Abstract: A chemical-electrochemical dissolution model for localized pitting corrosion of low alloyed cast irons in nature seawater is set up on the base of its really exposed experiment results, chemical dissolution, electrochemical dissolution and mass transport governed by diffusion and migration of active ions inside the occluded pitting. An equation for the potential of metal inside the occluded pitting is deduced. The equation shows that the potential depends on the chemical potential gradient of the active ions in the occluded pitting and partial potential drop corresponding to the same ions. Experimental results show that local marine biofouling and R(R=wCl–/who–under the biofilm play an important role on the initiation localized pitting corrosion of low alloyed cast irons, potential drop and mobility of active ions and pH inside occluded pitting on propagation of the corrosion inside pitting. However a face must be clearly understood that halogen existing and its concentration in nature seawater badly influence on the localized pitting corrosion of cast irons.

Key words: Chemical-electrochemical dissolution, Low alloyed cast irons Nature seawater, Pitting corrosion