ASSESSMENT OF CREEP DAMAGE OF FERROMAGNETIC MATERIAL USING MAGNETIC INSPECTION

Results of inspection creep damage by magnetic hysteresis measurements on Cr-Mo steel are presented. It is shown that structure sensitive pa rameters such as coercivity, remanence and hysteresis loss are sensiti ve to the creep damage. Previous metallographic studies have shown tha t creep changes the microstructure of the material by introducing void s, dislocations, and grain boundary cavities. As cavities develop, dis locations and voids move out to the grain boundaries; therefore the to tal pinning sources for domain wall motion are reduced. This, together with the introduction of a demagnetization field due to the cavities, results in the decrease of both coercivity and remanence. Numerical c omputations with a modified JiIes-Atherton model are presented which a re consistent with the proposed mechanisms.