Test of elaboration protocols for obtaining highly Co- or Ni -alloyedspheroidal cast irons from an industrial SGcast iron. Part C: Secondprotocol for 25M75Fe cast irons. Subpart 1:Obtainedmicrostructuresand roomtemperature hardness
Spheroidal Graphite cast irons highly alloyed with nickel or with cobalt were produced by foundry from parts of an industrial SG cast iron, by following a protocol which recently proved its efficiency, despite that no additional spheroidisation and inoculation treatments of the liquid metal was done. The same protocol was applied to obtain a control sample containing only iron. For the obtained 25wt.%Ni- and 25wt.%Co-containing cast irons the graphite issued from this protocol is very close to the spheroidal geometry. Obtaining highly alloyed SG cast iron following this original elaboration route was thus successful. The matrix of the obtained 25wt.%Ni- and 25wt.%Co-containing cast alloys was influenced by the presence of these new elements in so high quantities: absence of the hypoeutectic character of the control sample, respectively metallic matrix or ferrite-pearlitic matrix instead the ledeburite of the control sample. Graphitizing properties were found again for nickel and revealed for cobalt. The differences of Vickers hardness between the three cast irons were easily explained and hypothesis were formulated, from the response of the microstructures to the Nital etching, about the corrosion resistance of these two highly alloyed SG cast irons.