Crack initiation in tapered specimens - High Si stainless steels

Datum: 11 oktober 2019

Locatie: UAntwerp - Campus Groenenborger, lokaal U.408 - Groenenborgerlaan 171 - 2020 antwerpen (route: UAntwerpen, Campus Groenenborger)

Tijdstip: 11.30 - 12.30 uur

Organisatie / co-organisatie: EMAT

Korte beschrijving: Friday Lecture by Aäron Penders, SCK•CEN

About the lecture

Stainless steels (SSs) are extensively used in the internal components of the reactor pressure vessel (RPV) in nuclear power plants (NPPs) because of their notably high strength, toughness and corrosion resistant qualities at elevated temperatures. Said steels are subjected to high-energetic neutron fluxes which, amongst many other NPP operation stressors, impose changes on a microstructural level. One of the outcomes is irradiation-assisted stress corrosion cracking (IASCC), which is the continuation of plain SCC, which describes the non-ductile cracking effect in susceptible materials due to the combination of several prominent stressors and environmental influences.

In the pursuit of reliability and safe NPP operation, an accelerated test method based on a width-tapered geometry of A078 stainless steel specimens was applied in order to determine the individual stress thresholds for crack initiation for a number of samples exposed to different nominal strain rates. The specimens were strained in constant elongation rate tensile (CERT) tests while being subjected to a simulated pressurized water reactor (PWR) environment to induce SCC. Scanning electron microscopy (SEM) is utilized to investigate the crack statistics along the gauge length of the tapered specimens. The detections are based on the powerful built-in ridge detector tool of the open source image processing software Fiji. In the process of this investigation, detailed crack density, length, angle and cross-sectional crack depth analyses along the specimen’s fractured gauge surface were obtained. This allows for the calculation of the material’s critical stress threshold in a different manner than the widely-scattered, conventionally established methods in the literature.