Papers by Keyword: Pearlitic Steel

Abstract: This research investigates the cold cracking susceptibility of fully pearlitic rail steel during damage repair using the Flux-Cored Arc Welding (FCAW) process. Rail steel grade-R900A according to UIC 860V standard was used. The experiments were conducted using implant testing in accordance with ISO 17642-3, focusing on critical parameters such as tensile stress levels, lower critical stress (LCS), and time to failure (TTF). Furthermore, the effect of tempering welding techniques on fracture behavior was explored. The experimental results revealed that fracture surfaces could be distinctly categorized into quasi-cleavage and final rupture regions, with these regions varying according to the applied stress levels. Implant testing demonstrated that fractures predominantly occurred within the coarse-grained heat-affected zone (CGHAZ). A clear relationship was observed between stress levels and TTF, with lower stress levels resulting in longer times to failure. The LCS for single welds was approximately 290 MPa, whereas tempered welds showed higher LCS of about 792 MPa. Hardness profiles were measured across the weld metal, heat-affected zone (HAZ), and base metal. The highest hardness values for a single weld pass were provided in the CGHAZ, peaking at an average of 877 HV10. In contrast, tempered welds (double weld passes) significantly reduced peak hardness to 363 HV10. Metallurgical examination of the HAZ from single weld passes revealed a needle-like martensitic matrix, meanwhile tempering welds exhibited a finer structure with a tempered martensitic matrix. The average grain size within the HAZ was assessed, with the critical grain size of the CGHAZ at the fracture region measured at ASTM grain size No. of 10.63–10.75. Remarkably, under the given experimental conditions, specimens subjected to tempered welding exhibited no fractures. This indicates that appropriate welding procedures and controlled heat input can alleviate cold cracking susceptibility. The findings of this research provide deeply comprehension into the design of welding procedures to minimize cracking risks in fully pearlitic steels, contributing to safer and more reliable repair processes in future applications.

Abstract: Cold-drawn high-carbon steel wire with pearlite microstructure is one of the most popular raw materials for modern reinforcing ropes. Lamellae thinning, changes in interlamellar interface and metallographic texture, strain localization is the main property-forming phenomena in the wire drawing process. However, the experimental study of these phenomena dynamics is difficult and time-consuming. Drawing process of pearlitic steel wire was investigated. Behavior of pearlite colonies on the surface and the central layer of the wire were researched, based on the multiscale computer simulation. Cementite lamellae orientation in relation to the drawing axis, interlamellar spacing and shape of cementite inclusions were key factors. Regularities of the pearlite colonies reorientation, changing the shape and size of cementite lamellae and strain localization in the ferrite were established on the basis of FEM. It was established that the cementite lamellae, that are parallel to the drawing axis, had the maximum thinning. Interlamellar distance in pearlite colonies with such lamellae changed most intensively. Cementite lamellae, that are perpendicular to the drawing axis, are the most susceptible to fracture. It was found out that for certain values interlamellar distance this effect can be reduced. Intensive reorientation of pearlite colonies in relation to the drawing axis was observed in the case of their location at an angle to the drawing direction. At the same time, there was a significant bending of cementite lamellae and their susceptibility to fragmentation. Estimated values of the wire mechanical properties were compared with a real experiment. The simulation results were verified by metallographic analysis.

Abstract: This paper is concerned with the effects of process parameters on the shape changes of a micro cementite band in wire drawing of pearlitic steel. Two process parameters, an initial orientation of cementite band and its location, are chosen. In this study, a macro deformation behavior at a material point in macro wire drawing of pearlitic steel is represented by an averaged behavior of a unit model. This unit model is simulated by a micro finite element analysis, while a macro wire drawing of pearlitic steel is simulated by finite element method at a continuum scale. The shape changes of a cementite band would be traced, by solving the unit problem with the changes of boundary conditions corresponding to the macro deformation behaviors of material points along a particle path. The predicted shapes of cementite bands are compared to those by the experiments reported in the literature. Qualitative comparisons between the current predictions and experiments verify the proposed method. Effects of an initial orientation of cementite band and its location on its shpae changes are presented. It was also noted that the most micro deformation in a unit model occurs in the deformation zone.

Abstract: This paper analyzes the hierarchical microstructure of cold-drawn pearlitic steels. To this end, environmentally assisted fracture behavior and microstructural integrity in aggressive environments is analyzed in progressively cold-drawn pearlitic steels based on their microstructural evolution during the multi-step cold drawing manufacture process producing a slenderizing and orientation of the pearlitic colonies (first microstructural level), and orientation and densification of the ferrite/cementite lamellae (second microstructural level). Thus the microstructure of the cold-drawn pearlitic steel wires becomes progressively oriented as the cold-drawing degree increases and this microstructural fact affects their macroscopic behavior, inducing anisotropic fracture behavior and crack path deflection in aggressive environments. In addition, the hierarchical microstructure of cold-drawn pearlitic steel wires in two microstructural levels (colonies and lamellae) suggests a consideration of them as hierarchically structured materials (HSM). Furthermore, an analogy is established in the paper between the microstructural arrangement in cold-drawn pearlitic steels and the multi-level structure of Johann Sebastian Bach’s music.

