Degree Of Cold Drawing Research Articles

Multiscale approach to fatigue crack propagation paths in cold drawn pearlitic steels

This paper offers a multiscale approach (macro & micro) to the fatigue crack paths in progressively cold drawn pearlitic steels, with emphasis on the relationship between the pearlitic microstructure of the steels (progressively oriented as a consequence of the manufacturing process by cold drawing) and the fatigue behaviour at the macro- and micro-scopic levels. To this end, a detailed fracto-metallographic analysis was performed on the fatigue crack path (macro- and micro-crack path). With regard to the fatigue macro-crack path, it evolves following and elliptical shape with varying aspect ratio, the latter being modified by the presence of manufacturing-induced residual stress fields. In the matter of fatigue micro-crack paths, results showed that they exhibit certain roughness at the microscopic level, in the form of a zig-zag shape including micro-deflections whose length and angle both depend on the cold drawing degree.

Hydrogen assisted cracking paths in cold drawn pearlitic steels

This paper analyses hydrogen assisted cracking (HAC) paths in cold drawn pearlitic steels in which progressive cold drawing produces a preferential orientation of the pearlitic microstructure in the matter of colonies and lamellae, thereby inducing strength anisotropy in the steel, and thus the resistance to HAC is a directional property that depends on the angle in relation to the drawing direction. Therefore, an initial transverse crack changes its propagation direction to approach that of the wire axis, thus producing mixed mode propagation, the deflection angle being an increasing function of the cold drawing degree. This experimental result may be explained by micro-mechanical considerations on the basis of the lamellar microstructure of the steels. A relationship is established between the microstructural angles and the deflection angles of the macroscopic HAC path, thus providing a materials science type relationship between the microstructure and the macroscopic crack.

Stress corrosion cracking paths in cold drawn pearlitic steels

This paper analyses stress corrosion cracking (SCC) paths in cold drawn pearlitic steels in which progressive cold drawing produces a preferential orientation of the pearlitic microstructure in the matter of colonies and lamellae, thereby inducing strength anisotropy in the steel, and thus the resistance to SCC is a directional property that depends on the angle in relation to the drawing direction. Therefore, an initial transverse crack changes its propagation direction to approach that of the wire axis, thus producing mixed mode propagation, the deflection angle being an increasing function of the cold drawing degree. This experimental result may be explained by micro-mechanical considerations on the basis of the lamellar microstructure of the steels. A relationship is established between the microstructural angles and the deflection angles of the macroscopic SCC path, thus providing a materials science type relationship between the microstructure and the macroscopic crack.

On the cleavage hoop stress responsible for crack path deflection and notch-induced anisotropic fracture in cold drawn pearlitic steel: Revisiting John Ford’s Monument Valley

In this paper a study is presented of the fracture behaviour in the presence of notches of high-strength pearlitic steel with different cold drawing degree. To this end, axisymmetric notched samples with a circumferentially-shaped notch of very distinct geometries (sharp and blunt, deep and shallow) were taken from wires with different levels of drawing from the initial hot rolled bar (not cold drawn at all) to the final commercial product (prestressing steel wire: heavily cold drawn). Experimental results show that cold drawn steels exhibit a markedly anisotropic fracture behaviour in the form of fracture path deviation from the original transverse fracture path perpendicular to the wire axis or cold drawing direction. Present paper proposes a key variable governing the notch-induced anisotropic fracture process: the cleavage hoop stress as the relevant factor promoting this sort of fracture path deviation in the most heavily cold drawn pearlitic 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.

HELP versus HEDE in progressively cold-drawn pearlitic steels: Between Donatello and Michelangelo

