WO2014061699A1 - 軸受部品、転がり軸受および軸受部品の製造方法 - Google Patents
軸受部品、転がり軸受および軸受部品の製造方法 Download PDFInfo
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- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
- F16C33/58—Raceways; Race rings
- F16C33/62—Selection of substances
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C21D1/06—Surface hardening
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/36—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for balls; for rollers
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/40—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rings; for bearing races
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/28—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in one step
- C23C8/30—Carbo-nitriding
- C23C8/32—Carbo-nitriding of ferrous surfaces
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/80—After-treatment
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F17/00—Multi-step processes for surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by subclass C21D or C22F or class C25
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- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
- F16C33/32—Balls
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- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
- F16C33/34—Rollers; Needles
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- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
- F16C33/58—Raceways; Race rings
- F16C33/64—Special methods of manufacture
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D1/76—Adjusting the composition of the atmosphere
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- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C19/00—Bearings with rolling contact, for exclusively rotary movement
- F16C19/02—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows
- F16C19/04—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for radial load mainly
- F16C19/06—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for radial load mainly with a single row or balls
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- F16C19/00—Bearings with rolling contact, for exclusively rotary movement
- F16C19/22—Bearings with rolling contact, for exclusively rotary movement with bearing rollers essentially of the same size in one or more circular rows, e.g. needle bearings
- F16C19/30—Bearings with rolling contact, for exclusively rotary movement with bearing rollers essentially of the same size in one or more circular rows, e.g. needle bearings for axial load mainly
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- F16C19/00—Bearings with rolling contact, for exclusively rotary movement
- F16C19/22—Bearings with rolling contact, for exclusively rotary movement with bearing rollers essentially of the same size in one or more circular rows, e.g. needle bearings
- F16C19/34—Bearings with rolling contact, for exclusively rotary movement with bearing rollers essentially of the same size in one or more circular rows, e.g. needle bearings for both radial and axial load
- F16C19/36—Bearings with rolling contact, for exclusively rotary movement with bearing rollers essentially of the same size in one or more circular rows, e.g. needle bearings for both radial and axial load with a single row of rollers
- F16C19/364—Bearings with rolling contact, for exclusively rotary movement with bearing rollers essentially of the same size in one or more circular rows, e.g. needle bearings for both radial and axial load with a single row of rollers with tapered rollers, i.e. rollers having essentially the shape of a truncated cone
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- F16C2202/00—Solid materials defined by their properties
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- F16C2223/00—Surface treatments; Hardening; Coating
- F16C2223/10—Hardening, e.g. carburizing, carbo-nitriding
- F16C2223/16—Hardening, e.g. carburizing, carbo-nitriding with carbo-nitriding
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- F16C2240/00—Specified values or numerical ranges of parameters; Relations between them
- F16C2240/40—Linear dimensions, e.g. length, radius, thickness, gap
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Definitions
- the present invention relates to a bearing component, a rolling bearing, and a manufacturing method of the bearing component, and more particularly to a bearing component, a rolling bearing, and a manufacturing method of the bearing component that can ensure high durability even in a severe use environment. It is.
- a carbonitriding process is known in which carbon and nitrogen are introduced into the surface layer of the bearing parts prior to the quenching process (for example, Japanese Patent Laid-Open No. 5-118336 (Patent Document 1). JP, 2012-31456, A (patent documents 2)). It is known that the carbonitriding treatment improves the rolling fatigue life of the rolling bearing, particularly in an environment where hard foreign matter enters the rolling bearing (foreign matter intrusion environment).
- Carbonitriding process ammonia, carbon monoxide, carbon dioxide and bearing components made of steel in an atmosphere containing hydrogen and heated to a temperature range of not lower than the A 1 transformation point, to penetrate the carbon in the surface layer portion of the bearing parts, Or it is the process which makes nitrogen penetrate
- the carbon concentration of the surface layer is adjusted to an appropriate level by adjusting a c * defined by the following formula (1) and ⁇ defined by the formula (2) to an appropriate range.
- a c * defined by the following formula (1)
- ⁇ defined by the formula (2)
- the present invention has been made to solve the above-mentioned problems, and its object is to provide a bearing component, a rolling bearing and a method for manufacturing the bearing component that can ensure high durability even in a severe use environment. It is to be. Another object of the present invention is to provide a bearing component that can achieve both improvement in durability and improvement in dimensional stability.
- the bearing component according to the present invention comprises 0.95 mass% or more and 1.10 mass% or less carbon, 0.05 mass% or more and less than 0.3 mass% silicon, and 0.10 mass% or more and 0.50 mass%. It is made of steel consisting of the balance iron and impurities, containing manganese of not more than mass% and chromium of not less than 1.30 mass% and not more than 2.00 mass%, and is deep from the contact surface that is the surface in rolling contact with other parts.
- the average nitrogen concentration in the surface layer region which is a region within 20 ⁇ m is 0.2% by mass or more and 0.7% by mass or less, and carbide (including carbonitride) having a diameter of 0.5 ⁇ m or less is 100 ⁇ m in the surface layer region. the presence of 5 or more per 2.
- the inventor examined in detail the cause of the phenomenon that the durability is insufficient even when the carbonitriding treatment is applied to the bearing parts. As a result, the following knowledge was obtained and the present invention was conceived.
- Bearing parts are formed by precipitation strengthening of the carbide by setting the state in which five or more carbides having a diameter of 0.5 ⁇ m or less are present per 100 ⁇ m 2 in the surface layer region (the region having a depth of 20 ⁇ m or less from the contact surface) of the bearing component.
- the static load capacity is improved.
- the state in which five or more carbides having a diameter of 0.5 ⁇ m or less exist in the surface layer region per 100 ⁇ m 2 means that the bearing component is cut in a cross section perpendicular to the contact surface of the bearing component, and the surface layer region of the obtained cross section is When observed with a microscope, it means a state in which 5 or more carbides having a diameter of 0.5 ⁇ m or less are confirmed per 100 ⁇ m 2 .
- the average nitrogen concentration in the surface layer region to 0.2% by mass or more, the durability (life) of the bearing component in a foreign matter mixed environment and the durability in a clean oil lubrication environment are sufficiently improved.
- the bearing component of the present invention five or more carbides having a diameter of 0.5 ⁇ m or less per 100 ⁇ m 2 exist in the surface layer region (region within a depth of 20 ⁇ m from the contact surface that is a rolling contact surface with other components). By doing so, the static load capacity of the bearing parts is sufficiently secured. And by making the average nitrogen concentration of the surface layer region 0.2 mass% or more and 0.7 mass% or less, both improvement in durability due to nitrogen penetration and avoidance of formation of incompletely hardened structure due to nitrogen penetration are achieved. is doing. The above characteristics can be achieved by preventing nitrogen introduced into the surface region from being separated from the surface. Thus, according to the bearing component of the present invention, high durability can be ensured even in a severe use environment.
- the “contact surface” means a rolling surface of a raceway member such as a raceway, or a rolling surface of a rolling element such as a ball or roller (the surface of the ball, the outer peripheral surface of the roller).
- Carbon 0.95% by mass or more and 1.10% by mass or less
- the carbon content greatly affects the hardness and carbide content of the bearing parts after quench hardening.
- the carbon content of the steel By setting the carbon content of the steel to 0.95% by mass or more, sufficient hardness and carbide amount can be achieved without introducing much carbon into the steel by heat treatment.
- the carbon content exceeds 1.10% by mass, a large carbide is formed at the time of manufacturing the steel, which may adversely affect the durability of the bearing component. Therefore, the carbon content is set to 0.95 mass% or more and 1.10 mass% or less.
- Silicon 0.05 mass% or more and less than 0.3 mass% Silicon contributes to the improvement of the temper softening resistance of steel. If the silicon content is less than 0.05% by mass, the temper softening resistance becomes insufficient, and the hardness of the contact surface decreases beyond the allowable range due to tempering after quench hardening and temperature rise during use of bearing parts. there's a possibility that.
- the silicon content is 0.3% by mass or more, the hardness of the material before quenching increases, and the workability in cold working when the material is formed into a bearing part is lowered. Therefore, the silicon content is set to 0.05% by mass or more and less than 0.3% by mass. Silicon promotes hydrogen embrittlement peeling of bearing parts. Therefore, the lower limit of the silicon content is set lower than JIS standard SUJ2, which is the most common bearing steel. That is, when importance is attached to suppression of hydrogen embrittlement peeling, the silicon content can be less than 0.15% by mass lower than SUJ2.
- Manganese 0.10 mass% or more and 0.50 mass% or less Manganese contributes to the improvement of the hardenability of steel. If the manganese content is less than 0.10% by mass, this effect cannot be sufficiently obtained. On the other hand, if the manganese content exceeds 0.50% by mass, the hardness of the material before quenching increases, and the workability in cold working decreases. Therefore, manganese content was made into 0.10 mass% or more and 0.50 mass% or less.
