Feasibility study of formation of surface layer containing tungsten carbide on low carbon steel by TIG surface melting of pre placed layers of ferrotungsten and graphite powders

Abstract

In this study, possibility of formation of surface layers containing tungsten carbide on low carbon steel by tungsten inert gas (TIG) arc melting of pre placed layers of ferrotungsten and graphite powders were investigated. Microstructures, phases and micro hardness of the surface layers were greatly affected by the processing parameters like heat input, and ratio of ferrotungsten to graphite in the pre placed powder mixture. Microstructures of melted layers with high heat input included Fe rich dendrites and inter dendrite eutectics containing tungsten carbides (M3C type carbides). On the other hand, tungsten rich carbides and various faceted dendrites in different shapes formed in the layers with lower heat input. When the heat input was quite low some interesting finger print patterns were seen within primary dendrites. The degree of heat input affected the amount of the iron contribution from the substrate and hence resulted in formation of various microstructures in surface melted layers. This led to noticeable variations in micro hardness of the layers. The maximum hardness in layers which were produced by pre placing of ferrotungsten and graphite powders was approximately 1,100 HV.