Effect of Microstructure and Alloy Chemistry on Hydrogen Embrittlement of Precipitation-Hardened Ni-Based Alloys

Obasi, Gideon; Zhang, Z.; Sampath, Dhinakaran; Morana, Roberto; Akid, Robert; Preuss, Michael

doi:10.1007/s11661-018-4483-9

Cited by 44 publications

(14 citation statements)

References 41 publications

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“…If no grain boundary precipitates are present in the moderate aging condition, another cause, such as matrix precipitate coarsening, contributes to diminishing HE resistance with aging. In previous studies, γ' and γ" coarsening during aging has been shown to influence HE susceptibility in Ni-base alloys [2,4,10].…”

Section: Discussionmentioning

confidence: 99%

“…The objective of this initial survey was to identify conditions with comparable hardness but different degrees of δ formation in Alloy 718 and M23C6 formation in Alloy 945X. A similar hardness was sought to avoid strength-related effects causing differences in HE susceptibility between conditions [10,14]. The alloys were annealed at 1050 °C for 2.5 h to solutionize precipitates.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…There is no literature regarding M23C6 precipitate effects on HE susceptibility in Alloy 945X. Obasi et al found that the strength level had a large effect on HE susceptibility in smooth tensile specimens of Alloys 718 and 945X [10]. In Alloy 945X, increasing the size of γ" precipitates through coarsening increased the strength and HE susceptibility in the absence of δ phase.…”

Section: Introductionmentioning

confidence: 99%

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The Effects of Thermal History on Toughness of Ni-Based Corrosion Resistant Alloys During In-Situ Hydrogen Charging

Kent

2021

Heat Treating Conference

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Hydrogen embrittlement (HE) susceptibility was investigated for Alloy 718 and Alloy 945X specimens heat treated to a set of conditions within the specifications of API Standard 6ACRA. Heat treatments were selected to simulate the potential variation in thermal history in thick sections of bar or forged products and produce various amounts of discontinuous grain boundary δ phase in Alloy 718 and M23C6 carbides in Alloy 945X, while maintaining a constant hardness in the range of 35-45 HRC for Alloy 718 and 34-42 HRC for Alloy 945X. Time-temperature-transformation (TTT) diagrams and experimentation were used to select a set of heat treatments containing no δ phase, a small quantity of δ, and a larger quantity of δ in Alloy 718. The presence of δ phase has not been verified for the moderate condition. A similar approach was taken regarding M23C6 carbides in Alloy 945X. Incremental step loading (ISL) tests were conducted under in-situ cathodic charging on circular notch tensile (CNT) specimens in a 0.5 M H2SO4 solution. During the test, the direct current potential drop (DCPD) was measured across the notch to determine the stress intensity associated with unstable crack growth. Results indicate that even very small quantities of δ phase in Alloy 718 are detrimental to HE resistance. Both Alloy 718 and Alloy 945X show decreases in HE resistance with aging, with a greater degradation in Alloy 718.

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Section: Discussionmentioning

confidence: 99%

Section: Experimental Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Effects of Thermal History on Toughness of Ni-Based Corrosion Resistant Alloys During In-Situ Hydrogen Charging

Kent

2021

Heat Treating Conference

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“…The manufacturing route of bolts involves the API heat treatment followed by cold rolling of threads, whereas, samples extracted from RB undergo electrical discharge machining followed by the heat treatment. The objective was to perform subsurface cracking analysis for the subsea bolts on the basis of microstructural results and to critically discuss the 718 subsea bolt vulnerability to HE in-service with the already established HAC theories for alloy 718 (which were subjected to different thermochemical treatments and product forms) [ [37]. The non-standard higher solution treatment at 1250˚C (because the melting Figure 1.…”

Section: Purposementioning

confidence: 99%

Alloy 718 Subsea Bolt in Relation to Surface Cracking: A Microstructural Perspective

Saleem¹,

Dong²,

Patel³

2020

MSA

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The brittle fracture mode close to the surface of Inconel 718 subsea bolts is closely related to their nanostructure. When the bolts are used subsea under cathodic protection, hydrogen evolves. Intergranular precipitates and points of intersection of slip lines always held responsible for hydrogen enhanced decohesion. However, thus far, little attention has been paid to the bolts manufacturing method and to the characterization of the role of subsurface oversized nanoprecipitates on transgranular surface cracking. As-received subsea bolts were analyzed using multi-scale observation techniques such as focused ion beam milling, scanning electron microscopy, transmission electron microscopy, and in-air strain rate tensile tests. The results further demonstrated that under identical API aging, there was a difference in the morphological precipitation and strength of 718 as a bolt and rectangular billet. For the 718 rectangular billets, discrete intergranular stable δ/MC carbides precipitate and only γ' of 10-20 nm was observed for the bulk and subsurface. Whereas, for the CRA subsea bolt, γ' was approximately 30 nm, γ" was 30-50 nm for the bulk (370 HV); γ' was approximately 50 nm and γ" was 50-100 nm at subsurface (400 HV). As-received subsea bolts were investigated at subsurface (10 µm from the surface) at the thread and shank region, which revealed transgranular sheared oversized ~50 nm γ' (with dislocation networks) and metastable γ" > 100 nm particles, respectively. Thus, an effort was made to develop the hydrogen-assisted surface cracking theory for bolts.

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“…Some inclusions can initiate a pitting corrosion and could lead to environmentally assisted cracking, corrosion fatigue, hydrogen embrittlement. Therefore, the study of corrosion and mechanical properties of Ni-based alloys and their dependence on different inclusions became the object of attention in many studies [15,16,17,18,19,20].…”

Section: Introductionmentioning

confidence: 99%

Effect of Inclusions on the Corrosion Properties of Nickel Based Alloys 718 and EP718

Alekseeva¹,

Karasev²,

Jönsson³

et al. 2020

Preprint

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Inclusions in steels and alloys are known as factors that could lower deformation, mechanical, corrosion and other properties. Study of inclusions in nickel based alloys is important since these materials could suffer from corrosion degradation in harsh operational conditions, where inclusions could lead to a pitting initiation. For estimation of a harmful effect of different inclusions on corrosion resistance of Ni-based alloys, inclusion characteristics (such as composition, morphology, size, number and location) on film filter and dissolution of metal matrix around different inclusions on surfaces of metal samples after electrolytic extraction (EE) were investigated in two samples of industrial Ni-based alloys (alloy 718 and EP718). It was found that both Ni-based alloys have various inclusions: carbides (large size NbTi-C and small multicomponent carbides), nitrides TiNb-N and sulfides (TiNb-S in EP718 alloy). The higher harmful effect on corrosion resistance of metal was detected around sulfides and small carbides containing Mo, W, Cr. Dissolution effect was also observed around large carbides and nitrides, especially around inclusions having size more than 10 µm. Moreover, the dissolution of metal matrix around inclusions and clusters located on the grain boundaries is 2.1-2.7 times larger compared to that for those inclusions inside of grains of the given alloy samples.

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Effect of Microstructure and Alloy Chemistry on Hydrogen Embrittlement of Precipitation-Hardened Ni-Based Alloys

Cited by 44 publications

References 41 publications

The Effects of Thermal History on Toughness of Ni-Based Corrosion Resistant Alloys During In-Situ Hydrogen Charging

The Effects of Thermal History on Toughness of Ni-Based Corrosion Resistant Alloys During In-Situ Hydrogen Charging

Alloy 718 Subsea Bolt in Relation to Surface Cracking: A Microstructural Perspective

Effect of Inclusions on the Corrosion Properties of Nickel Based Alloys 718 and EP718

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