Microstructural characterization of ferrotitanium and ferroniobium

Ferroniobium and ferrotitanium, which are added during the steel-making process, may contain phases that do not melt or dissolve in molten steel. This can lead to the presence of coarse Ti- and Nb-rich particles in the resultant steel, which may have an adverse effect on the mechanical properties. In the present study, detailed microstructural characterization, using electron microscopy (both SEM and TEM) and X-ray diffraction (XRD), of commercial grades of ferrotitanium and ferroniobium alloys is carried out to identify the various phases. The ferrotitanium alloy was composed of mainly β-Ti solid solution and a Fe–Ti–Al ternary intermetallic. There were minor amounts of α-Ti solid solution, Ti(CxN1 − x) and FeTi. For the ferroniobium alloy, two main phases were present, a Nb-rich solid solution and μ-Fe7Nb6. The Fe7Nb6 intermetallic phase exhibited two different morphologies, a proeutectic form that was slightly Fe-rich and a eutectic form that was slightly Nb-rich.