Pearlitic Steel Wires Research Articles

Molecular Dynamics Analysis of Hydrogen Diffusion Behavior in Alpha-Fe Bi-Crystal Under Bending Deformation

The hydrogen embrittlement (HE) phenomenon occurring in drawn pearlitic steel wires sometimes results in dangerous delayed fracture and has been an important issue for a long time. HE is very sensitive to the amount of plastic deformation applied in the drawing process. Hydrogen (H) atom diffusion is affected by ambient thermal and mechanical conditions such as stress, pressure, and temperature. In addition, the influence of stress gradient (SG) on atomic diffusion is supposed to be crucial but is still unclear. Metallic materials undergoing plastic deformation naturally have SG, such as residual stresses, especially in inhomogeneous regions (e.g., surface or grain boundary). In this study, we performed molecular dynamics (MD) simulation using EAM potentials for Fe and H atoms and investigated the behavior of H atoms diffusing in pure iron (α-Fe) with the SG condition. Two types of SG conditions were investigated: an overall gradient established by a bending deformation of the specimen and an atomic-scale local gradient caused by the grain boundary (GB) structure. A bi-crystal model with H atoms and a GB structure was subjected to bending deformation. For a moderate flexure, bending stress is distributed linearly along the thickness of the specimen. The diffusion coefficient of H atoms in the bulk region increased with an increase in the SG value. In addition, it was clearly observed that the direction of diffusion was affected by the existence of the SG. It was found that diffusivity of the H atom is promoted by the reduction in its cohesive energy. From these MD results, we recognize an exponential relationship between the amount of H atom diffusion and the intensity of the SG in nano-sized bending deformation.

Effect of annealing on microstructure and mechanical properties of cold-drawn pearlitic steel wires

Effect of annealing on microstructure and mechanical properties of cold-drawn pearlitic steel wires

Unveiling the mechanisms behind texture formation and its impact on the torsional performance of cold-drawn pearlitic steel wires

High carbon pearlitic steel wires are widely used in the industry, such as for producing tyre cords and steel cables due to its excellent mechanical properties. Cold drawing is a crucial step in steel wire production. Due to the loading state during the cold drawing process, pearlitic wires tend to exhibit a <110> fiber texture. The non-uniform texture distribution on the cross-section of steel wires has been observed experimentally. The mechanisms yielding this non-uniformly distributed texture are carefully investigated in this study using a multi-scale computational approach. Firstly, a macroscale finite element model is established to simulate the deformation behaviour of pearlitic steel wires during cold drawing, with the aim of thoroughly investigating the inhomogeneous elastic-plastic deformation behaviours. Secondly, the macro mechanical responses are incorporated into the mesoscale representative volume element model as boundary conditions to comprehensively study the effect of inhomogeneous deformation characteristics on texture formation. The results present a significant advancement by revealing that the non-uniform texture distribution in a steel wire can primarily be attributed to the multiaxial stress state on the cross-section. Notably, at the center of the steel wire, the maximum principal stress aligns with the drawing axis, resulting in a dominant <110> fiber texture. Conversely, at the subsurface, the maximum principal stress progressively shifts towards the circumferential direction, yielding an evolving texture characterized by a {110}<110> circumferential texture. Furthermore, the research uncovers a crucial finding that it is the {110}<110> circumferential texture that significantly weakens the torsion ability of the wires. This is due to the limited activation of slip systems, marking a key advancement in understanding the mechanical properties of steel wires.

Instability of Spring Constant in Pearlitic Steel Wire Tensile Coil Springs Heat-Treated around the A&lt;sub&gt;0&lt;/sub&gt; Transformation Point

Instability of Spring Constant in Pearlitic Steel Wire Tensile Coil Springs Heat-Treated around the A&lt;sub&gt;0&lt;/sub&gt; Transformation Point

Evolution of Microstructure and Fe/Fe3C Interface Structure in Cold‐Drawn Pearlitic Steel Wires

The microstructure, texture, and dislocation configuration of cold‐drawn pearlitic steel wires were investigated by scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), and transmission electron microscopy (TEM). In addition, Fe/Fe3C interface structure at the atomic level was clearly observed and analyzed by high‐resolution TEM (HRTEM), and the microscopic deformation mechanism of cementite lamellae at different drawing strains is revealed. The results show that pearlite lamellae turn to the drawing direction to form ferrite &lt;110&gt; fiber texture, and the cementite and ferrite lamellae are simultaneously thinned with the increase of drawing strain. During the cold drawing process, shear‐bands(S‐bands) are formed in the cementite lamellae; the dislocation of ferrite transits from single slip to multi‐slip stage, and the dislocation density increases. After drawing, the lattice structures of cementite and ferrite phases show the evolution from single‐crystal to polycrystal, and the cementite lamellae are divided into a multilayer structure: central relative large‐size cementite crystal and outside relative small‐size cementite crystal layer; the dissolution of cementite lamellae in some regions results in the lattice expansion of ferrite phase and the occurrence of neck‐down regions in the cementite lamellae.

