Rail Steel Research Articles

Evolution of Non-metallic Inclusions in Si-Ca-Ba-Killed Heavy Rail Steel During Secondary Refining Process

Evolution of Non-metallic Inclusions in Si-Ca-Ba-Killed Heavy Rail Steel During Secondary Refining Process

Explore on the Mechanism of Action between Al2O3–SiO2 Refractory Materials and Rare Earth High Carbon Heavy Rail Steel

Explore on the Mechanism of Action between Al2O3–SiO2 Refractory Materials and Rare Earth High Carbon Heavy Rail Steel

Reduced spheroidization in rail flash-butt welding by selective alloying

Thermal cycle (welding simulations) at the inter-critical region were performed on an Si and V micro-alloyed (not heat-treated) rail steel. The beginning of austenitization temperature (Ac1) in the micro-alloyed rail steel occurred significantly above that observed in an alternative heat-treated rail steel. Very little pearlite alteration was observed until austenitization at a temperatures above 750°C, where there was a reduction in hardness and onset of spheroidization. The maximum spheroidization together with the lowest observed hardness occurred at 760°C. It was also observed that there is a linear correlation between hardness and volume fraction of spheroidization of cementite. By the dilatometric variation, contraction due to austenitization was observed only from 760°C onwards in the 60 s isothermal period at the austenitization temperature. These results may lead to a new approach to weldability and reduction of the softened region concerning rail welding.

Synchrotron X-ray radiation study of retained austenite stability and the effect on fatigue behavior of bainitic railway steels

The effect of retained austenite stability on the fatigue performance was studied in bainitic rail steel subjected to different heat treatments, including normalizing at 900 °C and normalizing at 900 °C combined with tempering at 320 °C. The normalized steel had yield strength of 851 MPa, tensile strength of 1131 MPa, uniform elongation 7.0 %, and total elongation 17.5 %. Tempering the steel at 320 °C resulted in similar strength and plasticity compared to the normalized condition. However, the fatigue performance of steel was improved significantly after tempering. The ultimate fatigue stress (endurance limit) after 1 × 107 cycles was 671 MPa, which was 38 MPa greater than the normalized steel. Microstructural analysis revealed similarities between normalized and tempered matrices at crystallographic interfaces and grain boundaries. Synchrotron X-ray radiation indicated that the initial retained austenite content was ∼15.5 % in both normalized and tempered conditions. However, at tensile stress of 800 MPa, the amount of retained austenite transformed in the normalized steel was ∼4 %, which was twice that of the tempered steel. The enhancement of retained austenite stability was an important aspect in improving the fatigue performance. The analysis of interphase spacing showed that the strain in the normalized matrix synchronized with the retained austenite, and the stress was concentrated in the retained austenite, which promoted transformation of retained austenite. The matrix of tempered steel was strained first, which prevented stress concentration in the retained austenite and rendered the retained austenite stable.

Study on the effect of rare earth Ce on the modification of sulfide inclusions in U71Mn heavy rail steel

In this paper, the directional modification behavior of rare earth Ce on sulfide inclusions in steel is studied by thermodynamic calculation and experiment methods, and the mechanism of directional modification of rare earth Ce on sulfide inclusions in U71Mn heavy rail steel is proved. The results show that U71Mn heavy rail steel contained more large-sized inclusions and their distribution is more concentrated without the addition of rare earth Ce element. After the addition of rare earth Ce element, the average size of sulfur-containing inclusions in the steel decrease from 5.22 μm to 1.85 μm, and the number density of sulfur-containing inclusions in the steel increase from 83.65 mm-2 to 217.68 mm-2, indicating that the number of sulfur-containing inclusions in the steel increases after the addition of Ce element, and more small-sized sulfur-containing inclusions will form in the steel. The addition of rare earth Ce element can effectively reduce the existence of large-sized inclusions in the steel and modify large-sized inclusions into small-sized inclusions.