- Chromium 1.30% by mass or more and 2.00% by mass or less Chromium contributes to improvement of hardenability of steel and improvement of rolling fatigue life of bearing parts. If the chromium content is less than 1.30% by mass, this effect cannot be sufficiently obtained. On the other hand, when the chromium content exceeds 2.00% by mass, there arises a problem that the material cost increases. Therefore, the chromium content is set to 1.30% by mass or more and 2.00% by mass or less. Note that when the silicon content is reduced as a measure against hydrogen embrittlement delamination, the hardenability of the steel may be insufficient. This lack of hardenability can be compensated by increasing the amount of chromium added.
- the upper limit value of the chromium content is set higher than JIS standard SUJ2, which is the most common bearing steel.
- the silicon content is less than 0.15% by mass lower than SUJ2 with emphasis on suppression of hydrogen brittle exfoliation, the chromium content can exceed 1.60% by mass higher than SUJ2. .
- the average nitrogen concentration is preferably 0.7% by mass or less over the entire region within a depth of 20 ⁇ m from the surface.
- the contact surface preferably has a hardness of 700 HV or more. Thereby, sufficient static load capacity can be given also to bearing parts used in a severe environment.
- the amount of retained austenite at the contact surface is preferably 20% by volume to 35% by volume.
- the total average retained austenite amount is preferably 18% by volume or less.
- the difference between the maximum value and the minimum value is 130 HV or more.
- introduction of a sufficient concentration of nitrogen is ensured.
- a carbonitriding layer is preferably formed in the surface region. Further, the area ratio of precipitates in the region where the carbonitrided layer is not formed is preferably 7% or less.
- a precipitate is present on a surface other than the contact surface.
- the carbon concentration in the region other than the surface layer region has reached the solid solution limit concentration, so that the lifetime is improved. As a result, a bearing component with improved durability can be provided.
- a c * defined by the following formula (1) is 0.88 or more and 1.27 or less, where P N is the undecomposed ammonia partial pressure and P H is the hydrogen partial pressure.
- the surface layer region may be nitrided by performing carbonitriding so that ⁇ defined by the formula (2) is 0.012 or more and 0.020 or less.
- the value of ⁇ is 0.012 or less, the amount of nitrogen intrusion into the steel within a predetermined time by carbonitriding increases at a substantially constant rate as the value of ⁇ increases.
- the value of ⁇ exceeds 0.012, the rate of increase in the nitrogen penetration amount decreases. Therefore, by setting the value of ⁇ to 0.012 or more, nitrogen can be efficiently introduced into the steel during carbonitriding.
- the value of ⁇ exceeds 0.020, the nitrogen penetration amount within a predetermined time is saturated, and sooting (a phenomenon in which soot is generated in the heat treatment furnace and adheres to the object to be processed) is likely to occur. There is a risk that quality defects such as surface carburization may occur in the object to be treated. Therefore, the value of ⁇ is preferably 0.020 or less, and more preferably 0.018 or less.
- the value of a c * is preferably 0.88 or more in order to prevent the steel surface layer from decarburizing.
- the value of a c * exceeds 1.27, excessive carbide (cementite: Fe 3 C) is formed in the surface layer portion of the steel, which may adversely affect the properties of the steel. Therefore, the value of a c * is preferably 1.27 or less.
- the value of a c * is more preferably 1.00 or less.
- the carbon concentration in the surface layer portion of the bearing component is appropriate by performing carbonitriding in an atmosphere where ⁇ is 0.012 or more and 0.020 or less and a c * is 0.88 or more and 1.27 or less.
- the carbonitriding process is made more efficient. As a result, it is possible to reduce the manufacturing cost of the bearing component.
- the surface layer region is nitrided by performing carbonitriding at a temperature of 820 ° C. or higher and 900 ° C. or lower.
- tempering may be performed at a temperature of 170 ° C. or higher and 220 ° C. or lower.
- the heat treatment conditions are suitable as conditions for bringing the area ratio of precipitates in the region other than the surface layer region, the amount of retained austenite on the contact surface, and the average amount of retained austenite of the entire bearing component within the above range.
- the rolling bearing according to the present invention includes a race member and a rolling element arranged in contact with the race member. At least one of the race member and the rolling element is the bearing component.
- the rolling bearing of the present invention has high durability by including a bearing component capable of ensuring high durability even in a severe use environment as at least one of a race member and a rolling element.
- the manufacturing method of the bearing component according to the present invention includes 0.95% by mass or more and 1.10% by mass or less carbon, 0.05% by mass or more and less than 0.3% silicon, and 0.10% by mass or more and 0% by mass.
- the step of carbonitriding the molded body by heating to a carbonitriding temperature in a carbonitriding atmosphere containing carbon monoxide, carbon dioxide and hydrogen, and the carbonitrided molded body with ammonia, carbon monoxide, carbon dioxide
- a step of diffusing nitrogen in the molded body by maintaining a diffusion temperature that is equal to or lower than the carbonitriding temperature in a diffusion atmosphere containing hydrogen.
- a carbonitriding process and a diffusion process are sequentially performed on a molded body made of steel having the appropriate component composition.
- this diffusion treatment local excessive nitrogen in the molded body is eliminated, and formation of an incompletely hardened structure is suppressed.
- the diffusion treatment by adjusting not only the above a c * but also ⁇ to an appropriate value, the separation of nitrogen in the surface layer region in the diffusion treatment is suppressed, and the surface layer region having an appropriate nitrogen content Can be obtained.
- a step of performing a tempering process for heating and cooling the molded body to a temperature range of 170 ° C. or higher and 220 ° C. or lower after the step of diffusing nitrogen in the molded body is further performed. You may have. Thereby, appropriate hardness can be provided to the contact surface of a bearing component, and sufficient static load capacity can be secured.
- the bearing component, rolling bearing and bearing component manufacturing method of the present invention the bearing component, rolling bearing and bearing component capable of ensuring high durability even in a severe use environment.
- the manufacturing method of can be provided.
- the bearing component according to the present invention it is possible to provide a bearing component capable of achieving both improvement in durability and improvement in dimensional stability.
- FIG. 4 is a schematic partial cross-sectional view of the raceway ring of FIG. 3. It is a schematic sectional drawing of the roller of FIG. It is a flowchart which shows the outline of the manufacturing method of a rolling bearing. It is a schematic sectional drawing which shows the structure of a tapered roller bearing. It is a figure for demonstrating the detail of the hardening hardening process included in the manufacturing method of a bearing component.
- the deep groove ball bearing 1 includes an outer ring 11 as a first race member as a bearing component, an inner ring 12 as a second race member as a bearing component, balls 13 as a plurality of rolling elements as bearing components, and a cage. 14.
- the outer ring 11 is formed with an outer ring rolling surface 11A as an annular first rolling surface.
- the inner ring 12 is formed with an inner ring rolling surface 12A as an annular second rolling surface facing the outer ring rolling surface 11A.
- the balls 13 are formed with ball rolling surfaces 13A (the surfaces of the balls 13) as rolling elements rolling surfaces.
- the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A are contact surfaces of these bearing components.
- the balls 13 are in contact with each of the outer ring rolling surface 11A and the inner ring rolling surface 12A on the ball rolling surface 13A, and are arranged at a predetermined pitch in the circumferential direction by an annular retainer 14. It is rotatably held on an annular track.
- the outer ring 11, the inner ring 12, and the ball 13, which are bearing parts, include carbon of 0.95 mass% to 1.10 mass% and 0.05 mass% to less than 0.3 mass%.
- nitrogen enriched layers 11D, 12D having a higher nitrogen concentration than the inner 11C, 12C, 13C, 13D is formed respectively.
- the surface layer regions 11B, 12B, and 13B whose distances from the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A as contact surfaces that are the surfaces of the nitrogen-enriched layers 11D, 12D, and 13D are within 20 ⁇ m.
- the average nitrogen concentration is 0.2% by mass or more and 0.7% by mass or less.
- the carbon concentration in the surface layer regions 11B, 12B, and 13B is 0.9 mass% or more and 1.3 mass% or less.
- 5 or more carbides having a diameter of 0.5 ⁇ m or less exist in 100 ⁇ m 2 in the surface layer regions 11B, 12B, and 13B.
- the nitrogen concentration in the surface layer regions 11B, 12B and 13B below the contact surface is 0.2 mass% or more and 0.7 mass% or less.
- the surface layer regions 11B, 12B, and 13B there are five or more carbides having a diameter of 0.5 ⁇ m or less per 100 ⁇ m 2 .
- the outer ring 11, the inner ring 12 and the ball 13 are bearing parts capable of ensuring high durability even in severe use environments.
- the abundance (number) of the carbides can be confirmed by, for example, observing the region with a scanning electron microscope (SEM) and subjecting the observation result to image analysis processing.
- SEM scanning electron microscope
- the outer ring 11, the inner ring 12 and the ball 13 preferably have an average nitrogen concentration of 0.7% by mass or less over the entire region within a depth of 20 ⁇ m from the surface.