High deformation and delamination mechanisms explained through mesoscale and nanoscale phenomena in pearlitic steel wires

Pearlitic steel wires subjected to severe cold drawing deformation exhibit a unique combination of high strength and excellent ductility, making them suitable for critical applications such as hanging bridge cables, crane cables and tire cord. Torsion tests up to rupture are commonly used in the industry for quality control purposes. A flat fracture surface is indicative of wire aptitude, while a delaminated surface suggests degradation of mechanical properties. This paper aims to expand the understanding of the structural evolution and deformation mechanisms that occur during wire drawing, as well as the origin of delamination problems. Different deformation and strengthening mechanisms are identified and discussed, applying different microscopy techniques (optical microscopy, scanning electron microscopy, electron backscatter diffraction), synchrotron diffraction and atom probe tomography. The information is correlated with the cementite stability on the structure studied at meso, nano, and atomic scale, reaching an understanding of the compositional evolution of cementite and ferrite even at the very lowest level. All the obtained information, including thermal analysis and thermodynamic simulation results, allow to identify the deformation mechanisms present during cold drawing and at the delamination process. In addition, the compositional evolution of cementite and ferrite is also clarified by atom probe tomography.

Effects of Hot Deformation on the Evolution of Microstructure in Pearlitic Steel Wire Rod

Effects of Hot Deformation on the Evolution of Microstructure in Pearlitic Steel Wire Rod

Effects of Rare Earth on the Microstructure and Mechanical Properties of a Pearlitic Steel Wire Rod

The effects of rare earth (RE) on the microstructure and mechanical properties of a pearlitic steel wire rod are investigated under the dual‐low‐oxygen condition. The results show that the wire rods with different RE contents all have pearlite microstructure. As RE content increases from 0 to 310 ppm, the pearlite substructures such as interlamellar spacing, pearlite colony size, and ferrite grain size decrease remarkably, indicating that the nucleation and growth behavior of pearlite change. This is attributed to the combined effects of stimulating nucleation by a large number of micrometer‐scale RE‐containing inclusions and decreased carbon diffusion due to RE in solution. As a result, the changes in microstructure lead to simultaneous enhancement of strength, plasticity, impact toughness, and microhardness of pearlite wire rod, demonstrating that adding appropriate content of RE under the dual‐low‐oxygen condition is an effective alloying method to optimize the microstructure and mechanical properties of pearlitic steel wire rod.

Pearlite Interlamellar Spacing and Vickers Micro-Hardness in the Necking Region of Cold-Drawn Pearlitic Steel Wires

The final aim of this paper is to study the microstructural changes in the necking region of progressively cold-drawn pearlitic steel wires by means of a thorough and detailed analysis of pearlite interlamellar spacing and Vickers micro-hardness in this special region. To this end, a set of progressively cold-drawn pearlitic steel wires belonging to a real manufacturing chain were subjected to standard tension tests, in such a manner that the tests were interrupted before the final fracture, i.e., the test development was aborted just at the necking instant. The microstructural changes during necking were evaluated by measuring the pearlite interlamellar spacing in the necking region, as well as the Vickers micro-hardness in the different points of it. The study of the afore-said microstructural changes preceding the final fracture was the final aim of the research, intending to determine the local areas in the necking region of the specimens in which microstructural changes are most evident, thereby affecting the local mechanical response of a specific cold-drawn steel at the moment of instability under load control during the standard tension test.

Hydrogen resistance and trapping behaviour of a cold-drawn ferritic–pearlitic steel wire

Abstract The present work investigates the resistance of a progressively cold-drawn carbon steel wire against hydrogen embrittlement. In this study, analytical and numerical methods are used to determine the critical hydrogen content, the critical hydrogen ratio and the embrittlement indices of the different material conditions. The wire with the highest degree of cold deformation shows the highest critical hydrogen content and improved resistance against hydrogen embrittlement. At higher degrees of deformation, the material shows stronger hydrogen trapping, which improves in combination with a change in the lamellar spacing and orientation of the pearlite the resistance to hydrogen embrittlement.

Intercolonial Microdamage and Cracking Micromechanisms during Wire Drawing of Pearlitic Steel

This paper studies the drawing-induced intercolonial microdamage (ICMD) in pearlitic microstructures. The analysis was performed from the direct observation of the microstructure of the progressively cold-drawn pearlitic steel wires associated with the distinct steps (cold-drawing passes) of a real cold-drawing manufacturing scheme, constituted by seven cold-drawing passes. Three types of ICMD were found in the pearlitic steel microstructures, all affecting two or more pearlite colonies, namely: (i) intercolonial tearing; (ii) multi-colonial tearing; and (iii) micro-decolonization. The ICMD evolution is quite relevant to the subsequent fracture process of cold-drawn pearlitic steel wires, since the drawing-induced intercolonial micro-defects act as weakest links or fracture promoters/initiators, thereby affecting the microstructural integrity of the wires.

