NEW MARTENSITIC STAINLESS STEEL HARDENABLE BY PRECIPITATION FOR HYDROPOWER TURBINES

Our study is focused on the obtaining of a new martensitic stainless steel having an unconventional chemical composition and designed for hydropower turbine applications. The proposed metallic material was produced in special conditions using an induction furnace with cold crucible under vacuum and argon atmosphere, ensuring an inclusion state free of impurities. The subsequent heat treatments (quenching and tempering) allowed to obtain special structures that determine interesting mechanical properties, very different comparing to classic martensitic stainless steels. Specifically, after tempering, the hardness values do not decrease as in other case of steels, but increase about 1.6 times. The structural and compositional investigations, carried-out by optical and scanning electronic microscopy associated with energy dispersive spectrometry were able to explain the structural modifications, mainly represented by precipitation phenomena of intermetallic compounds such as Ni3Mo. The resulted data are similar to the phenomena encountered in the maraging steels class, creating a new category with duplex properties.