Rail Steel Research Articles

Enhancing wear resistance of R220 rail steels by quenching and partitioning (Q&P) treatment

In this study, R220 steels were subjected to the Q&P treatment after austenitization at 900 °C for 15 min. The austenitized samples were immersed in cold, warm, and boiled water baths. The quenching step was interrupted, and the specimens were immediately placed in a furnace at 500 °C and held there for 5 min. The multiphase structure, including tempered martensite, retained austenite, bainitic ferrite, and fresh martensite, was achieved by the Q&P treatment. The wear rate of the untreated R220 rail steel was decreased by up to 89 % with a slight increase in corrosion losses. The best wear resistance was obtained in the sample cooled in warm water due to the balance between its tensile strength, toughness, and hardness.

Fatigue Crack Propagation on Uniaxial Loading of Biaxially Predeformed Pearlitic Rail Steel

Rolling contact fatigue loading causes the surface material in the top of the rail to severely deform. The microstructure aligns along the shear direction and the mechanical behavior in terms of plastic flow becomes anisotropic. Cracks are initiated in the severely deformed surface region and propagates along the direction of microstructure flow lines. However, the effect of large shear deformation on fatigue crack growth is not yet well understood. In this study, uniaxial fatigue crack propagation of undeformed and biaxially predeformed pearlitic rail steel R260 has been investigated. The material was predeformed to different deformation states using combined axial compression and shear deformation, corresponding to material found at different depths in the severely deformed surface layer of rails. Fatigue crack propagation rate was dependent on the material state and influenced by both work hardening and microstructural anisotropy. It was found that predeformed material exhibited lower crack growth rates than undeformed material under this loading condition. The influence of predeformation on the crack growth direction was limited.

Qualifying data on railroad track vibrations: a hybrid data preprocessing flow of statistical and machine learning approaches

ABSTRACT With the growing trend for increased train speed, steel rails may suffer from quality problems due to both overloading and/or the high speed of moving trains. However, before any further analysis can be performed to gain in-depth knowledge, the relevant vibration data sets must be curated, cleansed, preprocessed, and filtered very carefully after they are recorded and collected by the installed sensor equipment. This study proposes a systematic methodological flow to obtain data sets ready for subsequent analysis from messy source data. It hybridized several statistical and unsupervised machine learning methods, with the final aim to establish meaningful rules to determine suitable data sets by referring to domain knowledge. This flow was verified using a relatively large database of records of physical vibrations measured in 2019 at specific locations along a curve of an actual railroad track. As the flow can be used to qualify empirical data sets required in practice, further analysis is provided for the effectiveness of each rule, differences in determination between the rules, and the effects of combining more than one rule.

Experimental investigation on corrosion fatigue crack initiation and growth of heat-treated U75V rail steel

Understanding the corrosion fatigue mechanism of rail materials is of great importance to guide the assessment of the structural integrity of modern railway components. To this purpose, the corrosion fatigue crack (CFC) initiation and growth behaviors of heat-treated U75V rail steel are investigated under 3.5 wt% NaCl solution in terms of high-cycle fatigue, fatigue crack growth (FCG) rate, together with surface morphology and microstructure. Experimental results reveal that the U75V rail steel is susceptible to corrosion fatigue failure. Examinations on fractured samples clearly show that the electric potential difference between ferrite and cementite triggers the preferential anodic dissolution of ferrite, leading to corrosion fatigue crack initiation. The crack initiation is not only solely determined by the size of the corrosion pit, but also strongly influenced by its local shape. In comparison with the fatigue crack growth in air, the corrosion FCG tends to grow in a relatively straight path, because of hydrogen embrittlement. Additionally, the CFC behaviors indicate a tendency to transverse through soft-oriented grains and deflect upon encountering hard-oriented grains.

