JP2014020538A - Rolling bearing, method for manufacturing rolling bearing, high frequency thermal treatment equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing of which the life and the toughness of a bearing ring are suitable for an application of supporting rotational axes of a mill of an iron industry and a windmill or the like and wear of an engaging surface is suppressed as the rolling bearing having the bearing ring to be obtained by executing a surface hardening method by induction hardening.SOLUTION: An inner ring 1 is obtained by performing spheroidizing annealing, induction hardening, and temper after processing a raw material consisting of hyper-eutectoid steel whose DI value is 1.0 or more in a predetermined shape, and in an orbital plane 11, effective hardened layer depth Yo and a diameter Dw of a rolling element satisfy the following formula (2), surface hardness is Hv650 or more, the residual austenite quantity is 12 vol.% or more and 40 vol.% or less, and an old austenite crystal grain diameter is 30 μm or less. Surface hardness of 30% or more of an engaging surface 12 is Hv550 or more. 0.07Dw≤Yo≤0.07Dw+5...(2).

Description

  The present invention relates to a rolling bearing, a manufacturing method thereof, and a high-frequency heat treatment apparatus used in the manufacturing method of the rolling bearing.

Rolling bearings require longevity and toughness. Rolling bearings used in industrial machines, particularly large rolling bearings with an outer diameter of 180 mm or more, such as rolling mills for steel mills and windmills, are subjected to large loads and are often subjected to impact loads. Therefore, importance is placed on the balance between life and toughness.
The separation of the raceway surface, which causes the rolling life of the rolling bearing, can be broadly divided into internal origin type separation and surface origin type separation.

  Internally originated delamination occurs starting from non-metallic inclusions (oxide inclusions) contained in the steel. Therefore, by reducing the oxygen content of the steel material, it is possible to suppress the internally originated delamination. . Until now, various steelmaking processes have been improved to reduce the oxygen content of the steel material. However, regarding the alloy component, it is preferable for the oxygen content of the steel material to be reduced that the carbon content is large. In fact, it is known that bearing steel represented by SUJ2 (high carbon chromium bearing steel type 2) exhibits higher cleanliness than S53C, which is medium carbon steel.

Surface-origin type peeling is caused by the formation of indentations on the raceway surface due to the inclusion of foreign matter such as metal powder contained in the lubricant, and stress concentration on the edges of the indentations. Therefore, by controlling the amount of retained austenite on the raceway surface to relieve stress concentration, it is possible to suppress surface-origin type peeling.
In general, when surface-originating peeling occurs on the raceway surface of a rolling bearing, the rolling bearing reaches the end of its service life in a shorter time than when internally-originating peeling occurs, thus extending the life of the rolling bearing. For this purpose, it is important to suppress surface-origin separation.

  In order to suppress surface-origin type separation, it is necessary to deposit a large amount of residual austenite on the raceway surface. In order to precipitate a large amount of retained austenite on the raceway surface, it is necessary to form a carbon or nitrogen enriched region on the surface layer portion of the raceway surface. In order to form the enriched region, it is necessary to perform carburizing or carbonitriding (heat treatment in a special gas atmosphere) on the race.

  In addition, since a large amount of retained austenite is precipitated on the raceway surface, the surface hardness is reduced, and thus it is necessary to supplement the surface hardness with a hard carbonitride. For this purpose, for example, steel to which an expensive alloy element such as molybdenum is added needs to be used. Therefore, this method (a method in which a large amount of retained austenite is precipitated on the raceway surface to suppress surface-origin separation) is not preferable in terms of production cost.

On the other hand, toughness is in a trade-off relationship with the hardness of the material. Therefore, in order to improve toughness, basically, it is necessary to secure as many regions with low hardness as possible. From such a concept, a method is adopted in which only the surface of the raceway surface is hardened by performing carburizing treatment or carbonitriding treatment and quenching (hereinafter referred to as “carburizing quenching”) using low / medium carbon steel. .
However, in this method, in order to ensure the hardenability of the steel, it is necessary to use carburized steel to which a relatively expensive alloy element such as nickel, molybdenum or chromium is added. When this method is applied to a large-sized rolling bearing, the material cost is increased in addition to the complexity of the carburizing process and the carbonitriding process. Therefore, it is not preferable in terms of production cost to apply this method (a method of hardening only the surface of the raceway surface by carburizing and quenching using low / medium carbon steel) to a large-sized rolling bearing.

  On the other hand, in recent years, as shown in Patent Document 1, an induction hardening method in which only a surface portion requiring hardness is quenched and hardened has been attracting attention. According to the induction hardening method, the hardened surface portion becomes a hardened layer that can withstand high surface pressure, and the core portion that is not hardened becomes a non-hardened portion having excellent toughness. Therefore, by performing induction hardening on the raceway surface of the rolling bearing, both the life and toughness necessary for the rolling bearing can be provided. Moreover, since the surface layer part which is a hardened layer will be in a compression residual stress state by presence of the core part which is a non-hardened part, it can suppress that a crack generate | occur | produces in a raceway surface.

  Further, in the induction hardening method, since the hardness can be controlled during induction heating, high carbon steel such as bearing steel excellent in cleanliness can be used instead of low carbon steel containing an expensive alloy element. Furthermore, in the induction hardening method, the surface current density is increased during induction heating, so if the steel has a carbon content of about 0.7% by mass, residual austenite similar to carburized steel may be present only in the extreme surface layer. it can.

When a large amount of retained austenite is present, the dimensional stability decreases. However, when induction hardening is performed, the amount of retained austenite rapidly decreases along the depth direction from the surface. Therefore, it is possible to keep the total amount of retained austenite low while allowing a large amount of retained austenite to exist only in the portion on the surface side of the maximum shear stress depth of the raceway surface.
Therefore, if bearing steel is used as the material for the bearing ring and induction hardening is used, it is possible to suppress the separation of both the internal origin type and the surface origin type on the raceway surface. In addition, it is possible to obtain a rolling bearing excellent in cracking resistance.

Patent Document 2 discloses a method of induction hardening using steel having a carbon content of 0.5% by mass or more as a material for the raceway, which exceeds the A3 transformation point at least once before the induction hardening step. In other words, a method of performing a step of cooling to a temperature below the A1 transformation point after carbon is dissolved in the substrate by high-frequency heating and holding at a constant temperature is disclosed.
In Patent Document 3, the end surface (sliding surface to be lubricated) of a boss member made of low carbon steel is subjected to high-frequency induction heating over a plurality of locations so that the quenched portion is discontinuous, and then the heated portion is It is described that a boss member excellent in both weldability and wear resistance is obtained by carrying out a method of naturally cooling.

JP-A-11-37163 Japanese Patent No. 4208426 Japanese Patent No. 3824970

  However, when the raceway surface of the bearing ring of the rolling bearing is hardened by induction hardening, it is in the boundary region between the surface layer part (hardened layer) and the core part (non-hardened part) as compared with the case hardened by carburizing quenching. The resulting hardness gradient is increased. Therefore, in applications where high stress acts on the raceway surface, internal origin fracture (so-called case crash) is more likely to occur on the raceway surface when it is hardened by induction hardening than when it is hardened by carburizing and quenching. Become.

  And rolling bearings for applications that support rotating shafts such as rolling mills and windmills in the steel industry have higher shear stress acting on the raceway surface than rolling bearings that are used to support the axles of automobiles. In the case of curing with, it is necessary to reduce the hardness gradient to prevent internal origin fracture. However, if the hardened layer is formed deeper than necessary, sufficient toughness cannot be obtained.

