Effect of alloying elements on the microstructure and mechanical properties of high chromium white cast iron and Ni-Hard iron

Abstract

The present work deals with the effect of B, V, Ti on the microstructural evolution and mechanical behavior of high chromium white cast iron. The comparison is also made with Ni-hard iron in as-cast condition. The destabilization treatment provided after casting resulted in decomposition of austenite into martensite and secondary carbides and further tempering treatment resulted in decomposition of martensite into ferrite and secondary carbide phases. Phase analysis by x-ray diffraction revealed two main phases, i.e., a BCC-Fe matrix and a primary carbide phase. In addition to this, high chromium white cast iron and Ni-hard alloys contain austenitic phase (FCC-Fe) (Fig. 2(a)). The primary carbides are M7C3 for V additions whereas for all other cases, they are M3C2. Ti and B additions led to the formation of secondary carbides of M7C3 and M23C6, respectively. Effect of alloying elements on phases formed and further modification of the microstructure are discussed in detail. The hardness of unalloyed high chromium white cast iron is highest amongst all the alloys tested, however, Ti and V additions to it retained this hardness to almost the same extent. V addition to the alloy showed not only highest tensile strength but also longer elongation to fracture, thereby, resulting as toughest alloy in the lot. On the other hand, Ni-Hard iron showed the least tensile strength and elongation before fracture. This study, thereby concludes that high chromium white cast iron with V additions is suitable for manufacture of coal pulveriser grinding media owing to its higher hardness and toughness.