Optimal Hardness Ratio of Wheel Steel and Rail Steel for Minimum Wear

Optimal Hardness Ratio of Wheel Steel and Rail Steel for Minimum Wear

Investigation of the influence of hardening medium parameters during heat treatment of grinding balls from rail steel on the quality of their microstructure and hardness

Investigation of the influence of hardening medium parameters during heat treatment of grinding balls from rail steel on the quality of their microstructure and hardness

Cause analysis of surface cracks in flash butt welding joint of high manganese steel frog

Surface cracking is one of the typical failures in butt welding joints of high manganese steel railway frogs. Understanding the formation mechanism of such cracks can effectively prevent similar failures from occurring. Herein, assisted with multiple macro and micro characterization tools, we discussed the causes of surface crack formation for a flash butt welding joint of a high manganese steel frog. The results show that the surface cracks are typical intergranular stress corrosion cracks (IGSCC) distributed near the fusion line between the carbon steel rail and the stainless steel medium in the stainless steel side. Acicular martensite exists near the fusion line between carbon steel rail and stainless steel medium, and the residual stress is large. At the same time, there are continuous network chromium carbide precipitates on the austenitic grain boundary of stainless steel. The above two points should be the main reasons for the initiation of cracks on the weld surface. Reduce the proportion of martensite structure by reasonably optimizing the welding cooling rate. Properly temper martensite to reduce the hardness and internal stress in the transition zone. These measures can prevent the occurrence of intergranular cracks on the weld surface.

Dynamic Responses of Train-Symmetry-Bridge System Considering Concrete Creep and the Creep-Induced Track Irregularity

This work considers the influence of concrete creep on track irregularities and establishes the dynamic motion equation of the train-track-bridge coupling system. The track irregularity is obtained by superposition of the initial geometric irregularity and additional geometric irregularity of the steel rail caused by creep. When high-speed railway trains pass through bridges; the vertical acceleration and vertical displacement of continuous beam bridges are related to the train’s operating speed, and the influence of creep camber is relatively small. At the same time, considering the randomness of track irregularities, the dynamic responses of the train track bridge coupling system under the action of random track irregularities are analyzed, and the dynamic responses of trains at different operating speeds are obtained. The deterministic and uncertain dynamic responses of the train track bridge system were compared and analyzed to verify the accuracy of the Karhunen Loéve expansion (KLE)-Point estimate method (PEM) calculation results. The results indicate that the random characteristics of track irregularities have a significant impact on train dynamic response. Based on the random system vibration analysis and considering the safety and comfort indicators of high-speed railway trains, the creep deformation limit of a continuous beam bridge with a length of 48 m + 80 m + 48 m is obtained to be 19 mm. This is the first time that the dynamic responses of train-symmetry-bridge system are calculated by considering concrete creep and the creep-induced track irregularity, which has certain significance for understanding the dynamics of train -bridge system. In addition, the proposed creep threshold is also of great significance to ensure the safety of traveling.

Advanced Heat Treatment of Pearlitic Rail Steel.

The aim of this research is a systematic investigation of heat treatments of 60E1 profile rails made of steel R350HT, which would ensure the properties required by the standard EN 16273. Additionally, it presents a concept of cooling rails on a semi-industrial station, which will make it possible to obtain the desired properties. The dilatometric tests have demonstrated that the optimal cooling rate is within the scope of 3 °C/s to 6 °C/s, when both the EN 16273 standard's hardness distribution and microstructure requirements are fulfilled. The tests on the designed and built station showed that the optimal pressure with respect to the microstructure and properties of the rail equals 6.5 bar. For these parameters, measurements of the interlamellar distance were also performed-the cooling rate obtained at the surface was 3.68 °C/s, with an interlamellar distance of about 80 nm, whereas inside the rail the rate was 2.63 °C/s and the distance 110 nm. The achieved results confirm that the designed station can be used for controlled cooling of rail steels from R350HT steel.

A new scaled testing methodology for the analysis of rolling contact fatigue in railway steels.

