Hydrogen Environment Assisted Cracking of a Modern Ultra-High Strength Martensitic Stainless Steel

Abstract

A modern martensitic stainless steel (Ferrium® PH48S™) resists hydrogen environment assisted cracking (HEAC) in aqueous NaCl at ultra-high yield strengths (1,400 MPa to 1,600 MPa). HEAC is transgranular, because of increased steel purity and La addition, compared to severe intergranular HEAC in Custom® 465-H900 without rare earth elements. Minimum threshold for HEAC (KTH) is low (8 MPa√m to 17 MPa√m) for each steel under substantial cathodic polarization. Transgranular HEAC occurs along martensite packet and {110}α′-block interfaces in PH48S, likely a result of H decohesion enabled by localized plasticity. Martensite transformation produces a large area of coincident site lattice interfaces in the refined microstructure of PH48S. However, a susceptible network of random packet/block interfaces is connected in 3D to limit interface engineering. Nanoscale strengthening precipitates in PH48S reduce effective H diffusivity to the mid-10−10 cm2/s range, because of reversible H trapping with a binding energy of 12 kJ/mol. This diffusivity reduces the Stage II growth rate by 1 to 3 orders of magnitude compared to C465 and carbide strengthened ultra-high strength steels. PH48S and C465 are nearly immune to HEAC when cathodically polarized by 50 mV to 500 mV, attributed to a minimum in occluded-crack tip overpotential for H production. The breadth of this protective-potential window increases with decreasing steel strength. Increased Cr does not degrade HEAC resistance, suggesting that crack passivity dominates cation acidification to reduce H production and/or uptake. A quantitative decohesion model effectively predicts the potential dependence of da/dtII using crack tip H solubility reverse calculated from a KTH model.

Hydrogen Diffusivity and Trapping in Custom 465 Stainless Steel

“…A similar trend of a higher hydrogen concentration in the H900 condition of Custom 465 compared to the SA condition has been reported recently. 6 Figure 4 presents a series of TPD spectra obtained at various heating rates (5-20 • C/min) for the SA (Fig. 4a), H900 (Fig.…”

“…[1][2][3] Although this steel is recommended for engineering applications in corrosive environments that contain hydrogen, only little work has been published on hydrogen interaction with this steel, to the best of our knowledge. [4][5][6] Hydrogen diffusivity is affected by the microstructure that results from different thermal treatments. 4 The microstructure of Custom 465 steel 7 in the solution annealed (SA) condition consists of Fe-Ni martensite, which is characterized by blocks of parallel lamellae organized in packets along the prior austenite grains.…”

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

“…First, given the enhanced susceptibility of the H900 condition compared to H950 (as shown for Custom 465 (ref. 21 ) and for a similar precipitation-hardened martensitic steel, Ferrium PH48S 28,48 ), the K ISCC values reported for the H900 condition can be considered lower bounds for the H950 used in the current study. Second, even at the most aggressive polarizations on the more susceptible H900 condition, the K ISCC of ≈10 MPa√m is still greater than K max of ≈5 MPa√m, where IG was observed in Figs.…”

“…Further details of this method are presented elsewhere. 48 Regarding the K-shed cyclic loading (sinusoidal waveform), the notched SEN specimens were first cyclically loaded at a maximum stress (σ max ) of 300 MPa, R of 0.5, and a frequency (f) of 2 Hz to form a crack. The ΔK increased with crack extension (at constant Δσ) up to 27.5 MPa√m (thus, a K max of 55 MPa√m).…”

Behavioral Analysis of Hydrogen in Metals under the Effect of H2S Corrosion Using a Layer-stripping Micro-hardness Technique

“…Hydrogen is a ubiquitous element that enters metal materials from many different sources. Once metals are exposed to hydrogen, they may interact with it resulting in various kinds of structural damage, e.g., hydrogen environment assisted cracking [1], delayed hydride cracking (DHC) [2], and hydrogen embrittlement [3,4]. The exact assessment of hydrogen concentration behavior is the crux of the study of hydrogen damage in metals.…”