Additions have been made to foundry iron for castings to modify the graphite shape from flake to compacted form. This has been done to improve the mechanical properties of the iron to a level desirable for more diverse applications. The graphite modification has been accomplished by treatment with controlled levels of magnesium, magnesium-titanium combinations, and also rare-earth alloys.
Reportedly, compacted graphite iron has also been produced in blast furnace iron modified to near foundry iron composition.
The work reported here was instituted on the premise that compacted graphite iron could be made from blast furnace iron with only modest modification as would be possible and practical in a foundry producing large castings, such as ingot molds.
Preliminary work involved the confirmation of the ability of rare earths to produce compacted graphite in blast furnace irons. Three-hundred-pound laboratory heats were evaluated for a range of major element levels (carbon, sulfur, silicon, manganese, and silicon-manganese ratios), the effect of pouring temperatures, and cooling rates.
The castings were examined for graphite type and amount, as well as possible presence of carbides. The matrix structures were examined for ferrite and pearlite amounts and distributions. Mechanical properties were also determined.
With production of a desirable structure of compacted graphite surrounded by ferrite and containing a minimum of pearlite, it should be possible to produce castings from blast furnace iron with high strength, good thermal conductivity, and acceptable erosion resistance for an application such as ingot molds, with a resultant major improvement in the life of the mold.