抄録
In order to clarify the effect of carbide precipitation on the embrittlement of reduced-activation high-Mn austenitic steels suitable for fusion reactors, Charpy impact testing was carried out for 10%Cr-30%Mn steels with 0.07, 0.11, 0.26 and 0.55%C after aging at temperatures between 823 and 973 K for the periods from 3.6 to 10800 ks.
The embrittlement due to the aging increased with increasing carbon content, aging temperature and time. The solution-annealed specimens exhited a mode of ductile fracture with dimple pattern. The percentage of brittle grain boundary fracture in the fractured surface increased with aging time. The M23C6 carbide precipitated during aging preferentially along grain boundaries and the major component of the carbide was Cr. Therefore, the embrittlement resulted from the grain boundary precipitation of M23C6 which promoted grain boundary fracture. The activation energy for the embrittlement was evaluated to be 233-237 kJ/mol which correspond to that for diffusion of Cr in γ-iron. It was concluded that the rate-determining process of the transition from ductile to embrittlement was diffusion of Cr in the γ-matrix of the alloys for the grain boundary precipitation of the M23C6 carbide. The carbon content in the steels was recommended to be below 0.1% for preventing the grain boundary embrittlement.
