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This study aims to describe the wear and rolling contact fatigue (RCF) behavior of microalloyed forged railway wheel steel Class D (7NbMo), with microstructures of upper bainite (UB - 350 HV 0.5), lower bainite (LB - 450 HV 0.5), and pearlite (PE - 350 HV 0.5), against 7C steel with a tempered martensite microstructure (660 HV 0.5) in a twin-disc tribometer. The results showed that bainite (LB and UB) exhibited greater wear resistance compared to pearlite (PE). The primary wear mechanism for all three microstructures was the fatigue wear. An analysis of the PE disc revealed continuous (single-layer) RCF cracks, which were relatively large and deep. In contrast, UB and LB cracks were discontinuous (multiple layers), thin, and smaller but more numerous (higher crack density). These characteristics indicated that bainitic microstructures also had greater resistance to RCF than pearlite did. Therefore, the combination of mechanical properties and the morphological arrangement of the microstructure led bainite to develop a shallower depth of deformed layer with a higher capacity for plastic deformation per unit volume. The greater wear and RCF performance of bainite compared to those of pearlite may be associated with how they release the accumulated deformation energy after reaching saturation in relation to volume deformation absorption: regarding bainite, the material releases energy by opening crack surfaces; conversely, regarding pearlite, it is through the detachment of large and wide cracks. [Display omitted] • Bainites exhibit superior wear resistance/RCF compared to pearlite in rolling and sliding. • Surfaces of bainitic discs UB and LB display mild peeling with reduced spacing. • Bainite possesses a greater capacity to absorb plastic deformation per volume. • Tribological performance may relate to the microstructural morphology's deformation energy release. • Bainites release energy through crack surface opening. [ABSTRACT FROM AUTHOR]

• Vanadium addition causes an increase in both yield strength and yield ratio. • Vanadium addition reduces strain hardening ability, and weakens wear resistance. • RCF crack initiation of V-alloyed stee is delayed by increasing yield strength. • RCF crack growth size is restricted by reducing plastic deformation capacity. • Increasing yield ratio improves RCF resistance, but weakens wear resistance. This study aims to evaluate the effect of vanadium microalloying on rolling contact fatigue (RCF) and wear behavior of railway wheel steels. It involves microstructural analysis and mechanical testing, including hardness, tensile, and rolling/sliding tests on the test steels, followed by electron backscatter diffraction, residual stress, and microhardness analyses after rolling/sliding tests. The findings demonstrate that vanadium microalloying leads to the alleviation of dynamic recrystallization, strain hardening, and compressive residual stress within the outermost layer beneath the worn surface, indicating a reduction in the plastic deformation capacity during dry rolling/sliding conditions. RCF resistance of railway steel can be enhanced through vanadium microalloying, as it simultaneously delays crack initiation by increasing yield strength and restricts crack growth by reducing plastic deformation capacity. While vanadium microalloying enhances the matrix hardness of wheel steel, it concurrently diminishes its strain hardening ability, potentially compromising its wear resistance. In addition, this study found that the yield ratio, being indicative of plastic deformation capacity and strain hardening ability, can serve as a suitable parameter for characterizing the RCF and wear resistances of tested steels. It exhibits a positive correlation with RCF resistance and a negative correlation with wear resistance. [ABSTRACT FROM AUTHOR]

Wear and Rolling Contact Fatigue (RCF) on wheels and rails are influenced by relative motions between the studied rail and wheel pair, and therefore influenced by train dynamics. Wear and RCF assessments using a train dynamics approach provide more accurate and comprehensive results comparing with conventional assessments that often do not consider train dynamics. In addition, considering material property differences, currently available rail wear maps are not able to accurately describe the wear performance of materials that have significantly different properties. This paper presented a method for rail/wheel wear and RCF assessments using 3D train dynamics models. The use of train models allows the consideration of coupler forces, traction, and brakes during the assessment. Wear assessments were conducted by using an in-house rail wear map model developed from the twin disc wear machine at the Centre for Railway Engineering (CRE). The new rail wear map was developed by using the AS 60 rail material (hardness 340 HB). The results indicated that the methods proposed in this paper could be used for rail/wheel wear and RCF assessments. Traction/braking forces and coupler lateral forces had evident influences on wear and RCF assessment. Different wear maps were also shown to have significant influences on the wear rate results. • A more comprehensive method to assess wheel-rail wear and RCF. • A new wear map for the AS 60 rail material. • Evidence of influences of traction/brake, coupler forces, and wear maps for wear and RCF assessment. [ABSTRACT FROM AUTHOR]

A vision-based experimental methodology was developed for monitoring the surface state evolution of specimens during twin-disc rolling contact tests, aimed at providing information for identifying the damage phenomena. The system is based on a high-speed camera and three laser pointers for illuminating the specimen surface. Images of the specimen surface are acquired and processed, allowing the definition of synthetic surface state indexes, as well as the section profiles of the surface. The vision system was applied to alternated dry–wet rolling–sliding contact tests on railway wheel steel specimens, highlighting its effectiveness in the damage evaluation. The potential of the section profile reconstruction as a tool for surface topology analysis was shown. [ABSTRACT FROM AUTHOR]

