Railway Wheel Steel Research Articles

Effects of Heating Rate on Microstructure and Fracture Toughness of Railway Wheel Steel

The microstructure and fracture toughness KIC (or KQ) of railway wheel steel with 0.53 wt pct C were studied under various heating rates. The effects of the heating rate on the grain size and the relation between the grain size and the fracture toughness were discussed. The results show that rapid heating not only refines the grains but can also result in more homogeneous grains. The cleavage fracture toughness strongly relates to the grains with larger size. It can be observed that under different heating rates, the fracture toughness KQ increases with decreasing average diameter of the top 5 pct grains D5. KQ (MPa m1/2) = 194.3–29.8 ln(D5) when D5 is in the range of 30 to 73 μm. This result can be interpreted by the cleavage fracture critical event, which is grain-sized crack propagation controlled.

Effect of bi-directional operation on rolling-sliding wear of wheel steel under variable amplitude loading

The objective of this paper was to investigate the wear behaviour of railway wheel steel under the combined condition of bi-directional operation and variable amplitude loading. Rolling-sliding wear tests show that the wear rate of the wheel disc significantly drops at the moment of the bi-directional operation, and then it rises with the increase in reversed rolling cycles until a steady wear state is reached. When the test was conducted under the combined condition of the bi-directional operation and a two-step loading, the wear rate of the wheel disc after bi-directional operation decreases with the increase in the first step contact stress. These wear behaviours can be explained by the variation of the reversed plastic deformation and the movement of wave structure produced by the bi-directional operation. The wave structure moves down with the increase in reversed rolling cycles due to the reduction of the resistance to reversed plastic deformation. This reduces the resistance to the propagation of surface cracks and leads to the increase of wear rate. The resistance to reversed plastic deformation rises with the increase in the first step contact stress, which makes the wave structure move towards to the worn surface and reduces the wear rate of the wheel steel.

Wear Behavior of Newly Developed Bainitic Wheel Steels

The present work concentrates on the analysis of wear behavior of bainitic steels made by austempering from a microalloyed steel MAS2, meant for making railway wheel, and comparison with that of a conventional railway wheel steel, wheel-R19. Austempering of the MAS2 steel samples has been performed at different times and temperatures to obtain different morphologies of bainite. Linearly reciprocating dry sliding wear tests of these samples have been carried out at laboratory scale using five different loads. The wear behavior of the bainitic steels has been compared with that of the ferritic-pearlitic steel, wheel-R19. Mechanical properties of the bainitic MAS2 steels are found to be more than that of the wheel-R19 steel. Considerable enhancement in wear resistance of the bainitic steels is attributed to high hardness and strength of the steels. The wear mechanism has been critically analyzed by examining wear track morphology. The wear data gathered have been graphically presented in the form of wear mechanism map to understand the material behavior under different sliding conditions and subsequent morphological variations.

An integrated model for competitive damage mechanisms assessment in railway wheel steels

A procedure for damage assessment in wheel–rail contact is still an open task: much work has been done for understanding failure mechanisms such as wear, cyclic plasticity and Rolling Contact Fatigue, but only recently the competition between them has been taken into account. In this study, a numerical procedure for damage assessment of railway wheel steels, considering the complex interaction between various failure phenomena that can occur at the loaded region, is proposed. The procedure is based on various damage mechanism models, integrated into an overall simulation method able to take into account their reciprocal influence. The model was applied for characterising a railway wheel steel (ER8 EN13262), through the elaboration of the results of rolling–sliding experiments, determining the plasticity and the wear model constants that can be used for damage assessment of real wheels. The experiments showed that the main damage phenomenon was surface crack formation due to unidirectional plastic flow (ratcheting); in the presence of water these cracks propagated causing very severe damage. A role of manganese sulphides non-metallic inclusions as preferential site for subsurface crack nucleation was observed. A quantitative evaluation of these phenomena was provided.

Rapid thermomechanical tempering of iron–carbon martensite

Tempering of martensite under simultaneous compressive stress has been studied within the temperature range of 20–400°C. Resistive heating was utilised to obtain rapid heating and cooling cycles of a few seconds. Material was obtained from a medium carbon pearlitic railway wheel steel, quench hardened to obtain martensitic structure. Greater than ∼150°C dilatation effects where observed below the global yielding point of the material. Microstraining around dislocations in the body centred tetragonal crystallographic structure or viscous flow at higher temperatures was a probable explanation to this material behaviour. Hence, external stress may have an important influence on the tempering progression of martensitic steel. The trials also showed that tempering of martensite progresses fast, is near instantaneous and is independent of the presence of external stress or not.

