Wheel Steel Research Articles

Detection of Cut Notches and Corrosion on Anchor Bolts

The overhead catenary system (OCS) comprises of the pantograph which presses against the underside of the lowest overhead wire or the contact wire. Current collectors are electrically conductive and allow current to flow through to the train and back to the feeder station through the steel wheels on one or both running rails. With water seepage due to occurrence of monsoon rain and porosity of the cement material, the mineral rich rock structure can undergo much more rapid degradation under an electrochemical process due to the potential of the OCS. SEM images of the corroded bolts segment show high porosity surface with corroded voids. EDX study shows the presence of high oxide, chloride, and iron elements as indicative of a corroded bolt. The first backwall echo of the ultrasonic peak amplitude provides an understanding of the length of a bolt. Comparative study can provide a signature of the bolts which have been corroded with less fringe peaks due to the presence of bolts’ threads which tends to wear out with the duration of corrosion. Fatigue cracks are mimicked and modelled with cut notches of varying depths on bolts followed by immersion in corrosive peroxide solution for accelerated corrosion. A good clear distinction of the presence of such peak signal amplitudes due to cut notches with the referenced backwall echo peaks of the corroded bolts could be registered by the ultrasonic tests. The height of the signal peak amplitudes could give an indication of the depth of cut at the notch and the quantity of such peaks provide an indication of the number of cut notches. The ultrasonic test provides an effective means for non-destructive testing of such bolts which are embedded in concretized underground tunnel.

Simulation and Experimental Study on Rolling Friction and Wear of Heavy Haul Wheel Tread

Rolling friction and wear testing of heavy haul wheel tread was performed. The results show that a new and dominant vibration was generated owing to the surface wear, resulting in the polygonalization wear of the wheel specimen. The slip between wheel and rail specimens accelerated the formation of polygonalization wear. The pearlite and proeutectoid ferrite in the outermost layer were completely fragmented to form a fine grain layer. There was an extreme state for the deformation of the microstructure in the outermost layer, and there was a corresponding extreme value for the hardness. The slip accelerated the surface microstructure to reach the plastic hardening limit, but it had little effect on the extreme value of hardness. The stress distribution of the wheel specimen surface was simulated. The results show that there were alternating principal tensile and compressive stresses at the contact surface of the wheel specimen and shear stresses with alternating directions in the subsurface of the contact patch. The depth of the maximum shear stress from the surface was mainly related to the normal load, while the slip has no significant effect on it. A coupling modeling method of finite-element method (FEM) and smoothed particle hydrodynamics (SPH) was used to simulate the microstructure evolution of CL70 wheel steel. The simulation results show that there was mutual mechanical interaction between ferrite and cementite in pearlite. Their deformation was inconsistent owing to their different mechanical properties, resulting in large tensile stress at the boundary between them, even in the compressive stress area below the contact patch.

Thermomechanical testing and modelling of railway wheel steel

Studies of thermal effects of tread braking on railway wheels show that the wheel temperatures may reach above 600 °C, at which the mechanical properties of the wheel steel are significantly impaired. Computational models that simulate the thermomechanical behaviour of the wheels are commonly based on results from laboratory tests which do not reflect actual in-service scenarios. Anisothermal testing and modelling are omitted due to the difficulties in designing relevant experiments and implementation of the results. In this paper, a preexisting numerical material model is extended in order to implement fully anisothermal behaviour. This is done by performing several thermomechanical experiments mimicking real-world service and worst-case scenarios ranging from room temperature up to 650 °C. The results from the laboratory testing are then used in combination with data from traditional isothermal tests to optimise the numerical material model by calibrating its material parameters. As part of this process it was found necessary to include a time- and temperature-dependent, non-recoverable (irreversible) mechanism for material softening and microstructural changes which occur above 400 °C. Finite element simulations with the material model using the new parameters and the softening law show markedly improved adherence to anisothermal and strain-controlled experimental results compared to the preexisting model(s). The results demonstrate that anisothermal testing is a requirement for models that are intended to simulate material behaviour for thermomechanical loads and thermally induced microstructural changes.

