Corrosion Behaviour of Boronized Ductile irons in Formic and Nitric Acid Solutions

The corrosion behavior of boronized Cu, Ni, and Mo-alloyed and unalloyed ductile irons in two acid solutions was investigated using the gravimetric method. Ductile irons were pack boronized at 900 and 950°C for 2, 4, 6, and 8 h. The boride-layer compounds were detected using X-ray analysis. Boronized and untreated irons were immersed in 10 wt % formic acid and 10 wt % nitric acid solutions for 14 days (336 h). Every two days, mass losses were measured, and corrosion rates were estimated using these results. The corroded surfaces were examined with scanning electron microscopy. Untreated alloyed ductile cast iron lost less mass in both acid solutions than unalloyed cast iron. Pitting is the most common type of corrosion in formic acid solution. Higher corrosion rates after 48 h of immersion decreased dramatically in 96 h for all irons due to the passivation effect of the nitric acid solution.