Enhancing strength and toughness in a pearlitic rail steel via multi-alloying and accelerated cooling

The demand for higher speeds and heavier loads has emphasized the necessity to tackle the inherent trade-off between strength and toughness in pearlitic rail steels. Herein, the co-additions of Cr, Ni and Cu and accelerated cooling rate on the microstructure and mechanical properties of a medium carbon pearlitic steel were systematically investigated. In comparison with base alloy, the new steel exhibits smaller prior austenite grain size (PAGS) due to the drag effect of Cu and Ni solutes. The finer PAGS and lower C content increased the volume fraction of proeutectoid ferrite. The finer pearlitic nodule size (PNS) and pearlitic colony size (PCS) were attributed to the small PAGS and greater extent of undercooling due to the combined effect of multi-alloying and accelerated cooling. Additionally, the synergistic effects of multi-alloying and accelerated cooling rate decrease the pearlitic phase transformation temperature, accountable for the finer interlamellar spacing (IS). Compared with the base steel, the yield strength and ultimate tensile strength of the new steel increased from 587 MPa and 1069 MPa to 740MPa and 1178MPa, respectively, with a simultaneous increase of ductility from 12.4% to 14.7%. The strength increments are mainly attributed to the finer IS in the new steel. Meanwhile, the new steel possesses a higher impact toughness compared to the base steel due to the increased volume fraction of proeutectoid ferrite, and finer PNS and IS.

Study on thermo-plastic instability characteristics of machined surface localization in high-speed machining of rail steel

Study on thermo-plastic instability characteristics of machined surface localization in high-speed machining of rail steel

Measuring Vibrations of Subway Tunnel Structures with Cracks

In a study conducted in a metro tunnel, acceleration and displacement sensors were strategically placed along steel rails, track beds, and tunnel walls to capture real-time dynamic responses during train operations. Data were analyzed in the time and frequency domains, focusing on vibration levels and one-third octave bands. The results indicated that peak vibration acceleration significantly decreases from steel rails to tunnel walls, with different vibration frequencies observed at various locations: steel rails (200 Hz–1400 Hz), track beds, and tunnel walls (70 Hz–400 Hz). Cracks notably increase peak acceleration, vibration levels, peak frequency, and steel rail displacement but do not alter the overall vibration trends. Tunnel wall responses show the highest sensitivity to cracks, with a 300% increase in peak frequency, followed by track beds (100%) and steel rails (70%). Vibration levels under one-third octave band processing increased by 12.4% for tunnel walls, 8.8% for track beds, and 2.2% for steel rails. Cracks also caused steel rails’ vertical and lateral displacement to rise by 112% and 53%, respectively. These findings provide valuable insights for vibration reduction and crack repair in long-term subway operations.

Influence of Lubrication Cycle Parameters on Hydrodynamic Linear Guides through Simultaneous Monitoring of Oil Film Pressure and Floating Heights

Hydrodynamic linear guides in machine tools offer a high load capacity and excellent damping characteristics, improving stability, precision, and vibration reduction. This study builds on previous research where floating heights were verified with a simulation model limited to measured floating heights. Advancements include incorporating pressure sensors into a fixed steel rail, enabling simultaneous measurement of oil film pressure and floating heights for a comprehensive understanding of lubrication conditions within the lubrication gap. The experimental results explore the effects of different lubrication methods, providing valuable insights into cavitation and lubrication adequacy. The results demonstrate the feasibility of utilizing pressure sensors to measure oil film pressure within the lubrication gap, providing a nuanced understanding of lubrication dynamics. By measuring both floating heights and pressure measurement, distinctions between hydrodynamic lubrication, mixed friction regions, and instances of lubricant deficiency become readily discernible. The variations in real-time oil film pressure and floating heights help to optimize the lubrication cycle for hydrodynamic linear guides, enhancing system performance and longevity.

