Classifications

• • 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
  • C21D9/36—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for balls; for rollers
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/34—Methods of heating
  • C21D1/42—Induction heating
• • 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
  • 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
  • C21D2221/00—Treating localised areas of an article
  • C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively
• • 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

Definitions

• the present invention concerns a bearing component for a rolling bearing or a sliding bearing, and a method for surface hardening at least one part of a surface of such a bearing component
• bearing components are through-hardened or carburized in order to meet technical requirements for different applications. Bearing components may namely be subjected to high contact stresses and wear when in use and thus require high hardness.
• Induction hardening is a heat treatment in which a metal component is heated to the ferrite/austenite transformation temperature or higher by induction heating and then quenched. The quenched metal undergoes a martensitic transformation, increasing the hardness and brittleness of the surface of metal component. Induction hardening may be used to selectively harden areas of a bearing component without affecting the properties of the component as a whole.
• US patent no. 4 949 758 discloses a process for hardening the interior surface of a long (8-32 feet i.e. 244 - 975 cm), thin-walled (wall thickness 1/8 to 1 ⁇ 4 inch, i.e. 3-6 mm), small inside diameter (11 ⁇ 4 to 31 ⁇ 4 inch, i.e.
• a sharp demarcation in hardness results in a short transition zone that causes an increased level of tensile residual stresses, while a smooth demarcation between the hardened surface and the non-hardened core, i.e. a transitional region in which the hardness decreases steadily with depth rather than abruptly, minimizes or eliminates any stresses in the material in that region. Additional stresses, which arise from the application when the bearing component is in use can be withstood much better. Such a steadily decreasing hardness profile may be obtained by carburizing the surface of the bearing component.
• Carburizing is a heat treatment process in which iron or steel is heated in the presence of another material that liberates carbon as it decomposes.
• the surface or case will have higher carbon content than the original material.
• the higher carbon content on the surface becomes hard, while the core remains soft (i.e. ductile) and tough.
• An object of the invention is to provide an improved non-through hardened bearing component.
• a bearing component having a flat or non-flat surface, i.e. an interior or exterior surface, at least one part of which has been surface hardened by induction heating.
• the surface namely comprises a martensitic microstructure produced by induction hardening using an electromagnetic induction coil followed by quenching using a quenching device.
• a longitudinal or transverse cross section of the bearing component through the surface exhibits a hardness H surfa ce at the surface and a hardness H C ore at the non-hardened core of the bearing component (i.e. in the non-hardened base metal of the bearing component.
• the hardness profile of the cross section exhibits a first region whose hardness is substantially equal to the hardness H surfa ce at said surface, a third region whose hardness is substantially equal to the hardness ⁇ re at the non- hardened core of the bearing component and a second region between said first and third regions.
• the hardness profile in the first region has an average hardness and the hardness profile in the third region has an average hardness Y 3 . If a line is drawn on the hardness profile in the second region between the points — - + k and
• the bearing component in the second region determined along the line decreases by less than 50 HRC per mm.
• At least one part of the surface of such a non-through hardened bearing component will exhibit increased surface hardness, increased wear resistance and/or increased fatigue and tensile strength.
• the induction hardening heat treatment used to produce such a bearing component is more energy efficient and cost effective than a carburizing heat treatment and it has a shorter cycling time and provides better distortion control than a carburizing heat treatment.
• properties, such as the hardness, microstructure and residual stress, of the at least one part of the interior surface may be tailored as desired for a particular application.
• k is 1.
• k is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.1 , 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9.
• the hardness of the bearing component in the second region determined along said line decreases by less than 30 HRC, less than 25 HRC, less than 20 HRC or less than 15 HRC per mm.
• the hardness H surface at the surface is between 55-75 HRC on the Rockwell scale, preferably between 58-63 HRC.
• the hardness H core at the non- hardened core of the bearing component is between 15-30 HRC.
• the first region extends from the surface to a depth of up to 6 mm below the surface preferably to a depth of 1-4 mm below the surface, i.e. the volume of material of increased hardness may extend to a depth of about 0.5-6 mm below the surface, preferably 1-2 mm below the surface.