During the damage and defects related to rolling contact fatigue (RCF), together with wear occurring at the rail surface, the microscopic characteristics of the rail material change with the accumulation of wheel cycles. To find the relationship between rail material characteristics and RCF damage under wheel-rail contact situations, a series of twin-disc rolling-sliding tests, based on real wheel-rail contact situations at a radius of 80 mm rail profile, was established for a heavy-haul railway in China. The microscale characteristics of the rail disc contact surface was researched, including crack, wear, roughness, and hardness of the U75V rail with different load cycles. The results show that the damage mechanism of RCF and wear alternately dominates the rail disc surface at the microscale, taking a certain cycle as a boundary which makes the RCF crack number and wear rate have opposite evolutionary trends. The above factors also affect the wear at the surface rail discs, alternating between fatigue and adhesion. Meanwhile, increasing the surface micro-hardness leads to a decrease in the relative wear rate and an increase in the roughness, length and number of RCF cracks. The plastic deformation layers, including the severely deformed layer (SDL) and the transition layer (TL), almost maintain the same thickness and the dynamic equilibrium increases during the cycles. Two kinds of cracks are initiated and propagated at the rail disc surface, one at the SDL and the other at the junction of SDL and TL. The number of each kind of crack depends on the SDL thickness. • The RCF and wear mechanisms dominated the rail surface alternately by a certain cycle. • Increasing the microhardness makes wear decreasing followed by an increase in roughness and RCF cracks. • The adhesive and fatigue wear happened alternately during the cycles. • The fracture mode of along or through the crystal depends on plastic deformation layer. • The thickness of the severely deformed and transition layers changes on opposite while keeps the entire thickness constant. [ABSTRACT FROM AUTHOR]

• A 3D wheel-rail rolling contact FE model was established based on measured corrugation and hardness distribution of rails. • The effect of uneven hardness distribution on the stress-strain distribution within the wheel-rail contact area was analysed. • The wheel-rail rolling contact behaviour in the corrugation zone changes significantly after work hardening. • Work hardening has a major effect on the difference in wear between the crest and the trough. The process of work hardening in the corrugation zone of the steel rail results in an uneven distribution of hardness, with higher hardness in the corrugation troughs and lower hardness in the corrugation crests. To study the influence of hardness on the rolling contact behavior of the wheel-rail at corrugation zone, a three-dimensional wheel-rail transient rolling contact finite element model is established based on the measured corrugation and hardness distribution of the rail to reveal the influence of the non-uniform distribution of hardness at corrugation zone on the wheel-rail contact state and the wear and fatigue of the rail surface. The results indicate that: (1) work hardening in the corrugation zone leads to an increase in equivalent stress and strain within the contact patch between the wheel and rail. However, due to the increase in yield strength, plastic deformation and residual strain are somewhat reduced; (2) The uneven distribution of hardness in the corrugation zone results in an elevation of longitudinal shear strain between the wheel and rail, which may initiate tangential fatigue cracks and spalling of the steel rail surface; (3) the wear on the rail surface is large near the wave crest and small near the wave trough, work hardening will change the wear difference between the wave crest and wave trough while reducing the wear, resulting in the "peak shaving and valley filling" phenomenon developing faster in the early wave wear period and slower in the later period. [ABSTRACT FROM AUTHOR]

A new methodology to distinguish between the damage mechanisms wear only and RCF crack initiation in combination with wear in rolling contacts is proposed in this work. The new methodology distinguishes between the damage mechanisms by comparing the experimental crack depth against a critical crack depth which is governed by the surface roughness and by the plastic shear deformation depth in the near-surface layer. The new methodology is used to assess the results of twin disc experiments that have been conducted with three pearlitic rail steels at different normal contact pressures and different longitudinal creep values. The observed experimental results show agreement with the criterion and the threshold of the new methodology. • Methodology to distinguish between wear and RCF crack initiation in twin disc tests. • A threshold (critical crack depth) is proposed to recognise the damage mechanisms. • The critical crack depth threshold consists of two regimes. • The methodology was applied to twin disc tests under varied test conditions. • The near-surface layer that is influenced by the surface roughness is around 50 μm. [ABSTRACT FROM AUTHOR]

The application of coating gets exceptional importance since it improves the tribological properties of the contacting surfaces. Different input parameters like coating deposition processes, coating material properties and its thickness, use of lubricant and its additives, surface roughness and temperature affect the tribological properties and the rolling contact fatigue (RCF) life of coated rolling and sliding contact elements. In this paper, an attempt has been made to review for the clear understanding of the effect of these input parameters on the RCF life and tribological performance of coated rolling and sliding contact elements. It has been observed that coating deposition process must be chosen based on technical and economic aspects. Among the different techniques, thermal spraying technique is cost effective, and it also provides better bonding strength, which improves the RCF life in comparison with other techniques. Similarly, the effect of other input parameters has been reviewed and possible combination of the input parameters that help improve the performance of coated contacting elements summarized. Furthermore, the current status of research and the scope of future work to be carried out, in this area, have been outlined. [ABSTRACT FROM AUTHOR]

