Monitoring of low-cycle fatigue degradation in X6CrNiTi18-10 austenitic steel

The micro structural changes in the pre-crack stage of low-cycle fatigue da mage (LCF) in austenitic piping steels were investigated by neutron and X-r ay diffraction (XRD). The LCF damage evolution in the metastable austenitic steel causes a deformation-induced phase transformation from austenite to martensite. Thresholds exist for the formation of martensite as a function of accumulated plastic strain. Magnetic stray field and eddy current measur ements were chosen to transfer the results of material characterisation. to NDT methods. The density and distribution of martensite obtained by neutro n diffraction experiments were used to adjust the NDT signals. Both NDT tec hniques were able to detect the very low amount of martensite in the differ ent fatigued specimens (0.5-3.1 vol.% martensite) with usage factors from 0 up to 1.0. (C) 2001 Elsevier Science B.V. All rights reserved.