EP1512761A1 - Kontaktdruckbeständiges Bauteil und Verfahren zu seiner Herstellung - Google Patents

Kontaktdruckbeständiges Bauteil und Verfahren zu seiner Herstellung Download PDF

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Publication number
EP1512761A1
EP1512761A1 EP04019630A EP04019630A EP1512761A1 EP 1512761 A1 EP1512761 A1 EP 1512761A1 EP 04019630 A EP04019630 A EP 04019630A EP 04019630 A EP04019630 A EP 04019630A EP 1512761 A1 EP1512761 A1 EP 1512761A1
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EP
European Patent Office
Prior art keywords
mass
resistant member
contact pressure
rolling
steel material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP04019630A
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English (en)
French (fr)
Inventor
Keizo Otani
Nobuo Kino
Noriko Uchiyama
Takuro Yamaguchi
Toshimitsu Kimura
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Nissan Motor Co Ltd
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Nissan Motor Co Ltd
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Publication date
Application filed by Nissan Motor Co Ltd filed Critical Nissan Motor Co Ltd
Publication of EP1512761A1 publication Critical patent/EP1512761A1/de
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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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C21D1/78—Combined heat-treatments not provided for above
    • 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
    • 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
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces

Definitions

  • the present invention relates to an element useable as a power transmission part such as gears, bearings and rolling elements for a toroidal continuously variable transmission, which necessitates a high contact pressure strength. More specifically, this invention relates to a contact pressure-resistant member that is suitably used under relatively high contact pressure at a relatively high temperature ranging from about 120°C to about 300°C and in hydrogen generating atmosphere, and relates to a method of making the contact pressure-resistant member.
  • power transmission parts such as gears, bearings and rolling elements which are made of steels for machine structural use, for instance, JIS SCM420H (C: 0.17-0.23%, Si: 0.15-0.35%, Mn: 0.55-0.90%, P: not more than 0.030%, S: not more than 0.030%, Cr:0.85-1.25%, Mo: 0.15-0.35%, the substantial balance of Fe) and JIS SNCM420H.
  • the power transmission parts are formed by forging and machining, and heat-treated by carburizing, nitriding and carbonitriding for providing enhanced surface fatigue strength, and then case-hardened by quenching and tempering.
  • Japanese Patent Application First Publication No. 11-293392 discloses a carburized steel capable of preventing deterioration of its fatigue strength which is caused due to hydrogen.
  • the steel material contains C: 0.10-0.40 wt %, Si: 0.05-0. 50 wt %, Mn: 0.2-2.0 wt %, Ti: 0.05-0.20 wt %, A1: 0.010-0.50 wt %, N: not more than 0.0120 wt % and O: not more than 0.12 ppm and the balance of Fe and inevitable impurities.
  • the steel material may further contain at least one element selected from the group consisting of Ni: 0.10-2.0 wt %, Cr: 0.20-2.0 wt %, and Mo: 0.05-1.0 wt %.
  • the steel material has a microstructure in which Ti carbide and Ti carbonitride particles of not more than 70 nm in size are finely dispersed in the matrix. These precipitates trap hydrogen so that the steel material is improved in resistance to delayed fracture.
  • a temperature rise occurs at a rolling contact portion of power transmission parts which is in rolling contact with a counterpart.
  • WEC white etching constituent
  • WEC white etching constituent
  • the deterioration of surface fatigue strength is hereinafter referred to as hydrogen embrittlement.
  • the hydrogen is generated by chemical decomposition of components of lubricating oil used for the parts, and infiltrates into the material steel of the parts.
  • carburized steels capable of preventing softening of a hardened layer by increasing amounts of Si, Cr and Mo to be blended, in order to enhance surface fatigue strength.
  • high surface fatigue strength cannot be maintained.
  • the conventionally proposed carburized steels has such a problem that hydrogen trapped by precipitates (trap site) containing Ti is dissociated therefrom in a relatively-high to high temperature range, and therefore, deterioration of surface fatigue strength cannot be sufficiently suppressed.
