Diffusion of hydrogen in China Reduced Activation Ferritic-martensitic steels at low temperatures

Abstract

Reduced Activation Ferritic/Martensitic (RAFM) steels have been considered as the most promising candidate structural materials for a fusion reactor. In this paper, the hydrogen diffusion behavior of two types of RAFM steels, called China Low Activation Martensitic (CLAM) steel and China Low-activation Ferritic (CLF-1) steel, have been studied by electrochemical technique over the temperature range of 293–323 K. Before hydrogen permeation, both sides of the CLAM and CLF-1 steels were coated with a thin layer of uniform and dense palladium (Pd) membrane by electro-plating method. The results showed that the diffusion coefficients of hydrogen through CLAM and CLF-1 steels were submitted to the relationships of D(cm2/s) = 3.04 × 10−6exp[-4.72(kJ⋅mol-1)/RT] and D(cm2/s) = 1.82 × 10-5exp[-10.07(kJ⋅mol-1)/RT], which were far higher than that of some other austenitic stainless steels, such as 316 S.S. This indicates that if the RAFM steels as the structural material for fusion reactor are free from hydrogen environment, the hydrogen isotopes will escape from them quickly under low temperatures, which is conducive to keeping the mechanical properties of RAFMs.