INEW method for experimental-numerical locomotive studies focused on rail wear prediction

Locomotive-track interaction is commonly represented by a complex mechanical system which is modelled in numerical studies. Numerical studies alone are not enough to precisely describe the behaviour of this mechanical system due to the various elements that can only be delivered from field and laboratory experimental programs. One such element is wheel-rail wear that has been found to contribute a considerable portion of the total cost of maintaining heavily used railway systems. Simulation studies are typically used for predicting wear of wheels and rails, but the majority of these do not consider in-train forces nor provide detailed modelling of traction and braking events and often rely on historic wear rates for comparable materials, reducing the accuracy of the wheel-rail volume loss estimation. This paper proposes a methodology for wear rate experimental measurements that allow improving the accuracy of wear analyses using dynamic simulations. The proposed method considers in-train forces by performing longitudinal train simulations whose results are then implemented on a detailed locomotive vehicle dynamic model with a traction mechatronic system co-simulation approach. The wheel-rail contact stress and slip results are then post-processed into a Dynamic Load Spectrum that contains contact stress and wheel slip occurrences. The Dynamic Load Spectrum was used to measure the wear rates for Australian AS60 head hardened rail steel material operating in combination with Class B wheel steel material. The experimental program delivered more realistic wear rates that correspond to actual industry operational scenarios. The measured wear rates were used to estimate the rail material volume loss for a specific train trip.

Effect of Electrolytic-Plasma Surface Treatment on Structure, Mechanical, and Tribological Properties of Grade 1 Wheel Steel

Effect of Electrolytic-Plasma Surface Treatment on Structure, Mechanical, and Tribological Properties of Grade 1 Wheel Steel

Microstructure evolution and properties of wheel steel under different pearlite content and slip ratio conditions

Rolling wear tests of wheel steel were carried out on friction and wear testing machines, and the effects of pearlite content and slip ratio on the microstructure evolution and property change of wheel steel were studied. The results indicated that if the pearlite content is low, surface cracks propagate along the deformed proeutectoid ferrite and deformed pearlite after initiation, and the wear mechanism is mainly fatigue wear. With an increase in pearlite content, the surface cracks propagate along the plastic flow lines, and the wear mechanism is mainly fatigue wear and adhesive wear. The fatigue wear and adhesive wear gradually increase as the slip ratio increases, resulting in a gradual increase in mass loss. The fatigue wear degree at each slip ratio is significantly reduced as the pearlite content increases, as well as the crack length, resulting in a substantial reduction in mass loss. When the pearlite content is low, low-angle boundaries are formed first in the proeutectoid ferrite. With an increase in the degree of deformation, the cementite is bent, fractured, or even dissolved. The proportion of high-angle boundaries in the ferrite gradually increases, and the grains are refined. When the pearlite content is high, the low-angle boundaries are formed in the lamellar ferrite, which eventually transforms into high-angle boundaries, making it more refined than with low-pearlite content. The cementite is severely fragmented and dissolved on the worn surface, the ferrite is elongated or even fibrous, and the microstructure is the most severe, resulting in the maximum surface hardness. The dissolution of surface cementite and the degree of ferrite refinement increase as the pearlite content and slip ratio increase, as does the hardness.

Effect of Residual Stresses on Wheel Fatigue Life and Experimental Validation

Steel wheels, consisting of rims and spokes, are important load-bearing parts of vehicles, and the fatigue fractures’ life estimation accuracy directly determines the stability and safety when applied in the transportation industry. The most common form of failure is fatigue fracture. The strong elastic–plastic deformation during the rim roll-forming process generates a residual stress field in its surface layer, which changes the actual stress distribution in the rim when it is loaded and thus affects the fatigue life of the steel wheel. In this paper, ABAQUS software was used to establish a rim-rolling simulation model to obtain the residual stress field distribution after forming and compare it with the actual residual stress on the formed surface of the rim to verify the reliability of the model. On the basis of this model establishment, the service hazard areas and maximum stresses of steel wheels with or without superimposed residual stress fields were calculated separately, and their fatigue lives were predicted separately using the local stress-strain method. The simulation results show that the maximum stress of the rim before and after the superimposed residual stress occurs in the area of the bottom of the groove, which is consistent with the actual failure location. However, the maximum stress after superposition increased from 120.7 MPa to 332.9 MPa, and the corresponding calculated life decreased from 158,340,000 to 459,500 cycles, which is closer to the actual test results. The results of the study can provide a theoretical basis for the lightweight design and process improvement of automotive steel wheels.

