Thermal Analysis of the Formation of Chunky Graphite during Solidification of Heavy-section Spheroidal Graphite Iron Parts (original) (raw)
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This work is focused on the effect of pouring temperature on the thermal-microstructural response of an eutectic spheroidal graphite cast iron (SGCI). To this end, experiments as well as numerical simulations were carried out. Solidification tests in a wedge-like part were cast at two different pouring temperatures. Five specific locations exhibiting distinct cooling rates along the sample were chosen for temperature measurements and metallographic analysis to obtain the number and size of graphite nodules at the end of the process. The numerical simulations were performed using a multinodular-based model. Reasonably good numerical-experimental agreements were obtained for both the cooling curves and the graphite nodule counts.
International Journal of Cast Metals Research, 2013
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Influence of the Cooling Rate on the Morphology of Spheroidic Graphite Obtained by the CO2 Process
The mechanical properties of cast metallic materials are strongly influenced by processing parameters, such as percentage of silicate, sand granulometry, and metallurgical processing. The ductile iron cast produced by the CO2 process depends on variables that determine the behavior of the material in service, such as the cooling rate and chemical composition. This study evaluated the influence of the cooling rate on the spheroidic graphite. In order to determine this effect, a simulation was performed in specimens with 20, 25, and 30 mm in thickness, through the characterization of type, measurement of nodule size, and distribution of nodules. Chemical analysis and mechanical resistance tests were performed. The 25 mm thick specimen showed the best behavior among the three thicknesses evaluated, presenting the formation of many small nodules and a small amount of larger nodules in the center. The comparison of the nodule size, as well as the counting of these, associated to the used cooling rate is according to standard test method for structure evaluation of graphite in iron cast.
Study of the solidification structure of compacted graphite cast iron
International Journal of Cast Metals Research, 2016
This investigation focuses on the study of the solidification mechanism of compacted graphite cast iron (CGI). The solidification macrostructure was revealed in cast samples using a special technique known as direct austempering after solidification (DAAS). The microstructure was revealed by colour etching. The results were compared with earlier investigations of the solidification of spheroidal (SGI) and lamellar (LGI) graphite irons, and show that, similarly to other free graphite cast irons, the solidification of CGI is dominated by the presence of relatively large grains of austenite that can be observed with bare eyes. The CGI cast samples show a typical ingot structure, containing columnar and equiaxed grains, with a narrow columnar to equiaxed transition. The microstructure analysis showed that a dendritic substructure and a large number of eutectic colonies form the grains. Microsegregation is located inside the grains, mostly between secondary dendrite arms. The results indicate that the growth mechanism during solidification of CGI resembles that of LGI, but not the mechanism of SGI.