Effect of Heat Treatment Applied Potential on the Caustic Stress Corrosion Cracking of Inconel 600

The stress corrosion cracking (SCC) behavior of differently heat-treated specimens of Inconel(1) 600 in 25 molal (m) NaOH solution at 140 C was studied as a function of potential by using the slow strain rate technique (SSRT). It was found that the cracking susceptibility and the failure mode (intergranular vs transgranular) depends heavily on potential, heat treatment, and grain size. In the mill-annealed condition, intergranular stress corrosion cracking (IGSCC) was obtained at potentials extending from the active peak (-900 mVSCE) to the secondary anodic peak (- 400 mVSCE), while transgranular stress corrosion cracking (TGSCC) occurred at the open circuit potential (OCP), ~ -980 mVSCE, and at 0 mVSCE (secondary passive region). Solution-annealed material showed reduced IGSCC susceptibility with respect to the mill-annealed material, while almost complete IGSCC resistance was obtained by heat treatment at 700 C of both mill- and solution-annealed materials. Also, material with small grain size exhibited better IGSCC resistance. Electrochemical and metallurgical aspects relevant to the SCC behavior were also studied.