Intermetallic Phase Precipitation in Duplex Stainless Steels: Considerations on the Use of Johnson-Mehl-Avrami-Kolmogorov Equation

Despite the great interest in intermetallic phase precipitation in duplex and super duplex stainless steels, a common controlling factor in the kinetics of its formation has not been reached yet. For example, when the time-evolution of sigma phase precipitation is described by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation, or its modified forms, very different kinetic parameters were found in the literature, even if duplex stainless steels with very similar chemical composition and initial conditions are used in the experiments. In this work, some critical points that affect the evaluation of the kinetic constants and may cause erroneous interpretation of intermetallic phase precipitation (kinetics) are highlighted and discussed. It was shown that the choice of a high impingement coefficient in the modified JMAK equation leads to a significant improvement in experimental data description. A series of recommendations for the future application of the JMAK equation applied to intermetallic phase precipitation in duplex stainless steels are finally suggested.