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· A hyper-eutectoid alloy iron
precipitates iron carbide on the Austenite
grain boundaries when it is cooled
from the γ-phase to the eutectoid temperature.
The remaining Austenite then transforms to Pearlite
at the eutectoid
temperature.
· The pro-eutectoid
iron
carbide (Cementite) on the grain
boundaries of the Pearlite is brittle and
makes the room temperature hyper-eutectoid alloy a brittle
material.
· The
lever rule for the average composition,
C1
= 1.2 wt % C, at (723 - ε) C gives:
Wcarbide
= (1.2 - 0.02)/(6.67 - 0.02) = 18 wt %,
WαFe = (6.67 -
1.2)/(6.67 - 0.02) = 82 wt %.
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