USRE48336E1 - Rolling apparatus - Google Patents

Rolling apparatus Download PDF

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Publication number
USRE48336E1
USRE48336E1 US16/398,979 US200716398979A USRE48336E US RE48336 E1 USRE48336 E1 US RE48336E1 US 200716398979 A US200716398979 A US 200716398979A US RE48336 E USRE48336 E US RE48336E
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United States
Prior art keywords
rolling
mass
hardness
life
raceway
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US16/398,979
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English (en)
Inventor
Koji Ueda
Toru Ueda
Naoya Seno
Nobuaki Mitamura
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NSK Ltd
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NSK Ltd
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Publication date
Priority claimed from JP2006148497A external-priority patent/JP5372316B2/ja
Priority claimed from JP2006150375A external-priority patent/JP4997832B2/ja
Priority claimed from JP2007107250A external-priority patent/JP5194532B2/ja
Priority claimed from JP2007112995A external-priority patent/JP5194538B2/ja
Application filed by NSK Ltd filed Critical NSK Ltd
Priority to US16/398,979 priority Critical patent/USRE48336E1/en
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Publication of USRE48336E1 publication Critical patent/USRE48336E1/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C21D1/06—Surface hardening
    • 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
    • C21D1/06—Surface hardening
    • C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
    • C21D1/10—Surface hardening by direct application of electrical or wave energy; by particle radiation by electric induction
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • 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
    • 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
    • C23C8/08—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 only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces
    • 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
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
    • F16C33/30—Parts of ball or roller bearings
    • F16C33/32—Balls
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • 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
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • F16C19/22—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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • F16C2202/00—Solid materials defined by their properties
    • F16C2202/02—Mechanical properties
    • F16C2202/04—Hardness
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • F16C29/00—Bearings for parts moving only linearly
    • F16C29/04—Ball or roller bearings
    • F16C29/06—Ball or roller bearings in which the rolling bodies circulate partly without carrying load
    • F16C29/0633—Ball or roller bearings in which the rolling bodies circulate partly without carrying load with a bearing body defining a U-shaped carriage, i.e. surrounding a guide rail or track on three sides
    • F16C29/0635—Ball or roller bearings in which the rolling bodies circulate partly without carrying load with a bearing body defining a U-shaped carriage, i.e. surrounding a guide rail or track on three sides whereby the return paths are provided as bores in a main body of the U-shaped carriage, e.g. the main body of the U-shaped carriage is a single part with end caps provided at each end
    • F16C29/0638—Ball or roller bearings in which the rolling bodies circulate partly without carrying load with a bearing body defining a U-shaped carriage, i.e. surrounding a guide rail or track on three sides whereby the return paths are provided as bores in a main body of the U-shaped carriage, e.g. the main body of the U-shaped carriage is a single part with end caps provided at each end with balls
    • F16C29/0642—Ball or roller bearings in which the rolling bodies circulate partly without carrying load with a bearing body defining a U-shaped carriage, i.e. surrounding a guide rail or track on three sides whereby the return paths are provided as bores in a main body of the U-shaped carriage, e.g. the main body of the U-shaped carriage is a single part with end caps provided at each end with balls with four rows of balls
    • F16C29/0647—Ball or roller bearings in which the rolling bodies circulate partly without carrying load with a bearing body defining a U-shaped carriage, i.e. surrounding a guide rail or track on three sides whereby the return paths are provided as bores in a main body of the U-shaped carriage, e.g. the main body of the U-shaped carriage is a single part with end caps provided at each end with balls with four rows of balls with load directions in X-arrangement
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S148/00—Metal treatment
    • Y10S148/902—Metal treatment having portions of differing metallurgical properties or characteristics
    • Y10S148/906—Roller bearing element

Definitions

  • the present invention relates to a rolling apparatus, such as a rolling bearing, a ball screw, a linear guide, and the like.
  • a rolling bearing such as a ball bearing, a cylindrical roller bearing, a conical roller bearing, a self-aligning roller bearing, a needle bearing, and the like, used in an environment involving harsh lubrication conditions as in; for instance, an automobile, construction machinery, agricultural machinery, an iron and steel fixture, and the like
  • a rolling bearing such as a ball bearing, a cylindrical roller bearing, a conical roller bearing, a self-aligning roller bearing, a needle bearing, and the like
  • a method proposed for solving the problem is to make an attempt to elongate flaking life by subjecting inner and outer rings and rolling elements to carburizing or carbonitriding, to thus precipitates a predetermined amount of retained austenite and relax the concentration of stress due to the indentation developed in the raceway surface (see Patent Document 1).
  • Bearing steel typified by JIS SUJ2 or SUJ3 has hitherto been used for a rolling bearing, and the steel is usually used at hardness HRC 60 or more after having undergone quenching and tempering treatment.
  • a content of C in the rolling surface layer of the bearing, the amount of retained austenite, and a content of carbonitride should be set to appropriate values even when the rolling bearing is used in the foreign substances contaminated lubrication environment, to thus relax the stress concentrated at an edge of indentation caused by the foreign substances, prevent occurrence of cracking, and extend the life of the rolling bearing (Patent Publication 1).