- the hardness of the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A, which are contact surfaces of the outer ring 11, the inner ring 12 and the ball 13, is preferably 700 HV or more.
- the amount of retained austenite on the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A, which are contact surfaces of the outer ring 11, the inner ring 12 and the ball 13, may be 20% by volume or more and 35% by volume or less. Preferably, it is 25 volume% or more and 35 volume% or less. Thereby, durability of the outer ring 11, the inner ring 12 and the ball 13 in a foreign matter mixed environment can be improved while maintaining sufficient hardness on the outer ring rolling surface 11A, the inner ring rolling surface 12A and the ball rolling surface 13A. .
- the total average retained austenite amount is preferably 18% by volume or less, and more preferably 15% by volume or less.
- the outer ring 11 when the outer ring 11, the inner ring 12 and the ball 13 are held at 500 ° C. for 1 hour, and the hardness distribution is measured in the depth direction in the cross section perpendicular to the contact surface, the difference between the maximum value and the minimum value of the hardness is 130HV.
- the above is preferable. In such outer ring 11, inner ring 12 and ball 13, introduction of a sufficient concentration of nitrogen is ensured.
- a carbonitriding layer is formed in the surface layer regions 11B, 12B, and 13B, and the area ratio of precipitates in the region where the carbonitriding layer is not formed is preferably 7% or less, and 5% or less. More preferably.
- the precipitate is iron carbide or carbonitride in which part of carbon of the carbide is replaced with nitrogen, and includes Fe—C compounds and Fe—CN compounds.
- this carbonitride may contain the alloy component contained in steel, such as chromium.
- the lifetime of a bearing component can be further improved by lowering the area ratio of precipitates and increasing the amount of solid solution such as carbon in the matrix.
- deposits exist on surfaces other than the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A, which are contact surfaces of the outer ring 11, the inner ring 12, and the balls 13.
- the thrust needle roller bearing 2 has basically the same configuration as the deep groove ball bearing 1 and has the same effects. However, the thrust needle roller bearing 2 is different from the deep groove ball bearing 1 in the configuration of the raceway member and the rolling element. That is, the thrust needle roller bearing 2 has a disk-like shape, and a pair of race rings 21 as race members disposed so that one main surfaces thereof face each other, and a plurality of needle rollers 23 as rolling elements. And an annular retainer 24.
- the plurality of needle rollers 23 are in contact with a raceway rolling surface 21A formed on one main surface of the pair of raceways 21 facing each other on a roller rolling contact surface 23A that is an outer peripheral surface of the needle roller 23, and By being arranged at a predetermined pitch in the circumferential direction by the cage 24, the cage 24 is held so as 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.
- the bearing ring 21 of the thrust needle roller bearing 2 corresponds to the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1
- the needle roller 23 of the thrust needle roller bearing 2 corresponds to the ball 13 of the deep groove ball bearing.
- the bearing ring 21 and the needle roller 23 have the same configuration as that of the deep groove ball bearing 1, the bearing ring rolling surface 21A (corresponding to the outer ring rolling surface 11A and the inner ring rolling surface 12A), the rolling contact surface 23A ( Corresponding to ball rolling surface 13A), surface layer regions 21B, 23B (corresponding to surface layer regions 11B, 12B, 13B), internal 21C, 23C (corresponding to internal 11C, 12C, 13C) and nitrogen-enriched layers 21D, 23D (nitrogen) Corresponding to the enriched layers 11D, 12D, and 13D).
- the bearing ring 21 and the needle roller 23 are bearing parts that can ensure high durability even in a severe use environment.
- a molded object preparation process is first implemented as process (S10).
- process (S10) 0.95 mass% or more and 1.10 mass% or less carbon, 0.05 mass% or more and less than 0.35 mass silicon, and 0.10 mass% or more and 0.50 mass% or less.
- a steel material containing manganese and 1.30% by mass or more and 2.00% by mass or less chromium and comprising the remaining iron and impurities for example, a steel material comprising JIS standard SUJ2.
- a steel bar or a steel wire having the above composition is prepared.
- the steel material is subjected to processing such as forging and turning to form the outer ring 11, inner ring 12, ball 13, raceway ring 21, needle roller 23, and the like shown in FIGS. 1 to 5.
- a molded body is produced.
- a carbonitriding step is performed as a step (S20).
- the formed body prepared in step (S10) is subjected to carbonitriding.
- This carbonitriding process can be performed as follows, for example. First, the molded body is preheated in a temperature range of about 780 ° C. to 820 ° C. for a period of 30 minutes to 90 minutes. Next, the molded body is carbonitrided by heating the preheated molded body to a carbonitriding temperature in a carbonitriding atmosphere containing ammonia, carbon monoxide, carbon dioxide and hydrogen.
- a c * in the carbonitriding atmosphere is set to 0.88 to 1.27, and ⁇ is set to 0.012 to 0.020.
- ⁇ is adjusted by further introducing ammonia gas into an endothermic gas such as RX gas in which ac * is adjusted by adding propane gas or butane gas as an enriched gas
- the molded body is heated and carbonitrided.
- the temperature of carbonitriding can be, for example, 820 ° C. or higher and 900 ° C. or lower, and preferably 820 ° C. or higher and 880 ° C. or lower.
- the carbonitriding time can be set according to the desired nitrogen concentration of the nitrogen-enriched layer, and can be, for example, 4 hours or longer and 10 hours or shorter. Thereby, a nitrogen-enriched layer can be formed while appropriately distributing carbides in the surface layer region of the molded body.
- a diffusion step is performed as a step (S30).
- nitrogen in the molded body is brought into the interior by being held at a diffusion temperature that is lower than the carbonitriding temperature in a diffusion atmosphere containing ammonia, carbon monoxide, carbon dioxide, and hydrogen.
- a diffusion process for diffusing is performed.
- a c * in the diffusion atmosphere is set to 0.88 or more and 1.27 or less, and ⁇ is set to 0.003 or more and 0.012 or less.
- ⁇ is adjusted by further introducing ammonia gas into an endothermic gas such as RX gas in which ac * is adjusted by adding propane gas or butane gas as an enriched gas
- the molded body is heated and the diffusion treatment is performed.
- the temperature of the diffusion treatment (diffusion temperature) can be, for example, 780 ° C. or more and 900 ° C. or less, and preferably 820 ° C. or more and 900 ° C. or less.
- the time of the diffusion treatment can be set to 1 hour or more and 5 hours or less, for example.
- nitrogen is diffused to suppress the formation of an incompletely quenched structure, and nitrogen from the surface is suppressed to be separated from the surface region.
- the nitrogen concentration can be adjusted to an appropriate range.
- a quenching process is performed as a process (S40).
- the molded body on which the nitrogen-enriched layer is formed in steps (S20) to (S30) is quenched by being rapidly cooled from a predetermined quenching temperature.
- This quenching temperature can be, for example, 820 ° C. or more and 900 ° C. or less, and preferably 850 ° C. or more and 900 ° C. or less.
- the quenching treatment can be carried out, for example, by immersing the molded body in a quenching oil as a coolant maintained at a predetermined temperature.
- the region to be the surface layer portion below the contact surface in the molded body has an average of 20 ° C./sec or more in the temperature range from the quenching temperature to 600 ° C., and from the quenching temperature to 400 ° C. In this temperature range, it is preferable to cool at an average cooling rate of 30 ° C./sec or more. Thereby, the area
- a tempering step is performed as a step (S50).
- the molded body that has been quenched in the step (S40) is tempered. Specifically, for example, the molded body is held for 0.5 hours to 4 hours in an atmosphere heated to a temperature range of 170 ° C. to 220 ° C. (preferably 180 ° C. to 210 ° C.). A tempering process is performed.
- a finishing process is performed as a process (S60).
- the contact surface which is a surface that comes into contact with other components by processing the molded body tempered in step (S50), that is, the outer ring rolling surface 11A of the deep groove ball bearing 1,
- the ring rolling surface 12A and the ball rolling surface 13A, and the raceway rolling surface 21A and the rolling contact surface 23A of the thrust needle roller bearing 2 are formed.
- a grinding process can be performed.
- the outer ring 11, inner ring 12, ball 13, race ring 21, needle roller 23, etc., which are bearing parts in the present embodiment, are completed through the above steps.
- an assembly process is performed as a process (S70).
- the outer ring 11, the inner ring 12, the ball 13, the race ring 21, the needle roller 23 produced in steps (S10) to (S60) and the cages 14 and 24 prepared separately are assembled. Together, the deep groove ball bearing 1 and the thrust needle roller bearing 2 in the above embodiment are assembled. Thereby, the manufacturing method of the rolling bearing in this Embodiment is completed.
- the average nitrogen concentration in the surface layer region which is a region within a depth of 20 ⁇ m from the contact surface, to 0.2 mass% or more and 0.7 mass% or less
- Nitrogen-rich in the compact so that the nitrogen concentration in the surface layer regions 11B, 12B, 13B, 21B, and 23B below the contact surface is 0.2% by mass or more and 0.7% by mass or less by finishing in the subsequent step (S60).
