Microstructural evolution during tempering of an ausformed carbide-free low temperature bainitic steel

• Limited effect of temerping at 400 and 500°C on non-ausformed crabide-free bainite. Dilatometric contraction occurred for ausformed bainite sample due to cementite precipitation. Carbon diffusion was enhanced by dislocations generated during ausforming processes. The influence tempering 500 °C two bainitic ferrite microstructures obtained via pure isothermal transformation followed the studied in a medium C-Si rich steel. To understand dilatometric behaviour mechanisms carbide-free decomposition, extensive microstructural characterization using scanning electron microscopy, X-ray diffraction, microhardness measurements were conducted. softening negligible both microstructures. Tempering led remarkable signal an sample, while showed slight contraction. main mechanism governing changes decomposition as-ausformed highly dislocated plates and/or film-like retained austenite into as result carbon diffusion. While did not size plates, higher temperature thickening testing conditions. However, restricted bainite, which related pinning very small precipitates, moderate effects hardness reduction.