Rolling Contact Fatigue Properties Research Articles

Investigation of the Relation between Rolling Contact Fatigue Property and Microstructure on the Surface Layer of D2 Wheel Steel

Through the rolling contact fatigue experiment under the condition of the lubricating oil, this article investigated the relation between contact fatigue property and microstructure on the surface layer of D2 wheel steel. The results showed that although the roughness of the original specimen induced by mechanical processing would diminish to some extent in the experiment, the 0.5 - 1.5 μm thick layer of ultrafine microstructure on the original mechanically-processed specimen surface would still become micro-cracks and small spalling pits due to spalling, and would further evolve into fatigue crack source. Additionally, even under the impact of the load that was not adequate to make the material reach fatigue limit, the ferrite in the microstructure underwent plastic deformation, which led the refinement of proeutectoid ferrite grains. During the experiment, the hardening and the refinement caused by plastic deformation consisted with the theory that dislocation gave rise to plastic deformation and grain refinement. The distribution laws of hardness and ferrite grain sizes measured could be explained by the distribution law of the shearing stress in the subsurface.

Modeling of rolling contact fatigue in rails at the microstructural level

A micromechanical-based finite element framework is developed to investigate the rolling contact fatigue (RCF) in rails. The microstructure of a representative part of the rail in contact with the wheel during wheel passage is modeled using Voronoi tessellation algorithm. The geometry explicitly represents microstructural grain and grain interface features that represent actual microstructure of rail steel. The grain interface is modeled using cohesive elements. For higher computational efficiency, moving Hertzian load is applied to the rail surface instead of moving the wheel explicitly on top of the rail. The jump-in-cycles approach is employed to efficiently simulate a large number of loading cycles, while the material degradation at the grain interface is represented by an accurate damage evolution law. Additionally, the model is used to evaluate the effects of temperature change, traction coefficient, and grain size on initiation and progression of RCF. The results indicate that colder temperatures increase the progression of RCF, while warmer temperatures do not have any significant effects. Large traction forces at the wheel-rail interface significantly accelerate RCF growth, mainly through migration of subsurface micro-cracks to the surface of the rail. The surface cracks grow into larger ones that lead to loss of rail material. Controlling the grain size can have a positive effect on both the initiation and migration of sub-surface cracks. Changing yield strength of material with the Hall-Petch relation, the model evaluates the effect of refining the grain size. The results indicate that smaller grains can improve RCF properties of the rail. The effect of maximum contact pressure on RCF is studied, and the results show a power relation between maximum contact pressure and RCF life. Also several case studies are simulated and compared with the experimental observations. The simulation results are in close agreement with the experimental observations for the crack pattern and crack depth.

Rolling contact fatigue performance evaluation of Ti–6Al–4V parts processed by selective laser melting

Selective laser melting (SLM) of titanium components is gradually gaining popularity in various fields, such as aerospace, automobile, and medical for the purpose of saving material and reducing the carbon footprint. To capitalize on their benefits, the mechanical properties of parts fabricated by SLM must meet engineering requirements. Fatigue properties are particularly important for the performance of safety-critical structures. In this research, rolling contact fatigue (RCF) tests were performed for SLM fabricated Ti–6Al–4V samples in differently post-treated conditions to investigate the effect of different post-processing methods on the fatigue properties and, as a comparison, forgings of Ti–6Al–4V were also tested. It was found that the RCF properties of the Ti–6Al–4V generated by SLM were superior to those of the forged specimens and strengthened after polishing and heat treatment. The worn surfaces were observed by using an optical microscope, and the results indicated that surface and subsurface defects are the main causes of fatigue crack initiation and the residual stresses enhance fatigue crack growth.

