The paper presents the study of the microstructure and ultrasound measurments by proeminent part of the nodular iron castings. The experiment has been made in the Havy Machine Factory in Clausenburg. The crossing speed of the ultasound increases near the edge of the castings. Analising the nodular iron microstructure by smoler castings, there occurs no graphite change. By bigger mouldings the shape of the graphite can change to a vermicular graphite near the edges. The thickness of the transformed stratum is of 0,1 -0,3 mm.