• The multiphase microstructure obtained by B-QP process shows better RCF properties. • The B-QP steel with multiphase microstructure exhibits the better wear resistant. • The multiphase microstructure has higher hardness increasing ratios after RCF test. • The multiphase microstructure shows the larger strain accumulation under RCF test. • The RCF damage level of the multiphase microstructure is lower. Bainitic steel is considered to be the best potential candidate steel for rails due to its high strength and excellent toughness. The objective of this work was to investigate the fatigue property and microstructure deformation behavior of a medium-carbon bainitic steel with bainite/martensite/retained austenite multiphase microstructure obtained by a modified Q&P process (B-QP) under rolling contact condition. The analysis results of TEM indicated that the multiphase microstructure consists of lath bainitic ferrite, lath martensitic ferrite and film-like retained austenite which distributes mainly between bainite and martensite laths. The results showed that the multiphase microstructure has a better combination of toughness (103 J), hardness (47.8 HRC) and elongation (18.6%), along with better rolling contact fatigue (RCF) properties and wear resistance than that of full bainite microstructure obtained by the austempering process (BAT). After the steel subjected to 105 cycles of RCF testing, nanocrystalline grains (approximately 93 nm and 67 nm for the BAT and B-QP sample, respectively) were obtained at the deformed layer depth of 10 μm. Meanwhile, the multiphase microstructure demonstrated a higher microhardness increasing ratio (24.5%) than that of the full bainite (21.2%) and a larger plastic deformation zone (103 μm). The EBSD and XRD analysis indicated that the multiphase microstructure has a lower stress concentration possibility and higher percentage of high-angle boundaries as well as some film-like austenite retained in the plastic deformation layer. In addition, many pits on the contact surface of the BAT sample appeared, due to spalling damage caused by cyclic loading, and the crack propagation depth was larger. Conversely, the contact surface of the B-QP sample with a multiphase microstructure looked smooth, and the crack propagation depth was shallow under the contact surface. The enhanced rolling contact fatigue properties and wear resistance of multiphase microstructure can be mainly attributed to better a combination of strength and toughness, larger plastic strain accumulation and lower fatigue damage level. [ABSTRACT FROM AUTHOR]

In this article, a wheel life prediction model considering wear and rolling contact fatigue (RCF) is developed and applied to a heavyhaul locomotive. For wear calculations, a methodology based on Archard's wear calculation theory is used. The simulated wear depth is compared with profile measurements within 100,000 km. For RCF, a shakedown-based theory is applied locally, using the FaStrip algorithm to estimate the tangential stresses instead of FASTSIM. The differences between the two algorithms on damage prediction models are studied. The running distance between the two reprofiling due to RCF is estimated based on a Wöhler-like relationship developed from laboratory test results from the literature and the Palmgren-Miner rule. The simulated crack locations and their angles are compared with a five-year field study. Calculations to study the effects of electro-dynamic braking, track gauge, harder wheel material and the increase of axle load on the wheel life are also carried out. [ABSTRACT FROM AUTHOR]

This study presents the wear and damage behaviours of U71Mn rail material with a friction pair of ER8 wheel material under different temperature conditions, which were explored using a rolling-sliding wear testing device. It turns out that, compared to those at 20 °C room temperature, the adhesion coefficient, wear rate and hardness all increase at low temperatures. Meanwhile, three types of damage mechanisms are proposed according to wear and rolling contact fatigue (RCF) behaviours under different temperature conditions: (a) room temperature (RT) damage mechanism, (b) ductile-brittle transition temperature (DBTT) damage mechanism, (c) below ductile-brittle transition temperature (BDBTT) damage mechanism. With the temperature decreasing from room to low temperature, the wear mechanism transforms from abrasive wear to adhesive wear and surface fatigue. Meanwhile, the rail material gradually becomes brittle and the subsurface damage at low temperature is more serious than that at room temperature. Furthermore, the subsurface damage at −15 °C is the worst. At low temperature, there is a wider size range of wear debris than that at room temperature. [ABSTRACT FROM AUTHOR]

This paper extends the modelling approach towards the evaluation of wear and rolling contact fatigue, by including the effect of rail/wheel hardness ratio. We firstly perform wear and RCF tests in the laboratory with varied hardness ratios from 0.79 to 1.60. Then we formulated the new wear and RCF laws, and determined corresponding coefficients in the formulas. Proposed new wear laws are validated through a numerical example based on a prediction model. Comparison between the simulated results and in-field results shows that the results from the simulation are well consistent with those from field measurements. Sensitivity analysis provides an inspection of the effect of the hardness ratio on wear and RCF. • Effect of rail/wheel hardness ratio on wear and rolling contact fatigue. • New wear and RCF laws based on tests in laboratory. • Validation of the new wear laws by comparison with measured results. • Sensitivity analysis provides an inspection of the effect of the hardness ratio. [ABSTRACT FROM AUTHOR]

