Effects of thermal aging at 873 K on the impact properties of an ODS ferritic steel

This investigation presents the effects of long-term thermal aging on the impact properties of an ODS reduced activation ferritic steel. The ODS ferritic steel, with composition Fe-14Cr-2W-0.4Ti-0.3Y2O3 (wt. %), was manufactured by mechanical alloying, compacted by hot isostatic pressing and hot cross rolled. A 1273 K annealing treatment was applied, followed by thermal aging at 873 K for 2000 h in Ar, to evaluate the thermal stability of the alloy. Charpy impact testing was performed from 77 to 473 K to investigate the mechanical response of the material under dynamic loads. The ductile-to-brittle transition temperature (DBTT) showed a slight increase with values of 255 ± 12 K before aging, and 270 ± 20 K after aging. The aging treatment softened the steep character of the Charpy impact curves inducing a wider transition regime with mixed brittle and ductile fracture mechanisms. This behavior was confirmed by the analysis of Force vs. Displacement Charpy curves and fractographic observations. Hot cross rolling induced a crack divider geometry and secondary cracks formation by delamination. Ductile fracture was less evident after aging due to the redistribution and transformation of Cr-W-rich precipitates along grain boundaries. Electron Backscattered Diffraction highlighted the features of transgranular brittle cracks at temperatures below the DBTT and showed misoriented and deformed regions near the fracture surface at temperatures above the DBTT.

Effects of thermal aging at 873 K on the impact properties of an ODS ferritic steel Articles