  In the method disclosed in Patent Document 2, heating is performed at least once to the austenite single-phase region beyond the A3 transformation point (two-phase region of cementite and austenite) before the induction hardening step. However, in bearing steel, since a fine structure is maintained by the pinning effect of dispersed carbides, remarkable grain growth occurs when heated to the austenite single phase region. Further, there is a disadvantage that carbon is excessively dissolved in the base and residual austenite is excessively retained, resulting in a decrease in hardness.

On the other hand, the inner ring and the outer ring are slightly rotated in the same direction as or in the opposite direction to the traveling direction of the rolling element due to the rolling element moving on the raceway surface during use of the rolling bearing (that is, creep occurs on the mating surface). It is known. Along with this, there is a problem that wear occurs on the mating surface.
An object of the present invention is to provide a rolling bearing having a bearing ring obtained by carrying out a surface hardening method by induction hardening, which is lower in cost than carburizing and quenching. It is suitable for the use which supports rotating shafts, etc., and while providing the rolling bearing in which the wear of the fitting surface was suppressed, the manufacturing method and the apparatus which can be used conveniently with the method are provided.

  In order to solve the above problems, a rolling bearing according to the present invention has a raceway surface on an outer peripheral surface, an inner ring whose inner peripheral surface is a fitting surface with a shaft, a raceway surface on an inner peripheral surface, An outer ring whose surface is a mating surface with a housing, and a plurality of rolling elements arranged to roll between the raceway surface of the inner ring and the raceway surface of the outer ring, and the inner ring and the outer ring At least one of them is obtained by processing a material made of steel into a predetermined shape, and then performing spheroidizing annealing, induction hardening, and tempering, and has the following configurations (a) to (e): It is characterized by.

(a) The material steel contains carbon (C), chromium (Cr), manganese (Mn), and silicon (Si) as alloy components, and nickel (Ni) and molybdenum (Mo) as required. And a hypereutectoid steel (the steel in which proeutectoid ferrite does not precipitate in the prior austenite grain boundaries when heated to the austenite single-phase region and slowly cooled), and the carbon content [ C] is 0.5 mass% or more and 2.0 mass% or less, and the DI value defined by the following formula (1) is 1.0 or more.
DI = (0.2 [C] +0.14) (1 + 0.64 [Si]) (1 + 4.1 [Mn]) (1 + 0.52 [Ni]) (1 + 2.33 [Cr]) (1 + 3.14 [ Mo]) ... (1)
In the formula (1), [M] means the content (mass%) of the alloy component M.

(b) The effective hardened layer depth (thickness of the portion where the hardness is Hv550 or more) Yo (mm) and the diameter Dw (mm) of the rolling element satisfy the following formula (2).
0.07 Dw ≦ Yo ≦ 0.07 Dw + 5 (2)
(c) The surface hardness of the raceway surface is Hv650 or more, and the amount of retained austenite of the raceway surface is 12 volume% or more and 40 volume% or less.
(d) The prior austenite grain size of the raceway is 30 μm or less.

(e) The surface hardness of 30% or more of the fitting surface is Hv550 or more.
In the rolling bearing of the present invention, it is preferable that at least one of the inner ring and the outer ring has the configuration (f) (h).
(f) Hardness from the surface of the raceway surface and both axial end surfaces to a depth of 0.1 mm is Hv500 or more.
(h) The non-hardened portion has a portion where the amount of retained austenite is 0% by volume, and the amount of retained austenite on both axial end surfaces is 10% by volume or more less than the amount of retained austenite on the raceway surface.

  According to the rolling bearing of the present invention, the steel constituting at least one of the inner ring and the outer ring is a hypereutectoid steel, thereby preventing crystal grains from growing during heating during induction hardening. it can. Hypereutectoid steel is steel in which pro-eutectoid ferrite does not precipitate at prior austenite grain boundaries when heated to an austenite single phase region and slowly cooled. That is, in hypereutectoid steel, even when the base is completely austenitized, carbides remain so that grain growth is prevented. Whether or not it is a hypereutectoid steel was tested by heating and holding the sample at a temperature at which it becomes an austenite single phase in the furnace (900 to 1100 ° C. depending on the component), and then cooling in the furnace as it is. Can be confirmed.

In steels that do not contain alloy components other than carbon, the carbon content of the steel that is the eutectoid composition is 0.77% by mass, but in steels that also contain alloy components other than carbon, the carbon content of the steel that is the eutectoid composition. The rate varies depending on the content of each alloy component, and the carbon content of the steel having a eutectoid composition can be calculated using Thermocalc. Accordingly, the carbon content of the hypereutectoid steel is calculated.
Moreover, in order to ensure hardness HRC58 or more required for a rolling bearing, the lower limit of carbon content [C] of the steel to be used shall be 0.5 mass%. Hardness after quenching is determined by the carbon content, regardless of the type and content of the alloying elements. On the other hand, steel with a carbon content greater than 2.0% by mass does not have an austenite single phase structure in the raw material production process, and proeutectoid cementite that may have an adverse effect on the life remains. The upper limit of the content is set to 2.0% by mass.

Further, the steel used has a chromium content [Cr] of 4% by mass or less, a manganese content [Mn] of 2% by mass or less, a silicon content [Si] of 2% by mass or less, and a nickel content [Ni] of 3%. The molybdenum content [Mo] is preferably 1.5% by mass or less.
Chromium (Cr) is an important element for ensuring the hardenability of the steel, and the bearing steel usually contains 1.0 to 1.5% by mass. However, when [Cr] exceeds 4% by mass, it becomes easy to generate a huge carbide during melting, which tends to cause deterioration of rolling fatigue characteristics.

Manganese (Mn) is an element having an effect of improving the hardenability of steel, and is usually contained in the bearing steel by 1.0% by mass. However, when [Mn] is excessive, residual austenate is excessively precipitated.
Silicon (Si) is an element that imparts temper softening resistance to steel and is an effective element against rolling fatigue. However, it also has the drawbacks that the hardenability of ferrite is high and it is difficult to reduce the hardness during spheroidizing annealing. Considering productivity, it is preferable to set [Si] to 2% by mass or less.

Nickel (Ni) is an element that has an effect of improving the hardenability of steel and is an effective element that improves toughness that is insufficient for bearing steel. However, since it is an expensive element, [Ni] is preferably 3.5% by mass or less in consideration of economy.
Molybdenum (Mo) is an element that has the effect of improving the hardenability of steel and moves the eutectoid composition to the low carbon side. However, since it is an expensive element, [Mo] is preferably 1.5% by mass or less in consideration of economy.

  According to the rolling bearing of the present invention, the volume ratio of the incompletely quenched structure is 2% or less because the DI value of the steel constituting at least one of the inner ring and the outer ring is 1.0 or more. Therefore, the hardness of the raceway surface and the rolling life can be secured. The DI value defined by the formula (1) is an index representing quench hardening characteristics. When steel having a low DI value is used, an incompletely quenched structure is generated by quenching. When the volume fraction of the incompletely quenched structure exceeds 5%, the hardness of the raceway surface becomes insufficient, but when the volume fraction of the incompletely quenched structure is 2% or less, the hardness of the raceway surface becomes good.

