Non-destructive testing of material embrittlement by thermal ageing, neutron embrittlement and fatigue in fine-grained structural steels

This contribution presents findings of a EU project and national research projects on ferritic and austenitic structural steels commonly used in pipeline and container construction. Micromagnetic and thermal methods, positron annihilation and acoustic microscopy were used, with the following results: Micromagnetic methods are sensitive to Cu segregations from thermal embrittlement in steel WB36. In multiple linear regression, correlations with neutron fluency or brittle fracture transition temperature were sufficiently accurate. Fatigue of stabilized austenitic steels is often accompanied by phase transition into the ferromagnetic a' martenistic phase. The amount of martensite produced varies as a function of chemical composition, per volume segregation, thermal treatment, and loads. Positron annihilation tests were carried out on the fatigue test pieces as well. It was found that in the case of pieces with a life of more than 20 percent, the signal to be evaluated will have saturation character. Thermography, on the other hand, is well suited for monitoring fatigue experiments in the servohydraulic machine. The thermal energy dissipated in the material in case of fatigue damage will increase strongly at the onset of the experiment and then decrease continuously until fracture. (orig.)