&lt;i&gt;In Situ&lt;/i&gt; TEM and APT Analysis on the Dislocations Associated with Solute Carbons in Strain-Aged Low Carbon Pipeline Steels

Park, H.S.; Kang, Jee-Hyun; Yoo, Jae‐Young; Park, Chan Gyung

doi:10.4028/www.scientific.net/msf.654-656.122

Cited by 7 publications

(6 citation statements)

References 4 publications

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“…Pipeline steels usually experience the piping process followed by the coating process at 250 °C, and 3DAP results revealed the segregation of carbon atoms along dislocation lines in the ferrite region of both UOE (bending by U press, forming by O press, Expansion) pipes and coated pipes. It is believed that segregation of carbon along dislocations in pipeline steel usually causes strain aging phenomena, such as discontinuous yielding, decrease in yield strength, and uniform elongation after the pipe-making and coating processes [ 4 , 32 ]. Phosphorus exists in the form of solid solution when the segregation concentration of the grain boundary is low.…”

Section: Resultsmentioning

confidence: 99%

Strengthening Effect of Nb on Ferrite Grain Boundary in X70 Pipeline Steel

Tian

2020

Materials

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Understanding the strengthening effect of niobium on ferrite grain boundaries from the perspective of valence electron structures will help to use niobium and other microalloying elements more effectively to improve the performance of steel materials. In this paper, the effect of niobium element on ferrite grain boundary strengthening is studied based on microstructure analysis at the nanometer scale. The enrichment of niobium in pipeline steel at ferrite boundary was observed by a three-dimensional atomic probe test. Segregation of Nb is observed in the ferrite grain boundaries of X70 steel, and its maximum concentration is 0.294–0.466 at.%. The charges in the occupancy of the Fe 3d state in grain and grain boundary were 7.23 and 7.37, respectively, based on quantitative analysis of electron energy loss spectra (EELS). The first-principle calculation suggests that the charges in the occupancy of 3d state for grain boundary iron are 6.57 and 6.68, respectively, before and after the Nb doping (with an increase of 1.67%), which reveals a similar trend to that of the EELS results. Through Nb alloying, the 3d valence electronic density of the state of Fe in grain boundary moves to a lower energy, which can reduce the total energy of the system and make the grain boundary more stable. Meanwhile, the charges in the occupancy of the 3d state for Fe in the grain boundary increases, providing more electrons for grain boundary bonding. These improve the strength and toughness of the material. This work provides a fundamental understanding for pipeline steel strengthening by element alloying.

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Section: Resultsmentioning

confidence: 99%

Strengthening Effect of Nb on Ferrite Grain Boundary in X70 Pipeline Steel

Tian

2020

Materials

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“…The basic mechanism for strain aging of steels is well established [2] and entails the diffusion of either free carbon or free nitrogen to dislocations and the subsequent stabilisation/pinning of these dislocations. The segregation of carbon atoms to dislocations has been observed in steel with three-dimensional atom probe analysis [3,4]. The amount of free carbon and/or nitrogen (i.e.…”

Section: Strain Aging Mechanismmentioning

confidence: 99%

“…However, the magnitude and complexity (e.g. compression and/or tension and/or reversals) of the plastic strain depend on both the pipe diameter and the exact forming conditions [2][3][4][5][6][7]. The strain history can affect the initial mechanical properties of the pipe [17][18][19][20][21].…”

Section: Strain Aging Variablesmentioning

confidence: 99%

Strain aging on the yield strength to tensile strength ratio of UOE pipe

Wiskel

Valloton

et al. 2017

Materials Science and Technology

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Strain aging of microalloyed steel pipe can occur at the relatively low temperatures associated with the pipe coating process and/or during long-term storage. A Box–Behnken statistical design was used to determine the significant strain aging variables that affect the longitudinal yield strength to tensile strength (Y/TS) ratio for three uncoated X70 UOE pipes. The strain aging variables examined include time, temperature, steel composition/microstructure (vis-a-vis the C/Nb ratio) and position through the pipe wall thickness. Metallographic and electron backscattered diffraction examinations were undertaken to determine the grain size and phase percentages of the as-received pipe steel. Both position in the pipe and the C/Nb ratio were found to have a statistically significant effect on the yield strength to tensile strength ratio.

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“…Furthermore, the Luders plateau was also observed in the test of Specimen #2, which was interrupted deliberately when the strain reached about 1.1%. 5 Fig . 4 shows the variation of the strain along the tensile direction as detected by DIC in Specimen #2 at the moment of interruption.…”

Section: Methodsmentioning

confidence: 99%

“…During the coating process the pipe is usually heated to a certain temperature, which modifies the mechanical properties of pipeline steel in a number of ways: (1) higher yield strength, (2) higher ratio of yield stress to ultimate tensile stress and (3) occurrence of Luders bands in the tensile test [3,4]. This phenomenon is known as strain ageing, which has the similar mechanism with the Luders behaviour [5,6]. Pay attention to that the occurrence of Luders bands are not directly related to ageing temperature, because they are observed even without experiencing ageing process.…”

Section: Introductionmentioning

confidence: 99%

Innovative analysis of Luders band behaviour in X80 pipeline steel

Han

Lü

et al. 2017

Materials Science and Engineering: A

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In this study, the influence of Luders bands, which are frequently observed after the pipe coating process, is investigated. Stratified tensile test specimens, machined from different locations across the thickness of an X80 line pipe, were tested. The Luders bands were observed by using a digital image correlation (DIC) in the specimen machined from halfway across the pipe wall thickness. The specimens from the selected locations related to the Luders bands were studied and compared by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and standard mechanical testing. The results display that the microstructure, lattice constant, dislocation density and Schmid factors change when the Luders bands pass through the tensile test specimen, which brings about the difference in mechanical properties. The study of the influence of Luders bands on microstructures and mechanical properties enables better understanding of the strain-ageing mechanism. ABSTRACTIn this study, the influence of Luders bands, which are frequently observed after the pipe coating process, is investigated. Stratified tensile test specimens, machined from different locations across the thickness of an X80 line pipe, were tested. The Luders bands were observed by using a digital image correlation (DIC) in the specimen machined from halfway across the pipe wall thickness. The specimens from the selected locations related to the Luders bands were studied and compared by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and standard mechanical testing. The results display that the microstructure, lattice constant, dislocation density and Schmid factors change when the Luders bands pass through the tensile test specimen, which brings about the difference in mechanical properties. The study of the influence of Luders bands on microstructures and mechanical properties enables better understanding of the strain-ageing mechanism.

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<i>In Situ</i> TEM and APT Analysis on the Dislocations Associated with Solute Carbons in Strain-Aged Low Carbon Pipeline Steels

Cited by 7 publications

References 4 publications

Strengthening Effect of Nb on Ferrite Grain Boundary in X70 Pipeline Steel

Strengthening Effect of Nb on Ferrite Grain Boundary in X70 Pipeline Steel

Strain aging on the yield strength to tensile strength ratio of UOE pipe

Innovative analysis of Luders band behaviour in X80 pipeline steel

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