Electron Spectroscopic Investigations of the Solute Drag Like Effect in Fe-C-Mo Alloys

The role of various alloying elements on the kinetics of austenite decomposition in steels is well documented. One of the least understood aspects is the ability of some elements like Mo to drastically reduce the kinetics of ferrite (α) growth in austenite (γ).Within specific ranges of transformation temperatures and alloy compositions, the transformation of austenite can cease entirely for extended periods of time (transformation stasis). The phenomenon is quite pronounced in Fe-C-Mo alloys and is clearly evidenced by a horizontal region in the plot of the fraction transformed vs. isothermal reaction time. Based on microstructural and kinetic evidence, the occurrence of the transformation stasis phenomenon has been ascribed to a "solute drag like effect" caused by the segregation of Mo atoms to α : γ boundaries. The proposal that interface chemistry alters the growth kinetics of ferrite is quite difficult to verify as the segregation is expected to be confined to a boundary region less than a nanometer in width.