MICROSTRUCTURAL CHARACTERIZATION OF HIGH-CARBON FERROCHROMIUM

Light optical and scanning electron microscopy techniques were used fo r high-carbon ferrochromium microstructural analysis. Different micros tructures were observed for industrially and laboratory-produced ferro alloys. Primary carbides of M(7)C(3) with chromium ferrite were found in the industrially produced, slowly solidified, and cooled ferroalloy , while primary M(7)C(3) carbides accompanied a eutectic mixture of M( 7)C(3) carbides and chromium ferrite in the laboratory-melted and in t he water-solidified and water-cooled materials. Different microstructu ral arrangements are directly related to the friability properties of this material. which characterizes its resistance to abrasion on handl ing and impact. In ferrochromium upgraded by carbon content reduction, the eutectic M(7)C(3) hexagonal carbides are partly replaced by M(23) C(6) dendritic carbides. The presence of dendritic carbides in the fer rochromium eutectic microstructure can be interpreted as a proof of a lower carbon content, raising the commercial value of the ferroalloy. The hexagonal M(7)C(3) carbides exhibited a central hollow along the l ongitudinal axis, and on metallographic samples they looked like screw nuts. A model of the solidification mechanism for such crystals is pr oposed. (C) Elsevier Science Inc., 1996.