WO2013170995A1 - Rolling bearing part and method for the heat treatment of a rolling bearing part - Google Patents

Rolling bearing part and method for the heat treatment of a rolling bearing part Download PDF

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Publication number
WO2013170995A1
WO2013170995A1 PCT/EP2013/056642 EP2013056642W WO2013170995A1 WO 2013170995 A1 WO2013170995 A1 WO 2013170995A1 EP 2013056642 W EP2013056642 W EP 2013056642W WO 2013170995 A1 WO2013170995 A1 WO 2013170995A1
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WO
WIPO (PCT)
Prior art keywords
bearing part
rolling bearing
heat treatment
temperature
rolling
Prior art date
Application number
PCT/EP2013/056642
Other languages
German (de)
French (fr)
Inventor
Dieter Röll
Walter Götz
Reinhold GAUBMANN
Bernhard Wilm
Original Assignee
Schaeffler Technologies AG & Co. KG
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Application filed by Schaeffler Technologies AG & Co. KG filed Critical Schaeffler Technologies AG & Co. KG
Publication of WO2013170995A1 publication Critical patent/WO2013170995A1/en

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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
    • C21D9/40—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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/20—Isothermal quenching, e.g. bainitic hardening
    • 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
    • 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
    • C21D2211/002—Bainite
    • 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
    • F16C2204/00—Metallic materials; Alloys
    • F16C2204/60—Ferrous alloys, e.g. steel alloys
    • F16C2204/66—High carbon steel, i.e. carbon content above 0.8 wt%, e.g. through-hardenable steel
    • 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
    • F16C2326/00—Articles relating to transporting
    • F16C2326/01—Parts of vehicles in general
    • F16C2326/02—Wheel hubs or castors
    • 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
    • F16C33/583—Details of specific parts of races
    • F16C33/586—Details of specific parts of races outside the space between the races, e.g. end faces or bore of inner ring

