Effect of tempering treatment on pitting corrosion resistance of modified cast CA6NM stainless steel in 3.5 % NaCl solution

Martensitic stainless steels are commonly used in nuclear power plants, steam generators, pressure vessels, and turbine blades. CA6NM stainless steel is one of the martensitic stainless steels primarily prescribed to use for the steam turbine blade application. Pitting corrosion is one of the most common problems which could cause fatigue failure in the turbine blade application. Herein, we study the effect of tempering treatment on pitting corrosion resistance of modified cast CA6NM stainless steel in a 3.5 % NaCl solution. Three different CA6NM materials were used in this experiment: samples with an addition of 1 % Mo, 2 % Mo, and 2 % Mo-1 % N. The CA6NM stainless steel specimens were heated using heating furnace to 1050 °C for 3 hours and quenched to room temperature. Furthermore, tempering treatment was applied to the CA6NM stainless steel samples which were conducted in two types, single and double tempered. The open circuit potential measurement showed that samples with an addition of 2 % Mo-1 % N and double tempered had the highest free corrosion potential value of all the samples. The cyclic polarization test was conducted in a 3.5 % NaCl solution. The highest pitting potential was found in CA6NM with the addition of 2 % of molybdenum content with double tempered treatment.