An assessment of low cycle fatigue damage using magnetic Barkhausen emission in 9Cr-1Mo ferritic steel

A non-destructive, magnetic Barkhausen emission (MBE) technique has been us ed to assess various stages of low cycle fatigue (LCF) damage in 9Cr-1Mo fe rritic steel. The initial decrease in the MBE peak height in the early stag e of LCF cycling indicates the cyclic hardening stage, in which the formati on of dislocation tangles reduces the mean free path of the domain wall mov ement. The increase in the MBE level again on further cycling indicates the progressive cyclic softening stage where the rearrangement of dislocation tangles into cells enhances the domain wall movement. The unaltered behavio ur of MBE on continued cycling shows the saturation stage where the stabili zation of dislocation substructure maintains the MBE level. Finally, a shar p increase in the MBE peak value identifies surface crack initiation and pr opagation, which is ascribed to the movement of additional reverse domains produced at the crack surfaces. This study establishes that the MBE techniq ue can be used to assess the progressive degradation in the fatigue life of the ferritic steel components. (C) 1999 Elsevier Science Ltd. All rights r eserved.