Definitions

  • the invention relates to a rolling bearing part, in particular a bearing ring, and a method for heat treatment of a rolling bearing part and the use of a rolling bearing part.
  • DE 10 2007 044 950 B3 discloses a carbonitrided workpiece made of a hardening steel, which has a core zone with a bainite structure as its main constituent, and which is designed for a rolling load.
  • a marginal zone of the workpiece is a mixed structure of martensite and bainite, wherein the volume fraction of martensite is at least 20%.
  • the invention has the object of hardening roller bearing parts made of steel, in particular bearing rings of wheel bearings, particularly efficient and to produce predestined for a rolling load material properties.
  • the rolling bearing part is made of steel with a bainitic structure and a Restauste- nit content of 8 to 20%, with compressive residual stresses of at least 100 MPa to a depth of at least 100 ⁇ below the surface and the surface hardness of at least 59 HRC, in particular at least 60 HRC, is.
  • the structural composition of the heat-treated rolling bearing part is preferably the same over its entire cross-section.
  • the material properties mentioned are produced by first heating the rolling bearing part to the austenitizing temperature and then cooling it to a temperature above the martensite starting temperature and keeping it at that temperature, so that the formation of bainitic structure begins.
  • the transformation into bainitic structure is stopped before complete conversion by lowering the temperature of the rolling bearing part. This process of heat treatment is referred to as an interrupted isothermal transformation.
  • a chemical-thermal heat treatment of the rolling bearing part such as nitriding or carbonitriding, is not provided. After the said steps of the heat treatment, preferably neither renewed heating (tempering) nor deep cooling of the rolling bearing part takes place.
  • the particular advantage of the method according to the invention is that the duration of the heat treatment is significantly shortened compared to conventional methods.
  • the total process time is not more than six hours.
  • process times of less than three hours for example a process time of just one hour, can be achieved.
  • the short process time leads to an improved deformability of the rolling bearing part compared to a complete or even a stepped transformation.
  • the rolling bearing part has a very good rollover resistance and dirt resistance.
  • the temperature resistance is at least 120 ° C according to DIN 623 Part 1.
  • the roller bearing part according to the invention is designed for example as a bearing ring, in particular inner ring, a wheel bearing.
  • a bearing ring in particular inner ring
  • wheel bearing As prior art may be mentioned in this context, for example, the DE 10 2006 030 478 A1.
  • the rolling bearing part is a bearing ring of a wheel bearing, which has an end-face toothing, in particular a face toothing formed by non-cutting forming, wherein the bearing ring preferably directly adjoins a Wälznietbund, wel- rather the face toothing facing away from the bearing ring Side has.
  • wheel bearings are known in principle, for example, from DE 10 2005 009 938 A1, from DE 10 2005 016 427 A1, and from DE 10 2005 018 126 A1.
  • the internal compressive stresses in the roller bearing part namely bearing ring, in particular inner ring
  • the inner ring is widened noticeably. If there were no residual compressive stresses on the surface of the inner ring and near the surface near the surface, the expansion of the inner ring in this area would give rise to tensile stresses which had an unfavorable effect on the load capacity and durability of the rolling bearing. This undesirable effect is effectively counteracted by the residual compressive stresses in the edge zone of the bearing ring.
  • the printed matter Tensions which are in the mechanically unloaded bearing ring in said range of at least 100 MPa, ensure that even when assembled wheel bearing, that is expanded bearing ring still sustainable residual stresses, preferably only low tensile stresses in the edge zone of the bearing ring, which is a career for Rolling, typically balls or tapered rollers forms, are present.
  • the material of the rolling bearing part in particular bearing ring, for example, 100Cr6 (W3) or 100CrMn6 (W4) into consideration.
  • the material from which the rolling bearing part is made is a hardenable steel.
  • FIG. 1 shows a broken isothermal transformation in a ZTU diagram
  • FIG. 1 illustrates the process according to the invention (interrupted conversion) in a ZTU diagram (time-temperature conversion).
  • the workpiece that is to say the roller bearing part
  • the workpiece is cooled from a temperature which is at least at the level of the austenitizing temperature of 840 ° C. to a temperature which is above the martensite starting temperature.
  • the austenitic structure is gradually transformed into a Bavarian structure.
  • the conversion is deliberately interrupted by rapid cooling, so compared to a complete conversion sets a defined retained austenite content of at least 8% and at most 20%.
  • a generally designated by the reference numeral 1 wheel bearing is shown in principle known geometry.
  • reference numeral 1 wheel bearing With regard to the construction and the function of the wheel bearing 1, reference is made to the above-cited prior art.
  • the wheel bearing 1 has a wheel hub 2, two rows of rolling elements 3, namely balls, and an outer ring 4.
  • the geometric axis of the wheel bearing 1 is denoted by A. While a number of rolling elements 3 rolls directly on the wheel hub 2, the second row of rolling elements 3 rolls on a separate inner ring 5, more generally referred to as a bearing ring from.
  • the inner ring 5 is the rolling bearing part subjected to a heat treatment according to FIG. 1.
  • a Wälznietbund 6 is located on the front side, in welhern a spur gear 7 is formed. By Wälznietbund 6 thus the inner ring 5 is fixed to the hub 2.
  • the Wälznietbund 6 including the spur gear 7 is formed without cutting from a Niethals, which was part of the wheel hub 2 prior to the forming.
  • the Wälznietvorgang fixes the inner ring 5 on the hub 2 and on the other hand forms the spur gearing 7, the inner ring 5 undergoes a widening, but thanks to the heat treatment described above only low, easily bearable tensions in the near-surface region of the inner ring fifth leads.

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

Abstract

A rolling bearing part (5) of steel has a bainitic structure and a residual austenite content of 8 to 20%, wherein there are internal compressive stresses of at least 100 MPa to a depth of at least 100 µm below the surface and the surface hardness is at least 59 HRC. The rolling bearing part (5) is subjected to a heat treatment with discontinuous transformation and is formed in particular as a bearing ring of a wheel bearing with spur gearing.