Rotary barrel tumbling as a method of surface preparation for pin-on-disc wear testing samples

Surface preparation is essential to ensure sample homogeneity in terms of surface roughness and mechanical properties, as these factors can significantly affect wear behavior and test repeatability. Although conventional semi-automatic and automatic grinding and polishing processes are efficient and well established, limitations arise for the preparation of large numbers of samples of a hard material such as high-carbon steel, including issues with sample geometry, the need for on-demand sample holders, cost-related limitations, and even considerable human workload and expertise. This study aims to evaluate the use of rotary barrel tumbling—a polishing method that relies on the sliding of abrasive media over the samples’ surface inside a rotating barrel—as an alternative method to prepare the surface of wheel and rail steel samples for pin-on-disc wear testing. A 4-stage tumbling procedure was employed, using different compositions of tumbling media in each stage. Surface roughness and hardness were evaluated throughout the process via 2D and 3D profilometry, microhardness Vickers measurements, and optical microscopy. The proposed method resulted in significant reductions in the surface roughness and hardness of the samples, along with improved homogeneity between samples of different materials and within the same material. These findings suggest that rotary barrel tumbling is an effective alternative method for the surface preparation of pins and discs made of high-carbon steel, enhancing the samples’ suitability for subsequent wear tests.

Development of a flexible arrayed eddy current sensor with three-phase excitation for inspection of rail rolling contact fatigue cracks

A Flexible Arrayed Eddy Current (FAEC) sensor can inspect a large area in a single probe pass, which is beneficial for customizing the profile of the inspected part. This paper presents the development of a flexible arrayed eddy current sensor with three-phase excitation for inspection of Rolling Contact Fatigue (RCF) cracks in rail. The excitation coils are driven by three-phase currents that are 120° apart in phase. The induced eddy current in the conductive rail sample shifts electrically along the phase variation direction of the excitation currents. The sensor measures a small background signal to determine if there is no defect in the rail sample. Therefore, the sensor has a high relative sensitivity to defects. We study the operating principle of the sensor using a 3D finite element method (FEM) model. The numerical results demonstrate the sensor's viability for fast inspection and characterization to detect RCF defects in conductive rail steel samples.

Investigation into the Hot Workability of Rail Steel U75V

Investigation into the Hot Workability of Rail Steel U75V

Fatigue Crack Characteristics in Gradient Predeformed Pearlitic Steel under Multiaxial Loading

Rolling contact fatigue of railway rails not only severely deforms the surface material near the rail head, but also induces an anisotropy in the mechanical behavior due to work hardening and alignment of the microstructure along the shear direction. Cracks typically initiate in this region and propagate along the aligned microstructure. The fatigue behavior of rails is evaluated under uniaxial loading in the undeformed material state. However, this is not representative of the contact loading condition and material performance after years of service. Herein, the nonproportional multiaxial fatigue of as‐received and biaxially predeformed pearlitic rail steel R260 is investigated. Four material states are investigated, corresponding to the microstructure found at different depths from the severely deformed surface material at the rail head. A starting notch is machined by electrical discharge machining to control crack initiation and allow for comparable surface crack propagation measurements. The crack path is found to be strongly influenced by the degree of predeformation while the early surface crack propagation rate is found to be similar for all material states.

Mechanism and improvement of the rolling contact fatigue of the surface layer with heterogeneous microstructures of the rail steel treated by laminar plasma jet

