As-cast microstructures of {M-30Cr-0 to 5% C} ternary alloys. Part II: Cobalt-base alloys

Author(s): Patrice Berthod, Ophelie Hestin, Elise Souaillat

As seen before with nickel alloys, high carbides fractions can be easily obtained in cast alloys, simply by choosing sufficiently high carbon contents in presence of chromium. This allows obtaining alloys, potentially able to offer very high values of hardness. To quantify the carbides fractions which can be possibly obtained, cobalt alloys containing high contents in carbon and chromium were the subject of a preliminary study by thermodynamic calculations. Thereafter thirteen 30wt.%Cr-containing Co-based alloys with an increasing carbon content (from 0 to 5wt.%) were really elaborated by foundry and theirmicrostructureswere characterized by electronmicroscopy and image analysis. The alloys with less than 3-3.5wt.%C display a hypoeutectic microstructure composed of matrix dendrites and eutectic carbides. For higher carbon contents dendrites are replaced by coarse primary carbides. Graphite may also appear, but only for very high carbon contents (5wt.%C) which allows obtaining carbides fractions greater than for nickel alloys.

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