Most existing wheel/rail hardness matching studies have been carried out using pearlite steels with different hardnesses; no relevant wheel–rail hardness matching research has been carried out for other microstructure types such as bainite and other tempered materials. In this paper, a CL60 wheel (pearlite) was quenched and tempered to obtain wheel materials with a certain hardness gradient, and matching tests between different wheel materials and a quenched U75V rail were carried out to explore the influence of wheel microstructures on wheel–rail damage. The results showed that with increasing tempering temperature, the wheel microstructure changes from tempered troostite to tempered sorbite, with ferrite changing from a needle shape to a multilateral shape; additionally, the cementite particles grow obviously larger, resulting in a gradual decrease in wheel hardness. With the increase in the wheel/rail hardness ratio, the wear rate of the wheel and wheel–rail system first increases and then decreases; the wear rate of tempered sorbite is the highest. Wear surface analyses indicate that typical peeling appears on the wear surfaces of the CL60 wheel as well as the coupled rail. Tempered sorbite shows slight peeling; however, severe peeling and delimitation occur on the wear surface of its coupled rail. Moreover, severe peeling and serious material delamination are present on the wear surface of tempered troostite, and typical peeling appears on its coupled rail surfaces. The fatigue crack initiation and propagation behaviors of wheel and rail materials are closely related to their microstructures. The cracks in pearlite always initiate on the surface and propagate along the ferrite line. Short and shallow fatigue cracks appear on the tempered sorbite with a high wear rate, and the cracks in the tempered troostite easily expand into the centre of the samples, indicating poor rolling contact fatigue (RCF) resistance. Therefore, the pearlite structure shows better comprehensive mechanical properties for wheel service; moreover, more attention should be given to wheel microstructure when conducting research on wheel–rail matching. • The CL60 wheel were heat treated and wheel materials with a certain hardness gradient were obtained. • Matching tests between quenched U75V rail and different wheels were carried out. • Wear and rolling contact fatigue behaviours were proposed and studied. • Ratcheting behaviours and propagating mechanism of RCF cracks were analyzed and revealed. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue (RCF) and wear are competing phenomena in railway wheels, but they are typically studied as independent events. In this work, preliminary tests are carried out with a twin-disc bench to explore the relationship between RCF and wear. First, the collected tests are reported on the shakedown maps to assess the cyclic response and calculate the fatigue index parameter used to predict the surface-initiated fatigue damage. Second, the fatigue index and material cyclic yield strength are related to the experimental wear rate. This work proposes maps to predict how the wear rate and cyclic response change by varying the contact conditions (clean or contaminated with water or sand), slip ratio and extraction position of specimens. Furthermore, the estimated wear rate is superimposed to the shakedown map to investigate a possible relationship between RCF and wear. The proposed approach allows to understand how a railway wheel steel behaves as a function of the working conditions and whether some working parameters can be changed without compromising the material performance. • Predictive maps for bi-disc tests are proposed. • Wear rate is superimposed to shakedown maps. • A higher fatigue index results in a higher wear rate. • Water contaminant drastically reduces the wear rate. • Reprofile operations increase the fatigue index and wear in clean contact. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue and wear of rails are well-known problems. However, progress is not easy to predict because these problems interact with each other. Therefore, to reduce damage, the interactions between these two mechanisms must be clarified. In this study, the contact fatigue and wear of UIC 60 and KS 60 rail materials were investigated by twin-disc testing with various parameters. We found that ductility and fracture toughness are important factors on wear and contact fatigue. UIC 60 rail steel with higher ductility and fracture toughness than KS 60 rail steel has a higher resistance to contact fatigue but a lower resistance to wear. [ABSTRACT FROM AUTHOR]

The study aims to explore the effect of tangential force on wear and rolling contact fatigue (RCF) behaviors of wheel material using a JD-1 wheel/rail simulation facility. The normal, tangential and lateral forces between the wheel/rail rollers are controlled, and the magnetic power brake was used to generate the tangential forces (16–330 N). The results indicate that the surface hardness and wear loss of wheel rollers increase with the tangential force increasing. The surface cracks mouths are perpendicular to the resultant directions of the frictional forces. There are visible secondary cracks and multilayer cracks and the interlayer material of multilayer cracks are easy to break. The compositions of wear debris consist of Fe 2 O 3 , Fe 3 O 4 and iron. [ABSTRACT FROM AUTHOR]

Three types of differently shaped lasered microtextures (microdimples) were produced on the surface of a U75V hot-rolled rail roller with a TY-FM-20S laser marking machine. Wheel flange/rail gauge lubrication starvation tests of four kinds of rail samples running against CL60 wheel samples were carried out, and the friction properties of the wheel/rail steels were studied. The results indicate that the injection of lubricating grease dominates the friction coefficient reductions and that the lubricating effects are closely related to the shapes of the lasered microtextures; for instance, the rectangular and rhombic textures show a better lubricating effect. Furthermore, the wear rates depend on the wear mechanism of the wheel/rail steel; for example, delamination and spalling always result in severe wear while peeling results in mild wear. The materials from the rolling-sliding surface to the matrix region of the wheel/rail materials can be divided into three parts: the plastic deformation region, transition region and undeformed matrix region. The average crack length and angle values of the textured rail and coupled wheel steels are much smaller than those of the untextured rail and coupled wheel steels; thus, the textured rail and coupled wheel steels exhibit better rolling contact fatigue (RCF) resistance. The effects of the lasered microtextures shapes on the wear and fatigue damage are determined based on the fluid dynamic pressure on the microtexture. Notably, rhombic lasered microtextures can be adopted to improve the grease storage capacity, thereby reducing wear and fatigue damage. • Three types of differently shaped lasered microtextures were produced on the rail surface. • Lubrication starvation tests of four kinds of rail samples were carried out. • Lubricating effect, wear and rolling contact fatigue behaviours were proposed and studied. • The textured rail and coupled wheel steels demonstrated better RCF resistance. • The lubricating and damage mechanism of textured rail were analysed and revealed. [ABSTRACT FROM AUTHOR]

