Effect of sigma phase on thermophysical properties of Fe55Cr45 alloy

Abstract

This paper presents the results of an experimental and modelling study to determine the thermophysical properties of α and σ phases in Fe55Cr45 (wt%) alloy. A comprehensive analytical model was used to predict the temperature dependent variation of enthalpy and specific heat, which are compared with experimental results. σ phase was synthesized from homogenized α alloy through heat treatment at 973 K for 300 h. Analysis of high temperature phase stability showed a magnetic transformation for α phase at 831 K and σ→α structural transformation for sigma phase at 1120 K with an enthalpy of 2.6 ± 0.2 kJ mol−1. Room temperature linear thermal expansion coefficient (CTE) for α and σ phases were obtained as 7.39 × 10−6 and 15.03 × 10−6 K-1 respectively. While the α phase exhibited an increase of 118% in CTE up to 1000 K, only 1.7% increase was observed for σ phase. Room temperature thermal conductivity for σ was much lower (3.1 W m−1 K−1) than that of the α phase (16.22 W m−1 K−1). The systematic experimental investigations carried out in the present study, established that formation of σ has an adverse effect on the heat transport properties of structural steels and their welds.