  • An object of the present invention is to provide a contact pressure-resistant member for use in power transmissions including rolling elements such as gearings and bearings, and CVTs, which has excellent surface fatigue strength as compared to the conventionally proposed contact pressure-resistant members to thereby realize reduction of the size and weight and improvement in the torque capacity. Also, another object of the present invention is to provide a method of making the contact pressure-resistant member.
  • a contact pressure-resistant member comprising:
  • a contact pressure-resistant member having a rolling contact portion on a surface thereof, the rolling contact portion being adapted to come into rolling contact with a counterpart, the method comprising:
  • Figs. 1A to 1D are explanatory diagrams illustrating heat treatment patterns used in examples of the present invention.
  • Fig. 2 is a schematic diagram illustrating a thrust rolling fatigue tester used in examples of the present invention.
  • Fig. 3 is a schematic diagram illustrating a ball thrust bearing tester used in the examples of the present invention.
  • Figs. 4A and 4B are flowcharts illustrating a method of analyzing carbon concentration and nitrogen concentration, and a method of calculating a carbide area ratio and a mean carbide particle size, respectively.
  • a contact pressure-resistant member of the present invention is made of a steel material containing 0.15 to 0.40% by mass of C, 0.50 to 1.50% by mass of Si, 0.20 to 1.50% by mass of Mn, 0.50 to 1.50% by mass of Cr, and 0.05 to 0.50% by mass of Mo, 0.010% by mass or less of P, at least one element selected from the group consisting of 0.50 to 3.50% by mass of Ni, 0.03 to 0.20% by mass of Ti, 0.03 to 0.15% by mass of Nb and 0.01 to 0.10% by mass of A1, and the balance of Fe and inevitable impurities.
  • the contact pressure-resistant member has a rolling contact portion located on a surface thereof and adapted to come into rolling contact with a counterpart.
  • the rolling contact portion has a carbon concentration ranging from 0.8 to 1.2%.
  • a concentration ratio Cr/Si between Cr and Si may be in a range of 0.8 to 2.0% by mass, and a concentration ratio (Mn+Ni)/Mo of Mn+Ni to Mo may be 20 or less.
  • a V content may be in the range of 0.05 to 0.5% by mass.
  • C forms a solid-solution with ferrite to thereby enhance strength of the steel material and ensure quenching hardness of the steel material.
  • Si can act as a deoxidizing agent upon producing molten steel. Si increases hardenability of the steel material and maintains fatigue strength of the matrix under a relatively-high to high temperature condition. Si also enhances resistance to temper softening. Namely, Si inhibits deterioration of hardness of the steel material which is caused by tempering, to thereby improve fatigue strength of the steel material.
  • Mn can act as a deoxidizing agent upon producing molten steel, and increase hardenability of the steel material.
  • Cr increases hardenability and carburizing ability of the steel material.
  • Mo increases hardenability of the steel material. P segregates along the previous austenite grain boundaries upon carburizing or carbonitriding to thereby reduce interfacial cohesion of the previous austenite grain boundaries.
  • Ni maintains surface fatigue strength of the steel material.
  • Ti, Nb and A1 form precipitates for preventing coarse growth of crystal grains during carburizing or carbonitriding. Further, the precipitate containing Ti can trap hydrogen.
  • V forms one or both of carbide and carbonitride during heat treatment and effectively acts for strengthening the matrix microstructure of the steel material of the members subjected to quenching and tempering, to thereby suppress WEC.
  • the carbide and carbonitride of V more effectively traps hydrogen than the Ti-containing precipitate, and therefore, delays diffusion and accumulation of hydrogen in a stress-concentration portion of the members and prevents hydrogen embrittlement.
  • the C content is controlled to the range of 0.15 to 0.40% by mass.
  • the C content is preferably in the range of 0.16 to 0.40% by mass. If the C content is more than 0.40% by mass, the material will become too hard and thereby tends to be deteriorated in machinability.
  • the Si content is controlled to the range of 0.50 to 1.50% by mass. The Si content is preferably in the range of 0.50 to 1.25% by mass.
  • the Mn content is controlled to the range of 0.20 to 1.50% by mass.
