Article ID Journal Published Year Pages File Type
5435870 Acta Materialia 2017 10 Pages PDF
Abstract

The objective of the present study was to elucidate the complicated interrelationship between necking, post-uniform elongation (epu), strain rate sensitivity (SRS), fracture mechanism and Al concentration in Fe-18Mn-0.6C-xAl twinning-induced plasticity steels. Many tensile tests were conducted for in- and ex-situ observations of necking, fracture surfaces, crack propagation and the density and size of micro-voids with the assistance of a high-speed camera and X-ray tomographic equipment. The addition of Al increased epu, SRS and reduction ratios in dimension of the neck part of tensile specimens, and also changed fracture mode from quasi-cleavage to ductile fracture at the edge part. The quasi-cleavage surface of Al-free specimen was induced by edge and side cracks occurring along grain boundary junctions and twin boundaries within the edges and side surfaces where local deformation bands meet. The ductile-fracture surface of 1.5 %Al-added specimen was formed by the coalescence of micro-voids. While the side-to-middle crack propagation occurred in Al-free and 1 %Al-added specimens due to side cracks, the middle-to-side crack propagation was observed in 1.5 %Al-added specimen. The Al-free specimen had the larger size of the 20 largest voids compared to the 1.5 %Al-added specimen despite its lower void density and local strain due to the accelerated growth of voids near the tips of side cracks. Evaluating the negligible epu of Al-free specimen by SRS is not deemed to be reasonable due to its inappreciable necking and side cracks. The improvement of epu in 1.5 %Al-added specimen is primarily due to disappearance of edge and side cracks.

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Related Topics
Physical Sciences and Engineering Materials Science Ceramics and Composites
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