Thermal stability and thermal property characterisation of Fe-14.4Cr-15.4Ni-2.4Mo-2.36Mn-0.25Ti-1.02Si-0.042Ca 0.04P-0.005B (mass%) austenitic stainless steel (Alloy D91)

High temperature measurements of enthalpy increment (IHT degree ) and lattice parameter have been carried out on Alloy D91 by means of drop calorimetry and high temperature X-ray diffraction techniques, respectively. In addition, the thermal stability during heating and cooling from the melting range has been investigated by differential scanning calorimetry. It is found that under near equilibrium cooling conditions (3 K min-1), Alloy D9I exhibits L a gamma austenite a L + gamma + [d] ferrite a gamma + [d] a gamma solidification mode. However, the phase fraction of [d] ferrite and the temperature region of gamma + [d] two phase domain are found to be small. The on-cooling liquidus and solidus temperatures are found to be 1684 and 1631 +/- 5 K, respectively. The latent heat of solidification is found to be in the range, 190-220 J g-1. The thermal analysis study has revealed that solution treated Alloy D91 exhibits an endothermic dissolution of Ti(C,N) particles at about 1323 +/- 2 K, with an associated heat effect of 16-20 J g-1. The specific heat Cp and coefficient of linear thermal expansion alpha l at 298.15 K are estimated to be 486 J kg-1 K-1 and 1.15 X 10-5 K-1, respectively. The measured temperature dependencies of Cp and alpha l for Alloy D91 are in good agreement with the general trend exhibited by many austenitic steels. Further, an empirical linear correlation has been found between the measured temperature dependent molar volume and molar enthalpy values. The measured thermal property data have been modelled through Debye-Grueneisen formalism to obtain an integrated and self-consistent estimate of thermal properties in a comprehensive temperature domain ranging from 0 to 1400 K.