| 1. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Fe and Cr phase separation in super and hyper duplex stainless steel plates and welds after very short aging times
- 2021
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Ingår i: Materials & design. - : Elsevier Ltd. - 0264-1275 .- 1873-4197. ; 210
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Tidskriftsartikel (refereegranskat)abstract
- Fe and Cr phase separation in ferrite, causing 475°C-embrittlement, was studied after very short aging times in super duplex stainless steel (SDSS) and hyper duplex stainless steel (HDSS) plates and welds. Atom probe tomography showed that hot-rolled SDSS, experiencing significant metal working, had faster kinetics of phase separations compared to the SDSS and HDSS welds after 5 min aging at 475 °C. The surface of the 33-mm SDSS plate had faster Fe and Cr phase separation and larger toughness drop. A higher density of dislocations next to the austenite phase boundary in ferrite, detected by electron channeling contrast, can promote the phase separation at the surface of the plate with lower austenite spacing. The toughness dropped in HDSS welds after aging, but SDSS welds maintained their toughness. An inverse simulation method considering an initial sinusoidal nanometric Cr and Fe fluctuation showed that Ni increases the interdiffusion of Cr in the system, resulting a higher degree of phase separation in SDSS welds than the HDSS weld. Within the composition range of the studied SDSS and HDSS materials, the processing influences the Fe and Cr phase separation more than the variation in composition during short aging or typical fabrication times.
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| 2. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Influence of Fabrication Route and Copper Content on Nature and Kinetics of 475 °C- Embrittlement in Cu-Containing Super Duplex Stainless Steels
- 2023
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Ingår i: Steel Research International. - 1611-3683 .- 1869-344X. ; 4, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The influence of hot-rolling, hot isostatic pressing (HIP), welding, as well as copper content on 475 °C-embrittlement is studied in super duplex stainless steels. The as-received samples are solution annealed and quenched. Then, to study the kinetics and nature of phase transformations during fabrication, the samples are aged for a very short duration of 5 min at 475 °C. Atom probe tomography results reveal that the processes involving more plastic deformation such as hot rolling and HIP accelerate chromium and iron phase separation and cause precipitation of copper-rich particles (CRPs) in ferrite, resulting in significant toughness loss. In contrast, the weld does not show a high level of chromium and iron phase separation or CRPs precipitation, preserving its toughness after the short aging. The experiment and the inverse interdiffusion calculations reveal that raising the copper content slow down chromium and iron phase separation but significantly increase the CRP number density and decrease the toughness of the HIPed material. Precipitation simulation of CPRs show that the model must be modified based on each processing condition. It is concluded that hot rolling and HIP accelerate 475 °C-embrittlement, which cannot be prevented by raising the copper content.
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| 3. |
- Hosseini, Vahid, 1987-, et al.
(författare)
-
Precipitation kinetics of Cu-rich particles in super duplex stainless steels
- 2021
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Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854 .- 2214-0697. ; 15, s. 3951-3964
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Tidskriftsartikel (refereegranskat)abstract
- Complex precipitation behavior of Cu-rich particles (CRPs) was investigated and simulated in continuously cooled and quench-aged super duplex stainless steel. Atom probe tomography (APT) and scanning electron microscopy showed that slow cooling resulted in nonuniform multimodal CRP precipitation and spinodal decomposition, while in the fast cooled and quench-aged conditions, more uniform precipitation of CRPs with no visible spinodal decomposition was found. Depletion of Cu, Ni, and Mn was observed in the ferrite next to the CRPs during growth, but not during dissolution. Some evidence of Ostwald ripening was seen after slow cooling, but in the quench-aged condition, particle coalescence was observed. Large CRPs disappeared next to a ferrite–austenite phase boundary after slow cooling when Cu was depleted due to the diffusion to austenite as also predicted by moving boundary Dictra simulation. Comparing Cu depleted areas next to CRPs analyzed by APT and moving boundary Dictra simulation of CRP–ferrite showed that the effective Cu diffusion coefficient during the early-stage precipitation was about 300 times higher than the Cu diffusion coefficient in ferrite at 475 °C. Using the effective diffusion coefficient and a size-dependent interfacial energy equation, CRP size distribution was successfully predicted by the Langer–Schwartz model implemented in Thermo-Calc Prisma. Applying a short aging time and continuous cooling increased the hardness and decreased the toughness values compared to the solution annealed condition. A nonuniform distribution of Cu in ferrite, the duplex structure, and partitioning of alloying elements among different phases are factors making CRP precipitation in duplex stainless steels complex.
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