Electron backscattering diffraction study of acicular ferrite, bainite, and martensite steel microstructures

This study deals with acicular ferrite, bainite, and martensite microstruct ures observed in three low alloy steels, Electron backscattering diffractio n (EBSD) was used to assess crystallographic features of these microstructu res, In each area studied by EBSD mapping, 'crystallographic packets' defin ed as clusters of paints sharing the same crystallographic orientation were compared with 'morphological packets' observed in the corresponding light micrograph. Microtexture studies suggested that acicular ferrite and upper bainite grow with Nishiyama-Wassermann relationships with the parent austen ite phase, whereas lower bainite and martensite consist of highly intricate packets having Kurdjumov-Sachs relationships with the parent phase, In all cases three highly misoriented texture components were found within each f ormer austenite grain. Electron backscattering diffraction also gave inform ation about the cleavage and intergranular reverse temper embrittlement fra cture mechanisms of these steels, In conclusion, it is shown that EBSD is a powerful tool for studying phase transformation and fracture mechanisms in steels on a microscopic scale. MST/4312.