  • the present invention has been conceived in view of the drawbacks, such as those mentioned above, and aims at providing a rolling bearing apparatus which enhances flaking resistance, abrasion resistance, and seizure resistance to a much greater extent while preventing an increase in cost and which can extend its life even in a foreign substances contaminated lubrication environment.
  • the present inventors have carried out investigations in order to find out material factors which sufficiently ensure indentation-originated flaking life of the material (e.g., rolling elements); which enhances indentation resistance and abrasion resistance of the material; and which also extends the life of a partner member (e.g., a raceway ring) by preventing deterioration of surface roughness and surface geometry and reducing tangential force acting between two objects (the rolling elements and the raceway ring).
  • material factors e.g., rolling elements
  • a partner member e.g., a raceway ring
  • Si.Mn-based nitride an area percentage of nitride which is precipitated on a surface and which contains Si and Mn (hereinafter described as a “Si.Mn-based nitride”) are relevant material factors for enhancing indentation resistance and abrasion resistance, and has achieved the present invention.
  • the present invention provides the following rolling apparatus.
  • a rolling apparatus including:
  • a surface of at least one of the internal member, the external member, and the rolling elements is subjected to carbonitriding or nitriding,
  • an area percentage of a nitride containing Si and Mn is 1% or more and 20% or less
  • a hardness on a surface is HV750 or more
  • a concentration of nitrogen on a surface layer of at least one of the internal element, the external element, and the rolling elements is 0.2 mass % or more, and a number of nitride of which size is 0.05 ⁇ m to 1 ⁇ m and which contains Si and Mn in an area of 375 ⁇ m 2 is 100 or more.
  • At least one of the carbonitrided or nitrided internal member, external member, and rolling elements is made of steel which contains
  • a carbonitrided or nitrided member is the rolling elements.
  • At least one of the internal member and the external member is made of steel which contains:
  • At least one of the internal member and the external member is made of high-carbon chromium bearing steel.
  • a raceway surface of a raceway ring is made of high-carbon chromium bearing steel among the internal member and the external member, a surface layer section hardened by heat treatment including carburizing or carbonitriding is formed,
  • hardness of the surface layer section is HRC58 or more and HRC66 or less
  • hardness of an internal core of the surface layer section is HRC56 or more and HRC64 or less.
  • a surface nitrogen concentration on the raceway surface of the internal member and the external member is 0.05 mass % or less.
  • a Si content and a Mn content in the rolling elements is 1.0 mass % or more.
  • a rolling apparatus of the present invention enhances indentation resistance and abrasion resistance by defining the hardness of an internal member, the hardness of an external member, and the hardness of rolling elements which are achieved at a surface level and a specific depth and an area percentage of an Si.Mn-based nitride, thereby preventing an increase in tangential force between the rolling elements and the raceway ring during use of a bearing and enhancing flaking resistance strength.
  • FIG. 1 is a cross-sectional view of a deep groove ball bearing which is an example of a rolling apparatus
  • FIG. 2 is across-sectional view of a conical roller bearing which is another example of the rolling apparatus
  • FIG. 3 is a perspective view of a linear guide which is still another example of the rolling apparatus.
  • FIG. 4 is a cross-sectional view of a ball screw which is yet another example of the rolling apparatus
  • FIG. 5 is a graph showing a relationship between the distribution of static shearing force and yield pressure
  • FIG. 6 is a schematic view showing the structure of an indentation resistance test
  • FIG. 7 is a schematic view showing the structure of a two-cylinder abrasion test
  • FIG. 8 is a graph showing a relationship between surface hardness and indentation resistance
  • FIG. 9 is a graph showing a relationship between surface hardness and indentation resistance
  • FIG. 10 is a graph showing the influence of the concentration of surface nitride exerted on indentation resistance and abrasion resistance
  • FIG. 11 is a graph showing a relationship between the surface nitrogen concentration acquired through a Charpy impact test and absorbed energy
  • FIG. 12 is a graph showing the influence of an area percentage of a Si.Mn-based nitride exerted on indentation resistance and abrasion resistance;
  • FIG. 13 is an example electron microscope photograph of the surface of a rolling element at the time of measurement of an area percentage of the Si.Mn-based nitride;
  • FIG. 14 is a graph showing a relationship between the amount of nitride and an area percentage of the Si.Mn-based nitride
  • FIG. 15 is a graph showing a relationship between an area percentage of the Si.Mn-based nitride and indentation-originated flaking life
  • FIG. 16 is a graph showing a relationship between the area percentage of the Si.Mn-based nitride acquired through a Charpy impact test and absorbed energy;
  • FIG. 17 is a graph showing a relationship between the number of pieces of Si.Mn-based nitride measuring 0.05 to 1 ⁇ m and the life thereof;
  • FIG. 18 is a graph showing a relationship between the amount of Si+Mn and the indentation depth
  • FIG. 19 is an example analysis result of components of the Si.Mn-based nitride
  • FIG. 20 is a graph showing a relationship between the amount of retained austenite on a rolling element and the life thereof.
  • FIG. 21 is a graph showing a relationship between a ratio of a Si/Mn and the area percentage of the Si.Mn-based nitride.
  • a rolling bearing can be mentioned as an example of the rolling apparatus of the present invention. No limitations are imposed on the type and structure of a rolling bearing, and a deep groove ball bearing shown in FIG. 1 can be exemplified.
