Nodule count effect on microstructure and mechanical properties of hypo-eutectic ADI alloyed with nickel

Samples of ductile iron alloyed with 0.88 % Ni a nodule count 606, 523, and 290 nod/mm2 were obtained from sand cast plates different thickness in the range 8.46 to 25.4 mm. The effect was evaluated during austempering process held at 285?C times 15, 30, 45, 60, 70, 90 min. volume fraction high carbon austenite increased when increased, however, content kept almost constant. window narrow, requiring lower time increased. combination higher low temperature allowed obtaining fine ausferritic microstructure which led Brinell hardness tensile strength. determined by XRD measurements it good agreement microstructural evolution as