Quantitative analysis of grain boundaries in carbon- and nitrogen-added ferritic steels by atom probe tomography

Takahashi, Jun; Kawakami, Kazuto; Ushioda, Kohsaku; Takaki, Setsuo; Nakata, Nobuo; Tsuchiyama, Toshihiro

doi:10.1016/j.scriptamat.2011.10.026

Cited by 48 publications

(26 citation statements)

References 12 publications

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“…They thought that this was because grain boundary ledges were suppressed to act as dislocation sources by grain boundary segregation of carbon, based on the grain boundary ledge mechanism for explaining HallPetch relationship by Li,4) although no evidence of grain boundary segregation and no evidence supporting that the grain boundary ledges were the main dislocation sources in the materials were shown. 6) Takahashi et al 7) carried out 3-dimensional atom-probe analysis of the pure irons used in Ref. 6) and confirmed segregation of carbon and nitrogen atoms at grain boundaries.…”

Section: Resultsmentioning

confidence: 96%

“…They also discussed a significant difference between carbon and nitrogen in the effects on HallPetch slope (if the grain boundary segregation really controlled k y ), but the reason of the difference was unclear. 6,7) According to the grain boundary ledge model, if the carbon content is constant in the material, a decrease in k y is expected by grain refinement because the density of carbon on the grain boundary decreases with increasing the grain boundary area per unit volume (i.e., with decreasing the mean grain size). Such a decreasing in k y by grain refinement (in the range of several hundred nm to several µm) has not been found in any previous experiments, but an extra hardening has rather been reported in ultrafine grained materials.…”

Section: Resultsmentioning

confidence: 99%

“…On the other hand, recently Takeda et al 6,7) revealed that the k y significantly decreased with decreasing the carbon content from 56 to 4 mass ppm in pure irons. Furthermore, it has been found that the k y of ultra-low carbon interstitial free (IF) steels, in which solute interstitial atoms (C and N) are scavenged by Ti and Nb through forming carbides and nitrides, is very small around 120 MPa·µm 1/2 .…”

Section: )mentioning

confidence: 93%

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Correlation between Continuous/Discontinuous Yielding and Hall–Petch Slope in High Purity Iron

et al. 2014

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High purity iron specimens containing 11 ppm carbon and 8 ppm nitrogen with different grain sizes were fabricated by cold rolling and subsequent annealing. It was found that the specimens exhibited entirely different yielding behavior in tensile tests depending on different cooling processes after annealing. The water-cooled specimens exhibited continuous yielding while the air-cooled ones exhibited discontinuous yielding. It was found that the HallPetch slope, k y , significantly changed depending on the different yielding behaviors.

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Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

Section: )mentioning

confidence: 93%

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Correlation between Continuous/Discontinuous Yielding and Hall–Petch Slope in High Purity Iron

et al. 2014

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“…Figure 12 displays the results of three-dimensional (3D) atom probe analysis showing the amount of C and N segregated at the grain boundaries in FeC and FeN alloys. 27) Each specimen was prepared to have the same atomic fraction of C or N, 0.02 at%, and it was confirmed that the amount of solute C and N was 0.0019 at% in both specimens. However, apparent differences can be seen between carbon and nitrogen in terms of grain-boundary segregation behavior, in that carbon has an approximately 34 times greater segregation potential.…”

Section: Grain-boundary Segregation Of Carbon and Nitrogenmentioning

confidence: 91%

Effect of Grain Boundary Segregation of Interstitial Elements on Hall–Petch Coefficient in Steels

et al. 2014

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The yielding behavior of interstitial-free steels and low-carbon steels with varying amounts of C and N were investigated in connection with the HallPetch relation. The HallPetch coefficient is as small as 150 MPa·µm 1/2 in interstitial-free steels but it increases to 600 MPa·µm 1/2 by adding solute carbon up to 60 ppm. Nitrogen does not have a significant effect on the HallPetch coefficient. The results of three-dimensional (3D) atom probe analysis indicated that carbon has 34 times greater segregation potential in comparison with nitrogen. The small effect of nitrogen on the HallPetch coefficient in steel is probably due to the small segregation potential of nitrogen. It was also confirmed that discontinuous yielding occurs when the difference between the yield stress and friction stress is increased by grain-refinement strengthening and that yielding occurs by dislocation emission from grain boundaries where primary dislocations have piled up. Carbon atoms segregated at grain boundaries seem to play a role in stabilizing dislocation emission sites at the grain boundaries, which enhances the HallPetch coefficient of iron. These results support the dislocation pile-up model of explaining yielding in polycrystalline metals.

