Plate C 



(Artificial Irons) 



1. Eutectic cast iron (carbon 4.24 percent). The structure is a eutectic of cementite and 

 pearlite. The groundmass (white) Is cementite, FesC; the black particles are pearlite and at 

 high magnification would show a lamellar structure similar to that in plates A and B. Fairly 

 strong nital etching; X 60. 



2. Martensite. The photograph shows the martensitic structure in a 0.55 percent steel, 

 quenched in water from the gamma range. Fairly strong nital etching; X 600. 



3. Fine pearlite (troostite) in martensite. The dark component, an unresolved black at 

 lower magnification, is here shown to be not an amorphous aggregate but lamellar, essentially 

 pearlite. \'ery light picral etching; X 1,200. 



4. Spheroidized cementite. A steel of about the eutectoid composition, after prolonged 

 annealing in the upper alpha range. The pearlitic structure has disappeared, the cementite 

 lamellae having coalesced into spheroids. Light nital etching; X 600. 



120 



