Rail Steel Research Articles

XRD Observation on the Weld Metal of Resurfaced Rail Steel

The current research studied two samples of rail steel grade 900A deposited with different electrodes, namely, electrodes A and B, using the Shielded Metal Arc Welding (SMAW) process. This research fi nds out the suitable hardness values of the various electrodes. The phase identifi cation and microstructural analysis of weld metal were conducted using X-ray diffraction (XRD) and an optical microscope, respectively. The micro-hardness profi les along the cross-section of the weldment were acquired using a micro-Vickers hardness tester, and a Brinell hardness tester measured the hardness values on the top surface of the weld metal. According to the results, the diffraction angles of the XRD patterns for all weld metal samples differed due to their distinct microstructures. The microstructure of the weld metal, in particular, produced the primary infl uence on the hardness

Three-Dimensional Measurement of Full Profile of Steel Rail Cross-Section Based on Line-Structured Light

The wear condition of steel rails directly affects the safety of railway operations. Line-structured-light visual measurement technology is used for online measurement of rail wear due to its ability to achieve high-precision dynamic measurements. However, in dynamic measurements, the random deviation of the measurement plane caused by the vibration of the railcar results in changes in the actual measured rail profile relative to its cross-sectional profile, ultimately leading to measurement deviations. To address these issues, this paper proposes a method for three-dimensional measurement of steel rail cross-sectional profiles based on binocular line-structured light. Firstly, calibrated dual cameras are used to simultaneously capture the profiles of both sides of the steel rail in the same world coordinate system, forming the complete rail profile. Then, considering that the wear at the rail waist is zero in actual operation, the coordinate of the circle center on both sides of the rail waist are connected to form feature vectors. The measured steel rail profile is aligned with the corresponding feature vectors of the standard steel rail model to achieve initial registration; next, the rail profile that has completed the preliminary matching is accurately matched with the target model based on the iterative closest point (ICP) algorithm. Finally, by comparing the projected complete rail profile onto the rail cross-sectional plane with the standard 3D rail model, the amount of wear on the railhead can be obtained. The experimental results indicate that the proposed line-structured-light measurement method for the complete rail profile, when compared to the measurements obtained from the rail wear gauge, exhibits smaller mean absolute deviation (MAD) and root mean square error (RMSE) for both the vertical and lateral dimensions. The MAD values for the vertical and lateral measurements are 0.009 mm and 0.039 mm, respectively, while the RMSE values are 0.011 mm and 0.048 mm. The MAD and RMSE values for the vertical and lateral wear measurements are lower than those obtained using the standard two-dimensional rail profile measurement method. Furthermore, it effectively eliminates the impact of vibrations during the dynamic measurement process, showcasing its practical engineering application value.

Formation of white etching layer on rails due to coupled thermal and mechanical actions

The formation mechanism of the white etching layer (WEL) on the rail steel material has been confirmed via two different routes; thermal-induced WEL by phase transformation and mechanical-induced WEL by severe plastic deformation. In this study, a combination of thermal and mechanical processes was performed to examine the synergistic interaction of two formation mechanisms of the WEL on rails. An experiment was conducted on the rail steel material using a Gleeble thermo-mechanical simulation system. The results confirmed that the martensitic WEL is formed by phase transformation from rapid quenching at a temperature below the critical point of material phase transformation, under 550 °C, when high hydrostatic pressure is applied. The application of combined thermal and mechanical action induced martensite with the presence of retained austenite. The microstructure of the transition zone between the WEL and the base material contains partial and full dissolution of cementite, broken pearlite lamella, and dislocation density, confirming that both thermal and mechanical processes are involved in the phase transformation of the material.

Methodology to assess damage mechanisms of rail steels based on small-scale experiments

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.

