On modeling of thermal embrittlement in PWR steels using the local approach to fracture

Antoine Andrieu (1) , André Pineau (1) , Pierre Joly (2) , François Roch (2)

1 CDM - Centre des Matériaux
2 AREVA

Experiments on Charpy and CT specimens were carried out on one heat of A533B steel under two conditions: (i) as received, and (ii) thermally aged (450°C - 5000h). A shift of the ductile to brittle transition temperature (DBTT) was measured after aging. In both cases SEM observations showed that fracture occurred both by intergranular and transgranular cleavage fracture modes when the materials were tested at sufficiently low temperature. Detailed examinations revealed that intergranular fracture was associated with micro-segregated zones, enriched in carbon and phosphorus. A recent model developed by the authors for predicting the fracture toughness of inhomogeneous materials was applied to describe the large scatter related to the bimodal failure modes observed in both conditions and the DBTT shift after aging. It is shown that thermal aging produces a slight decrease of the critical cleavage stress (due to the crossing of grain boundaries embrittled by phosphorus segregation) and a larger decrease of the critical intergranular fracture stress. The McLean-Guttmann- Militzer model is used to predict the kinetics of segregation during aging. An attempt is made to show how these results can be used to model DBBT variations under in-service conditions.

Mots clés: Ductile to brittle transition; intergranular; phosphorus segregation

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

Antoine Andrieu, André Pineau, Pierre Joly, François Roch. On modeling of thermal embrittlement in PWR steels using the local approach to fracture. 13th international conference on fracture, Jun 2013, Beijing, China. 10 p. ⟨hal-00853417⟩