  • the deep groove ball bearing has an inner ring 1 (an internal member) having a raceway surface 1 a on an outer peripheral surface thereof; an outer ring 2 (an external member) having a raceway surface 2 a on an inner peripheral surface thereof opposing the raceway surface 1 a of the inner ring 1 ; balls which are rotatably provided between the raceway surfaces 1 a and 2 a and which correspond to a plurality of rolling elements 3 ; a cage 4 for retaining the rolling elements 3 between the inner ring 1 and the outer ring 2 ; and seals 5 and 5 for covering an opening of clearance between the inner ring 1 and the outer ring 2 .
  • Lubrication between the raceway surfaces 1 a and 2 a and rolling surfaces 3 a of the rolling elements 3 is embodied by lubricant 6 such
  • a conical roller bearing having bearing number L44649/610 such as that shown in FIG. 2
  • the rolling bearing wherein conical rollers serving as the rolling elements 3 are retained between the inner ring 1 and the outer ring 2 by the cage 4 .
  • an angular ball bearing, a cylindrical roller bearing, a self-aligning roller bearing, a needle roller bearing and the like are also available.
  • a linear guide such as that shown in FIG. 3
  • the linear guide 10 has a guide rail 11 (an internal member), a slider 12 (an external member) which is provided on a guide rail 11 and which is attached to the guide rail 11 so as to be movable in an axial direction, and a plurality of balls 13 serving as rolling elements.
  • a rail surface 14 is formed over an upper surface of the guide rail 11
  • rail raceway surfaces 15 , 16 for enabling slidable movement of the rolling elements 13 are formed in two rows; namely, one is an upper row and the other is a lower row, along either side surface of the guide rail 11 .
  • a bolt hole 17 vertically penetrating through the rail surface 14 is formed at a plurality of positions along the axial direction.
  • the guide rail 11 is secured to a machining bed.
  • slider raceway surfaces 19 for enabling slidable movement of the rolling elements 13 are formed in a rolling-element circulation channel 18 which retains the rolling elements 13 in a circulating manner.
  • a ball screw such as that shown in FIG. 4 , can also be exemplified as the rolling apparatus.
  • a ball screw 21 has a screw shaft 22 (an internal member) having a helical thread groove 22 a on an outer peripheral surface thereof; a ball screw nut 23 having a helical thread groove 23 a on an inner peripheral surface thereof corresponding to the thread groove 22 a of the screw shaft 22 and which is screw-engaged with the screw shaft 22 by way of a plurality of balls 24 serving as rolling elements which are fitted into a helical ball rolling space formed from the thread groove 22 a of the screw shaft 22 and the thread groove 23 a of the ball screw nut 23 (an external member) rotatably and which are spaced apart from each other with a spacer 26 sandwiched therebetween; and a circulator tube 25 .
  • the circulator tube 25 is for circulating the balls 24 rotatably in conjunction with the spacers 26 by rotation of either the screw shaft 22 or the ball screw nut 23 , and is attached to the ball screw
  • the balls 24 moving rotatably, through the ball rolling space travel through the ball rolling space along with the spacers 26 and are guided upwardly at one end of the circulator tube 25 after turning around the screw shaft 22 a plurality of times; and pass through the circulator tube 25 and return to the ball rolling space from the other end of the circulator tube, thereby repeating a circulation.
  • a cross-sectional profile of the thread grooves 22 a and 23 a can be selected appropriately, as required, and may also be realized as a Gothic arch; namely, an essentially-V-shaped form made by combination of two circular arcs whose curvature centers are different, or a circular-arc form.
  • the present invention is characterized in that the hardness of a material forming the internal members (the inner ring, the guide rail, and the screw shaft), the hardness of the external members (the outer ring, the slider, and the ball screw nut), and the hardness of the rolling elements (balls, conical rollers, and balls) of the rolling apparatus are specified.
  • a material factor which is most effective for enhancing indentation resistance is hardness.
  • the type of indentation includes foreign substance indentation generated as a result of biting of foreign substances and Brinell indentation which is formed as a result of rolling elements biting into a raceway ring when excessive load acts on the rolling apparatus, thereby flattening the rolling elements.
  • formation of indentation can be prevented by increasing the hardness of a neighborhood of the surface.
  • the hardness of a core of a material as well as the hardness of a surface thereof is important.
  • Indentation is formed by static shearing force (shearing force in a direction at an angle of 45° with respect to the direction of rolling) arising in a material as a result of the raceway ring contacting the rolling elements, thereby imposing load on the rolling elements.
  • a phenomenon of formation of indentation is caused by plastic deformation of the material. Hence, when yield shearing stress of the material is equal to or greater than the static shearing stress, indentation is not formed.
  • the load acting on the rolling bearing is usually designed so as to be come equal to or less than static rated load. Therefore, it is important for a material to have material strength which prevents formation of indentation even when static rated load acts on the material.
  • static rated load is defined as load which causes contact pressure of 4200 MPa for the case of a ball bearing, as well as being defined as load which causes contact pressure of 4000 MPa for the case of a rolling bearing. Indentation does not arise, so long as the static shearing force caused when the contact pressure has acted on the bearing is equal to or smaller than the yield shearing stress of a material of the bearing.
