The structure and properties of drawn pearliteStructure et proprietes d'une perlite etireeStruktur und eigenschaften von gezogenem perlit
Abstract
The microstructures of drawn, coarse and fine pearlite have been examined by transmission and replica electron microscopy. The observations indicate that a cellular dislocation substructure is developed during drawing and that the mean distance between substructural barriers measured perpendicular to the wire axis decreases continuously with increasing strain.
An empirical model has been developed to relate the flow stress of the drawn wire to the spacing of substructural barriers in terms of the drafting strain. Qualitative evidence is presented which indicates that this type of strengthening mechanism is operative in the case of drawn iron wire of commercial purity. Some observations on the plastic deformation and fracture of cementite are also included.
Résumé
Les microstructures après étirage de perlites fines et grossières ont été examinées en microscopie électronique sur des lames minces et par réplique. Les observations ainsi obtenues montrent le développement au cours de l'étirage d'une structure cellulaire de dislocations; la distance moyenne entre les limites de ces sous-structures mesurée perpendiculairement à l'axe du fil décroît avec un accroissement du taux de déformation.
Les auteurs ont développé un modèle empirique reliant la contrainte d'écoulement du fil étiré è la distance entre les limites des sous-structures et au taux de déformation. Il est de plus montré d'une façon qualitative que ce mode de durcissement se présente dans le cas de fils de fer étirés de pureté commerciale. Cette étude comporte également quelques observations sur la déformation plastique et la rupture de la cémentite.
Zusammenfassung
Die Mikrostrukturen von gezogenem, grobkörnigem und feinem Perlit wurden mit Hilfe der Durchstrahlungs-Elektronenmikroskopie und der Replika-Methode untersucht. Die Beobachtungen zeigen, daβ während des Ziehvorganges eine zellulare Versetzungsstruktur gebildet wird, und daβ der senkrecht zur Drahtachse gemessene, mittlere Abstand zwischen den substrukturellen Hindernissen mit zunehmender Dehnung kontinuierlich abnimmt.
Es wird ein empirisches Modell angegeben, um die Flieβspannung des gezogenen Drahtes mit dem Abstand der substrukturellen Hindernisse und damit mit der im Zug erreichten Dehnung zu verknüpfen. Es ist qualitativ evident, daβ dieser Typ von Verfestigungsmechanismus im Fall eines gezogenen Eisendrahtes dommerzieller Reinheit betätigt wird. Einige Beobachtungen über die plastische Deformation und den Bruch von Zementit werden ebenfalls mitgeteilt.
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Study on thermal fatigue stability in microstructure and mechanical property of Fe35Ni35Cr20Mn10 high-entropy alloy wire and pearlite wire at high/medium temperature environment
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Dynamic mechanical behaviors of pearlitic U71MnG rail steel: Deformation mechanisms and constitutive model
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Evolution of mechanical properties of ferrite and pearlite phases during spheroidization process and their relationship to the overall properties of low alloy steel
2024, Journal of Materials Research and TechnologyMechanical properties of ferrite-pearlite low alloy steel are strictly determined by the properties of ferrite and pearlite phases. In this present paper, the evolution of mechanical properties of ferrite and pearlite phases during spheroidization process is investigated by using nanoindentation tests. Meanwhile, the overall mechanical properties of the material were measured using uniaxial tensile tests. Test results indicate that with the intensification of spheroidization of layered cementite in pearlite, the hardness and yield strength of pearlite phase decrease from 2.72 GPa to 1.73 GPa and 411.5 GPa–256.1 GPa, respectively. However, the mechanical properties of ferrite phase exhibit an opposite trend, with hardness and yield strength increasing from 1.6 GPa to 1.67 GPa and 188.1 GPa–208.4 GPa, respectively. Uniaxial tensile tests results indicate that overall yield strength of steel decreases significantly as the degree of spheroidization increases, from the original 276 MPa–229 MPa. Although the strength of pearlite decreased by 38%, the overall strength of alloy steel decreased by only 15% due to an 11% increase in ferrite strength. During spheroidization process, the relationship between pearlite hardness, yield strength, and interlayer spacing of cementite in pearlite can be expressed in Hall-Petch type relationships as: and ; and the relationship between the strengths of ferrite-pearlite aggregate and ferrite and pearlite phases is .
