Effect of rare earths on the properties of cast iron

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Virginia Polytechnic Institute and State University


The rare earth metals cerium, mischmetal, lanthanum, and didymitun were added to irons in the amounts of 0.08 to 0.20 per cent. Silicon and graphite were added to the iron at the electric furnace to change the carbon equivalent of the base metal.

The base metal was super-heated to temperatures of 2740º to 2780°F. The molten metal was poured onto the rare earth with a one per cent silicon addition for inoculation. It was then poured into the tensile molds in a temperature range of 2490° to 2540°F.

The appearance of the tensile fracture indicated the presence of carbon flotation. The chemical analysis and micro-structure. examination verified this. All of the tensile specimens with carbon equivalent above the eutectic had flotation. As the carbon equivalent increased the carbon flotation increased.

The graphite structure in the carbon flotation region was deteriorated from the nodular, and the graphite was nodular in form in the lower portions of the specimens. Cementite was scattered throughout the matrix of all samples except those. with silicon contents above 2.70 per cent.

The metal with didymium additions had the most consistent physical properties, while lanthanum produced the lowest physical properties. The tensile and yield values were comparable to those reported in the literature for similar additions. However, the elongation values were low due to the carbon flotation.