Investigating the effect of tungsten and heat treatment on microstructure and wear behavior of Ni-hard 4 cast iron

Wear is a major cause of damage occurring in workpieces and industrial machins, especially in construction and mining industry. One of the most common and widely used alloys in the above-mentioned industries is Ni-hard 4 cast iron. In the present study, the addition of tungsten to Ni-hard 4 cast iron and its effect on the morphology, structure and wear resistance have been investigated. For this purpose, samples containing of 0, 0.3, 0.7 and 1.1 wt % tungsten were prepared by casting and then heat treatment was applied. After the heat treatment the effect of tungsten on the structure and wear behavior of different alloys in the as-cast and heat treated samples were examined. The structures of the samples were studied by optical microscope and scanning electron microscope furthermore EDS analysis was used to determine the distribution of chromium and tungsten in the different phases in the microstructure. The results showed that the tungsten was solved in the existing phases present in Ni-hard 4 cast iron and fishbone-type and spongy tungsten carbides were formed due to the long-range segregation of tungsten during solidification and also due to the eutectic reaction. Furthermore by applying heat treatment the tungsten carbides dissolved in the eutectic carbides and in various parts of the matrix had a higher potential for a more homogeneous nucleation of secondary carbides. In addition the distribution of the secondary carbide precipitations becomes finer and more uniform. The area fraction of the carbides increased by 4.23% and the average diameter of the carbides decreased from 47.2 to 20.6 μm. As a result the abrasion properties improves.