Microstructural Refinement and Mechanical Properties of High‐Speed Niobium‐Microalloyed Railway Wheel Steel

The relationship between microstructure and mechanical properties was studied in a Nb‐bearing high‐speed railway wheel steel and compared with a traditional low‐alloyed medium carbon steel. The microstructure of medium carbon steel comprised of ferrite and pearlite and the percentage of ferrite was increased from 4 to 24% on the addition of 0.06 wt% Nb and the grain size was refined. The addition of Nb inhibited mixed microstructure and delayed the coarsening temperature of austenite grains from 880 to 960 °C. The yield strength of Nb‐bearing steel was increased from 385 to 455 MPa and the Charpy v‐notch energy at −20 °C was increased from 7.0 to 19.0 J with no apparent reduction in tensile strength. Niobium formulates grain refinement and transformation of austenite to ferrite and pearlite over a wide region of cooling rate (<10 °C s−1) and temperature range (530–690 °C) in the medium carbon steel. With the calculation of Thermal‐Calc software and solid solubility formula, Nb exists in the form of precipitates. The grain refining and precipitation strengthening are roles of niobium in promoting ferrite–pearlite transformation and improve toughness in the medium carbon steel.

Experiments and Characterization on the Probabilistic Fatigue Lives and Strengths of D1 Railway Wheel Steel

Experiments and Characterization on the Probabilistic Fatigue Lives and Strengths of D1 Railway Wheel Steel

혼합모드 하중조건에서의 철도 차륜재의 피로균열 실험에 관한 연구

Fatigue crack growth tests were conducted on urban railway wheel steel under mode I and mixed-mode conditions. Fatigue crack growth rates were evaluated in terms of equivalent stress intensity factor ranges, using both the extended and projected crack lengths. The equivalent stress intensity factor range with the growth rate results obtained under mode I loading conditions can be used to predict the crack growth rate under mixed-mode loading conditions. Extended crack length rather than projected crack length is appropriate for the prediction of the crack growth rate under the mixed-mode loading conditions.

Influence of laser dispersed treatment on rolling contact wear and fatigue behavior of railway wheel steel

The aim of this paper is to improve the rolling contact wear and fatigue resistance of ferrite–pearlite railway wheel steel by laser dispersed treatment. Such treatment creates isolated glazed regions on the surface layer of railway wheel steel, which are composed of fine martensite and retained austenite and have an average hardness of 762HV0.3. The wear rate and rolling contact fatigue life of treated and untreated railway wheel steel were evaluated and compared by Amsler twin-disc testing machines in dry and lubricated condition, respectively. The test results show that laser dispersed treatment improves the rolling contact wear and fatigue resistance of railway wheel steel. The stable wear rate of the laser treated railway wheel steel is about 0.3 times that of untreated railway wheel steel and the average rolling contact life of treated railway wheel steel is about double that of the untreated steel. Further investigations show that the glazed regions suppress the plastic deformation of railway wheel steel. This inhibits the treated railway wheel steel from delamination wear and delays the formation of fatigue crack initiation.

Evaluation of Wear Behavior of Wheel Steel Using Twin-Disc Test

The wheel/rail contact is chracterized by high contact forces and small contact areas. Although the standard of railway wheel has sustained, the damages of railway wheel have been occurred in service running. The railway wheel damage can be divided into three types; wear, contact fatigue failure and thermal crack due to braking. In curves, especially, large sliding on the contact patch occurs at the wheel tread and flange. Due to this sliding, wear increases in the wheel/rail contact under the dry condition. To reduce wear, more durable wheel steels are required. In order to develop new materials and predict wear, It is important to understand the wear mechanism in wheel steels. In this study, we have investigated the wear characteriscs of RSW1 railway wheel steel using twin disc wear testing. Also the comparative wear behavior of RSW1 and R7 wheel steel under rolling-sliding contact was performed.

Multiaxial fatigue criteria versus experiments for small crack under rolling contact fatigue

Rolling contact fatigue (RCF) is traditionally a very critical loading condition for fatigue and, moreover, material defects (as inclusions and inhomogeneities) play a significant role in determination of the service life of materials exposed to out-of-phase stresses, which typically occur at the interface and below the surface of contacting bodies.In this paper we summarize the results previously obtained for two different hard steels (that is, a bearing and a gear steel), together with a new set of experimental data for a mild railway wheel steel, that have been subjected to out-of-phase multiaxial fatigue loading, simulating RCF conditions in presence of small shallow pre-cracks.Then, the experimental results obtained have been discussed by employing the Dang Van and Liu–Mahadevan criteria, which are criteria extensively applied in the case of RCF problems.The results show that the Liu–Mahadevan criterion is close enough to experimental RCF tests, while the Dang Van criterion needs a substantial modification for the load cases when a negative hydrostatic stress component is present.

Prediction of residual stresses in low carbon bainitic–martensitic railway wheels using heat transfer coefficients derived from quenching experiments

Low carbon bainitic–martensitic (LCBM) steels have been recently developed for railway wheels and have been shown to provide superior properties compared to conventional pearlitic railway wheel steel grades. Pearlitic railway wheels are generally quenched at the tread region to promote the formation of compressive residual stresses in the rim to mitigate the initiation and propagation of cracks due to fatigue. However, this conventional quenching method has been shown to be unsuitable for LCBM railway wheels. Alternative quenching methods were evaluated using a FE model to develop a successful quenching process to produce LCBM railway wheels. Heat transfer coefficients were determined by employing a full scale experimental rig and were used in the FE model to model various coolant spray intensities and configurations. The FE model was used to determine optimal quenching conditions that impart compressive residual stresses to the rim of the LCBM railway wheel and the prediction of residual stresses were verified experimentally.

