Microstructures
by
George
Langford, Sc.D., Massachusetts Institute of Technology, Cambridge, MA,
1966
Copyright©2005 by George Langford
Cast Irons, High Alloy Steels,
and Superalloys - Lesson 1 - Second specimen
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Here we have an example of a pearlitic grey cast iron, shown
at 200X at left.
Cooling of the casting was rapid enough that the carbon rejected by the
decomposing austenite could not reach the graphite flakes.
Therefore, pearlite formed everywhere that the austenite was thereby
retained, except where the carbon was depleted by atmospheric oxidation.
Note the "flat" white appearance of the ferrite in the image at left
compared to the yellowish appearance of the iron - iron phosphide
eutectic in the photomicrograph below.
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Here the magnification is 500X, and there is an exaggeration
of the volume fraction of phosphide eutectic in this particular area,
because this is the lowest freezing microconstituent in this cast iron,
and so it is concentrated in the last portions of the casting that
freeze.
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