High Temperature Elastic Properties of Reduced Activation Ferritic-Martensitic (RAFM) Steel Using Impulse Excitation Technique

The polycrystalline elastic constants of an indigenous variant of 9Cr-1W-based reduced activation ferritic-martensitic (RAFM) steel have been determined as a function of temperature from 298 K to 1323 K (25 A degrees C to 1000 A degrees C), using impulse excitation technique (IET). The three elastic constants namely, Young's modulus E, shear modulus G, and bulk modulus B, exhibited significant softening with increasing temperature, in a pronounced non-linear fashion. In addition, clearly marked discontinuities in their temperature variations are noticed in the region, where ferrite + carbides -> austenite phase transformation occurred upon heating. Further, the incidence of austenite -> martensite transformation upon cooling has also been marked by a step-like jump in both elastic E and shear moduli G. The martensite start M (s) and M (f) finish temperatures estimated from this study are, M (s) = 652 K (379 A degrees C) and M (f) =580 K (307 A degrees C). Similarly, the measured ferrite + carbide -> austenite transformation onset (Ac (1)) and completion (Ac (3)) temperatures are found to be 1126 K and 1143 K (853 A degrees C and 870 A degrees C), respectively. The Poisson ratio mu exhibited distinct discontinuities at phase transformation temperatures; but however, is found to vary in the range 0.27 to 0.29. The room temperature estimates of E, G, and mu for normalized and tempered microstructure are found to be 219 GPa, 86.65 GPa, and 0.27, respectively. For the metastable austenite phase, the corresponding values are: 197 GPa, 76.5 GPa, and 0.29, respectively. The measured elastic properties as well as their temperature dependencies are found to be in good accord with reported estimates for other 9Cr-based ferritic-martensitic steel grades. Estimates of theta (D) (el) , the elastic Debye temperature and gamma (G), the thermal Gruneisen parameter obtained from measured bulk elastic properties are found to be theta (D) (el) = 465 K (192 A degrees C) and gamma (G) = 1.57.