Microstructural Alterations of Rolling—Bearing Steel Undergoing Cyclic Stressing

One form of damage due to rolling contact fatigue is the formation of localised regions of extremely hard material forming within the body of a bearing. These regions have a relatively homogeneous structure and hence etch mildly with respect to the surrounding unaffected matrix. They, therefore, appear white in a darker background when examined using optical microscopy. We assess here the cause of this damage and propose solutions that are backed by evidence that already is available. The issue is important because of the spate of unexpected failures in large wind turbine bearings and of generic importance in determining the life of more well behaved bearing applications.

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“…14,32,34,38,39,[70][71][72][73][74][75][76][77] Further experiments of this type are likely to yield diminishing value.…”

Section: Hypothesis and Solutionsmentioning

confidence: 99%

Critical Assessment 13: Elimination of white etching matter in bearing steels

Bhadeshia

Solano-Alvarez

2015

Materials Science and Technology

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“…Although having been discussed for several decades, a plausible formation mechanism for DERs is still unavailable. Some authors [5,6] argued that DERs formation results from the over-tempering of martensite, and the fact that DERs have never been observed in the fatigued bearing samples initially tempered to a hardness of around 700 HV [13,17] supports this argument. However, the operation temperatures of bearings, which are usually lower than 100 C, are not sufficiently high to thermally activate the growth of carbides [18], and there is no evidence showing distinct temperature rise in DERs caused by cyclic stressing.…”

Section: Introductionmentioning

confidence: 99%

“…Besides, Bush et al [5] found threshold contact pressures below which DERs were never formed, indicating the essential role played by stress. Moreover, the depth range where a DER is formed is considered to be related to the stress state of Hertzian contact, although there is still in disagreement as to the stress component responsible for such phenomenon with some authors [15,19] arguing it is the maximum shear stress, others [13,20] that it is the 45 shear stress, the orthogonal shear stress [5,6] or the vonMises stress [9]. Nevertheless, it was experimentally proved [15] that increasing either contact pressure or operation temperature can accelerate DER formation.…”

Section: Introductionmentioning

confidence: 99%

Strain-induced martensite decay in bearing steels under rolling contact fatigue: Modelling and atomic-scale characterisation

Song

Galindo-Nava

et al. 2017

Acta Materialia

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a b s t r a c tMartensite decay in bearing steels manifested as dark etching regions (DERs) under rolling contact fatigue (RCF) is modelled. The proposed model is established based on a dislocation-assisted carbon migration mechanism. The proposed model is capable of predicting the progress of DER formation and the corresponding mechanical property evolution with increasing number of cycles, in good agreement with the experimental data reported throughout seventy years. The effects of RCF testing conditions on DER formation are studied and a useful tool, DER% maps, is developed for illustrating the temperature, contact pressure and number of cycles for DER occurrence. Moreover, an atom probe tomography study is carried out, revealing the nature of DER ferrite and obtaining strong evidence supporting the postulated DER formation mechanism. The successful application of the dislocation assisted carbon migration mechanism to DER formation provides a plausible explanation to the phenomenon of martensite decay under rolling contact fatigue.

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“…Grundlegende Untersuchungen zur Entstehung der Weißen Bänder (WB) stammen von [8,10,11,12]. Sie stellten bei Lebensdaueruntersuchungen an dem Rillenkugellager 6309 fest, dass -erst nach längeren Laufzeiten -zunächst "flache" und dann "steile weiße Bänder" (FWB und SWB) entstehen (Bild 7).…”

Section: Flache Und Steile Weiße Bä Nder (Fwb Swb)unclassified

Über adiabatic shearbands und die Entstehung der „Steilen Weißen Bänder”︁ in Wälzlagern

Schlicht¹

2008

Materialwissenschaft Werkst

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Bei der Ü berrollung von Wälzelementen entstehen nach überela-stischen Beanspruchungen unter der Laufbahnoberfläche strukturelle Veränderungen. Mikro-und makroplastische Verformungen des Gefüges infolge der dreiachsigen Beanspruchung begleiten den Wälzermüdungsprozess vom ersten Lastwechsel an. Sie bestimmen die Lebensdauer des Wälzelements.Man beobachtet neben den plastischen Verformungen des Gefü-ges des Weiteren die sog. "butterflies" und die sog. flachen und steilen "Weißen Bänder". Diese Gefüge sind nicht anätzbar. Die weißen Bänder entstehen bei Kugellagern erst nach einer größeren Anzahl von Ü berrollungen und liegen im Umfangsschnitt unter % 30 bzw. % 80 zur Kontaktfläche. Die butterflies und die weißen Bän-der entstehen offenbar infolge einer zweiachsigen Werkstoffbeanspruchung. Ein Einfluss auf die Lebensdauer ist nicht erwiesen. Struktur und Entstehungsmechanismus sind strittig.Es gibt Gefügeerscheinungen, die den butterflies und den weißen Bändern ähnlich sind, die sog. adiabatic shearbands. Diese entstehen nach einer lokalen Makro-Scherung des Gefüges, ausgelöst durch eine einmalige, extrem kurzzeitige Druck-Scher-Beanspruchung. Blitztemperaturen nahe dem Schmelzpunkt verursachen im Scherbereich bei martensitisch gehärteten Werkstoffen die Bildung von Neuhärtungszonen; auch diese Gefüge sind nicht anätz-bar.Der vorliegende Aufsatz beschäftigt sich mit der Frage, ob wäh-rend des stetig und langzeitig ablaufenden Prozesses der plastischen Verformungen eine Beanspruchungskonstellation entsteht, die die adiabatische Bildung von butterflies und von weißen Bändern ermöglicht. Berücksichtigt man jüngste Erkenntnisse zur Wälzermü-dung sowie zur Werkstoffbeanspruchung durch eine EHD-Strö-mung, dann darf man zumindest die "Steilen Weißen Bänder" als adiabatic shearbands ansehen.Schlüsselworte: Wälzlager, adiabatic shearbands, butterflies, weiße Bänder During the rolling motion of roller components structural changes are generated by over-elastic distressing below the bearing face. Micro-and macro-plastic distortions of the microstructure due to the three-axial distressing accompany the process of rolling contact fatigue with the start from the first load cycle. They determine the life-duration of the roller component.Further structural changes in ball bearings besides the plastic deformations are the so called "butterflies" and the so called low-and high-angle "white bands". The "white bands" you only can detect later, after an extended number of rolling actions. They are inclined to average circumferential angles at % 30 respectively % 80 . Butterflies and white bands develop obviously due to a two-axial material stressing. An influence on the life duration is not proved. The structure and the mechanism of their generation are under discussion.There exist phenomena of the microstructure which are similar to the white bands, the so called adiabatic shear bands. These generate after a local macro-shear process of the microstructure, caused by a single, rapid shock-shear stressing. Flash-temperatures near the me...

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Microstructural Alterations of Rolling—Bearing Steel Undergoing Cyclic Stressing

Cited by 137 publications

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Critical Assessment 13: Elimination of white etching matter in bearing steels

Critical Assessment 13: Elimination of white etching matter in bearing steels

Strain-induced martensite decay in bearing steels under rolling contact fatigue: Modelling and atomic-scale characterisation

Über adiabatic shearbands und die Entstehung der „Steilen Weißen Bänder”︁ in Wälzlagern

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