A study on detection of creep damage before crack initiation in austenitic stainless steel

The magnetic property changes in Type 304 stainless steel as creep damage progresses. The microstructure related to this magnetic property changes has been investigated by using SEM-EDX, SEM-EBSP, magneto-optical Kerr effect microscope and magnetic force microscope. One reason for magnetic property changes is the transformation from face-centered cubic to body-centered cubic phases with lower chromium content. These magnetic body-centered cubic phases are observed in grains along the stress axis or near the triple points, at which are sites of severe deformation. On the other hand, for aged materials magnetic phases are observed only at grain boundaries. The formation of magnetic phases is related to creep damage in Type 304 stainless steel.