STRESS-CORROSION OF ALUMINUM-COATED AUSTENITIC STAINLESS-STEELS

Stress-corrosion tests have been conducted on austenitic stainless steel specimens with and without protective aluminium coatings provided by electrodeposition. Coated specimens were subjected to diffusion heat treatments to obtain protective substantial solid solutions. The behaviour 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 temperature with loads of 80% of sigma(p(0.2)) stress corrosion is intergranular, whereas at 120% of sigma(p(0.2)) it is transgranular. At 80 degrees C and 120 mV, transgranular stress corrosion occurs under both loading 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.