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CET IN SOLIDIFYING ROLL -THERMAL GRADIENT FIELD ANALYSIS KRT W KRYSTALIZUJĄCYM WALCU -ANALIZA GRADIENTOWEGO POLA TEMPERATURYAs the first step of simulation, a temperature field for solidifying cast steel and cast iron roll was created. The convection in the liquid is not comprised since in the first approximation, the convection does not influence the analyzed occurrence of the C → E (columnar to equiaxed grains) transition (CET) in the roll. The obtained temperature field allows to study the dynamics of its behaviour observed in the middle of the mould thickness. This midpoint of the mould thickness was treated as an operating point for the C → E transition. A full accumulation of the heat in the mould was postulated for the C → E transition. Thus, a plateau at the T (t) curve was observed at the midpoint. The range of the plateau existence t C ↔ t E corresponded to the real period of transition, t R C ↔ t R E that occurs in the solidifying roll. At the second step of simulation, the thermal gradients field was studied. Three ranges were distinguished: a/ for the formation of the columnar structure (the C -zone):b/ for the C → E transition (from columnar to fully equiaxed structure):c/ for the formation of the fully equiaxed structure (the E -zone):The columnar structure formation was significantly slowed down during incubation period. It resulted from a competition between columnar growth and equiaxed growth expected at that period of time.≈ 0 relationship was postulated to correspond well with the critical thermal gradient, G crit. . A simulation was performed for the cast steel and cast iron rolls solidifying as if in industrial condition. Since the incubation divides the roll into two zones (columnar and equiaxed) some experiments dealing with solidification were made on semi-industrial scale.A macrosegregation equation for both mentioned zones was formulated. It was based on a recent equation for redistribution after back-diffusion. The role of the back-diffusion parameter was emphasized as a factor responsible for the redistribution in columnar structure and equiaxed structure.Keywords: solidifying roll, thermal gradient field, columnar into equiaxed structure transition, macro-segregation index W pierwszym etapie symulacji wygenerowano numerycznie pole temperatury dla krzepnącego walca staliwnego oraz żeliwnego. Nie uwzględniono konwekcji uznając, że w pierwszym przybliżeniu konwekcja nie wpływa na przebieg transformacji C → E (struktura kolumnowa w równoosiową, CET). Uzyskane pole temperatury pozwala na analizę jego zachowania w środku grubości wlewnicy. Ten punkt wlewnicy zostałpotraktowany jako punkt operacyjny dla transformacji C → E. Postuluje się w tym modelu, że zachodzi pełna akumulacja ciepła we wlewnicy właśnie dla tej transformacji. Stąd, spłaszczenie krzywej T (t) jest obserwowane dla punktu operacyjnego. Zakres tego spłaszczenia oznaczony t C ↔ t E odpowiada rzeczywistemu okresowi transformacji, t Symulacja została przeprowadzona zarówno dla walców staliwnych jak i żeliwnych dla warunków zbl...

Structures obtained during Zn-Cu-Ti single crystal growth by the Bridgman method were investigated. The alloys of composition Zn-Cu0.1wt.%-Ti0.1wt.% were used for single crystals growth, which were produced at rate in the range of 1.8mm/h to 16mm/h. The Zn-Cu-Ti alloys were characterized by multiphase structure; in the solute-hardened matrix by Cu atoms exists a needle-shaped intermetallic phase Zn16Ti. The strong anisotropy of the hexagonal structure gives a significant influence on a second phase distribution in the matrix volume. In the range of the low growth rates (from 1.8mm/h to 10mm/h) oscillatory structures were observed. That effect vanished at the growth rates higher than 10mm/h. The observed oscillatory structures were characterized by existing periodic layers rich in the intermetallic phase of Zn16Ti interlaid with pure matrix (alpha phase Zn with Cu solute).

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Two different steel substrates are applied to the hot dip (Zn) -coating formation. The influence of the substrate composition on the (Zn) -coating thickening is recorded. Morphologies of both coatings are compared to each other. The transition from stable into meta-stable solidification is revealed. The criterion for the competition between stable and meta-stable solidification is applied to justify the analyzed transition.Keywords: (Zn) -coatings; Fe-Zn phase diagrams; growth kinetics; kinetics law Zastosowano dwie różne stale jako podłoża dla uzyskania dwu zróżnicowanych powłok (Zn). Dokonano porównania wpływu składu obydwu rodzajów podłoża na kinetykę wzrostu powłok (Zn). Dokonano zestawienia morfologii obydwu powłok. Ujawnione zostało przejście od krystalizacji stabilnej do meta-stabilnej. Zastosowano kryterium współzawodnictwa między krystalizacją stabilną a meta-stabilną dla uzasadnienia analizowanego przejścia.