Quantification and microstructural origin of the anisotropic nature of the sensitivity to brittle cleavage fracture propagation for hot-rolled pipeline steels

• Published in: International journal of fracture 2018-08, Vol.212 (2), p.143-166
• Main Authors: Tankoua, F., Crépin, J., Thibaux, P., Cooreman, S., Gourgues-Lorenzon, A.-F.
• Format: Article
• Language: English
• Subjects: Anisotropy; Automotive Engineering; Brittle fracture; Characterization and Evaluation of Materials; Chemistry and Materials Science; Civil Engineering; Classical Mechanics; Cleavage; Condensed Matter; Crack propagation; Crack sensitivity; Delamination; Drop tests; Ferritic stainless steels; Fracture mechanics; Fracture toughness; Hot rolling; Impact strength; Materials Science; Mechanical Engineering; Microstructure; Microtexture; Morphology; Original Paper; Physics; Plastic flow; Rolling resistance; Size distribution; Tear tests; Tensile tests; Weight
• ISSN: 0376-9429; 1573-2673
• DOI: 10.1007/s10704-018-0297-4

This work proposes a quantitative relationship between the resistance of hot-rolled steels to brittle cleavage fracture and typical microstructural features, such as microtexture. More specifically, two hot-rolled ferritic pipeline steels were studied using impact toughness and specific quasistatic tensile tests. In drop weight tear tests, both steels exhibited brittle out-of-plane fracture by delamination and by so-called “abnormal” slant fracture, here denoted as “brittle tilted fracture” (BTF). Their sensitivity to cleavage cracking was thoroughly determined in the fully brittle temperature range using round notched bars, according to the local approach to fracture, taking anisotropic plastic flow into account. Despite limited anisotropy in global texture and grain morphology, a strong anisotropy in critical cleavage fracture stress was evidenced for the two steels, and related through a Griffith-inspired approach to the size distribution of clusters of unfavorably oriented ferrite grains (so-called “potential cleavage facets”). It was quantitatively demonstrated that the occurrence of BTF, as well as the sensitivity to delamination by cleavage fracture, is primarily related to an intrinsically high sensitivity of the corresponding planes to cleavage crack propagation across potential cleavage facets.