The chemical composition of tested alloys is listed in Table 1. The melting of various alloys has been conducted in induction furnace. Test samples for structural analysis have been cut from the bars (200mm long and 30mm in diameter) cast in the sand molds.
The microstructure was examined using conventional optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Samples for optical microscope examinations were prepared using standard metallographic technique (etched with picric acid solution (1g) in methanol (100ml) by adding 5ml of hydrochloric acid or etched with Murakami). The size and volume fraction of the phases present in the structure were determined using image analyzer. The morphology of carbide was examined by a scanning electron microscope, JEOL 733-FCXA, using an accelerating voltage of 25kV. For this examination, the polished samples were deep etched in a 10% HCl solution in methanol for 24h then cleaned in an ultrasonic bath. The chemical composition of the carbides was determined using energy dispersive X-ray spectroscopy (EDS). Discs for TEM examinations were prepared by using a twin-jet electropolisher. These samples were examined at 200kV in a JEOL-2000FX transmission electron microscope