Effect of ageing heat treatment on corrosion behaviorof 17-4 PH stainless steel in 3.5% NaCl

The 17-4PH alloy is a martensitic stainless steel with 3–5 wt% Cu, strengthened by the precipitation hardening. Due to excellent mechanical properties, corrosion resistance and ease of heat treatment, this alloy has unique applications in nuclear power plants and marine constructions. In this paper, the influence of ageing heat treatment, solution annealing followed by ageing at 480, 550 and 620 °C on the corrosion behavior of 17-4PH stainless steel in 3.5% NaCl is reported. Various DC electrochemical measurements and microscopical examination was used. The slow scan rate potentiodynamic polarization revealed that by increasing ageing temperature from 480 to 550 °C, the pitting potential is significantly increased, but further increasing the ageing temperature to 620 °C reduces the pitting potential. Microscopical observation also confirmed the formation of several metastable and stable pits in the sample aged at 620 °C.