- a layer is formed. That is, in consideration of the allowance in the step (S60), the amount of nitrogen is adjusted so that the nitrogen concentration in the surface layer portion after completion of the contact surface can be 0.2% by mass or more and 0.7% by mass or less.
- Adjusted nitrogen-enriched layers 11D, 12D, 13D, 21D, and 23D are formed. At this time, it is preferable to suppress the generation of an incompletely hardened structure by setting the nitrogen concentration to 0.7% by mass or less even in a region where the surface layer portion is not removed by finishing (for example, a thin portion). For this purpose, it is necessary to adjust the nitrogen concentration in the surface layer region to 0.7 mass% or less at the time of completion of the step (S30).
- the tempering temperature can be set to 170 ° C. or higher and 220 ° C. or lower, for example. Further, in order to adjust the amount of retained austenite of the outer ring 11, the inner ring 12, the ball 13, the race ring 21, and the needle roller 23 to an appropriate value, it is necessary to adjust the quenching temperature in the step (S40).
- the bearing component and the rolling bearing in the present embodiment can be manufactured.
- the deep groove ball bearing and the thrust roller bearing described in the above embodiment and the bearing components constituting them are examples of the rolling bearing and the bearing component of the present invention.
- the rolling bearing and bearing component of the present invention can be applied to various types of rolling bearings.
- the tapered roller bearing 4 includes an annular outer ring 41 and an inner ring 42, a plurality of rollers 43 that are rolling elements, and an annular retainer 44.
- An outer ring rolling surface 41 ⁇ / b> A is formed on the inner circumferential surface of the outer ring 41, and an inner ring rolling surface 42 ⁇ / b> A is formed on the outer circumferential surface of the inner ring 42.
- the inner ring 42 is arranged inside the outer ring 41 so that the inner ring rolling surface 42A faces the outer ring rolling surface 41A.
- the rollers 43 are in contact with the outer ring rolling surface 41A and the inner ring rolling surface 42A on the rolling surface 43A, and are arranged at a predetermined pitch in the circumferential direction by the cage 44. As a result, the roller 43 is rotatably held on an annular track of the outer ring 41 and the inner ring 42. Further, the tapered roller bearing 4 has a cone including the outer ring rolling surface 41A, a cone including the inner ring rolling surface 42A, and a cone including the locus of the rotation axis when the roller 43 rolls at the vertex of the bearing. It is configured to intersect at one point on the line.
- the outer ring 41 and the inner ring 42 of the tapered roller bearing 4 are rotatable relative to each other.
- wheel 42, and the roller 43 are bearing components which concern on this Embodiment.
- the bearing parts according to the present embodiment are made of steel having basically the same composition as the bearing part according to the first embodiment, and the bearing according to the first embodiment. It has basically the same configuration as the parts.
- the bearing component manufacturing method according to the present embodiment basically the same steps as those of the bearing component and the rolling bearing manufacturing method according to the first embodiment are performed, so that the bearing component according to the present embodiment is performed.
- the outer ring 41, the inner ring 42, the roller 43, and the tapered roller bearing 4 are manufactured.
- a molded body preparation step is first performed as a step (S10).
- a steel material having the same composition as in the first embodiment is prepared, and a molded body obtained by processing the steel material and forming it into an approximate shape such as the outer ring 41, the inner ring 42, and the roller 43 is obtained.
- steps (S20) to (S60) are performed in the same manner as in the first embodiment.
- the outer ring 41, the inner ring 42, and the rollers 43 (see FIG. 7), which are bearing parts according to the present embodiment, are manufactured, and the manufacturing method of the bearing part according to the present embodiment is completed.
- the tapered roller bearing 4 (refer FIG. 7) is manufactured by combining the outer ring
- the diffusion step (S30) may be omitted in the method for manufacturing a bearing component according to the present embodiment, and in this case as well, the bearing components (the outer ring 41, the inner ring 42, and the roller 43) according to the present embodiment are similarly used. Can be manufactured.
- FIG. 8 is a diagram for explaining the carbonitriding step (S20) and the quenching step (S40) in detail.
- 9 is a diagram for explaining the undecomposed ammonia (NH 3) partial pressure control step included in the atmosphere control step of FIG.
- FIG. 10 is a diagram for explaining a hydrogen (H 2 ) partial pressure control step included in the atmosphere control step of FIG.
- FIG. 8 is a diagram for explaining the carbonitriding step (S20) and the quenching step (S40) in detail.
- NH 3 undecomposed ammonia
- H 2 hydrogen
- FIG. 11 is a figure which shows an example of the heating pattern (temperature history) in the heating pattern control process included in the carbonitriding process of FIG.
- the horizontal direction indicates time, and the time has passed as it goes to the right.
- steps (S20) to (S40) which are quench hardening steps included in the method of manufacturing a bearing component according to the present embodiment, will be described.
- a carbonitriding process is performed in which a steel material is carbonitrided. Then, after a diffusion step (not shown) is performed, a quenching step is performed in which the steel is cooled from a temperature of A 1 point or higher to a temperature of M s point or lower.
- the carbonitriding process is performed by heating the steel material prepared in the above step (S10) in an atmosphere containing ammonia, carbon monoxide, carbon dioxide, and hydrogen.
- the carbonitriding process includes an atmosphere control process 50 in which the atmosphere in the heat treatment furnace is controlled, and a heating pattern control process 60 in which the temperature history applied to the steel material that is the object to be processed in the heat treatment furnace is controlled. .
- the atmosphere control process 50 and the heating pattern control process 60 can be performed independently and in parallel.
- the atmosphere control step 50 includes an undecomposed NH 3 partial pressure control step 51 in which the undecomposed ammonia partial pressure in the heat treatment furnace is controlled, and an H 2 partial pressure control step 52 in which the hydrogen partial pressure in the heat treatment furnace is controlled. And a CO / CO 2 partial pressure control step 53 in which the partial pressure of at least one of carbon monoxide and carbon dioxide in the heat treatment furnace is controlled.
- a c * is controlled by controlling the partial pressure of at least one of carbon monoxide and carbon dioxide in the heat treatment furnace with reference to equation (1). Is done.
- a c * defined by the formula (1) is in the range of 0.88 to 1.27
- ⁇ in the formula (2) is in the range of 0.012 to 0.020.
- an undecomposed NH 3 partial pressure control step 51, an H 2 partial pressure control step 52, and a CO / CO 2 partial pressure control step 53 are performed.
- an undecomposed NH 3 partial pressure measuring step (S11) for measuring the undecomposed ammonia partial pressure in the heat treatment furnace is performed. Is done.
- the measurement of the undecomposed ammonia partial pressure can be performed using, for example, a gas chromatograph.
- S13 the NH 3 supply amount adjustment step for increasing or decreasing the supply amount of ammonia gas to the heat treatment furnace is necessary.
- a decomposition NH 3 partial pressure determination step (S12) is performed.
- the determination is made by comparing the target undecomposed ammonia partial pressure, which is determined in advance so that the value of ⁇ is in the range of 0.012 to 0.020, and the measured undecomposed ammonia partial pressure. The determination is made by determining whether the undecomposed ammonia partial pressure is the target undecomposed ammonia partial pressure.
- the step (S13) includes, for example, a mass flow controller in which the amount of ammonia (amount of ammonia gas) flowing into the heat treatment furnace per unit time from an ammonia gas cylinder connected to the heat treatment furnace via a pipe is attached to the pipe. It can implement by adjusting with the flow control apparatus provided with.
- the step (S13) can be performed by decreasing the flow rate and increasing the flow rate when the partial pressure is low. .
- this step (S13) when there is a predetermined difference between the measured undecomposed ammonia partial pressure and the target undecomposed ammonia partial pressure, it was experimentally determined in advance how much the flow rate should be increased or decreased. It can be determined based on the relationship between the increase / decrease in the flow rate of ammonia gas and the increase / decrease in the partial pressure of undecomposed ammonia.
- the step (S11) is performed again without performing the step (S13).
- the H 2 partial pressure control step 52 is performed in the same manner as the undecomposed NH 3 partial pressure control step 51 described above. That is, referring to FIG. 10, in H 2 partial pressure control step 52, first, an H 2 partial pressure measurement step (S21) for measuring the hydrogen partial pressure in the heat treatment furnace is performed. The measurement of the hydrogen partial pressure can be performed using, for example, a heat conduction gas analyzer. Then, based on the hydrogen partial pressure measured in the step (S21), it is determined whether or not the H 2 supply amount adjusting step (S23) for increasing or decreasing the supply amount of hydrogen gas to the heat treatment furnace is necessary. A determination step (S22) is performed. The determination is made by comparing the target hydrogen partial pressure determined in advance so that the value of ⁇ is in the range of 0.012 or more and 0.020 or less and the measured hydrogen partial pressure. Is carried out by determining whether or not is at the target hydrogen partial pressure.
