumulative failure probability was 10% was calculated. And the rolling fatigue life was evaluated by the ratio to the rolling fatigue life of Comparative Example C.

(7) Rolling fatigue life of ball bearings (clean oil)
A ball bearing of JIS standard 6206 model number was prepared, and the outer ring was fixed and the inner ring was rotated at a rotational speed of 3000 rpm under the conditions of load: 6.86 kN, lubrication: circulating oil supply of turbine oil VG68, temperature 60 ° C. The lubricating oil used was a clean oil that does not contain foreign matter. Then, peeling statistically analyzed to investigate the load number of the load (lifetime) until generation was calculated L ₁₀ life. Then, to evaluate the rolling fatigue life ratio L ₁₀ life of Comparative Example C.

(8) Rolling fatigue life of ball bearings (foreign oil)
The lubrication is oil bath lubrication of turbine oil VG68 mixed with 0.4 g of powder of JIS standard SKH material (high speed tool steel) having a hardness of 800 HV and a particle size of 100 to 180 μm per liter (liter), (7) was investigated JIS standard 6206 type of ball bearing of _{L 10} life under the same conditions as those of. Then, to evaluate the rolling fatigue life ratio L ₁₀ life of Comparative Example C.

(9) Rolling fatigue life of ball bearings (semi-high temperature clean oil)
L ₁₀ of the ball bearing of JIS standard 6206 model number under the same conditions as (7) except that lubrication is performed with high-temperature ether oil, the rotation speed of the inner ring is 2000 rpm, and the test temperature is 200 ° C. The lifespan was investigated. Then, to evaluate the rolling fatigue life ratio L ₁₀ life of Comparative Example C.

(10) Charpy impact value In accordance with JIS standard Z2242, a Charpy impact test was performed using a test piece in which a U notch having a notch depth of 2 mm and a notch bottom radius of 1 mm was formed. And Charpy impact value was evaluated by the ratio with respect to the impact value of Comparative Example C.

(11) Fracture toughness value (K _IC )
A plane strain fracture toughness test was performed according to JIS standard G0564. The fracture toughness value (K _IC ) was calculated by the following formula.

And the fracture toughness value was evaluated by the ratio to the fracture toughness value of Comparative Example A.
Next, test results will be described. The test results of the above (1) to (11) are shown in Table 1.

(1) Hardness Referring to Table 1, the hardness of Examples and Comparative Example A is 61HRC or more, and can be used sufficiently as a machine part used in an environment where high stress is applied. Hardness level. On the other hand, the hardness of each of Comparative Examples B and C is 59 HRC or less, which is clearly lower than that of Examples and Comparative Example A. Moreover, it is confirmed from the measurement result of an Example and the comparative example B that the hardness level of a bainite structure improves clearly by making nitrogen penetrate | invade.

(2) Amount of retained austenite As shown in Table 1, in any of the Examples and Comparative Examples A to C, the amount of retained austenite is less than 1%. This is considered to be because decomposition of residual austenite is almost completed because bainite transformation or high-temperature tempering is performed at a high temperature of 250 ° C. in any of the Examples and Comparative Examples A to C. .

(3) Dimensional stability As shown in Table 1, in any of the examples and comparative examples A to C, the amount of dimensional change is a value close to zero. From this, it can be said that sufficient dimensional stability is ensured even when the mechanical component having the same configuration as the example and the comparative examples A to C is used in a semi-high temperature environment.

(4) Crack strength Referring to Table 1, the crack strength is higher in order of Comparative Example B, Example, Comparative Example C, and Comparative Example A. It is clearly lower than the comparative example. Moreover, when nitriding is performed, the tendency for the static crack strength of steel to fall is confirmed. However, from the above results, it was found that even when nitriding was performed, the crack strength could be greatly improved by subsequently transforming the steel to bainite.

(5) Crack fatigue strength Referring to Table 1, those subjected to nitriding treatment tend to have higher crack fatigue strength than those not subjected to nitriding treatment, and those subjected to bainite transformation treatment The crack fatigue strength tends to be higher than that obtained by high-temperature tempering after quenching. And the crack strength of the Example which combined the nitriding process and the bainite transformation process is the highest, and especially the crack fatigue strength much higher than Comparative Examples B and C which did not implement the nitriding process was obtained. Yes.

