Alloying element accumulation at ferrite/austenite boundaries below the time–temperature–transformation diagram bay in an Fe–C–Mo Alloy

A scanning transmission electron microscope (STEM)-energy dispersive X-ray (EDX) analysis was made of the Mo concentration at boundaries between degenerate ferrite and austenite in an Fe–0.28mass%C–3mass%Mo alloy isothermally reacted below the bay temperature of the time–temperature–transformation (TTT)-diagram. The measured Mo concentration scattered widely from one boundary to another and varied considerably along the individual boundaries. The enrichment factor of Mo corrected for the sampling volume (beam diameter) to boundary thickness ratio showed an increasing tendency with isothermal holding time and reached as large as 15 when the alloy entered the transformation stasis. The amount of Mo in the boundary is compared with that calculated under the assumption of quasi-steady state diffusion that is used to analyze the solute drag effects on the motion of interphase boundaries.