• Segregation bands could improve the wear resistance of the rail. • Segregation bands severely reduced the rolling contact fatigue of the rail. • Segregation caused inhomogeneous strain and crack initiation in the test. • The friction heat caused dynamic recovery of dislocation. Rolling contact fatigue (RCF) is the main failure mode of wheel-rail system. In this work, the influence of non-uniform microstructure on the rolling contact fatigue performance in bainitic rail steel was investigated. According to the results, an increase in degree of segregation enabled material to improve the wear resistance through the improvement of the local hardness of the rail, but seriously reduced the rolling contact fatigue performance of the rail. The crack propagated along the segregation band, thereby leading to the failure of the specimen. The main cause of fatigue crack initiation was the non-uniform strain distribution under cyclic loading due to different hardness values between the matrix and the segregation region. A large number of dislocations produced by plastic deformation on the surface of the specimen segmented grains into nanocrystals. Meanwhile, it can be seen from the in-situ heating transmission electron microscope (TEM) that the friction heat generated during RCF test was enough to support the occurrence of dynamic recovery. [ABSTRACT FROM AUTHOR]

Railway transport companies in Brazil and worldwide have become more productive and efficient by increasing the weight transported and using faster locomotives. These actions have caused the premature exchange of wheels and rails due to excessive wear and rapid growth of rolling contact fatigue (RCF) cracks, and both consequences have been minimized by the improvement of pearlitic steels of wheels and rails. However, these pearlitic materials have already shown that there is a limit to the optimization of their mechanical properties. The bainitic microstructure could replace the pearlitic one, however few studies on the bainitic microstructure variants have been carried out, which still makes its behavior in rolling and sliding wear – especially in high carbon microalloyed steels – a matter of debate. Those studies are far from reaching a consensus, and, therefore, an important question arises regarding the materials used in the wheel-rail contact: which microstructure has better tribological and fatigue properties being produced from the same steel, having the same hardness, and being influenced by the same tribological variables: bainite or pearlite? In order to answer this question, twin-disc tests were performed on forged railway wheel microalloyed steel (7NbMo) with pearlitic and bainitic microstructures with the same bulk hardness and on high carbon steel (7C) with tempered martensite. The results revealed that the microstructure had a significant role in wear and RCF performance. The bainitic microalloyed steel (7NbMo–B) showed lower wear rates and greater resistance to RCF than the pearlitic one (7NbMo–P). Similar behavior was observed for their counter-bodies, indicating that the use of bainite in rolling and sliding wear applications would cause the joint benefit of the body and counter-body. • The bainitic microalloyed steel showed lower wear rates and greater resistance to RCF than the pearlitic one. • The best wear performance by the bainitic disc is because of its greater capacity to absorb energy with less volume. • The bainite cracks made a tortuous propagation path due to the interlocking caused by cementite carbides. • The ratchetting was the main mechanism of wear for both microstructures. [ABSTRACT FROM AUTHOR]

Plasma selective quenching is a technology which can significantly improve the wear resistance of rail material. However, there are few studies on damage characteristics of rail materials with plasma selective quenching (PSQ). In this study, the influence of PSQ on wheel-rail wear and damage characteristics was studied. The research results show that PSQ has a great influence on damage characteristics of rail materials; PSQ can significantly reduce rail wear; The damage characters of quenched specimens could be divided into three stages: quenched zone wear, quenched zone wear and spall pits, substrate wear. •The influence of the plasma selective quenching on wheel-rail wear and RCF damage was studied. •An electron microscope was used to observe the damage of the wheel/rail surface. •Plasma selective quenching has a great influence on RCF damage of wheel and rail. •An excessive proportion of the quenched area of rail leads to increased wheel wear. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni-Cr-Fe (N), 17-4PH (MP) and 18Ni300 (MS) coating are deposited on rail by LIHC. • The microstructure and hardness of N coating show little change in different layer. • The grain size and precipitates' content of MP and MS coating vary in different layer. • Wear rate, PD depth and surface damage of rail with MP and MS coating are all reduced. • LIHC deposited MS coating shows the best competitiveness in the rail repairing. In this paper, Ni-Cr-Fe, 17-4PH and 18Ni300 alloy coating were deposited on the rail surface by laser-induction hybrid cladding (LIHC), respectively. The microstructure, microhardness of different coatings, and their influences on the wear properties and contact fatigue behaviors of rails were studied systematically. Results indicate that the as-deposited Ni-Cr-Fe coating is constituted of the dendrite structure, and the as-deposited 17-4PH and 18Ni300 coating mainly consist of the lath martensite structure. The microstructure and microhardness of Ni-Cr-Fe coating are little influenced by the in-situ thermal cycling in LIHC process, whereas the grain size and precipitates' content in 17-4PH and 18Ni300 coating are affected significantly, making the microhardness therein increased along the depth direction. Compared with the untreated rail, the wear rate and plastic deformation (PD) depth of rails with 17-4PH and 18Ni300 coating are both decreased significantly, while the contact surface damage is alleviated simultaneously. Especially for that with 18Ni300 coating, the decreased proportions are as high as 40.2% (mass wear rate), 60.1–81.2% (dimensional wear rate) and 78.7% (plastic deformation depth), respectively. By contrast, the wear rate of rail with Ni-Cr-Fe coating is increased conversely than that of the untreated rail although its microhardness is 32% higher. Therefore, the LIHC deposited 18Ni300 coating is a competitive choice for repairing the rail in engineering. [ABSTRACT FROM AUTHOR]

