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Hafnium carbides in cast chromium-rich refractory alloys. Part 3: Case of iron-based alloys

Patrice Berthod

After having tested the metallurgical effect of the addition of hafnium in nickel-based and cobalt-based alloys in presence of carbon in the two first parts of this work, the same procedure was followed in this third and final part to complete the study by considering the case of iron-based alloys. Three Hf-added iron alloys, with the same contents in Cr, C and Hf as the previous Ni-based and Co-based alloys, were elaborated and metallographically characterized.Here too hafniumcarbides tended forming instead chromium carbides, with mainly a script-like shape for the eutectic carbides and also some blocky carbides unfortunately tending to migrate outwards during solidification under the electromagnetic stirring. The hardening due to the presence of hafnium carbides previously seen for the nickel-based and cobalt-based alloys was not found for iron alloys by comparison with ternary alloys especially elaborated containing only chromium carbides, probably because of the loss of carbides in the ingot core due to the later phenomenon.Hafniumappeared thus as amore constant {MC carbide}-former element than tantalum, with maybe a better high temperature stability as earlier observed in cobalt-based alloys but which remains to be verified for the two other nickel and iron bases.