Formation of "carbide-free zones" resulting from the interplay of C redistribution and carbide precipitation during bainitic transformation

Advanced bainitic steels exploit their constitution of a phase mixture of bainitic ferrite and retained austenite. The desired microstructures are usually adjusted via isothermal or continuous cooling treatments below the bainite-start-temperature. In the present work, we analyze the microstructural evolution during bainite formation in detail and we report on a novel mechanism for the formation of “carbide-free zones” in the close proximity of austenite. Carbides are formed in the interior of bainitic ferrite, which is isolated from surrounding austenite, while the depletion of C in the vicinity of austenite suppresses their formation.