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Effect of cooling rate and silicon content on graphite morphology and austenite transformation in solid solution strengthened ferritic ductile cast irons

Effect of the cooling rate (section thickness) on the graphite morphology and austenite transformation in solid solution strengthened ferritic ductile cast irons was analysed in this paper. Three melts with the following silicon contents were made: 3.11, 3.8 and 4.22 wt.%. The analysis was carried out on test castings containing seven different section thicknesses: 3, 12, 25, 38, 50, 75, and 100 mm. Obtained results show that the nodule count and nodularity decrease with increasing section thickness (i.e. with a decrease in the cooling rate). The increase in silicon content from 3.11 to 4.22 wt.% resulted in an increase in nodule count and nodularity in section thicknesses of 3, 12, 25 and 38 mm. However, in thick sections, i.e. in section thicknesses of 50, 75 and 100 mm, the increase in silicon content resulted in a decrease in nodule count and nodularity. In these sections, the number of very small irregular graphite particles and clusters of graphite particles that look like chunky graphite increased with the increase in silicon content. In test castings containing 3.8 and 4.22 wt.% Si the amount of ferrite in the metal matrix increases with increasing section thickness. Fully ferritic metal matrix is obtained in section thicknesses of 25, 38, 50, 75 and 100 mm. All sections of the test casting containing 3.11 wt.% Si have a certain proportion of pearlite.

solid solution strengthened ferritic ductile cast iron, cooling rate, microstructure

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