A study of microstructural analysis for nondestructive evaluation of thermal annealing using magnetic properties. (July 2017) - Park, D.G.
Abstract: Two kinds of thermally aged Fe-Cu alloys with different Cu proportions 0.05% and 0.45% were prepared and their magnetic properties were investigated to apply magnetic nondestructive testing techniques for the assessment of irradiation embrittlement of materials. Initially, the alloy is 10% cold rolled and then isothermally aged at 500 °C and 400 °C with different aging time up to 1000 h in order to create Cu-precipitates in the Fe metal matrix. The hysteresis loop (HL), Barkhausen noise (BN) and Magnetic Adaptive Testing (MAT) parameter were measured for magnetic properties studies and mechanical properties were investigated by Vickers hardness. The HL, BN were decreased and the MAT parameter was increased by thermal aging. The changes of these parameters were explained by copper rich precipitations (CRPs) formation, interaction with domain walls and dislocation movement pinned by CRPs. It was confirmed by TEM and EDX analysis. Highlights: Magnetic methods were incorporated in the evaluation of irradiation embrittlement of RPV steel. The Magnetic parameters such as coercivity, Barkhausen noise and minor loops were perfectly correlated to the CRPs mechanism, number and volume density of CRPs. Residual stress and Vickers hardness changes with ageing were explained supporting with magnetic parameters. Micro imaging methods were used for micro structural change studies.