Abstract: Wear and rolling contact fatigue were investigated on unfilled PEEK and on three PEEK short fiber reinforced composites. For this aim, roller-shaped specimens were subjected to rolling contact tests at different contact pressure levels. Wear rate-pv product and contact pressure-life diagrams were obtained, depending on material hardness. Microscopic observations of rolling contact surfaces and sections of the rollers highlighted damages at two different scales, surface and bulk, leading independently to wear and rolling contact fatigue. These damages were also of different typology for unfilled PEEK and composites: micro-pitting and deep transversal cracks occurred on unfilled PEEK rollers, while delamination and spalling phenomena where found on composite rollers. [Copyright &y& Elsevier]

Abstract: In order to know the relationship between the occurrence of flaking leading to the rail breakage and wear of the rail, on-site investigations and analysis of the broken rail were carried out. As a result, it was found out that the occurrence rate of the flaking damage was high at gauge corner side of high rail in moderate curves with radius from 800m to 1800m. It was also found that the rail wear in the section where lubrication was applied was about a half of that in the section without lubrication. Moreover, it was found that flaking damage was generated on the running surface or in the close vicinity of the surface of rail head under the condition of repeated loading of shear and tangential forces caused by the rolling contact with wheels. It could be assumed that the balance between the wear and the accumulation of micro-strain or fatigue was a key to occur the flaking damage. [Copyright &y& Elsevier]

Abstract: Continuing from research reported at CM2006, we report further investigation of the interaction of rail with friction modifiers (FM) related to wear and RCF generation. This work examines the relative effects of FM on standard (R260) and premium (R350HT) rail using a test rig. Under dry conditions, the premium rail shows clearly reduced wear and RCF generation compared to the standard rail. Application of FM reduces wear and RCF propensity for both standard and premium rail, with the best result achieved by a combination of R350HT and FM. Results on plastic flow were similar and consistent with the wear and RCF pattern. Longer term testing with FM application was terminated after four times the normal test cycle length without any RCF formation. Application of FM to pre-existing RCF cracks did not lead to acceleration of crack growth (e.g. by hydropressurization) under the experimental conditions used. Field results were reviewed for both premium rail and FM effects on RCF, and are found to be generally consistent with test rig results. [Copyright &y& Elsevier]

Abstract: This paper investigates the wear and RCF behaviour of several pearlitic and bainitic rail steels on a full scale test rig at voestalpine Schienen GmbH and also in several track tests. On the test rig a clear dependence between hardness of the pearlitic grades and the resistance against wear and RCF is seen. The same is found in track tests however the results especially in low wear regimes concerning higher hardness grades are not as distinct as on the test rig. Track behaviour also indicated the improved RCF resistance of higher hardness steels. Bainitic steels show a slightly different behaviour – the wear resistance is reduced compared to a pearlitic steel with the same hardness level though the RCF resistance is higher (both on the rig and in track if data available). Although the trends are consistent on the rig and in track, the absolute values concerning wear and RCF differ. Finally an outlook concerning modifications and upgrades for the test rig to shorten this gap is given. [Copyright &y& Elsevier]

The objective of this study is to investigate the wear and rolling contact fatigue (RCF) damage of wheel and rail materials under alternating temperature conditions. Two series of rolling-sliding tests were performed: (1) at 20 °C for 75,000 cycles, and then continued at −40 °C for 10,000, 30,000, and 75,000 cycles, respectively; (2) at −40 °C for 75,000 cycles, and then continued at 20 °C for 10,000, 30,000, and 75,000 cycles, respectively. The results indicated that the decrease in the temperature would alleviate the wheel wear due to the formation of wear debris layer. Both the rising and dropping of the environmental temperature during the tests could lead to the increase in the rail wear. Besides, the decrease in the temperature could increase the plastic deformation and work hardening of wheel and rail discs. In addition, the crack initiation was correlated with the behaviour of plastic flow on the wheel. At 20 °C, long single cracks initiated and propagated along the highly deformed ferrite boundaries. At −40 °C, white-etching layer (WEL) was observed only on the wheel surface, which was mainly attributed to the severe plastic deformation. Then, the refined ferrites and WELs were the main crack initiation sources on the wheel. • Wear and RCF of wheel and rail were studied under alternating temperatures. • The adhesion wear of wheel and rail was strengthened at low temperature. • The decrease in temperature would alleviate the wear of wheel material. • Low temperature accelerated the plastic deformation of wheel and rail rollers. • The WEL was observed on wheel at −40 °C, but not observed at 20 °C. [ABSTRACT FROM AUTHOR]

