Pearlitic Steel Wires Research Articles

Effects of Process Parameters on the Shape Changes of a Micro Cementite Band during Macro Drawing of a Pearlitic Steel Wire

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.

Cold drawn pearlitic steel wires for wind turbines structures: In the wake of Miguel de Cervantes and Johann Sebastian Bach

Wind turbines are key elements in the field of renewable energies. They can be considered as engineering evolutions of old-fashion windmills appearing in the master work by Miguel de Cervantes: Don Quijote de la Mancha. The main subject of this paper is related to fracture behaviour and structural integrity of cold drawn pearlitic steel wires for wind turbine structures and foundations. At the microscopic level, cold drawing generates progressive slenderizing and orientation of the pearlitic colonies (first microstructural level) and increasing orientation and densification of the ferrite/cementite lamellae (second microstructural level), thereby inducing anisotropic fracture behaviour and crack path deflection. In addition, the hierarchical structure of cold drawn pearlitic steel wires in two microstructural levels (colonies and lamellae) allows 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.

Torsion performance of pearlitic steel wires: Effects of morphology and crystallinity of cementite

The torsion behavior of pearlitic steel wires is investigated and the conditions responsible for torsion delamination are determined. Experimental results reveal that the morphology and crystallinity of cementite regulate the torsion response of pearlitic steel wires. Specifically, both the torsion strength and torsion fracture strain of the wires increase with cold drawing strain up to ε < 0.68. After annealing treatment at 250 °C, the torsion strength increases at the expense of torsion fracture strain irrespective of drawing strains. Moreover, the torsion delamination occurs in the wires prepared at ε > 1.76 and also subjected to annealing treatment between 150 °C and 350 °C. It was found that annealing treatment turns the amorphous cementite to nanocrystalline state, which prevents dislocations from bowing out. Consequently, localized and severe plastic deformation takes place, resulting in the torsion delamination. By contrast, the cementite with a mix of amorphous and nanocrystalline phases is capable of withstanding plastic deformation during torsion tests. Moreover, annealing-induced spheroidization of cementite is effective in preventing the pearlitic steel wires from torsion delamination.

Microstructure and Mechanical Properties of Ultra-High Strength Pearlitic Wire in Single-pass Cold Drawing

The effect of compression ratio on the microstructure and mechanical properties of ultra-high strength pearlitic wire in single-pass cold drawing has been studied. The ultra-high tensile strength cord steel with a carbon content of 1.02 wt% were pulled through a single-pass drawing to different compression ratios (0-30%). With the increase of the single-pass compression ratio, the tensile strength, microhardness and torsional properties of the steel wire increased gradually. When the compression rate increased from 0 to 30%, the tensile strength of the steel wire increased from 1263.4 MPa to 1553.7 MPa, the torsional strength of steel wire increased from 1126.83 MPa to 1279.66 MPa. In the single-pass drawing process, the strengthening mechanism of the pearlitic steel wire are mainly the work hardening caused by the dislocation slip in the ferrite, and the fine grain strengthening caused by the decrease of the pearlite sheet spacing.

Microstructural Development and Mechanical Properties of Multi-pass Cold Drawn Hypereutectoid

In the present work, processes of multi-pass cold drawn were conducted on hypereutectoid pearlite steel wires with carbon content of 1.02 w.t.%. Relationship between microstructural development and mechanical properties of hypereutectoid steel wires after drawing was investigated. It was found that when the strain was relatively small, lamellar morphology of the pearlite in the steel wire after cold drawn remained, and the spacing of lamella was refined. With the increase of the compression ratio, coordinated deformation of ferrite and cementite occurred and pearlite lamella were bended and folded. As the strain increased, fibrous morphology of pearlite lamella was observed in longitudinal section of the wire. High magnification TEM observation revealed the fragmentation of cementite and a large number of nano-crystalline. Tensile strength, microhardness and torsion strength of the steel wires after multi-pass drawn process increased significantly with the increase of accumulated strain. The results of XRD analysis show that the <110> peak of the ferrite shifted to the left and widened following the multi-pass cold drawn deformation, indicating that the lattice constant of ferrite was increased. The increase of lattice constant of ferrite was the result of the distortion of ferrite lattice due to the dissolution of carbon atoms.

