Influence of lead on the morphology of graphite in gray iron

The degradation of gray cast iron microstructures as a result of the presence of trace amounts of lead has frequently been reported in the literature. However, the available literature does not present sufficient information for the foundryman to judge whether a given amount of lead in the metallic charge will result in detrimental effects on the casting quality, and the effect of other factors involved in addition to amounts of lead present.; The detrimental effect of the presence of trace amounts of lead in gray irons results in the formation of graphite “appendages” on the preexisting graphite flakes. It is obvious that the stress concentration factor for non-flake graphite shapes (e.g., spiky, mesh, Widmanstätten) will be higher than that for Type A flake graphite. During the cooling stage of heavy castings, even a low internal stress in the bulk of the material could result in extremely high stresses at the tips of abnormal graphite shapes, which could be sufficient to cause yielding, or plastic flow, or even nucleation of cracks at the root of the suitably oriented flakes.; It is apparent that there is a lack of knowledge concerning the detrimental effects of Pb and the parameters involved in controlling the morphology of graphite in commercial gray cast iron. The purpose of this study was to more adequately develop the metallurgical understanding of the factors involved in flake graphite shape control and the practices required to minimize the influence of lead to insure the reliability of structure and properties of commercial gray iron castings.