Abstract This paper reviews previous research by the author in the field of hydrogen effects on progressively cold-drawn pearlitic steels in terms of hydrogen degradation (HD), hydrogen embrittlement (HE) or, at the micro-level, hydrogen-assisted micro-damage (HAMD), thus affecting their microstructural integrity and compromising the (macro-)structural integrity of civil engineering structures such as prestressed concrete bridges. In particular, the two classical hydrogen-assisted deterioration micro-mechanisms are discussed, namely, hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE), together with their role in the embrittlement process as a function of the degree of cold-drawing undergone by each steel (associated with a different level of microstructural orientation of pearlitic colonies and lamellae). It is seen that hydrogen effects in pearlitic microstructure (either oriented or not) are produced at the finest micro-level by plastic tearing in the form, in general, of hydrogen damage topography (HDT) with different appearances depending of the cold drawing degree, evolving from the so-called tearing topography surface (TTS) in hot-rolled (not cold-drawn at all) or slightly cold-drawn pearlitic steels to a sort of enlarged and oriented TTS (EOTTS) in heavily drawn steels (the pronounced enlargement and marked orientation being along the wire axis or cold drawing direction). Whereas the pure TTS mode (null or low degree of cold drawing) resembles the Michelangelo stone sculpture texture (MSST), the EOTTS mode does the same in relation to the Donatello wooden sculpture texture (DWST).

Hydrogen-Assisted Micro-Damage in Cold-Drawn Pearlitic Steels: Resembling Donatello Wooden Sculpture Texture

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).

Initiation and propagation of fatigue cracks in cold-drawn pearlitic steel wires

In this paper the important role of manufacturing by progressive cold drawing on initiation and propagation of fatigue cracks in cold-drawn pearlitic steel wires is addressed by analyzing the initiation (from surface defects) and propagation of fatigue cracks in two pearlitic steels with very different cold drawing degree or cumulative plastic strain (and the subsequent very distinct microstructural arrangement): a hot rolled pearlitic steel bar and a commercial high-strength cold-drawn prestressing steel wire to be used asa component of prestressed concrete in structural engineering. Experimental results show that the initiation of fatigue cracks in pearlitic steels takes place at the location of small surface defects, many of them in the form of localized damage in the area of material surface (in the case of hot rolled bar) or voids created by tearing during drawing due to the existence of particles near the wire surface (in the case of the cold drawn wire). In both materials, fatigue cracks are mostly transcollonial and tend to fracture pearlite (ferrite/cementite) lamellae, so that different micro-mechanisms of fatigue damage appear in the material such as non-uniform crack opening displacement, micro-discontinuities, branchings, bifurcations and frequent local deflections, all creating a sort of microstructural roughness in the fatigue crack path that is different in the hot rolled bar and in the cold drawn wire, thereby determining their distinct fatigue performance.

Hydrogen Effects on Progressively Cold-Drawn Pearlitic Steels: Between Donatello and Michelangelo

This paper reviews previous research by the author in the field of hydrogen effects on progressively cold-drawn pearlitic steels in terms of hydrogen degradation (HD), hydrogen embrittlement (HE) or, at the micro-level, hydrogen-assisted micro-damage (HAMD), thus affecting their microstructural integrity and compromising the (macro-)structural integrity of civil engineering structures such as prestressed concrete bridges. It is seen that hydrogen effects in pearlitic microstructure (either oriented or not) are produced at the finest micro-level by plastic tearing in the form, in general, of hydrogen damage topography (HDT) with different appearances depending of the cold drawing degree, evolving from the so-called tearing topography surface (TTS) in hot-rolled (not cold-drawn at all) or slightly cold-drawn pearlitic steels to a sort of enlarged and oriented TTS (EOTTS) in heavily drawn steels (the pronounced enlargement and marked orientation being along the wire axis or cold drawing direction). Whereas the pure TTS mode (null or low degree of cold drawing) resembles the Michelangello stone sculpture texture (MSST), the EOTTS mode does the same in relation to the Donatello wooden sculpture texture (DWST).

Stress Corrosion Cracking of Progressively Cold-Drawn Pearlitic Steels: From Tintoretto to Picasso

