Influence of Grain Size on the Isothermal Oxidation of Fe–40Ni–24Cr Alloy

Abstract

The influence of grain size on the oxidation of Fe–40Ni–24Cr alloy was studied in this work. The present paper focuses on the isothermal oxidation behaviour at 700 °C. Solution treatment at three different temperatures, namely 950, 1050 and 1150 °C, was applied to Fe–40Ni–24Cr alloy to alter the average grain size of the samples. The results showed that the average grain size increased with increase in solution treatment temperature. Optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were employed in this study to analyse the oxidation behaviour of solution-treated samples. The solution-treated samples were subjected to oxidation experiment under isothermal conditions for 500 h. The oxide scales formed during oxidation were generally complex, and their morphologies and structure were influenced by the alloy structure and expose conditions and environment. The kinetics of oxidation followed the parabolic law which represents diffusion-controlled oxide growth rate. After 500-h exposure, all alloy displayed protective oxidation with the fine grain samples exhibiting the lowest weight gain, hence the superior oxidation resistance. Smaller grain size improves the protective oxidation behaviour by enhancing exfoliation resistance and reducing oxidation rate.