Partitioning of a microstructure produced during laser powder bed fusion of 17−4 PH steel

This study focused on the characterization of a complex microstructure in 17−4 PH martensitic steel produced during laser powder bed fusion. Due to the specific nature of the LPBF process, the additive material undergoes an extremely high cooling rate (~ 10⁶ K/s) and pronounced thermal cycling. This usually gives rise to the complex microstructures consisting of δ-ferrite, austenite, and martensite. In this work, a two-step approach was developed for the partitioning of the δ-ferrite and martensite phases. The elaborated method was based on the electron backscatter diffraction technique and involved a two-factor filtration of the electron backscatter diffraction data using the distinct differences between the δ-ferrite and martensite in stored energy and grain size. From experimental observations, it was shown that the proposed technique was highly effective for an analysis of the complex microstructures produced during LPBF of 17−4 PH martensitic steel.