(6) Rolling fatigue life of test piece Referring to Table 1, those subjected to nitriding treatment tend to have improved rolling fatigue life compared to those subjected to nitriding treatment, and bainite transformation treatment. The rolling fatigue life tends to be improved in the case of performing the annealing compared with the case of performing high temperature tempering after quenching. And the rolling fatigue life of the Example which combined the nitriding process and the bainite transformation process was the longest, and it quenched without performing a nitriding process, 3 of the comparative example C which performed high temperature tempering The rolling fatigue life was more than doubled.

(7) Rolling fatigue life of ball bearings (clean oil)
Referring to Table 1, the same tendency as in the above (6) was also confirmed in the rolling life test using ball bearings. And the rolling fatigue life of the Example which combined the nitriding process and the bainite transformation process became 2.7 times of the comparative example C which implemented quenching without implementing a nitriding process and performed high temperature tempering. It was.

(8) Rolling fatigue life of ball bearings (foreign oil)
Referring to Table 1, the same tendency as in the above (6) and (7) was confirmed even in an environment where hard foreign matter invades. And the rolling fatigue life of the Example which combined the nitriding process and the bainite transformation process is 2.8 times that of Comparative Example C in which quenching was performed without performing the nitriding process and high temperature tempering was performed. It was.

(9) Rolling fatigue life of ball bearings (semi-high temperature clean oil)
With reference to Table 1, the tendency similar to said (6)-(8) was confirmed also in the semi-high temperature environment. And the rolling fatigue life of the Example which combined the nitriding process and the bainite transformation process is 2.1 times that of Comparative Example C in which quenching was performed without performing the nitriding process and high temperature tempering was performed. It was.

(10) Charpy impact value Referring to Table 1, it was confirmed that those subjected to the bainite transformation treatment tend to have higher impact values than those subjected to high temperature tempering after quenching.

(11) Fracture toughness value (K _IC )
Referring to Table 1, when nitriding is performed, the static cracking strength of steel tends to be slightly reduced, which is also due to the fact that the hardness is increased by performing nitriding. It is thought that. And the Example had a toughness value 1.2 times that of Comparative Example A.

  From the above experimental results, according to the embodiment of the present invention, it is possible to provide a machine part having excellent durability not only in a normal temperature environment but also in a quasi-high temperature environment and a foreign matter mixed environment while ensuring dimensional stability and toughness. confirmed.

  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.

  A steel heat treatment method, a machine part manufacturing method, a machine part and a rolling bearing according to the present invention include a steel heat treatment method containing 0.7% by mass or more and 1.2% by mass or less of carbon, 0.7% by mass or more and 1% by mass. The present invention can be applied particularly advantageously to a method of manufacturing a machine part made of steel containing carbon of 2% by mass or less, a machine part, and a rolling bearing including the machine part.

It is a schematic sectional drawing which shows the structure of the deep groove ball bearing in one embodiment of this invention. It is a schematic fragmentary sectional view which expands and shows the principal part of FIG. It is a schematic sectional drawing which shows the structure of the thrust needle roller bearing which is the 1st modification in this Embodiment. FIG. 4 is a schematic partial cross-sectional view showing an enlarged main part of the raceway ring in FIG. 3. It is a schematic sectional drawing which expands and shows a needle roller among FIG. It is a schematic sectional drawing which shows the structure of the constant velocity joint which is the 2nd modification in this Embodiment. It is a schematic sectional drawing in alignment with line segment VII-VII of FIG. It is a schematic sectional drawing which shows the state in which the constant velocity joint of FIG. 6 made the angle. It is a schematic fragmentary sectional view which expands and shows the principal part of FIG. It is a schematic fragmentary sectional view which expands and shows the principal part of FIG. It is a figure which shows the outline of the manufacturing method of the machine component and the machine element provided with the said machine component in one embodiment of this invention. It is a figure for demonstrating the detail of a heat processing process. It is a schematic front view which shows the structure of the principal part of a point contact rolling life tester. It is a schematic side view which shows the structure of the principal part of a point contact rolling life tester.