Description

Bezeichnung der Erfindung  Name of the invention
Wälzlagerteil sowie Verfahren zur Wärmebehandlung eines Wälzlagerteils Beschreibung Rolling bearing part and method for heat treatment of a rolling bearing part Description
Gebiet der Erfindung Field of the invention
Die Erfindung betrifft ein Wälzlagerteil, insbesondere einen Lagerring, sowie ein Verfahren zur Wärmebehandlung eines Wälzlagerteils und die Verwendung eines Wälzlagerteils. The invention relates to a rolling bearing part, in particular a bearing ring, and a method for heat treatment of a rolling bearing part and the use of a rolling bearing part.
Aus der EP 1 774 187 B1 ist ein für eine Wälzbelastung ausgelegtes carbo- nitriertes Maschinenteil bekannt, welches vollständig aus einem Stahl mit mar- tensitischem Gefüge gebildet ist, und das unter seiner Oberfläche bis zu einer Tiefe von mindestens 40 μιτι Druckeigenspannungen von mindestens 300 MPa aufweist. From EP 1 774 187 B1 a carbo-nitrided machine part designed for rolling load is known, which is completely formed from a steel with a martensitic structure and which under its surface has compressive residual stresses of at least 300 MPa up to a depth of at least 40 μιτι having.
Aus der DE 10 2007 044 950 B3 ist ein für eine Wälzbeanspruchung ausgebil- detes carbonitriertes Werkstück aus einem durchhärtenden Stahl bekannt, welches eine Kernzone mit einem Bainit-Gefüge als Hauptbestandteil aufweist. In einer Randzone des Werkstücks liegt ein Mischgefüge aus Martensit und Bainit vor, wobei der Volumenanteil des Martensits mindestens 20% beträgt. Der Erfindung liegt die Aufgabe zugrunde, Wälzlagerteile aus Stahl, insbesondere Lagerringe von Radlagern, besonders rationell zu härten und dabei für eine Wälzbelastung prädestinierte Materialeigenschaften zu erzeugen. DE 10 2007 044 950 B3 discloses a carbonitrided workpiece made of a hardening steel, which has a core zone with a bainite structure as its main constituent, and which is designed for a rolling load. In a marginal zone of the workpiece is a mixed structure of martensite and bainite, wherein the volume fraction of martensite is at least 20%. The invention has the object of hardening roller bearing parts made of steel, in particular bearing rings of wheel bearings, particularly efficient and to produce predestined for a rolling load material properties.
Diese Aufgabe wird erfindungsgemäß gelöst durch ein Wälzlagerteil sowie durch ein Verfahren zur Wärmebehandlung eines Wälzlagerteils gemäß dem jeweiligen unabhängigen Patentanspruch. Im Folgenden im Zusammenhang mit dem Verfahren erläuterte Ausgestaltungen und Vorteile der Erfindung gelten sinngemäß auch für das Wälzlagerteil und umgekehrt. This object is achieved by a rolling bearing part and by a method for heat treatment of a rolling bearing part according to the respective independent claim. In the following context With the method explained embodiments and advantages of the invention apply mutatis mutandis to the rolling bearing and vice versa.
Das Wälzlagerteil ist aus Stahl mit bainitischem Gefüge und einem Restauste- nitgehalt von 8 bis 20 % gebildet, wobei Druckeigenspannungen von mindestens 100 MPa bis zu einer Tiefe von mindestens 100 μιτι unter der Oberfläche vorliegen und die Oberflächenhärte mindestens 59 HRC, insbesondere mindestens 60 HRC, beträgt. Die Gefügezusammensetzung des der Wärmebehandlung unterzogenen Wälzlagerteils ist vorzugsweise über dessen gesamten Querschnitt gleich. The rolling bearing part is made of steel with a bainitic structure and a Restauste- nit content of 8 to 20%, with compressive residual stresses of at least 100 MPa to a depth of at least 100 μιτι below the surface and the surface hardness of at least 59 HRC, in particular at least 60 HRC, is. The structural composition of the heat-treated rolling bearing part is preferably the same over its entire cross-section.
