Application of various observational techniques to the characterization of MX in F82H

Abstract

ABSTRACT Reduced activation ferritic/martensitic steels (RAFMs) have been developed for the structural material of fusion reactor blanket. Extensive researches were conducted using transmission electron microscopy (TEM) to define the precipitation behavior of MX (M: Metallic elements, X: C and/or N) precipitates such as vanadium and tantalum carbides and/or nitrides, since they strongly affect material properties. However, it is not completely defined yet. TEM can obtain detailed information, but the observable volume is limited and it needs a long time to obtain representative and statistically reliable microstructural information. It is fruitful to complement TEM results applying other characterization techniques together. In this work, we studied the precipitation behavior of MX in the RAFM, F82H, through the application of various techniques with larger observable volumes and compared with TEM past results. We additionally tried to find sub-nanometric MX precipitates that can be hardly observed through TEM. From the result, the TaX (X: C and/or N) phase surely varied depending on the chemical composition of alloy and heat treatment; some TaX precipitates were unstable during tempering, MX precipitates were intergranular, and sub-nanometric MX were not found in the matrix. These obtained results were helpful to define the precipitation behavior of MX in F82H.