Abstract
Microstructural, mechanical, and fatigue properties of solution strengthened ferritic ductile iron have been evaluated as functions of different solidification times. Three types of cast samples with increasing thickness have been produced in a green sand automatic molding line. Microstructural analyses have been performed in order to evaluate the graphite nodules parameter and matrix structure. Tensile and fatigue tests have been carried out using specimens taken from specific zones, with increasing solidification time, inside each cast sample. Finally, the fatigue fracture surfaces have been observed using a scanning electron microscope (SEM). The results showed that solidification time has a significant effect on the microstructure and mechanical properties of solution strengthened ferritic ductile iron. In particular, it has been found that with increasing solidification times, the microstructure becomes coarser and the presence of defects increases. Moreover, the lower the cooling rate, the lower the tensile and fatigue properties measured. Since in an overall casting geometry, same thicknesses may be characterized by different microstructures and mechanical properties induced by different solidification times, it is thought that the proposed methodology will be useful in the future to estimate the fatigue strength of cast iron castings through the numerical calculation of the solidification time.
Highlights
Since 2012, solution strengthened ferritic ductile irons (SSF-DI) have been introduced in the UNI EN 1563 standard [1]
The result of thermaltheanalysis is the curve of thetemperature, alloy from which it is possible to the liquidus temperature, minimum andcooling maximum eutectic the temperature at the calculate the liquidus temperature, the minimum maximum eutectic temperature, end of solidification, and the temperatures duringand the solid phase transformation
From the comparison between the curves of traditional cast irons and solution strengthened ferritic ductile irons during the eutectic and the eutectoid transformation (Figures 4 and 5, respectively), it is visible that there are little variations in the solidification behavior, while the main difference is related to the solid-state transformation
Summary
Since 2012, solution strengthened ferritic ductile irons (SSF-DI) have been introduced in the UNI EN 1563 standard [1]. These alloys are characterized by a fully ferritic matrix, reinforced by the addition of a balanced amount of Silicon, which provides a combination of high strength and ductility [2]. It has been found that by increasing the section thickness, the nodule count decreases, while the ferrite content increases. Under these conditions, tensile strength and hardness decrease, while elongation at failure increases [4,5,6]
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