Quantitative investigation of brittle out-of-plane fracture in X70 pipeline steel

Franck Tankoua (1) , Jérôme Crépin (1) , Philippe Thibaux (2) , Steven Cooreman (2) , Anne-Françoise Gourgues-Lorenzon (1)

1 MAT - Centre des Matériaux
2 ArcelorMittal

Brittle out-of-plane cracking (by delamination or brittle tilted fracture) affects the impact toughness of pipeline steels. It has been investigated on notched tensile specimens using a local approach to fracture. Smooth and notched bars taken along four directions (including the short transverse direction, ND) have been tested in tension at temperatures between 20 °C and -196 °C. Delamination partly results from the lower value of the critical cleavage stress along ND, linked to the microtexture anisotropy, but also from the presence of ductile microcracks acting as stress concentrators triggering fracture along the rolling plane. Brittle tilted fracture was associated to a relatively lower value of the critical cleavage stress in that plane, but prior delamination was necessary to trigger it. The relevance of a macroscopic critical stress criterion for delamination is finally discussed.

Mots clés: Delamination fracture; Brittle tilted fracture; Cleavage; Anisotropy; Microtexture

Domaines: Sciences de l'ingénieur [physics]; Matériaux

Franck Tankoua, Jérôme Crépin, Philippe Thibaux, Steven Cooreman, Anne-Françoise Gourgues-Lorenzon. Quantitative investigation of brittle out-of-plane fracture in X70 pipeline steel. 20th European conference on fracture (ECF 20), Jun 2014, Trondheim, Norway. pp.1149-1154, ⟨10.1016/j.mspro.2014.06.187⟩. ⟨hal-01053645⟩