Twin disc testing is a relatively cost effective and practical method of investigating the damage resistive properties of rail steels in a scaled environment. The loading conditions and dimensions used in testing are scaled in such a way that the Rolling Contact Fatigue (RCF) generated on a twin disc rig are representative of the conditions experienced at the full-scale. Typical methodologies to generate RCF on a twin disc rig involve the application of water to the contact patch throughout the test, with perhaps a few thousand dry cycles being run beforehand. This research explores the use of weather data to reflect the real-world contact conditions more accurately between a wheel and rail. Met Office weather data collected from 1981 to 2010 shows the average annual precipitation in the UK is around 133 days of rain or snow, which is nearly 36 % of the year. In this study, weather data was used to determine the ratio of wet to dry cycles in the testing methodology.  50k dry cycles are run in intervals of 5k and then transitioned to 25k of wet cycles, which is 30% of the total cycles. Intervals were kept at 5k so attaining 36%. If RCF is not initiated after the first 75k cycles, which ends with 25k wet cycles, then the same dry and wet cycles are repeated. RCF data generated using this methodology demonstrated expected differences in the RCF resistive properties of two rail steel grades, R260 and R350HT. In test 1 the point of initiation for each grade was not captured, though cracks were visible around the expected cycles to initiation, which was verified using optical microscopy. The cracks viewed on the softer R260 steel samples, ‘’260’’ referring to the Brinell hardness value of the steel, were more developed at 85k cycles and showed signs of spalling, whilst the cracks on the harder R350HT sample were much smaller. In test 2 the point of initiation was found for each grade. Optical microscopy was also used to show the depth and direction of head check cracks to ensure the damage viewed from the head was RCF and not plastic flow or cyclic wear. This paper shows the necessity for considering the number of wet cycles applied during twin disc testing and demonstrates it is possible to run a high number of wet cycles which are more representative of real-world conditions when generating RCF on twin disc rigs.  

Strengthening mechanisms of rail steel under compression.

The evolution of structural-phase states and dislocation substructure of rail steel under uniaxial compression to the degree of 50% was studied by transmission electron microscopy. The obtained data formed the basis for a quantitative analysis of the mechanisms of rail steel strengthening at degrees of deformation by compression 15, 30, 50%. Contributions to the strengthening caused by the friction of matrix lattice, dislocation substructure, presence of carbide particles, internal stress fields, solid solution and substructural strengthening, pearlite component of the steel structure are estimated. Using the adaptivity principle, which assumes the independent action of each of the strengthening mechanisms, the dependence of rail steel strength on the degree of plastic deformation by compression is estimated. A comparative analysis of the stress-strain curves σ(ε) obtained experimentally and calculated theoretically is performed

Laminar plasma quenching-tempering: A rapid surface heat treatment technique for controllable modification of the rail steel

Plasma selective quenching is promising in enhancing the rail's wear resistance by preparing martensitic hardened zones discretely embedded in the substrate on the surface layer. However, severe cracks and spalling occur in the hardened zone during the rail service, which may be related to its microstructure and hardness. To modify the microstructure and hardness of the hardened zone, a novel laminar plasma quenching-tempering (LPQT) technique that consists of performing laminar plasma quenching (LPQ) and laminar plasma tempering (LPT) successively was proposed to obtain the hardened zone with desired microstructure and hardness. LPQ is firstly performed on the rail surface to prepare martensitic hardened zones with high hardness. LPT is then performed on each hardened zone to modify its microstructure and hardness. The numerical simulation of LPT was established to determine the processing parameters of LPT for accurately controlling the tempering temperature of the hardened zone. The effects of the tempering temperature on the microstructure and hardness of the hardened zone were investigated. Results showed that with the increase of the tempering temperature from Ms temperature to austenitizing temperature, the hardness of the hardened zone was decreased from 800 HV to 450 HV as the acicular martensite in the hardened zone precipitated carbides and was transformed into the tempered martensite. Besides, the total processing time of LPQT for treating a hardened zone is normally <2 s. Application of LPQT in modification of the rail steel showed that it helped to eliminate the severe cracks and spalling in the LPQ treated hardened zone while its wear resistance was still improved compared with that of the untreated rail steel. Overall, LPQT is a rapid and controllable surface heat treatment technique for modifying the microstructure and hardness of the rail surface, which is promising to be used to balance the wear and RCF resistances based on the service condition of the rail.

Use of a modified critical fracture strain model for fracture toughness estimation of high strength rail steels

This paper explores the feasibility of estimating fracture toughness (KIC,pred) for nine high-strength rail steels using data from smooth tensile and instrumented ball indentation test methods via a modified critical fracture strain model. The modification focuses on determining the equivalent plastic fracture strain and equivalent plastic strain from tensile and indentation tests, respectively, as well as the characteristic distance needed for estimation of fracture initiation. It shows that stress triaxiality plays a vital role by decreasing the ductility required to initiate fracture, based on the kinetic damage evolution law for a multiaxial stress state. A void growth index model was established from average grain sizes, and then used as the characteristic distance for fracture initiation. At the end, the KIC,pred defined based on equivalent plastic strain from tensile tests showed a strong correlation with KIC determined from ASTM standard method. KIC,pred from indentation also offers the opportunity for ascertaining the possibility of estimating the fracture toughness of high strength rail steels, non-destructively by focusing on the equivalent plastic strain and pressure at the tip of the indenter.

