Abstract
The kinetics of precipitation and austenite reversion phase transformations in an as-built arc-directed energy deposition (arc-DED) PH13–8Mo stainless steel are studied. The material in the as-built condition is analyzed using the differential scanning calorimetry (DSC) technique to determine the fraction of transformed precipitates and reverted austenite at any time/temperature during non-isothermal transformations. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) kinetic equation is employed to model the transformed phase volume fraction during precipitation and austenite reversion processes. Using the non-isothermal phase transformation kinetics, an isothermal kinetics model is developed. The isothermal kinetics modeling results are then employed to design and develop direct aging heat treatments to enhance the hardness and strength of arc-DED-PH13–8Mo steel. The developed heat treatment results in the concurrent enhancement of strength and ductility in the material. Such an achievement is a result of the evolution of nano-scaled β-NiAl clusters. It appears that the formation of β-NiAl clusters increases the dislocation storage capability in the material, resulting in the evasion of the strength-ductility trade-off. The results of the current study provide great insight into the crucial role of clusters in the strength-ductility trade-off in PH stainless steels.
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