Sigma Phase Influence on Cavitation Damage in AISI 309L Austenitic Stainless Steel Weld Repair

Abstract:

Welding repair of cavitation damage in hydraulic turbine runners can be carried out using 309L austenitic stainless steel. Thermal cycles produced by the subsequent passes as well as the stress relief heat treatment after welding induce sigma phase precipitation in the weld microstructure. In this work results of cavitation tests performed according to the ASTM G32-10 standard obtained in weld deposits of AISI 309L steel, with and without sigma phase resulting from heat treatments, are presented. Cavitation test revealed that sigma phase caused a 78% reduction in the incubation period and a 30% increase in the maximum erosion rate compared to the material without this phase. It is inferred that the reduction in the incubation period would, in principle, be related to differences in mechanical properties between the sigma phase and the austenitic matrix. On the other hand, it was found that the maximum erosion rate would be the result of the presence of the sigma phase, which promoted a reduction in the toughness of the material

Keywords:
Austenitic stainless steel; Sigma phase; Cavitation