About the Optimal Range of Hardness of Wheel and Rail Steel

About the Optimal Range of Hardness of Wheel and Rail Steel

Analysis of rail–bridge interaction of a high-speed railway suspension bridge under near-fault pulse-type earthquakes

Abstract Due to the limitations of railway route selection, some high-speed railways are inevitably built near or across fault zones. To study the distribution of rail–bridge interaction under different load history states of suspension bridges under three types of near-fault pulse-type earthquakes, this paper takes China's longest high-speed railway suspension bridge—Wufengshan Yangtze River Bridge—as the background and establishes a spatial model of the rail–bridge interaction of a suspension bridge. The results show that: under the constant load state, the distribution of additional force under three types of pulse-type earthquakes is generally consistent, and pulse-type earthquakes produce more significant responses than non-pulse-type earthquakes; with fling-step pulse being the largest, it is advised to specifically consider the influence of the fling-step pulse in the calculation. Under the initial condition of the main beam temperature loading history, all rail-bridge additional forces increase significantly, particularly affecting the steel rail system. The value of the rail–bridge interaction additional force under the near-fault earthquake in the initial state of the suspension bridge when the train deflection load is loaded from the tower to the mid-span is more significant and particularly unfavourable. The initial effect of the braking load will weaken the effect of the deflection load loading history. The results of the study indicate that the effect of the initial state of suspension bridges is an important factor influencing the rail–bridge interaction under near-fault pulse-type earthquakes, which needs to be considered in future seismic design.

Evolution of structural-phase state and properties of hypereutectoid steel rails at long-term operation

The methods of modern physical materials science were used to analyze the evolution of microhardness, tribological properties, dislocation substructure and phase composition of the rails with increased wear resistance and contact endurance of DT 400 IR category after missed tonnage of 187 million gross tons on the experimental ring of Russian Railways. It is shown that extremely long-term operation of the rails is accompanied by a decrease (3.1 times) in wear parameter of the rolling surface and an increase (1.4 times) in microhardness, scalar dislocation density (1.5 times) and Fe3C carbide content (1.24 times). Operation of the rails led to a decrease in the crystal lattice parameter, which correlates with an increase in the content of iron carbide. We made the assumptions about physical causes of the change in parameters.

Study of Mechanical Properties of Pearlitic Rail Steel by Modeling

Study of Mechanical Properties of Pearlitic Rail Steel by Modeling

Microstructural evolutions and impact toughness in simulated welding heat affected zones for a high-strength carbide-free bainitic rail steel

Systematic experimental investigations were conducted to study the microstructures and impact toughness of each heat affected zone (HAZ) formed during rail flash-butt welding. A high-strength carbide-free bainitic rail steel was subjected to different thermal simulation cycles to separately reproduce each HAZ subzone by tailoring the peak temperature (PT) with respect to 700, 850, 920, 1000 and 1350 °C, and hence to generate the corresponding microstructures by using Gleeble-3500 simulator. Results show that the HAZ subzones exhibit complicated microstructures depending on the PTs, and with increasing PT the dominant bainitic microstructure type evolves from polygonal bainitic ferrite (700 °C) to a mixture of fine bainitic ferrite and granular bainite (850–1000 °C), and finally to coarse bainitic ferrite and granular bainite (1350 °C). Impact tests demonstrate that the impact toughness initially increases significantly as the PT reaches 920 °C (i.e., fine-grained HAZ), beyond which the impact toughness starts to decrease. The fine-grained HAZ displays optimal impact toughness in HAZs, yet which is lower than the base metal. Moreover, the morphology and distribution of martensite-austenite (M-A) constituents is strongly dependent on the welding PT, and the high fraction blocky and coarse slender M-A constituents is considered to be detrimental for the impact toughness.