According to the rolling bearing of the present invention, the effective hardened layer depth (thickness of the portion where the hardness is Hv550 or more) Yo (mm) and the rolling element of at least one of the inner ring and the outer ring. When the diameter Dw (mm) satisfies the above formula (2), both life and high toughness can be achieved in applications that support rotating shafts such as rolling mills and windmills in the steel industry.
Specifically, when Yo is 0.07 Dw or more, the hardness gradient generated in the boundary region between the surface layer portion (hardened layer) and the core portion (non-hardened portion) can be measured by a steel mill rolling mill, windmill, or the like. It can be set to a value appropriate for a rolling bearing for supporting a rotating shaft (a value at which internal origin fracture or crack does not occur).

In addition, in a bearing ring that constitutes a rolling bearing for supporting a rotating shaft such as a rolling mill or a windmill in the steel industry, if the Yo is less than 0.07 Dw, the stress acting on the core side exceeds the strength of the material. The internal origin fracture occurs on the raceway surface. When Yo exceeds “0.07 Dw + 5”, the toughness of the raceway becomes insufficient.
According to the rolling bearing of the present invention, the surface hardness of at least one of the inner ring and the outer ring is Hv650 or more, and the retained austenite amount on the raceway surface is 12% by volume or more and 40% by volume or less. It is possible to prevent the surface starting type peeling from occurring on the surface and the internal starting point fracture of the raceway ring. When the surface hardness of the raceway surface is less than Hv650 and when the amount of retained austenite is less than 12% by volume, surface-initiated peeling is likely to occur. If the amount of surface retained austenite is larger than 40% by volume, there may be a case where a burning crack occurs.

  According to the rolling bearing of the present invention, since the crystal grain size of the prior austenite on at least one raceway surface of the inner ring and the outer ring is 30 μm or less, the material has good material strength. That is, even when used in applications that support rotating shafts such as rolling mills and windmills in the steel industry, good impact resistance can be obtained. When the crystal grain size is larger than 30 μm, the impact resistance in the application is insufficient.

  According to the rolling bearing of the present invention, the surface hardness of 30% or more of the fitting surface of at least one of the inner ring and the outer ring is Hv550 or more (that is, 30% or more of the fitting surface is hardened by induction hardening). Therefore, the wear resistance of the mating surface is improved. By using 30% or more of the mating surfaces as a hardened layer (surface hardness of Hv550 or higher), almost the same wear resistance as that obtained when the whole is a hardened layer can be obtained.

  The inner ring or outer ring satisfying the configuration (b) to (e) is made of steel satisfying the configuration (a), and the raceway surface and the axial end surfaces of the material processed into the shape of the inner ring or the outer ring after spheroidizing annealing. In contrast, induction hardening and tempering are performed after induction heating so that the internal structure becomes a two-phase structure of cementite and austenite, and then induction hardening and tempering are performed on the mating surfaces. It can manufacture by the method to do (method of this invention).

  When the steel has a high chromium content, as a pretreatment for induction hardening of the raceway surface and both end surfaces in the axial direction, the raceway surface remains in the range of 1 mm from the surface, and cementite and austenite remain 3% by volume or more of cementite. (The heating in the pretreatment step may be either furnace heating or induction heating), and then cooling is performed at a cooling rate equal to or lower than air cooling, so that the martensite volume ratio is 50 % Or less is preferable.

The maximum temperature during heating in this pretreatment is set to a temperature at which 3% by volume or more of cementite remains depending on the amount of spheroidized carbide. If the residual ratio of cementite is less than 3% by volume, the crystal grains may be partially coarsened. The ratio of chromium carbide in all carbides varies depending on the holding time in the temperature range of 500 ° C. or more and A1 transformation point or less, but by performing cooling in the pretreatment of induction hardening at a rate of air cooling or less, The proportion of chromium carbide is not so high as to retard carbide penetration during induction hardening.
And by performing such pretreatment, even if the chromium content of the steel is high, the amount of retained austenite on the raceway surface can be made 12% by volume or more, and the prior austenite crystal grain size on the raceway surface can be increased. It can be 30 μm or less.

In addition, by having the configuration (f), that is, when the hardness from the surface of the raceway surface and both axial end surfaces to a depth of 0.1 mm is Hv 500 or more, wear due to contact with other parts occurs. Can be difficult.
Further, by having the configuration (h), that is, there is a portion in which the amount of retained austenite is 0% by volume in the non-hardened portion of the raceway ring, and the amount of retained austenite at both axial end surfaces is the amount of retained austenite on the track surface. When the volume is less than 10% by volume, the dimensional change of the bearing ring is small, and the same dimensional stability as when carburizing and quenching is performed instead of induction hardening is obtained.

  In the method of the present invention, as an apparatus for carrying out the induction heating process so that the internal structure becomes a two-phase structure of cementite and austenite simultaneously with respect to the raceway surface and the axial end faces, the raceway surface and the axial direction It is possible to use a high-frequency heat treatment apparatus (high-frequency heat treatment apparatus of the present invention) having a main coil having a U-shaped portion that surrounds both end faces and is heated simultaneously, and an auxiliary coil that heats the raceway surface. Moreover, the induction hardening with respect to the said fitting surface can be implemented by the method of this invention using a general purpose movable coil.

  The rolling bearing according to the present invention is such that at least one of the inner ring and the outer ring satisfies the configurations (a) to (e), so that the life and toughness of the raceway ring are compared with those not satisfying these. This is suitable for use in supporting a rotating shaft such as a rolling mill or a windmill in industry, and wear of the mating surface is suppressed.

It is sectional drawing which shows the rolling bearing corresponded to one Embodiment of this invention. It is a perspective view which shows a part of high frequency heat processing apparatus used with the method of embodiment. It is a figure which shows an example of the hardened layer pattern formed in the fitting surface of an inner ring | wheel. It is a graph which shows the relationship between L10 life ratio and effective hardened layer depth. It is a graph which shows the relationship between L10 life ratio and the crystal grain size (d) of prior austenite. It is a graph which shows the relationship between crushing strength ratio and effective hardened layer depth. It is a graph which shows the relationship between L10 life ratio and a retained austenite amount. It is a graph which shows the relationship between an effective hardened layer depth and the diameter (Dw) of a cylindrical roller. It is a graph which shows the difference in roundness by the difference in a pre-processing method. It is a graph which shows the relationship between a wear depth and the ratio of the hardened layer currently formed in the fitting surface regarding a fitting surface.

Embodiments of the present invention will be described below.
The cylindrical roller bearing shown in FIG. 1 is a rolling bearing corresponding to an embodiment of the present invention, and includes an inner ring 1, an outer ring 2, a plurality of cylindrical rollers (rolling elements) 3, and a cage 4.
The inner ring 1 has a raceway surface 11 on the outer peripheral surface, and the inner peripheral surface 12 is a fitting surface with a shaft. The outer ring 2 has a raceway surface 21 on the inner peripheral surface, and the outer peripheral surface 22 is a fitting surface with the housing. The plurality of cylindrical rollers 3 are arranged between the raceway surface 11 of the inner ring 1 and the raceway surface 21 of the outer ring 2 so as to be able to roll. The cage 4 is disposed between the inner ring 1 and the outer ring 2 and holds the plurality of cylindrical rollers 3 one by one in the pocket 41.

