High alloyed steels’ lifetime expectancy may be drastically reduced in geothermal environments due to corrosion fatigue. Using a specially built corrosion chamber, the corrosion fatigue (CF) of duplex stainless steel X2CrNiMoN22-5-3 was examined in the Northern German Basin electrolyte at 369 K. Despite the fact that the failure mechanism is unaffected by surface roughness (low scatter ranges technical surface: TN=1:1.35, polished surface: TN=1.1.95), the life expectancy in a simply alternating axial cyclic load to failure was clearly related to surface finish and applied stress amplitude. Specimens with technical surfaces persisted longer (cycles to f) when evaluated at high stress amplitudes (>275 MPa). specimens with polished surfaces (cycles to failure: P50 percent at Sa 300 MPa=1.5×105) than specimens with polished surfaces (cycles to failure: P50 percent at Sa 300 MPa=5×105). When a protective potential was applied, the CF life range increased significantly from 4.7 x 105 (free corrosion potential) to 107 cycles (potential range from USHE = –450 to –900 mV). Horizontal grain attack within corrosion pit cavities, many fatigue cracks, and preferred austenitic phase degeneration were shown by microstructural investigation of the CF damage. Pitting initiates fracture growth at low stress amplitudes, whereas the production of micro cracks causes crack propagation and failure at large stress amplitudes.
Author (s) Details
Marcus Wolf
HTW University of Applied Sciences Berlin, 12459 Berlin, Germany and BAM Federal Institute for Materials Research and Testing, Berlin, Germany.
Anja Pfennig
HTW University of Applied Sciences Berlin, 12459 Berlin, Germany.
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