  • the surface hardness of at least one of the inner ring, the outer ring, and the rolling element is set to HV750 or more; preferably to HV800 or more; and more preferably to HV820 or more;
  • the surface hardness Hv of the rolling surface of the rolling element is preferably 750 or more, more preferably 800 or more, furthermore preferably 820 or more.
  • the most important fact or of a material for enhancing indentation resistance and abrasion resistance is surface hardness.
  • an indentation resistance test shown in FIG. 6 and a two-cylinder abrasion test shown in FIG. 7 were carried out.
  • the indentation resistance test was conducted by a method for pressing a steel ball having a diameter of 2 mm against a sample at 5 GPa and subsequently measuring the depth of an indentation.
  • the two-cylinder abrasion test was carried out under a method for rotating a drive side (a high-speed side) at 10 min ⁇ 1 under conditions including a contact pressure of 0.8 GPa; rotating a driven side (a low-speed side) at 7 min ⁇ 1 by reducing the speed with a gear, to thus forcefully impart slippage to both the drive side and the driven side.
  • a mean value of amounts of abrasion of the drive side acquired after elapse of 20 hours since initiation of the test and a mean value of amounts of abrasion of the driven side acquired after elapse of 20 hours since initiation of the test were measured.
  • FIG. 8 is a graph showing a relationship between surface hardness and an indentation resistance characteristic
  • FIG. 9 is a graph showing a relationship between surface hardness and an abrasion resistance characteristic.
  • carbonitriding is performed in order to enrich predetermined nitrogen on the surface layer of the raceway ring or the surface layer of the rolling elements.
  • nitrogen has also the property of forming a nitride or carbonitride to enhance the indentation resistance characteristic and the abrasion resistance characteristic, as well as having the property of intensifying solid-solution of martensite and stable securing of residual austenite.
  • FIG. 10 shows the influence of nitrogen exerted on the indentation resistance characteristic and the abrasion resistance characteristic determined by an indentation resistance characteristic test and a two-cylinder abrasion test analogous to those mentioned above.
  • An electron probe micro analyzer (EPMA) is used for measuring the amount of surface nitrogen.
  • EPMA electron probe micro analyzer
  • FIG. 10 shows that the abrasion resistance characteristic and the indentation resistance characteristic become superior with an increase in the surface nitrogen concentration. A noticeable effect appears when the surface nitrogen concentration exceeds 0.2 mass %.
  • the surface nitrogen concentration is set to more preferably 0.45 mass % or more.
  • FIG. 11 shows results of a Charpy impact test, and it is seen that a drastic drop arises in toughness when the concentration of nitrogen exceeds 2.0 mass %. Accordingly, the upper limit of the nitrogen concentration in the present invention is set to 2.0 mass %.
  • the indentation resistance characteristic and the abrasion resistance characteristic of the material are enhanced as the surface nitrogen concentration increases.
  • the present inventors also found that, even in the case of the same nitrogen concentration, the indentation resistance characteristic and the abrasion resistance characteristic change according to the state of presence of nitrogen in the material.
  • Nitrogen is present in two cases; namely, a case where nitrogen is present in the form of a solid solution within a material and a case where nitrogen is precipitated as a nitride.
  • a nitrogen content included in a material in the form of a solid solution becomes greater, even at the same concentration of nitrogen, than a nitrogen content in an Si.Mn-based nitride precipitated on the surface of the material when a material containing large amounts of Si and Mn is carbonitrided.
  • FIG. 12 shows area-percentage influence of the Si.Mn-based nitride exerted on the indentation resistance characteristic and the abrasion resistance characteristic determined by the indentation resistance characteristic test and the two-cylinder abrasion test analogous to those mentioned above.
  • hardness, the amount of residual austenite, and the concentration of nitrogen other than the area percentage of the Si.Mn-based nitride are made constant.
  • the rolling surface is observed at an accelerated voltage of 10 kV by use of a field emission scanning electron microscope (FE-SEM). After photographs of at least three visual fields (see FIG.
  • the abrasion resistance characteristic and the indentation resistance characteristic are superior as the area percentage of the Si.Mn-based nitride increases.
  • the area percentage of the Si.Mn-based nitride exceeds 1%, an effect noticeably appears.
  • an area percentage of 2% or more is more preferable.
  • Table 1 shows components of materials used in the test; steel type 1 is a material corresponding to JIS SUJ3; and steel type 2 is a material corresponding to JIS SUJ2.
  • the materials of Table 1 were machined into a disk of which diameter is 65 mm and thickness is 6 mm by turning process. After being subjected to carbonitriding in a gas mixture of an RX gas, a propane gas, and ammonium at 820 to 900° C.
  • the disk was subjected to oil hardening and subsequently to tempering at 160 to 270° C. for 2 hours.
  • Specimens having various nitrogen concentrations were formed by changing a processing temperature, a processing time, and the flow rate of an ammonium gas. After heat treatment, the surfaces of the specimens were mirror-finished by polishing and lapping.
  • Table 2 shows a relationship among the concentration of nitrogen, an area percentage of the Si.Mn-based nitride, and life achieved after contamination. Results of the life test are provided as ratios on condition that life L10 of a comparative example 1 is taken as 1.
