Effect of Thermal Aging on Ductile-Brittle Transition Temperature of Modified 9Cr-1Mo Steel Evaluated with Reference Temperature Approach Under Dynamic Loading Condition

The effect of thermal aging on the ductile-brittle transition behavior has been assessed for a modified 9Cr-1Mo steel (P91) using the reference temperature approach under dynamic loading condition (T (0) (dy) ). The steel in normalized and tempered (NT) condition and in different levels of subsequent cold work (CW) was subjected to thermal aging at temperatures of 873 K and 923 K (600 A degrees C and 650 A degrees C) for 5000 and 10,000 hours. For the NT and all the cold work conditions of the starting material, a drastic increase in T (0) (dy) has been noticed after aging at 923 K (650 A degrees C) for 10,000 h. A moderate increase was observed for the NT steel aged at 873 K (600 A degrees C) for 5000 hours and for the 10 pct CW steel aged at 873 K (600 A degrees C) for 10,000 h. A detailed transmission electron microscope (TEM) study of the embrittled materials aged at 923 K (650 A degrees C)/10,000 hours and 873 K (600 A degrees C)/10,000 hours has indicated presence of hexagonal Laves phase of Fe-2(Mo,Nb) type with different size and spatial distributions. The increase in the T (0) (dy) is attributed to the embrittling effect of a network of Laves phase precipitates along the grain boundaries. DOI: 10.1007/s11661-012-1510-0 (C) The Minerals, Metals & Materials Society and ASM International 2013