Kinetics of isothermal martensitic transformations in an iron-nickel-manganese alloy

Abstract

The kinetics of isothermal martensitic transformations in an Fe-24Ni-3Mn alloy can be satisfactorily analyzed in terms of autocatalytic nucleation, wherein the nucleation rate first increases and then decreases as a function of reaction time. When the volume per martensitic plate is measured by quantitative metallography, instead of relying on calculation by geometric partitioning, the autocatalytic factor is found to be relatively insensitive to the transformation temperature, and amounts to about 10 10 new embryos per cm 3 of martensite formed. The activation energy characteristic of the overall isothermal reaction (and hence, of the autocatalytic nucleation) decreases with decreasing temperature, and is of the order of 10 kcal/mole, as previously reported for the activation energy corresponding to the initial transformation.