  • FIG. 14 shows a relationship between the nitrogen concentrations of the steel types 1 and 2 and the area percentage of the Si.Mn-based nitride
  • FIG. 15 shows a relation between the area percentage of the Si.Mn-based nitride and indentation-originated flaking life.
  • the amount of the Si.Mn-based nitride precipitated is understood to increase in proportion to the concentration of nitrogen.
  • larger amounts of precipitated Si.Mn and longer life are achieved by the steel doped with larger amounts of Si and Mn.
  • life is considerably elongated when the area percentage of the Si.Mn-based nitride comes to 1 percent or more and when the nitrogen amount comes to 0.2 mass %.
  • FIG. 16 shows results of a Charpy impact test, and it is seen that a drastic drop arises in toughness when the area percentage of the Si.Mn-based nitride exceeds 20%. Accordingly, the upper limit of the area percentage of the Si.Mn-based nitride in the present invention is 20%, more preferably 10%.
  • Nitride whose size exceeds 1 ⁇ m does not much contribute to strength of the material.
  • the material is strengthened when fine particles of nitride are dispersed.
  • the reason for this is that, since a precipitation having a smaller particle-to-particle distance exhibits superior strengthening capability according to a theory of strengthening precipitation, the particle-to-particle distance becomes relatively shortened and intensified even at the same area percentage of the Si.Mn-based nitride when the number of precipitated particles is large.
  • the Si.Mn-based nitride measuring 0.05 ⁇ m to 1 ⁇ m is preferably 100 or more within an area of 375 ⁇ m 2 .
  • a technique for achieving this state is preferably to set a carbonitriding temperature within a range from 800° C. to 870° C. When the temperature is exceeded, the nitride becomes bulky, so that the number of fine Si.Mn-based nitride particles is decreased. Moreover, when the temperature exceeds the processing temperature, the solubility limit of nitrogen becomes greater, and hence the amount of nitride becomes smaller, whereby there may arise a case where a desired area percentage cannot be obtained.
  • Table 3 shows a relationship between an area percentage of the Si.Mn-based nitride and the number and life ratio of the Si.Mn-based nitride measuring 0.05 ⁇ m to 1 ⁇ m
  • FIG. 17 shows, in the form of a graph, a relationship between an area percentage of the Si.Mn-based nitride and the number and life ratio of the Si.Mn-based nitride measuring 0.05 ⁇ m to 1 ⁇ m.
  • a base structure is strengthened as a result of lob Si.Mn-based nitride particles or more being dispersed over a measured area of 375 ⁇ m 2 , and longer life is achieved despite of contaminated lubrication.
  • rolling elements should contain elements provided below.
  • Carbon is an element which is important for ensuring required strength and life of steel.
  • a carbon content is set to 0.3 mass % or more, preferably 0.5 mass % or more.
  • a carbon content is preferably 0.95 mass % or more.
  • the upper limit of the carbon content is set to 1.2 mass %, preferably 1.10 mass %.
  • a steel material having a high Si content and a high Mn content must be used.
  • SUJ2 which is a common bearing material has 0.25% of Si content and 0.4% of Mn content. Even when nitrogen is excessively added to the material by carbonitriding, Si.Mn-based nitride content is low. Therefore, in relation to the Si content and the Mn content, the following values are taken as critical values.
  • Si is an element which is necessary to precipitate an Si.Mn-based nitride.
  • Si By presence of Si; namely, by addition of 0.3 mass % or more of Si, Si effectively reacts with Mn, to thus become noticeably precipitated.
  • the Si content is set preferably to 0.4 to 0.7 mass %.
  • Mn is an element necessary to precipitate an Si.Mn-based nitride.
  • Si namely, addition of 0.3 mass % or more of Mn
  • Mn exhibits the property of promoting precipitation of an Si.Mn-based nitride.
  • Mn has the property of stabilizing austenite.
  • the Mn content is set to 2.0 mass % or less in order to prevent occurrence of a problem of the amount of austenite still remaining after hardening heat treatment increasing more than necessary.
  • the Mn content is preferably set to 0.9 to 1.15 mass %. More preferably, an Si/Mn ratio is set to a value of five or less for reasons provided below.
  • the Si.Mn-based nitride is formed as a result of nitrogen intruded during carbonitriding process reacting with Si while taking in Mn within a domain of austenite. Accordingly, when an additive amount of Mn is smaller than an additive amount of Si, precipitation of the Si.Mn-based nitride is not promoted even when nitrogen is sufficiently diffused.
  • Cr is an element which enhances hardenability and which is used for forming a carbide; promotes precipitation of a carbide which strengthens a material; and further miniaturizes the precipitate further.
  • the Cr content is less than 0.5 mass %, hardenability is deteriorated, to thus fail to achieve sufficient hardness or make a carbide bulky during carbonitriding process.
  • the Cr content exceeds 2.0 mass %, a Cr oxide film is formed over the surface of the material during carbonitriding, thereby hindering diffusion of carbon and nitrogen.
  • the Cr content is preferably set to 0.5 mass % to 2.0 mass %; more preferably 0.9 mass % to 1.2 mass %.
  • At least one type of element selected from Mo, Vi, and V may also be added, as necessary.