The inner ring 1 is manufactured by the following method. The outer ring 2, the cylindrical roller 3, and the cage 4 are conventional products.
A high-frequency heat treatment apparatus used in this method is shown in FIG.
The high frequency heat treatment apparatus of FIG. 2A includes a main coil 5, an auxiliary coil 6, and a roller 7. The main coil 5 has a U-shaped part 50. The U-shaped portion 50 extends in the axial direction so as to be opposed to the raceway surface 11 of the inner ring 1, and extends in a direction perpendicular to the axial direction so as to be disposed outside the axial end surface 13 in the axial direction. It consists of a pair of horizontal portions 52. The front end portion 61 of the auxiliary coil 6 has a short arc shape and is disposed so as to face the raceway surface 11 of the inner ring 1. The rollers 7 are for rotating the inner ring 1 and are arranged at three equally spaced locations in the circumferential direction of the axial end surface 13 of the inner ring 1.

The main coil 5 is preferably one in which a plurality of U-shaped portions 50 of FIG. In the example shown in FIGS. 2 (b) and 2 (c), the three U-shaped portions 50 </ b> A to 50 </ b> C arranged along the circumferential direction of the inner ring 1 are connected in series by the connecting portion 55, and both end portions 56. , 57 are connected. FIG.2 (c) is an A arrow view of FIG.2 (b).
First, an annular material made of SUJ3 (high carbon chromium bearing steel type 3) and subjected to spheroidizing annealing is prepared, and this material is turned into the shape of the inner ring 1. The composition of SUJ3 is [C] = 1.00 mass%, [Cr] = 0.60 mass%, [Mn] = 1.00 mass%, [Si] = 0.60 mass%, [Ni] = 0. 0.05% by weight, balance iron and inevitable impurities. The DI value defined by the equation (1) of SUJ3 is 8.2.

Next, induction hardening and tempering are performed on the raceway surface 11 and the axial end surfaces 13 of the inner ring 1.
That is, first, using the high-frequency heat treatment apparatus shown in FIG. 2, the raceway surface 11 and the axial end surfaces 13 of the inner ring 1 are simultaneously induction-heated so that the internal structure becomes a two-phase structure of cementite and austenite. The induction heating conditions are a frequency of 5 to 100 kHz, a heating time of 5 to 200 seconds, and an inner ring rotational speed of 20 to 100 min ⁻¹ . Specifically, in a state where the inner ring 1 is rotated by the roller 7, the longitudinal part 51 and the lateral part 52 of the main coil 5 surround the raceway surface 11 and both axial end faces 13 of the inner ring 1, and simultaneously heat them. At the same time, the track surface 11 of the inner ring 1 is heated by the auxiliary coil 6. Next, the inner ring 1 is cooled by spraying cooling water of 20 to 50 ° C. Next, the inner ring 1 is put in a heating furnace and maintained at 180 ° C. for 2 hours, and then tempered by allowing to cool.

Next, induction hardening and tempering are performed on the fitting surface 12 of the inner ring 1.
That is, using a general-purpose moving grilling coil having a heating width of about 10 mm, the fitting surface 12 of the inner ring 1 is spirally formed, and after induction heating so that the internal structure becomes a two-phase structure of cementite and austenite, The inner ring 1 is cooled by spraying cooling water at 20 to 50 ° C. Next, the inner ring 1 is put in a heating furnace and maintained at 180 ° C. for 2 hours, and then tempered by allowing to cool. This induction hardening is performed under the condition of Hv550 or higher from the surface of the fitting surface 12 to a depth of 1.0 mm. The induction heating conditions are, for example, a frequency of 30 kHz, an output of 50 kW, and a coil moving speed of 10 mm / second.

  Thus, a hardened layer 12a having an effective hardened layer depth of 1.0 mm is formed on the fitting surface 12 of the inner ring 1 in a spiral pattern as shown in FIG. The width (dimension in the axial direction of the spiral) L1 of the hardened layer 12a is about 10 mm, and the distance L2 between the hardened layers is about 5 mm (1 mm or more). FIG. 3 is a developed view of a part of the fitting surface 12 of the inner ring 1.

Next, the inner ring 1 is completed by performing post-processing such as polishing.
Since SUJ2 and SUJ4 have a high chromium content and a low Mn content, which is an austenite stabilizing element, it is necessary to normalize the raceway surface 11 of the inner ring 1 as a pretreatment for induction hardening. However, when steel with a low chromium content or steel with a high Mn content (SUJ3, SUJ5) is used, pretreatment is not necessary.
When performing the pretreatment, first, the auxiliary coil 6 of the high-frequency heat treatment apparatus shown in FIG. 2 is used, and the inner ring 1 is rotated by the roller 7 and the raceway surface 11 of the inner ring 1 is induction-heated by the auxiliary coil 6. . The induction heating conditions are a frequency of 5 to 100 kHz, a heating time of 5 to 200 seconds, and an inner ring rotational speed of 20 to 100 min ⁻¹ . Thereby, the range from the surface to 1 mm becomes a “two-phase structure of cementite and austenite” in which cementite remains at 3 volume% or more.

Next, the mixture is allowed to cool to room temperature (cooled at a cooling rate equal to or lower than air cooling) so that the volume ratio of martensite is 50% or less.
The effective hardened layer depth (thickness of the portion where the hardness is Hv550 or more) Yo (mm) and the diameter Dw (mm) of the cylindrical roller (rolling element) 3 of the raceway surface 11 of the inner ring 1 of this embodiment are as follows. The following equation (2) is satisfied.
0.07 Dw ≦ Yo ≦ 0.07 Dw + 5 (2)

Further, the surface hardness of the raceway surface 11 of the inner ring 1 is Hv650 or more, and the retained austenite amount of the raceway surface 11 is 12% by volume or more and 40% by volume or less. Further, the prior austenite crystal grain size of the raceway surface 11 of the inner ring 1 is 30 μm or less. The surface hardness of 30% or more of the fitting surface 12 of the inner ring 1 is Hv550 or more.
Furthermore, the hardness from the surface of the raceway surface 11 of the inner ring 1 and both end surfaces 13 in the axial direction to a depth of 0.1 mm is Hv 500 or more.

Further, the amount of retained austenite at the core of the inner ring 1 is 0% by volume, and the amount of retained austenite at both axial end surfaces 13 is 10% by volume or less than the amount of retained austenite at the raceway surface 11.
That is, in the cylindrical roller bearing of this embodiment, the inner ring 1 satisfies the configurations (a) to (e) that are essential requirements of the invention and the configurations (f) and (h) that are preferable requirements. Compared to cylindrical roller bearings that differ only in having an inner ring 1 that does not satisfy configurations (a) to (f) and (h), the life and toughness of the bearing ring have a rotating shaft such as a rolling mill or a windmill in the steel industry. It is suitable for a use for supporting the fitting, and wear of the fitting surface is suppressed.

The cylindrical roller bearing including the inner ring 1 that does not satisfy the requirements (f) and (h) and satisfies the configurations (a) to (e) is also included in the scope of the present invention. Further, a cylindrical roller bearing in which only the outer ring 2 or both the inner ring 1 and the outer ring 2 satisfy the above-described configurations (a) to (e) and the preferable configurations (f) and (h) is also within the scope of the present invention. included.
When induction hardening is performed on the raceway surface 21 and the axial end surfaces 23 of the outer ring 2, the main coil 5 and the auxiliary coil 6 are arranged inside the outer ring 2.
Furthermore, rolling bearings (ball bearings, tapered roller bearings, self-aligning roller bearings, etc.) other than cylindrical roller bearings are also included in the present invention as long as an inner ring and / or an outer ring satisfying the configurations (a) to (e) are provided. Included in the range.