Reduction of Residual Stresses in Cold Drawn Pearlitic Steel by a Soft Secondary Wire Diameter Reduction

In this paper, the effects of the skin pass technique on the residual stress and plastic strain fields generated in cold drawn pearlitic steel wires are analyzed. The aim is to find out the optimal conditions to be used in the design of a manufacturing process for obtaining more reliable structural components in terms of the main cause of failure: the hydrogen embrittlement (HE). To achieve this goal, diverse numerical simulations were performed by using finite elements (FE) and considering, on one hand, the first step of a real cold drawing chain, using (i) a conventional drawing die and (ii) modified drawing dies with different soft diameter reductions, and, on the other hand, numerical simulations by FE of the hydrogen diffusion assisted by stress and strain states to estimate the hydrogen distributions. Obtained results revealed the secondary reduction degree as a key parameter in the die design for reducing the drawing-induced residual stress. According to the results, low values of the reduction ratio cause radial distributions of residual stress with significant reductions at both the wire core and at the wire surface. In addition, the hydrogen accumulation at the prospective damage zone (near the wire surface) given by FE simulations is lower in the wires drawn with modified drawing dies including a skin pass zone.

Reverse aging of pearlitic carbon steel wire rod

ABSTRACT High carbon steels are employed for the production of critical components, such as ropes, cables and springs. After hot rolling, their microstructure is controlled by Stelmor cooling, since they are often subjected to strong drawing operations. The as-rolled deformability is a basic property to prevent damages in the following plastic deformation. In the industrial world, it is known that their deformability improves significantly after a storage of a certain time, ranging from some days up to 15–20 days. In this experimental work, the deformability of a high carbon steel was investigated after different storage times varying the wire rod diameter. The percentage reduction of area (ROA) increased after some days until a stable value was reached after about 7–15 days depending on the considered diameter. The fracture surfaces of the aged specimens were analysed by SEM.

An Effective Formability Model of Pearlitic Steel Wires in Multi-stage Drawing Process Based on the Stress-Based Forming Limit Criterion

An Effective Formability Model of Pearlitic Steel Wires in Multi-stage Drawing Process Based on the Stress-Based Forming Limit Criterion

Characteristic of Near-surface Microstructure and Its Effects on the Torsion Performance of Cold Drawn Pearlitic Steel Wires for Bridge Cables

Characteristic of Near-surface Microstructure and Its Effects on the Torsion Performance of Cold Drawn Pearlitic Steel Wires for Bridge Cables

Effect of drawing strain rate on microstructure and mechanical properties of cold-drawn pearlitic steel wires

Effect of drawing strain rate on microstructure and mechanical properties of cold-drawn pearlitic steel wires

Structure evolution of the Fe3C/Fe interface mediated by cementite decomposition in cold-deformed pearlitic steel wires

Cold-drawn pearlitic steel wire is irreplaceably used in industry owing to its outstanding mechanical property which is dominated by the cementite/ferrite (Fe3C/Fe) interfaces in the material. However, the fine structures of the Fe3C/Fe interfaces in the deformed wires are less known to date. In this work, transmission electron microscopic investigation was performed on the atomic structures of the interfaces with the Isaichev orientation relationship (OR) in the wires with progressive deformation strains. In addition to the effect of the dislocation/interface interactions, this work revealed that the deformation-induced partial decomposition of cementite plays an important role in the interface reconstruction during deformation. The interfacial carbon vacancies generated by cementite decomposition and particularly, the amorphization of cementite layers in the sample with ε > 1 could effectively annihilated the interfacial dislocations and consequently relaxed the interfacial stress. The correlations between the interface structure changes and the mechanical properties of the wires were discussed.

Microstructure Evolution and Its Effects on the Mechanical Behavior of Cold Drawn Pearlite Steel Wires for Bridge Cables

Microstructure Evolution and Its Effects on the Mechanical Behavior of Cold Drawn Pearlite Steel Wires for Bridge Cables

Micro- and nano-structural integrity of cold drawn pearlitic steels: drawing-induced evolution of intracolonial micro-defects

This article deals with the analysis of the evolution of intracolonial micro-defects produced in pearlitic steel wires as a direct result of the cold drawing process. The study was carried out from the observation of the microstructure of wires belonging to the different steps of a real cold drawing chain, formed by seven stages of cold drawing. The evolution of intracolonial micro-defects can be key in the subsequent fracture process of the cold drawn pearlitic steel. The analysis of these micro-defects has been carried out after the observation of micrographs obtained by scanning electron microscopy (SEM).

Environmentally-assisted microstructural integrity of commercial cold drawn pearlitic steel wires

This paper deals with environmentally-assisted microstructural integrity of commercial cold drawn pearlitic steel wires to be used as prestressing steel wires for prestressed concrete in civil engineering structures. The article contains a fractographic analysis of the fracture surfaces of initially-smooth samples of commercial prestressing steel wires subjected to tensile tests in aggressive environment promoted by a corrosion cell consisting of the metallic sample and a three-electrode assembly. Two testing rates were used: one moderately fast (0,1 mm/min) and another moderately slow (0,01 mm/min). The electro-chemical potential used covers a wide range (from –400 to –1400 mV SCE), thus including from anodic to cathodic conditions. The main objective is focused on the study of the fracture surface for those specimens that failed due to the aggressive environment (inside corrosion cell). The analysis of the fracture surface is made by considering the different domains of the micro-fracture map (MFM).