| Abstract: | Electrochemical investigation into the pitting corrosion of corrosion resistant steels In view of the fact that the characteristics termed pitting potential depend from the measuring methods and nonstationary defects and hysteresis phenomena produced thereby these condition have been investigated on three different systems. In sulphate inhibited chloride solution an actual hysteresis is found with two critical boundary potentials for pit formation and pit passivation. The first of these potentials may be found either by potentiocinetic or by potentiostatic methods, the second only galvanostatically. In the case of 35% Cr steel no hysteresis is found; in this case there is no connection between pitting potential and the current and potential variations found during the investigation. With this material pitting corrosion may occur below the pitting potential while the pit passivation potential is a function of the properties of the measuring circuit. The pitting behaviour of austenitic CrNi steels containing various amounts of molybdenum may be characterized potentiostatically or potentiocinetically, but at low voltage feed rates only. |
