Observation of Three-dimensional Crack Path in a Dual Phase Steel

Abstract

Fatigue cracks were initiated in a dual-phase ferritic-martensitic steel using smooth specimens. Tiny sub-specimens containing typical crack configurations were then cut out by spark erosion which could be put in a synchrotron beam-line (spring8 in Japan). This allowed determining the three-dimensional shape of the cracks. Afterwards, the local microstructure in the vicinity of the crack front was investigated in the SEM including the crystallographic orientations via EBSD. This was done on the specimen surface as well as in depth direction by polishing in well defined steps. Consequently, the local microstructure along the crack front was known and its influence on three-dimensional crack could be analyzed.