In sparsely populated areas single-track railway lines are still common. Despite the low-density traffic and low axle loads, rail damage is observed to initiate in the rails of these lines. Not only large cracks requiring repair are found, but also newly initiated, post-grinding damage is observed. Rail specimens from the track containing representative damages are extracted to identify the reasons for the damage initiation in the R260Mn steel rail. At the rail surface, three years after the preventive grinding maintenance, the characteristic grinding facets and roughness patterns are still present. White etching layers are observed to surround the residual grinding grooves, maintaining the roughness as a result of the high wear resistance of these layers. The strain orientation at the gauge side of the rail is uni-directional due to lateral creep in the wheel–rail contact while in the center of the contact surface the strain patterns evidence shear stress reversal associated with the bi-directional traffic. The damage initiation mechanism after preventive grinding is associated with low-wear conditions and stresses concentrated around long-lasting grinding grooves. The findings show that preventive grinding maintenance specifications for regional single-stock railway lines must be improved. Specific points of interest are stringent requirements on the number of facets and surface roughness, as well as directions for the removal of corrugation.

Composite wires obtained from aluminium shell, micron sized aluminium powder and nano - sized TiN, SiC and Al2O3 powders were fabricated by a two stage process. The stages included ultrasonic treatment and hot extrusion. TEM and SEM observations were performed to investigate the wires’ microstructure. Individual nano powder particles as well as particle agglomerations were observed by two microscopic methods, as well as nanoparticles distribution and localization in the matrix. It was found that the observed nanoparticles and clusters were in the volume of micron-sized Al particles and along the grain boundaries of the matrix. The provided EDX analysis confirms the presence of nanoparticles in the aluminium matrix. From the obtained results, it can be concluded that the two stage fabrication process of nanocomposite wires leads to better wetting of the nano powders from the aluminium melt. Nanocomposites obtained by mixing and extruding TiN, SiC and Al2O3 nano powders and Al micro powders can be used as modifiers of aluminium alloys, as the nanoparticles will contribute to grain refinement and will participate as additional crystallization centers.

The combination of mechanical properties (strength, toughness, and crack arrestability) and weldability that is required of steel pipelines has led to the pipeline steel grades that are used today. The only way to control the mechanical properties of these grades is by controlling microstructure and crystallographic texture of the steel plates. In this chapter, descriptions are provided of the microstructure and texture in the most commonly used pipeline steel grades. The composition ranges of these grades are summarized, together with a brief discussion of segregation effects. After a short historical review, the general principles of microstructure and texture formation during the thermomechanically controlled processing of plate and sheet are discussed. These are illustrated with examples taken from the literature and the authors' research. Special attention is paid to texture formation, methods of texture control, and the influence of texture on mechanical properties, anisotropy, and fracture behavior of these microalloyed steels.

Liquid metal embrittlement (LME) presents a major barrier to the widespread adoption of advanced high-strength steels in automotive applications. Despite extensive research, decoupling its early-stage cracking and propagation micromechanisms remains challenging and is a key research gap. Distinguishing these stages is crucial to understanding the conditions and factors that are favourable for LME and to developing mitigation strategies. Moreover, it can improve the accuracy of predictive models through detailed knowledge from initiation to propagation. In this study, this challenge is addressed by performing interrupted Gleeble hot tensile tests on a Zn-galvanised twinning-induced plasticity steel, simulating resistance spot welding conditions. This approach enables tracking LME progression under applied stress and identifying fracture micromechanisms at early and advanced stages of cracking. Additionally, existing theories on LME micromechanisms are often contradictory, highlighting the need for fundamental research in this area. The findings reveal that LME begins with the contact between liquid Zn and the substrate, leading to Zn diffusion into the substrate by diffusion-induced grain boundary migration and dissolution of the substrate by erosion-corrosion. This dissolution generates defects on the substrate and facilitates Fe diffusion into liquid Zn. Subsequently, defects are filled with liquid and the Zn-rich defect tips, connected to grain boundaries, enhance Zn grain boundary diffusion and weaken intergranular cohesion. Under tensile stress, these weakened boundaries decohere and lead to crack nucleation. Newly formed crack surfaces allow fresh Fe-rich liquid Zn to penetrate, continuing the process until fracture. Future work will focus on the influence of microstructure on LME crack growth.