• the bearing component has a contact surface that allows a relative movement between the bearing component and another component, e.g. a second bearing component.
• the contact surface comprises the at least one part that has been hardened.
• the at least one part essentially corresponds to the contact surface.
• the contact surface may constitute any of a raceway, a sliding surface, or at least a part of a guide flange or similar.
• the bearing component may be an inner ring.
• the bearing component may be an outer ring.
• the bearing component may be a rolling element, for instance a roller or a ball.
• the roller may be spherical, cylindrical, tapered, conical, or toroidal.
• the bearing component may for example be used in automotive, aerospace, mining, wind, marine, metal producing and other machine applications which require high wear resistance and/or increased fatigue and tensile strength.
• the bearing component may for example be at least part of a roller, plain bearing, bushing, journal bearing, sleeve bearing, slewing bearing or a rolling element bearing, such as a ball bearing or roller bearing.
• the rolling bearing may be any one of a cylindrical roller bearing, a spherical roller bearing, a toroidal roller bearing, a taper roller bearing, a conical roller bearing or a needle roller bearing.
• the bearing component comprises, or consists of a carbon or alloy steel with an equivalent carbon content of 0.40 to 1.10%, preferably a high carbon chromium steel.
• the bearing component comprises/consists of 50CrMo4 steel, 100Cr6 steel, or SAE 1070 steel.
• the present invention also concerns a method for surface hardening at least part of the surface of a bearing component.
• the method comprises the steps of heating the at least one part of the surface with an electromagnetic induction coil to the ferrite/austenite transformation temperature or higher by induction heating, maintaining the at least one part of the interior surface at that temperature in order to allow for sufficient heat transport below the surface resulting in a sufficient austenitization of the at least one part, and immediately quenching the at least one part of the surface in order to obtain a cross section of the bearing component through the surface which exhibits a hardness H surface at the surface and a hardness H core at the non-hardened core of the bearing component (i.e. in the non-hardened base metal of the bearing component.
• the hardness profile of the cross section exhibits a first region whose hardness is substantially equal to the hardness H surf ace at said surface, a third region whose hardness is substantially equal to the hardness H ⁇ re at the non- hardened core of the bearing component and a second region between said first and third regions.
• the hardness profile in the first region has an average hardness and the hardness profile in the third region has an average hardness Y 3 . If a line is drawn on the
• the hardness of the bearing component in the second region determined along the line decreases by less than 50 HRC per mm.
• in-homogeneous austenite is formed.
• heat is allowed to spread through the bearing component for a period of 10 seconds, 20 seconds, 30 seconds, 40 seconds, 50 seconds, 60 seconds, 70 seconds or more than 70 seconds so that homogeneous austenite is formed.
• the expression "in order to allow for sufficient heat transport below the surface resulting in a sufficient austenitization of the at least one part,” is therefore intended to mean for a time period sufficient for homogeneous austenite to form in the at least one part of the surface.
• the hardness of the bearing component in the second region determined along said line decreases by less than 30 HRC, less than 25 HRC, less than 20 HRC or less than 15 HRC per mm.
• k is 1. According to another embodiment of the invention k is 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.1 , 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9.
• an induction coil as used throughout this document with reference to the bearing component and method according to the present invention is intended to mean one or more induction coils.
• a plurality of induction coils operating in the same or a different manner, for example at the same or different frequencies, may for example be used to simultaneously or consecutively heat a plurality of parts of an exterior surface and/or an interior surface of a bearing component, or one or more parts of a plurality of the bearing components.
• the induction coil(s) may be arranged to surround one or more parts of a bearing component that is to be hardened or the entire mechanical component.
• the induction coil is removed from the bearing component, and a quenching device, such as a quench spray or ring, is used to immediately quench the at least one part of the surface that has been heat treated.
• a quenching device such as a quench spray or ring
• the bearing component is removed from the induction coil, and a quenching device, such as a quench spray or ring, is used to immediately quench the at least one part of the surface that has been heat treated.