- the step (S23) includes, for example, a mass flow controller in which the amount of hydrogen (flow rate of hydrogen gas) flowing into the heat treatment furnace per unit time from a hydrogen gas cylinder connected to the heat treatment furnace via a pipe is attached to the pipe It can implement by adjusting with the flow control apparatus provided with. That is, when the measured hydrogen partial pressure is higher than the target hydrogen partial pressure, the step (S23) can be performed by decreasing the flow rate, and when it is low, increasing the flow rate.
- this step (S23) when there is a predetermined difference between the measured hydrogen partial pressure and the hydrogen partial pressure, how much the flow rate is increased or decreased is experimentally determined in advance as in the case of ammonia. It can be determined based on the relationship between the increase or decrease of the hydrogen gas flow rate and the increase or decrease of the hydrogen partial pressure.
- the step (S21) is performed again without performing the step (S23).
- the supply amount of propane (C 3 H 8 ) gas, butane gas (C 4 H 10 ), etc. as an enriched gas is adjusted, so that CO 2 is adjusted.
- the partial pressure of at least one of the partial pressure of CO 2 and CO 2 is controlled, and a c * is adjusted.
- the partial pressure P CO2 partial pressure P CO and carbon monoxide to carbon dioxide in the atmosphere by using an infrared gas concentration measurement device are measured.
- propane (C 3 H as an enriched gas) is set so that a c * defined by the formula (1) becomes a target value within a range of 0.88 to 1.27. 8 )
- the supply amount of gas, butane gas (C 4 H 10 ), etc. is adjusted.
- the value of ⁇ is determined by the undecomposed NH 3 partial pressure control step 51, the H 2 partial pressure control step 52, and the CO / CO 2 partial pressure control step 53 with reference to the equation (2), respectively. It can be controlled by changing at least one of partial pressure, hydrogen partial pressure, and a c * . That is, the value of ⁇ is determined by, for example, the H 2 partial pressure in a state where the undecomposed NH 3 partial pressure control step 51 and the CO / CO 2 partial pressure control step 53 hold the undecomposed ammonia partial pressure and a c * constant.
- the control step 52 may control by changing the hydrogen partial pressure, or the hydrogen partial pressure and a c * value are kept constant by the H 2 partial pressure control step 52 and the CO / CO 2 partial pressure control step 53.
- the undecomposed NH 3 partial pressure control step 51 may change the undecomposed ammonia partial pressure.
- the heating history provided to steel materials is controlled.
- a temperature of 820 ° C. or higher and 900 ° C. or lower (preferably 820 ° C. or higher) which is a temperature of A 1 point or higher. It is heated to a temperature of 880 ° C. or lower (for example, 880 ° C.) and held for a predetermined time. As the holding time elapses, the heating pattern control process ends, and at the same time, the atmosphere control process ends. Thereafter, referring to FIG.
- the steel material is immersed (oil-cooled) in oil, thereby cooling from a temperature of A 1 point or higher to a temperature of M s point or lower.
- a quenching process is performed.
- the surface layer portion of the steel material is carbonitrided and hardened and hardened.
- a carbonitriding layer is formed by performing carbonitriding at 820 ° C. or more and 900 ° C. or less (for example, 880 ° C.) in the step (S20).
- tempering is performed at a temperature of 170 ° C. or higher and 220 ° C. or lower (eg, 210 ° C.).
- a large amount of carbon is dissolved in a region (matrix) where the carbonitriding layer is not formed, and durability is improved by balancing the amount of retained austenite in the surface layer portion with the total amount of average austenite.
- the outer ring 41, the inner ring 42, and the roller 43 which are bearing parts according to the present embodiment in which improvement in dimensional stability is achieved, can be manufactured.
- the undecomposed ammonia partial pressure P N, the hydrogen partial pressure in an P H, a c * defined by the above formula (1) is 0.88 or more 1.27 or less
- the carbonitriding process is performed so that ⁇ defined by the above formula (2) is 0.012 or more and 0.020 or less.
- Example 1 An experiment was conducted to confirm the necessity of atmosphere control during carbonitriding. Specifically, carbon nitride treatment was performed on a test piece made of SUJ2 while changing the values of a c * and ⁇ , and an experiment was conducted to confirm the carbon concentration and nitrogen concentration near the surface.
- FIG. 12 shows carbon and nitrogen concentration distributions when carbonitriding for 2.5 hours is performed in an atmosphere in which a c * is adjusted to 0.80 and ⁇ is set to 0.017.
- FIG. 13 shows carbon and nitrogen concentration distributions when carbonitriding is performed for 2.5 hours in an atmosphere where a c * is 0.95 and ⁇ is 0.017. 12 and 13, the thin line indicates the carbon concentration distribution, and the thick line indicates the nitrogen concentration distribution. Since ⁇ is the same value, nitridation is normal in both cases. However, in FIG. 12, since a c * is less than 0.88, carbide near the surface disappears, and the carbon of the parent phase is slightly removed. Yes.
- a nitrogen concentration distribution when carbonitriding for 5 hours is performed in an atmosphere of 005 is shown.
- the carbonitriding time is the same, but in FIG. 15 where ⁇ is small, the amount of nitrogen intrusion is smaller than in FIG. 14 where ⁇ is in an appropriate range.
- Example 2 An experiment was conducted to confirm the necessity of diffusion treatment after carbonitriding. Specifically, the carbonitriding process which changed conditions on the test piece which consists of SUJ2 was performed, the sample from which nitrogen concentration differs was produced, and the experiment which investigates the relationship between nitrogen concentration, surface hardness, and half width was conducted.
- the “half width” means the half width of the peak (142.3 to 170.2 °) corresponding to martensite measured using the K ⁇ ray of the Cr tube.
- FIG. 16 shows the relationship between the nitrogen concentration (average nitrogen concentration), the surface hardness, and the half-value width in the surface layer region obtained as a result of the experiment.
- the nitrogen concentration in the surface layer region is 0.7% by mass or more
- the hardness is 700 HV or less
- the half-value width is 7.0 or less. From this, it can be seen that when the nitrogen concentration in the surface layer region is 0.7% by mass or more, an incompletely hardened structure is generated in the region.
- FIG. 17 is a photograph of the microstructure when the nitrogen concentration in the surface layer region is 1.0 mass%. From this photograph, it is confirmed that an incompletely hardened structure is formed near the surface.
- the nitrogen concentration in the surface layer region that has a great influence on the rolling fatigue life should be 0.7% by mass or less. Is confirmed.
- a high-concentration nitrogen-enriched layer is formed on the surface of the workpiece by carbonitriding. Then, it is preferable to adopt a process for performing a diffusion treatment. At this time, the formation of an incompletely hardened structure can be suppressed by setting the nitrogen concentration in the vicinity of the surface to 0.7 mass% or less by diffusion treatment. If the nitrogen concentration in the surface layer of the entire part is reduced to 0.7% by mass or less by diffusion treatment, incompletely hardened structures remain in the product even in areas that are not processed in the subsequent process (for example, thinning parts). Is done.
- Example 3 An experiment was conducted to confirm the necessity of atmosphere control in the diffusion treatment. Specifically, after carbonitriding the test piece made of SUJ2, the diffusion treatment was performed by changing the ⁇ value, and an experiment was conducted to investigate the effect of the ⁇ value on the nitrogen concentration in the surface layer region. It was. 18 shows the nitrogen concentration distribution in the vicinity of the surface when ⁇ is 0, and FIG. 19 shows the vicinity of the surface when ⁇ is 0.005.
- the diffusion treatment when the diffusion treatment is performed in an atmosphere where ⁇ is 0, that is, PN is 0, it can be seen that nitrogen is detached from the surface and the nitrogen concentration in the surface layer region is lowered.
- the value of ⁇ when the value of ⁇ is set to 0.005, it can be seen that the above-described separation of nitrogen is suppressed and a surface region having an appropriate nitrogen concentration is obtained. From this, it is understood that it is important to manage the value of ⁇ also in the diffusion process. According to the study by the present inventor, the surface region having an appropriate nitrogen concentration can be obtained by setting the value of ⁇ in the range of 0.003 to 0.012.
- Example 4 Experiments were conducted to investigate the relationship between surface hardness and static load capacity. Specifically, a test piece made of SUJ2 was prepared, and after carbonitriding, diffusion, and quenching were performed under the same conditions, samples with different surface hardness were produced by changing the tempering temperature. Then, the surface hardness of the sample was measured, and a ball made of silicon nitride having a diameter of ⁇ 9.525 mm was pressed against the surface of the sample with a constant load to form an indentation. And the depth of the formed indentation (residual indent after removing the load) was investigated. The experimental results are shown in FIG. In FIG. 20, the horizontal axis indicates the stress applied to the surface, and the vertical axis indicates the depth of the indentation.
- the depth of the indentation becomes deeper as the surface hardness becomes lower. Only when the surface hardness is 700 HV or higher and the hardness is 730 HV, the indentation depth is allowed even when used in applications requiring high static load capacity. From this, it can be said that the hardness at the contact surface of the bearing component is preferably 700 HV or more.
