The interaction of corrosion fatigue and stress-corrosion cracking in a precipitation-hardened martensitic stainless steel

Fracture mechanics-based testing was used to quantify the stress-corrosion cracking and corrosion fatigue behavior of a precipitation-hardened martensitic stainless steel (Custom 465-H950) in full immersion chloride-containing environments at two applied electrochemical potentials. A plateau in the cycle-based crack-growth kinetics (da/dN) was observed during fatigue loading at low Delta K and [Cl-] at and above 0.6M. Evaluation of the fracture morphology and frequency dependence of this plateau behavior revealed an intergranular fracture surface morphology and constant time-dependent growth rates. These data strongly support a controlling stress-corrosion cracking mechanism occurring well below the established K-ISCC for quasi-static loading. Low-amplitude cyclic loading below Delta K-TH (i.e., ripple loads) is hypothesized to enable time-dependent intergranular-stress-corrosion cracking to occur below the K-ISCC via mechanical rupturing of the crack-tip film and enhancement of the H embrittlement-based SCC mechanism. Stainless steels: quantifying environmental fatigue failureModern high-strength stainless steels offer combined mechanical and corrosion resistance, but are susceptible to environmental cracking in aqueous chloride solutions, typical of coastal and marine environments. New insight into environmentally enhanced fatigue behavior is thus of practical value. A team led by James Burns at University of Virgina has now quantitatively characterized the stress-corrosion cracking and fatigue fracture behavior of a precipitation-hardened martensitic stainless steel in various aqueous chloride solutions and elucidated the relative contribution of each factor to overall crack growth. The obtained data indicates an interesting mechanism that governs intergranular-stress-corrosion cracking. The present understanding may enable rational design and prognosis of engineering materials for use in the field.