  • the Mn content is preferably in the range of 0.20 to 1.31% by mass. If the Mn content is more than 1. 31% by mass, the material will become too hard and thereby tends to be deteriorated in workability. Further, in the case where the Mn content is more than 1. 31% by mass, a transformation termination time in which the material is subjected to annealing will be prolonged so that the production cost will be increased.
  • the Cr content is controlled to the range of 0.50 to 1.50% by mass.
  • the Cr content is preferably in the range of 0.50 to 1.31% by mass. If the Cr content is more than 1.31% by mass, the material will become too hard and thereby tends to be deteriorated in workability.
  • the Mo content is controlled to the range of 0.05 to 0.50% by mass.
  • the Mo content is preferably in the range of 0.05 to 0.45% by mass. If the Mo content is more than 0.45% by mass, the material will become too hard and thereby tends to be deteriorated in workability.
  • the P content is limited to 0.010% by mass or less.
  • the Ni content is controlled to the range of 0.50 to 3.50% by mass.
  • the Ni content is preferably in the range of 0.50 to 3.00% by mass. If the Ni content is more than 3.00% by mass, the material will become too hard and thereby tends to be deteriorated in workability.
  • the Ti content is controlled to the range of 0.03 to 0.20% by mass
  • the Nb content is controlled to the range of 0.03 to 0.15% by mass
  • the A1 content is controlled to the range of 0.01 to 0.10% by mass. If the Ti content, the Nb content and the A1 content are larger than the respective ranges, coarse precipitates will be grown to thereby cause deterioration in workability of the material.
  • the content of the selected one must be controlled to the range described above.
  • a combination of Ni, Ti, Nb and Al can be used. In such a case, the contents of the respective elements used in combination must be controlled to the range described above.
  • the C concentration of the rolling contact portion of the member must be controlled to the range of 0.8-1.2%.
  • a total concentration of C and N of the rolling contact portion is preferably in the range of 0.8-1.2%. This can suppress the WEC without deteriorating the effect of preventing hydrogen embrittlement.
  • the addition of Cr is essentially required as described above.
  • the addition amount of Cr increases, precipitation of cementite at the grain boundaries of austenite grains will remarkably occur during carburizing or carbonitriding.
  • the precipitation of cementite can be avoided by adding Si that serves for suppressing carburizing ability or carbonitriding ability of the material. Therefore, it is preferred to control a concentration ratio Cr/Si between Cr and Si to the range of 0.8-2.0.
  • Mo exhibits an effect of preventing embrittlement that occurs in a region of the previous austenite grain boundaries where the amount of microsegregation of Mn and Ni is small.
  • the concentration ratio (Mn + Ni)/Mo of Mn and Ni to Mo is preferably 20 or less.
  • the V content is preferably in the range of 0.05-0.40% by mass. If the V content is larger than the range, coarse precipitates will be grown in the matrix to thereby deteriorate workability of the material.
  • a concentration of carbon in the rolling contact portion which forms a solid solution of carbon and Fe may be in a range of 0.60 to 0.95% by mass.
  • the concentration of carbon forming a solid solution of carbon and Fe is hereinafter referred to as a solid-solution carbon concentration.
  • the solid-solution carbon concentration on the surface of the contact pressure-resistant member gives influences on the shape and grain size of a quenched structure, specifically, a martensite structure. Particularly, in order to suppress WEC, it is effective to produce a fine martensite structure containing a lath-shaped martensite and a lens-shaped martensite in a mixed state, by controlling the solid-solution carbon concentration to the range of 0.60 to 0.95% by mass.
  • the solid-solution carbon concentration is less than 0.60% by mass, the martensite structure is composed almost exclusively of the lath-shaped martensite so that the martensite structure is deteriorated in hardness due to a low hardness of the lath-shaped martensite. If the solid-solution carbon concentration is more than 0.95% by mass, the martensite structure is composed almost exclusively of the lens-shaped martensite so that the grain size of the martensite structure becomes coarse. As a result, in these cases where the solid-solution carbon concentration is out of the above-described range, WEC will occur, thereby causing deterioration of the rolling fatigue life of the contact pressure-resistant member.