Austenite Grain Size Evolution in Railway Wheel During Multi-Stage Forging Processes

The knowledge of microstructure evolution of railway wheel during hot forming process is the prerequisite of improving mechanical properties of the final product. In order to investigate the austenite grain size evolution of railway wheel during multi-stage forging process, mathematical models of recrystallization and austenite grain growth were derived firstly by hot compression tests for railway wheel steel CL50D, which then were integrated with a thermal-mechanical finite element model by the developed subroutines. The information about kinetics of recrystallization and grain size distribution during the forging process was obtained by simulation. The predicted results were validated by experiments in an industrial scale, and the average error between the predicted grain sizes and the measured ones is about 5%. The result shows that, under the current railway wheel forging process, the grain size distribution after final forging is inhomogeneous extremely. There is a narrow coarse grain zone between the external part and center of the hub caused by Static recrystallization after final forging. With cooling of 60 s after final forging, the grain size is about 85 μm for the areas near the web surface and 175 μm for center areas of the hub and rim.

鉄道車輪鋼のシェリング損傷に及ぼす材料強度の影響

鉄道車輪鋼のシェリング損傷に及ぼす材料強度の影響

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.

A study of airborne wear particles generated from the train traffic—Block braking simulation in a pin-on-disc machine

Recently, much attention has been given to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles. In this study airborne particles from railway block brakes are studied using cast iron and composite block material on railway wheel steel. A pin-on-disc tribometer equipped with airborne particle counting instrumentation was used as experimental set-up. The result shows differences for the two tested block brake material combinations in particle size distribution, morphology and elemental content.

Investigation of influence of white layer geometry on spalling property in railway wheel steel

Spalling is rolling contact fatigue (RCF) damages of railway wheels, as a result of unexpected wheel slides on a rail. The major characteristic in spalling is that fatigue cracks initiate from white layers. In this study, in order to evaluate the influence of the white layer geometries on spalling properties, RCF tests and elasto-plastic FEM analyses were carried out. Moreover, the Dang Van model, which is the multiaxial fatigue strength evaluation methods, was applied to predict the crack initiations in RCF tests. There are three main results from this study. Firstly, RCF tests yielded that the crack initiations were less in the smaller white layers than in the larger ones. In addition, the crack initiations of the matrices were less than those of the white layers. Secondly, FEM analysis results showed that the maximum stresses were lower in the smaller white layers than in the larger ones. This result corresponded to the crack initiation behaviours of RCF tests. Finally, the fatigue strength prediction results by the Dang Van model were reasonably equivalent to the RCF test results. Therefore, it was concluded that the crack initiations in spalling could be reduced by the smaller white layer.

Monotonic and cyclic deformation of a high silicon pearlitic wheel steel

The development of railway wheel steel grades has gone towards higher strength to enhance rolling contact fatigue resistance and ability to withstand thermally induced damage throughout the service lifetime. In this study a recently developed wheel steel material for passenger trains containing high levels of manganese and silicon, approximately 1 wt% of each, was tested in low cycle fatigue at different total strain amplitudes. In addition, monotonic tensile and Charpy V-notch impact testings in the temperature range −60 °C to 180 °C were performed. The results were compared to another steel grade commonly used in Europe for railway wheels. The low cycle fatigue results show similar cyclic lifetime Nf, and fatigue stress amplitude development for both materials, but the highly alloyed steel exhibits reduced cyclic softening and hardening during the fatigue life and is in this respect more stable in its behaviour. As is typical for pearlitic–ferritic steels both materials show a pronounced monotonic strain hardening. It was concluded that the increased levels of manganese and silicon have minor effects on monotonic behaviour but substantial influence on cyclic behaviour at ambient temperatures. At increased temperatures, though, there are indications of additional effects on monotonic behaviour. However, the high temperature properties have to be investigated further to gain full understanding of mechanisms and effects.

Cyclic deformation behaviour of railway wheel steels in the very high cycle fatigue (VHCF) regime

In the present contribution, the cyclic deformation behaviour of the railway wheel steels SAE 1050 and SAE 1060 was investigated in the very high cycle fatigue (VHCF) regime using a resonance testing device at a frequency of 200 Hz. The specimens were machined from the area of the ‘limiting-diameter’ of original monobloc-wheels. The wheels were provided by a system supplier of the Deutsche Bahn AG. The cyclic deformation behaviour is analysed by using highly precise methods for measuring the frequency, temperature and electrical resistance, which show deformation-induced changes of the microstructure within the bulk material during the fatigue process. The initial state of the material is investigated thoroughly by using light-, scanning- and transmission electron microscopy. The dislocation structure was investigated in defined fatigue states showing dislocation walls at 5% N f and dislocation cells at 85% N f . S– N (Woehler) curves are presented for both wheel steels. Fatigue failures at N f > 10 7 were observed.

The assessment of the degree of softening during the hardened steel wheels tempering

The issues re. estimation of changes in hardness and sound vibration propagation velocity after tempering the hardened railway wheel steel are considered.