Assessment of thermal embrittlement in duplex stainless steels 2003 and 2205 for nuclear power applications

Duplex stainless steels are desirable for use in power generation systems because of their attractive combination of strength, corrosion resistance and cost. However, thermal embrittlement at intermediate homologous temperatures of 475 C and below, limits upper service temperatures for many applications. New lean grade duplex alloys have improved thermal stability over standard grades and potentially increase the upper service temperature or the lifetime at a given temperature for this class of material. The present work compares the thermal stability of lean grade, alloy 2003, to standard grade, alloy 2205, through a series of isothermal agings between 260 C and 482 C for times between 1 and 10,000 h. Aged samples were characterized by changes in microhardness and impact toughness. Additionally, atom probe tomography was performed to illustrate the evolution of the a–a0 phase separation in both alloys at select conditions. Atom probe tomography confirmed that phase separation occurs via spinodal decomposition for both alloys, and identified the presence of Ni–Cu–Si–Mn–P clusters in alloy 2205, which may contribute to the embrittlement of this alloy. The impact toughness model predictions for the upper service temperature show that alloy 2003 may be viable for use in 288 C applications for 80-year service lifetimes based on a Charpy V-notch criteria of 47 J at room temperature. In comparison, alloy 2205 should be limited to 260 C applications for the same room temperature toughness of 47 J. 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.