Progressive cold drawing in eutectoid steels produces a preferential orientation of the pearlitic microstructure in the wire axis or drawing direction. This affects the posterior behaviour of the steels under conditions of stress corrosion cracking (SCC). The experimental results show that cold drawing induces strength anisotropy in the steel, and thus the resistance to SCC is a directional property that depends on the angle in relation to the drawing direction. Therefore, an initial transverse crack changes its propagation direction to approach that of the wire axis, thus producing mixed mode propagation, the deflection angle being an increasing function of the cold drawing degree. This experimental result may be explained by micro-mechanical considerations on the basis of the lamellar microstructure of the steels. A relationship is established between the microstructural angles and the deflection angles of the macroscopic SCC crack, thus providing a materials science type relationship between the microstructure and the macroscopic crack paths with regard to hydrogen assisted cracking (HAC) associated with the cathodic regime and in the matter of localised anodic dissolution (LAD) linked to the anodic regime. Whereas in hot rolled (not cold drawn at all) and slightly drawn steels the phenomenon of SCC develops in mode I, i.e., the SCC crack is a straight line linked with the classical linear perspective painting by Tintoretto, in the case of heavily drawn steels, the SCC deflected crack is a polygonal line associated with the multi-perspective cubist painting by Picasso, these conclusions being valid for both HAC and LAD.

Structural integrity of progressively cold-drawn pearlitic steels: From Raffaello Sanzio to Vincent van Gogh

Abstract: This papers deals with fracture behavior and structural integrity of progressively cold-drawn pearlitic steels on the basis of their microstructural evolution during manufacturing by multi-step cold drawing. It is seen that the manufacture technique by progressive cold drawing in several steps produces a microstructural evolution in the form of progressive slenderizing and orientation (in the wire axis or cold drawing direction) of the pearlitic colonies (first microstructural level), as well as increasing orientation and densification of the ferrite/cementite lamellae (second microstructural level) linked with a decrease of pearlite (ferrite/cementite) interlamellar spacing. Thus the microstructure of the cold-drawn pearlitic steel wires becomes progressively oriented as the cold-drawing degree increases and this microstructural fact influences their macroscopic behavior by inducing anisotropic fracture and crack path deflection. Therefore, this paper offers a micro- and macro-approach to the fracture and structural integrity of cold-drawn pearlitic steels, introducing the new concept of microstructural integrity .

Influence of the Degree of Cold Drawing on the Microstructure and Properties of Pipes Used for Dampers

Dumpers are the main components of the suspension system with vertical oscillations role in the absorption of the automobile. The combination of suspension coil with dumper is forming the main body of the suspension system. Shock absorber pipe is mainly used for production of motorcycles, cars (sedan) car shock absorber, is the size of the relatively high precision seamless pipe products, its manufacturing costs and lower selling prices relatively seamless, with excellent cost performance, got the car and motorcycle manufacturing industry recognition, are gradually replacing the use of seamless pipes in the area. The cold work process of pipes drawing consists of reducing the cross-section of a pipe by pulling the pipe through series of conical dies. The metal pipe drawing technology has been widely used to manufacture fine pipes. The influence of the degree of cold drawing on the mechanical properties of the carbon steel material were studied using the tensile test and hardness test experiments in order to replicate the service condition of the pipes used for automotive dumpers. Microstructure analysis were perfomed using optical analysis on a LEICA 5000DMI microscope up to 1000X magnitude and SEM images with a dual beam QUANTA 200 3D FEI SEM scanning electron microscope. The purpose of the work is to observe the main effects of the degree of reduction at different gradations by analysing the microstructure and mechanical proprieties behavior. The study used the stress-strain relationship of the tensile test experiment to study the effect of the degree of cold-drawing deformation on the yield strength and tensile strength properties of the dumpers used in automotive industry. The toughness of the low carbon steel used for the dumper manufacture reduces as the degree of drawing deformation increases. The ductility of the material also reduces with increasing degree of rawing deformation. The yield strength of the material was observed to reduce with increasing degree of cold-drawing, an indication of reduction in the ductility and the tensile strength of the material reduced with increasing degree of cold-drawn deformation. After high degrees of cold deformation by drawing, the hardness proprieties are increasing highlighted by cold-straining.

Influence of the Degree of Cold Drawing over the Wear Test and XRD Analysis of Pipes Used for Dampers

Dumpers have studied intensively in the last years and they are the main parts of the suspension system with vertical oscillations role in the absorption of the automobile. The combination of suspension coil with dumper is forming the main body of the suspension system. Dumpers are mainly used for production of automotive industry. The influence of the degree of cold drawing on the mechanical properties of the carbon steel material were studied for the XRD and wear test point of view using microtribometer and diffractometer test machines. The purpose of the work is to observe the main effects of the degree of reduction at different gradations by analysing the X-Ray diffraction – crystallographic determination and scratch test by observing the wear tracks. It was finally measured the loss of material during the wear test, the sample with the highest grade of plastic deformation had the lowest material loss.