Three generations of advanced high strength steels (AHSS) have attracted considerable attention due to their excellent mechanical properties and relatively low cost. While there has been extensive research on the basic mechanical properties of AHSS, the impact energy absorption capacity, a critical property for ensuring passenger safety, has not been systematically investigated. In addition, the absence of standardized impact testing protocols for materials or structures hinders the comparison of results across different studies. The present review aims to provide a comparative analysis of the impact performance of thin-walled structures and sheet specimens made from the three generations of AHSS. First, an introduction to the background of AHSS is presented. Widely used experimental techniques and specimen geometries are then reviewed. This is followed by a detailed review of recent relevant studies on the first, second, and third generations of AHSS. Emphasis is placed on investigating the influence of microstructure on impact performance and the underlying mechanisms governing high-strain-rate plastic deformation under impact loading. Various strategies to improve the impact performance of AHSS are also discussed.

Wire arc additive manufacturing (WAAM) is a significant area of interest within the field of additive manufacturing (AM). In the present research, WAAM technology was employed to deposit a Ni-based alloy on a ductile cast iron substrate to fabricate a bimetallic structure of Ni-45 %Fe alloy and ductile cast iron. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron back scattered diffraction (EBSD) and X-ray diffraction (XRD) were used to study phase transformations, microstructure and crystallographic texture development in interfacial regions as well as deposited material. The mechanical properties were also studied using micro-hardness and profilometry-based indentation plastometry (PIP) measurements. The results showed that a wide variety of phases are generated within the heat-affected zone (HAZ) and partially melted zone (PMZ). These phases form complex microstructures with single and double shell morphology. The deposited alloy has a face-centred cubic (FCC) structure, with some carbides and graphite that are formed during the solidification of the first deposited layer. The compositional changes were also observed across the interface. The texture of the deposited alloy showed around 30° deviation from 〈100〉 II building direction due to the shape and overlap of the melt pools. The present results provide a better understanding of interface development mechanisms during WAAM of bimetallic structures. The peak of the hardness across the interface was observed in PMZ because of the formation of a martensitic matrix. The PIP measurements showed that the σ_y and the UTS of deposited alloy are lower than the cast iron base metal.

This study compares the fracture toughness of high-speed steel produced by powder metallurgy and subjected to different heat treatments to obtain either martensitic or bainitic/martensitic microstructures. The heat-treatment process involved austenitization at 1150 °C, followed by either martempering or austempering at 235 °C, and final tempering. Microstructural analysis was performed using electron backscatter diffraction (EBSD), field-emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD). Fracture toughness was evaluated using circumferential notched tensile (CNT) specimens. The results showed that austempered CNT samples exhibited significantly higher fracture toughness compared to martempered ones, indicating improved resistance to crack propagation. Microstructural characterization revealed distinct differences: the austempered samples featured bainitic laths, retained austenite blocks, and martensite plates, whereas the martempered sample contained martensite plates and austenite islands. However, small differences in prior austenite grain size, lath thickness, and dislocation density were insufficient to fully account for the enhanced toughness in the austempered sample. Further analysis indicated that the increased fraction of high-angle grain boundaries and higher kernel average misorientation (KAM) in the austempered sample acted as effective barriers to crack propagation. Additionally, a greater volume fraction of nano-sized carbides contributed to a more pronounced strengthening effect, further enhancing fracture toughness.

Improving the reliability of advanced high-strength steels (AHSS) for automotive applications requires a thorough understanding of liquid metal embrittlement (LME) crack propagation micromechanisms. This study investigates how microstructural features govern crack propagation paths in Zn-galvanised twinning-induced plasticty steel. LME was induced via Gleeble hot tensile tests at 800 °C, and a correlative analysis of the fracture surface's transversal plane revealed key crack-microstructure interactions. The results show that LME fracture is predominantly intergranular, preferentially occurring along high-angle, high-energy random grain boundaries (40°–56°). To quantify the effect of tensile stress on grain boundary segments, a normalised grain boundary stress factor was defined, ranging from 0 (no tensile stress, only shear) to 1 (pure tensile stress). Generally, high-angle grain boundaries require a stress factor below 0.2 for LME, while low-angle grain boundaries (θ <15°) require at least 0.5. Most coincident site lattice boundaries between Σ5 and Σ29 are affected by LME, whereas Σ3 boundaries remain resistant, even at high stress factor. However, cases where Zn penetration was absent despite high misorientation angles and stress factors, or where cracking occurred under the lowest stress factor (parallel to the loading axis), suggest additional, unidentified factors influence LME. These findings highlight the need for advanced three-dimensional modelling to capture the complex interaction between microstructure, stress state, and Zn penetration, not fully resolved in experiments. These insights could guide the development of LME-resistant steels, supporting their safe and reliable use in the automotive industry.

