Room temperature hardness of carbide strengthened cast alloys in relation with their carbon content and aging temperature Part 2-Case of cobalt alloys

Nine cobalt alloys, all containing 30 wt-% Cr, various carbon contents and two amounts of tantalum (for two of them), were elaborated by casting and aged at 1000, 1100 and 1200 degrees C for 50 h. The hardness of each sample was measured by macro and micro Vickers indentation, and studied in accordance with the carbon content, the nature and fractions of carbides. The hardness increases from about 250-270 up to 500-550, which is the prolongation of the range for nickel alloys with similar compositions. The increase in hardness with the carbon content obeys a linear function of the carbon content, which allows choosing a carbon content to achieve a targeted hardness, in the studied range of carbon or by extrapolation to higher values. For a same carbide fraction, hardness significantly depends on the nature of carbides (e.g. higher for TaC than for M7C3 carbides).