[1] Verification of configuration (b) (c) (d)
[1-1] Examples 1 to 14 and Comparative Examples 1 to 10
The cylindrical roller bearing of FIG. 1 was assembled and a life test was conducted. The inner ring 1 has an inner diameter of 30 mm, an outer diameter of 60 mm, an axial dimension of 23 mm, and a wall thickness (diameter thickness: difference between the diameter of the raceway surface 11 and the diameter of the mating surface 12) is 15 mm. What was produced by the method of (24 types of samples) was used.

As the outer ring 2, the cylindrical roller 3, and the cage 4, those for a cylindrical roller bearing with an identification number NU2210ET (inner diameter is 50 mm, outer diameter is 90 mm, axial dimension is 23 mm, and cylindrical roller diameter Dw is 11 mm) are used. did. The outer ring 2 and the cylindrical roller 3 are made of SUJ2 (high carbon chrome bearing steel type 2) and subjected to normal heat treatment, and the cage 4 is an ordinary machined type cage.
In the case of a large bearing having an outer diameter of 180 mm or more, the average thickness of the inner ring is 15 mm. Therefore, in this embodiment, an inner ring having a thickness of 15 mm is incorporated as the inner ring of the medium bearing. A test was conducted to know the life of the case.

The inner ring 1 is made of SUJ3 (High Carbon Chromium Bearing Steel Type 3) and is made of a spheroidized and annealed annular material. After turning this material into the shape of the inner ring 1, various heat treatments shown in Tables 1 to 3 are performed. And finished by post-processing such as polishing.
“IH” in the heat treatment in Tables 1 to 3 means that induction hardening and tempering were performed on the raceway surface 11 and the axial end surfaces 13 of the inner ring 1 by the method described in the embodiment. The induction heating conditions were changed for each sample in a range of a frequency of 5 to 100 kHz, a heating time of 5 to 200 seconds, and an inner ring rotational speed of 20 to 100 min ⁻¹ .

In the heat treatment of Tables 1 to 3, "Zub" means that the inner ring 1 is placed in a heating furnace and held at 800 to 900 ° C for 1 hour, then oil-cooled, after tempering and then tempered at 180 ° C for 2 hours. Means that
In the heat treatment of Tables 1 to 3, “carburization” means that the inner ring 1 is put into a heating furnace, a carburizing gas is introduced, and carburizing treatment is performed at 900 to 1000 ° C. and held for 10 to 20 hours. This means that quenching and tempering were performed under the same conditions as in the above “Zubu”.

<Life test>
First, using the cylindrical roller bearings obtained as Examples 1 to 10 and Comparative Examples 1 to 4, the rotation test was performed under the following condition 1 (in a clean lubricating environment in which no foreign matter was mixed in the lubricant: clean lubrication) Under the environment), and the time until peeling occurred was measured. Further, using the cylindrical roller bearings obtained as Examples 11 and 12 and Comparative Examples 5 to 7, the rotation test was performed under the following condition 2 (in a lubrication environment in which foreign matter is mixed in the lubricant: foreign matter mixed lubrication environment The time until peeling occurred was measured.

Condition 1
Radial load: 50kN (P / C = 0.6)
Rotational speed: 1000 min ^-1
Lubricating oil: Lubricating oil whose ISO viscosity grade is ISO VG68 Condition 2
Radial load: 25kN (P / C = 0.3)
Rotational speed: 1000 min ^-1
Lubricating oil: Lubricating oil whose ISO viscosity grade is ISO VG68 Foreign matter mixed state: Instead of mixing foreign matter into the lubricant, 8 pseudo indentations are formed by the Rockwell hardness tester at the center of the inner raceway surface in the width direction. did.

  The rotation test was carried out by preparing seven cylindrical roller bearings of the same type, and the L10 life was obtained from the result of the Weibull distribution obtained by plotting the time until separation occurred. The results are shown in Tables 1 and 2. “L10 life ratio” in Table 1 is a value obtained by dividing the L10 life of each sample by the L10 life value of Comparative Example 3. “L10 life ratio” in Table 2 is a value obtained by dividing the L10 life of each sample by the L10 life value of Comparative Example 6.

  In each sample, the inner ring raceway surface and the hardness at each depth position from the raceway surface were measured with a Vickers hardness tester. The measurement of the hardness at each depth position was performed on the polished surface after preparing a cross-section sample cut at each depth position and mirror-polishing the cut surface of each cross-section sample. By plotting the results, the depth profile of the hardness of the raceway surface of the inner ring was obtained. And the effective hardened layer depth (depth from the surface whose hardness is Hv550 or more) Yo of the raceway surface was investigated from the profile obtained by each sample. The results are shown in Tables 1-3.

Since the cylindrical roller 3 constituting this cylindrical roller bearing has a diameter (Dw) of 11 mm, the equation (2) is satisfied if Yo is 0.77 mm or more and 5.77 mm or less.
The amount of retained austenite (γ _R : volume%) was measured with an X-ray diffractometer. Prior to the measurement, the race effect surface was removed by electrolytic polishing of the raceway surface of the inner ring. The results are shown in Tables 1-3.
In addition, the inner ring is cut along the radial direction at the position of the raceway surface, the cut surface is mirror-finished, and further subjected to corrosion treatment, and then the cut surface is observed with a microscope, whereby the crystal of the former austenite on the raceway surface is obtained. The particle size (d) was measured. The results are shown in Tables 1-3.

Moreover, about Examples 1-10 and Comparative Examples 1-4, the effective hardened layer depth (depth from the surface whose hardness is Hv550 or more) Yo and L10 life obtained from this test FIG. 4 shows the relationship, and FIG. 5 shows the relationship between the crystal grain size of the orbital plane and the L10 life. 5 is not the crystal grain size d (μm) itself but the value of 1 / √d (unit: 1 / √m). When the crystal grain size is 30 μm, 1 / √d = 183.
Moreover, about Example 11, 12 and Comparative Examples 5-7, the relationship between the amount of retained austenite of a track surface and L10 lifetime obtained from this test is shown in FIG.

As shown in Table 1, the effective hardened layer depth Yo, the surface hardness (Hv), the prior austenite crystal grain size d (μm), and the retained austenite amount γ _R (volume%) of the raceway surface are all of the present invention. In Examples 1 to 10, which are within the range, L10 life 2.5 times or more that of Comparative Example 3 was obtained in a clean lubrication environment. Comparative Examples 1 to 3 in which any one of these (four configurations of the raceway surface) deviates from the scope of the present invention had a short L10 life in a clean lubrication environment. Note that all four configurations of the raceway surface are within the scope of the present invention, and the L10 life in the clean lubrication environment of Comparative Example 4 in which the heat treatment is carburizing was 2.4 times that of Comparative Example 3.

As shown in Table 2, all of the effective hardened layer depth Yo, surface hardness (Hv), prior austenite crystal grain size d (μm), and retained austenite amount γ _R (volume%) of the raceway surface are as shown in Table 2. In Examples 11 and 12, which are within the range, an L10 life of 2.5 times or more that of Comparative Example 6 was obtained in a foreign matter-mixed lubrication environment. In Comparative Examples 6 and 7 in which any one of these (four configurations of the raceway surface) is out of the scope of the present invention, the L10 life in a foreign matter-mixed lubrication environment is short. All four configurations of the raceway surface are within the scope of the present invention, and the L10 life in a foreign matter-mixed lubricating environment of Comparative Example 7 in which heat treatment is carburizing was 2.0 times that of Comparative Example 6.