Interactions of stress corrosion cracks in cold drawn pearlitic steel wires: An X-ray micro-computed tomography study

X-ray micro-computed tomography (micro-CT) was used for analysis of stress corrosion cracking (SCC) of cold drawn pearlitic steel wires from a cable bolt from an underground coal mine. The results were compared to those obtained from magnetic particle inspection (MPI) of the wire surface and optical microscopy (OM) and scanning electron microscopy (SEM) examination of sections through the wires. The high-resolution two-dimensional (2D) OM and SEM images were registered into the micro-CT image to allow direct comparison with the corresponding slice from the three-dimensional (3D) micro-CT image. Subsequently, the micro-CT image was processed to segment the cracks in the steel body and the attributes of each crack, i.e. the surface area, surface exposure, and maximum radial and longitudinal penetration depths, were calculated and plotted to determine their intercorrelation. It was found that MPI and micro-CT had a similar ability in revealing surface cracks. The 2D techniques provided high-resolution information but unlike micro-CT they were unable to map the complex 3D structures of the cracks and their interactions.

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.

Chloride-induced corrosion behavior of cold-drawn pearlitic steel wires

The chloride induced corrosion behavior of cold drawn pearlitic steel wires was systematically investigated using electrochemical measurements, namely, electrochemical impedance spectroscopy, and local electrochemical impedance spectroscopy for micro-areas. A 0.05 mol/L NaCl solution mixed with borate buffer solution (pH = 8.45) was used. The results suggest that the corrosion resistance of cold-drawn pearlitic steel decreases with increasing strain to 0.8, but increases with strain up to a value of 1.6. Microstructure evolution was characterized by electron back scatter diffraction in combination with scanning electron microscopy and transmission electron microscopy. Atom probe tomography was used to quantify the cementite decomposition. The quantitation of microstructural parameters with strain suggests that the evolution of defect structure markedly increases the corrosion susceptibility of pearlite for strain up to 0.8. In the case of strain 1.6, refinement of the lamellar structure and cementite decomposition can reduce the volume fraction of cementite that acts as the cathode per corrosion unit (a pearlite/cementite “cell”), giving rise to an increase in the corrosion resistance.

Macro- and Micromechanics of Pearlitic-Steel Deformation in Multistage Wire Production

Ninefold drawing of pearlitic steel wire is investigated. On the basis of multiscale computer models, the behavior of pearlite colonies at the surface of the wire and in its central layer is analyzed. The key factors are the orientation of the cementite lamellae relative to the drawing axis, the interlamellae distance, and the shape of the cementite inclusions. On the basis of finite-element models, the laws governing the reorientation of the pearlite colonies, change in shape and size of the cementite lamellae, and localization of the deformation in the ferrite are determined. The model results are verified by means of metallographic results and industrial experiments.

Effects of Chromium Additions upon Microstructure and Mechanical Properties of Cold Drawn Pearlitic Steel Wires

Cr-containing pearlitic steel wires were prepared through cold drawing and simulated galvanization process. Effect of chromium microalloying on microstructural and mechanical properties of the steel wires was investigated. Experimental results show that size of pearlitic colonies of the steel rods decreased as Cr content increased from 0.2 to 0.6 wt.%; meanwhile, interlamellar spacing was little affected because of isothermal phase transition in salt bath. The tensile strength of the pearlitic steel rods was increased from 1480 to 1550 MPa. The tensile strength of the Cr-containing cold drawn wires (e = 1.58) was increased about 33%, and the torsion circle of the wires were about 15 with cleavage fracture. After annealing at 450 °C for 2 min, tensile strength of the wires increased, but torsion circle was decreased to less than 5. As the annealing time increased, the torsion circle of the steel wires with 0.2 wt.% Cr was improved to about 10 with cleavage fracture, while the torsion performance of the wires having high Cr contents remained low because of delamination fracture. The cementite platelets in Cr-containing wires turned into cementite crystal particles during cold drawing. Microstructure observation and thermal analysis have confirmed that thermal stability of cementite was enhanced with the increase of Cr content.