  • the solid-solution carbon concentration (%) is calculated by the following formula (1). [carbon concentration (%) obtained by electron probe microanalyzer (EPMA)]-[carbide area ratio X 6.67 (%)]/100 Hz (1) Meanwhile, the calculation of the solid-solution carbon concentration will be in detail explained later.
  • the surface of the contact pressure-resistant member may contain carbide particles or carbonitride particles having a mean particle diameter of 1.2 ⁇ m or less.
  • the carbide particles or carbonitride particles effectively trap hydrogen to thereby cause delay in diffusion and accumulation of hydrogen to a stress-concentration portion of the contact pressure-resistant member. This can suppress rolling fatigue of the contact pressure-resistant member which is caused by hydrogen.
  • the mean particle diameter of the carbide particles or carbonitride particles is larger than 1.2 ⁇ m, substantially no effect of suppression of the rolling fatigue is exhibited.
  • the surface of the contact pressure-resistant member may have a carbide area ratio of a carbide-precipitated portion to the whole surface, in a range of 2 to 8%. If the carbide area ratio lies within the above-specified range, a rolling fatigue life of the contact pressure-resistant member can be increased. If the carbide area ratio is out of the above-specified range, the effect of increasing the rolling fatigue life will not be exhibited.
  • the rolling contact portion may have a Ni plating layer on at least a part thereof. Namely, a part of the rolling contact portion or the whole rolling contact portion may be formed with the Ni plating layer.
  • the Ni plating layer can prevent a neo-surface from being newly produced on the rolling contact portion by the catalytic action of a microscopic metal catalyst.
  • the Ni plating layer can act as a protective coat protecting the rolling contact portion from hydrogen infiltration. Hydrogen is generated by tribochemical reaction occurring during a relative rolling movement between the contact pressure-resistant member and a counterpart.
  • the Ni plating layer can prevent the hydrogen from infiltrating into the matrix of the steel material.
  • a thickness of the Ni plating layer is preferably in the range of 0.1 to 20 ⁇ m.
  • the contact pressure-resistant member may be applied to a rolling bearing for an automobile and a rolling element of a toroidal CVT.
  • the contact pressure-resistant member has the rolling contact portion on the surface which is brought into rolling contact with a counterpart during a relative rolling movement therebetween.
  • the method includes: subjecting a workpiece made of a steel material containing 0.15 to 0.40% by mass of C, 0.50 to 1.50% by mass of Si, 0.20 to 1.50% by mass of Mn, 0.50 to 1.50% by mass of Cr, and 0.05 to 0.50% by mass of Mo, 0.010% by mass or less of P, at least one element selected from the group consisting of 0.50 to 3.50% by mass of Ni, 0.03 to 0.20% by mass of Ti, 0.03 to 0.15% by mass of Nb and 0.01 to 0.10% by mass of A1, and the balance of Fe and inevitable impurities, to either carburizing or carbonitriding to control a carbon concentration on a surface of the workpiece, to a range of 0.8 to 1.2%; and subjecting the workpiece to quenching and temper
  • the carbon concentration on the surface of the workpiece, the solid-solution carbon concentration, and the carbide area ratio and the mean particle diameter of carbides can be respectively controlled to the desired ranges by carburizing or carbonitriding.
  • the nitrogen concentration on the surface of the workpiece also can be controlled to the desired range by carbonitriding.
  • the method may further include: holding at least a surface of the workpiece at a first temperature ranging from an Ac 1 transformation point to less than a temperature of an Acm transformation point plus 150°C, after the carburizing or carbonitriding; heating the workpiece to a second temperature ranging from 550°C to less than an Ar 1 transformation point, after holding the at least the surface of the workpiece at the first temperature; holding the workpiece at the second temperature; holding the workpiece at a third temperature ranging from the Ac 1 transformation point to less than the Acm transformation point; and subjecting the workpiece to rapid cooling.
  • the method may further include forming a Ni plating layer on at least a part of the surface of the workpiece which is adapted to act as the rolling contact portion of the contact pressure-resistant member.