  Further, in Comparative Example 1 where Yo = 0.7, it is considered that the lifetime was shortened as a result of internal destruction. In Example 1 where Yo = 0.9, it is considered that the hardness of the material was sufficiently ensured, so that destruction from the inside did not occur and the life was long. Thus, it can be seen that the hardness of the material needs to be larger than the stress applied to the raceway surface in order to sufficiently suppress the destruction from the inside.

As shown in FIG. 4, in Examples 2 to 10, the effective hardened layer depth Yo (mm) of the raceway surface is 1.5 mm or more, and as in Example 1, no breakage from the inside was observed. The L10 life ratio in a clean lubrication environment was 2.5 or more and a long life was obtained.
From the above results, it can be seen that the effective life of the raceway surface Yo (mm) is 0.07 times or more the diameter of the rolling element, so that the life can be extended.

As shown in FIG. 5, when the crystal grain size d of the prior austenite on the raceway surface is 30 μm or more (“1 / √d” is 183 or less), the lifetime is drastically reduced.
In addition, as shown in Table 2, Comparative Example 5 and Examples 11 and 12 have no significant difference in the configuration other than the amount of retained austenite, but as shown in FIG. There was a difference in the L10 life below. A large amount of retained austenite is effective for extending the service life in a lubricating environment containing foreign matter.

  Specifically, the L10 life in a foreign matter-mixed lubricating environment of Example 11 in which the amount of retained austenite is 13% by volume is more than three times that in Comparative Example 5 in which the amount of retained austenite is 10% by volume, and retained austenite. The L10 life of the Example 12 in which the amount was 37% by volume in the lubricating environment with foreign matters was 7 times or more that of Comparative Example 5 in which the amount of retained austenite was 10% by volume.

<Toughness test>
Next, the crushing test for evaluating toughness was done using each cylindrical roller bearing obtained as Examples 13 and 14 and Comparative Examples 8 to 10.
Specifically, first, a pre-crack having a depth of 1 mm along the width direction (axial direction) was formed over the entire length in the width direction on the raceway surface of the inner ring using a wire cutter. Next, the inner ring was mounted on a crushing test apparatus so that the pre-crack extends horizontally, and a load was applied to the raceway surface of the inner ring from above to compress the inner ring. The load when the crack progressed from the pre-crack and the inner ring broke was examined, and the value was taken as the crushing strength. The results are shown in Table 3. The “crushing strength ratio” in Table 3 is a value obtained by dividing the crushing strength of each sample by the crushing strength value of Comparative Example 9.

As shown in Table 3, the effective hardened layer depth Yo, the surface hardness (Hv), the prior austenite crystal grain size d (μm), and the retained austenite amount γ _R (volume%) of the raceway are all of the present invention. In Examples 13 and 14 within the range, a crushing strength 2.2 times or more that of Comparative Example 9 was obtained. In Comparative Examples 9 and 10 in which any of these (four configurations of the raceway surface) is out of the scope of the present invention, the crushing strength is small. All four configurations of the raceway surface were within the scope of the present invention, and the crushing strength of Comparative Example 7 in which the heat treatment was carburizing was 2.1 times that of Comparative Example 9.

FIG. 7 shows the relationship between the effective hardened layer depth (depth from the surface where the hardness is Hv550 or higher) Yo and the crushing strength obtained from this test. In the cylindrical roller bearing used for the test, the value of Yo, which is 0.07 Dw + 5, is 5.77 mm.
In Comparative Example 8 and Examples 13 and 14, as shown in Table 3, there is no significant difference in the configuration other than the effective hardened layer depth Yo of the raceway surface. However, as shown in FIG. Differences in crushing strength were caused by differences in depth Yo.

Specifically, the crushing strength of Example 13 where Yo is 2.1 (≦ 5.77 mm) is 1.8 times that of Comparative Example 8 where Yo is 6.8 mm (> 5.77 mm), The crushing strength of Example 14 where Yo is 5.3 mm (≦ 5.77 mm) was 2.5 times that of Comparative Example 8 where Yo was 6.8 mm (> 5.77 mm). From this result, it is understood that when Yo exceeds “0.07 Dw + 5”, the hardened layer is too thick and the toughness of the raceway is insufficient.
From the above, it can be seen that when Yo (mm) and the diameter Dw (mm) of the rolling element satisfy the formula (2), both life and high toughness can be achieved.

[1-2] Examples 15 to 17 and Comparative Examples 11 and 12
As the cylindrical roller bearing of FIG. 1, a cylindrical roller bearing having an identification number NU2326 (inner diameter 130 mm, outer diameter 280 mm, axial dimension 93 mm, cylindrical roller diameter Dw 40 mm) was assembled, and a life test was performed. In this cylindrical roller bearing, the value of Yo that becomes 0.07 Dw is (0.07 × 40 =) 2.80 mm, and the value of Yo that becomes 0.07 Dw + 5 is 7.80 mm.
The outer ring 2 and the cylindrical roller 3 are made of SUJ2 (high carbon chrome bearing steel type 2) and subjected to normal heat treatment, and the cage 4 is an ordinary machined type cage.

The inner ring 1 used was prepared by the following method (5 types of samples).
First, an annular material made of SUJ3 (high carbon chromium bearing steel type 3) and subjected to spheroidizing annealing is prepared, and this material is turned into the shape of the inner ring 1. Next, by the method described in the embodiment, heat treatment (IH) including induction hardening and tempering is performed on the raceway surface 11 and the axial end surfaces 13 of the inner ring 1. The induction heating conditions were changed for each sample in a range of a frequency of 5 to 100 kHz, a heating time of 5 to 200 seconds, and an inner ring rotational speed of 20 to 100 min ⁻¹ . Next, the inner ring 1 is completed by performing post-processing such as polishing.

About these 5 types of cylindrical roller bearings, the rotation test in the clean lubrication environment was done by the same method as the rotation test for the cylindrical roller bearings of Examples 1 to 10, and the L10 life was obtained. Further, in the same method as the method for the inner ring constituting the cylindrical roller bearing of Examples 1 to 10, the effective hardened layer depth Yo, the surface hardness (Hv) of the raceway surface, the prior austenite crystal grain size d (μm), and The amount of retained austenite γ _R (volume%) was measured.
These results are shown in Table 4. “L10 life ratio” in Table 4 is a value obtained by dividing the L10 life of each sample by the L10 life value of Comparative Example 3.

As shown in Table 4, the effective hardened layer depth Yo, the surface hardness (Hv), the prior austenite crystal grain size d (μm), and the retained austenite amount γ _R (volume%) of the raceway surface are all of the present invention. In Examples 15-17 which are in the range, L10 life of 2.5 times or more of Comparative Example 3 was obtained in a clean lubrication environment. In Comparative Examples 11 and 12 in which any one of these (four configurations of the raceway surface) is out of the scope of the present invention, the L10 life in a clean lubrication environment is 0.7 times or shorter than that in Comparative Example 3.