ANALYSIS WITH ASSESSMENT OF THE CONDITION OF THE RAIL STEEL AT VARIOUS STAGES OF ITS OPERATION

Studies on the influence of defects of various nature on the mechanical and operational properties of rail steel are presented. The results of studying and analyzing the condition of rail steel at various stages of its operation, as well as the reasons for removing rails from rolling stock, are considered. The increased interest and increase in information in this area is due both to the practical significance associated with the increasing requirements for the reliability of rails in conditions of high traffic intensity, and the increase in loads on the axles of rolling stock, increasing speeds and weight of trains, in severe conditions of the upper structure of the track in various climatic conditions, and the desire for a deeper understanding of the fundamental knowledge of physical metallology.

Rail Corrugation Index Development by Sound-Field Excitation on the Carriage Floor of In-Service Train.

The steel rail and wheel in the railway system offer a high precision and smooth-running surface. Nevertheless, the point of contact between the rail and wheel presents a critical area that can give rise to rail corrugation. This phenomenon can potentially elevate sound and vibration levels in the vicinity considerably, necessitating advanced monitoring and assessment measures. Recently, many efforts have been directed towards utilizing in-service trains for evaluating rail corrugation, and the evaluation has primarily relied on axle-box acceleration (ABA). However, the ABA measurements require a higher threshold for vibration detection. This study introduces a novel approach to rail corrugation detection by carriage floor acceleration (CFA), aimed at lowering the detection threshold. The method capitalizes on the acceleration data sensed on the carriage floor, which is induced by the sound pressure (e.g., sound-field excitation) generated at the wheel-rail contact point. An exploration of the correlation between these datasets is undertaken by simultaneously measuring both ABA and CFA. Moreover, a pivotal aspect of this research is the development of the eigenfrequency rail corrugation index (E-RCI), a mechanism that culminates energy around specific eigenfrequencies by CFA. Through this index, a focused analysis of rail corrugation patterns is facilitated. The study further delves into the stability, repeatability, and sensitivity of the E-RCI via varied measurement scenarios. Ultimately, the CFA-based rail corrugation identification is verified, establishing its practical applicability and offering a distinct approach to detecting and characterizing rail corrugation phenomena. This study has introduced an innovative methodology for rail corrugation detection using CFA, with the principal objective of lowering the detection threshold. This approach offers an efficient measurement technique for identifying rail corrugation areas, thereby potentially reducing maintenance costs and enhancing efficiency within the railway industry.

Investigation on the transient rolling contact behaviour of corrugated rail considering material work hardening

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.

On the Change in Hydrogen Diffusion and Trapping Behaviour of Pearlitic Rail Steel at Different Stages of Production.

To avoid hydrogen flaking in rail production, it is of crucial importance to understand the differences in hydrogen diffusion and trapping between different production steps. Therefore, as-cast unfinished material was compared with two finished rails, hot-rolled and head-hardened, using electron backscattered diffraction (EBSD), electrochemical permeation, and thermal desorption spectroscopy (TDS). A significant increase in dislocation density was in the head-hardened rail compared with the other material states. This leads to an effective hydrogen diffusion coefficient of 5.8 × 10-7 cm2/s which is lower by a factor of four than the diffusion coefficients examined in the other states. Thermal desorption spectroscopy analyses show a clear difference between unfinished and finished rail materials. While a peak in activation energy between 32 and 38 kJ/mol is present at all states, only as-cast unfinished material shows a second peak with an activation energy of 47 kJ/mol, which is related to microvoids. The results show that in the investigated material, the effect of increasing dislocation density has a stronger influence on the effective diffusion coefficient than the presence of a second active trapping site.

