Crystallographic aspects of 17-4 PH martensitic steel produced by laser-powder bed fusion

Microstructural evolution during laser-powder bed fusion of 17-4 PH martensitic steel was studied. Particular emphasis was paid to the crystallographic aspects of this process. The crystallization of 6-ferrite from the liquid phase was shown to be governed by an epitaxial mechanism which gave rise to the solidification <100> -fiber texture. The austenitic phase preferentially nucleated at the ferrite grain boundaries, while the subsequent migration of phase boundaries was accompanied by extensive annealing twinning. Remarkably, the grain -boundary austenite was related to both adjacent ferrite grains via the Nishiyama-Wasserman orientation rela-tionship. The multiple crystallographic variants associated with the phase transformation and annealing twin-ning resulted in a comparatively weak <110> + <100> -fiber texture in austenite. The subsequent austenite -> martensite phase transformation was governed by the mixed orientation relationship, which included both the Nishiyama-Wasserman and Kurdjumov-Sachs ones. The nearly-random texture in martensite suggested no essential variant selection during the phase transformation.

Automated summary

This study focuses on the crystallographic aspects of laser-powder bed fusion of 17-4 PH martensitic steel. The crystallization process showed an epitaxial mechanism and resulted in a specific crystal structure relationship between ferrite and austenite. Grain-boundary austenite was found to have a relationship with adjacent ferrite grains. The phase transformation from austenite to martensite did not exhibit significant variant selection.