- Example 5 An experiment was conducted to investigate the influence of nitrogen concentration in the surface layer on the durability of the bearing ring of a rolling bearing. Specifically, a rolling fatigue life test was performed in a state where indentations were formed on the rolling surface of the race (inner ring). The experimental procedure is as follows.
- the test was carried out using a deep groove ball bearing of JIS standard 6206 model number (inner diameter 30 mm, outer diameter 62 mm, width 16 mm, 9 rolling elements, manufactured by SUJ2).
- an inner ring was produced by the same procedure as in the above embodiment.
- the concentration distribution of nitrogen penetrating near the inner ring surface is controlled by adjusting the undecomposed ammonia partial pressure, hydrogen partial pressure, carbon activity, heat treatment time, quenching temperature, etc. in the atmosphere during carbonitriding did.
- an inner ring without carbonitriding was also produced.
- inner rings having the five nitrogen concentration distributions shown in FIGS. 21 to 25 were obtained.
- the horizontal axis indicates the distance from the surface (rolling surface), and the vertical axis indicates the nitrogen concentration. Further, the measurement of the nitrogen concentration distribution was performed twice for each condition, and the results of the two measurements are shown in an overlapping manner in FIGS.
- indentations were formed on the obtained inner ring.
- a life test under lubrication mixed with foreign matter may be performed as a method for evaluating the life of a rolling bearing that simulates an actual use environment.
- This test method operates by mixing particles having a particle diameter of 100 to 180 ⁇ m (hardness of about 800 HV) produced by gas atomization into the lubricating oil of a rolling bearing and evaluating the failure life.
- the reason why the particle size is 100 to 180 ⁇ m is that hard foreign matters having a maximum particle size of about 100 ⁇ m may be mixed in an actual use environment.
- FIG. 26 shows the surface shape (indentation shape) of the raceway ring damaged by the life test under the foreign matter mixed lubrication.
- the horizontal axis indicates the distance from the reference point along the surface (rolling surface), and the vertical axis indicates the height. From the reference point on the horizontal axis to the vicinity of 0.3 mm corresponds to the initial rolling surface, from 0.3 mm to 1.1 mm to the indentation, and the area of 1.1 mm or more corresponds to the peeling portion.
- FIG. 26 shows that the indentation formed by the hard foreign matter has a depth of about 15 to 20 ⁇ m.
- the shape and microstructure of the raised portion of the indentation are major factors that determine the life.
- the shape of the raised portion of the indentation is considered to be determined by the microstructure of the material up to the depth of the indentation.
- the microstructure of steel changes with the nitrogen concentration. From these facts, it is considered that the lifetime in an environment where hard foreign matter intrudes depends not only on the surface nitrogen concentration but also on the nitrogen concentration from the surface to the indentation depth.
- the indentation depth is about 20 ⁇ m at the maximum. Therefore, in the present specification and the like, a region from the surface to a depth of 20 ⁇ m is defined as a surface layer region (surface layer portion), and attention is paid to the average nitrogen concentration in the surface layer region (surface layer portion). Specifically, the average nitrogen concentration in this surface layer region is obtained by performing line analysis in the depth direction with EPMA (Electron Probe Micro Analysis) on a cross section perpendicular to the surface, and calculating an average value from the surface to a depth of 20 ⁇ m. Can be investigated.
- EPMA Electro Probe Micro Analysis
- the inner ring has an indenter for measuring the Rockwell hardness of a conical diamond at the center of the groove bottom of the rolling surface (an indenter having a spherical surface with a curvature of 0.2 mm at the apex of a cone having an apex angle of 120 °). ) was pressed with a load of 196 N to form an indentation.
- the shape of the formed indentation was measured with a three-dimensional surface shape apparatus, it was confirmed that the raised shape at the periphery of the indentation was substantially symmetrical with respect to the axial direction and the circumferential direction with the center of the indentation as the axis of symmetry.
- FIG. 27 shows a typical indentation shape.
- the applied indentations were 30 per inner ring, and were formed at equal intervals in the circumferential direction (that is, every 12 ° of the central angle).
- the bearings were assembled by combining rolling elements, cages, etc., in addition to the normal outer ring that was not carbonitrided and formed no indentation on the inner ring thus produced.
- the obtained bearing was subjected to a life test.
- the test results are shown in FIG.
- bearings in which the formation of indentations was omitted in the same procedure were created, and the life in a normal clean oil lubrication environment was also investigated.
- FIG. 29 shows the test results of the life in the clean oil lubrication environment.
- the horizontal axis represents the average nitrogen concentration in the surface layer region
- the vertical axis represents the time (L 10 life) when the cumulative failure probability is 10%.
- the indentation origin type peeling life is twice or more as compared with the case where the average nitrogen concentration is 0.
- the life in the cleaning oil lubrication environment is also more than twice that in the case where the average nitrogen concentration is 0. Yes.
- the average nitrogen concentration in the surface layer region should be 0.2% by mass or more in order to obtain a clear effect of formation of the nitrogen-enriched layer (carbonitriding treatment). . Further, from the experimental results described in Example 2 above, considering that the average nitrogen concentration in the surface layer region should be 0.7% by mass or less in order to suppress the formation of an incompletely quenched structure, it is appropriate. It can be said that the surface nitrogen concentration is 0.2% by mass or more and 0.7% by mass or less.
- Example 6 An experiment was conducted to investigate the relationship between the amount of retained austenite on the contact surface and the indentation-origin peel life. Specifically, a sample was prepared in which the average nitrogen concentration in the surface layer region was constant (0.4% by mass), and the amount of retained austenite was changed by changing the tempering temperature. A starting-type peel life test was conducted. The experimental results are shown in FIG. The amount of retained austenite in the inner ring of the rolling surfaces is horizontal axis 30, the vertical axis represents the L 10 life.
- the indentation origin peeling life becomes longer as the amount of retained austenite increases.
- the indentation origin type peeling life is twice or more that of the case of the average nitrogen concentration of 0 in Example 5.
- the amount of retained austenite exceeds 35% by volume, the hardness on the rolling surface (contact surface) may be insufficient. From the above examination results, it can be said that the amount of retained austenite at the contact surface is preferably 20% by volume or more and 35% by volume or less.
- Example 7 Experiments were conducted to investigate the relationship between retained austenite content and dimensional stability of the entire part. Specifically, by preparing a ring-shaped test piece made of SUJ2 having an outer diameter ⁇ : 60 mm, an inner diameter ⁇ : 54 mm, and an axial length t: 15 mm, and performing heat treatment such as carbonitriding under different conditions Quenched and hardened samples with different overall average retained austenite amounts were obtained. The residual austenite amount distribution of the sample is shown in FIG. In FIG. 31, the horizontal axis indicates the distance from the surface, and the vertical axis indicates the amount of retained austenite. Based on FIG. 31, the average retained austenite amount of the entire sample was calculated. In the legend of FIG.
- quenching temperature ⁇ tempering temperature ⁇ average nitrogen concentration in the surface region is displayed.
- the display of 850 ° C.-180 ° C.-0.4 mass% N indicates that the quenching temperature is 850 ° C., the tempering temperature is 180 ° C., and the average nitrogen concentration in the surface layer region is 0.4% by mass. .
- FIG. 32 shows the relationship between the average retained austenite amount and the dimensional change rate.
- the horizontal axis represents the average retained austenite amount in the entire sample
- the vertical axis represents the dimensional change rate of the outer diameter.
- the average retained austenite amount of the entire part is preferably 18% by mass or less from the viewpoint of setting the aging dimensional change rate to a preferable value of 60 ⁇ 10 ⁇ 5 or less.
- Example 8 As described in Example 5 above, in order to impart sufficient durability to the bearing component, the average nitrogen concentration in the surface layer region needs to be 0.2% by mass or more. Here, the nitrogen concentration can be confirmed by, for example, EPMA as described above. However, performing quality confirmation using EPMA in the mass production process of bearing parts complicates the quality confirmation work. Therefore, it is desirable that quality confirmation in the mass production process is performed by a simpler method. Therefore, the present inventor has studied a method for confirming the quality by utilizing the fact that nitrogen that has entered the steel improves the temper softening resistance.
- FIG. 33 shows the relationship between the nitrogen concentration and the hardness difference.
- the horizontal axis represents the nitrogen concentration
- the vertical axis represents the difference between the maximum value and the minimum value in the cross-sectional hardness distribution.
- the hardness difference after the heat treatment is the largest when the nitrogen concentration is about 0.2 to 0.3 mass%. Further, in the range where the nitrogen concentration is 0.2% by mass or more and 0.3% by mass or less, the hardness difference is 130HV or more with a probability of 95% or more. Therefore, when the hardness distribution is measured in the depth direction in a cross section perpendicular to the surface after being held at 500 ° C. for 1 hour, if the difference between the maximum value and the minimum value of the hardness is 130 HV or more, the nitrogen concentration is 0.00. It can be judged that it is 2 mass% or more. By adopting such a determination method, it is possible to easily check the quality of bearing parts.