Observation of Flaking Process in Rolling Contact Fatigue by Laminography Using Ultra-bright Synchrotron Radiation

The flaking failure in rolling contact fatigue (RCF) results from crack initiation and propagation has been believed to originate from non-metallic inclusions located beneath the surface. With conventional microscopies, however, damage process in the internal region of materials could not be observed, then RCF crack initiation and propagation behaviours were observed by using synchrotron radiation computed laminography (SRCL) in the brightest synchrotron facility in Japan, and the effect of the inclusion orientation on the RCF property was examined. In our previous studies, crack initiation and propagation behaviours caused by extended MnS inclusions distributed in depth or transverse (width) direction was observed by the SRCL. In the present study, the fracture mechanism under RCF was discussed on specimens with MnS inclusions distributed in the rolling direction. As a result, vertical cracks were initiated on the surface, parallel to the ball-rolling direction in specimens. The crack propagation direction was then changed perpendicular to the rolling direction. Thereafter, similar with our previous studies, vertical cracks caused the horizontal cracks beneath the surface, when the vertical cracks reached to a critical length. The ratio of the vertical crack initiation life to the flaking life was higher than specimens with other inclusion orientation.

Effect of carburization on microstructure and rolling contact fatigue property of 95W–3.4Ni–1.6Fe heavy alloy

95W–3.4Ni–1.6Fe heavy alloy was carburized by pack carburization. Microstructure and hardness of the carburized alloy were investigated by SEM, EDS XRD. Effect of carburization on the rolling contact fatigue (RCF) property of the alloy was studied. The results showed that the carburized layer was composed of the outer, porous WC layer and the modified subsurface layer with each W grain surrounded by a WC shell. Carburization not only decreased the RCF performance of the alloy but also aggravated the wear of the counter balls. The untreated alloy was damaged by two modes of spalling and delamination under RCF condition. The subsurface main crack of the untreated alloy initiated where the maximum shear stress existed and preferentially propagated along the W–W interfaces. Spalling was the main failure mode of the carburized alloys, and the crumbling WC particles intensified the abrasion of the carburized surface.

표면 강화처리 레일의 마모 및 피로 특성

Railway tracks are repeatedly overstressed and damaged owing to increase in passing tonnage and numerous contact cycles between wheels of train and rails. In order to ensure safe train operation, heat-treated rails are used in addition to regular inspection and maintenance of these rails. Normal rails were treated using ultrasonic nanocrystal surface modification (UNSM) to strengthen the surface of rails. A few changes in surface properties were detected with respect to hardness and compressive residual stress after UNSM treatment. Wear and rolling contact fatigue tests were performed using rails whose surfaces were hardened by UNSM and heat-treated rails. The amount of wear and fatigue life cycles were measured to estimate the effect of UNSM on the rail material. The material of the surfacehardened rail showed improved wear and rolling contact fatigue properties.

Rolling Contact Fatigue Properties of SAE 8620 Steel after Case Carburizing

Rolling contact fatigue (RCF) properties of SAE 8620 steel after case carburizing have been investigated under two contact stresses of 4.0 and 5.5 GPa. Results show that the RCF life ranges from 2.5 × 106 to 3 × 107 cycles under the contact stress of 5.5 GPa, while it can be more than 1 × 108 cycles under the contact stress of 4.0 GPa. The rated fatigue life L10 (lives with the 10% failure) is also drastically shortened from 9.8 × 106 to 5.4 × 105 cycles when the contact stress is increased from 4.0 to 5.5 GPa. Theoretical calculations and fractographs show that the maximum shear stress and the contact area increase with increasing the contact stress, making RCF tend to occur earlier.

Rolling contact fatigue property and failure mechanism of carburized 30CrSiMoVM steel at elevated temperature

Rolling contact fatigue (RCF) behavior of carburized 30CrSiMoVM steel was experimentally investigated at elevated temperature. The results show that RCF crack was drive by asperity contact rather than the orthogonal shear stress or the maximum shear stress. The value of L10, L50, La life at 100°C decreased by 48.3%, 44.1%, 43.2%, respectively, compared with that at 40°C, which was attributed to lubrication status changing from mixed lubrication regime to boundary lubrication regime. The formation of the synergistic tribofilm containing Fe2O3, FeS, ZnS, FePO4 and Ca3(PO4)2 around the center of the contact area effectively prevented initiation and propagation of RCF crack under boundary lubrication status, resulting in the obvious variation of the failure mode of the carburized layer.

