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Arthur H Heuer - One of the best experts on this subject based on the ideXlab platform.
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colossal interstitial supersaturation in Delta Ferrite in stainless steels ii low temperature nitridation of the 17 7 ph alloy
Acta Materialia, 2017Co-Authors: Danqi Wang, F Ernst, H Kahn, Arthur H HeuerAbstract:Abstract Low-temperature gas-phase nitridation has been studied in interstitially-hardened 17-7 precipitation-hardening stainless steel. After nitridation, conventional transmission electron microscopy reveals that Delta Ferrite grains in such alloys show a uniform weak diffraction contrast. Chemical analysis reveals that the weak-contrast Ferrite grains contain an enormous interstitial nitrogen supersaturation (>20 at.%). Surprisingly, there is no significant tetragonality in these weak-contrast Ferrite grains. Such weak diffraction contrast is attributed to a nanometer-scale nitridation-induced spinodal decomposition of Delta Ferrite grains. In addition, nitride nanoparticles are observed in the steel, and were identified as rocksalt-structured MN nitride (M: Fe, Cr, Ni, and Al). Further, platelets of hexagonal M 2 N 1- x are observed at low nitriding temperatures (623 and 653 K), but were absent during nitridation at a higher temperature (713 K).
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colossal interstitial supersaturation in Delta Ferrite in stainless steels i low temperature carburization
Acta Materialia, 2015Co-Authors: Danqi Wang, Reza Sharghimoshtaghin, F Ernst, H Kahn, C W Chen, J C Dalton, Fan Yang, Richard E A Williams, David W Mccomb, Arthur H HeuerAbstract:Abstract Low-temperature carburization has been successfully used to surface harden 17-7 precipitation-hardening (PH) and 2205 duplex stainless steels. After carburization, the Delta Ferrite grains in both alloys near the free surface show a uniform weak contrast under conventional transmission electron microscopy (TEM). Spatially resolved compositional analysis shows that these Delta Ferrite grains possess enormous carbon contents (as high as 18 at.%) in solid solution, but structurally there is no detectable tetragonality (
Danqi Wang - One of the best experts on this subject based on the ideXlab platform.
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colossal interstitial supersaturation in Delta Ferrite in stainless steels ii low temperature nitridation of the 17 7 ph alloy
Acta Materialia, 2017Co-Authors: Danqi Wang, F Ernst, H Kahn, Arthur H HeuerAbstract:Abstract Low-temperature gas-phase nitridation has been studied in interstitially-hardened 17-7 precipitation-hardening stainless steel. After nitridation, conventional transmission electron microscopy reveals that Delta Ferrite grains in such alloys show a uniform weak diffraction contrast. Chemical analysis reveals that the weak-contrast Ferrite grains contain an enormous interstitial nitrogen supersaturation (>20 at.%). Surprisingly, there is no significant tetragonality in these weak-contrast Ferrite grains. Such weak diffraction contrast is attributed to a nanometer-scale nitridation-induced spinodal decomposition of Delta Ferrite grains. In addition, nitride nanoparticles are observed in the steel, and were identified as rocksalt-structured MN nitride (M: Fe, Cr, Ni, and Al). Further, platelets of hexagonal M 2 N 1- x are observed at low nitriding temperatures (623 and 653 K), but were absent during nitridation at a higher temperature (713 K).
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colossal interstitial supersaturation in Delta Ferrite in stainless steels i low temperature carburization
Acta Materialia, 2015Co-Authors: Danqi Wang, Reza Sharghimoshtaghin, F Ernst, H Kahn, C W Chen, J C Dalton, Fan Yang, Richard E A Williams, David W Mccomb, Arthur H HeuerAbstract:Abstract Low-temperature carburization has been successfully used to surface harden 17-7 precipitation-hardening (PH) and 2205 duplex stainless steels. After carburization, the Delta Ferrite grains in both alloys near the free surface show a uniform weak contrast under conventional transmission electron microscopy (TEM). Spatially resolved compositional analysis shows that these Delta Ferrite grains possess enormous carbon contents (as high as 18 at.%) in solid solution, but structurally there is no detectable tetragonality (
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NiAl precipitation in Delta Ferrite grains of 17-7 precipitation-hardening stainless steel during low-temperature interstitial hardening
Scripta Materialia, 2015Co-Authors: Danqi Wang, H Kahn, Frank Ernst, A.h. HeuerAbstract:Abstract Interstitial hardening via low-temperature carburization and nitridation has been studied in 17-7 precipitation-hardening stainless steel. During such interstitial hardening, nanometer-scale NiAl precipitates form in Delta Ferrite in the bulk, but not in the hardened surface layer. In the carburized Ferrite grains, regions of NiAl stoichiometry could be identified, but cannot be identified as regions with a different crystal structure. In the nitrided grains, NiAl particles could neither be detected by corresponding changes in local composition nor by their crystal structure.
H Kahn - One of the best experts on this subject based on the ideXlab platform.
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colossal interstitial supersaturation in Delta Ferrite in stainless steels ii low temperature nitridation of the 17 7 ph alloy
Acta Materialia, 2017Co-Authors: Danqi Wang, F Ernst, H Kahn, Arthur H HeuerAbstract:Abstract Low-temperature gas-phase nitridation has been studied in interstitially-hardened 17-7 precipitation-hardening stainless steel. After nitridation, conventional transmission electron microscopy reveals that Delta Ferrite grains in such alloys show a uniform weak diffraction contrast. Chemical analysis reveals that the weak-contrast Ferrite grains contain an enormous interstitial nitrogen supersaturation (>20 at.%). Surprisingly, there is no significant tetragonality in these weak-contrast Ferrite grains. Such weak diffraction contrast is attributed to a nanometer-scale nitridation-induced spinodal decomposition of Delta Ferrite grains. In addition, nitride nanoparticles are observed in the steel, and were identified as rocksalt-structured MN nitride (M: Fe, Cr, Ni, and Al). Further, platelets of hexagonal M 2 N 1- x are observed at low nitriding temperatures (623 and 653 K), but were absent during nitridation at a higher temperature (713 K).
