Early Stages of Cu Precipitation in 15-5 PH Maraging Steel Revisited - Part II: Thermokinetic Simulation

Abstract

In this part II of the authors' investigation of Cu-precipitation in 15-5 PH steel, the authors complement the experimental analysis of part I with thermokinetic modeling and simulation to aid in the interpretation of processes and mechanisms involved in the two precipitation reactions between around 300 and 500 °C. The kinetic simulations are founded on extended classical nucleation theory, a mean-field model for precipitate growth, a predictive model for interface energy calculation, and CALPHAD-based Gibbs-energy and mobility databases. The authors modeling supports the interpretation that the first peak in the continuous differential scanning calorimetry (DSC) signal is the result of nucleation of Fe-rich Cu clusters, which leads to a partial Cu-depletion of the matrix and produces the first observed DSC signal. The second DSC peak has its origin in the Cu-enrichment of precipitate clusters above approximately 500 °C and the associated enthalpy change. A quantitative reproduction of both exothermic reactions is performed within the framework of the thermokinetic simulation.