Microstructural examination of two experimental high-strength bainitic low-alloy steels containing silicon

Abstract

A detailed microstructural characterization of two silicon-containing low-alloy steels, Fe–0·2C–2Si–3Mn and Fe–0·4C–2Si–4Ni (nominal wt-%), isothermally transformed in the bainitic temperature range (~ 400–250°C), has been carried out using principally electron microscopy, X-ray diffraction, and dilatometry. Upper bainite in these silicon-containing steels consists of bainitic ferrite laths and interwoven thin films of retained austenite instead of cementite. Coarser granular regions of retained austenite may also be obtained. The bainitic ferrite laths (or plates) in lower bainitic structures contain intralath carbides, but the interlath morphology of retained austenite still occurs. The variations in these microstructures with isothermal transformation temperature, and the thermal stability of the retained austenite phase is described and discussed.

MST/526