Effects and Neutralization of Trace Elements in Gray and Ductile Irons

Abstract

The trace elements Pb, Ti, Sb, Te and Bi along with mischmetal (rare earths) . Most melts were inoculated in the ladle with 0.25% Si, as ferrosilicon. Results show small amounts (0.05%) of Pb, Ti, Sb, Te and Bi cause nodule degeneration and loss of strength and/or ductility. Graphite degenerating from 0.05% of these , .trace (tramp) elements is completely neutralized by 0.01% mischmetal added to the ladle. Neutralization of trace elements in many cases is also obtained from very ' small amounts (0.0007-0.0015%) of RE present in the nodularizing alloy. The mechanisms by which these. trace elements affect the stnicture and how these effects are neutralized by rare earths are discussed. Antimony exerts a marked effect on pearlite stabilization in , both ductiJv" and were added to ductile and gray irons and their effects on microstructure and mechanical properties studied. Melts were prepared from low impurity charge materials melted in an induction furnace and subsequently cast into keel blocks, ,1.2- and 4-in. round bars. The ductile irons were treated by plunging with lots . of magnesium-ferrosilicon some of which contained various amounts of rare earths (RE) ' either chemically combined or as a mechanical mixture . gray irons. This i�fluence is so strong that gray iron castings . with type D graphite have a fully pearlitic matrix when 0.2% Sb is present. The impact properties with ductile irons containing Sb ar.e comparable to other pearlitic ductile irons, provided sufficient RE are present to neutralize the effect of Sb on the graphite nodules. The pearlite produced by Sb and Sn additions resists ferritization at 1350 F. (732 G).