Micro-Magnetic, Multiple Parameter, Microstructure and Stress Analysis (3MA) to characterise Toughness Degradatioh after Heat-treatment in JRQ-Reference Material

In Europe recently a research network was established under the headline of the EURATOM programme in order to identifiy non-destructive techniques for insitu-characterisation of materials damage and degradation in nuclear power pressure vessels. Test specimens were prepared from plates of the JRQ reference material and characterised by destructive (analytical, metallography, REM and TEM) as well as non-destructive techniques bevor ("state as delivered") and after a heat-treatment ("thermally treated" 18 hours at 700°C+ quenching in water) of the bar-shaped specimen. Parallel micro-hardness measurements and Charpy-notch impact tests were performed to document the state of ageing in reduction of the upper shelf value of the impact energy and shift in the fracture-appearance-transistion temperature (FATT). The paper discusses the results obtained by use of micromagnetic techniques (Barkhausen noise, incremental permeability, eddy current impedance, higher harmonics in the tangential magnetic field). Results documented by positron annihilation (Doppler-line-shaping and lifetime), ultrasonic absorption and back-scattering are tackled not in detail. The micro-structure degradation which is manly based on the development of martensite at former austentic grain boundaries and more pronounced in segregation bands with higher carbon content can clearly and uniquely characterised by the proposed 3MA-technique.