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Abstract

Some metallographic studies performed on the basis of the massive forging steel static ingot, on its cross-section, allowed to reveal the following morphological zones: a/ columnar grains (treated as the austenite single crystals), b/ columnar into equiaxed grains transformation, c/ equiaxed grains at the ingot axis. These zones are reproduced theoretically by the numerical simulation. The simulation was based on the calculation of both temperature field in the solidifying large steel ingot and thermal gradient field obtained for the same boundary conditions. The detailed analysis of the velocity of the liquidus isotherm movement shows that the zone of columnar grains begins to disappear at the first point of inflection and the equiaxed grains are formed exclusively at the second point of inflection of the analyzed curve. In the case of the continuously cast brass ingots three different morphologies are revealed: a/ columnar structure, b/ columnar and equiaxed structure with the CET, and c/ columnar structure with the single crystal formation at the ingot axis. Some forecasts of the temperature field are proposed for these three revealed morphologies. An analysis / forecast of the behavior of the operating point in the mold is delivered for the continuously cast ingot. A characteristic delay between some points of breakage of the temperature profile recorded at the operating point and analogous phenomena in the solidifying alloy is postulated.
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Abstract

During the Polish Antarctic Geodynamic Expeditions, 1979-91, a wide geophysical and geological programme was performed in the transition zone between the Drake and South Shetland microplates and the Antarctic Plate, in West Antarctica. In the Bransfield Strait area, and along passive continental margin of the Antarctic Peninsula, 20 deep seismic sounding profiles were made. The interpretation yielded two - dimensional models of the crust and lithosphere down to 80 km depth. In the coastal area between the Palmer Archipelago and the Adelaide Island, the Earth's crust has a typical continental structure. Its thickness varies from 36 to 42 km in the coastal area, decreasing to about 25-28 km toward Pacific Ocean. In the surrounding of Bransfield Strait, the Moho boundary depth ranges from 10 km beneath the South Shetland Trench to 40 km beneath Antarctic Peninsula. The crustal structure beneath the Bransfield Strait trough is highly anomalous. Presence of a high-velocity body, with longitudinal seismic wave velocities Vp > 7,0 km/s, was detected there in the 6-32 km depth range. This inhomogeneity was interpreted as an intrusion, coinciding with the Deception-Bridgeman volcanic line. In the transition zone from the Drake Passage to the South Shetland Islands, a seismic boundary in the lower lithosphere occurs at a depth ranging from 35 to 80 km. The dip of both the Moho and this boundary is approximately 25° towards the southeast, indicating the direction of subduction of the Drake Plate lithosphere under the Antarctic Plate. Basing on the results of four Polish Geodynamic Expeditions, the map of crustal thickness in West Antarctica is presented.
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Abstract

During the Polish Antarctic Geodynamical Expeditions in 1979-91, deep seismic sounding measurements were performed in the transition zone between the Drake and South Shetland Microplates and the Antarctic Plate in West Antarctica. For the Bransfield Strait area, the seismic records of five land stations in South Shetland Islands and two stations at the Antarctic Peninsula were used. The interpretation yielded two—dimensional models of the crust and lithosphere down to 80 km depth. In the uppermost crust, the unconsolidated and poorly consolidated young sediments with velocities of 1.9 — 2.9 km/s cover the layers 4.0—4.2 and 5.6—5.9 km/s. The crustal structure beneath the trough of Bransfield Strait is highly anomalous. The presence of a high velocity body, with longitudinal seismic wave velocities vp > 7.0 km/s, was detected in the 6 — 30 km depth range. This inhomogeneity was interpreted as an intrusion, coinciding with the Deception—Bridgeman volcanic line. For the uppermost crust, a qualitative comparison was made between the results from the reflection profiles (GUN) and deep seismic sounding profiles (DSS). In the study area, the Moho boundary depth ranges from 10 km beneath the South Shetland Trench to 40 km under the Antarctic Peninsula. In the transition zone from the Drake Passage to the South Shetland Islands, a seismic boundary in the lower lithosphere occurs at a depth ranging from 35 to 80 km. The dip of both the Moho and this boundary is approximately 25°, and indicates the direction of subduction of the Drake Plate lithosphere under the Antarctic Plate. The results obtained were compared with earlier results of seismic, gravity and magnetic surveys in West Antarctica. A scheme of geotectonic division and a geodynamical model of the zone of subduction of the Drake Plate under the Antarctic Plate is compared with subduction zones in other areas of the circum-Pacific belt.
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Abstract

The Structural Peclet Number has been estimated experimentally by analyzing the morphology of the continuously cast brass ingots. It allowed to adapt a proper development of the Ivantsov’s series in order to formulate the Growth Law for the columnar structure formation in the brass ingots solidified in stationary condition. Simultaneously, the Thermal Peclet Number together with the Biot, Stefan, and Fourier Numbers is used in the model describing the heat transfer connected with the so-called contact layer (air gap between an ingot and crystallizer). It lead to define the shape and position of the s/l interface in the brass ingot subjected to the vertical continuous displacement within the crystallizer (in gravity). Particularly, a comparison of the shape of the simulated s/l interface at the axis of the continuously cast brass ingot with the real shape revealed at the ingot axis is delivered. Structural zones in the continuously cast brass ingot are revealed: FC – fine columnar grains, C – columnar grains, E – equiaxed grains, SC – single crystal situated axially.
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