Cold-drawn Pearlitic Steel Wires Research Articles

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.

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.

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.

On the cleavage stress promoting crack path deflection and anisotropic fracture in cold drawn pearlitic steel

Crack path deflection is a phenomenon appearing in cold-drawn pearlitic steel wires as a consequence of the pearlite microstructure orientation induced by the manufacturing procedure, the deflection angle being approximately 90º, thereby representing a crack propagation step (fracture wall), a signal of splitting, delamination or debonding in the form of axial cracking (or micro-cracking) by means of a microscopic fracture mode in the form of enlarged and oriented cleavage in the direction of the wire axis (cold drawing direction). The described phenomenon is a signal of anisotropic fracture behaviour (strength anisotropy) associated with mixed-mode propagation. This paper demonstrates that, in addition to the oriented microstructure of the cold drawn pearlitic steels (at the two microstructural levels of pearlite colonies and lamellae), a sufficient level of stress triaxiality (constraint) is required, as in the case of cracked specimens in which a cleavage stress appears as a consequence of the singular stress distribution in the close vicinity of the crack tip (crack tip stress-strain field).

Micro-axial cracking in unnotched, cold-drawn pearlitic steel wire: Mechanism and beneficial effect on the resistance to hydrogen embrittlement

Effects of cold drawing ratio (CDR) on the microstructure, tensile properties, H absorption and hydrogen embrittlement (HE) of pearlitic steel wire were investigated by means of thermal desorption analysis, slow strain rate tensile testing, fractography and silver decoration. The ultimate tensile strength (UTS) and diffusible H content of unnotched tensile specimens were raised with increasing CDR due to the reduction of interlamellar spacing and the increase in dislocation density. Nevertheless, the resistance to HE was improved as the CDR became above 30% due to micro-axial cracking. Elongations of H-uncharged and charged specimens decreased until the CDR of 30%, and then were maintained despite of a continuous rise of UTS with increasing CDR further. This is because micro-axial cracking occurred in the specimens with CDRs above 30% so that tensile fracture was retarded. As the CDR was over ∼30%, a fracture mode changed from brittle fracture featured by tearing topography surface and cleavage to ductile-like fracture characterized by many dimples and micro-axial cracks. Micro-axial cracking occurred as follows: Some micro-cracks preexisted inside well-aligned pearlite colonies of specimens with CDRs above 30%. While an unnotched, H-uncharged specimen was strained, micro-cracks additionally formed to be coalesced. The merged cracks traversed the pearlite colonies to be propagated into neighboring misaligned colonies and grew along the direction of cold drawing and tensile deformation, resulting in micro-axial cracking. In H-charged specimens, H atoms near micro-cracks clustered into micro-cracks so that micro-axial cracking was accelerated and the regions near micro-cracks underwent ductile fracture, leaving many dimples.

Strain localization and delamination mechanism of cold-drawn pearlitic steel wires during torsion

Pearlitic steel wires are cold-drawn in order to attain high strength from the alignment of the pearlite colonies along the wire axis, as well as achieve a considerable reduction in the thickness of the ferrite lamellae. However, this high level of stress, in addition to surface defects and residual stresses, drastically decreases the strain ductility in tension and often in torsion. A significant limitation in torsion is the nucleation and growth of delamination cracks which propagate along the wire. Although this fracture phenomenon has long been studied, its origin and the underlying mechanisms remain debatable. This paper presents new microstructure investigations of drawn wires during torsion. The stages of initiation and propagation are defined towards a chronology of the development phases of delamination cracks based on the study of the microstructure of cold-drawn pearlitic steel wires before and after torsion. The curling of the grains leads to the creation of long grooves on the surface of the wire. These grooves increase stress concentration during twisting, thus localizing the formation of shear bands. Deformation and strain rate are so high in these bands that nanograins (10–30 nm) are formed. The delamination then appears to be mainly due to the localization of the single-shear deformation along the wire axis with mainly intergranular crack propagation.

Fracture behaviour of high-strength cold-drawn pearlitic steel wires: The role of non-metallic inclusions

This paper analyses the role of non-metallic inclusions in the fracture behaviour of high-strength cold-drawn pearlitic steel wires. To this end, a metallographic and scanning electron microscope (SEM) analysis was performed of the microstructural defects in pearlitic steels and their evolution with the manufacturing process by cold drawing, analysing the consequences of such defects on the isotropic/anisotropic fracture behaviour of the different steels. Results show the very relevant role of non-metallic inclusions in the fracture behaviour of high-strength cold-drawn pearlitic steel wires.