As a result, even when the diameter Dw of the cylindrical roller (rolling element) is 40 mm, the effective hardened layer depth Yo (mm) of the raceway surface of the inner ring becomes 0.07 times or more the diameter of the cylindrical roller (rolling element). It can be seen that the lifetime can be extended.
FIG. 8 shows effective hardening layers for Examples 1 to 5 and Comparative Example 1 in which the diameter Dw of the cylindrical roller is 11 mm, and Examples 15 and 16 and Comparative Examples 11 and 12 in which the diameter Dw of the cylindrical roller is 40 mm. It is a graph which shows the relationship between the depth and the diameter Dw of a cylindrical roller.

[2] Verification of composition (a) The occurrence of an incompletely quenched structure was examined when a plurality of steels having different DI values and alloy compositions defined by the above formula (1) were quenched. Specifically, it is composed of 8 types of steels, SUJ2 to SUJ5, steel types A to C and SK5 shown in Table 5, and a disk sample having a thickness of 15 mm and a diameter of 60 mm is prepared and heated to 840 ° C. for 1 hour in a heating furnace. After holding, after performing oil quenching into 60 ° C. oil, the occurrence of incompletely quenched structure was examined.
Each disk sample was heated to 950 ° C. in a heating furnace and then cooled in the furnace as it was (gradual cooling) to examine whether or not pro-eutectoid ferrite was precipitated at the prior austenite grain boundaries. These results are shown in Table 5.

Both samples are hypereutectoid steel in the calculation. As shown in Table 5, no precipitation of proeutectoid ferrite was observed in any of the samples.
Moreover, SUJ2 (DI value 4.9), SUJ3 (DI value 8.2), SUJ4 (DI value 7.3), SUJ5 (DI value 13.1), Steel type A (3.4), and Steel type B ( With a DI value of 2.2), an incompletely quenched structure did not occur. In steel type C (DI value 1.1), an incompletely quenched structure was generated by 1%. Even if an incompletely quenched structure is formed, if its volume is 1%, the mechanical properties are not affected. With SK5 (DI value 0.7), an incompletely hardened structure was generated by 8% (over 5%).

  From the above, it can be seen that a steel having a DI value of 1.0 or more is a good steel material in which an incompletely quenched structure does not substantially occur (2% by volume or less). Therefore, the hardness of the raceway surface and the rolling life can be ensured by using a material made of steel having a DI value of 1.0 or more as a material constituting at least one of the inner ring and the outer ring.

[3] Verification of pre-processing method
[3-1] Selection of pre-treatment method Pre-treatment using an inner ring (inner diameter is 130 mm, outer diameter is 167 mm, axial dimension is 93 mm) of a cylindrical roller bearing having the structure of FIG. A test was conducted to examine the effect of the treatment performed before induction hardening on the raceway surface and both end surfaces in the axial direction. The material is a spheroidized annular body of SUJ3.

Pretreatment A: The inner ring is placed in a heating furnace and held at 800 ° C. for 0.5 hours, and then normalization is performed to cool to room temperature.
Pretreatment B: The entire outer peripheral surface including the raceway surface of the inner ring and the end surface are subjected to normalization in which the whole surface and the end surface are heated to high frequency (induction) to 900 ° C. and then allowed to cool to room temperature.
Pretreatment C: After only high-frequency (induction) heating to 900 ° C. only on the raceway surface of the inner ring, normalization is performed to cool to room temperature.

Induction hardening after the pretreatment was performed so that the hardened layer depth was 4.2 mm at the raceway surface and 2.0 mm at the end surface. After quenching, tempering was performed immediately at 200 ° C.
The roundness of the outer circumference circles of the respective inner rings that differed only in the pretreatment method thus obtained was measured. For each inner ring, the amount of retained austenite on the raceway surface, the minimum value of the amount of retained austenite inside, the amount of retained austenite on the end surface, and the amount of average retained austenite were measured. Furthermore, each inner ring was held at 200 ° C. for 300 hours, and the dimensional change rate before and after that was measured.
FIG. 9 shows the difference in roundness due to the difference in the pretreatment method, and Table 6 shows the difference in the amount of retained austenite.

From the results shown in FIG. 9, the roundness is small in the case of the pretreatment C compared to the pretreatment A and the pretreatment B, that is, in the case where only the raceway surface is normalized by high frequency heating as the pretreatment. It can be seen that the effect of reducing the deformation amount is great.
Moreover, it can be seen from the results in Table 6 that the dimensional change rate can be reduced in the case of the pretreatment C as compared with the pretreatment A and the pretreatment B.

[3-2] Pre-treatment or non-treatment Pre-treatment (high-frequency quenching of both the raceway surface and both axial end surfaces) using a flat specimen made of SUJ2 to SUJ5 and steel types A to C having the composition shown in Table 5 A test was conducted to examine the necessity of the treatment performed before.
In the sample with pretreatment, first, as a pretreatment, the flat plate surface of each test piece was heated with an induction coil having a frequency of 30 kHz and then allowed to cool to room temperature. As a result, the range from the surface to 1 mm is converted into a “two-phase structure of cementite and austenite” where the cementite remains by 3% by volume or more by induction heating, and then the martensite volume fraction is reduced to 50% or less by cooling. I made it.

  Next, after heating the flat plate surface of each test piece with an induction coil having a frequency of 30 kHz so that the internal structure becomes a two-phase structure of cementite and austenite, the plate is cooled in 25 ° C. cooling water to cool the plate. Quenching was performed. Next, the flat plate surface of each test piece was placed in a heating furnace and held at 180 ° C. for 2 hours, and then tempered by allowing to cool.

In the sample without pretreatment, the plate surface of each test piece was heated with an induction coil having a frequency of 30 kHz so that the internal structure became a two-phase structure of cementite and austenite without performing the above-described pretreatment. Induction hardening was performed by cooling in cooling water at 0 ° C. Next, the flat plate surface of each test piece was placed in a heating furnace and held at 180 ° C. for 2 hours, and then tempered by allowing to cool.
About the flat plate surface in which the heat treatment of each obtained test piece was performed, the amount of retained austenite (γ _R : volume%) and the crystal grain size (d) of prior austenite were measured. The results are shown in Table 7.

From this result, it can be seen that when a material made of the same steel is used, the amount of retained austenite on the surface is increased and the prior austenite grains on the surface are refined by pretreatment.
Even when a material made of SUJ2 and SUJ4 (steel having a high chromium content and a low austenite stabilizing element Mn content) is used, the amount of retained austenite on the surface is 12 vol% or more by performing pretreatment. It can be seen that the prior austenite grain size on the surface can be reduced to 30 μm or less.

  In addition, when a material made of steel types A to C (steel with a low chromium content), SUJ3 and SUJ5 (a steel containing a large amount of Mn even if the chromium content is high) is used, the surface can be used without performing pretreatment. It can be seen that the amount of retained austenite can be increased to 12% by volume or more and the prior austenite grain size on the surface can be decreased to 30 μm or less.

[4] Verification of configuration (h) As materials for the inner ring (inner diameter is 130 mm, outer diameter is 167 mm, axial dimension is 93 mm) of the cylindrical roller bearing of the designation number NU2326 having the structure of FIG. 1, SCM420, SUJ2, And a spheroidized and annealed annular material made of SUJ3, and this material was turned into an inner ring shape.

