Abrasive wear of V–Nb–Ti alloyed high-chromium white irons

Abstract

The effect of 2% V, 2% Nb plus 2% Ti added to a 17% Cr white iron was studied. The experimental alloys were made in an induction furnace by using high-purity raw materials. Alloying elements were added at the end of the ironmaking process before pouring. Thin bars of 25×15mm2 cross section and 250mm length were solidified into sand molds. Several bars of alloyed and unalloyed white irons were obtained for the present study. The as-cast microstructure consisted of eutectic M7C3 carbides in a matrix of austenite for the unalloyed iron, while for the alloyed iron the structure was composed of austenite, eutectic M7C3 carbides and MC primary carbides. The alloys were heat treated at 900°C to destabilize the austenitic matrix; a stronger mainly martensitic matrix reinforced with secondary carbides resulted from such treatment. The as-cast and heat treated alloys were tested under abrasive wear by using a rubber wheel testing machine and SiO2 as abrasive particles of 0.3mm diameter. The wear tests were undertaken by placing the rubbing surfaces against each other with loads of 25, 40 and 54N and pouring the abrasive SiO2 particles between the surfaces. The results indicate a considerable better wear resistance for the alloyed heat treated iron compared with those as-cast and unalloyed irons. The responsible for such better wear behavior is the strengthening of the matrix by the MC carbides plus the precipitation of secondary M7C3 carbides and the partial transformation of matrix from austenite to martensite after heat treatment. The strengthening of the matrix provides better support to the eutectic carbides against cracking which in turn prevents the surface destabilization.