Boride layers on the ductile iron surface had saw tooth morphology
and layer/matrix interfaces were rather smooth. Underneath
the boride layers, ductile irons had different matrix
structures with acicular lower ausferrite at 250 C, acicular upper
ausferrite at 300 C, upper ausferrite at 350 C and rude upper ausferrite
matrix structure at 400 C depending on tempering temperature.
While the hardness of boride layer varied between 694 and