Comparative study on the influence of initial deformation and temperature of thermally induced white etching layers on rail wheels

Detailed investigations of white etching layers (WELs) formed on rails and wheels are of utmost importance to improve railway safety. This calls for lab-generated WELs with well-comparable characteristics to conduct further testing such as in twin-disc experiments. In this work, laser surface treatments were applied on wheel steels to induce thermally induced WELs. To evaluate the influence of the initial deformation state of the sample, undeformed and severely plastically deformed ER7 wheel steels were selected. In this study, it is shown that surface temperatures of > 640 °C lead to thermally induced WELs, with differences based on the initial deformation state. The thermally induced WELs are compared to a field-WEL present on an ex-service railway wheel. Results indicate that the WEL induced by laser treatment on an initially deformed wheel material provides the best match with the field-WEL. The most distinct difference is a grain size gradient within the outermost 30 µm of the field-WEL caused by deformation after the formation in service. This study clearly shows that the variation in initial microstructures and laser process parameters leads to differences in microstructural characteristics of thermally induced WELs and must be considered when imitating and testing WELs in laboratories.

Vision-based damage analysis in shoe-braking tests on railway wheel steels

Small-scale experimental tests were carried out by a bi-disc machine to reproduce the phenomena occurring in shoe-braked railway wheels. Wheel specimens of three different steels were subjected first to a braking step against cast iron brake-block specimens in full sliding condition, then to a running step against a rail steel in rolling-sliding condition. To monitor the damage occurring at the wheel specimen surface, a vision system, based on a high-speed camera acquiring the surface images during the tests, was implemented. An image analysis procedure was elaborated to evaluate the surface state by means of quantitative synthetic indexes. The correlation of such indexes with the damage was validated by means of comparison with the subsurface state, obtained by optical microscope observation of cut specimens. Finally, the synthetic indexes were used to analyse the evolution of the damage on a long-duration test, proving to be effective as a non-destructive damage monitoring tool.

Predictive maps for the rolling contact fatigue and wear interaction in railway wheel steels

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.

A Novel Hydroforming Process by Combining Internal and External Pressures for High-Strength Steel Wheel Rims.

As one of the key safety components in motor vehicles, the steel wheel rim is commonly fabricated with the roll forming process. However, due to the varied cross-sections of the rim and the low formability of high-strength steel, it is difficult to produce thin-wall and defect-free wheel rims to realize the purpose of light weight. To solve these problems, a novel hydroforming process by combining internal and external pressures (HIEP) was proposed to produce thin-wall wheel rims in the current study. The designed initial tube with diameter between the maximum and minimum diameter of the wheel rim ensures dispersed deformation and effectively avoids local excessive thinning. During HIEP, a hydroforming process was performed with two successive stages: the external pressure and internal pressure stages. Theoretical analysis and finite element method (FEM) were jointly used to investigate the effect of process parameters on the wrinkling and thinning. With the optimized parameters for internal and external pressure, the wrinkling of wheel rims is prevented under compressive state during the external pressure forming stage. Additionally, HIEP was experimentally carried out with high-strength steel rims of 650 MPa ultimate tensile strength (UTS). Finally, wheel rims with weight reduction of 13% were produced successfully, which shows a uniform thickness distribution with a local maximum thinning ratio of 11.4%.

Damage behavior and microstructure evolution of ER8C wheel steel under rolling wear conditions

In this study, the damage behavior and microstructure evolution of ER8C wheel steels at strip-quenched martensite white-etched areas (WEA) of a rail steel surface were studied based on rolling wear experiments. The results showed that with an increase in the number of rolling cycles, the wear rate appeared stable even though the friction coefficient decreased continuously. The surface wear mechanism of friction with a rail steel substrate area (S-CA) and that of friction with martensite white-etched area (WEA-CA) changed from oxidation wear and adhesion wear to oxidation wear and fatigue wear. The proeutectoid ferrite and pearlite in both areas underwent severe plastic deformation in the surface layer, resulting in the ferrite being elongated and refined into fibers and the cementites in the pearlite being fractured and partially dissolved. The surface hardness increased, and the depth of the hardened layer also increased. Fatigue cracks propagated mainly along the deformed proeutectoid ferrite and pearlite interface after surface formation. Under the same wear parameters, the plastic deformation degree and hardening degree of the WEA-CA were considerably higher than those of S-CA, indicating that the martensite WEA on the rail surface accelerated the wear of the wheel. Therefore, an increase in the slip ratio (0.5%–1%) promoted the wear and microstructure evolution process.

