Nodularity as per Japanese International Standard refers to number of nodular (rounded) graphite particles in microstructure against total number of graphite particles. Meaning thereby 80% nodularity consists of 80 particles qualifying under nodular (round or globular) in nature out of 100.
Nodularity as per ASM is mentioned as "The volumetric proportion of spheroidal or nodular graphite to total graphite in a ductile iron or a compacted graphite iron matrix".
The term Nodularity is useful for acceptance / rejection of inventory material. Higher is the nodularity more is the Cast Iron's ductility. As such, cast irons are famous for their good wear resistance but at the same time they possess less toughness. Malleable cast irons are having optimized property for toughness.
Normal acceptance value for a good Malleable cast iron is 80% nodularity. However, this figure does not bind to all the cases. Actual figure may be agreed between buyer and seller.
ASM states that very high nodule counts are sometimes associated with low hardenability and non-uniform tempering. Generally, a nodule count of 80 to 150 discrete graphite particles per square millimeter appears to be optimum.
MiC shape identifier engine works on the principle of two-dimensional projection of particles. Especially, graphite particles possess quite a different morphology. For qualifying them to be nodular, their two dimensional projection is compared to the normal circularity index. Index of 80 is considered for qualification to be called "nodular". This guideline has been adopted from the Japanese International Standard.
MiC provides three distinguished results. (1) Total count (2) Total nodular count (3) Nodularity as percent of nodules of total counts in a given image. Besides a list of all the particles is provided for reference to find which particle on the screen identified as nodular and irregular ; with area covered under each discrete particle is listed.
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