Dilatometric study of high silicon bainitic steels: Solid-state transformations

Abstract

High silicon bainitic steels have gained significant recognition in various applications due to their exceptional properties, such as high strength, favourable corrosion resistance, and excellent high-temperature stability. This study investigates an alloy capable of generating a finer bainitic structure through a transformation at 260 °C, leading to the desired microstructure. Interestingly, other phenomena were discovered while pursuing optimal heat treatment conditions. At temperatures exceeding 850 °C, the alloy exhibits a tendency for graphite formation, which has intriguing implications for its mechanical properties. The high silicon concentration in the alloy significantly retards cementite growth, resulting in a microstructure composed solely of bainitic ferrite and residual austenite through the transformation of austenite below the bainite start temperature. Furthermore, it is observed that pearlite formed during rapid transformation at 650 °C does not exhibit the predicted equilibrium chemical composition. This discrepancy challenges the existing models of pearlite growth, which assume local equilibrium at the shared interface with austenite. This research aims to investigate the influence of silicon content on solid-state transformations in high-silicon steels using dilatometry, optical microscopy, scanning electron microscopy, and X–ray diffraction techniques. These analytical methods will provide insights into the intricate processes occurring during isothermal transformation temperatures, contributing to a deeper understanding of the material's behaviour and its potential applications.