Increasing train speeds and the reduction of maintenance slots places high demands on the railway rails. To meet the challenging demands, producers regularly introduce new steel types. In this experimental investigation is the mechanical behavior of an air-cooled vanadium-alloyed hypereutectoid rail steel presented. The rail is produced applying conventional hot rolling of a reheated bloom and is then cooled on a cooling bed. The mechanical behavior is determined by performing standardized linear elastic fracture mechanics tests. The necessary specimens are extracted from new rails that are made in series production. Monotonic tensile test results have shown that the strain-hardenability of the steel is comparable to standard grade eutectoid rail steel and is higher than that of an accelerated-cooled eutectoid rail grade. The fracture toughness test results showed, statistically, no difference when compared with the fracture toughness values of the accelerated-cooled eutectoid rail grade. The tests were performed at room temperature. The fatigue crack growth rates are, in the linear Paris-regime, slightly higher than in the previously mentioned steels. The results are explained considering the distinct microstructural characteristics of the air-cooled vanadium-alloyed hypereutectoid steel and the fractured surface of the specimens. This experimental investigation contributes to selecting railway steels and predicting the actual in-service behavior.

This study investigates the transformation behavior of advanced high-strength dual-phase (DP) steel subjected to thermal cycling, aiming to support improved automotive steel-processing technologies in terms of properties, cost, and speed. The heat treatment applied consisted of 1–7 cycles through the intercritical region at a conventional heating rate. Results were compared with the conventional dual-phase steel treatment currently used in industry, as well as with variants that combine thermal cycling and fast heating, the latter offering potential for carbon-free methods. The goal is to gain a deeper understanding of the transformations that occur in the material and the potential benefits that may result. Characterization was performed using dilatometry, electron microscopy techniques, and Vickers hardness testing. Findings show the initial ferrite–martensite microstructure remained largely unchanged after cycling, though preferential austenite nucleation within ferrite and Mn segregation remained. The resulting microstructure consisted of ferrite, bainite, martensite, and retained austenite. Crystallographic orientation analysis revealed texture memory effects, with preferred orientations persisting after multiple cycles. Grain refinement occurred mainly in transformed zones, while ferrite showed slight growth with more cycles, correlating with a reduced bainite/martensite fraction. Hardness increased significantly after the first cycle but declined with subsequent cycles, reflecting a reduction in bainite/martensite fraction. It is found that when up to two cycles are used, the process can be beneficial for the steel properties; otherwise, other alternatives, such as fast heating, can be applied to optimize production.

Preventive grinding of rails is a recurring maintenance routine to remove damage initiated in the wheel–rail contact. The grinding routine increases the service life of rails and reduces operational costs. Despite these benefits, grinding-related defects are observed. In this work a field test is performed to investigate the contact-surface formation and to better understand its durability. Surfaces after grinding are studied at different stages of the test to characterize wear mechanisms and deformation. The freshly ground surface exhibits a higher roughness and is composed of facets. It is determined that roughness asperities are extruded and fill grinding grooves in the process. High contact stresses at the facet transitions accelerate the extrusion of roughness asperities and the fast formation of the contact surface. The analysis further shows that deeper grinding grooves prevent homogeneous deformation. Strain concentrations arise due to the inhomogeneous deformation leading to damage initiation sites. These grooves are still present in the rail surface after the test. The evolution of the ground surface is captured in a schematic wear model.

Numerous studies have demonstrated the viability of lightweight Fe-Mn-Al-C steels for exhibiting an improved balance of high strength and high ductility in automotive applications. However, their high-cycle fatigue behaviour has been scarcely studied. This work examines the effect of κ-carbides formed during the aging treatment on the high-cycle fatigue performance of an austenitic Fe-29Mn-8.7Al-1C (wt. %) steel. The material is studied in solution-treated, under-aged, and peak-aged conditions. High-cycle fatigue tests and analysis of fatigue fracture surfaces were performed using SEM and EBSD techniques. The results indicate satisfactory high-cycle fatigue performance in the aged material, somewhat better than for high Mn steels. Fatigue crack formation and growth occur predominantly via a quasi-cleavage mechanism along the [1 1 1] crystallographic planes, which is also a plane for planar glide and the formation of persistent slip bands during plastic deformation. The nanoscale intragranular κ-carbides in the aged samples interact with the gliding dislocations, resulting in the shearing of nanoscale κ-carbides in a weakly coupled regime. The resistance of particles to shearing is determined by their size, volume fraction, and antiphase boundary energy (γ_APB), which vary during the aging process. The aged Fe-29Mn-8.7Al-1C steel significantly improves the fatigue strength as the formation of persistent slip bands is delayed due to an additional energy barrier related to the shearing of the κ-carbides. This improvement peaks in the under-aged condition and decreases with further aging time.