The research on the high strength and anti-arc ablation coatings applied in steel conductive rail

In order to enhance the ablation-resistant performance of stainless-steel conductive rails, Mo coating, 410 stainless steel coating and 15 wt% Cr2AlC particles reinforced 410 stainless steel composite coating were prepared and evaluated. Different from the weak interfacial strength caused by the dissimilar metals between Mo and steel rails, 410 stainless steel coating has better interfacial contact with steel rails. The introduction of Cr2AlC into 410 stainless steels further strengthened the mechanical properties of coating by alloy strengthening effect and particle strengthening effect, as the decomposition of Cr2AlC into nano CrC particles is accompanied with the diffusion of Al atoms into 410 stainless steels. It was found that the composite coating can still resist arc erosion at 150 A current, as a dense oxide film formed during the ablation process and the decomposition of Cr2AlC contributed to the heat absorption.

Development of technological solutions to improve the quality of railway rails by improving the technology of smelting, out-of-furnace processing and continuous casting of rail electric steel.

Based on a complex of metallographic and X-ray phase studies for the conditions of EVRAZ ZSMK, which is a leading domestic manufacturer of railway rails, the nature of characteristic defects of rails of metallurgical origin has been determined. These defects, which are the cause of rejection of rails during ultrasonic quality control in the flow of rail-block mill, are stratifications, in the localities of which accumulations of silicate, alumina and sulfide non-metallic inclusions are concentrated; at the same time, these defects in the vast majority of cases are located in the neck of the rail profiles. Analysis of contamination with non-metallic inclusions of suitable rails of the current production of EVRAZ ZSMK showed that, unlike the locations of defects in rejected rails, alumina non-metallic inclusions have an extremely low concentration, while manganese sulfides and silicate inclusions have the highest relative concentration. Based on the results obtained, technological measures were developed, pilot-industrial and implemented to improve the production technology of rail steel in the conditions of the electric steelmaking workshop of EVRAZ ZSMK. In order to reduce the concentration of oxide nonmetallic inclusions in rail steel, a new technology of ladle treatment of steel using a low-ash carburizer and calcium carbide for slag deoxidation has been developed. To reduce sulfide inclusions contamination, measures have been implemented to ensure the sulfur content in the finished steel at a level of no more than 0.008%. The optimization of the modes of electromagnetic mixing in the mold and the temperature regimes of continuous casting of steel was carried out, which also had an effect on reducing the concentration of non-metallic inclusions in continuously cast billets of rail steel and finished rails. The introduction of a set of these technological solutions and measures allowed to reduce the rejection of rails for internal defects from 7% to less than 2%

Development of technological solutions to improve the quality of railway rails by improving the technology of smelting, out-of-furnace processing and continuous casting of rail electric steel.

Based on a complex of metallographic and X-ray phase studies for the conditions of EVRAZ ZSMK, which is a leading domestic manufacturer of railway rails, the nature of characteristic defects of rails of metallurgical origin has been determined. These defects, which are the cause of rejection of rails during ultrasonic quality control in the flow of rail-block mill, are stratifications, in the localities of which accumulations of silicate, alumina and sulfide non-metallic inclusions are concentrated; at the same time, these defects in the vast majority of cases are located in the neck of the rail profiles. Analysis of contamination with non-metallic inclusions of suitable rails of the current production of EVRAZ ZSMK showed that, unlike the locations of defects in rejected rails, alumina non-metallic inclusions have an extremely low concentration, while manganese sulfides and silicate inclusions have the highest relative concentration. Based on the results obtained, technological measures were developed, pilot-industrial and implemented to improve the production technology of rail steel in the conditions of the electric steelmaking workshop of EVRAZ ZSMK. In order to reduce the concentration of oxide nonmetallic inclusions in rail steel, a new technology of ladle treatment of steel using a low-ash carburizer and calcium carbide for slag deoxidation has been developed. To reduce sulfide inclusions contamination, measures have been implemented to ensure the sulfur content in the finished steel at a level of no more than 0.008%. The optimization of the modes of electromagnetic mixing in the mold and the temperature regimes of continuous casting of steel was carried out, which also had an effect on reducing the concentration of non-metallic inclusions in continuously cast billets of rail steel and finished rails. The introduction of a set of these technological solutions and measures allowed to reduce the rejection of rails for internal defects from 7% to less than 2%