- Example 9 When bearing steel such as JIS standard SUJ2 containing Cr is infiltrated into the steel by carbonitriding or the like, the Cr concentration in the base material decreases and the austenite single phase region expands. The limit concentration increases. As a result, if a carbonitriding treatment with a high concentration (for example, forming a nitrogen-enriched layer of 0.2% by mass or more) is performed without taking any special measures, even if decarburization does not occur, carbide (carbonitride) Decrease or disappear.
- a carbonitriding treatment with a high concentration for example, forming a nitrogen-enriched layer of 0.2% by mass or more
- carbide carbonitride
- FIG. 34 is a cross-sectional SEM photograph of a sample made of SUJ2 that has been subjected to carbonitriding by a conventional carbonitriding method. In the photograph of FIG. 34, the carbide is almost lost. On the other hand, FIG.
- FIG. 35 shows a cross section of a sample made of SUJ2 that has been subjected to carbonitriding by the carbonitriding method (with the value of a c * being 1) employed in the method for manufacturing a bearing component according to the present embodiment. It is a SEM photograph. In the photograph of FIG. 35, 5 or more carbides having a diameter of 0.5 ⁇ m or less exist per 100 ⁇ m 2 .
- the carbonitriding process was implemented on the test piece which consists of SUJ2 on different conditions, and the sample which made hardness 750HV, changing the abundance (number density) of a carbide
- An experiment was conducted to measure the depth of indentation formed by pressing a ball made of silicon nitride having a diameter of 9.525 mm against the surface of the sample.
- the experimental results are shown in FIG.
- the horizontal axis indicates the pressing pressure of the silicon nitride balls, and the vertical axis indicates the depth of the indentation formed by pressing the balls.
- the square mark corresponds to the measurement result of the sample in which the carbide has disappeared, and the diamond mark corresponds to the measurement result of the sample having 5 or more carbides having a diameter of 0.5 ⁇ m or less per 100 ⁇ m 2 .
- Example 10 Next, the relationship between the area ratio of the internal carbides and the lubrication life of foreign matters was investigated.
- Bearing steel can be solid solution strengthened by dissolving carbide. Since the area ratio of carbide in the bearing steel before quenching is constant, the solid solution amount of carbon can be estimated from the area ratio of carbide inside after carbonitriding. Regardless of the quality of the surface after grinding that affects the life of the bearing, the reason why the solid solution amount of carbon in the matrix is estimated from the area ratio of carbide inside is carburizing. This is because it is difficult to estimate the solid solution amount of carbide in the matrix because the surface is nitrided by the nitriding treatment and the solid solubility limit concentration of carbon increases.
- Table 2 shows the relationship between the heat treatment conditions and the area ratio (%) of the internal precipitates (carbides).
- the heat treatment conditions in Table 2 are indicated by the expression “quenching temperature ⁇ tempering temperature ⁇ nitrogen concentration on the outermost surface after grinding”.
- the display of 800 ° C.-180 ° C.-0.1 mass% N indicates that the quenching temperature is 800 ° C.
- the tempering temperature is 180 ° C.
- the nitrogen concentration in the surface layer portion is 0.1% by mass.
- the area ratio of the internal precipitates decreased as the heating temperature increased. That is, by increasing the treatment temperature during carbonitriding, the solid solubility limit concentration of carbon in the matrix increases, and the amount of solid solution increases, so the amount of precipitates decreases.
- the carbon concentration at the matrix has reached the solid solubility limit concentration, and the carbon concentration at the surface matrix is also high. Become.
- FIG. 37 shows the test results of the foreign material mixed lubrication life (the test method is as described above).
- the horizontal axis represents the life (time from the start of the test to the occurrence of peeling) (h), and the vertical axis represents the cumulative failure probability (%).
- the legend of FIG. 37 as in Table 2, “Quenching temperature ⁇ Tempering temperature ⁇ Nitrogen concentration on the outermost surface after grinding” is displayed. As shown in FIG.
- the bearing component, rolling bearing, and bearing component manufacturing method of the present invention can be applied particularly advantageously to bearing components, rolling bearings, and bearing component manufacturing methods that are required to ensure high durability even in severe use environments. .
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Abstract
Description
炭素含有量は、焼入硬化後における軸受部品の硬度および炭化物量に大きな影響を与える。鋼の炭素含有量を0.95質量%以上とすることにより、熱処理によって鋼中に多くの炭素を導入することなく、十分な硬度および炭化物量を達成することができる。一方、炭素含有量が1.10質量%を超えると、鋼の製造時点において大型の炭化物が形成され、これが軸受部品の耐久性に悪影響を及ぼすおそれがある。そのため、炭素含有量は0.95質量%以上1.10質量%以下とした。
珪素は、鋼の焼戻軟化抵抗の向上に寄与する。珪素含有量が0.05質量%未満では、焼戻軟化抵抗が不十分となり、焼入硬化後の焼戻や、軸受部品の使用中における温度上昇により接触面の硬度が許容範囲を超えて低下する可能性がある。一方、珪素含有量が0.3質量%以上になると、焼入前の素材の硬度が高くなり、素材を軸受部品に成形する際の冷間加工における加工性が低下する。そのため、珪素含有量は0.05質量%以上0.3質量%未満とした。なお、珪素は、軸受部品の水素脆性剥離を助長する。そのため、珪素含有量の下限値は、最も一般的な軸受用鋼であるJIS規格SUJ2よりも低く設定している。つまり、水素脆性剥離の抑制を重視する場合、珪素含有量はSUJ2よりも低い0.15質量%未満とすることができる。
