Effects of titanium addition on microstructure and wear resistance of hypereutectic high chromium cast iron Fe–25wt.%Cr–4wt.%C

A finer microstructure generally helps to increase the wear resistance of materials. It was reported that Ti could act as an inoculant to generate fine microstructure for white cast iron, one of widely used in industrial materials. To confirm this, we investigated influences of Ti addition (up to 6 wt.%) on microstructure of a hypereutectic high chromium cast iron (Fe–25wt.%Cr–4wt.%C). Ingot samples were prepared using an arc furnace by melting pieces of the cast iron with titanium powder. Microstructures of the samples were examined by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction. It was demonstrated that the added titanium did not act as an inoculant to reduce the size of coarse primary carbides. Instead, as the titanium amount was increased, the cast iron changed from a hypereutectic microstructure to a hypoeutectic one due to the depletion of carbon that was consumed by Ti to form titanium carbides. When 2 wt.% Ti was added, the finest microstructure was achieved, which corresponded to the eutectic structure with mixed chromium carbides and titanium carbides. The eutectic structure exhibited the highest wear resistance and hardness due to the refined microstructure as well as the fact that an amount of chromium carbides were replaced by Ti carbides, which are harder than the former.