Measurement of transformation temperatures and specific heat capacity of tungsten added reduced activation ferritic–martensitic steel

The on-heating phase transformation temperatures up to the melting regime and the specific heat capacity of a reduced activation ferritic–martensitic steel (RAFM) with a nominal composition (wt%): 9Cr–0.09C–0.56Mn–0.23V–1W–0.063Ta–0.02N, have been measured using high temperature differential scanning calorimetry. The α-ferrite + carbides → γ-austenite transformation start and finish temperatures, namely Ac1, and Ac3, are found to be 1104 and 1144 K, respectively for a typical normalized and tempered microstructure. It is also observed that the martensite start (MS) and finish (Mf) temperatures are sensitive to the austenitising conditions. Typical MS and Mf values for the 1273 K normalized and 1033 K tempered samples are of the order 714 and 614 K, respectively. The heat capacity CP of the RAFM steel has been measured in the temperature range 473–1273 K, for different normalized and tempered samples. In essence, it is found that the CP of the fully martensitic microstructure is found to be lower than that of its tempered counterpart, and this difference begins to increase in an appreciable manner from about 800 K. The heat capacity of the normalized microstructure is found to vary from 480 to 500 J kg−1 K−1 at 500 K, where as that of the tempered steel is found to be higher by about, 150 J kg−1 K−1.