STRESS-CORROSION OF ALUMINUM-COATED AUSTENITIC STAINLESS-STEELS

Stress-corrosion tests have been conducted on austenitic stainless ste el specimens with and without protective aluminium coatings provided b y electrodeposition. Coated specimens were subjected to diffusion heat treatments to obtain protective substantial solid solutions. The beha viour in 1 N H2SO4+0.2 N NaCl solution was investigated. For uncoated steel at +850 mV (sce) in the imperfect passivity range at room temper ature with loads of 80% of sigma(p(0.2)) stress corrosion is intergran ular, whereas at 120% of sigma(p(0.2)) it is transgranular. At 80 degr ees C and 120 mV, transgranular stress corrosion occurs under both loa ding conditions. For a coated steel in the imperfect passivity range, there is no stress corrosion at room temperature with loads up to 80% of sigma(p(0.2)). In the active field at higher loads the breakdown of protective intermetallic compounds occurs, leaving the steel exposed to stress corrosion.