マンガンは、鋼の焼入性の向上に寄与する。マンガン含有量が0.10質量%未満では、この効果が十分に得られない。一方、マンガン含有量が0.50質量%を超えると、焼入前の素材の硬度が高くなり、冷間加工における加工性が低下する。そのため、マンガン含有量は0.10質量%以上0.50質量%以下とした。
クロムは、鋼の焼入性の向上および軸受部品の転動疲労寿命の改善に寄与する。クロム含有量が1.30質量%未満では、この効果が十分に得られない。一方、クロム含有量が2.00質量%を超えると、素材コストが高くなるという問題が生じる。そのため、クロム含有量は1.30質量%以上2.00質量%以下とした。なお、水素脆性剥離の対策として珪素含有量を低減した場合、鋼の焼入性が不十分となるおそれがある。この焼入性の不足は、クロム添加量の増加にて補うことができる。そのため、クロム含有量の上限値は、最も一般的な軸受用鋼であるJIS規格SUJ2よりも高く設定している。特に、水素脆性剥離の抑制を重視して珪素含有量をSUJ2よりも低い0.15質量%未満とした場合、クロム含有量はSUJ2よりも高い1.60質量%を超えるものとすることができる。
まず、図1および図2を参照して、軸受部品である軌道輪および玉を備えた転がり軸受を例に、本発明の一実施の形態について説明する。深溝玉軸受1は、軸受部品である第1軌道部材としての外輪11と、軸受部品である第2軌道部材としての内輪12と、軸受部品である複数の転動体としての玉13と、保持器14とを備えている。外輪11には、円環状の第1転走面しての外輪転走面11Aが形成されている。内輪12には、外輪転走面11Aに対向する円環状の第2転走面としての内輪転走面12Aが形成されている。また、複数の玉13には、転動体転走面としての玉転動面13A(玉13の表面)が形成されている。外輪転走面11A、内輪転走面12Aおよび玉転動面13Aは、これらの軸受部品の接触面である。そして、当該玉13は、外輪転走面11Aおよび内輪転走面12Aの各々に玉転動面13Aにおいて接触し、円環状の保持器14により周方向に所定のピッチで配置されることにより円環状の軌道上に転動自在に保持されている。以上の構成により、深溝玉軸受1の外輪11および内輪12は、互いに相対的に回転可能となっている。
次に、図7を参照して、本発明の他の実施の形態に係る転がり軸受である円錐ころ軸受4の構造について説明する。円錐ころ軸受4は、環状の外輪41および内輪42と、転動体である複数のころ43と、円環状の保持器44とを備えている。外輪41の内周面には外輪転走面41Aが形成されており、内輪42の外周面には内輪転走面42Aが形成されている。内輪42は、内輪転走面42Aが外輪転走面41Aと対向するように外輪41の内側に配置されている。
浸炭窒化処理時における雰囲気管理の必要性について確認する実験を行った。具体的には、ac *およびαの値を変化させてSUJ2からなる試験片に浸炭窒化処理を行い、表面付近の炭素濃度および窒素濃度を確認する実験を行った。
浸炭窒化処理後の拡散処理の必要性について確認する実験を行った。具体的には、SUJ2からなる試験片に条件を変えた浸炭窒化処理を行って窒素濃度の異なるサンプルを作製し、窒素濃度と表面硬度および半価幅との関係を調査する実験を行った。ここで、「半価幅」は、Cr管球のKα線を用いて測定されたマルテンサイトに対応するピーク(142.3~170.2°)の半価幅を意味する。
拡散処理における雰囲気管理の必要性について確認する実験を行った。具体的には、SUJ2からなる試験片に浸炭窒化処理を行った後、αの値を変化させて拡散処理を実施し、表層領域の窒素濃度に及ぼすαの値の影響を調査する実験を行った。図18はαを0とした場合、図19はαを0.005とした場合の表面付近の窒素濃度分布を示している。
表面硬度と静的負荷容量との関係を調査する実験を行った。具体的には、SUJ2からなる試験片を準備し、浸炭窒化処理、拡散処理、焼入処理を同一条件で行った後、焼戻温度を変化させて表面硬度が異なるサンプルを作製した。そして、当該サンプルの表面硬度を測定するとともに、サンプルの表面に直径φ9.525mmの窒化珪素製のボールを一定の荷重で押し付け、圧痕を形成した。そして、形成された圧痕(荷重を除荷した後の残留圧痕)の深さを調査した。実験結果を図20に示す。図20において、横軸は表面負荷された応力、縦軸は圧痕の深さを示している。
転がり軸受の軌道輪の耐久性に及ぼす表層部の窒素濃度の影響を調査する実験を行なった。具体的には、軌道輪(内輪)の転走面に圧痕を形成した状態で転動疲労寿命試験を実施した。実験の手順は以下の通りである。
接触面における残留オーステナイト量と圧痕起点型剥離寿命との関係を調査する実験を行った。具体的には、表層領域の平均窒素濃度を一定(0.4質量%)とし、焼戻温度を変化させることにより残留オーステナイト量を変化させたサンプルを作製し、上記実施例5において説明した圧痕起点型剥離寿命試験を実施した。実験結果を図30に示す。図30において横軸は内輪の転走面における残留オーステナイト量、縦軸はL10寿命を示している。
部品全体の残留オーステナイト量と寸法安定性との関係を調査する実験を行なった。具体的には、外径φ:60mm、内径φ:54mm、軸方向長さt:15mmのSUJ2からなるリング状試験片を準備し、異なった条件で浸炭窒化処理等の熱処理を実施することにより、全体の平均残留オーステナイト量の異なる焼入硬化されたサンプルとした。サンプルの残留オーステナイト量分布を図31に示す。図31において横軸は表面からの距離、縦軸は残留オーステナイト量を示している。この図31に基づいてサンプル全体の平均残留オーステナイト量を算出した。図31の凡例において、「焼入温度-焼戻温度-表層領域の平均窒素濃度」が表示されている。たとえば、850℃-180℃-0.4mass%Nの表示は、焼入温度が850℃、焼戻温度が180℃、表層領域の平均窒素濃度が0.4質量%であることを示している。
上記実施例5において説明したように、十分な耐久性を軸受部品に付与するためには、表層領域における平均窒素濃度は0.2質量%以上とする必要がある。ここで、窒素濃度は、上述のように、たとえばEPMAにより確認することができる。しかし、軸受部品の量産プロセスにおいてEPMAを用いた品質確認を実施することは、品質確認作業を煩雑なものとする。そのため、量産プロセスにおける品質確認は、より簡便な方法により実施されることが望ましい。そこで、本発明者は鋼中に侵入した窒素が焼戻軟化抵抗を向上させることを利用して、品質確認を実施する方法を検討した。
Crを含有するJIS規格SUJ2などの軸受鋼は、浸炭窒化処理などにより鋼中に窒素を侵入させると、母材中のCr濃度が低下して、オーステナイト単相領域が拡大するため、炭素の固溶限濃度が上昇する。その結果、特に対策を講じることなく高濃度の(たとえば0.2質量%以上の窒素富化層を形成するような)浸炭窒化処理を施すと、脱炭は生じなくとも、炭化物(炭窒化物を含む)が減少または消失する。ここで、軸受部品の高強度化の観点からは、炭化物を残存させ、当該炭化物による析出強化機能を利用することが好ましいと考えられる。本実施の形態に係る軸受部品の製造方法では、ac *の値を0.88以上1.27以下に設定し、窒素富化層の炭素固溶限の上昇よりも早く浸炭を行うことで、炭化物の消失を抑制している。この炭化物残存の効果を確認する実験を行なった。図34は従来の浸炭窒化処理方法によりに浸炭窒化処理を実施したSUJ2からなるサンプルの断面SEM写真である。図34の写真では、炭化物がほとんど消失している。これに対し、図35は本実施の形態に係る軸受部品の製造方法において採用される浸炭窒化方法(ac *の値を1としたもの)により浸炭窒化処理を実施したSUJ2からなるサンプルの断面SEM写真である。図35の写真では、直径0.5μm以下の炭化物が100μm2あたりに5個以上存在している。
次に、内部の炭化物の面積率と異物混入潤滑寿命との関係について調査した。軸受鋼は、炭化物を溶け込ませることにより固溶強化することができる。焼入前の軸受鋼の炭化物の面積率は一定であるため、浸炭窒化処理後における内部の炭化物の面積率により炭素の固溶量を推測することができる。ここで、軸受の寿命に影響するのは研削後の表面の品質であるのに関わらず、内部の炭化物の面積率から母地中への炭素の固溶量を推測している理由は、浸炭窒化処理により表面が窒化されて炭素の固溶限濃度が上昇するため、母地への炭化物の固溶量を推測するのが困難だからである。表2に、熱処理条件と内部の析出物(炭化物)の面積率(%)との関係を示す。
Claims (13)
- 0.95質量%以上1.10質量%以下の炭素と、0.05質量%以上0.3質量%未満の珪素と、0.10質量%以上0.50質量%以下のマンガンと、1.30質量%以上2.00質量%以下のクロムとを含有し、残部鉄および不純物からなる鋼からなり、
他の部品と転がり接触する面である接触面から深さ20μm以内の領域である表層領域における平均窒素濃度が0.2質量%以上0.7質量%以下であり、
前記表層領域には、直径0.5μm以下の炭化物が100μm2あたり5個以上存在する、軸受部品。 - 表面から深さ20μm以内の領域全域において平均窒素濃度が0.7質量%以下である、請求項1に記載の軸受部品。
- 前記接触面の硬度は700HV以上である、請求項1または2に記載の軸受部品。
- 前記接触面における残留オーステナイト量が20体積%以上35体積%以下である、請求項1~3のいずれか1項に記載の軸受部品。
- 全体の平均残留オーステナイト量が18体積%以下である、請求項1~4のいずれか1項に記載の軸受部品。
- 500℃に1時間保持した後、前記接触面に垂直な断面において深さ方向に硬度分布を測定した場合、硬度の最大値と最小値との差が130HV以上である、請求項1~5のいずれか1項に記載の軸受部品。
- 前記表層領域には浸炭窒化層が形成されており、
前記浸炭窒化層が形成されていない領域における析出物の面積率が7%以下である、請求項1~6のいずれか1項に記載の軸受部品。 - 前記接触面以外の面に析出物が存在している、請求項1~7のいずれか1項に記載の軸受部品。
- 820℃以上900℃以下の温度で浸炭窒化処理を行うことにより前記表層領域が窒化されており、
前記浸炭窒化処理の後、170℃以上220℃以下の温度で焼戻処理が施されている、請求項1~9のいずれか1項に記載の軸受部品。 - 軌道部材と、
前記軌道部材に接触して配置される転動体とを備え、
前記軌道部材および前記転動体の少なくともいずれか一方は、請求項1~10のいずれか1項に記載の軸受部品である、転がり軸受。 - 0.95質量%以上1.10質量%以下の炭素と、0.05質量%以上0.3質量%未満の珪素と、0.10質量%以上0.50質量%以下のマンガンと、1.30質量%以上2.00質量%以下のクロムとを含有し、残部鉄および不純物からなる鋼からなる成形体を準備する工程と、
前記成形体を、アンモニア、一酸化炭素、二酸化炭素および水素を含む浸炭窒化雰囲気中で浸炭窒化温度に加熱することにより、前記成形体を浸炭窒化する工程と、
浸炭窒化された前記成形体を、アンモニア、一酸化炭素、二酸化炭素および水素を含む拡散雰囲気中で前記浸炭窒化温度以下の温度である拡散温度に保持することにより、前記成形体中の窒素を拡散させる工程とを備え、
未分解アンモニア分圧をPN、水素分圧をPHとし、ac *を以下の式(1)、αを以下の式(2)で定義した場合、前記浸炭窒化雰囲気におけるac *が0.88以上1.27以下、αが0.012以上0.020以下に設定され、前記拡散雰囲気におけるac *が0.88以上1.27以下、αが0.003以上0.012以下に設定される、軸受部品の製造方法。
- 前記成形体中の窒素を拡散させる工程よりも後に、前記成形体を170℃以上220℃以下の温度域に加熱して冷却する焼戻処理が実施される工程をさらに備えた、請求項12に記載の軸受部品の製造方法。
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