Depending on the alloy composition, intercritical annealing may provide different phases in the microstructure. For low-alloyed dual-phase (DP) steels it is usually ferrite and martensite, while for medium-Mn steels retained austenite is also formed. In a present study, a wide intercritical temperature range was applied to a 5% Mn steel to investigate possible microstructure combinations: ranging from fully ferritic, through ferritic-austenitic, multiphase, to fully martensitic, which were next investigated in terms of mechanical properties to clarify the behavior of this type of material. The obtained results together with technological issues and economic indicators were next compared to mechanical properties of typical DP steels in order to assess the possibility of replacing this material in car production. The mechanical properties were evaluated using static tensile and hardness tests. The phase composition was determined qualitatively and quantitatively using dilatometry, X-ray diffraction measurements, and electron backscatter diffraction analysis. The results suggest that both initial austenite and martensite fractions have a decisive influence on the yielding and elongation of steel; however, the tensile strength depends mainly on the sum of martensite initially present in the microstructure and the strain-induced martensite formed from the plastically deformed austenite regardless of the initial retained austenite—martensite ratio. The results indicate superior total elongation of medium-Mn steels reaching 30% compared to DP steels with a similar strength level in the range between 900 and 1400 MPa. However, medium-Mn steels could be a significant competitor to dual phase steels only if some technological problems like discontinuous yielding and serrations are significantly reduced.

Additively manufactured Nitinol (NiTi) architectured materials, designed with unit cell architectures, hold promise for customisable applications. However, the common assumption of homogeneity in modeling and additive manufacturing of these architectured materials needs further investigation because geometric-dependent melt pool behaviour results in inhomogeneous microstructure and thermomechanical properties. This study shows that property inhomogeneity at the mesoscale is one reason for pseudo-linear response and partial superelasticity of the fabricated NiTi body-centered cubic (BCC) architectured materials. We modeled using a phenomenological constitutive relation and additively manufactured NiTi architectured materials with varying relative densities. These fabricated samples showed distinct microstructural textures and compositions that affected their local recoverability. The edge effects and laser turn regions were identified as the causes underlying the observed microstructural inhomogeneity. The dimensionless Fourier number is used to describe the transition of printing modes. This study provides valuable information on rigorous experimental/computational consistency in future work.

Rolling and annealing is a crucial technology to produce electrical steel sheets. This technology is not just aimed to control the geometry of steel sheets but more importantly to enhance the magnetic properties of the final products via appropriate microstructure and crystallographic texture. In this study, the evolution of microstructures and textures of an Fe-1.2 wt.% Si alloy through the entire processing route (from reheating, warm rolling to annealing) is monitored by electron back-scatter diffraction. Plastic flows of the material during conventional and asymmetric rolling are analyzed in detail based on geometric parameters of the rolling gaps. Deformation textures are accurately predicted by the full-constraint Taylor and advanced Lamel (ALAMEL) crystal plasticity models. The development of recrystallization textures is accounted for by the plastically stored energy in deformed crystals, which in turn is approximated by the plastically dissipated power (i.e., the Taylor factor) as predicted by the full constraint Taylor model. Although asymmetric warm rolling does not produce an improved texture or microstructure for electrical steels, the present study provides useful information on the evolution of the recrystallization microstructure and texture in steels with a complex strain history after asymmetric warm rolling.

A novel double-step intercritical annealing (DSIA) process was conducted on Fe-0.16C-4.7Mn-1.6Al-0.2Si transformation induced plasticity (TRIP) steel. In a present study, an effect of different heating and cooling rates applied to the second intercritical annealing (IA) step on the microstructure was studied in detail by using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques. The quantitative analysis of the retained austenite fractions for particular heat treatment variants was carried out via X-ray diffraction (XRD). The formation of complex microstructures containing a small fraction of ferrite, retained austenite and two types of martensite was observed regardless on the applied heating and cooling rates. It was found that the soft ferrite can be replaced by martensite through the incomplete stabilization of austenite with C and Mn during short second intercritical annealing step. The heating rate influences significantly the kinetics of austenite formation during the second heat treatment step. Low heating rates ensure more time for formation and homogenization of austenite during heating improving its thermal stability. Thus, the best balance of martensite and austenite fractions in combination with homogenous morphology of the microstructure was noted for the specimen heated at a rate of 3 °C/s, which was the lowest one in the reported experiment.

