Lead-induced stress corrosion behavior of Alloy 690

Reverse U type specimens of Alloy 690 were put in an autoclave to conduct the stress corrosion test for 4400 h.The stress corrosion behavior of the alloy in a high-temperature and high-pressure water solution containing Pb was studied by scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS).The results show that transgranular stress corrosion cracking occurs in the alloy.Corrosion products with Pb can be found to accumulate in the crack.EDS face scanning of the crack zone indicates that the corrosion film formed in the test solution is a double-layer structure,the outer layer is rich in Ni and the inner layer is rich in Cr.The difference of expansion coeffcients between corrosion products in the crack and the matrix causes a faster crack propagation.Due to different surface treatments,the inner surface and outer surface of the specimens have different corrosion morphologies,the inner surface is lattice-like,but the outer surface shows a certain direction groove.