Graphite Morphology Essay

The figure - 2 shows a deep etched SEM micrograph of the three dimensional compacted graphite morphology indicating interconnected “coral-like” graphite cluster. As compared to flake graphite these are shorter, thicker and have rounded edges and roughened surfaces & this roughened surface improves adhesion to the ferritic matrix and minimises both initiation and propagation of cracks which results in improved tensile, fatigue strength and elastic modulus which has been indicated.

Figure -3. Proportions of Nodularity in the Microstructure of
Compacted Graphite Iron.

Nodules 5 % Nodules 15 %

Nodules 30

is effectively constant with 90
% Nodularity. In curve two it can be seen that nodularity of 2.5 % also gives hardness of 235 B.H.N. in C.G.I. ( Refer figure 8 Left and Right Curves)

D) Magnesium Treatment after Melting:

Magnesium Treatment: The magnesium treatments are divided in two stages (A) Melting Process and (B) Magnesium Treatment.

( A ) The effect of all important elements are discussed above. The Magnesium Treatment is given after once the composition is achieved as per requirement. Ferrosilicon Magnesium with Magnesium 5 % Titanium 9 % Calcium 1 % Ceriumo.o2 to o.05 % and balance Silicon & Iron is used to control the Nodularity as low as possible to obtain C.G.I.

Figure - 9 The classification of Grey, Compacted Graphite and Ductile Irons based of the % of residual magnesium in the metal.

The stable magnesium range for compacted graphite growth is separated by an abrupt transition to flake graphite and gradual transition to nodular graphite. It can be observed from the Table No.- 3 that the % of residual magnesium is in the range of 0.007 to 0.010 and higher than this increases the nodularity of about 80 % with residual magnesium of 0.03