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Dong Hyuk Shin - One of the best experts on this subject based on the ideXlab platform.
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fatigue properties of ultrafine Grained low carbon Steel produced by equal channel angular pressing
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Hokyung Kim, Myungil Choi, Chinsung Chung, Dong Hyuk ShinAbstract:Abstract Ultrafine Grained low carbon (0.15 wt.% C) Steel produced by equal channel angular pressing (ECAP) was tested for investigating fatigue properties, including cyclic softening and crack growth rate. Emphasis was placed on investigating the effect of load ratio on the fatigue crack growth rates of ultrafine Grained microstructure. The ECAPed Steel exhibited cyclic softening. After the first cycle, the tension and compression peak stresses decreased gradually with the number of cycles. Fatigue crack growth resistance and the threshold of ECAPed ultrafine Grained Steel were lower than that of an as-received coarse Grained Steel. This was attributed to a less tortuous crack path. The ECAPed Steel exhibited slightly higher crack growth rates and a lower Δ K th with an increase in R ratio. The R ratio effect on growth rates and Δ K th was basically indistinguishable at a lower load ratio ( R >0.3) compared with other alloys, indicating that the contribution of the crack closure vanished. This was explained by the fact that finer Grained materials produce a lower opening load P op due to a relatively less serrated crack path. Consequently, K min can reach K op readily with a smaller increment of load ratio. The crack growth rate curve for the ECAPed ultrafine Grained Steel exhibited a linear extension to the lower growth rate regime than that for the coarse Grained as-received Steel. This behavior can be explained by a reverse crack tip plastic zone size ( r p ) that is always larger than the grain size.
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Plastic flow characteristics of ultrafine Grained low carbon Steel during tensile deformation
Metals and Materials International, 2001Co-Authors: Dong Hyuk ShinAbstract:In order to explain steady-state plastic deformation, i.e. the absence of strain hardening in ultrafine Grained low carbon Steel during tensile deformation, Steel of different ferrite grain sizes was prepared by intense plastic straining followed by static annealing and then tensile-tested at room temperature. A comparison between the ferrite grain size of ultrafine Grained Steel and the dislocation cell size of coarse Grained Steel formed during tensile deformation revealed that uniform dislocation distribution with high density and cell formation were unlikely to occur in this ultrafine Grained Steel. This is ascribed to the fact that the ultrafine grain size is comparable to or smaller than the cell size at the corresponding stress level. In addition, from a consideration of dynamic recovery, it was found that the characteristic time for trapped lattice dislocations to spread into the grain boundaries was so fast that the accumulation of lattice dislocation causing strain hardening could not occur under this ultrafine grain size condition. Therefore, the extremely low strain hardening rate of ultrafine Grained low carbon Steel during tensile deformation is attributed to the combined effects of the two main factors described above.
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thermal stability and mechanical properties of ultrafine Grained low carbon Steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000Co-Authors: Kyungtae Park, Yongseog Kim, Jung Guk Lee, Dong Hyuk ShinAbstract:Ultrafine Grained low carbon Steel manufactured by equal channel angular pressing was annealed at 753 K, where negligible grain growth occurred, up to 72 h and the microstructural change and the mechanical properties were examined. This investigation was aimed at providing the guiding information for the effective use of ultrafine Grained low carbon Steel manufactured by severe plastic deformation processes. Under the present annealing conditions, the microstructural change was dominated by recovery. The tensile behavior of annealed ultrafine Grained Steel was characterized by much higher strength and the absence of strain hardening compared with that of large Grained Steel. In addition, the present ultrafine Grained Steel became mechanically stable by 24 h annealing treatment although recovery was in progress. The microstructure of the deformed sample of annealed ultrafine Grained Steel exhibited the elongated grains and dislocations distributed densely in the vicinity of grain boundaries. This finding indicated that dynamic recovery during deformation was associated with the absorption of dislocation by grain boundaries. The mechanical behavior of the present ultrafine Grained low carbon Steel was discussed in light of the recent development explaining that of nanocrystalline materials, i.e. the dislocation bow-out mechanism for high strength and the spreading kinetics of trapped lattice dislocation into grain boundary for the absence of strain hardening.
