Limit of pitting corrosion at high-alloyed special steels and NiCrMo alloys in chloride solution

The phenomenon of the limit of pitting corrosion in direction to positive p otentials is studied by potentiokinetic polarization after a jump in the tr anspassive range and by potentiostatic tests at technical wrought materials and at model alloys of the systems NiCrMO and NiMo in CaCl2 solution in th e concentration range 1 to 9 mol/l chloride at pH-values of 1 to 9 at tempe ratures of 30 to 110 degreesC. Surface-analytical investigations gives in c onnection with knowledges from anodic polarization studies directions to th e mechanism of the limit of pitting corrosion. Ranges of the limit of pitti ng corrosion are obtained at materials with a Mo content above 6.5% and con tents of chloride of the media above 2 mol/l chloride. Increasing temperatu res, increasing contents of chloride and sulfate shift the potential of the limit of pitting corrosion being always above 0.2 V (SCE) at potentiostati c determination to noble direction. There are indications that the mechanisms of limit of pitting corrosion is resulting from an inactivation of pitting nuclei by the formation of hardly soluble molybdenum chlorides in the potential range of limit of pitting co rrosion.