Investigation of Hydrogen Production and Uptake on Ultra-High Strength Steels Exposed to Laboratory Accelerated Life Test and Natural Atmospheric Environments

Presently, many components of military and mass transportation vehicles; landing gear, turbine blades and fasteners, are constructed of high performance alloys.   For parts composed of ferrous, nickel and/or aluminum-based alloy materials, exposure to atmospheric corrosion and high stress (often greater than their yield strength), can result in hydrogen production, absorption and accumulation.  Most of these alloys were not designed to provide intrinsic corrosion resistance and were coated with metallic coatings for improved corrosion resistance.  Federally mandated replacement of heavy metals has driven interest in designing ultra-high strength alloys with improved intrinsic corrosion resistance in an effort to eliminate environmentally hazardous materials.  These new alloys, specifically ferrous martensitic stainless steels, often exhibit a modest resistance to Cl- induced localized corrosion. General and local corrosion can lead to hydrogen production and uptake which can lead to hydrogen environment assisted cracking (HEAC). Thus, interest in hydrogen embrittlement at atmospheric conditions has become increasingly important to the development of these alloys.  Materials may be screened for hydrogen embrittlement susceptibility through lab accelerated life testing (LALT) or field exposures of stressed tensile samples. Trapped and diffusible hydrogen, the cause of HEAC, are often not determined during these exposures. This study explores the effects of lab and atmospheric environments on hydrogen uptake in two ferrous alloys, martensitic, secondary age hardened Aermet 100 (Fe-3Cr-11Ni-13Co-1.2Mo; wt%) and Custom 465 (Fe-12Cr-11Ni-1Mo-2Ti; wt%).  A variety of environment factors were considered including full immersion, salt spray, relative humidity, thin film layers, times of wetness, Cl- deposition density, and cycling.  Hydrogen absorption measurements were established through hydrogen permeation, barnacle cell testing and thermal desorption spectroscopy. These results are being used to create a connection between the severity of field environments and LALT testing environments and a “corrosion intensity factor” is being established to directly compare the atmospheric, field and full immersion testing.