Rationalization of the blading material for steam turbines: Their requirements and selection

In steam turbines a wide range of blading materials, which are basically modified 12% Cr martensitic steel with additions of ferrite strengthening and carbide forming alloying elements viz. Mo, W, V, Nb etc. individually or in suitable combination, have been used. The choice of blading materials is to a large extent a function of design considerations. The grades used in different stages of steam turbine of a given capacity vary between different manufacturers, as is true with the three BHEL Units in India. Rationalization of blading materials both for HP and LP stages can lead to considerable saving on their development and testing cost. With this object in mind, a detailed and comparative study has been carried out of available grades of blading materials. The inter-relationships between chemical compositions, heat treatment, microstructure and their influence on long-term creep-rupture behaviour have been discussed in the light of the desired properties from design view points and service conditions. (Shri R. Singh, Shri R. Choubey and Dr. R. Kumar, Scientists, National Metallurgical Laboratory)