In this paper we present the theoretical background of the New Rheocasting (NRC) process, which is based on the thixotropic behavior of a melt with a globulitic primary phase. The NRC process ...represents an economic alternative to the forging process. The main goal of this study was an evaluation fo the microstructure of this innovative and ecologial production process. We present some characteristic microstructures observed during the evaluation of a slurry and a real automotive component. Some dendritic forms of the primary alphaAl phase were observed in the component, which means there are possibilities for a further improvement of the temperature regime. An increased content of the eutectic phase near the surface was observed and inclusions with strontium were found in the eutectic phase.
Based on experimental data and transmission electron micrographs an explanation of the mechanism of the change of Charpy notch transition temperature after strain ageing is proposed. The explanation ...involves the interplane ordering of carbon atoms at ageing annealing at 250 deg C as a synergy of the dislocation structure and the redistribution of carbon atoms in solid solution in ferrite. The induced internal stresses decrease the cleavage fracture strength of the ferrite matrix and increase the Charpy notch toughness transition temperature.
Inclusions in primary aluminium were analysed with an electron-probe microanalyser and a high-resolution Auger electron spectrometer. In multiphase eutectic and complex inclusions the presence of ...calcium, magnesium, iron, copper, molybdenum and aluminium was detected. Prior to Auger analysis, sufficient ion etching is necessary for the elimination of oxides from the surface. The complex inclusions, with calcium content, reacted with water which demanded the choice of a suitable technique for the preparation of metallographic samples.
The investigation was carried out on two laboratory steels elaborated from identical base materials, one with 0.05% Sb and an industrial steel as‐delivered and after decarburisation. Cold rolled 0.5 ...mm sheets were prepared by laboratory rolling and investigated after annealing in temperature range 550 to 800°C for 0.5 to 60 m. Antimony has no effect on recovery in temperature range 550 to 625°C. Rare recrystallization nuclei were found at grain boundaries only in the decarburized steel, in all other steels nucleii appeared and grew only inside of deformed grains. At recrystallization finished grains were coarser in antimony and decarburized steels. The explanation is that less numerous nuclei grew for a longer time in the deformed matrix. The size of recrystallized grains was proportional to the square root of the annealing time. Recrystallized grain growth was faster in antimony‐free laboratory and in decarburized industrial steels, while the growth activation energy is very similar in antimony and decarburized steels. The growth activation energy was greater in antimony‐free laboratory and in as‐delivered industrial steels. It was similar to the activation energy of part of the recovery and near to the activation energy of iron self‐diffusion in ferrite. No difference was found in grain growth topology between the antimony and the comparative laboratory steels. Results indicate a similar effect of the presence of 0.05% of antimony and the decreased carbon content in steel.
Zwei Versuchsstähle, die auf gleichem Ausgangswerkstoff basieren, einer davon mit 0.05% Sb, und ein industriell hergestellter Stahl im Lieferzustand und nach Entkohlung sind Gegenstand dieser Untersuchung. Kaltgewalzte 0.5 mm dicke Feinbleche wurden im Laborwalzwerk hergestellt und nach anschließender Glühung bei 550 – 800°C, 0.5 – 60 min untersucht. Antimon hat keinen Einfluß auf die Erholung im Temperaturbereich 550 – 625°C. Wenige Rekristallisationskeime traten nur auf den Korngrenzen des entkohlten Stahls auf; in allen anderen Proben wuchsen Keime nur innerhalb deformierter Körner. Nach Rekristallisation lagen gröbere Körner im Antimon‐legierten Stahl als auch in der entkohlten Sorte vor. Das läßt sich damit erklären, daß weniger keime eine längere Zeit in der verformten Matrix wachsen können. Die Größe der rekristallisierten Körner ist proportional zur Wurzel der Glühdauer. In Stählen ohne Antimon bzw. den industriellen entkohlten Sorten wuchsen die rekristallisierten Körner schneller. Demgegenüber ist die Aktivierungsenergie für das Wachstum in beiden Werkstoffen vergleichbar, im Fall der Laborschmelzen ohne Antimon und der industriellen Sorten im Anlieferungszustand ist sie jedoch größer. Sie lag im Bereich der Aktivierungsenergie für einen Teil der Erholung bzw. der Eisenselbstdiffusion in Ferrit. Hinsichtlich der Topologie des Kornwachstums konnte kein Unterschied zwischen Antimon‐legierten und vergleichbaren Laborschmelzen festgestellt werden. Die Ergebnisse lassen den Schluß zu, daß 0.05% Antimon sich ähnlich auswirken wie ein abgesenkter Kohlenstoffgehalt im Stahl.