The impacts of retained austenite on the microstructure and property changes of carbide-free bainite during sliding wear

With the rapid development of Chinese railway industry, there is an increased demand for better toughness, wear resistance and fatigue resistance of wheel/rail materials, and the development of carbide-free bainitic wheel/rail materials with stable and outstanding comprehensive properties is of great significance to the acceleration of railway development. This paper conducts sliding wear experiment on the currently developed FCB bainitic wheel steel (abbreviated as FCB in the following content) and AB1 bainitic rail steel (abbreviated as AB1 in the following content), and investigates the impacts of retained austenite (RA) on the microstructure and property changes of carbide-free bainite. During the process of sliding wear, the wear morphology of FCB is chiefly featured by abrasive wear; As wear rotations increase, adhesion wear and fatigue wear gradually appear. Compared with AB1, FCB with similar chemical composition has more RA, which causes it to undergo plastic deformation more easily during sliding wear. The deformation gives rise to higher strain in the surface layer and makes the grains caused by it much smaller, leading to white etching layers (WELs) with higher thickness and hardness more easily. Meanwhile, more RA means that more martensite phase with high thickness will be generated during the wear process, which increases the hardness of FCB. These two factors work together to make wear resistance of FCB better.

Research on wear performance of new type CL60 steel for metro wheel

Purpose The CL60 steel wheels of metro vehicles running on a specific line need frequent reprofiling due to rapid wear. Considering this problem, a new material for metro wheels was designed. The friction and wear properties of the new material were studied, to reduce the wear rate and extend the service life of metro wheels. Design/methodology/approach Wheel specimens made of the two steel materials were tested using a GPM-60 wear tester under laboratory conditions. A field test was conducted on a specific metro line to track the wear in wheels made of the new material and CL60 steel wheels. Findings Under the laboratory conditions, the wear loss in the new material was 24.44% lower than that in CL60 steel. The field test revealed that compared to CL60 steel wheels, the new CL60 steel wheels showed a 19.42% decrease in tread wear on average. The field measurements for the wheels made of the new material are consistent with the results of laboratory simulation, suggesting relatively high wear resistance of the new material. Practical implications The results of the study can provide guidance on how to properly select steel material for metro wheels to avoid rapid wear and frequent reprofiling and reduce operating costs. Originality/value A new material for metro wheels was designed and developed by optimizing the content of Cr, Si, Mn, V and other elements. This material proved to have better wear resistance in both laboratory and field testing.

Influence of the Contents of Chemical Elements and the Procedure of Deformation and Heat Treatment on the Formation of Phase Composition of Wheel Steel

Influence of the Contents of Chemical Elements and the Procedure of Deformation and Heat Treatment on the Formation of Phase Composition of Wheel Steel

Field data to investigate the impact of initial air-voids on the performance of bituminous pavements – a case study

The aim of this study was to examine the relationship between initial compaction and pavement performance of a road with low-volume traffic. Data was collected from Telangana State in India. Binder was extracted from the field core samples after measuring the volumetric properties. The binder rheology was then compared with laboratory-aged VG30 bitumen. Higher air-voids in the newly constructed bituminous surface have caused binder ageing and raveling. Flaky, water-absorptive trap-aggregate worsened the problem. The fine aggregate and bitumen were stuck to the rubber-coated steel wheel in the Hamburg wheel tracking study indicating raveling. Binder reduction due to raveling was shown by slicing 30 mm field cores into two sub-layers; the bitumen content was reduced in the top slice (5.3% to 4.3%) and not in the bottom. For roads with low-volume traffic, a target density of 94% Gmm is recommended instead of the usual 92% to minimize binder ageing and raveling.

