EBSD study of microstructure produced during laser powder bed fusion of 17-4 PH martensitic steel

Electron backscatter diffraction was applied to investigate the broad aspects of the microstructure produced during laser powder beam fusion of 17-4 PH steel. It was found that the laser powder beam fusion process involved the -ferrite-to-austenite-to-martensite phase transformation sequence. Remarkably, the solidification <100> + <111> fiber texture in -ferrite was essentially inherited by the final martensitic phase, i.e., the texture-memory effect was observed. It was also revealed that the -ferrite-to-austenite transformation involved a strict selection of crystallographic variants. This led to a pronounced crystallographic preference of 60° <111> boundaries in the austenitic phase. The core result of this study was an integral pattern of microstructural changes during laser powder beam fusion from a solidification stage down to ambient conditions.