Mechanical Properties and Texture Evolution of High-Carbon Steel Wires during Wire Drawing: Strand Manufacturing

In this paper, the evolution of texture in the ferrite phase and mechanical behavior of cold-drawn pearlitic steel wires produced for strand manufacturing at Trefisoud company was investigated. Wire drawing induces the development of dislocation density, reduction of interlamellar spacing and the refinement of grains size which leads to a strong hardening of the wires. That explains the increase of the tensile strength from 1242 MPa to 2618 MPa with higher deformation. Also, the cementite lamellae are rotated toward the drawing axis and the thickness of lamellae further decreases when strain level increases, this phenomenon leads to a somewhat fibrous structure. The quantitative analysis obtained by EBSD data shows the development of a strong (<110> // ND) texture of the ferrite phase leading to a structural transformation from isotropic to anisotropic.

Strain-Induced Dissolution of Cementite in Cold-Drawn Pearlitic Steel Wires

Strain-induced dissolution of cementite is one of the most important microstructural changes undergone by a pearlitic steel wire during cold drawing, and hence must be adequately taken into account in the microstructure–property relationship. Despite extensive studies of cementite dissolution, the kinetics of dissolution is still lacking. The traditional electrolytic phase extraction technique appears well suited to quantifying the residual cementite in drawn pearlite. This work also shows how this basic technique can shed new light on the mechanism of dissolution.

Microstructure–Property Relationship in Cold-Drawn Pearlitic Steel Wires

The difficulty in predicting flow stress of a cold-drawn pearlitic steel wire arises from the complex microstructural transformations induced by cold drawing. For assessing properly the different contributions to strengthening, four quantities must first be expressed as a function of strain $$ \varepsilon $$: (i) residual volume fraction of cementite; (ii) interlamellar spacing $$ \lambda $$, taking initial orientation of cementite lamellae into account; (iii) carbon concentration in ferrite deduced from strain-induced carbon partitioning between ferrite and cementite; and (iv) density of dislocations. Combination of these four expressions shows that cementite is able to significantly deviate from stoichiometry before dissolving, and that dislocations alone in ferrite are not able to control the decomposition of cementite unless $$ \varepsilon $$ reaches 4, implying involvement of solid solution. At $$ \varepsilon > 1.5 $$, when all lamellae are parallel to the wire axis and Voigt model can be applied, it is found that strain hardening is negligible, ferrite hardening by carbon in solid solution is canceled out by cementite softening and flow stress is better described by the Orowan mechanism ($$ 1/\lambda $$ dependence) than by the Hall–Petch law ($$ 1/\sqrt \lambda $$ dependence).

The role of local plasticity in the redistribution of stress fields caused by in-service fatigue overloads

The aim of this paper is to analyze the effect of diverse cyclic loading conditions on the residual stress field in cold-drawn pearlitic steel wires. To this end, on one hand, a numerical simulation by the finite element method of the manufacturing process (cold drawing) of a prestressing steel wire was carried out for revealing the residual stress state induced by the manufacture technique. On the other hand, a numerical simulation was performed of the in-service fatigue loading applied to a cold drawn wire (including the manufacturing-induced residual stress-strain state). According to the obtained results, the plastic strain generated during fatigue loading causes a reduction of the initial residual stress at the surface and a redistribution of the residual stress field.

Unconventional pearlitic pseudocolonies affecting macro-, micro- and nano-structural integrity of cold-drawn pearlitic steel wires: Resembling van Gogh, Bernini, Mantegna and Picasso

Prestressing steel wires are manufactured by cold drawing during which a preferential orientation is achieved in the matter of pearlitic colonies and lamellae. In addition to this general trend, special (unconventional) pearlitic pseudocolonies evolve during the heavy-drawing manufacture process affecting the posterior macro-, micro- and nano-structural integrity of the material. This paper discusses the important role of such a special microstructural unit (the pearlitic pseudocolony) in the fracture process in air (inert) environment in the presence of crack-like defects, as well as in the case of environmentally assisted cracking (stress corrosion cracking by localized anodic dissolution) or hydrogen embrittlement. Results clearly demonstrate the key role of pearlitic pseudocolonies in promoting crack deflection (and thus mixed-mode propagation) after a global mode I cracking, especially in the case of fracture in air and stress corrosion cracking.