• a quenching device such as a quench spray or ring
• the first region extends from the surface to a depth of up to 6 mm below the surface preferably to a depth of 1-4 mm below the surface.
• the bearing component may be any one of an inner ring or an outer ring.
• the bearing component may be a rolling element, for instance a roller or a ball.
• the roller may be spherical, cylindrical, tapered, conical, or toroidal.
• the roller may comprise a hole or a bore. In an embodiment of the invention, the hole or the bore may be hardened.
• the bearing component may for example be at least part of a roller, plain bearing, bushing, journal bearing, sleeve bearing, slewing bearing or a rolling element bearing, such as a ball bearing or roller bearing.
• the rolling bearing may be any one of a cylindrical roller bearing, a spherical roller bearing, a toroidal roller bearing, a taper roller bearing, a conical roller bearing, or a needle roller bearing.
• Figures 1 & 2 show the steps of a method according to an embodiment of the present invention
• Figure 3 shows a cross section of a bearing component according to an embodiment of the present invention
• Figures 4 & 5 show hardness profiles of a bearing component according to an embodiment of the present invention
• Figure 6 shows a comparison of hardness profiles obtained using carburization and induction hardening.
• Figure 1 schematically shows a rotationally symmetrical bearing component 10 manufactured from bearing steel, namely a cylindrical roller, in cross section.
• the roller 10 is, for example, made of 50CrMo4 steel and comprises a uniform circular cross section which extends all the way through the centre of the component in the longitudinal direction thereof.
• An electromagnetic induction coil 14 is used to harden at least one part of the exterior 10a, 10b of the roller 10.
• a source of high frequency electricity (about 1 kHz to 400 kHz) is used to drive a large alternating current through the induction coil 14.
• the relationship between operating frequency and current penetration depth and therefore hardness depth is inversely proportional, i.e. the lower the frequency the greater the hardness depth.
• the passage of current through the induction coil 14 generates a very intense and rapidly changing magnetic field, and the part of the exterior surface 10a, 10b to be heated is placed within this intense alternating magnetic field. Eddy currents are generated within that part of the exterior surface 10a, 10b and resistance leads to Joule heating of the metal in that part of the exterior surface 10a, 10b.
• the exterior surface 10a, 10b of the roller 10 is heated to the ferrite/austenite transformation temperature or higher by induction heating and preferably maintained at that temperature for 10-40 seconds.
• the induction coil 14 is then removed and a quenching device 16, such as a quench spray or ring is used to immediately quenching the at least one part of the exterior surface 0a, 10b that has been heat treated.
• a quenching device 16 such as a quench spray or ring is used to immediately quenching the at least one part of the exterior surface 0a, 10b that has been heat treated.
• the at least one part of the exterior surface 10a, 10b may for example be quenched to room temperature (20- 25°C) or to 0°C or less.
• the quenching device 16 is arranged to provide a water-, oil- or polymer-based quench to the heated exterior surface layer 10a, 10b whereupon a martensitic structure which is harder than the base metal of the roller 10 is formed.
• the microstructure of the remainder of the roller 10 remains essentially unaffected by the heat treatment and its physical properties will be those of the bar from which it was machined.
• a 60-200kW power supply a frequency of 20-60 kHz, preferably 10-30 kHz or 15-20 kHz a total heating time of 10-40 seconds and a quenching rate and time of 200l/min and quenching time of 40-70s respectively may be used to obtain a bearing component according to the present invention.
• Figure 2 shows the position of the quenching device 16 while quenching is taking place. It should be noted that at least one other part of the outside surface 10a, 10b of the roller 10 may alternatively be subjected to another surface hardening heat treatment, such as induction hardening, flame hardening or any other conventional heat treatment.
• another surface hardening heat treatment such as induction hardening, flame hardening or any other conventional heat treatment.
• roller 10 in the illustrated embodiment has been shown in a horizontal position with the induction coil 14 and quenching device 16 being inserted horizontally, it should be noted that the roller 10 may be oriented in any position.
