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Characteristics and Mechanisms of Hydrogen-Induced Quasi-Cleavage Fracture of Lath Martensitic Steel

Published

Author(s)

Lawrence Cho, Peter E. Bradley, Damian S. Lauria, May L. Martin, Matthew J. Connolly, Jake Benzing, Eun Jung Seo, Kip O. Findley, John G. Speer, Andrew J. Slifka

Abstract

This study presents an in-depth characterization of the microstructures, crystallographic orientations, and dislocation characteristics beneath the hydrogen-induced quasi-cleavage features of an as-quenched, lath martensitic (') 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 clearly quasi-cleavage fracture, while intergranular cracks along prior austenite grain boundaries were also noted. The quasi- cleavage involved significant plasticity, evidenced by plastic zones near tear ridges and a high density of dislocations beneath the quasi-cleavage facets. Both the martensitic constituent sizes and variant orientations influenced the quasi-cleavage surface morphologies. In particular, the current fractography revealed the occurrence of 100}'-type cleavage across martensitic laths, developing relatively "flat" quasi-cleavage surfaces, in addition to 110} '-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. Furthermore, 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 the crack deviations at those boundaries. The fracture paths and possible mechanisms for the martensite quasi- cleavage were discussed in the context of the role of hydrogen.
Citation
ACTA Materialia
Volume
206

Keywords

Lath martensitic steel, quasi-cleavage, cleavage, gaseous hydrogen, press-hardened steel

Citation

Cho, L. , Bradley, P. , Lauria, D. , Martin, M. , Connolly, M. , Benzing, J. , , E. , , K. , , J. and Slifka, A. (2021), Characteristics and Mechanisms of Hydrogen-Induced Quasi-Cleavage Fracture of Lath Martensitic Steel, ACTA Materialia, [online], https://doi.org/10.1016/j.actamat.2021.116635 (Accessed October 19, 2021)
Created January 9, 2021, Updated March 1, 2021