Prospects of development of Fe-based hardfacing materials by its complex alloying with Nb, Mo, Ti and V carbides

Abstract

In most cases formation of binary and solid solutions between refractory compounds such as carbides and borides of Ti, Nb, Mo and V leads to the significant increasing of microhardness and grain refinement in comparision with pure components. It is caused by differences in atomic radii together with electron-electron interactions leading to the appearance significant stresses in crystal lattice. In multicomponent systems the values of such stresses increase when number of solution components becomes more than two and continue to increase up to its decomposition into several phases. The goal of this study was to determine the temperature and concentration ranges of existence of solid solution based on four refractory carbides (NbC, TiC, Mo2C and VC) in system with Fe during step by step alloying in equimolar amounts and its general properties. Theoretical determination of the temperature dependencies of the stable phase regions, phase amounts and its composition were performed using CALPHAD technique. Calculations were performed for Fe-rich alloys of Fe-Nb-Ti-Mo-V-C system which were presented in form of pseudobinary Fe - carbide diagrams. Samples for structure and properties investigations were prepeared using flux-cored arc welding with hardfacing alloys corresponding to typical sections of pseudobinary systems on low carbon steel substrate. Microstructure investigations were performed using scanning electron microscopy (SEM) and microhardness measurements. Hardness was also measured by Rockwell technique (scale C). Results show, that equimolar alloying with chosen carbides leads to the formation of a complex (Nb, Mo, Ti, V)C carbides with high thermodynamic stability. During proposed step by step aloying hardness increases from 27 to 52 HRC when number of carbide components increases. It alows to use proposed alloying system in specified concentration ranges for development of new hardfacing materials for working conditions, where failure of surface layer caused by high dynamic and (or) cyclic loads may occur.