This research centres on surface initiated damage on back-up rolls whereby rolling contact fatigue cracks can propagate into the rolls potentially reaching the internal stress fields and leading to catastrophic failure and has sought to establish design criteria for avoiding such failures. The project objectives have been achieved by examining field evidence, determining the loading and tribological conditions at the work roll/back-up roll interface and investigating both theoretically and experimentally the mechanisms involved in rolling contact fatigue in this case. The presented rolling contact, fatigue and fracture mechanics model includes criteria for crack branching either upwards (i.e.relative safety) or downwards (i.e.potentially catastrophic) and the link between these two cases is related, quantitatively, to the properties of the roll material. After linking mechanics to microstructure, the influence of work roll test disc surface roughness on both the surface wear of and the interaction between wear and rolling contact fatigue at the surface of back-up roll test discs has been quantified using the results obtained from experimental simulations carried out on a rolling–sliding testing machine. Finally practical quantitative recommendations are made for the mechanical and microstructural design of bainitic back-up roll materials, back-up roll redressing procedures and the surface roughness of both work rolls and back-up rolls presented to the mill. [ABSTRACT FROM AUTHOR]

This study reports the results of laboratory tests carried out to evaluate the rolling contact fatigue (RCF) resistance of ductile iron with different treatments. Tests were conducted in a flat washer type RCF apparatus, at loading and lubricating conditions leading to the interaction of surface microasperities, i.e. with specific oil film thickness, λ<1. The microstructures evaluated correspond to different austempered ductile iron (ADI) grades, obtained at different austempering temperatures, and one variant of a partially chilled ductile iron (PCDI). The ADI variants have shown the highest RCF resistance for the lowest austempering temperature evaluated. The PCDI samples, in the as-cast condition, have shown the highest RCF resistance among the different ductile iron variants evaluated. It was observed that nodules play an important role on the nucleation stage of the failure process, and also the reduced nodule size of the PCDI could be responsible for its high RCF life. [Copyright &y& Elsevier]

Rail grinding and wheel turning can effectively remove surface defects and unevenness, which is a crucial process for the safe and smooth operation of trains. Machined surface integrity of wheel/rail materials significantly influences their tribological property. In this study, firstly, the rail blocks were ground via a cylindrical grinding machine, and the wheel rings were turned by a computer numerical control (CNC) lathe with varied parameters. Then, the sliding wear and damage characteristics of the machined wheel/rail samples under dry conditions were studied by virtue of a block-on-ring tribometer. The results show that the surface microhardness of the ground rail blocks is larger than that of wheel rings, while the surface roughness and the thickness of the subsurface plastic deformation layer (SPDL) of rail blocks are much smaller than those of wheel rings. After sliding, the surface microhardness of wheel/rail samples increases remarkably. The thickness of the SPDL, the wear loss, and the increase degree of surface microhardness of rail blocks are larger than those of wheel rings. Surface microhardness, roughness and the SPDL of the machined wheel/rail samples impose a combined influence on the anti-wear property, and the tribological pair with proper initial surface roughness and microhardness engenders the smallest amount of total wear loss. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue has a significant impact on the service life of the infrastructure, in particular on the rail, which undergoes various defects, the severity of which threatens transport safety. Our study focused on the investigation of a curved track on the Algerian railway network laid in the 1980s by checking the design, the rail material, and the operating conditions of the track, and then the degradation of the rail for a classification and defect analysis based on standards. The methodology used consists of a visual field study using conventional measurement methods, supported by on-site and laboratory ultrasonic inspection to highlight the severity of defects for railway safety and to measure the effectiveness of the operator's maintenance policies, which must be improved in terms of defect's detection and removal to extend the infrastructure's life. [ABSTRACT FROM AUTHOR]

To reproduce the rolling contact fatigue (RCF) damage of rail steel used in heavy haul railways and to clarify its possible mechanism, the RCF characteristics of pearlitic steel with different carbon content and initial hardness values are evaluated using a two-disk-type machine. The results indicate that the number of spalls and the crack depth decrease with increasing carbon content of pearlitic steel even when the initial hardness is almost the same level. Furthermore, an increase in the carbon content increases the hardness of the rolling contact surface, resulting in the suppression of the plastic flow development. Results also indicate that the crack inclination angle varies depending on the carbon content. According to these results, a possible mechanism for the suppression of fatigue crack propagation in higher carbon pearlitic steel is proposed on the basis of the fracture mechanics approach. • Carbon content of rail steel affects heavy loaded rolling contact fatigue resistance. • Increase in carbon content increases in hardness of the rolling surface. • Increase in carbon content suppresses development of plastic flow. • Crack inclination angle varies depending on plastic flow. • Increase in carbon content results in suppression of crack propagation. [ABSTRACT FROM AUTHOR]