Structure and strength of sub-100 nm lamellar structures in cold-drawn pearlitic steel wire

ABSTRACTPearlitic steel wire, with a representative sub-100 nm lamellar structure, is the strongest mass-produced steel with an excellent combination of formability and strength. This overview summarises investigations of cold-drawn pearlitic steel wire in the last decades, covering the microstructural evolution and strengthening mechanisms. Based on quantitative structural parameters, this overview covers a quantitative and extensive analysis of structure–strength relationships. By focusing on the structure, challenges and future strategy are outlined to further improve the mechanical behaviour and performance of pearlitic steel wire to widen its use in society.This is part of a thematic issue on Pearlitic Steel Wires.

Application of texture inheritance on manufacturing ultra-high strength pearlitic steel wire

ABSTRACTTo obtain both ultra-high strength and good ductility in pearlitic steel wires, a new processing technique was proposed following the principle of inherited texture. Microstructure evolution of pearlitic wires was investigated by FE-SEM, EBSD and TEM, and while mechanical properties were determined by tensile and torsional tests. Two types of wires with different ferrite <110> texture intensity were obtained by varying pre-drawing strain. The orientation between ferrite <110> and drawing direction exhibited a great effect on the deformation behaviour of pearlite. For the ferrite <110> parallel to drawing direction, cementite lamellae were straightened and dislocations within ferrite were evenly distributed. However, for the ferrite <110> at an angle to drawing direction, the cementite was bent and the distribution of dislocations within ferrite was uneven. Consequently, pearlitic wires with a higher texture level exhibited an extremely high tensile strength, coupled with a remarkable torsion tolerance.This is part of a thematic issue on Pearlitic Steel Wires.

Effect of Si on the partitioning of Mn between cementite and ferrite

ABSTRACTThe interlamellar spacings of pearlitic steels gradually increase as the isothermal transformation temperatures, correspondingly, the tensile strengths decrease, satisfying the Hall–Petch relationship. Si virtually completes its partitioning process during the eutectoid transformation. A depletion of Mn and an accumulation of Si are found in the concentration profiles of 0.95%-Si steel transformed at 793 K in the ferrite, but not in 0.22%-Si steel. It may attribute them to the Si–Mn diffusional flux couplings, which due to the strong interaction between Si and Mn atoms in the α-Fe. Transformation temperature increases to 873 K, a large amount of Mn atoms coming from ferrite cannot timely diffusion to cementite lamella core, forming a localised retention of Mn in the cementite phase side nearby the interface.This is part of a thematic issue on Pearlitic Steel Wires.

Strain-hardening characteristics of ferrite layers in pearlite microstructure

ABSTRACTStrain hardening of ferrite layers in pearlite microstructures plays a crucial role in the stability of elasto-plastic deformation of pearlite. The effects of layer thickness, crystal orientation relationship and loading direction on the strain-hardening characteristics of the ferrite layers were studied by crystal plasticity analysis. The results show that the strain-hardening rate increases in the ferrite layers with small thickness, whereas at the same thickness, the strain-hardening rate varies depending on the loading direction and crystal orientation relationship. When the Schmid factors and mean-free paths of the activated systems are small and short, the strain-hardening rate tends to be high. The ferrite layer exhibits a remarkably high strain-hardening rate when slip systems are sequentially activated with the increase of deformation.This is part of a thematic issue on Pearlitic Steel Wires.

Effect of high magnetic field on the pearlite transformation of Al-containing steel

ABSTRACTComparative studies were carried out on the effect of high magnetic field on the pearlite transformation of Al-containing high carbon steels under the furnace slow cooling condition. For 1.37Al-bearing high carbon steel, the amount of pearlite was only 6 ± 3 vol.-% without magnetic field, whereas full pearlite was obtained under a 12-T high magnetic field. For free-Al high carbon steel, no pearlite transformation occurred, whereas lots of bainite were formed under a 12-T high magnetic field. In addition, the interlamellar spacing of pearlite increased from 100 ± 7 to 112 ± 18 nm by the application of a 12-T magnetic field. It has been proved that the pearlite transformation of high carbon steel was promoted by high magnetic field and by the addition of aluminium.This is part of a thematic issue on Pearlitic Steel Wires.

Oxidation kinetics in pearlite: The defining role of interface crystallography

Five different pearlitic steel wires were produced through controlled thermomechanical processing. These wires had significant (~2 times) differences in the pearlite alignment and also exhibited nearly one order of magnitude difference in the oxidation kinetics. Though the nature of the oxide films was not remarkably different, the stresses in the majority hematite phase scaled with the experimentally measured oxidation rates. Careful correlation between substrate microstructure and oxide stresses established that the stresses were highest at the ferrite-cementite interface. And the interface crystallography, in case of the coarse pearlite, determined such stresses and the oxidation kinetics.

