Detection of microstructural changes of 9% Cr-martensitic steels during heat treatment and aging by polarization tests

9-12% chromium martensitic steels are widely used as pipe material in steam power plants. Their good creep behavior is based on a finely adjusted microstructure, which is strengthened by precipitates. During long-term use at higher temperatures degredation mechanisms occur, which affect the initial microstructure. Subgrain and precipitate coarsening as well as phase formation like Laves-phase ((Fe, Cr)(2)(Mo, W)) proceed and lead to a reduced creep resistance. For lifetime assessment a nearly nondestructive electrochemical test method would be beneficial to identify microstructural changes during periodical inspections. The paper is focussed on the usability of an adapted electrochemical potentiodynamic reactivation (EPR)-method and deals with the adjustment of test conditions like electrolyte composition and polarization parameters. The results obtained under optimized test conditions show a clear indication of precipitate formation by changing the characteristics of the EPR-curves for the well established alloy T/P91 (X10CrMoVNb9-1) as well as for the boron containing advanced alloy MARBN (X10CrWCoVNb9-3-3).