Influence of Shot Peening on Corrosion Properties of Steam Turbine Blading Steel

Author:  M S Rawat, T R Jayaraman, C R K Prasad, Y Kalpana
Source:  Conf Proc: ICSP-7 (pg 184-191)
Doc ID:  1999029
Year of Publication:  1999
Abstract:  
12% Chromium steels are extensively used as steam turbine blading material due to their good corrosion resistance and moderately high strength. These steels are however susceptible to environmentally assisted cracking in chloride containing media. Controlled shot peening is a prestressing technique conducted to impart a residual compressive stress which considerably increases the fatigue life of the components. Corrosion fatigue and stress corrosion studies carried out on 12% Cr turbine blading steel on virgin and shot peened material, after optimizing the shot peening parameters have yielded highly encouraging results. Virgin and shot peened samples were polarized anodically for observing potentiodynamic characteristics in I N H2So4. Samples were also subjected to pitting scan for observing the localized corrosion characteristics in chloride containing media. The formation of a passivating film becomes complex when the surface has been altered by shot peening in comparison to mirror finish polished surface. Interesting observation has been made in the present work that the pitting susceptibility of the material in chloride environment is not affected adverssely inspite of surface modification brought about by shot peening as compared to virgin material.