Mechanical Properties of Cold-Drawn Low Carbon Steel for Nail Manufacture: Experimental Observation

The objective of this study is to investigate the influence of service situation on the mechanical properties of plain nails manufactured from low carbon steel. The influence of the degree of cold drawing on the mechanical properties and strain hardening of the material is investigated by tensile test experimentation. The stress-strain relationships of the cold-drawn low carbon steel were investigated over the 20, 25, 40 and 55% degree of drawn deformation for the manufacture of 4, 3, 21⁄2 and 2 inches nails, respectively. The true stress-strain curves were analyzed to obtain the yield strength and tensile strength of the cold drawn steel. It is shown that the yield strength, tensile strength, hardness and toughness of the low carbon steel reduce with increasing degree of cold-drawn deformation. The micrographs of the deformed samples obtained using optical microscope shows that the grain structure elongates in the direction of the drawing operation and misorientation of the grains set in at 40 and 55% degree of deformation. The difference in yield strength was attributed to the strain hardening, resulting from the different degrees of drawn deformation.

Influence of Degree of Cold-Drawing on the Mechanical Properties of Low Carbon Steel

Low carbon steel metal is used for the manufacture of nails. Steel wire with <0.3% C content is cold-drawn through a series of drawing dies to reduce the diameter of the wire to the required diameter of the nails. A 0.12%w C steel wire cold drawn progressively by 20%, 25%, 40% and 50% was investigated. The influence of the degree of cold drawing on the mechanical properties of the carbon steel material were studied using the tensile test, impact test and hardness test experiments in order to replicate the service condition of the nails. The tensile test was done on a Montanso® tensometer to investigate the yield strength and the tensile strength of the material as the degree of deformation increases. An Izod test was used to determine the impact toughness of the steel using the Hounsfield impact machine and the hardness numbers were obtained for the different degrees of drawn deformation of the steel on the Brinnel tester. The study used the stress-strain relationship of the tensile test experiment to study the effect of the degree of cold-drawing deformation on the yield strength and tensile strength properties of the low carbon steel. The yield strength of the material was observed to reduce with increasing degree of cold-drawing, an indication of reduction in the ductility and the tensile strength of the material reduced with increasing degree of cold-drawn deformation. The ability of the material to resist impact loads when nails are hammered reduced with increasing degree of drawn deformation as a result of strain hardening of the material after the drawing operation. However the resilience of the material to further cold drawn deformation increased with increasing degree of deformation as evident in the Brinnel hardness number which increases with the degree of drawing deformation. This is an indication of the material’s approach to brittleness as the degree of drawn deformation increases.

Micro- and macro-approach to the fatigue crack growth in progressively drawn pearlitic steels at different R-ratios

This paper deals with the role of microstructure on the fatigue behaviour of pearlitic steels with different degrees of cold drawing. The analysis is focussed on the region II (Paris) of the fatigue behaviour, measuring the constants ( C and m) for the different degrees of drawing. From the engineering point of view, the manufacturing process by cold drawing improves the fatigue behaviour of the steels, since the fatigue crack growth rate decreases as the strain hardening level in the material increases. In particular, the coefficient m (slope of the Paris laws) remains almost constant and independent of the drawing degree, whereas the constant C decreases as the drawing degree rises. The paper focuses on the relationship between the pearlitic microstructure of the steels (progressively oriented as a consequence of the manufacturing process by cold drawing) and the macroscopic fatigue behaviour. To this end, a detailed metallographic analysis was performed on the fatigue crack propagation path after cutting and polishing on a plane perpendicular to the crack front ( fracto-metallographic analysis). It is seen that the fatigue crack growth path presents certain roughness at the microscopic level, such a roughness being related to the pearlitic colony boundaries more than to the ferrite/cementite lamellae interfaces. Fatigue cracks are transcollonial and exhibit a preference for fracturing pearlitic lamellae, with non-uniform crack opening displacement values, micro-discontinuities, branchings, bifurcations and frequent local deflections that create microstructural roughness. The net fatigue surface increases with cold drawing due to the higher angle of crack deflections. With regard to the influence of the R-ratio, an increase of such a stress ratio produces microcracking with a higher number of branchings for the same stress intensity range.

