Literature review of microstructure formation in compacted graphite Iron

Abstract

The literature concerning microstructure formation in compacted graphite iron is reviewed. Compacted graphite iron has an intermediate graphite morphology between lamellar graphite iron and spheroidal graphite iron. The formation of compacted graphite morphology is controlled by small changes in alloy composition. Several important factors influencing the formation of the as solidified microstructure, as well as the microstructure formation during the eutectoid transformation are also reviewed. The focus of this review is to compare mechanisms in which compacted graphite iron differs from lamellar graphite iron and spheroidal graphite iron. The effects of microstructure on some properties that are relevant in commercial applications are included in the study. Additionally the relatively few models for microstructure formation are also summarised.

New Experimental Technique for Nodularity and Mg Fading Control in Compacted Graphite Iron Production on Laboratory Scale

“…[1] The nucleation of graphite is commonly assumed heterogeneous in main graphite nucleation theories. [2] This concept assumes that graphite particles nucleate on a pre-existing inclusion in the liquid. [3][4][5][6][7] In the case of lamellar graphite iron (LGI), these inclusions are complex sulfides (Mn,X)S that at the same time have nucleated on complex oxides of Al, Si, Zr, Mg, and Ti.…”

“…[8,9] The surface-active impurities are absorbed in the prismatic face of the hexagonal graphite lattice, creating a non-faceted interface, that requires low driving forces to grow, i.e., low undercooling, like in the case of LGI, while for SGI the faceted interface requires larger undercooling to grow. [2,4,7] Previous experiments show that a completely impurities-free melt would solidify as SGI, indicating that the preferential shape for graphite is spheroids in the total absence of active surface impurities. [9] However, the amount of impurities needed to promote the formation of LGI is extremely low, [2] being the presence of O and S the most detrimental to that effect due to their strong tendency to reduce the surface energy.…”

“…[2,4,7] Previous experiments show that a completely impurities-free melt would solidify as SGI, indicating that the preferential shape for graphite is spheroids in the total absence of active surface impurities. [9] However, the amount of impurities needed to promote the formation of LGI is extremely low, [2] being the presence of O and S the most detrimental to that effect due to their strong tendency to reduce the surface energy. [1,8,9] The presence of dissolved oxygen in the melt has been shown to have a direct impact in the nodularity of the iron.…”

“…The main element used for this purpose is Mg, even though some other elements like Ce or a RE mixture are also used with the same objective. [2,13,14] Mg added to the melt, usually as FeSiMg, is used to combine most of the O dissolved in the melt by formation of oxides. The presence of dissolved S is also eliminated by Mg, producing MgS.…”

Thermal Conductivity of Thin Walled Compacted Graphite Iron Castings

“…This feature should be attributed primarily to short and thick compacted graphite with rounded edges (when compared to normal type A flake eutectic graphite) which are randomly oriented and can be connected to their nearest neighbours within an eutectic cell (as in grey cast iron). 35) Figure 6(b) showed values of thermal conductivity for cast iron with compacted graphite in accordance with the ISO 16112 Standard 29) compared to the value of thermal conductivity of cast iron obtained for alloy IV. It can be concluded, that the obtained values of thermal conductivity in thin-walled castings with a wall thickness of 3 mm are within the limits prescribed for CGI.…”