Die genannten Materialeigenschaften werden erzeugt, indem das Wälzlagerteil zunächst auf die Austenitisierungstemperatur erhitzt und anschließend auf eine Temperatur oberhalb der Martensitstarttemperatur abgekühlt und auf dieser Temperatur gehalten wird, so dass die Bildung von bainitischem Gefüge einsetzt. Die Umwandlung in bainitisches Gefüge wird vor der vollständigen Umwandlung durch Senkung der Temperatur des Wälzlagerteils abgebrochen. Dieser Vorgang der Wärmebehandlung wird als unterbrochene isotherme Umwandlung bezeichnet. The material properties mentioned are produced by first heating the rolling bearing part to the austenitizing temperature and then cooling it to a temperature above the martensite starting temperature and keeping it at that temperature, so that the formation of bainitic structure begins. The transformation into bainitic structure is stopped before complete conversion by lowering the temperature of the rolling bearing part. This process of heat treatment is referred to as an interrupted isothermal transformation.
Eine chemisch-thermische Wärmebehandlung des Wälzlagerteils, etwa ein Nitrieren oder Carbonitrieren, ist nicht vorgesehen. Nach den genannten Schritten der Wärmebehandlung erfolgt vorzugsweise weder eine erneute Erwärmung (Anlassen) noch ein Tiefkühlen des Wälzlagerteils. A chemical-thermal heat treatment of the rolling bearing part, such as nitriding or carbonitriding, is not provided. After the said steps of the heat treatment, preferably neither renewed heating (tempering) nor deep cooling of the rolling bearing part takes place.
Der besondere Vorteil des erfindungsgemäßen Verfahrens liegt darin, dass die Dauer der Wärmebehandlung im Vergleich zu konventionellen Verfahren deutlich verkürzt ist. In bevorzugter Ausgestaltung beträgt die gesamte Prozesszeit nicht mehr als sechs Stunden. Je nach verwendetem Werkstoff und Bauteilge- ometrie sind sogar Prozesszeiten unter drei Stunden, beipielsweise eine Prozesszeit von nur einer Stunde, realisierbar. Die kurze Prozesszeit führt zu einer im Vergleich zu einer kompletten oder auch zu einer gestuften Umwandlung verbesserten Verformungsfähigkeit des Wälzlagerteils. Gleichzeitig weist das Wälzlagerteil eine sehr gute Überrollfestigkeit und Schmutzunempfindlichkeit auf. Die Temperaturbeständigkeit beträgt mindestens 120°C nach DIN 623 Teil 1 . The particular advantage of the method according to the invention is that the duration of the heat treatment is significantly shortened compared to conventional methods. In a preferred embodiment, the total process time is not more than six hours. Depending on the material used and the geometry of the component, even process times of less than three hours, for example a process time of just one hour, can be achieved. The short process time leads to an improved deformability of the rolling bearing part compared to a complete or even a stepped transformation. At the same time, the rolling bearing part has a very good rollover resistance and dirt resistance. The temperature resistance is at least 120 ° C according to DIN 623 Part 1.
Das erfindungsgemäße Wälzlagerteil ist beispielsweise als Lagerring, insbesondere Innenring, eines Radlagers ausgebildet. Als Stand der Technik sei in diesem Zusammenhang beispielhaft die DE 10 2006 030 478 A1 genannt. The roller bearing part according to the invention is designed for example as a bearing ring, in particular inner ring, a wheel bearing. As prior art may be mentioned in this context, for example, the DE 10 2006 030 478 A1.
In bevorzugter Anwendung handelt es sich bei dem Wälzlagerteil um einen Lagerring eines Radlagers, welches eine stirnseitige Verzahnung, insbesondere eine durch spanlose Umformung ausgebildete Stirnverzahnung, aufweist, wobei der Lagerring vorzugsweise direkt an einen Wälznietbund grenzt, wel- eher die Stirnverzahnung auf dessen dem Lagerring abgewandter Seite aufweist. Derartige Radlager sind prinzipiell beispielsweise aus der DE 10 2005 009 938 A1 , aus der DE 10 2005 016 427 A1 , sowie aus der DE 10 2005 018 126 A1 bekannt. Gerade in diesen Anwendungsfällen, das heißt bei Radlagern mit aus einem umgeformten Niethals gebildeter Verzahnung, wirken sich die Druckeigenspannungen in dem Wälzlagerteil, nämlich Lagerring, insbesondere Innenring, besonders positiv aus, wie im Folgenden erläutert wird: Durch die Umformung des Niethalses unter Ausbildung der Stirnverzahnung bei gleichzeitiger Fixierung des Innenringes auf der Radnabe wird der Innenring merklich aufgeweitet. Lägen an der Oberfläche des Innenrings und im o- berflächennahen Bereich keine Druckeigenspannungen vor, so entstünden durch die Aufweitung des Innenrings in diesem Bereich Zugspannungen, wel- che sich auf die Belastbarkeit und Haltbarkeit des Wälzlagers ungünstig auswirkten. Diesem unerwünschten Effekt wird durch die Druckeigenspannungen