Micro-fracture maps in progressively drawn pearlitic steels under triaxial stress states

In this paper, the fracture performance of axisymmetric notched samples taken from prestressing steels with different levels of cold drawing is studied. Fractographic analysis of the samples by means of scanning electron microscope (SEM) revealed the microscopic topographies after failure and allowed the assembly of micro-fracture maps (MFM) covering the whole fracture surface and containing relevant information on the micromechanisms of fracture in the material. With regard to the influence of the stress triaxiality (constraint), the behaviour is more ductile in the case of blunt notches than in the case of sharp notches. In the matter of the influence of the cold drawing degree, the fracture behaviour becomes more ductile as the strain hardening level of the steel increases, so that cleavage is predominant in the fracture area of slightly drawn steels, whereas the presence of micro-void coalescence (MVC) increases with the degree of cold drawing and becomes predominant in the case of the most heavily drawn steels in which cleavage can hardly be detected as an extended region.

Multi-Scale Approach to the Fatigue Crack Propagation in High-Strength Pearlitic Steel Wires

Abstract This paper deals with the influence of the manufacturing process on the fatigue behavior of pearlitic steels with different degrees of cold drawing. The fatigue crack growth rate (da/dN) is related to the stress intensity range (ΔK) by means a compliance method to evaluate the crack depth a in the samples at any instant during the tests. The analysis is focused on the Region II (Paris) of the fatigue behavior in which da/dN=C(ΔK)m, measuring the constants (C and m) for the different degrees of drawing. From the engineering point of view, the manufacturing process by cold drawing improves the fatigue behavior of the steels, since the fatigue crack growth rate decreases as the strain hardening level in the material increases. In particular, the coefficient m (slope of the Paris Law) remains almost constant and independent of the drawing degree, whereas the constant C decreases as the drawing degree rises. The paper focuses on the relationship between the pearlitic microstructure of the steels (progressively oriented as a consequence of the manufacturing process by cold drawing) and the macroscopic fatigue behavior. To this end, a detailed metallographic analysis was performed on the fatigue crack propagation path after cutting and polishing on a plane perpendicular to the crack front. It is seen that the fatigue crack growth path presents certain roughness at the microscopic level, such a roughness being related to the pearlitic colony boundaries more than to the ferrite/cementite lamellae interfaces.

Hydrogen assisted cracking in progressively drawn pearlitic steel

This paper analyses the hydrogen assisted cracking (HAC) behaviour of cold drawn prestressing steels with different degrees of cold drawing. The experimental results showed a progressively anisotropic behaviour as the degree of cold drawing increases, with an evolution in the fracture behaviour from mode I (isotropic behaviour in slightly drawn steels) to mixed mode propagation (strongly anisotropic behaviour in heavily drawn steels). The fractographic analysis revealed changes in the microscopic topography depending on the fracture propagation mode, with evolution from pure tearing topography surface (TTS) in slightly drawn steels to a kind of very deformed TTS in heavily drawn steels.

Failure analysis of cold drawn prestressing steel wires subjected to stress corrosion cracking

This paper analyzes the stress corrosion performance of cold drawn prestressing steels with different degrees of cold drawing, in the two cases of pure stress corrosion cracking and fracture by hydrogen embrittlement. Results show a progressively anisotropic stress corrosion behaviour with cold drawing, and this anisotropy could be induced by the microstructural orientation. Consequences for engineering design are derived on the basis of the calculation of the transition stress intensity factor (from the stress corrosion subcritical crack growth to the critical cleavage propagation). While in situations of pure stress corrosion cracking such a value is even higher than the fracture toughness of the material in air (due to crack tip blunting), in the case of hydrogen embrittlement there is a marked reduction of stress intensity factor value, which indicates that these steels are highly susceptible to this phenomenon.