Rail Surface Defect Detection Based on Image Enhancement and Improved YOLOX

During the long and high-intensity railway use, all kinds of defects emerge, which often produce light to moderate damage on the surface, which adversely affects the stable operation of trains and even endangers the safety of travel. Currently, models for detecting rail surface defects are ineffective, and self-collected rail surface images have poor illumination and insufficient defect data. In light of the aforementioned problems, this article suggests an improved YOLOX and image enhancement method for detecting rail surface defects. First, a fusion image enhancement algorithm is used in the HSV space to process the surface image of the steel rail, highlighting defects and enhancing background contrast. Then, this paper uses a more efficient and faster BiFPN for feature fusion in the neck structure of YOLOX. In addition, it introduces the NAM attention mechanism to increase image feature expression capability. The experimental results show that the detection of rail surface defects using the algorithm improves the mAP of the YOLOX network by 2.42%. The computational volume of the improved network increases, but the detection speed can still reach 71.33 fps. In conclusion, the upgraded YOLOX model can detect rail surface flaws with accuracy and speed, fulfilling the demands of real-time detection. The lightweight deployment of rail surface defect detection terminals also has some benefits.

Experimental and Numerical Visualisation of Subsurface Rail Deformation in a Full-Scale Wheel–Rail Test Rig

To tackle the problem of various types of rail damage, such as rolling contact fatigue (RCF) or wear, a profound knowledge of the occurring mechanisms is necessary. This paper presents a newly developed full-scale test rig experiment that involves inserting softer pins into the rail head. These tests help deepen our understanding of shear deformation in rail steels. Furthermore, a finite element (FE) simulation approach is introduced that can be related to the test rig experiments. With these experiments, in combination with the FE simulation, valuable information regarding the plastic deformation can be obtained. This methodology allows predictions regarding a rail’s material behaviour during cyclic wheel loading. Moreover, it enables an effective and rapid qualitative material assessment, reducing the costs of expensive and time-consuming experiments.

Occurrence of characteristic defects of grinding balls from rejects of continuously cast billets of rail steel

On the basis of metallographic studies, the authors determined the characteristic defects of grinding balls rolled from the rejects of continuously cast billets of K76F rail steel. Relationship of the presence of internal defects of the balls with their impact resistance was established. Defects in the form of internal cracks with accumulations of non-metallic inclusions in the area of their localization and flocks have the greatest impact on the reduction of balls impact resistance. Such defects are the cause of balls destruction during impact resistance tests in 62 and 17 % of cases, respectively. The effect of internal cracks without significant accumulations of non-metallic inclusions and quenching microcracks located along the boundaries of the phase interface was estimated at 12 and 9 %. The regularities and mechanism of influence of the rejects chemical composition of K76F rail steel billets on the probability of destruction of the balls produced from them during impact resistance tests were established. An increase in sulfur content in the billets of the studied rail steel reduces impact resistance of the balls produced from them, as it contributes to formation of non-plastic sulfides that concentrate in the area of internal cracks. An increase in hydrogen content in rail steel naturally contributes to an increase in probability of formation of the flocks, which significantly reduce the balls stability to shock loads. An increase in carbon content in the initial billets affects the increase in probability of destruction of K76F steel balls during copra tests. It is explained by formation of cementite-type carbides when carbon content corresponding to the eutectoid steel is reached. In general, the relative degree of influence of the K76F rail steel chemical composition on impact resistance of grinding balls is 48 %.

Nano and micro-indentation driven characterisation of asperity and bulk plasticity at the surface of modern premium rail steels

