Isothermal fcc/hcp Transformation in Fe-Si-C-Alloy Thermally Treated at Lower Bainitic Transformation Temperature

Abstract

  High resolution transmission electron microscopic observations have revealed that isothermal fcc (γ) to hcp (ε) transformation accompanies the bainitic transformation from γ austenite to bcc (α) bainite in an Fe-2Si-1.4C(mass%) alloy heated at lower bainitic transformation temperature of 570 K. The ε plates are formed at the ledges of α bainite/γ austenite interfaces. The unit volume of the ε phase with respect to that of the γ austenite increases by as much as 16% when the ε plate has grown from 4 nm to 100 nm in thickness, probably due to enhancement of interstitial carbon. There is no visible stacking fault in the ε phases. These experimental results are interpreted by the concept of bainitic transformation both with shear-type and diffusion-type nature.