• An induction coil 14 and quenching device 16 may for be moved vertically into place from the same or different ends of the roller 10.
• An induction coil 14 may for example be vertically lowered into place and a quenching device may be vertically raised as the induction coil 14 is withdrawn by raising it vertically.
• Figure 3 shows a longitudinal cross section of the roller 10 after the heat treatment.
• Part 18 of exterior surface material 10a, 10b of the roller 10 comprises a martensitic microstructure produced by induction hardening using an electromagnetic induction coil 14 followed by immediate quenching using a quenching device 16.
• the method according to the present invention results in the formation of a transition zone visible in both hardness and in microstructure.
• the heat treated part 18 of the exterior surface material 10a, 10b may namely have a hardness within the range of 55-75 HRC on the Rockwell, preferably 59-63 HRC.
• the volume of material of increased hardness 18 may for example extend to a depth of up to 6 mm.
• Such a roller 10 may be used for any application in which a part of the exterior surface 10a, 10b is subjected to increased wear, fatigue or tensile stress.
• Figure 4 shows a hardness profile 22 of a longitudinal cross section of a bearing component according to an embodiment of the invention measured radially through a surface hardened region 18 in the direction of arrow 20 shown in figure 3.
• the hardness profile 22 exhibits a first region 24 whose hardness is substantially equal to the hardness Hsurface a the outer surface 10a, 10b of the bearing component 10, between 55-75 HRC, preferably between 58-63 HRC for example.
• the hardness profile 22 also comprises a third region 26 whose hardness is substantially equal to the hardness H core at the non- hardened core 10c of the bearing component 10, between 15-30 HRC for example.
• the hardness profile 22 also comprises a second region 25 between said first region 24 and the third region 26 in which the hardness profile exhibits a smooth transition between the hardness of the first region 24 and the third region 26, i.e. the hardness profile exhibits a transitional region in which hardness decreases steadily with depth below the surface rather than abruptly.
• the hardness profile in the first region 24 has an average hardness YL and the hardness profile in the third region 26 has an average hardness Y 3 , and if a line is drawn on the hardness profile in the second region 25 between the points
• the depth of the first region 24 and second region 25 may be chosen depending on the application in which the bearing component 10 is to be used.
• the dashed line in figure 4 shows a hardness profile 30 having a sharp demarcation between the hardness H surface at the outer surface 10a, 10b of the bearing component 10 and the hardness H core at the non-hardened core 10c of the bearing component 10 in which the hardness decreases by more than 50 HRC per mm.
• Figure 5 shows a hardness profile 22 obtained using the method according to the present invention and determined from measured hardness values (measured using Vicker's Hardness Test or any other suitable method).
• the values may be extrapolated to a depth of 0 mm in order to obtain the hardness H surfaC e at the outer surface 10a, 10b of the bearing component 10.
• the hardness of the bearing component 10 at a depth of 6-8 mm below the surface of the bearing component 10 may be considered to be the hardness ⁇ ⁇ at the non-hardened core 10c of the bearing component 10.
• Figure 6 shows a comparison between hardness profiles obtained using carburization 24, conventional induction hardening 26 and the method according to the present invention 22. It can be seen that the hardness profile resulting from conventional induction hardening 26 decreases abruptly in the transitional region corresponding to the second region 25, as shown in figure 4. It can also be seen that the hardness profile obtained using the method according to the present invention 22 decreases much more steadily with depth.
• a bearing component may be moved into position relative to a stationary induction device and/or quenching device.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Articles (AREA)
• Rolling Contact Bearings (AREA)

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• 2011
  • 2011-05-27 JP JP2013518315A patent/JP2013535623A/ja not_active Ceased
  • 2011-05-27 CN CN2011800391531A patent/CN103080344A/zh active Pending
  • 2011-05-27 US US13/808,071 patent/US20140144558A1/en not_active Abandoned
  • 2011-05-27 WO PCT/SE2011/000095 patent/WO2012002864A1/en active Application Filing
  • 2011-05-27 EP EP11801221.0A patent/EP2598663A1/en not_active Withdrawn

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