The plastic deformation behaviour of rail steels due to cyclic rail-wheel contacts is important to understand due to its connection to wear and rolling contact fatigue (RCF) damage initiation in service. Simulation models such as the ‘Layer’ and ‘Brick’ model have previously been developed to estimate the accumulation of plastic damage in a rail steel; however, the data available to drive these models is currently sparse, with limited applicability to modern rail steel grades. This paper presents the research examining the shear stress-strain curve relationships of rail steels derived from plastic shear strain and shear yield stress data collected from twin-disc test samples. A combination of microhardness and nanohardness testing was used to derive the shear yield stress data, whereas the plastic shear strain was acquired from optical microscopy. Six different conditions were investigated for this research for the purpose of examining how shear stress-strain curve relationships compared between the standard R260 and the premium HP335 and R350HT rail steels and how this compares to wear damage data. The influence of the maximum Hertzian contact pressure on the shear stress-strain curve relationships of R260 between 600 and 1500 MPa contact pressure was also investigated. The wear rate results derived from the mass loss in interrupted twin-disc tests showed HP335 wearing the least, followed by R350HT and then R260 for 1500 MPa, dry contact conditions. However, the highest shear yield stress achieved was for R350HT, then HP335, and R260. The results show that the shear stress-strain curve relationships by themselves are insufficient to determine rail steel wear performance in a laboratory environment. The shear stress-strain curve relationships for R260 collected under different contact pressures showed the results are near independent of the contact pressure within the range explored.

Several tests for verification of material deterioration evaluation method of rail steel using X-ray diffraction analysis

Quantitative evaluation of rail deterioration due to rolling contact contributes to the optimization of rail maintenance such as rail grinding. A technique for evaluating rail deterioration due to rolling contact using X-ray diffraction has been reported. To use this method as a practical method for quantifying the degree of influence of rolling contact on rails, we should clarify experimentally the basic issues such as the correlation between the calculated index and the degree of rolling contact fatigue.In this study, the validity of this X-ray diffraction analysis method is verified by evaluating specimens at different loading stages via tensile and rolling tests. The results are also compared with Kernel average misorientation (KAM) values from electron back scattered diffraction. The same method was also used to evaluate rail degradation conditions for 700 million tons of passing tonnage.The following findings are identified from the above results. Dislocation density, one of the indicators obtained by X-ray diffraction, is directly related to crack initiation in rail steels. The X-ray crystallite size, which is also linked to the increase in the KAM value, makes it suitable for evaluating the degree of strain due to rolling contact.

A coupled thermo-mechanical cohesive zone model for strain rate-dependent fracture of hat-shaped specimens under impact

A coupled thermo-mechanical cohesive zone model for strain rate-dependent materials is proposed to illustrate the shear failure in the hat-shaped specimens made of U75V rail steel at various impact loads and temperatures.The cohesive energy and the maximum cohesive stress in the proposed cohesive zone model depend on strain rates and temperatures. The coefficients in the functions of cohesive energy, maximum cohesive stress, and the cohesive law are obtained through a combination of experimental and simulation data. The experimental strain waveforms are obtained by a split Hopkinson pressure bar system and the cohesive zone model is implemented using ABAQUS finite element software with the assistance of user subroutines.The findings substantiate the efficacy of the proposed cohesive zone model in accurately predicting the shear failure of hat-shaped specimens under high-speed impacts, as evidenced by the notable concurrence between experimental and computational outcomes within an acceptable margin of error. Notably, the cohesive energy and maximum cohesive stress in the model demonstrate a dual dependency on strain rates and thermal conditions, emphasizing the significance of considering both thermal and mechanical effects when simulating shear failure in materials experiencing high temperatures and high strain rates.

Change in the Properties of Rail Steels during Operation and Reutilization of Rails

The paper considers the possibility of reusing previously used railway rails. The analysis is conducted using the standards and operating conditions of the rails of one of the Central Asian states, Kazakhstan, as an example. The operation of these rails causes significant stresses, while the surface layers are strengthened as a result of cold hammering. These phenomena significantly change the physical and mechanical characteristics of rails. As a result, they may not be suitable in terms of parameters for basic use but can be suitable for installation on other tracks. The conducted studies have shown that when the standard service life of the RP65 rail expires, the surface layer is deformed to a depth of up to 300 microns, hardness increases, and internal residual stresses are formed. These changes lead to an increase in the strength properties of the rails. However, at the same time, cracks originate in the surface layer of the rail, thus worsening operational characteristics. The RP65 rails are used under a cyclic load of 700 kN (which is determined by the national standard), withstanding 790,000 cycles. When the load is reduced to 510 kN, these rails can withstand the 2,000,000 cycles required by the standard without failure. Thus, these rails can be reutilized only on non-loaded and non-critical sections.