Impact of interlamellar spacing and non-pearlitic features on mechanical properties and cyclic damage initiation in near-eutectoid pearlitic steels
2024, Materials Science and Engineering: AThe relationship between microstructural characteristics and mechanical properties was investigated for C72 and C82 pearlitic steel rods patented at temperatures between 500 °C and 600 °C using a lead bath. Results revealed a refinement of interlamellar spacing upon reduction of patenting temperature. At the same time, the fraction of grain-boundary ferrite and Widmanstätten ferrite as common non-pearlitic regions was slightly increased, reaching a maximum of nearly 1.3 vol.-% in the case of C72 steel patented at 500 °C. Reduction of patenting temperature was associated with strengthening, as confirmed by tensile, fatigue and hardness tests. The strengthening was explained in terms of the Hall-Petch effect for ferrite due to increase in the boundary area. The Hall-Petch coefficient, obtained by taking the apparent interlamellar spacing as the mean free path of dislocations, was in the range 70–140 . To some extent, these low values could be related to the low solute interstitial content of pearlitic ferrite. More importantly, the coefficients are underestimated due to the plate-shaped morphology of pearlitic ferrite, which causes the average mean free path of dislocations be longer than the apparent interlamellar spacing. Scanning electron microscopy examinations after interrupted fatigue tests indicated the preferred occurrence of intrusions and extrusions, as precursors to fatigue crack, in the non-pearlitic ferrite. The enhancement of fatigue limit at lower patenting temperatures—in spite of slight increase in the fraction of ferrite—is justified by the stress shielding effect of pearlite and necessity of crack propagation into pearlitic regions for stable crack propagation. In effect, as long as the fraction of non-pearlitic features remains low, the interlamellar spacing of pearlite serves as the most efficient strength-controlling microstructural parameter. Furthermore, due to the preferred growth of fatigue cracks parallel to lamellae and deflection at colony boundaries, the refinement of colonies at reduced patenting temperatures is an additional contribution to the fatigue strength.
Assessing the influence of cyclic bending on pearlitic wire's microstructural evolution: a simulation of spiraling and armoring processing effects
2023, Journal of Materials Research and TechnologyFlexible pipelines are widely used offshore for oil and gas transportation and are subjected to several complex stress modes during service. Stress tensors cause different alterations in the macro and microstructure of the material. Therefore, studies involving the relationship between mechanical behavior and the crystallographic orientation of tensile armor wires need deep investigation. This work investigated the role of complex plastic deformation during the spiraling tensile armor on the microstructure and crystallographic texture of pearlitic steel with 0.74 wt%C. A heat-treated sample was prepared as a starting point. Further specimens were subjected to cold bending to investigate the strain accumulation during spiraling and armoring processing and then compared to an industrial twisted tensile armor sample. The microstructural and texture evolution was characterized by scanning electron microscopy, X-ray diffraction, and backscattered electron diffraction. Specimens were submitted to the Vickers microhardness and tensile tests to evaluate the mechanical properties. Results revealed that the bending deformation causes a reduction of (001)//ND fiber and increases the mechanical resistance of the material, which may prevent the onset and crack propagation. (111)//ND fiber increased while (110)//ND decreased, leading to stability in the slip systems. The formation of shear band structural changes resulted from the increase of (110)//ND with armoring and a decrease of (111)//ND fibers. Bending strains enhance the desirable texture components while diminishing the undesirable ones. Deformations to which the materials were subjected provide less mobility of dislocations, which causes an increase in mechanical strength. Little change in texture and microstructure was also observed.
Local measurement of geometrically necessary dislocation densities and their strengthening effect in ultra-high deformed pearlite
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