Osmond, shows the structure of a silver-copper alloy containing considerably Eutectic more silver than the eutectic.
The reason is that the particles of temper graphite which are thus formed within the solid casting in its long annealing are so finely divided that they do not break up the continuity of the mass in a very harmful way; whereas in grey cast iron both the eutectic graphite formed in solidifying, and also the primary graphite which, in case the metal is hypereutectic, forms in cooling through region 3 of fig.
Here the mass consists of (1) primary austenite, (2) eutectic austenite and cementite interstratified and (3) pro-eutectoid cementite.
Both the primary and eutectic austenite have changed in cooling into a mixture of pearlite and pro-eutectoid cementite, too fine to be distinguished here.
Second, the very genesis of so bulky a substance as the primary and eutectic graphite while the metal is solidifying (fig.
The residual liquid would thus become richer in B, and the tem perature and composition would pass along the curve till E, the eutectic point, was reached.
The pearlite when highly magnified somewhat resembles the lead-tin eutectic of fig.
The higher eutectic D may correspond to a complex of solid thallium and the compound; but the possible existence of solid solutions makes further investigation necessary here.
If it differs widely from the eutectic in composition, then when solidified it consists of only a small quantity of eutectic and a very large quantity of the excess metal.
It is evident that every mixture except the eutectic mixture C will have two halts in its cooling, and that its solidification will take place in two stages.