A new mircoelectrochemical method was applied to perform potentiodynamic polarisation experiments on areas in the range of 10 μm. For the first time, the individual corrosion behaviour of both single phases in super duplex stainless steels was determined. The results show a good correlation with the empirical pitting resistance equivalent number (PREN) of the corresponding single phase. The microelectrochemical experiments have revealed two different kinds of interactions between the ferrite and the austenite phase at the phase boundary, namely a superposition or a separation of the two polarisation curves of the single phases. Potentiodynamic polarisation of large areas with representative amounts of both phases are performed in hydrochloric acid electrolyte in order to compare the corrosion behaviour of the single phases with the corrosion behaviour of the entire alloy. Both, the pitting potentials, evaluated by means of macroelectrochemical experiments in pH-neutral lithium chloride electrolyte, and the critical crevice corrosion temperatures show a good correlation with the PREN of the weaker phase. Part I of this paper deals primarily with solution annealed materials. Solution annealing of the samples was performed at temperatures where minimal amounts of precipitates were formed and where the element partitioning determines the corrosion resistance of the single phases. Part II deals with the influence of precipitations on the corrosion behaviour.