Delamination of Pearlitic Steel Wires: The Defining Role of Prior-Drawing Microstructure

This article reports the occasional (< 10 pct of the actual production) delamination of pearlitic wires subjected to a drawing strain of ~ 2.5. The original wire rods which exhibited post-drawing delamination had noticeably lower axial alignment of the pearlite: 22 ± 5 pct vs 34 ± 4 pct in the nondelaminated wires. Although all wires had similar through-thickness texture and stress gradients, delaminated wires had stronger gradients in composition and higher hardness across the ferrite–cementite interface. Carbide dissolution and formation of supersaturated ferrite were clearly correlated with delamination, which could be effectively mitigated by controlled laboratory annealing at 673 K. Direct observations on samples subjected to simple shear revealed significant differences in shear localizations. These were controlled by pearlite morphology and interlamellar spacing. Prior-drawing microstructure of coarse misaligned pearlite thus emerged as a critical factor in the wire drawing-induced delamination of the pearlitic wires.

Microstructural Evolution of a Pearlitic Steel Subjected to Thermomechanical Processing

The microstructural alterations suffered during the process of drawing deformation and subsequent annealing of pearlitic steel wires, were evaluated by scanning electron microscopy and atomic force microscopy. The deformed material showed the curling structure in cross section while, in the longitudinal section, the lamellae was aligned with the drawing direction. The microstructural characterization of deformed samples also allowed observing an interlamellar spacing reduction and the intermediate lamellae alignment process. After the heat treatment at 1000oC for 5 min the microstructure was restored, however, few recrystallized grains were observed. The recovery was the dominant phenomenon, due to factors associated with curling structure that inhibited recrystallization.

Molecular dynamics study on nano-sized wiredrawing: possible atomistic process and application to pearlitic steel wire

The process of nano-sized wiredrawing is investigated by using molecular dynamics (MD) simulation in this study. The authors have constructed novel computation models of wiredrawing, in which a single wire of just a several nanometers in diameter is smoothly drawn through a perfectly rigid die together with lubrication mechanism and is forced to be shaped into thinner one. Interatomic potentials used in MD simulation is a conventional pairwise type useable for iron-carbon binary system (for pearlitic steel). For MD model of pearlite steel wire, it is recognized that ferrite-cementite interface effectively offers high-speed diffusion path for carbon atoms from cementite side to ferrite side (elementary mechanism of cementite decomposition). As conclusion, we showed by using atomistic simulation that nano-sized wiredrawing process is theoretically quite possible.

Microstructure-based anisotropic fatigue behavior of hot rolled and cold drawn pearlitic steel wires and the corresponding crack paths: Following the wake of Antonio Machado and Fray Luis de León

This paper deals with the microstructure-based anisotropic fatigue behavior of hot rolled and cold drawn pearlitic steel wires, showing that: (i) the corresponding fatigue crack paths in both the hot rolled bar and the heavily cold drawn wire develop in global mode I in both materials, i.e., no macroscopic (apparent) anisotropic effect arise in the matter of fatigue crack propagation, in spite on the inherent microstructural anisotropy produced by heavy drawing in the commercial prestressing steel in the form of orientation and alignment in the wire axis or cold drawing direction of both microstructural levels of pearlitic colonies and lamellae; (ii) at a finer microstructural level, the associated fatigue crack paths in both the hot rolled bar and the heavily cold drawn wire develop in local mixed mode in both materials (anisotropic fatigue behavior; locally multiaxial fatigue crack growth), i.e., a microscopic (real) anisotropic effect arise in the matter of fatigue crack propagation linked with the lamellae alignment and orientation; (iii) this local anisotropy of fatigue resistance allows a correction of the fatigue crack growth equation (Paris Law) to consider the real fatigue crack path in local mixed mode instead of the apparent fatigue crack path in global mode I; (iv) these fatigue crack paths recall the words by Antonio Machado “se hace camino al andar” and the composite lamellar microstructure of pearlite recalls Fray Luis de León “y entrambas a porfía mezclan una dulcísima armonía”.