Abstract
High temperature tensile fracture behavior has been characterized for the ferritic alloy 14YWT (SM10 heat) with the composition of Fe-14Cr-3W-0.4Ti (in wt.%) and strengthened by dispersion of nanometer-sized oxygen, titanium, and yttrium rich clusters. Tensile tests were performed at various temperatures ranging from room temperature to 1000°C in a vacuum condition using a nominal strain rate of 10-3s-1. Comparing with the existing oxide dispersion strengthened (ODS) steels such as Eurofer 97 and PM2000, the nanostructured alloy showed much higher yield and tensile strength over the test temperature range, but with lower elongation. Microstructural characterization for fractured tensile specimens was focused on the details of fracture morphology and mechanism to provide a feedback for process improvement. Below 600°C, the fracture surfaces exhibited a quasi-ductile behavior presented by a mixture of dimples and cleavage facets. At or above 600°C, however, the fracture surfaces were fully covered with dimples. The spherical particles that seemed to be oxide or carbide particles were found inside of dimples. It was notable that numerous microcracks were observed on the side surface of broken specimens. Formation of these microcracks is believed to be the main origin of the poor ductility of 14YWT alloy. It is suggested that any grain boundary strengthening measure is essential to improve the fracture property of the alloy.
