The purpose of this work is to evaluate the stress corrosion cracking (SCC) of two Ni-Cr-Mo-V Italian-made alloys that are materials used for low-pressure (LP) turbine discs in light water reactor (LWR) nuclear plants.
All the tests reported in this investigation have been performed using the slow strain rate technique (SSRT). The first set of experiments was conducted in pure deaerated caustic solutions in a static Ni autoclave system in order to determine the effects of temperature and NaOH concentration on the SCC behavior of these materials. Both alloys showed a decreasing SCC susceptibility as NaOH concentration and temperature decreased and the threshold value of temperature/NaOH concentration combinations for SCC to occur was lower for the heat with the higher Ni content and the larger grain size.
In the second set of tests, the influence of dissolved oxygen on cracking in water was studied; for this purpose, specimens were strained to fracture at 200 C in pure oxygenated water with various amounts of oxygen and at a suitable strain rate to induce SCC; a refreshed autoclave system was used to permit continuous monitoring of the chemical parameters.
Results showed that the minimum value of oxygen to promote SCC was lower for the heat with the higher Ni content and the larger grain size.