Abstract: This paper deals with hydrogen embrittlement of cold-drawn pearlitic steel wires to be used in prestressed concrete structures in civil engineering. Special attention is given to the micro-level of hydrogen degradation, i.e, the hydrogen-assisted micro-damage (HAMD) that takes place in pearlitic steels in the form of the so-called tearing topography surface (TTS). It is shown that the appearance of this special topography evolves with the degree of cold drawing in the steels (level of cumulative plastic strain undergone by the wires) from standard TTS in hot rolled pearlitic steels (not cold-drawn at all) to a special hydrogen damage topography (HDT) consisting of a sort of enlarged and oriented TTS in heavily cold-drawn pearlitic steels (prestressing steel wires), thereby resembling Donatello wooden sculpture texture (DWST).

Abstract: This work is concerned with the development of a new process map for wire drawing of pearlitic steel considering damage evolution. In this study, a ductile damage is defined as a porosity or void volume fraction and the porosity evolution model proposed by Lee and Dawson is adopted. Dilatational plastic deformation due to growth of micro voids is also considered. Correspondingly, an Eulerian finite element analysis coupled with damage evolution model is utilized in order to reflect the effects of dilatational plasticity due to growth of micro voids. Also, the accumulated damage in wire drawing could be evaluated. Finite element simulation for wire drawing of pearlitic steel are performed for various process conditions such as a half die angle and an area reduction ratio. Especially, the effects of process parameters on the deformation characteristic as well as damage evolution in wire drawing are carefully examined. Finally, a new process map is presented in terms of a half die angle and an area reduction ratio, which can identify the successful process conditions for wire drawing of pearlitic steel. Thus, it would be expected that this process map will help an engineer for the design of wire drawing of pearlitic steel.

Abstract: This paper analyses the role of cold drawing in the fatigue and fracture behaviour of pearlitic steels with distinct drawing degree (a hot rolled bar and a commercial prestressing steel wire). Fatigue crack growth develops globally in mode I and locally in mixed mode in both steels, the micro-crack deflection angle depending on the drawing degree. With regard to fracture behaviour, it takes place in mode I in the hot-rolled bar and in mixed mode (with a strong component of mode II) in the case of the cold-drawn wire, so that strength anisotropy appears in the drawn steel and a sort of directional toughness can be defined.

Abstract: Residual stresses produced by cold drawing are an undesirable effect of the non-uniform plastic strain distribution generated during the conforming process used for obtaining prestressing steel wires. Among the diverse parameters of the process influencing the residual stress generation, one of the most relevant is the geometry of the drawing die and, in particular, the inlet die angle. Wires drawn with die angles as low as possible will exhibit a lower and more homogeneous plastic strain state and, therefore, a smaller and more uniform residual stress state. Thus, the hydrogen embrittlement (HE) susceptibility of such wires is also lower, thereby enlarging the life in service of these components. In this paper an innovative design of the drawing die is proposed using two consecutive angles (i.e., varying die angle) for reducing the residual stress-strain state in the cold drawn wires and, consequently, for improving the resistance to HE of prestressing steel wires.

Abstract: The effect of interlamellar spacing on monotonic behavior of C70 pearlitic steel was investigated. Tensile tests under X-ray diffraction coupled with self-consistent model have been used to identify the role of interlamellar spacing on the ferrite plasticity parameters and residual stresses. It has been established that yielding of pearlite is controlled by ferrite critical shear stresses ( τc 0α) which is higher for the smaller interlamellar spacing. Moreover, the residual stress level in ferrite is higher for the largest interlamellar spacing under the same imposed total strain. Lattice strains, measured by synchrotron X-ray diffraction, show an elastic and plastic anisotropy of ferrite crystallites and high stresses in cementite which confirm the self-consistent model calculation. Keywords: Pearlitic steel, X-ray diffraction, Synchrotron radiation, Self-consistent model, Critical shear stress, Lattice strains.

Abstract: The effect of austenitizing temperatures and isothermal transformation temperatures on microstructure size and mechanical properties of 70 steel was studied. The experimental results show that the grain size increases with the increasing of austenitizing temperature. And the tensile strength increased with isothermal temperature decreasing. The grain size has a great influence on tensile strength. The strength increase of the samples with fine grain is greater than the samples with coarse grain. With the decreasing of isothermal temperature, the pearlite colony size and interlamellar spacing decreases and the reduction of area of the specimens increase.