The development of superior mechanical properties in medium-Mn requires the optimization of microstructural parameters such as retained austenite (RA) stability, volume fraction, and morphology. The present work explores the possibility of using a continuous annealing approach instead of conventional batch annealing to perform an intercritical annealing (IA) treatment in a hot-rolled strip of an Al-alloyed 5Mn steel. Dilatometric studies were performed at a temperature of 680 ºC with soaking times ranging from 1 to 300 min to follow the microstructural changes as a function of time. The microstructures thus obtained were thoroughly characterized by means of X-ray diffraction, SEM and TEM, TEM-EDS microanalysis and EBSD phase and orientation maps. It was observed that with increasing soaking times, the volume fraction of retained austenite gradually increases, albeit at the cost of its stability. The comparison of martensite start temperatures (M_s) based on the chemical composition of austenite at 680 ºC with that experimentally obtained at higher process temperature revealed the effect of the grain size on the reduction of RA stability for longer process times. Accordingly, mechanical tests results showed that the yield stress, tensile strength and hardness decrease with an increase in the IA soaking time.

In many commercial steel processing routes, steel microstructures are reverted to an austenitic condition prior to the final processing steps. Understanding the microstructure development during austenitization is crucial for improving the performance and reliability of the microstructure that forms from austenite. In this work, austenite formation in a high-C steel (0.85 wt%) from a microstructure containing martensite/austenite and bainite bands is investigated. It is shown that austenite formation from bainite results in a refined austenite grain structure, and the martensite matrix thus obtained on quenching has a homogeneous distribution of carbides with a relatively low fraction of retained austenite (24%). On the other hand, a coarser austenite microstructure is obtained when austenite forms from a mixture of martensite and retained austenite. The reason for the coarse austenite grains is argued to be a memory effect, which is substantiated by in situ X-ray diffraction analysis. After quenching, an inhomogeneous carbide distribution and a higher retained austenite fraction (30%) are observed in the regions that were initially martensite/austenite. The global microstructure, hence, has a bimodal size distribution of prior austenite grains and carbide-dense bands. The causes for these heterogeneities are discussed with the help of interrupted quench experiments, equilibrium phase calculations, and DICTRA simulations.

The influence of carbon concentration variations on pearlite formation (20 h at 600 °C) in a case-carburized steel is investigated. The resultant microstructure shows three distinct regions: carburized case, a transition region, and the original core. The microstructural transition from the case to the core regions is observed to be relatively sharp. The investigated region of the carburized case (0.9 wt.% C) contains two types of pearlite: ferrite + cementite and ferrite + M₂₃C₆, where the pearlitic aggregate with M₂₃C₆ shows faster formation kinetics. The kinetics of pearlite formation in the transition region (0.3 wt.% C) is very slow and is observed with only M₂₃C₆ carbide. Only around 40% austenite decomposes into pearlite in the transition region, which, in comparison to the carburized case region of 0.9 wt.% C is a fraction that is lower by a factor of two. Pearlite is absent in the investigated core region (0.16 wt.% C). The microstructure in this region is predominantly martensite and pro-eutectoid ferrite, with a fraction of ferrite well below the equilibrium fraction. Ferrite formation in this region is limited by the redistribution of mainly Ni, Mn, and Cr, and their resulting solute drag effect on the austenite/ferrite interface. A thermodynamic and kinetic argumentation of these observations is provided with the help of thermodynamic data, precipitation simulations, and a general mixed-mode Gibbs energy balance model.

The phase transformations, microstructure and properties of two Medium-Mn processed via quenching and partitioning steels were compared in this contribution and a new strategy for controlling mechanical properties by introducing and controlling cold-worked ferrite prior to heat treatment is proposed. It was found that during heating, the recovery and recrystallization of cold-worked ferrite compete with austenitization, thereby inhibiting the coarsening of austenite. The cold-worked ferrite interface will significantly delay the austenitization kinetics during the partitioning local equilibrium stage compared to martensite. These results lead to a diverse parent austenite, as well as a refined martensite substructure. As a result, the randomly distributed variants increase the number of effective grain boundaries, thus enhancing yield strength. The intercritical annealing process at a temperature of 860 °C resulted in the formation of fresh martensite-retained austenite (M/RA) constituents exhibiting a remarkably fine (<2 μm) and uniform grain morphology. Such microstructure yielded substantial improvement in both the strength and ductility of the steel. The proposed treatment led to excellent elongation (24%) at fracture, combined with very high ultimate tensile strength and yield strength of 1345 MPa and 1163 MPa, respectively, of the steel, resulting in a product of strength and elongation that exceed 32 GPa%.