Evaluation of rate constants in tempering reaction of hardened steels from dilatometric data on continuous heating at controlled rates

A new method of analysis has been suggested whereby the characteristic constants of the rate equation in the second and third stages of the tempering reaction of hardened steels may be evaluated rapidly from the dilatometric data obtained during continuous heating at a controlled rate. Using the new method, the kinetic order, activation energy, and frequency factor of the second and third stages in the tempering reaction can be obtained from a plot of the length fraction of the reactant remaining on continuous heating versus the temperature. The tempering kinetics can thereby be investigated continuously over an entire temperature range. In the new method only one pair of test specimens containing different but known quantities of retained austenite is required; decomposition to a time scale is not required. Thus, the method can serve as means of comparing rapidly the thermal stability of the decomposition of martensite and retained austenite in various hardened steels using fewer test specimens.

MST/554