Exploring high strength metallic materials: a lesson from pearlitic steel wire

In human history, the development of stronger materials through the ages is reflected with names of eras illustrating our progress. Besides phase transformations, plastic deformation is one of the major methods to produce products with reliable and predictable mechanical properties such as strength. Pearlitic steel wire, the strongest mass-produced steel, shows an excellent combination of formability and strength. The present overview summarizes the investigation of cold-drawn pearlitic steel wires over the last 150 years, covering the pearlite phase transformation, chemical composition design for wires with high strength, microstructure evolution during wire drawing, strengthening mechanisms and structure-strength relationships. By focusing on the structure, challenges and future strategy are outlined to further improve the strength and performance of pearlitic steel wire, where these routes may also applicable to other metals.

Ratchetting in Cold-Drawn Pearlitic Steel Wires

The microscopic mechanisms that accommodate uniaxial ratchetting in cold-drawn pearlitic steel wires were explored. A two-stage evolution of ratchetting strain as a function of cycle numbers was observed. The initial sudden increase of plastic strain leads to a rapid decomposition of cementite, followed by a constant ratchetting strain rate with critical role of decomposed carbon atoms played in blocking dislocation motion. The dislocation configuration transforms from low-density lines and tangles to high-density cells and sub-grains with increasing strain. A possible mechanism of cementite decomposition is discussed in terms of carbon-dislocation interactions and an unfavorable cementite surface-to-volume ratio.

Effect of Microstructure and Microtexture on the Mechanical Properties of Small-Strain Cold-Drawn Pearlite Steel Wires

The effect of microstructure and microtexture on the mechanical properties of small-strain (e < 0.8) cold-drawn pearlitic steel wires was investigated by scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction. A quantitative statistical analysis of the measured parameters of interlamellar spacing indicated a slight decrease during the testing and a relatively high deviation from the calculated values. Calculations on the dislocation density increased from approximately $$ 4.25\; \times \; 10^{14} \;{\text{m}}^{ - 2} $$ at e = 0 to approximately $$ 4.33 \times 10^{15} \;{\text{m}}^{ - 2} $$ and then to $$ 5.81 \times 10^{15} \;{\text{m}}^{ - 2} $$ with increasing cold-drawing strain. As calculated using the misorientation angle across the dislocation boundaries and the dislocation boundary area per unit volume, the dislocation density generally increased consistently. Under these conditions, a microstructure tends to form through the deflection of pearlitic colonies, consequently affecting the crack propagation path and improving the yield and tensile strengths.

Correlation between Microstructural Evolution and Mechanical Properties of 2000 MPa Cold-Drawn Pearlitic Steel Wires during Galvanizing Simulated Annealing

In the present experiment, hot-dip galvanizing simulated annealing of 2000 MPa cold-drawn pearlitic steel wires was carried out at 450 °C. The effects of microstructural evolution on the mechanical properties of the as-prepared wires were analyzed through scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile test, torsion test, and Vickers hardness test. In addition, the relationship between torsion laps and microstructural evolution of cold-drawn pearlitic steel wires was investigated in detail. It was found that the torsional performance of the wires deteriorated after annealing at 450 °C for 2–5 min, and the corresponding microstructural evolution was accompanied by the partial degradation of lamellar pearlites due to the diffusion and dislocation pinning of dissolved carbon atoms in ferrites, and it is not feasible to achieve the matching of strength and torsion laps by prolonging the holding time. The deterioration in torsional performance can be attributed to the microstructural difference between the surface and the center of the annealed wires. When the proportion of non-lamellar structure between the surface and the center in each specimen exceeded 8%, the microhardness difference was found to be greater than 40 HV and the torsion lap was less than 3 circles.

Effect of Low Temperature Annealing on Microstructure and Mechanical Properties of Ultra-Heavy Cold-DrawnPearlitic Steel Wires

Effect of Low Temperature Annealing on Microstructure and Mechanical Properties of Ultra-Heavy Cold-DrawnPearlitic Steel Wires

Cold-Drawn Pearlitic Steels as Hierarchically Structured Materials: An Approach to Johann Sebastian Bach

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.