Chemical Composition and Morphology of M_7C_3 Eutectic Carbide in High Chromium White Cast Iron Alloyed with Vanadium

摘要

The chemical composition and morphology of M_7C_3 eutectic carbides in 19 mass% Cr-2.8 mass% C white iron with up to 4.7 mass% V additions have been studied. Eutectic colonies are mainly composed of a very fine rod-like carbides at the center and become coarser rod-like or blade-like with increased distance from the center. The volume fraction, size and distribution of rod-like and blade-like carbides in the eutectic colonies are changing with increasing vanadium content in the alloys. The formation of the eutectic colonies of different morphology is the consequence of the segregation of alloying elements in the alloy melt, which was confirmed by EDS analysis of the chemical composition of carbides. Three different compositions of M_7C_3 carbides were found in all tested alloys. The main difference between them is in the amount of chromium and iron and in the degree of their replacement by vanadium. Due to different melt composition in particular zones, the constitutional undercooling, and subsequently the growth rate, will be different, which will induce the formation of eutectic colonies of different morphologies.