  • Mo is an element which enhances hardenability and which is used for forming a carbonitride, and has the property of promoting precipitation of a carbide, a carbonitride, and a nitride which strengthens a material and miniaturizes the precipitates further.
  • An effect of Mo becomes noticeable when 0.2 mass % or more of Mo is added.
  • the Mo content is preferably set to 0.2 mass % to 1.2 mass %.
  • Ni has the property of enhancing toughness as well as hardenability, and an effect of Ni becomes noticeable when 0.5 mass % or more of Ni is added.
  • Ni is an element which stabilizes austenite. When 3.0 mass % or more of Ni is added, residual austenite becomes excessive, and the hardness of a core decreases. Accordingly, the Ni content is preferably set to 0.5 mass % to 3.0 mass %.
  • V has the property of forming a hard carbide or carbonitride by carbonitriding, thereby enhancing the abrasion resistance characteristic. This effect becomes noticeable when 0.5 mass % or more of V is added. When 1.5 mass % or more of V is excessively added, V combines with solid-solution carbon of the material to form a carbide, thereby decreasing hardness of the material. Accordingly, the V content is preferably set to 0.5 mass % to 1.5 mass %.
  • ⁇ r AB when the amount of retained austenite on the raceway surfaces of the inner and outer rings is taken as ⁇ r AB and when the amount of retained austenite on the rolling surface of the rolling elements is taken as ⁇ r C , setting of ⁇ r AB ⁇ 15 ⁇ r C ⁇ r AB +15 (0 ⁇ r AB , ⁇ r C ⁇ 50) is preferable.
  • a unit of the amount of retained austenite is vol. %.
  • the indentation resistance characteristic and the abrasion resistance characteristic are enhanced.
  • the flaking life is extended.
  • the indentation resistance characteristic and the abrasion resistance characteristic of the rolling elements are enhanced with a decrease in the amount of austenite on the surface of the rolling elements.
  • the life of the raceway ring is extended, the life of the rolling elements decreases. Accordingly, although austenite is present on the rolling elements in amount optimum for rendering the life of the bearing longest, the optimum range of residual austenite varies according to the amount of retained austenite on the raceway ring.
  • the amount of retained austenite on the raceway ring when the amount of retained austenite on the raceway ring is large, the amount of retained austenite on the rolling elements must also be increased.
  • the range of the amount ( ⁇ r C ) of retained austenite on the rolling elements for achieving the longer life of the bearing varies according to the amount ( ⁇ r AB ) of retained austenite on the raceway ring, and hence setting of ⁇ r AB ⁇ 15 ⁇ r C ⁇ r AB +15 (0 ⁇ r AB , ⁇ r C ⁇ 50) is preferable.
  • the upper limit for the amount of residual austenite is set to 50 vol. %.
  • At least one of the inner and outer rings is preferably formed from high-carbon chromium bearing steel; for instance, SUJ2 or SUJ3 specified by Japanese Industrial Standard JIS G4805. Since the quality of the high-carbon chromium bearing steel, including an index of cleanliness of steel, is considerably stable, the raceway ring formed from the high-carbon chromium bearing steel is less vulnerable to internally-originated flaking which originates from inclusions and the like, and the sufficient life of the rolling bearing can be ensured. Moreover, since the material is the high-carbon chromium steel, the hardness of the raceway ring from its surface to core can be made high by appropriately quenching and tempering the steel.
  • the quality of the high-carbon chromium bearing steel is preferably of a level (bearing quality) satisfying a cleanliness regulation stipulated by Japanese industrial Standard JIS G4805.
  • a cleanliness regulation stipulated by Japanese industrial Standard JIS G4805.
  • use of SUJ2 is preferable because of superior ease of machining achieved when the steel is taken as a raw material, ease of machining achieved after heat treatment of the steel, low cost of the raw material, and the like.
  • the hardness of the surface layer section formed on the raceway surface is preferably HRC58 or more, and the hardness of an inner core of the surface layer section is preferably HRC56 or more. Further, both the hardness of the surface layer section and the hardness of the core are preferably HRC60 or more.
  • the hardness of the surface layer section is preferably HRC66 or less and more preferably HRC64 or less.
  • the hardness of the core is preferably HCR64 or less.
  • the surface layer section used herein designates an area extending from a surface to a depth of 200 ⁇ m.
  • Nitrogen is present in the form of a nitride as well as in the form of a precipitated nitride.
  • the indentation resistance characteristic is enhanced as a result of an increase in the amounts of Si and Mn in a raw material; especially, when Si and Mn are of 1.0 mass % or more, the indentation resistance characteristic is enhanced conspicuously.
  • the indentation resistance characteristic is enhanced further even at the same level of the nitrogen concentration when Si and Mn are present in the form of an Si.Mn-based nitride having higher hardness rather than when nitrogen is present in the form of a solid solution in a base structure.
  • FIG. 18 shows results of the indentation resistance characteristic tests analogous to that mentioned above which were performed while quantities of Si and Mn in samples were changed.
  • the nitrogen concentration is essentially constant at about 0.3 mass %.
  • the indentation resistance characteristic is enhanced with an increase in the quantities of Si and Mn in a raw material.
