The long-term creep behavior and damage mechanism of RAFM steel for fusion reactors

Abstract

The reduced-activation ferritic-martensitic (RAFM) steel serves as the structural material for the blanket of the International Thermonuclear Experimental Reactor (ITER) and future fusion reactors. In order to achieve a design lifetime of 2–3 years for the blanket in the fusion reactor, it is imperative to thoroughly understand the long-term (>20,000 h) creep behavior of RAFM steel. In this regard, the present study investigated the long-term creep damage mechanism of RAFM steel under creep periods greater than 20 000 h. The results indicated that the creep exponent decreases as the creep rupture time increases from several thousand hours to more than 20,000 h. The microstructure analysis revealed that dislocation slip was effectively pinned by the precipitates in the long-term creep process. Additionally, the M23C6 and Laves phase played a critical role in inhibiting interfacial slip and preventing lath coarsening. However, a few micron-scale M23C6 and Laves phases led to the formation of cavities in the boundary. These cavities subsequently polymerized and aggravated into cracks, ultimately becoming the primary mechanism for the long-term creep fracture.