Aging kinetics of 17-4 PH stainless steel

The influence of aging condition and the precipitation kinetics of 17-4 PH stainless steel (AISI 630) were studied in this paper. The effect of aging temperature and time in terms of tempering parameter on the strengthening behavior of this steel was modeled and analyzed by means of artificial neural networks (ANNs). The hardening, overaging and softening behaviors in accordance to aging reactions (precipitation and coarsening of Cu, recovery, and reversion of martensite to austenite) were determined from this ANN model. Moreover, Johnson–Mehl–Avrami–Kolmogorov (JMAK) analysis were applied to characterize precipitation kinetics of this martensitic age hardenable alloy. Time exponents (0.465 on average) were within the range reported for maraging steels. The activation energy for precipitation reaction was determined as 262 kJmol−1 which is consistent with the activation energy for diffusion of copper in ferrite. Furthermore, precipitation rate showed exponential dependence on aging temperature.