A multi-step FE modeling strategy has been proposed to predict the temperature evolution, thermo-mechanical response, surface fatigue life and wear behaviors in railway rail for multi wheel passages. Equivalent contact pressure and heat source were coupled and moved simultaneously on rail surface to achieve a balanced advantage of low computational cost and high accuracy. Wheel configuration at locomotive plays a significant role on rail temperature. The highest temperature of 776.05 °C was developed with a slip ratio of 9.43% after 9 wheel passages. Rolling contact fatigue life of rail material decreased quickly with slip ratio due to significant thermal softening effect. Transition from mild to severe wear was found at slip ratio of 2.38% according to the corresponding rail flash temperatures. • A modelfor multi wheel passages of train locomotives considering both contact pressure and thermal effects was proposed. • Practical scenario of two locomotives was introduced to study the temperature evolution on rail surface. • Relation between slip ratio and rolling contact fatigue life of rail material was predicted. • Wear of rail was mild when slip ratio was ≤2.38% but transited into severe wear when slip ratio was higher. [ABSTRACT FROM AUTHOR]

Although both wear and fatigue are inevitably associated with the wheel/rail contact, they are normally studied as different phenomena and both are commonly considered excluding. Wear of railway wheels and rails is usually studied by relating wear rate to the T γ or T γ / A parameters or by plotting the so called "wear maps", where different rolling parameters are related to the wear rate. On the other hand, fatigue in wheel/rail contact is mainly studied from the surface and subsurface stress or deformation fields and from the crack growth rate. However, one of the main causes of wear in rolling contact is the loss of material due to delamination processes that have their origin in the presence of surface fatigue cracks. So, if wear and fatigue are related, it should be possible to study both of them using the same method. In this paper, the fatigue index, based on the shakedown theory and used to predict the surface initiated fatigue of railway wheels, is proposed as a means to study the wear rate in rolling contact. The fatigue index is directly related to the apparition and growth of fatigue cracks at the surface and, thus, directly related to the peeling and spalling processes that constitute the severe and catastrophic wear mechanisms. The data collected from a series of twin-disc tests show that the wear rate correlates with the fatigue index following an exponential evolution independently of the normal load. Furthermore, a fatigue index around 0 marks the onset of severe wear. • The fatigue index is a suitable option to predict rolling contact wear. • Severe wear in takes place when the fatigue index is equal or greater than 0. • The relation between delaminative wear and the fatigue index is exponential. [ABSTRACT FROM AUTHOR]

Railway steel that offers a greater quality and extended life is described by the industry as premium rail. It is mainly used on areas of rail networks where accelerated wear, rolling contact fatigue or other rail related damage phenomena prevail. However, little performance data exists for these materials and where it does it is limited to a narrow set of contact conditions. The aim of this work was therefore to map premium rail performance across a range of Tγ contact conditions to benchmark against standard grade R260 rail. Laboratory tests using a twin disc machine were performed to determine the wear performance of four premium rail grades against R8 wheel material, at various slip conditions of 1–20%. Comparison with Martensitic Stainless Steel (MSS) laser clad material was made as a further benchmark. The results are shown in terms of Tγ and wear rate for both the rail and wheel discs. Material hardness maps were obtained of the full rail and the laboratory small scale specimen materials in order to correlate hardness with their wear behaviour. The purpose of this work is to understand the likelihood and rate of wear in different wheel/rail contact conditions and to produce enough wear information for the premium rail that could be used in prediction tools for comparison with other materials and contact conditions. • Wear rates were obtained at high Tγ for R260 and premium rail. • "System Wear" was compared at different Tγ values. • Through thickness hardness mapping was performed for premium railhead and twin disc samples. • Extreme plastic deformation was observed for some materials at high Tγ. [ABSTRACT FROM AUTHOR]

Rail damages in railway turnout switch panels are closely related to the complicated wheel-rail contact conditions in the turnouts. In order to assess the applicability of different non-Hertzian contact models for simulating rail damages in railway turnout switch panel, three engineering approaches, i.e. Kik-Piotrowski, Ayasse-Chollet and Sichani, are adopted to simulate rail wear and surface initiated rolling contact fatigue (RCF) damages by studying a Chinese CN60-1100-1:18 high-speed turnout switch panel. A comparison is then carried out taking into account the results calculated by Kalker's three-dimensional (3D) theory and an elastic-plastic FEM (Finite Element Method) model. The analyzed results show that the computational efficiencies of the three engineering approaches are all quite high for simulating rail damages in switch panel. Under elastic conditions, the calculation accuracy of the Sichani approach is found to be the highest, meaning that this would appear to be the preferred method for simulating rail damages in railway turnout switch panel. The research findings can be taken as theoretical guidance for selecting wheel-rail contact models and analyzing these types of damages in railway turnout switch panels. • Effect of non-Herztian contact models on simulation of rail damages in switch panel is evaluated. • Prediction models for wear and surface initiated rolling contact fatigue in switch panel are introduced. • The wear and surface initiated rolling contact fatigue of rails in switch panel are simulated. • The Sichani approach is most suitable for numerical simulation of rail damages in switch panel under elastic conditions. [ABSTRACT FROM AUTHOR]