in der Randzone des Lagerrings wirksam entgegengewirkt. Die Druckeigen- Spannungen, welche beim mechanisch unbelasteten Lagerring im genannten Bereich von mindestens 100 MPa liegen, sorgen dafür, dass selbst beim zusammengebauten Radlager, das heißt bei aufgeweitetem Lagerring, noch ertragbare Eigenspannungen, vorzugsweise lediglich geringe Zugspannungen, in der Randzone des Lagerings, welche eine Laufbahn für Wälzkörper, typischerweise Kugeln oder Kegelrollen, bildet, vorhanden sind. In a preferred application, the rolling bearing part is a bearing ring of a wheel bearing, which has an end-face toothing, in particular a face toothing formed by non-cutting forming, wherein the bearing ring preferably directly adjoins a Wälznietbund, wel- rather the face toothing facing away from the bearing ring Side has. Such wheel bearings are known in principle, for example, from DE 10 2005 009 938 A1, from DE 10 2005 016 427 A1, and from DE 10 2005 018 126 A1. Especially in these applications, that is to say in wheel bearings with toothing formed from a deformed neck neck, the internal compressive stresses in the roller bearing part, namely bearing ring, in particular inner ring, have a particularly positive effect, as will be explained in the following: By forming the neck neck to form the spur toothing with simultaneous fixation of the inner ring on the wheel hub, the inner ring is widened noticeably. If there were no residual compressive stresses on the surface of the inner ring and near the surface near the surface, the expansion of the inner ring in this area would give rise to tensile stresses which had an unfavorable effect on the load capacity and durability of the rolling bearing. This undesirable effect is effectively counteracted by the residual compressive stresses in the edge zone of the bearing ring. The printed matter Tensions, which are in the mechanically unloaded bearing ring in said range of at least 100 MPa, ensure that even when assembled wheel bearing, that is expanded bearing ring still sustainable residual stresses, preferably only low tensile stresses in the edge zone of the bearing ring, which is a career for Rolling, typically balls or tapered rollers forms, are present.
Als Werkstoff des Wälzlagerteils, insbesondere Lagerrings, kommt beispielsweise 100Cr6 (W3) oder 100CrMn6 (W4) in Betracht. Allgemein handelt es sich bei dem Werkstoff, aus welchem das Wälzlagerteil gefertigt ist, um einen durchhärtbaren Stahl. The material of the rolling bearing part, in particular bearing ring, for example, 100Cr6 (W3) or 100CrMn6 (W4) into consideration. In general, the material from which the rolling bearing part is made is a hardenable steel.
Ein Ausführungsbeispiel der Erfindung wird nachfolgend anhand von Figuren beschrieben. Dabei zeigen: An embodiment of the invention will be described below with reference to figures. Showing:
Fig. 1 : in einem ZTU-Schaubild eine unterbrochene isotherme Umwandlung, FIG. 1 shows a broken isothermal transformation in a ZTU diagram; FIG.
Fig. 2: in einer Schnittdarstellung ein Radlager mit Stirnverzahnung. Ausführliche Beschreibung der Zeichnung  2 shows a sectional view of a wheel bearing with spur toothing. Detailed description of the drawing
In Figur 1 ist in einem ZTU-Schaubild (Zeit-Temperatur-Umwandlung) das erfindungsgemäße Verfahren (unterbrochene Umwandlung) veranschaulicht. Zum Vergleich sind auch zwei nicht beanspruchte Varianten, nämlich eine ge- stufte Umwandlung sowie die komplette Umwandlung, in Fig. 1 eingezeichnet. Gemäß dieser Darstellung wird das Werkstück, das heißt das Wälzlagerteil, ausgehend von einer mindestens auf dem Niveau der Austenitisierungstempe- ratur in Höhe von 840°C liegenden Temperatur, auf eine Temperatur abgekühlt, welche oberhalb der Martensitstarttemperatur liegt. Bei dieser Tempera- tur von 220 bis 230°C wandelt sich das austenitische Gefüge allmählich in bai- nitisches Gefüge um. Die Umwandlung wird gezielt durch rasche Abkühlung unterbrochen, so dass sich im Vergleich zu einer vollständigen Umwandlung ein definierter Restaustenitgehalt einstellt, welcher mindestens 8% und höchstens 20% beträgt. Der gemäß Fig. 1 durch verkürzte isotherme Wärmebehandlung mit unterbrochener Umwandlung behandelte Werkstoff, nämlich 100CrMn6 (1 .3520), alternativ 100Cr6 (1 .3505), weist eine Oberflächenhärte von mindestens 59 HRC und