Characteristics and mechanisms of hydrogen-induced quasi-cleavage fracture of lath martensitic steel

This study presents an in-depth characterization of the microstructures, crystallographic orientations, and dislocation characteristics beneath hydrogen-induced quasi-cleavage fracture features of an as-quenched, lath martensitic (α') 22MnB5 steel. The fracture surfaces of gaseous hydrogen-embr...

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Veröffentlicht in:Acta materialia 2021-03, Vol.206 (C), p.116635, Article 116635
Hauptverfasser: Cho, L., Bradley, P.E., Lauria, D.S., Martin, M.L., Connolly, M.J., Benzing, J.T., Seo, E.J., Findley, K.O., Speer, J.G., Slifka, A.J.
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Sprache:eng
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Zusammenfassung:This study presents an in-depth characterization of the microstructures, crystallographic orientations, and dislocation characteristics beneath hydrogen-induced quasi-cleavage fracture features of an as-quenched, lath martensitic (α') 22MnB5 steel. The fracture surfaces of gaseous hydrogen-embrittled martensitic specimens were analyzed by a combination of multiple analytical tools: scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and transmission Kikuchi diffraction (TKD). The dominant fracture mode in the hydrogen-affected zones was quasi-cleavage fracture, which involved significant plasticity, evidenced by plastic zones near tear ridges and a high density of dislocations beneath the quasi-cleavage facets. The martensite constituent sizes, variant orientations, and boundaries influenced the quasi-cleavage surface morphologies. Fractography revealed the occurrence of {100}α'-type cleavage across martensitic laths, developing relatively “flat” quasi-cleavage surfaces, in addition to {110}α'-type cracking likely along lath and block boundaries, and fracture along non-cleavage planes. The likelihood of the formation of the relatively “flat” quasi-cleavage surfaces increased with increasing martensitic constituent sizes. Substantial dislocation bands formed on intersecting {112}α' slip planes within a martensite block below the hydrogen-induced cleavage fractures on {100}α' planes. River markings on the quasi-cleavage surfaces were found to originate from the complex, hierarchical lath martensitic microstructure. Steps and ridges on the quasi-cleavage facets generally linked with the various martensitic boundaries, suggesting that they were produced as a result of crack deviations at those boundaries. The fracture paths and martensite quasi-cleavage mechanisms are discussed in the context of the role of hydrogen and Cottrell cleavage model. [Display omitted]
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2021.116635