Investigation into the evolution of tribological white etching layers

When wheels and rails are in operation, their complicated and changeable contact conditions contribute to the formation of white etching layers on their contact surface. Martensite white etching layers (M-WELs) can induce the initiation of rolling contact fatigue (RCF) cracks, accelerating wheel/rail failure; Tribological white etching layers (T-WELs) can improve wear resistance. Therefore, to investigate the formation of T-WELs is to provide theoretical bases for developing surface strengthening technology. In order to delve into the mechanism for the formation of T-WELs, this paper conducted dry friction sliding wear experiment on ingot iron (equiaxed ferrite), D1 wheel steel (lamellar eutectoid ferrite) and FCB wheel steel (lath-like bainite-ferrite), and generalized the impacts of ferrite with different morphology and the second phase on the evolution of T-WELs. The result showed that T-WELs formed on the worn surfaces of all of these materials under the condition of sliding wear, and the evolution of T-WELs displayed similarities. Under the impact of dislocation slip mechanism, size reduction and dimension reduction were realized and finally ultrafine ferrite grains formed. But the second phase would increase the critical shear stress value of the transformation of ultrafine ferrite grains, hindering the formation of T-WELs and eventually affecting the size of ultrafine ferrite grains inside T-WELs.

Investigation into the evolution of the microcosmic surface of bainitic wheel steel material suffering polygonal wear

With the rapid development of high-speed railway, it is imperative to develop highly comprehensive wheel/rail materials to improve the safe and stable operation of trains. Even though bainitic steel shows excellent resistance to rolling contact fatigue (RCF), its wear resistance is not good enough and whether it is qualified for high-speed wheel materials still needs further investigation. Through conducting rolling wear experiment on carbide-free bainite (FCB) wheel steel, this paper observed the changes of the surface profile lines of the worn specimens regularly and the wear morphology in different stages, and analyzed the changes of the microstructures and hardness on the surface layer, in order to explore the formation of polygonization wear (PolyW) from the angle of the microcosmic surface of bainitic wheel steel. The research revealed that during the process of rolling wear, the nonuniform load caused by mechanical vibration could lead to the appearance of PolyW on the surface of the two-disc specimens of FCB wheel steel. Based on the surface morphology and size variations, three stages could be divided to explain the formation of PolyW: The incubation stage where macromorphology underwent cyclic changes, the development stage where PolyW appeared in some regions and the mature stage where PolyW spread all over the circumference. The wear mode in wave crests was mainly featured by oxidative wear and adhesion wear, and the one in wave troughs was marked by fatigue wear with wear rotations increasing, PolyW on the surface was exacerbated. Compared with wave crests, wave troughs had a larger slip ratio and the additional impact load, so the microstructures experienced severer deformation, the hardness increase was higher and the depth of the hardening layer was greater.

Temperature-dependent crack induced by microstructure evolution in 20Mn2SiMoCuV bainite wheel steel

Several severe cracks were found in novel 20Mn2SiMoCuV bainite wheel tread after 100,000 km test running, which will significantly affect bainite wheel’s service safety. The reason for cracks generation was investigated through microstructure observation and wheel/shoe contact analysis. Results showed that cracks were caused by microstructure evolutions resulting from temperature variations during quickly heating and cooling repeatedly in braking at contact interface of wheel tread and brake shoe. Temperature increased to above 500 °C at contact area will reduce the bainite wheel microstructure stability, leading to retained austenite decomposition to brittle martensite and cementite precipitation along grain boundary and lath boundary. Both above brittle martensite and cementite provided location for crack initiation and propagation. Therefore, some measures can be suggested to prevent initiation and propagation of cracks such as optimizing heat treatment process parameters to improve microstructure stability and adjusting matching of wheel tread/brake shoe to coordinate thermal conductivity.

Effect of annealing on microstructure in railway wheel steel

Railway wheels are commonly made from medium carbon steels (~0.55 wt.% C), heat treated to a near pearlitic microstructure with 5–10% pro-eutectoid ferrite. During the operation of freight trains, where block brakes are used, high thermal loads occur together with the high contact stresses, which combined can affect the mechanical properties of the material. In this study, the effects of annealing on local microstructure and mechanical properties in pearlitic railway wheel steel were investigated using electron microscopy and micro-hardness. It is found that after annealing at 650 °C, the room temperature hardness reduces about 25%, accompanied by significant spheroidization of cementite in the pearlitic colonies, though the size and the orientation gradients of the pearlitic colonies have not changed much. The relationship between the microstructural changes and the mechanical properties are discussed.