Druckeigenspannungen in Höhe von mindestens 100 MPa (Absolutwert) in einer Tiefe bis mindestens 100 μιτι auf. FIG. 1 illustrates the process according to the invention (interrupted conversion) in a ZTU diagram (time-temperature conversion). For comparison, two unclaimed variants, namely a stepped conversion as well as the complete conversion, are shown in FIG. According to this illustration, the workpiece, that is to say the roller bearing part, is cooled from a temperature which is at least at the level of the austenitizing temperature of 840 ° C. to a temperature which is above the martensite starting temperature. At this temperature, from 220 to 230 ° C, the austenitic structure is gradually transformed into a Bavarian structure. The conversion is deliberately interrupted by rapid cooling, so compared to a complete conversion sets a defined retained austenite content of at least 8% and at most 20%. The material treated by shortened isothermal heat treatment with interrupted transformation according to FIG. 1, namely 100CrMn6 (1 .3520), alternatively 100Cr6 (1 .3505), has a surface hardness of at least 59 HRC and compressive residual stresses of at least 100 MPa (absolute value) a depth of at least 100 μιτι on.
In Fig. 2 ist ein insgesamt mit dem Bezugszeichen 1 gekennzeichnetes Radlager prinzipiell bekannter Geometrie dargestellt. Hinsichtlich des Aufbaus und der Funktion des Radlagers 1 wird auf den oben zitierten Stand der Technik verwiesen. In Fig. 2, a generally designated by the reference numeral 1 wheel bearing is shown in principle known geometry. With regard to the construction and the function of the wheel bearing 1, reference is made to the above-cited prior art.
Das Radlager 1 weist eine Radnabe 2, zwei Reihen Wälzkörper 3, nämlich Kugeln, sowie einen Außenring 4 auf. Die geometrische Achse des Radlagers 1 ist mit A bezeichnet. Während eine Reihe Wälzkörper 3 direkt auf der Radnabe 2 abrollt, rollt die zweite Reihe an Wälzkörpern 3 auf einem gesonderten Innenring 5, allgemeiner als Lagerring bezeichnet, ab. Bei dem Innenring 5 handelt es sich um das gemäß Fig. 1 einer Wärmebehandlung unterzogene Wälzlagerteil. Am Innenring 5 liegt stirnseitig ein Wälznietbund 6 an, in wel- ehern eine Stirnverzahnung 7 ausgebildet ist. Durch den Wälznietbund 6 ist somit der Innenring 5 auf der Radnabe 2 fixiert. Die Stirnverzahnung 7 ist zur Zusammenwirkung mit einer nicht dargestellten Gegenverzahnung vorgesehen und ermöglicht damit den Antrieb der Radnabe 2. Der Wälznietbund 6 einschließlich der Stirnverzahnung 7 ist spanlos aus einem Niethals umgeformt, welcher vor der Umformung Teil der Radnabe 2 war. Durch den Wälznietvorgang, der einerseits den Innenring 5 auf der Radnabe 2 befestigt und andererseits die Stirnverzahnung 7 ausbildet, erfährt der Innenring 5 eine Aufweitung, die jedoch dank der oben beschriebenen Wärmehand- lung lediglich zu geringen, problemlos erträglichen Spannungen im oberflächennahen Bereich des Innenrings 5 führt. Bezugszeichen The wheel bearing 1 has a wheel hub 2, two rows of rolling elements 3, namely balls, and an outer ring 4. The geometric axis of the wheel bearing 1 is denoted by A. While a number of rolling elements 3 rolls directly on the wheel hub 2, the second row of rolling elements 3 rolls on a separate inner ring 5, more generally referred to as a bearing ring from. The inner ring 5 is the rolling bearing part subjected to a heat treatment according to FIG. 1. On the inner ring 5, a Wälznietbund 6 is located on the front side, in welhern a spur gear 7 is formed. By Wälznietbund 6 thus the inner ring 5 is fixed to the hub 2. The Wälznietbund 6 including the spur gear 7 is formed without cutting from a Niethals, which was part of the wheel hub 2 prior to the forming. By the Wälznietvorgang, on the one hand fixes the inner ring 5 on the hub 2 and on the other hand forms the spur gearing 7, the inner ring 5 undergoes a widening, but thanks to the heat treatment described above only low, easily bearable tensions in the near-surface region of the inner ring fifth leads. reference numeral
1 Radlager 1 wheel bearing
2 Radnabe  2 wheel hub
3 Wälzkörper, Kugel 3 rolling elements, ball
4 Außenring  4 outer ring
5 Wälzlagerteil, Lagerring, Innenring 5 rolling bearing part, bearing ring, inner ring
6 Wälznietbund 6 Wälznietbund
7 Stirnverzahnung  7 spur toothing
A Achse A axis

