Micro-Crack Initiation in High-Silicon Cast Iron during Tension Loading

This paper focuses on measuring local strain at micro-crack initiation in fully ferritic cast iron alloys, using micro-scale strain mapping. Strain mapping was achieved using in-situ tensile test under optical microscope combined with digital image correlation (DIC). A previously developed pit etching procedure was used to create microscale random speckle patterns in the microstructure of the tensile specimens. Real-time microscope images were recorded during tensile deformation and analyzed by using DIC technique. Local strain values were measured around early formed micro-cracks during deformation. Results showed a heterogeneous deformation in microscale level. The micro-cracks were initiated at well-defined local strain levels but with large variations in the global strain level. Crack initiation was strongly associated with the graphite particles and their morphology.