Surface layer with heterogeneous microstructures (SLHM), characterized by hardened spots discretely embedded in a soft substrate, can be prepared by laminar plasma quenching (LPQ) to improve the wear resistance of the railway rail. However, severe rolling contact fatigue (RCF) cracks and spalling would occur in the hardened spots that only consist of quenched microstructure. This study analyzed the RCF damage mechanism of the LPQ prepared hardened spots by contact simulation. To improve the RCF resistance while maintaining the high wear resistance of the treated rail, a novel SLHM, whose discrete hardened spots are surrounded by transitional zone with the hardness lower than that of the quenched zone but higher than that of the substrate, was proposed and prepared by laminar plasma quenching-tempering (LPQT). Then, twin-disc tests and contact simulations were conducted to investigate the wear and RCF resistances of the LPQT treated rail steel. Results showed that the cause of the severe RCF cracks and spalling at the entry side of the LPQ prepared hardened spots was that the cyclic tensile stress at the entry side was always higher than that at the exit side under the cyclic rolling contact loading. The high tensile stress at the entry side of the LPQ prepared hardened spots resulted from the elastic deformation induced by tensile plastic deformation of the neighboring substrate. When the thickness of the transitional zone was about 0.1 mm, the generation of severe RCF cracks and spalling was significantly inhibited in the LPQT prepared hardened spots because the transitional zone decreases the cyclic tensile stress at the entry side of the quenched zone. Besides, the wear loss of such LPQT treated rail steel was only increased by 18.1 % compared with that of the LPQ treated rail steel, indicating that the wear resistance of the LPQT treated rail steel was not significantly reduced. These findings are promising for designing the microstructure of the surface layer to obtain wear-resistant rail with high RCF resistance.

Effects of microstructure on the corrosion behavior of pearlitic rail steel under simulated salt fog conditions

In this paper, the corrosion resistance and mechanisms of rail specimens with different lamella spacings in a salt spray environment were evaluated and investigated. This investigation was achieved by controlling different cooling rates of pearlitic bodies through heat treatment to obtain various lamella spacings. The results indicated that the corrosion resistance of all the specimens decreased during the salt spray test. The specimens with slow cooling rates (resulting in large pearlitic sheet layer spacings) had poorer corrosion resistance than those with fast cooling rates. Specimens obtained with both fast and slow cooling rates (air cooling at a 0.01 °C/s cooling rate) displayed similar corrosion patterns. However, the corrosion stability of the specimen obtained at a cooling rate of 0.03 °C/s fluctuated considerably after 144 h of salt spray corrosion. This fluctuation was attributed to the transformations of corrosion products within the rust layer. The structural stability of the rust layer was related to the defects present in the material. Large defects increase the instability of the rust layer, thereby increasing the susceptibility to corrosion in a salt spray environment.

Strain‐Induced Martensitic Transformation and the Mechanism of Wear and Rolling Contact Fatigue of AISI 301LN Metastable Austenitic Stainless Steel

AISI 301LN metastable austenitic stainless steels (MASSs) are known to exhibit high work‐hardening rates attributed to martensite evolution during straining which results in the second‐phase strengthening mechanism. This enhances surface hardness and potentially reduces wear and rolling contact fatigue (RCF). The aim of this study is therefore to evaluate the work hardening, wear, and RCF performance of AISI 301LN metastable austenitic stainless steel as a possible alternative material for rolling and sliding applications by varying the contact conditions such as slip ratio against the standard R350HT rail steel using a twin‐disc simulator. The results show that 301LN MASS has high surface work hardening and increased hardness because of martensitic transformation, while R350HT rail steel has only slightly changed. The formation of a hard martensitic phase is also confirmed by X‐ray diffraction analysis as well as by two other techniques, indicating a secondary hardening effect. Although it shows potential for work hardening, its susceptibility to wear‐related problems may make it less suitable for rolling and sliding applications due to a cracking and spalling mechanism induced by martensite formation. The surface strains required for the observed martensite formation are calculated and found to be very high, approaching 0.4.

Observing and identifying fouled ballast bed: On-site testing with infrared thermography (IRT) and uncovering thermodynamic transfer mechanisms within the ballast bed

