Susceptibility of Dissimilar IN600 Welded Joints to Stress Corrosion Cracking Using Slow Strain Rate Test in Sodium Electrolytes

Abstract

The stress corrosion cracking (SCC) behavior of aged plates of Inconel 600 welded to Inconel 600 plates in the as-received condition was studied using the slow strain rate test (SSRT) in two sodium containing electrolytes at 25 and 80 °C. The aged plate was used to simulate damage by the operation service. Electrochemical noise (EN) was used to monitor the SCC. The plates were gas metal arc welded (GMAW) employing ERNiCrMo-3 and ER310 filler wires along with 95% Ar + 3% N2 + 2% O2 and 97% Ar + 3% N2 as the shielding gas, respectively. The microstructure of the welded joints was characterized using optical and scanning electron microscopy. The results of the SCC revealed that when sodium thiosulfate was used, the loss in plasticity was higher in the NiCrMo-3 joint with around a 20 percent decrease. Conversely, in the 310 welds, the loss in plasticity was higher in the sodium hydroxide, which diminished by 12 percent. A few secondary microcracks were observed in the transversal section in specimens of both welds. The results of the EN showed an increase in the potential and current when the sample reached the tensile strength and then decreased when the neck was formed; these changes indicate that some events occurred during the SSRT. The EN data showed two types of corrosion: general corrosion for NiCrMo-3 and mixed corrosion for the 310 welded joint in both environments. Electrochemical polarization was also employed to understand the mechanism of SCC.

The Performance of Different Etchants on the Carbides of Ni600 and Ni625

“…Despite the varying concentrations of niobium, titanium, aluminum, and other elements in these alloys, the primary types of carbides are largely confined to MC, M 6 C, M 7 C 3 , and M 23 C 6 (where M represents the metal elements) [1,5,6]. Ni625 predominantly contains MC, M 6 C, and M 23 C 6 , while Ni600 contains M 7 C 3 and M 23 C 6 [7][8][9][10][11]. Titanium nitrides are readily identifiable, as they are visible when the magnification exceeds 50 times (i.e., micrometer-sized objects can be resolved), and they are observed as particles with orange color under an optical microscope.…”

Corrosion and Protection in Aeronautical Alloys

“…Granados-Becerra et al [8] report on the stress corrosion cracking (SCC) behavior of aged plates of Inconel 600 welded to Inconel 600 plates in the as-received condition using a slow strain rate test (SSRT) on two sodium-containing electrolytes at 25 and 80 • C. The aged plate was used to simulate the damage caused by the operation. Electrochemical noise (EN) was used to monitor the SCC.…”