The cooling rate has a great influence on the transformation of austenite into ferrite and graphite and perlite. Higher cooling rates contribute to a higher proportion of perlite in the microstructure, which results in higher mechanical properties such as Rm and Rp0.2 and lower elongation A.
We used 3 different cooling regimes of Y probes. The first was that the Y probe remained in sand form until it cooled to room temperature, the second, that the sand form was deformed 30 minutes after the melt was cast and then left to cool on the air, and the third that the form was deformed 30 minutes after the melt was cast and then transferred to continue the journey along with serial casts, which were later also used as samples for measurements. Samples for tensile testing were then prepared from all these types and serial casts. We found out that higher cooling rates result in higher perlite content in the microstructure, which in turn results in higher mechanical properties and lower elongation. Y probes that were in form until the end of solidification, had the most similar mechanical properties to serial casts, while those that were left to cool on the air after 30 min were the least similar. Y probes left to cool on the air had a final perlite to ferrite ratio of 94.5% and 5.5%, respectively, while casts had a ratio of 39.46% and 60.53%. In the microstructures, the most present were spheroidal graphite particles of type VI according to the ISO 945-1 standard, up to 3 mm in size at 100 × magnification. Y samples with the highest cooling rate were found to have the highest mechanical properties and the lowest elongation, while the slowest cooled Y probes and serial casts had the lowest mechanical properties and at the same time the maximum elongation, both within tolerances of EN-GJS-500-7C standard, according to which they are supposed to be made.
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