Hydrogen embrittlement susceptibility and permeability of two ultra-high strength steels

“…For example, the effect of aging temperature on hydrogen diffusivity in PH 13-8Mo was reported. 8,9 The effect of aging temperatures on the detrapping energies and solubility in PH martensitic stainless steel has not been reported yet, to the best of our knowledge. Here, the effects of heat-treatment on hydrogen diffusivity, solubility, permeability and the average detrapping energies in the H900 and H1000 age conditions as well as in the SA condition are reported.…”

mentioning

confidence: 99%

Hydrogen Diffusivity and Trapping in Custom 465 Stainless Steel

Ifergane

Ruch

Sabatani³

et al. 2018

J. Electrochem. Soc.

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Custom 465 is an advanced precipitation hardened martensitic stainless steel exhibiting a combination of high strength, high fracture toughness and good corrosion resistance. This steel is recommended for use in hydrogen atmospheres, yet only little research has been published on hydrogen behavior in this alloy. Here, the diffusivity, solubility and average detrapping energy for hydrogen were compared in various thermal conditions (solution annealed, H900 and H1000), employing electrochemical permeation and thermal programmed desorption measurements. It is suggested that reversible (low energy) traps in the H900 and H1000 conditions, associated with (semi)coherent η-Ni 3 Ti precipitates, are responsible for the high hydrogen solubility and low diffusivity. At the peak of coherency of the precipitates in the H900 condition, higher solubility and lower diffusivity and detrapping energy were measured. The value of the diffusion coefficient is found to change during different stages of charging and discharging, depending on the level of occupancy of the reversible traps. Carpenter Technology's Custom 465 (UNS S46500) is an advanced precipitation hardened (PH) martensitic stainless steel, characterized by a combination of high strength and fracture toughness with good corrosion resistance, compared to other PH stainless steels. 1-3 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. During aging, η-Ni 3 Ti nano-precipitates are formed inside the lamella, and reverted austenite at grain boundaries and interlamella boundaries. For engineering applications, both H900 and H1000 age conditions are mostly recommended. 1 In the H900 (482 • C/ 4 hours) age condition, 7 the (semi)coherent rod-shape nanoprecipitates of η-Ni 3 Ti, about 3 nm in diameter and 8 nm long, are formed, and a maximal ultimate tensile strength (UTS) of about 260 ksi (1793 MPa) is obtained. In the H1000 (540 • C/ 4 hours) age condition, precipitates grow to about 9 nm in diameter and 27 nm in length. Due to the lower coherency of the precipitates and their lower density in the H1000 condition, the UTS decreases to 225 ksi (1551 MPa). At the same time, the ductility, fracture toughness, general corrosion and stress corrosion cracking (SCC) resistance all improve. 1 In both the H900 and H1000 age conditions, the reverted austenite concentration is less than 5 vol.%, and it is dispersed as discrete particles. 7 The fundamental correlation between the microstructure change during aging and hydrogen behavior in PH martensitic stainless steels has been studied to li...

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“…The trend is that the specimens with lower HE susceptibilities exhibited more of the ductile dimple fracture on the fracture surfaces. HE or hydrogen-assisted fatigue crack growth would lead to an intergranular fracture mode of ultra-high strength steels in a more severe environment [20][21][22][23], however, it was not the case for PH 13-8 Mo steel in gaseous hydrogen; intergranular fracture of the specimens was not observed.…”

Section: Fractographic Examinationsmentioning

confidence: 56%

“…Additionally, high strength steel is generally associated with a small plastic zone ahead of the crack tip; hence, a critical hydrogen concentration can be reached promptly and can induce cracking thereafter. The low hydrogen diffusivity of the specimens aged at or above 593°C, in addition to their reduced strength level, implies that a high concentration of hydrogen is less likely to be attained in the plastic zone in front of the crack tip, resulting in a decreased sulfide stress cracking susceptibility (or HE) of the material [10,20]. In this work, the trend of the hydrogen-accelerated fatigue crack growth of aged PH 13-8 Mo specimens was consistent with the susceptibilities to gaseous HE evaluated by slow extension rate tensile tests.…”

Section: Discussionmentioning

confidence: 99%