Effect of α–α′ phase separation on notch impact behavior of oxide dispersion strengthened (ODS) Fe20Cr5Al alloy

The effects of Fe-rich (α) and Cr-enriched (α′) phase separation, occurring during aging at 475 °C on the microstructure and mechanical properties of Fe–20Cr–6Al ODS alloy (PM2000™) hot-rolled tube, were investigated by means of atom probe tomography, microhardness, tensile and V-notched Charpy impact tests. Disregarding of the aging treatment, this material presents splitting of crack-divider type in longitudinal-transverse (LT) specimens, whereas crack-arrester type is observed in longitudinal-short transverse (LS) specimens, which induces significant differences in ductile-to-brittle transition temperature (DBTT) and upper shelf energy (USE). Additionally, a significant increase in DBTT and decrease in USE were recorded during aging at 475 °C as a function of aging time. The main cause of embrittlement is the α–α′ phase separation with an apparent activation energy measured in the range of 214–240 kJ/mol, which is consistent with the activation energy for Cr diffusion in this type of alloy.