Effect of chloride concentration on the corrosion–fatigue crack behavior of an age-hardenable martensitic stainless steel

Abstract

Crack growth rate and S-N fatigue testing of Custom 465-H950 was performed in 0.0006-3M NaCl with different levels of pre-exposure. Custom 465-H950 exhibited a strong corrosion resistance to various NaCl-based exposures. Concurrent exposure and loading did not result in corrosion damage sufficiently severe to drive crack formation away from microstructure features (TiC particles). The total fatigue life of precorroded specimens (pit depth ≈40 μm, surface diameter ≈175 μm) increased 4-9 fold as [Cl-] decreased from 3.0M to 0.0006M. Detailed analysis demonstrated that the varying [Cl-] most strongly influenced the initiation life, with secondary contributions from the long-and short-crack propagation regimes.

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

“…Consistent with a companion study of this material lot (at constant R of 0.5), the growth rates do not scale with increasing NaCl over this concentration range. 13 Critically, the deionized (DI) water and 0.6 M NaCl results deviate from these data trends. Specifically, the growth rates measured in 0.6 M NaCl tests at −200 and −550 mV SCE are well aligned with the lower concentration results for ΔK > 6.6 and 8.2 MPa√m, respectively, but at lower ΔK deviate to a constant da/dN of ≈8 × 10 −5 and 3 × 10 −5 mm/cycle, respectively.…”

“…4c) that is consistent with the previously reported morphology for this material in NaCl environments. 13 This morphology transitions to a ductile microvoid appearance during final fracture. No significant differences are observed between fracture surfaces of each test in the range of 0.0006-0.06 M NaCl at −200 mV SCE .…”

“…7,8 Despite these attributes, high-strength steels are highly susceptible to environmental cracking in aqueous chloride environments. Specifically, researchers have demonstrated aqueous chloride environments can: induce localized corrosion damage [9][10][11][12] causing a severe reduction in overall fatigue life, 10,[13][14][15][16][17][18][19][20][21] accelerate fatigue crack-growth rates, 13,16,[21][22][23][24][25][26][27] and enhance susceptibility to stress-corrosion cracking (SCC). 21,28 Enhancement of the environmental cracking kinetics is widely attributed to hydrogen embrittlement (HE).…”

“…21,28 Enhancement of the environmental cracking kinetics is widely attributed to hydrogen embrittlement (HE). 24 Recent research on Custom 465, a precipitation-hardened martensitic stainless-steel based on the Fe-Cr-Ni system, quantified and analyzed the corrosion and H-uptake behavior, 29,30 the pit-to-fatigue crack transition, the short-crack growth and long-crack growth behavior, 13 and the stress-corrosion cracking behavior. 21,28 Critically, a time-dependent intergranular (IG) fracture process was observed at stress intensity ranges (ΔK) below the threshold value (ΔK TH ) during fracture mechanics-based fatigue testing in high [Cl − ] environments.…”

“…21,28 Critically, a time-dependent intergranular (IG) fracture process was observed at stress intensity ranges (ΔK) below the threshold value (ΔK TH ) during fracture mechanics-based fatigue testing in high [Cl − ] environments. 13 Detailed examination of this behavior was outside of the scope of the prior effort but serves as the motivation for the current study.…”