1212 繰返し焼入れを施した高炭素クロム軸受鋼の重荷重下における転がり疲労特性(OS8-6 材料力学と計算力学の新展開)

1212 繰返し焼入れを施した高炭素クロム軸受鋼の重荷重下における転がり疲労特性(OS8-6 材料力学と計算力学の新展開)

Rolling contact fatigue and wear properties of 0.1C–3Cr–2W–V nitrided steel

Rolling contact fatigue (RCF) characteristics of 0.1C–3Cr–2W–V nitrided and untreated steel have been investigated at ambient temperature. The results indicate that the friction coefficients of the nitrided specimens decreased from 6% to 29%, and the RCF life of the nitrided specimens have been significantly prolonged. The failure modes of the nitrided surface could be classified as spalling and delamination within the layer, and the inner defects generated by the plasma nitriding play an important role in the surface and subsurface initiated RCF. Meanwhile, decreased surface roughness and better wear-resistance are demonstrated to be useful to improving the RCF performance.

405 高周波焼入れ焼戻しを施した13Cr-2Ni-2Moステンレス鋼の転がり疲労特性(機素潤滑設計1)

405 高周波焼入れ焼戻しを施した13Cr-2Ni-2Moステンレス鋼の転がり疲労特性(機素潤滑設計1)

916 チタン合金ベアリングの表面被覆による水中転がり疲労特性の向上(機械材料・材料加工1)

916 チタン合金ベアリングの表面被覆による水中転がり疲労特性の向上(機械材料・材料加工1)

Microstructure and Rolling Contact Fatigue Strength of Induction Heated AISI 52100 Bearings

In the present work the microstructure and the rolling contact fatigue properties of induction heated AISI 52100 bearings are investigated. The bearings were heat treated by using a flat coil at 30 kW power and 60 kHz frequency, cooled with water and subsequently tempered for 1 hour at 180 °C. The hardness at the surface of the material was close to 900 HV0.3kgf/15s. The hardening depth of the induction heated sample was higher than 5 mm. The retained austenite content was around 18% at the surface and decreases along with the depth. The samples were rolling contact fatigue (RCF) tested up to 107 and 4.5x107 cycles, at Hertzian stress 4 GPa. No flaking failure was observed on the bearing races. For tests up to 107 cycles the track size was around 690 um and this remained unchanged up to 4.5x107 cycles. The residual stresses at the material surface before testing were close to zero and became highly compressive after the RCF testing. Stress induced transformation occurred at the surface and the retained austenite content after testing reached around 10%. Induction heating was successfully applied to induce martensitic transformation in AISI 52100 steel and the bearings showed very high fatigue strength under rolling contact.

S116052 ショットピーニング処理面の転がり疲労特性

S116052 ショットピーニング処理面の転がり疲労特性

The effect of slip ratio on the rolling contact fatigue property of railway wheel steel

Shelling is one of the typical rolling contact fatigue (RCF) failures of railway wheels. Creepage between wheels and rails due to rolling radius difference in curves is inevitable on railway tracks. Therefore, there are tangential stresses and slip phenomena on wheel treads. Eventually, initiation of RCF cracks being the origin of shelling is accelerated by creepage. The objective of the present paper is to evaluate RCF property of railway wheel steel. The effect of the slip ratio on the RCF strength of the railway wheel steel was evaluated. RCF tests were conducted using two cylindrical contact specimens under water lubrication at a slip ratio of 0.0–1.0%. The range of slip ratio is determined to assume a creepage between wheel and rail during curving. As a result, it was found that the traction coefficient increased with the increase in the slip ratio, and the fatigue strength decreased simultaneously. The results were evaluated by a shakedown map and Hirakawa’s RCF map. Experimental fatigue limits could be expressed more precisely by the criterion of Hirakawa’s RCF map than that expressed by the well-known shakedown map. Stress intensity factors (SIFs) of the cracks produced by the RCF test were calculated by finite element (FE) analysis where the effect of water pressure due to the penetration of water into the cracks is taken into account. Two peaks of the maximum tangential SIF occurred during one cycle of rolling contact. The direction of the crack propagation was estimated by the maximum tangential stress criteria. The results of the RCF test showed that the cracks were initiated at the surface, propagated obliquely in the depth direction and then branched into two directions. One was towards the surface and the other was towards the depth. These two crack directions were inspected experimentally, corresponding to the estimated crack directions from the two peaks of SIF by FE analysis. The effect of slip ratio on RCF crack propagation was discussed by using the SIFs of the RCF cracks where water penetration into the cracks was considered.