  • the amounts of Si and Mn exceed 1.0 mass %, the indentation resistance characteristic is enhanced noticeably. Therefore, in order to make a raw material less vulnerable to indentation, it is better to set the amounts of Si and Mn in a raw material to 1.0 mass % or more.
  • FIG. 19 shows example results of analysis of components of the Si.Mn-based nitride.
  • Test conditions are as follows:
  • High-carbon chromium bearing steel (SUJ2) was used for inner and outer rings of the test bearing, and the bearing was subjected to carbonitriding for 1 to 3 hours at 830 to 850° C. in an atmosphere consisting of an RX gas, an enriched gas, and an ammonium gas. Subsequently, the bearing was subjected to tempering at 180 to 240° C., whereby three types of bearings: one type of bearing including about 10 vol. % of retained austenite on the raceway surfaces of the inner and outer rings; another type of bearing including about 20 vol. % of retained austenite on the raceway surfaces of the inner and outer rings; and the other type of bearing including about 30 vol. % of retained austenite on the raceway surfaces of the inner and outer rings.
  • SUJ2 High-carbon chromium bearing steel
  • the surface of the rolling elements was directly subjected to analysis and measurement.
  • the rolling surface was observed at an accelerated voltage of 10 kV by use of the field emission scanning electron microscope (FE-SEM). After capture of photographs of at least three visual fields (see FIG. 13 ) at a 5000 magnification, the photographs were binarized, and an area percentage was computed by use of the image analyzer. A value of 0.045 d and a value of 0.18 d were measured in relation to the surface hardness of the rolling elements.
  • Table 4 shows results of life tests of the respective bearings of the examples and the comparative examples.
  • the life tests were performed twelve times for each of the test bearings, thereby studying a life time lasting until occurrence of flaking, preparing a Weibull plot, and determining life L10 from a result of the Weibull distribution.
  • the thus-determined life is taken as a life value.
  • Life is provided in the form of a value of a ratio on condition that the life of a first comparative example having the shortest is taken as one.
  • FIG. 20 shows a relationship between the amount of retained austenite on the rolling surface of the rolling elements and a life ratio, which is acquired when the residual austenite on the raceway surface of the raceway ring is 10, 20, and 30 vol. %.
  • the bearing tends to exhibit longer life.
  • the life is dependent on the amount of retained austenite on the raceway surface of the rolling elements.
  • the amount of residual austenite on the rolling elements being defined so as to fall within the range of the present invention, the entire bearing achieves longer life.
  • the amount of residual austenite on the rolling elements is less than the range of the present invention, all of the rolling elements become broken.
  • ratio example 1 1.01 0.56 1.10 1.10 0.51 795 777 734 0.37 2.02 140 10 10 2.5 example 2 0.30 0.60 1.00 1.10 0.60 769 653 405 0.40 2.35 139 10 10 2.1 example 3 1.20 0.50 0.90 1.00 0.56 790 779 752 0.40 2.51 141 10 10 2.5 example 4 1.01 0.30 0.70 1.00 0.43 786 765 733 0.40 1.80 138 10 10 2.2 example 5 0.99 2.20 1.00 0.93 2.20 810 772 726 0.45 2.95 145 10 10 2.6 example 6 0.98 0.50 0.30 0.95 1.67 780 761 735 0.47 1.92 143 10 10 2.1 example 7 1.03 1.00 2.00 0.92 0.50 822 776 736 0.44 3.21 149 10 10 2.5 example 8 1.10 0.40 1.15 1.20 0.35 824 754 747 0.42 3.46 155 10 10 2.6 example 9 0.89 0.70 0.90 0.90 0.78 826 738 693 0.46 3.66 166 10 10 2.7 example 10 1.06
  • Table 5 shows, in relation to each of the steels, chemical components, Si/Mn ratio, the concentration of nitrogen, an area percentage of Si.Mn-based nitride, and the number and life of Si.Mn-based nitride of 0.05 ⁇ m to 1 ⁇ m. Life is shown as a ratio on condition that the life L10 of a comparative example 6 (corresponding to SUJ2) is taken as 1.
  • FIG. 21 shows, in the form of a graph, a relationship between the Si/Mn ratio and the area percentage of the Si.Mn-based nitride in the table.
  • the eighth and ninth comparative examples use the steels falling within the range of the present invention and also adopt the nitrogen concentration set to 0.2 mass % or more, the Mn content is smaller than the Si content, and the amount of deposited Si.Mn-based nitride is an area percentage of less than one percent. As is obvious from FIG. 21 , precipitation of the Si.Mn-based nitride can be promoted by setting the Si/Mn ratio to a value of five or less.
  • a conical roller bearing (bearing number L44649/610) was prepared.
  • the inner and outer rings were formed from high-carbon chromium bearing steel (SUJ2) and subjected to heat treatment including carbonitriding, and carburizing or quenching and tempering.
  • carbonitriding the rings were held at 830 to 850° C. for 1 to 3 hours in an atmosphere consisting of the RX gas, the enriched gas, and the ammonium gas.
  • carburizing the rings were held at 830 to 850° C. for 1 to 3 hours in an atmosphere consisting of the RX gas and the enriched gas.
  • quenching the rings were held at 830 to 850° C.