  Carburizing and quenching (Comparative Example 13) is performed on the obtained inner ring, or induction hardening (Examples 18 to 21 and Comparative Example 14) is performed on the raceway surface and both axial end surfaces after performing the above-described pretreatment C. Then, by performing tempering treatment at 200 ° C., the amount of retained austenite at each part of the inner ring was set to each value shown in Table 8 in each example. Moreover, each inner ring | wheel was hold | maintained at 200 degreeC for 300 hours, and the dimensional change rate before and behind that was measured. The results are also shown in Table 8.

As shown in Table 8, the dimensional change rate of the inner ring of Examples 18 to 21 in which the difference (Δγ _R ) in the retained austenite amount between the raceway surface and the end surface is 10 to 21% by volume is a comparative example in which carburizing and quenching was performed. It was the same as 13 inner rings. The dimensional change rate of the inner ring of Comparative Example 14 in which the difference (Δγ _R ) in retained austenite amount between the raceway surface and the end surface was 6% by volume was larger than that of the inner ring of Comparative Example 13.

  From this result, SUJ2 or SUJ3 made by induction hardening after pretreatment, the remaining austenite amount of the raceway surface is 15 to 28% by volume, and the core part (non-hardened part) includes a part of the retained austenite amount of 0% by volume. It can be seen that the inner ring in which the amount of retained austenite on the end face is 10% by volume or less than the amount of retained austenite on the raceway surface has the same dimensional stability as the inner ring carburized and hardened made of SCM420. In addition, when using the material made from SUJ3, the inner ring | wheel of the said structure can be obtained even if it does not pre-process.

[5] Verification of Configuration (e) Six disc-shaped test pieces made of SUJ3 and having a thickness of 6 mm and a diameter of 60 mm were prepared. For five of them (No.9-1 to No.9-5), a plurality of linear hardened layers were radially formed at equal intervals on the disk surface of each test piece by induction hardening and tempering. It was formed with an extended pattern. At that time, by changing the number of linear hardened layers formed, hardened layers were formed on 7%, 15%, 27%, 30%, and 56% of the disk surface of each test piece. .

Induction hardening was performed under the condition that the depth from the surface to 1.5 mm was Hv550 or higher. The tempering was carried out by a method of allowing to cool in a furnace at 180 ° C. for 2 hours and then allowing to cool.
The remaining one (No. 9-6) was put in a heating furnace and held at 840 ° C. for 0.5 hours, followed by oil quenching and then held at 180 ° C. for 2 hours. Then, the hardening layer was formed in all the disk surfaces of a test piece by performing tempering to cool.

  The abrasion test for each test piece was performed by the following method. First, each test piece is fixed with screws on a horizontal base of an abrasion tester, and a single-type thrust ball bearing having a nominal number 51305 is arranged on the center thereof. Next, the shaft fixed to the upper race of the ball bearing is rotated under the following conditions to cause a slight slip between the lower race and the test piece.

<Wear test conditions>
Load: 8820N
Lubrication: Oil bath (VG68)
Rotational speed: 1000min ^-1
Test time: 20 hours After completion of the test, the surface of the contact surface with the lower race of each test piece is subjected to a line analysis of the surface state toward the outside along the radial direction, starting from a position with a radius of about 15 mm from the center. The depth of the most recessed position was measured as the wear depth. The results are shown in Table 9. Moreover, the relationship between the ratio of the hardened layer in the disk surface of each test piece and the wear depth obtained from this result is shown in a graph in FIG.

  From this result, it can be seen that when the hardness of the hardened layer having a surface hardness of Hv550 or higher is 30% or higher, almost the same wear resistance as that obtained when the whole is a hardened layer can be obtained. Therefore, the surface hardness of 30% or more of the fitting surface of at least one of the inner ring and the outer ring is Hv550 or more (that is, 30% or more of the fitting surface is a hardened layer by induction hardening) The wear resistance of the mating surface can be improved.

DESCRIPTION OF SYMBOLS 1 Inner ring 11 Inner ring raceway surface 12 Inner ring inner peripheral surface (fitting surface)
12a Hardened layer 13 End surface in the axial direction of the inner ring 2 Outer ring 21 Race surface of the outer ring 22 Inner circumferential surface (fit surface) of the outer ring
23 Axial end face of outer ring 3 Cylindrical roller (rolling element)
4 Cage 41 Pocket 5 Main coil 51 Vertical portion 52 Horizontal portion 6 Auxiliary coil 61 Tip portion 7 Roller

Claims (5)

An inner ring having a raceway surface on the outer peripheral surface and the inner peripheral surface being a fitting surface with the shaft;
An outer ring having a raceway surface on the inner peripheral surface and the outer peripheral surface being a fitting surface with the housing;
A plurality of rolling elements disposed between the raceway surface of the inner ring and the raceway surface of the outer ring so as to be freely rollable,
At least one of the inner ring and the outer ring is obtained by processing a material made of steel into a predetermined shape, and then performing spheroidizing annealing, induction quenching, and tempering, and the following configuration (a) to A rolling bearing characterized by having (e).
(a) The material steel contains carbon (C), chromium (Cr), manganese (Mn), and silicon (Si) as alloy components, and nickel (Ni) and molybdenum (Mo) as required. It is a hypereutectoid steel that is contained and the balance iron and inevitable impurities, and the carbon content [C] is 0.5 mass% or more and 2.0 mass% or less, and is defined by the following formula (1) The DI value is 1.0 or more.
DI = (0.2 [C] +0.14) (1 + 0.64 [Si]) (1 + 4.1 [Mn]) (1 + 0.52 [Ni]) (1 + 2.33 [Cr]) (1 + 3.14 [ Mo]) ... (1)
In the formula (1), [M] means the content (mass%) of the alloy component M.
(b) The effective hardened layer depth (thickness of the portion where the hardness is Hv550 or more) Yo (mm) and the diameter Dw (mm) of the rolling element satisfy the following formula (2).
0.07 Dw ≦ Yo ≦ 0.07 Dw + 5 (2)
(c) The surface hardness of the raceway surface is Hv650 or more, and the amount of retained austenite of the raceway surface is 12 volume% or more and 40 volume% or less.
(d) The prior austenite grain size of the raceway is 30 μm or less.
(e) The surface hardness of 30% or more of the fitting surface is Hv550 or more.   2. The rolling bearing according to claim 1, wherein at least one of the inner ring and the outer ring has a hardness of Hv500 or more from a surface of both axial end surfaces to a depth of 0.1 mm.   At least one of the inner ring and the outer ring has a portion in which the amount of retained austenite is 0% by volume in the non-hardened portion, and the amount of retained austenite at both axial end surfaces is 10% by volume or more than the amount of retained austenite on the raceway surface. The rolling bearing according to claim 1 or 2, wherein there are few. A method of manufacturing the rolling bearing according to claim 1,
Concerning the raceway surface and both axial end surfaces of the material made of steel satisfying the above configuration (a) and processed into the shape of an inner ring or an outer ring after spheroidizing annealing, the internal structure is a two-phase structure of cementite and austenite at the same time. A method of manufacturing a rolling bearing, characterized by performing induction quenching and tempering that is cooled after induction heating so as to become, and then performing induction quenching and tempering on the fitting surface. A high-frequency heat treatment apparatus used in the method of manufacturing a rolling bearing according to claim 4,
A high-frequency heat treatment apparatus comprising: a main coil having a U-shaped portion that surrounds the raceway surface and both end surfaces in the axial direction and simultaneously heats; and an auxiliary coil that heats the raceway surface.

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