Solidification of multi-alloyed white cast iron: type and morphology of carbides

摘要

Type and three-dimensional morphology of carbide precipitated in as-cast multi-alloyed white cast iron, which contains 5 mass% Cr, ]-8 mass% Mo and W, 1-15 mass% V, 0-12 mass% Co and 1.3-3.2 mass% C, were investigated using an optical microscope,scanning electron microscopy (SEM) and x-ray diffraction (XRD). The types of carbides identified are MC, M{sub}2C and M{sub}7C{sub}3. The morphology of MC carbide is classified into three configurations: flaky, nodular and coral-like. The M{sub}2C carbide exhibits two morphologies: lamellar and plate-like. The morphology of M{sub}7C{sub}3 is rod-like or ledeburitic.The type and morphology of carbide varies remarkably, depending on chemical composition of the cast iron-particularly carbon, vanadium and tungsten equivalent(Weq)-when chromium and cobalt contents are constant. However, they do not change according tocobalt content. The region of chemical compositions in which each type of carbide precipitates is given by simple equations in relation to the contents of carbon and vanadium and Weq value. Solidification rate hardly influences the type of precipitatedcarbide, but the carbide tends to become fine with an increase in solidification rate. M{sub}3C carbide may appear at very low solidification rate, when carbon content is high.