Raja Devesh Kumar Misra - One of the best experts on this subject based on the ideXlab platform.
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relationship of grain size and deformation mechanism to the fracture behavior in high strength high ductility nanostructured austenitic stainless Steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Raja Devesh Kumar Misra, Veerabhadra Swamy Challa, Mahesh C. Somani, Lawrence E MurrAbstract:Abstract In this study we underscore the dependence of grain structure and deformation mechanism on the fracture behavior in a high strength–high ductility bearing nanoGrained/ultrafine-Grained austenite stainless Steel. In high strength nanoGrained Steel, deformation twinning contributed to excellent ductility, while in the low strength coarse-Grained Steel, the high ductility is attained as a consequence of strain-induced martensite transformation. Interestingly, the differences in deformation mechanism of Steels deformation mechanisms of Steels with different grain structures but with similar elongations influenced the mode of fracture, a behavior that is governed by the change in austenite stability with grain size. The areal density of voids and their average diameter in the fracture surface also increased with increasing grain size, which ranged from 320 nm to 22 μm.
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Significance of interplay between austenite stability and deformation mechanisms in governing three-stage work hardening behavior of phase-reversion induced nanoGrained/ultrafine-Grained (NG/UFG) stainless Steels with high strength-high ductility com
Scripta Materialia, 2014Co-Authors: Veerabhadra Swamy Challa, Mahesh C. Somani, Raja Devesh Kumar MisraAbstract:In the context of obtaining high strength-high ductility combination in nanoGrained/ultrafine-Grained austenitic stainless Steels, we underscore the dependence of grain structure and deformation mechanism. In high strength nanoGrained/ultrafine-Grained Steel, deformation twinning contributed to the excellent ductility and high strain hardening rate, while in the low strength coarse-Grained Steel, ductility and strain hardening ability was also good, but due to strain-induced martensite. The change in deformation mechanism with grain size is attributed to austenite stability-strain energy relationship.
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Fatigue behavior of ultrafine-Grained and coarse-Grained Cr–Ni austenitic stainless Steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: A.s. Hamada, P.k.c. Venkata Surya, Raja Devesh Kumar MisraAbstract:Abstract High-cycle bending fatigue behavior of an ultrafine-Grained Cr–Ni Type 301LN austenitic stainless Steel, obtained by reversion annealing, was investigated and compared to that of the conventional coarse-Grained counterpart. The fatigue limit was significantly increased from 350 MPa to 630 MPa, reaching 59% of the tensile strength, a behavior attributed to grain refinement. Fatigue cycling resulted in hardness increments that were very different between these structures; in the coarse-Grained Steel 47%, but only 6–10% in the ultrafine-Grained Steel. The fatigue damage was observed to occur by grain boundary cracking in the ultrafine-Grained Steel, while mostly by slip band formation and crack propagation along these slip bands and grain boundaries in the coarse-Grained counterpart. Dislocation structures observed reflected these pronounced differences in the cyclic behavior.
Kaneaki Tsuzaki - One of the best experts on this subject based on the ideXlab platform.
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Matrix strength evaluation of ultra-fine Grained Steel by nanoindentation
Journal of Materials Research, 2004Co-Authors: Takahito Ohmura, Kaneaki Tsuzaki, Nobuhiro Tsuji, Naoya KamikawaAbstract:Nanoindentation was performed to evaluate the matrix strength of the ultra-fine Grained Steel produced by accumulative roll-bonding and subsequently annealed. The nanohardness, associated with the matrix strength, decreases with increasing annealing temperature. Because the matrix strength corresponds to the first term σ 0 of the Hall-Petch relation, this result suggests that the σ 0 might not be constant for these Steels between various grain sizes. Therefore, it is suggested that the change of the macroscopic strength during annealing is dominated by not only the grain coarsening leading to a reduction of grain refinement strengthening, but also the softening of the matrix strength.
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Thermal stability of ultra fine-Grained Steel containing dispersed oxides
Scripta Materialia, 2001Co-Authors: Andrey Belyakov, Y. Sakai, Toru Hara, Yuji Kimura, Kaneaki TsuzakiAbstract:Abstract Annealing behaviour of an ultra fine-Grained Steel was studied at temperatures of T=600–900 ° C. At T⩽800 ° C, recovery develops more readily at grain boundaries as compared to grain interiors, leading to a fast release of lattice distortions associated with the non-equilibrium state of grain boundaries.
