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Compositions and Microstructures


Table 2 shows that all the as-cast and heat treated ductile cast irons have typical compositions for their corresponding ASTM9


or SAE10


than 90%), and almost all have standard nodule counts be- tween 100 to 300 mm-2


grades, all have high nodularity (greater . Due to its heavier section size, the


76 mm section size for the 100-70-03 grade has lower nod- ule count than the other seven conditions.


The Table 2 results were chosen to display the most signifi- cant data for each of the selected conditions. Figures 10 to 17 each contain one example micrograph selected for each of the eight conditions.


The microstructures in the grades obeyed expectations as follows:


1. The ferrite content in the as-cast grades decreased with increasing strength and decreasing ductility in the first three grades listed in Table 2, as also shown in Figures 10, 13 and 14.


2. The ferrite contents in Table 2 and the micrographs in Figures 10 to 12 show that the annealing treat- ments converted the as-cast 60-40-18 grade to all ferrite, as expected.


3. For as-cast 100-70-03, Figure 14 shows that the ferrite surrounded nodules, and this is commonly called bulls-eye ferrite. After normalizing, Figures 15 and 16 show that the ferrite is more randomly distributed throughout the matrix.


4. For grade 120-90-02, Figure 17 shows that the fer- rite-pearlite microstructure converted to tempered martensite after quenching and tempering (Q&T).


Figure 18. The yield strength and elongation of the ferrite and pearlite microstructures obeyed a quadratic relationship. The open points represent the heat treatment conditions and the closed points represent the as-cast condition. The tempered martensite microstructure had greater strength than the locus of points for the ferrite and pearlite grades.


Table 3. Monotonic Properties and Coefficients for Selected Database Conditions


International Journal of Metalcasting/Spring 2012


17


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