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colossal interstitial supersaturation in Delta Ferrite in stainless steels i low temperature carburization
Acta Materialia, 2015Co-Authors: Danqi Wang, Reza Sharghimoshtaghin, F Ernst, H Kahn, C W Chen, J C Dalton, Fan Yang, Richard E A Williams, David W Mccomb, Arthur H HeuerAbstract:Abstract Low-temperature carburization has been successfully used to surface harden 17-7 precipitation-hardening (PH) and 2205 duplex stainless steels. After carburization, the Delta Ferrite grains in both alloys near the free surface show a uniform weak contrast under conventional transmission electron microscopy (TEM). Spatially resolved compositional analysis shows that these Delta Ferrite grains possess enormous carbon contents (as high as 18 at.%) in solid solution, but structurally there is no detectable tetragonality (
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NiAl precipitation in Delta Ferrite grains of 17-7 precipitation-hardening stainless steel during low-temperature interstitial hardening
Scripta Materialia, 2015Co-Authors: Danqi Wang, H Kahn, Frank Ernst, A.h. HeuerAbstract:Abstract Interstitial hardening via low-temperature carburization and nitridation has been studied in 17-7 precipitation-hardening stainless steel. During such interstitial hardening, nanometer-scale NiAl precipitates form in Delta Ferrite in the bulk, but not in the hardened surface layer. In the carburized Ferrite grains, regions of NiAl stoichiometry could be identified, but cannot be identified as regions with a different crystal structure. In the nitrided grains, NiAl particles could neither be detected by corresponding changes in local composition nor by their crystal structure.
Binhan Sun - One of the best experts on this subject based on the ideXlab platform.
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revealing fracture mechanisms of medium manganese steels with and without Delta Ferrite
Acta Materialia, 2019Co-Authors: Binhan Sun, Dhanalakshmi Palanisamy, Dirk Ponge, Baptiste Gault, Fateh Fazeli, Colin Scott, S Yue, Dierk RaabeAbstract:Abstract Medium Mn steels possess a composite like microstructure containing multiple phase constituents like metastable austenite, Ferrite, δ-Ferrite and α′-martensite with a wide range of fractions for each constituent. The high mechanical contrast among them and the deformation-driven evolution of the microstructure lead to complex fracture mechanisms. Here we investigate tensile fracture mechanisms of medium Mn steels with two typical types of microstructures. One group consists of Ferrite (α) plus austenite (γ) and the other one of a layered structure with an austenite-Ferrite constituent and δ-Ferrite. Samples with the first type of microstructure show a dimple-type fracture due to void formation primarily at the Ferrite/strain-induced α′-martensite (α′) interfaces. In contrast, the fracture surface of δ-Ferrite containing steels shows a combination of cleavage in δ-Ferrite and dimple/quasi-cleavage zones in the γ-α (or γ/α′-α) constituent. The embrittlement of δ-Ferrite is due to the formation of B2 ordered phase. Failure of these samples is govern by crack initiation related to δ-Ferrite and crack-arresting ability of the γ-α layers. Austenite stability is critical for the alloys' fracture resistance, in terms of influencing void growth and coalescence for the first type of microstructure and crack initiation and termination for the microstructure containing δ-Ferrite. This effect is here utilized to increase ductility and toughness. By tailoring austenite stability towards higher fracture resistance, the total elongation of δ-Ferrite containing steels increases from ∼13% to ∼33%. This approach opens a new pathway towards an austenite-stability-controlled microstructural design for substantially enhanced damage tolerance in steels containing metastable austenite and δ-Ferrite.
Chong Soo Lee - One of the best experts on this subject based on the ideXlab platform.
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dissolution kinetics of Delta Ferrite in aisi 304 stainless steel produced by strip casting process
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Selim Kim, H. K. Moon, Taewook Kang, Chong Soo LeeAbstract:Abstract Strip casting process has been developed to manufacture thin steel strip, 2–4 mm thick, directly from molten metal fed in between two water-cooled casting rolls, and is being applied to the industrial steelmaking plants. The cast strip contains typically 2–6% Delta Ferrite in the microstructure at room temperature. This work studied the dissolution kinetics of Delta Ferrite in strip cast specimen in the temperature range of 1050–1200 °C by varying the annealing time. The morphology of Delta Ferrite in the cast strip was a vermicular type with a three-dimensional honeycomb network structure. At the early stage of Delta Ferrite dissolution, more than 50% of Delta Ferrite dissolved very rapidly regardless of annealing temperature. The rapid dissolution was mainly attributed to the excess Cr depletion in the Delta Ferrite resulting from the (Fe, Cr) carbide precipitation at interface boundary between Delta Ferrite and austenite phases. Subsequently, the dissolution was controlled by volume diffusion of Cr and Ni in the austenite phase. The analytical solution assuming the austenite phase as semi-infinite was successfully applied for the analysis of experimental data at 1150 °C. The activation energy for the dissolution was measured as 251.4 kJ mol−1, which is consistent with activation energy for volume diffusion of Cr.