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Fatigue failure of turbine blades originating from pitting corrosion is a critical issue for power plant. Herein, we study the pitting corrosion resistance of cast CA6NM as turbine blade material in simulated geothermal environment with and without CO2 gas by using cyclic polarization measurement. Three different molybdenum and nitrogen content of CA6NM were used for experiments: (i) CA6NM with a molybdenum content of 1 wt.% and without addition of nitrogen, (ii) CA6NM with a molybdenum content of 2 wt.% and without addition of nitrogen, (iii) CA6NM with a molybdenum content of 2 wt.% and nitrogen content 0.1 wt.%. The measurement reveals CA6NM with molybdenum 2 wt.% and nitrogen 0.1 wt.% is the most resistance to pitting corrosion in simulated artificial geothermal brine with and without CO2 gas.

Pitting corrosion is an importance phenomena in power generation steam turbine, as it is one of the main causes for blade failure, particularly in the last row of low pressure blading. In this work, the pitting corrosion resistance of the widely used blading alloy of wrought 410 stainless steel and that of the candidate alloy of cast CA6NM stainless steel were investigated. Cyclic polarization measurements for all samples were conducted in simulated solution of thermal and geothermal power plants. The experimental results show that the pitting potentials of the cast CA6NM steel were higher compared to those of the wrought 410 steel in all simulated solution. Both steels exhibited higher pitting potentials in CO2 containing simulated geothermal water than those in the other solutions. These results were correlated with microstructure of the steels observed by Scanning Eectron Microscope (SEM).

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