Ductile iron is an iron-carbon casting material whose matrix includes carbon in the form of nodular graphite particles. Rounded graphite nodules in the ductile iron matrix offer greater resistance to stress concentration when compared to graphite flakes (as in gray cast iron) and, therefore, inhibit the creation of cracks.
Safety-critical automotive components cast from ductile iron must be tested to verify that they include the correct percentage of nodularity since catastrophic failure of one of these parts can result in damage, injury, and even loss of life. Manufacturers routinely employ a destructive test method, microstructure analysis, to verify the correct nodularity for sample parts. Microstructure analysis is typically conducted in the metallurgical laboratory and, at best, represents only a small sample of the total production.