Anisotropic intergranular damage development and fracture in a 14Cr ferritic ODS steel under high-temperature tension and creep

Hubert Salmon-Legagneur (1, 2, 3) , S. Vincent (2) , J. Garnier (2) , Anne-Françoise Gourgues-Lorenzon (1) , Eric Andrieu (3)

1 CDM - Centre des Matériaux
2 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)
3 CIRIMAT - Centre interuniversitaire de recherche et d'ingenierie des matériaux

This work addresses damage mechanisms at high temperature of a hot extruded 14Cr oxide dispersion strengthened steel rod, in particular, anisotropy induced by its strong morphological and crystallographic texture. Under uniaxial tension, intergranular damage and unstable fracture increased with test temperature; they appeared much easier along the rod axis than perpendicular to it. Creep fracture of smooth specimens involved crack initiation from the side surfaces and intergranular crack propagation, accompanied by intergranular damage. In order to get rid of fracture surface oxidation by the air environment, a methodology promoting crack nucleation from inside the specimen was built. From tensile and creep tests on notched specimens the fracture initiation location and fracture stability were first mapped as a function of test temperature, maximal stress triaxiality and loading direction. Then, for the first time to the authors' knowledge, interrupted tests on notched tensile and creep specimens, followed by low-temperature fracture allowed revealing fracture surfaces formed at high temperature, but unconnected to the external environment. Intergranular fracture and grain boundary grooving were evidenced there, together with strong chemical reactivity at the surface of internal cavities during damage development at high temperature.

Mots clés: Oxide dispersion strengthened ferritic steels; tension; creep; intergranular damage

Domaines: Mécanique des matériaux [physics.class-ph]

Hubert Salmon-Legagneur, S. Vincent, J. Garnier, Anne-Françoise Gourgues-Lorenzon, Eric Andrieu. Anisotropic intergranular damage development and fracture in a 14Cr ferritic ODS steel under high-temperature tension and creep. Materials Science and Engineering: A, 2018, 722, pp.231-241. ⟨10.1016/j.msea.2018.02.102⟩. ⟨hal-01759149⟩