Identification of Retained Austenite in 9Cr-1.4W-0.06Ta-0.12C Reduced Activation Ferritic Martensitic Steel

Reduced activation ferritic martensitic (RAFM) 9Cr steels, which are candidate materials for the test blanket module (TBM) of nuclear fusion reactors, are considered to be air hardenable. However, alloy composition and the processing conditions play a significant role during the transformation of austenite to martensite/ferrite on cooling. The presence of retained austenite is known to influence the mechanical properties of the steel. Identifying very low amounts of retained austenite is very challenging though conventional microscopy. This paper aims at identifying a low amount of retained austenite in normalized 9Cr-1.4W-0.06Ta-0.12C RAFM steel using synchrotron X-ray diffraction and Mossbauer spectroscopy and confirmed by advanced automated crystal orientation mapping in transmission electron microscopy. Homogeneity of austenite has been understood to influence the microstructure of the normalized steel, which is discussed in detail.