Microstructural Characterization of Some Turbine Blade Martensitic Stainless Steels

The paper presents microstructural features of three stainless steels utilized in making hydropower turbine parts. Two of these steels were already used in producing these parts, the third one is newly conceived. Aiming better mechanical and corrosion resistance characteristics, steels were produced using an induction furnace with cold crucible under vacuum and argon atmosphere, striving for an inclusion free state. Quenching and tempering heat treatments were subsequently applied. The microstructural investigations, carried-out by microhardess testing, optical and scanning electron microscopy (SEM) associated with energy dispersive spectrometry (EDS), were able to explain the structural modifications. Refined microstructures were found in the two first steels. Concerning the third one, a precipitation phenomenon of intermetallic compounds such as Ni3(Ti,Mo) was reported, similar to that encountered in the maraging steels class. Mechanical properties of this steel are very different from classic martensitic stainless steels ones. Specifically, after tempering the hardness values do not decrease as in other steels, but increase about 1.6 times. Thus a new steel category with duplex properties is reported.