THE MORPHOLOGY OF DUCTILE CAST IRON SURFACE DAMAGED BY CAVITATION

The study was designed to investigate the cavitation behavior of the ductile cast iron with microstructure consisting of spheroidal graphite in a predominantly ferrite matrix with 10% pearlite. The experiments were conducted using the ultrasonically induced cavitation test method. The frequency of vibration and the peak-to-peak displacement amplitude of the horn were 20 +/- 0.5 kHz and 50 mu m, respectively, with separation of 0.5 mm between the sample and the horn tip. In order to obtain the erosion curve, the mass loss measurements were performed after each exposure interval. The mass loss was recorded every 30min for a test period of 240 min. Roughness parameter Ra (the mean roughness), was used to characterize the surfaces. The cavitation rate was 1.85 higher for ductile iron compared with that of carbon steel with similar hardness, because graphite removal produces high stress concentration in cast iron. Compared with conventional mass loss measurements in assessing material degradation in cavitation erosion, surface roughness measurements provide an alternative and convenient method.