Claims

Patentansprüche claims
Verfahren zur Wärmebehandlung eines Wälzlagerteils (5), mit folgenden Merkmalen: a) das Wälzlagerteil (5) wird auf die Austenitisierungstemperatur erwärmt, b) das Wälzlagerteil (5) wird auf eine Temperatur oberhalb der Mar- tensitstarttemperatur abgekühlt und auf dieser Temperatur gehalten, so dass die Bildung von bainitischem Gefüge einsetzt, c) die Umwandlung in bainitisches Gefüge wird durch Senkung der Temperatur des Wälzlagerteils (5) abgebrochen, so dass sich ein Restaustenitgehalt von 8 bis 20 %, eine Oberflächenhärte von mindestens 59 HRC, sowie eine Druckeigenspannung von mindestens 100 MPa bis zu einer Tiefe von mindestens 100 μιτι einstellt. Method for heat treatment of a roller bearing part (5), having the following features: a) the rolling bearing part (5) is heated to the austenitizing temperature, b) the rolling bearing part (5) is cooled to a temperature above the martensite starting temperature and kept at this temperature, then c) the transformation into bainitic structure is stopped by lowering the temperature of the rolling bearing part (5), so that a retained austenite content of 8 to 20%, a surface hardness of at least 59 HRC, and a compressive residual stress of at least 100 MPa to a depth of at least 100 μιτι adjusts.
Verfahren nach Anspruch 1 , dadurch gekennzeichnet, dass die Dauer der Wärmebehandlung maximal 6 h beträgt. A method according to claim 1, characterized in that the duration of the heat treatment is a maximum of 6 h.
Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass das Werkstück nach dem Schritt c) nicht angelassen wird. A method according to claim 1 or 2, characterized in that the workpiece after step c) is not started.
Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass das Werkstück nach dem Schritt c) nicht tiefgekühlt wird. Method according to one of claims 1 to 3, characterized in that the workpiece after step c) is not deep-frozen.
Wälzlagerteil (5) aus Stahl mit bainitischem Gefüge und einem Restaustenitgehalt von 8 bis 20 %, wobei Druckeigenspannungen von mindestens 100 MPa bis zu einer Tiefe von mindestens 100 μιτι unter der Oberfläche vorliegen und die Oberflächenhärte mindestens 59 HRC beträgt. Rolling bearing part (5) made of steel with bainitic structure and a Austenitgehalt Restausten from 8 to 20%, wherein residual compressive stresses of at least 100 MPa to a depth of at least 100 μιτι below the surface and the surface hardness is at least 59 HRC.
Wälzlagerteil (5) nach Anspruch 5, dadurch gekennzeichnet, dass des- sen Gefügezusammensetzung über den gesamten Querschnitt einheitlich ist. Rolling bearing part (5) according to claim 5, characterized in that structural composition over the entire cross section is uniform.
Wälzlagerteil (5) nach Anspruch 5 oder 6, dadurch gekennzeichnet, dass dieses aus dem Werkstoff 100CrMn6 gefertigt ist. Rolling bearing part (5) according to claim 5 or 6, characterized in that this is made of the material 100CrMn6.
Verwendung eines Wälzlagerteils (5) nach Anspruch 5 als Lagerring eines Radlagers (1 ). Use of a roller bearing part (5) according to claim 5 as a bearing ring of a wheel bearing (1).
Verwendung nach Anspruch 8, wobei das Radlager (1 ) eine durch spanlose Umformung ausgebildete Stirnverzahnung (7) aufweist. Use according to claim 8, wherein the wheel bearing (1) has a spur toothing (7) formed by chipless forming.
PCT/EP2013/056642 2012-05-16 2013-03-28 Rolling bearing part and method for the heat treatment of a rolling bearing part WO2013170995A1 (en)

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