  • the disk-shaped specimens and the inner and outer race-shaped specimens were subjected to carburizing or carbonitriding and quenching and tempering according to heat treatment patterns A-D as shown in Figs. 1A-1D.
  • the heat treatment patterns will be explained in detail later.
  • a rolling contact portion on a surface of each of the specimens which come into rolling contact with a counterpart of a rolling fatigue tester as described later was subjected to grinding and superfinishing to provide a surface roughness of about Ra 0.03 ⁇ m.
  • a Ni plating layer was formed on the rolling contact portion of the specimens in the following manner.
  • a Ni strike plating coat is formed on the rolling contact portion in Ni-based strike plating bath for 10 minutes at a current density of 2A/dm 2 .
  • the Ni plating layer was formed on the Ni strike plating coat in a Ni-based plating bath for 10 minutes at a current density of 2A/dm 2 until a thickness of the Ni plating layer reached 5 ⁇ m.
  • the specimens were obtained.
  • Figs. 1A-1D illustrate the heat treatment patterns A-D, respectively.
  • carburizing is performed within a gas carburizing furnace under the following conditions: temperature of 950°C, carbon potential (CP) of 1.1-1.3%, and carburizing time of 10-17 hours.
  • CP carbon potential
  • the temperature is lowered to 850°C and held at 850°C for 0.5 hour at CP of 0.9%.
  • oil quenching is performed in a 80°C oil, followed by tempering at 170°C for 2 hours.
  • the temperature is raised to 970°C in a vacuum atmosphere within a vacuum furnace and held at 970°C for 1 hour.
  • the temperature is then lowered to 650°C at a rate of 2.0°C to 15.0°C per minute and held at 650°C for 6 hours.
  • the temperature is raised to 880°C and held at 880°C for 0.75 hour, and then lowered to 830°C and held at 830°C for 0.5 hour.
  • Oil quenching is performed in an oil at 80°C, followed by tempering at 170°C for 2 hours.
  • the heat treatment pattern B shown in Fig. 1B is the same as described in the heat treatment pattern A, except that, instead of carburizing, carbonitriding is performed within a gas carburizing furnace under the following conditions: temperature of 950°C, CP of 1.1-1.3%, NH 3 of 3 vol %, and carburizing time of 10-17 hours.
  • the heat treatment pattern C shown in Fig. 1C differs in heat treatment subsequent to the tempering after the holding at 850°C, from the heat treatment pattern A.
  • the temperature is raised to 550°C in a vacuum atmosphere within a vacuum furnace and held at 550°C for 6 hours. Then, the temperature is raised to 880°C and held at 880°C for 0.75 hour, and then lowered to 830°C and held at 830°C for 0.5 hour. After that, oil quenching is performed in an oil at 80°C, followed by tempering at 170°C for 2 hours.
  • the heat treatment pattern D shown in Fig. 1D differs in heat treatment subsequent to the tempering after the holding at 850°C, from the heat treatment pattern A.
  • the temperature is raised to 880°C and held at 880°C within a gas carburizing furnace at CP of 1.0% for 1 hour.
  • secondary oil quenching is performed in an oil at 80°C, followed by tempering at 170°C for 2 hours.
  • the thus-prepared specimens were set to a thrust rolling fatigue tester and a thrust ball bearing tester and subjected to rolling fatigue test under the following conditions to evaluate the rolling fatigue life.
  • the evaluation of the rolling fatigue life was conducted using a vibration sensor to detect vibrations during rolling of the specimens, and measuring a time elapsed until flaking was caused on the disk-shaped specimen and either one of the inner race- and outer race-shaped specimens.
  • flaking was caused on power rollers of the testers during the rolling fatigue test, the power rollers were replaced with new ones and the rolling fatigue test was continued.
  • Fig. 2 shows the thrust rolling fatigue tester 1 to which disk-shaped specimen 10 is set to undergo the rolling fatigue test.
  • arrow A indicates a direction of compressive load.
  • Fig. 3 shows thrust ball bearing tester 2 to which inner race-shaped specimen 20 and outer race-shaped specimen 30 is set to undergo the rolling fatigue test.
