Determination of thermochemical properties of stainless steels type D-9 and T-91 using Knudsen Effusion Mass Spectrometry

Abstract

High temperature vaporisation thermodynamic studies over D-9 and T-91 stainless steel samples were carried out in the temperature range 1202–1529 K and 1232–1530 K respectively, by using Knudsen Effusion Mass Spectrometry (KEMS). These studies revealed that both the alloys undergo incongruent vaporisation. Cr(g), Mn(g), Fe(g) and Ni(g) were the neutral vapour species observed over the D-9 alloy. Cr(g), Mn(g) and Fe(g) were the neutral vapour species observed over the T-91alloy. Partial pressure-Temperature relations were derived using KEMS for the first time. Apparent enthalpies of vaporisation data were deduced by second law method. Chemical activities of all the major metallic elements (Fe, Cr, Ni and Mn) in the commercial grade D-9 austenitic stainless steel were determined in the temperature range of 1202–1529 K. In case of T-91 ferritic steel, chemical activities of Fe, Cr and Mn were determined in the temperature range of 1232 -1530 K.