IN SITU OBSERVATION OF LOWER BAINITIC CARBIDES PRECIPITATION

The lower bainitic carbides precipitation in 40CrMnSiMoV steel previously austempered at310℃ was observed in situ by employing a high temperature stage of an ultra high voltageTEM(JEM-1000).The typical lower bamitic carbides were found to have precipitated fromwithin the carbide-free bainitic ferrite after tempering for certain period at a temperaturehigher than that of the isothermal transformation.This revealed that the lower bainitic ferriteis supersaturated with carbon to some extent.The carbide may also precipitate from austenite,but they have no typical morphological features of lower bainitic carbide.