Hydrogen Induced Delayed Failure of Type 310 Stainless Steel Foils

Abstract

Hydrogen has been generally dismissed as playing a significant role in the mechanism of stress corrosion cracking of stable austenitic stainless steels because of the absence of brittle, delayed failures under cathodic charging conditions. In this investigation, 5-µm-thick foils of T310 (25Cr-20Ni) stainless steel have been embrittled with the application of cathodic potentials. Static delayed failures were observed in 1 N sulfuric acid (H2SO4) at ambient temperatures. Increased cathodic polarization resulted in decreased times to failure. The presence of 5-ppm arsenic greatly reduced the time to failure at a given applied potential. At a given current density, the time to failure for foils was considerably longer in solutions with pH 6 than in 1 N H2SO4. Scanning electron microscopy of fracture surfaces from cathodically charged specimens demonstrated a severe loss in ductility. The fracture mode following hydrogen charging was planar and was distinctively different from the ductile mode of failure in the absence of hydrogen. Classical hydrogen embrittlement of high-strength steels may be shown to be a reversible phenomenon by alternate hydrogen charging and degassing for many cycles. This results in a long total charging time with no concomitant permanent damage. In the present experiments, this was demonstrated for the T310 stainless steel by application of the proper potentials. The ductility of hydrogen charged specimens was recovered after baking at 400°F for 4 h. The hydrogen content of foils was found to exceed 4000-ppm hydrogen after charging in arsenic poisoned acid solutions. Charging times, high-hydrogen content and embrittlement of the stainless steel foils were related.