Influence of Material, Environment and Strain Rate on Environmentally Assisted Cracking of Austenitic Nuclear Materials (DEFSPEED): DEFSPEED summary report

The DEFSPEED project (Influence of material, environment and strain rate on environmentally assisted cracking on austenitic nuclear materials) focussed on increasing the understanding of environmentally assisted cracking (EAC) and irradiation assisted stress corrosion cracking (IASCC) mechanisms in austenitic nuclear materials. Several sub-tasks were performed to achieve the set objectives during the four year project. The Super Slow Strain Rate Testing technique (SSSRT) was developed and employed for initiation studies on austenitic nuclear materials in LWR environments followed by in-depth investigations on deformation distribution. Austenitic nuclear materials show dynamic strain ageing behaviour, as described in a thesis work. The effect of environment on fracture toughness properties in nickel-based welds at slow strain rate in hydrogenated water was determined both for materials from dissimilar metal welds as well as on pure weld metal specimens. Irradiated austenitic stainless steels from plant internals were characterized using transmission electron microscopy (TEM) to increase the knowledge of radiation induced segregation and defect structures, which both play a role in IASCC. The latest international knowledge, applied for customer work, was brought to Finland by participating in international co-operation within the fields of EAC and IASCC. Education of new experts in the field of nuclear materials is an important objective for all SAFIR 2010 projects. In addition to participation of young experts in the project, a digital report archive was built, containing reports on nuclear materials written by VTT.