  • arrow B indicates a direction of supply of lubricating oil.
  • the slide ratio at the end portion of the rolling contact ellipse was small so that the flaking due to WEC occurred.
  • thrust ball bearing tester 2 shown in Fig. 3 the slide ratio at the end portion of the rolling contact ellipse was remarkably large so that the flaking due to hydrogen embrittlement occurred.
  • the rolling fatigue test using thrust rolling fatigue tester 1 is hereinafter referred to as WEC rolling fatigue test
  • the rolling fatigue test using thrust ball bearing tester 2 is hereinafter referred to as hydrogen-embrittlement rolling fatigue test.
  • the specimens were subjected to measurements of surface carbon concentration (%), surface nitrogen concentration (%), mean carbide particle diameter ( ⁇ m), carbide area ratio (%) and solid-solution carbon concentration (%) in a surface portion of each of the specimens.
  • the surface carbon concentration and the surface nitrogen concentration were determined by a method of analyzing carbon concentration and nitrogen concentration.
  • the mean carbide particle diameter and the carbide area ratio were determined by a method of calculating the mean carbide particle diameter and the carbide area ratio.
  • Fig. 4A a flow of the method of analyzing carbon concentration and nitrogen concentration is explained. As illustrated in Fig. 4A, first, the specimen was cut. Subsequently, a surface of a cross section of the specimen cut was polished and then subjected to EPMA analysis. The EPMA analysis was conducted over a region extending from the cross sectional surface of the specimen to 0.1 mm in depth.
  • a flow of the method of calculating the mean carbide particle diameter and the carbide area ratio is explained.
  • the specimen was cut vertically, and then a surface of the vertical cross section of the specimen was polished.
  • the cross sectional surface of the specimen was subjected to etching with an etchant composed of 3% nitric acid alcohol solution.
  • a region of the cross sectional surface was observed using a scanning electron microscope (SEM) at the magnification of 10,000. The region had a depth of 0.1 mm from the outer surface of the specimen. The observation was conducted over the depth at intervals of 0.01 mm. Eleven fields of view were photographed, and then the photograph was subjected to image analysis.
  • SEM scanning electron microscope
  • the specimens were made of steel materials 1-8.
  • the steel materials 1-8 contain 0.15 to 0.40% by mass of C, 0.50 to 1.50% by mass of Si, 0.20 to 1.50% by mass of Mn, 0.50 to 1.50% by mass of Cr, and 0.05 to 0.50% by mass of Mo, 0.010% by mass or less of P, at least one element selected from the group consisting of 0.50 to 3.50% by mass of Ni, 0.03 to 0.20% by mass of Ti, 0.03 to 0.15% by mass of Nb and 0.01 to 0.10% by mass of A1, and the balance of Fe and inevitable impurities.
  • the specimens were subjected to the heat treatment pattern A or B.
  • Example 12 the specimens were made of steel material 3 and subjected to the heat treatment pattern D.
  • M 23 C 6 carbide was not precipitated because of a small amounts of Cr and Mo contained in the steel material.
  • Comparative Examples 1-2 the specimens were made of steel material 10 which had the Si content of less than 0.5% by mass as shown in Table 1. In these cases, the resistance to temper softening was reduced. Therefore, the flaking lives of the specimens were reduced in a relatively-high to high temperature condition in the WEC rolling fatigue test.
  • Comparative Example 3 the specimens were made of steel material 11 which had the Cr content of less than 0.5% by mass and the concentration ratio Cr/Si of less than 0.8% as shown in Table 1. The specimens had a small amount of carbide precipitated and a solid-solution carbon concentration of more than 0.95%. In this case, the flaking lives of the specimens were reduced in the WEC rolling fatigue test.
  • Comparative Example 4 the specimens were made of steel material 12 which had a concentration ratio (Mn+Ni)/Mo of more than 20 as shown in Table 1. Therefore, the amount of microsegregation of Mn and Ni became too large relative to Mo. Crack occurred from the segregation boundary of Mn and Ni upon high pressure being applied to the rolling contact portions of the specimens. As a result, the flaking lives of the specimens were reduced in both of the WEC rolling fatigue test and the hydrogen embrittlement rolling fatigue test.