  • the rings were left to cool after held at 180 to 240° C.
  • the amount of retained austenite on the raceway surfaces of the inner and outer rings is set to 10, 20 and 30 vol. %.
  • the inner and outer rings were formed from wp case-hardened steel SCr420 and subjected to heat treatment carburizing and tempering.
  • carburizing the rings were held at 920 to 950° C. for 3 to 8 hours in an atmosphere consisting of the RX gas and the enriched gas and then subjected to oil cooling.
  • tempering the rings were held at 180 to 240° C. and subsequently left to cool.
  • the steels having the compositions shown in Table 6 were used for the rolling elements, and member having the shape of a conical roller were manufactured from a steel wire by header machining and rough grinding.
  • the members were subjected to carbonitrided quenching at 830° C. for 5 to 20 hours in an atmosphere consisting of the RX gas, the enriched gas, and the ammonium gas, and subsequently to tempering at 180 to 270° C.
  • the members were subjected to processing pertaining to post-processes, such as finishing, whereby rolling elements were obtained.
  • the surface hardness HRC the hardness of the surface layer section of the raceway surface of the raceway ring
  • the hardness HRC of the core of the raceway ring core hardness
  • the surface hardness Hv the hardness of the surface layer section of the rolling surface of the rolling element
  • the concentration of nitrogen on the surface layer section of the rolling element the amount of the Si.Mn-based nitride deposited on the surface layer section of the rolling element (an area percentage).
  • the concentration of nitrogen was measured by use of the electron probe micro analyzer (EPMA). Further, the amount of retained austenite on the surface layer was measured by X-ray diffraction. In either case, the surface of the rolling elements was directly subjected to analysis and measurement.
  • the amount of the Si.Mn-based nitride was measured by use of the field emission scanning electron microscope (FE-SEM). Specifically, the rolling surface was observed at an accelerated voltage of 10 kV; photographs of at least three visual fields at a 5000 magnification; the photographs were binarized; and the amount of the Si.Mn-based nitride was computed in the form of an area percentage by use of the image analyzer. Hardness was measured by a hardness meter. Results are provided in Table 6.
  • the conical roller bearings were subjected to the life test and an excessive static load-carrying test.
  • the life test was conducted by rotating the conical roller bearings in the environment of lubrication contaminated with foreign substances and under the following conditions. A rotation time elapsing until flaking arises in the raceway surface of the raceway ring or the rolling surface of the rolling elements is taken as life. Twelve bearings were tested for one type of bearing, and a Weibull plot was prepared. Life L10 was determined from a Weibull distribution of results, and the thus-determined life was taken as life. Table 6 shows results, but the results are provided as relative values acquired when the life of the eighteenth comparative example having the shortest is taken as one.
  • the excessive static load-carrying test was conducted by exerting 32 kN of radial load on the conical roller bearing analogous to that used in the life test for 30 seconds, thereby causing permanent deformation in the raceway ring and the conical roller. After removal of the load, the permanent deformation occurred in the inner ring and the permanent deformation occurred in the center of the conical roller were measured. A sum of the amounts of permanent deformation of both the inner ring and the conical roller was computed, and the thus-computed sum was taken as the amount of permanent deformation in the conical roller bearing. The amount of permanent deformation was measured by use of Form Talysurf manufactured by Talor Hobson Ltd. Table 6 shows results, but the results are provided as relative values acquired when the value of the seventeenth comparative example exhibiting the greatest amount of permanent deformation is taken as one.
  • ⁇ R designates the amount of retained austenite on a surface layer section, and a unit is vol. %.
  • (2) Surface hardness of a rolling surface is Vickers hardness Hv.
  • ⁇ R designates the amount of retained austenite on a surface layer section, and a unit is vol. %.
  • a unit of nitrogen concentration is mass %.
  • a unit of nitride amount (area percentage) is percent.
  • High-carbon chromium bearing steel (SUJ2) or chromium steel (SCr420) was used for the inner and outer rings, and steel having chemical components corresponding to SUJ3 was used for the rolling element except the amounts of Si+Mn.
  • materials corresponding to SUJ2 and SUJ3 were quenched in the atmosphere of the RX gas at 830 to 850° C. or subjected to carburizing or carbonitriding at 830 to 850° C. in the atmosphere consisting of the RX gas+the enriched gas+the ammonium gas (the ammonium gas is used for carbonitriding) for 1 hour to 20 hours.
  • the materials were subsequently tempered at 180 to 240° C.
  • SCr240 was subjected to secondary quenching at 800 to 850° C. and then to tempering at 150 to 200° C.
  • Table 7 shows the quality of raceway rings and rolling elements, which were used in the test, and results of the life test.
  • the electron probe micro analyzer (EPMA) was used for measuring the surface nitrogen concentration in the raceway surface and the rolling surface, thereby performing quantitative analysis.
  • JP-A-2006-148497 Japanese Patent Application
  • JP-2006-140111 Japanese Patent Application
  • JP-2006-150375 Japanese Patent Application
  • JP-2007-107250 Japanese Patent Application
  • JP-2007-112995 Japanese Patent Application

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JP5233305B2 (ja) * 2008-02-12 2013-07-10 日本精工株式会社 ころ軸受及びその製造方法
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