Crack resistance tests were performed at high temperature, 550 and 650°C, on the 12%Cr– and 14%Cr– ODS steels. Specimens were taken in two orientations, L–T and T–L for the KOBELCO 12%Cr–ODS prismatic plate and in L–Rx and L–Ry for the CEA 14%Cr–ODS cylindrical bar. It is found that both materials are clearly anisotropic. The crack resistance of both materials is relatively low in comparison to standard non–ODS Cr steels. The lowest toughness, corresponding to about 22 MPaVm, is found in the T–L orientation of the 12%Cr–ODS steel. Similarly, the tearing resistance follows the trend of initiation toughness. As a result, for heavily loaded components at high temperatures for which fracture is not permitted, these 12%Cr– and 14%Cr–ODS–steels cannot be used. This is inherent of this kind of materials due to the presence of a high density of strong nano–oxide particles in a soft matrix facilitating crack initiation and propagation at their interface. Their high temperature crack resistance could be increased if the particle–matrix bonding is improved. For thin walled components such as fuel cladding and where cracking is not a critical safety issue, application is possible if it can be demonstrated that specific post–irradiation properties are not severely degraded.
|Number of pages
|Published - 15 Nov 2011
|Studiecentrum voor Kernenergie