Computer modeling of a temperature field and a solid phase fraction in casted billets is the base of any numerical simulation of the continuous casting technology. Temperature distribution in an ingot longitudinal and cross section for the same technological parameters is a function of solidification rate and rate of the solidification heat release. Nucleation rate and solid grain growth velocity depend on a melt undercooling below the liquidus temperature, and consequently depend on a temperature value. The results of the primary grain growth and temperature distribution modeling are presented for the square steel continuous casting 160×160 mm produced by CELSA Steel Works in Ostrowiec. For the modeling the ProCAST R software was used. Virtual structure of primary grains in the continuous ingot cross section was compared with a structure of a real ingot.Keywords: ProCAST, structure, solidification, continuous casting, modelingPodstawą modelowania matematycznego procesu ciągłego odlewania stali (COS) jest symulacja komputerowa pola temperatury i składu fazowego w obszarze wlewka. Rozkład temperatury wzdłuż wlewka i w jego przekroju przy zadanych parametrach odlewania zależy m.in. od intensywności przemiany fazowej, której towarzyszy wydzielanie się ciepła krystalizacji. Szybkości zarodkowania i wzrostu ziaren fazy stałej z ciekłej stali są uzależnione od jej przechłodzenia poniżej temperatury likwidus, a więc, w sposób pośredni od wartości temperatury. W pracy przedstawiono wyniki modelowania pola temperatury i procesu tworzenia się struktury pierwotnej stali B500 SP podczas krzepnięcia wlewka ciągłego o przekroju 160×160 mm, odlewanego w warunkach CELSA HUTA OSTROWIEC. Do celów modelowania wykorzystano oprogramowanie ProCAST. Uzyskaną w symulacji strukturę ziaren pierwotnych w przekroju poprzecznym skonfrontowano z wynikami badań struktury rzeczywistej przekroju poprzecznego wlewków kwadratowych. Mathematical modeling of the continuous casting solidificationIn the earlier papers about the heat transfer in a continuous casting ingot the numerical solutions of the Fourier (or Fourier-Kirchhoff) partial differential equations were used [1][2][3][4][5][6][7][8][9][10][11]. For the numerical solution the Euler meshes were used. This kind of computational mesh is fixed in space. That is why additional calculations are needed to describe quantitatively the convectional heat transport generated by the movement of an ingot solid part in a stationary coordinate system connected with an installation. The phenomena of the grain nucleation and growth in the aforementioned publications are not taken into account.The attempts of the microstructure formation modeling in the continuous casting as results of the grains nucleation and growth are shown in [12,13]. The so-called micro-macro model was used in these papers. In the micro-macro modeling the heat transfer process was analyzed in scale of an ingot (macro). Mathematical model of the nucleation and growth of solid grains in the micro-scale make it possible to predict the s...
We analyzed the formation of biphase superstructures on the (111)-oriented epitaxial magnetite films on Pt(111) as a function of controlled film stoichiometry. The stoichiometry of the films several nanometers thick was changed by ultra-high vacuum in situ deposition of a few monolayers of metallic iron onto the stoichiometric film, followed by annealing. The samples were characterized in situ. The surface structure was determined using low-energy electron diffraction and scanning tunneling microscopy, whereas the phase composition and electronic structure were verified using X-ray photoemission spectroscopy and conversion electron Mossbauer spectroscopy (CEMS) with isotopic 57 Fe probe layers. As a function of the added-Fe (ad-Fe) dose and annealing temperature, we identified four types of superstructures that were homogeneously distributed over the entire surface, and we associated them with an increasing degree of surface reduction. We have proposed a coherent atomic-scale model of the observed superstructures that explains them in terms of the modifications of the two outermost Fe atomic layers. CEMS also allowed us to follow in-depth changes accompanying the biphase occurrence. An excess of ad-Fe, which stabilizes a given surface superstructure, migrates toward the substrates, partially dissolves in Pt, and partially forms an interfacial layer with FeO stoichiometry.
Antiferromagnet/ferromagnet (AFM/FM) bilayers that display the exchange bias (EB) effect have been subjected to intensive material research, being the key elements of novel spintronics systems. In a commonly accepted picture, the antiferromagnet, considered as a rigid material due to its high anisotropy and magnetic hardness, controls the magnetic properties of the ferromagnet, such as a shift of the hysteresis loop or coercivity. We show that this AFM-FM master-slave hierarchy is not generally valid and that the influence of the ferromagnet on the magnetic anisotropy (MA) of the neighbouring antiferromagnet must be considered. Our computer simulation and experimental studies of EB in an epitaxial CoO/Fe(110) bilayer show that the ferromagnetic layer with strong uniaxial magnetic anisotropy determines the interfacial spin orientations of the neighbouring AFM layer and rotates its easy axis. This effect has a strong feedback on the EB effect experienced by the FM layer. Our results show new physics behind the EB effect, providing a route for grafting a desired anisotropy onto the AFM and for precise tailoring of EB in AFM/FM systems.
We report on in-plane magnetic anisotropy in epitaxial bcc Co/Fe(110) bilayers on W(110). The magnetic surface anisotropy in the Co/Fe(110) bilayers exhibited a strong nonmonotonic dependence on Co coverage. Magneto-optical studies revealed a sharp maximum of the magnetic surface anisotropy, 2.44 mJ/m 2 , at d Co = 5Å. This giant interfacial magnetic anisotropy allowed a small fraction of a Co monolayer to reorient the magnetization of the bulk-like Fe film. We conclude that the mono-and double-layer bcc Co(110) exhibited in-plane magnetic anisotropy with a [110] easy axis.
A ferromagnet/antiferromagnet (FM/AFM) Fe/NiO bilayer was grown using molecular beam epitaxy on MgO(001) and Cr buffered MgO(001) substrates. X-ray linear dichroism measurements showed a dominating out-of-plane component for the NiO spins in Fe/NiO/MgO and an in-plane spin direction for NiO layers grown on the Cr buffer. Furthermore, systematic studies on the magnetic properties of Fe/NiO grown on the wedge-shaped Cr buffer revealed a continuous strain-induced spin reorientation transition from out-of-plane to in-plane NiO spin directions when the Cr thickness increased from 0 nm to 3.5 nm. The analysis of the in-plane magnetic structure of NiO in Fe/NiO/Cr showed a pronounced uniaxial anisotropy in thin AFM layers. The AFM spins are perpendicular to the Fe spins due to spin–flop interaction. These results demonstrate the feasibility of using strain and coupling with FMs to manipulate spin structures in NiO.
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