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<div class="csl-entry">Jacob, A. A. F., Schuster, R., & Povoden-Karadeniz, E. (2022, May 23). <i>Exploring the formation mechanism of σ phase in hyper duplex steels by in-situ experiments and computation</i> [Conference Presentation]. Calphad XLIX International Conference on Computer Coupling of Phase Diagrams and Thermochemistry, Stockholm, Sweden.</div>
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dc.identifier.uri
http://hdl.handle.net/20.500.12708/137051
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dc.description.abstract
In contrast to previous suggestions of eutectoid σ phase formation in hyperduplex stainless steel (HDSS), our recent thermodynamic modeling of the multicomponent Fe-Cr-Mo-Mn-Ni [1] prove the σ phase formation to be monovariant. Further investigation by kinetic simulation [2] with Matcalc [3] using Mean Field approach allow us to find out that the formation of σ phase in hyperduplex stainless steel is most likely associated to the segregation of elements at grain boundaries.
In order to further understand the mechanism of the early stage precipitation of σ phase in HDSS, the time-temperature-precipitation behavior of σ phase was analyzed by in-situ XRD was. It was found that the precipitation of σ phase occurs after only few seconds of aging and there is a very fast growth of the phase at the expense of ferrite. This was confirmed by short term annealing experiments using dilatometry, and subsequent microanalysis by FESEM-EDX.
The role of moving boundary for the fast phase evolution kinetics in HDSS was tested with Dictra. It is seen that the mobility of elements plays a major role by enriching the grain boundaries of ferrite/austenite. Due to the accumulation of favorable elements for σ phase, its nucleation and growth along the boundaries is favored. Moreover, ferrite, as pool for σ phase stabilizing elements, feeds the σ phase evolution until its complete dissolution. Simulation shows appearance of σ phase within a couple of seconds. Its formation is already complete after 5 min at the nose temperature of T=900°C.
[1] A. Jacob, E. Povoden-Karadeniz, Calphad 71 (2020) 101810.
[2] A. Jacob, E. Povoden-Karadeniz, Calphad 71 (2020) 101998.
[1] Kozeschnik, Ernst. (2022) "Mean-Field Microstructure Kinetics Modeling". In: Francisca G. Caballero (ed.), Encyclopedia of Materials: Metals and Alloys. vol. 4, pp. 521–526. Oxford: Elsevier.
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dc.language.iso
en
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dc.subject
Calphad
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dc.subject
Diffusion
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dc.subject
Precipitation
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dc.title
Exploring the formation mechanism of σ phase in hyper duplex steels by in-situ experiments and computation