Rolling Contact Fatigue Property of Low-Temperature Bainite in Surface Layer of a Low Carbon Steel

Rolling contact fatigue (RCF) properties of low-temperature bainitic microstructure in the surface layer of a low-carbon steel, obtained by means of carburization and successive lowtemperature austempering were studied. Comparisons were made with those properties of a martensite steel obtained by quenching and tempering. The results showed that the low-temperature bainitic steel exhibits an excellent RCF resistance and reaches a RCF life more than twice that of the martensite steel, presumably as a consequence of the very thin bainite plates (~80 nm in thickness) and the fine-scale dispersion of austenite between the plates. The apparently increased hardness in the surface layer may partly be the cause of the enhanced RCF resistance.

Investigation on rolling contact fatigue and wear properties of railway rails

The rolling wear tests of rail material were conducted under unlubricated condition using a JD-1 wheel/rail simulation facility. The fatigue damage and wear behaviours of rail rollers were investigated in detail by examining the microhardness, wear volume, and wear scars using optical microscopy and scanning electronic microscopy. The results indicate that wear volume of a rail roller increases rapidly with the increase of axle load and decrease of curve radius. Wear volume of U71Mn rail is bigger than that of PD3 rail. It is observed that PD3 rail roller has some fatigue microcracks on the surface of wear scar. Furthermore, the microcrack propagates along depth direction with an angle of 15–30°. By comparison, U71Mn material has better fatigue resistance performance. The results indicate when the wear is serious, the fatigue damage is relatively slight. The relationship between fatigue crack damage and wear seems as competitive and restrictive coupling mechanisms.

Influence of Deep-Nitriding and Shot Peening on Rolling Contact Fatigue Performance of 32Cr3MoVA Steel

The effects of deep-nitriding and following shot peening on microhardness, rolling contact fatigue property of 32Cr3MoVA steel were investigated and Scanning Electron Microscope (SEM) was employed to evaluate the failure surface of rolling contact fatigue specimens. The fatigue results indicate that the depth of deep-nitrided layer is about 0.75 mm and following shot peening can improve the rolling contact fatigue life. The SEM test shows that the area of failure for nitrided and following shot-peened specimens is smaller and the depth of pit is lower compared with nitrided specimens.

Volume defect fatigue failure of ceramic balls under rolling condition

A newly developed pure rolling fatigue test rig with three contact points is used to test the rolling contact fatigue properties of silicon nitride ceramic balls. Ball surfaces are examined after failure with optical microscopy and scanning electron microscopy. The failure cause,fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material and propagate,to form elliptical fatigue spalls under the action of principal tensile stresses. The principal tensile stress increases with increasing contact load,causing spall formation and reduction of rolling contact life. The greater the principal tensile stress is,the more severe the peeling of near surface is. Under the same condition,the closer volume defects are to the surface,the more likely failure occurs,the shorter the rolling contact life is.

Rolling Contact Fatigue Property of Sintered and Carburized Compacts Made of Molybdenum Hybrid-Alloyed Steel Powder

A new molybdenum hybrid-alloyed steel powder has been developed. The powder is based on a molybdenum prealloyed steel powder to which molybdenum powder particles have been diffusion bonded. The sintered compact made of the developed powder has a finer pore structure than that of the conventional molybdenum prealloyed steel powder, because the ferritic iron phase (α-phase) with a high diffusion coefficient is formed in the sintering necks where molybdenum is concentrated resulting in enhanced sintering. The rolling contact fatigue strength of the sintered and carburized compacts made of this powder improved by a factor of 3.6 compared with that of the conventional molybdenum prealloyed steel powder. The improvement in the rolling contact fatigue strength should result from the fine pore structure without coarse pores acting as stress concentration points.