Effect of thermal aging on the microstructure and mechanical properties of 7–11 CrW steels

The aim of this paper is to present the evolution of the microstructure, tensile and impact properties of Fe–7.5/11CrWVTa reduced activation martensitic (RAM) steels after thermal aging performed at relevant temperatures for fusion applications (250–550°C). The materials investigated are experimental alloys with different contents of Cr (7.5–11%), Ta (0–0.1%), W (0.8–3%) and interstitial elements, such as carbon (0.09–0.17%) and nitrogen (0.004–0.045%). Thermal aging was performed for up to 13 500 h on steels with different metallurgical conditions: normalized and tempered (N&T) and normalized and tempered + 10% cold worked (N&T-CW). The characterization of the microstructure was performed by transmission electron microscopy (TEM) and by small angle neutron scattering (SANS). The evolution of tensile properties depends essentially on the initial metallurgical conditions, whereas the modification of impact properties is mainly defined by the chemical composition that governs the occurrence of alpha prime and Laves phase precipitation.