Dynamic Analysis of CRTS II Ballastless Track-Vehicle System Based on Moving Unit Method

On account of the influence of the discontinuity of CRTS II ballastless track slabs and the discrete support of track pads on the high-speed rail vehicle-ballastless track system, a vibration analysis calculation model of the ballastless track-vehicle coupling system was established on the basis of the moving unit method. The dynamic response of the system at different travel speeds and with and without consideration of the track plate discontinuities was investigated. The effect of the random process discontinuity on the dynamic response of the steel rails was analyzed by Fourier inverse transform on the high and low discontinuity spectra of ballastless rails on China’s high-speed rail. We also generated time domain samples of the track discontinuity corresponding to the three percentile spectra. The results show that the dynamic response of the track structure increases with the speed of the train under the condition of track unevenness, with the dynamic response of the steel rail being the most significant, while the dynamic response of the track slab and concrete foundation decreases step by step compared with that of the steel rail; the discontinuity of the track slab has a low impact on the vertical acceleration of the vehicle and does not affect the smoothness of the train; the magnitude of the dynamic response of the rail increases as the amplitude of the irregularities increases or the wavelength decreases. In the wavelength of 2~30 m, the maximum and as the wavelength of the discontinuity sample increases, the oscillation of the power response time curve decreases significantly and tends to be smooth.

Rail rolling contact fatigue response diagram construction and shakedown map optimization

The shakedown map is one of the key prediction models used in railway engineering to evaluate rolling contact fatigue (RCF) damages of wheels and rails. The objective of this work is to construct the response diagram of RCF and optimize the classical shakedown map based on the rolling-sliding tests. A method based on rolling-sliding tests for constructing the response diagram was presented. Firstly, the traction coefficient (μ) and load factor (P0/ke) were taken as the X-axis coordinate and Y-axis coordinate of the coordinate system of the classical shakedown map, respectively. Then, test parameters (P0 and μ) were designed and obtained using the various X and Y coordinate in four different regions of shakedown map (i.e., different plots of μ versus P0/ke). After that, for various test parameters, the rolling-sliding tests were carried out using a twin-disc testing apparatus under dry condition to investigate the RCF damages of U75V rail steel. The results showed that three types of damage states could be observed after rolling-sliding tests under different test parameters: (I) neither plastic flow of materials nor fatigue cracks, (II) plastic flow, and (III) fatigue cracks with plastic flow. Thus, the response diagram consists of the above three damage regions. Furthermore, with the increase of P0 and μ, all the depth of plastic flow, the length of fatigue cracks and the wear rates were increased. Moreover, materials were work hardened in the damage states of plastic flow and fatigue cracks. The hardness increment was increased with P0 and μ. In addition, the boundary of ratchetting region (i.e., shakedown limit) in the classical shakedown map for partial slip was optimized based on the RCF damages and the new response diagram. The shape of optimized shakedown limit curve was same as that of the classical one, whereas the position of the optimized curve was decreased.

Microstructure Evolution of RE Rail Steel During Hot Deformation

Microstructure Evolution of RE Rail Steel During Hot Deformation

An innovative small-scale testing procedure to study damage in shoe-braked wheels

The diffusion of brake-shoe system has made it necessary to study brake–wheel–rail interactions. This study aims to elucidate this topic with an innovative small-scale test rig, the ‘4-contact machine’. A test procedure is designed in which an ER7 steel wheel is coupled with a R260 steel rail and two different brake-shoe materials (cast iron and sintered material). The results show that the 4-contact machine reproduces the effects of wheel–rail–brake shoe contact and damage similar to those observed on a railway wheel at the end of its life, highlighting marked differences in behaviour between the two brake materials.