The ballast bed serves as the foundation of the ballasted track, and its performance is maintained through periodic ballast cleaning. Early detection of fouled ballast bed significantly reduces maintenance workload and capital investment. Some scholars have studied the feasibility of utilizing infrared thermography (IRT) for detecting fouled ballast bed (DBF) and have made some progress. Existing studies have predominantly employed simulated boxes to simulate the ballast bed. To better reflect real-world conditions, this study established two sections of ballast bed on a newly constructed line: one with clean ballast and the other fouled, with a volumetric fouling rate (VFR) of 27.6 % (FI ≈ 21.5 %). Moreover, this paper takes a pivotal step in exploring the thermodynamic transfer mechanisms within the ballast bed, the influences of meteorological factors on the detection effectiveness of IRT, and other detection indicators that could be used for DBF.The results demonstrate that the different void fractions and composition substances of the clean and fouled ballast beds (CFB) contribute to their distinct thermodynamic properties. Furthermore, the high specific heat capacity of water exacerbates the thermodynamic property difference between the CFB. In terms of meteorological factors, both the solar radiation intensity (S) and air temperature (T) have a significant positive impact on the temperature of the ballasted structure (STT) and the temperature difference between the CFB (CF-S). Throughout the day, as the S and T increase, the ballast bed surface absorbs more solar heat than it loses, leading to an increase in its surface temperature. When it exceeds the soil temperature (S-S), heat is transferred downward. Since the poor heat conduction of the clean ballast bed, it has a higher surface temperature. As the S and T decrease, heat convection and conduction become dominant, leading to a decrease in the surface temperature of the ballast bed (BT-S). When the BT-S is lower than the S-S, heat is transferred upward, causing the surface temperature of the fouled ballast bed (F-S) to potentially exceed that of the clean ballast bed (C-S). Furthermore, the humidity (H) has a strong negative impact on the STT, while on sunny days following rain, it has a significantly positive impact on the CF-S. The effects of wind speed (W) on the STT and the CF-S are not prominently observed due to its low values during the experiment. Without considering rainfall, higher S and T, combined with reduced W, result in a greater CF-S and are more conducive to advancing fouling detection. Hence, the CF-S can reach up to about 3 °C on a sunny day and may even rise to about 5 °C after rainfall. Nonetheless, the CF-S is only around 0.71 °C on a cloudy day and 0.25 °C at night. Unexpectedly, there is a significant temperature difference between the sleeper and the ballast bed or the steel rail. These indicators could potentially be used for DBF on cloudy days. Overall, these findings demonstrate the feasibility of using IRT for DBF in the field, provding a broader theoretical support for its advancement and implementation.

Effects of hydrogen on the formation of nanocrystalline at rolling contact surface of bainitic rail steel

A newly discovered peculiar microstructure at the rolling contact surface of bainitic rail steel has been investigated via positron annihilation technique and X-ray diffraction. The results show that the nanocrystalline layer is produced through low-temperature dynamic recrystallization. After hydrogen charged, low temperature dynamic recrystallization has been inhibited by hydrogen, and nanocrystalline layer at the surface decreases or disappears.

Ratcheting Assessment of Rail Steel at Elevated Temperatures in the Presence of Dynamic Strain Aging

Ratcheting Assessment of Rail Steel at Elevated Temperatures in the Presence of Dynamic Strain Aging

Influence of stratified tribologically transformed structure layers on contact fatigue crack initiation of bainitic rail steel

This study investigated the effect of stratified tribologically transformation structure (TTS) layers on contact fatigue crack initiation of bainitic rail steel serviced on a heavy-haul railway. Results demonstrate that the heterogeneous stratified TTS layer consists of alternating white etching layer and brown etching layer (WEL and BEL, respectively). The formation of stratified TTS is accompanied with the initiation of contact fatigue cracks, including vertical cracks, intra-layer cracks and inter-layer cracks. Unlike the current findings in conventional pearlitic rail steel, the intra-layer cracks are mostly initiated within BEL on bainitic rail steel. With help of transmission electron microcopy, nano-indentation techniques and in-situ micropillar compression tests, the initiation mechanism of contact fatigue cracks associated with stratified TTS on the bainitic rail are discussed in detail. The formation of brittle twined martensite and coarse oxidized particles is responsible for the intra-layer cracks initiated within BEL, while the inter-layer cracks nucleated from the interface are attributed to the difference in mechanical properties between different layers.