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Test of elaboration protocols for obtaining highly Co- or Ni -alloyed spheroidal cast irons from an industrial SGcast iron. Part D: Second protocol for 75M25Fe cast irons. Subpart 1:Obtainedmicrostructures and roomtemperature hardness

KamelMeridja, Patrice Berthed, ElodieConrath

In this new part of the work the elaboration of spheroidal graphite cast irons very rich (75wt.%) in either nickel or cobalt was undertaken using the second protocol which gave good results when the wished content in alloying element was 25wt.% or 50wt.%. The obtained microstructures were characterized by the presence of a double population of graphite particles. In the two highly alloyed (75wt.%Ni and 75wt.%Co) alloys some rare more or less coarse graphite nodules were present, but also coarse graphite plates. A second population was also present, very numerous fine lamellae, in the interdendritic spaces. The interpretation of these observations led to interpret the coarsest graphite particles as being the ones which took benefit of the rare nucleus present in the melt, and the fine graphite lamellae as being the undercooling-type of graphite which suddenly precipitated at the end of solidification. These experiment led thus to novel microstructures which may present specific properties which merit to be explored.