Explanation of symbols

  1 deep groove ball bearing, 2 thrust needle roller bearing, 3 constant velocity joint, 11 outer ring, 11A outer ring rolling surface, 11B outer ring nitrogen enriched layer, 11C, 12C, 13C inside, 12 inner ring, 12A inner ring rolling surface, 12B inner ring Nitrogen-enriched layer, 13 balls, 13A ball rolling surface, 13B ball nitrogen-enriched layer, 14, 24 cage, 21 raceway, 21A raceway rolling surface, 21B raceway nitrogen-enriched layer, 21C, 23C inside, 23 needle roller, 23A roller rolling surface, 23B roller nitrogen enriched layer, 31 inner race, 31A inner race ball groove, 31B inner race nitrogen enriched layer, 31C, 32C, 33C inside, 32 outer race, 32A outer race ball Groove, 32B Outer race nitrogen enriched layer, 33 balls, 33A Ball rolling surface, 33B Ball nitrogen Layer, 34 cage 35, 36 shaft, 90 point contact rolling contact fatigue life tester, 91 .phi.12 specimens, 92 driving roller, 93 guide roller, 94 steel balls.

Claims (9)

0.7% by mass or more and 1.2% by mass or less of carbon, 0.1% by mass or more and 1.1% by mass or less of silicon, and 0.25% by mass or more and 1.5% by mass or less of manganese. Preparing a steel composed of the remaining iron and impurities;
A step of forming a nitrogen-enriched layer, which is a layer having a higher nitrogen concentration than the inside, in a region including the surface of the steel by nitriding the steel at a temperature of A ₁ point or more;
The steel greater than M _S point of the nitrogen-enriched layer, by holding the M _S 50 ° C. higher temperature below the temperature than point, residual austenite amount of the nitrogen-enriched layer and a 5% by volume or less And a step of transforming the nitrogen-enriched layer to a bainite transformation. 0.7% by mass or more and 1.2% by mass or less of carbon, 0.1% by mass or more and 1.1% by mass or less of silicon, and 0.25% by mass or more and 1.5% by mass or less of manganese. And steel comprising at least one element selected from the group consisting of 2.0% by mass or less of chromium, 0.5% by mass or less of molybdenum and 0.5% by mass or less of nickel, and the balance iron and impurities. The process of preparing
A step of forming a nitrogen-enriched layer, which is a layer having a higher nitrogen concentration than the inside, in a region including the surface of the steel by nitriding the steel at a temperature of A ₁ point or higher;
The steel greater than M _S point of the nitrogen-enriched layer, by holding the M _S 50 ° C. higher temperature below the temperature than point, residual austenite amount of the nitrogen-enriched layer and a 5% by volume or less And a step of transforming the nitrogen-enriched layer to a bainite transformation. A step of preparing a steel member made of steel and formed into a general shape of a machine part;
And a step of performing a heat treatment on the steel member,
The said heat processing is a manufacturing method of a machine component implemented using the heat processing method of the steel of Claim 1 or 2.   A machine part manufactured by the method for manufacturing a machine part according to claim 3. 0.7% by mass or more and 1.2% by mass or less of carbon, 0.1% by mass or more and 1.1% by mass or less of silicon, and 0.25% by mass or more and 1.5% by mass or less of manganese. Composed of steel, the balance iron and impurities,
In the region including the surface, a nitrogen-enriched layer that is a layer having a higher nitrogen concentration than the inside is formed,
The nitrogen-enriched layer is a machine part that includes a bainite structure and the amount of retained austenite is suppressed to 5% by volume or less. 0.7% by mass or more and 1.2% by mass or less of carbon, 0.1% by mass or more and 1.1% by mass or less of silicon, and 0.25% by mass or more and 1.5% by mass or less of manganese. Further, steel comprising at least one element selected from the group consisting of 2.0% by mass or less of chromium, 0.5% by mass or less of molybdenum and 0.5% by mass or less of nickel, and the balance iron and impurities Consisting of
In the region including the surface, a nitrogen-enriched layer that is a layer having a higher nitrogen concentration than the inside is formed,
The nitrogen-enriched layer is a machine part that includes a bainite structure and the amount of retained austenite is suppressed to 5% by volume or less.   The nitrogen-rich layer contains 0.8% by mass or more and 1.2% by mass or less of carbon and 0.1% by mass or more and 0.8% by mass or less of nitrogen. Machine parts.   The machine part according to any one of claims 4 to 7, which is used as a part constituting the bearing. A track member;
A plurality of rolling elements that are in contact with the raceway member and disposed on an annular raceway,
The rolling bearing according to claim 8, wherein at least one of the race member and the rolling element is a machine part.

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