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“…Furthermore, it is recently revealed that the segregation of alloy elements, such as C, N and Ni, at grain boundary can raise the yield strength up by increase of stress for generating dislocation from grain boundaries. 19,20) The effect of the segregation at the grain boundary to the strength at high temperature is also should be taken into account, but will be discussed in the future.…”

Section: The Influence Of Nbc(n) Clustersmentioning

confidence: 99%

High Temperature Tensile Properties and Its Mechanism in Low-Carbon Nb-Bearing Steels

et al. 2014

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The aim of this study is to clarify the high-temperature strengthening mechanism of Nb-bearing ultra-low carbon steel, which is wellknown as superior steel for high-temperature applications. Observations by Three-dimensional Atom Probe (3DAP) suggested that the Nb atoms are either distributed in a solid solution within the grain or segregated at the grain boundary after hot-rolling. The strength at 600°C increases significantly upon addition of Nb, and the corresponding dominant strengthening mechanism is considered to consist of the following: the resistance for the dislocation gliding motion due to solute Nb, the retardation of the dislocation climbing-up motion due to solute Nb and NbC dipoles, and the resistance of the dislocation motion caused by the NbC(N) clusters formed when the materials are heated up to 600°C within 10 s and then held for 600 s. Further, compared with Nb-free steel or 0.1% Nb-bearing steel, 0.3% Nb-bearing steel has considerably reduced ductility at 600°C. This is attributed to the retardation of recovery due to the Nb addition. TEM observations imply that the dynamic recovery takes place easily during the tensile deformation at 600°C in Nb-free steel or 0.1% Nb-bearing steel, whereas the tensile stress increases significantly because of the work hardening presumably caused by the retardation of the restoration process by further addition of Nb. Hence, a rupture followed by necking is thought to occur easily. Moreover, there is a possibility that the segregated Nb at the ferrite grain boundary might affect the dislocation behavior resulting in an increase in the steel strength at a high temperature and a retardation of the recovery process. This possibility will be investigated in a future work.

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Quantitative analysis of grain boundaries in carbon- and nitrogen-added ferritic steels by atom probe tomography

Cited by 48 publications

References 12 publications

Correlation between Continuous/Discontinuous Yielding and Hall–Petch Slope in High Purity Iron

Correlation between Continuous/Discontinuous Yielding and Hall–Petch Slope in High Purity Iron

Effect of Grain Boundary Segregation of Interstitial Elements on Hall–Petch Coefficient in Steels

High Temperature Tensile Properties and Its Mechanism in Low-Carbon Nb-Bearing Steels

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Quantitative analysis of grain boundaries in carbon- and nitrogen-added ferritic steels by atom probe tomography

Cited by 48 publications

References 12 publications

Correlation between Continuous/Discontinuous Yielding and Hall&ndash;Petch Slope in High Purity Iron

Correlation between Continuous/Discontinuous Yielding and Hall&ndash;Petch Slope in High Purity Iron

Effect of Grain Boundary Segregation of Interstitial Elements on Hall&ndash;Petch Coefficient in Steels

High Temperature Tensile Properties and Its Mechanism in Low-Carbon Nb-Bearing Steels

Contact Info

Product

Resources

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Correlation between Continuous/Discontinuous Yielding and Hall–Petch Slope in High Purity Iron

Correlation between Continuous/Discontinuous Yielding and Hall–Petch Slope in High Purity Iron

Effect of Grain Boundary Segregation of Interstitial Elements on Hall–Petch Coefficient in Steels