Cavitation erosion of grey cast irons containing 0.2 and 1.0% phosphorous in corrosive waters

Abstract

The effect of 0.2 and 1.0% P in a sand cast flake graphite grey iron on the cavitation erosion behaviour in distilled, NaCl, and NaCl/inhibitor waters, has been investigated. Techniques used include an ultrasonic vibratory apparatus at 50°C and 15 μm amplitude, electrochemical polarization, profilometry, and microscopy. Salt in the water increased the electrochemical corrosion rate, the erosion rate, the number of pits/cracks in the surface, the roughness of the surface, and reduced the nominal incubation time. For the 0.2% P iron in 3% salt water the nominal incubation time was reduced by 0.2 times, the steady-state erosion rate increased by 7.0 times and 90% of the increase was due to corrosion-induced erosion. The presence of a continuous brittle phosphide network in the 1.0% P iron had a negligible effect on the erosion rate but reduced the incubation time by a factor of 0.3. The inhibitor eliminated completely the effects of corrosion up to a salt concentration of 0.25%. The processes and mechanisms are discussed.