  • the specimens were made of steel materials 13-15 which had a Ti content, a Nb content or an Al content larger than the specified range of the present invention as shown in Table 1. In these cases, coarse particles of carbide or nitride were precipitated along grain boundaries. The solid-solution carbon concentration was less than 0.6%, and therefore, the flaking lives of the specimens were not greatly improved in both of the WEC rolling fatigue test and the hydrogen embrittlement rolling fatigue test.
  • the specimens were made of steel material 16 which had a P content of more than 0.01% by mass as shown in Table 1. In this case, the amount of P segregated along grain boundaries was increased. Therefore, the flaking lives of the specimens were reduced in the hydrogen embrittlement rolling fatigue test.
  • Comparative Example 9 the specimens were made of steel material 3 having the specified composition of the present invention, but the carbon concentration in the rolling contact portion thereof was more than 1.2%. In this case, coarse particles of carbide were precipitated along grain boundaries, and the solid-solution carbon concentration was reduced. As a result, the flaking lives of the specimens were reduced in both of the WEC rolling fatigue test and the hydrogen embrittlement rolling fatigue test.
  • Comparative Examples 10-11 the specimens were made of steel material 11 which composition was out of the range specified by the present invention as shown in Table 1, but the rolling contact portion thereof had a carbon concentration of 0.8-1.2% by using the heat treatment pattern C.
  • the step of holding at 970°C after carburizing, quenching and tempering was omitted.
  • the M 3 C carbide precipitated along grain boundaries during the primary carburizing and quenching step made it difficult to form the solid solution in the matrix again. Therefore, the carbon concentration at and near grain boundaries became larger than that within the crystal grain, so that M 23 C 6 carbide was able to be readily precipitated at and near the grain boundaries.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Heat Treatment Of Articles (AREA)
  • Rolling Contact Bearings (AREA)
  • Gears, Cams (AREA)
  • Friction Gearing (AREA)
EP04019630A 2003-08-28 2004-08-18 Kontaktdruckbeständiges Bauteil und Verfahren zu seiner Herstellung Withdrawn EP1512761A1 (de)

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JP2003209275A JP2005068453A (ja) 2003-08-28 2003-08-28 耐高面圧部品及びその製造方法

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EP2514844A3 (de) * 2011-04-22 2014-03-26 Jtekt Corporation Wälz-Gleitelement, Herstellungsverfahren dafür und Wälzlager
EP2889394A3 (de) * 2013-12-26 2015-09-02 Doosan Infracore Co., Ltd. Gussstahl für baumaschinenausrüstungs-schaufelteile und teile für baumaschinenschaufel damit

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CN102383136B (zh) * 2011-11-17 2015-05-06 国家电网公司 输电线路杆塔钢材的热处理工艺
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EP2746409A1 (de) * 2012-12-21 2014-06-25 Voestalpine Stahl GmbH Verfahren zum Wärmebehandeln eines Mangan-Stahlprodukts und Mangan-Stahlprodukt mit einer speziellen Legierung
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JP6410613B2 (ja) * 2015-01-08 2018-10-24 日産自動車株式会社 耐焼付性に優れた浸炭部材
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KR101705168B1 (ko) * 2015-04-20 2017-02-10 현대자동차주식회사 내구성이 향상된 침탄 합금강 및 이의 제조방법
JP2017125232A (ja) * 2016-01-13 2017-07-20 株式会社神戸製鋼所 浸炭窒化用鋼材および浸炭窒化部品
CN109423581A (zh) * 2017-09-05 2019-03-05 宝山钢铁股份有限公司 一种森吉米尔轧机的二中间辊及其制造方法
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CN112872736A (zh) * 2021-01-20 2021-06-01 陕西茂凇新材科技有限公司 一种低成本的Tc4钛环生产工艺
WO2023026621A1 (ja) * 2021-08-24 2023-03-02 日本精工株式会社 転がり軸受
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