Veerabhadra Swamy Challa - One of the best experts on this subject based on the ideXlab platform.
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relationship of grain size and deformation mechanism to the fracture behavior in high strength high ductility nanostructured austenitic stainless Steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Raja Devesh Kumar Misra, Veerabhadra Swamy Challa, Mahesh C. Somani, Lawrence E MurrAbstract:Abstract In this study we underscore the dependence of grain structure and deformation mechanism on the fracture behavior in a high strength–high ductility bearing nanoGrained/ultrafine-Grained austenite stainless Steel. In high strength nanoGrained Steel, deformation twinning contributed to excellent ductility, while in the low strength coarse-Grained Steel, the high ductility is attained as a consequence of strain-induced martensite transformation. Interestingly, the differences in deformation mechanism of Steels deformation mechanisms of Steels with different grain structures but with similar elongations influenced the mode of fracture, a behavior that is governed by the change in austenite stability with grain size. The areal density of voids and their average diameter in the fracture surface also increased with increasing grain size, which ranged from 320 nm to 22 μm.
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Significance of interplay between austenite stability and deformation mechanisms in governing three-stage work hardening behavior of phase-reversion induced nanoGrained/ultrafine-Grained (NG/UFG) stainless Steels with high strength-high ductility com
Scripta Materialia, 2014Co-Authors: Veerabhadra Swamy Challa, Mahesh C. Somani, Raja Devesh Kumar MisraAbstract:In the context of obtaining high strength-high ductility combination in nanoGrained/ultrafine-Grained austenitic stainless Steels, we underscore the dependence of grain structure and deformation mechanism. In high strength nanoGrained/ultrafine-Grained Steel, deformation twinning contributed to the excellent ductility and high strain hardening rate, while in the low strength coarse-Grained Steel, ductility and strain hardening ability was also good, but due to strain-induced martensite. The change in deformation mechanism with grain size is attributed to austenite stability-strain energy relationship.
Jose María Cabrera - One of the best experts on this subject based on the ideXlab platform.
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Tensile and compressive test in nanocrystalline and ultrafine carbon Steel
Journal of Materials Science, 2010Co-Authors: R. Rodríguez-baracaldo, J. A. Benito, Jose María CabreraAbstract:Plastic deformation behavior was investigated in near fully dense nanostructured and ultrafine-Grained bulk samples of carbon Steel (0.55 wt% C) under compression and tension tests. The specimens were obtained by hot pressure from mechanically milled powder at 400 and 500 °C. Subsequent heat treatments at temperatures going from 600 to 900 °C produced samples with ferrite grain sizes from 30 nm to 17 μm. Nanocrystalline Grained Steel samples presented very high strength with low ductility. Once, in the ultrafine range, as the ferritic grain size was increased, the strength was decreased and the ductility was improved. The porosity and carbon atoms within the structure were analyzed in order to explain the results of strength and strain obtained.
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Microstructural evolution and mechanical response of nanocrystalline and ultrafine-Grained Steel obtained by mechanical milling
Materials Science and Engineering: A, 2008Co-Authors: R. Rodríguez-baracaldo, J. A. Benito, Jose María Cabrera, Robert Tejedor, Jose Manuel PradoAbstract:High dense bulk specimens of 0.55% C Steel with ferrite grain sizes in the nanocrystalline and ultrafine regimes have been produced by a warm consolidation process from ball-milled iron powder and subsequent heat treatments. The resulting microstructure was investigated and related to the mechanical behavior studied by uniaxial compression tests. It was found that the samples containing nanocrystalline ferrite presented very high strength with low ductility. As the ferrite grain size increased to the ultrafine regime, larger cementite particles appeared inside ferrite grains and along the grain boundaries. As a consequence, the amount of strain hardening and total plastic strain increased and the maximum strength diminished. With a consolidation temperature of 500 °C and a heat treatment temperature of 775 °C, an average ferritic grain size of 0.85 μm was obtained. This Steel showed a yield strength of 1070 MPa and strain hardening up to a plastic strain of 31%.
