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Hardness of iron (and/or) nickel-based alloys strengthened by varying fractions of chromium and tantalum carbides

Patrice Berthod, Yassin Hamini, C�?�?�?�?�?�?�?©line V�?�?�?�?�?�?�?©bert

Easiness ofmachining is of great importance, especially for cast superalloys for which strength at high temperature is sometimes obtained by carbides which may induce an increase in hardness. Knowing how hardness varies versus microstructure is then interesting to predict machinability. Microandmacro- Vickers indentationwas performed on nine {30 wt.%Cr}-containing alloys, based on Fe, both Fe and Ni, or Ni, and containing various fractions of chromium carbides and tantalum carbides. For similar carbon and tantalum contents, the natures and volume fractions of carbides vary with the nature of the base element. The hardness is a function of both the matrix nature and the carbide volume fraction. Hardness increases when the base element is changed from{FeNi} to Fe, then fromFe to Ni. It also increases when the volume fraction of carbides increases, e.g. when the carbon content is higher (0.4 wt.%instead 0.2), or if tantalumis also present in the alloy (between 2.5 and 6 wt.%). The hardness can be lowered after an exposure of 50 hours at high temperature.