However, it should be taken into account that the steel studied has already been severely deformed before ECAP, the cementite
particles have been fragmented, and this would cause the unusual behavior.
Baumann (1998) also holds that an extremely high level of deformation and shearing stress leads to dissolution of cementite
and diffusion of carbon.
Image analysis of pearlite spheroidization based on the morphological charact-erization of cementite
9b in the centre of the photograph, surrounded by residual cementite
or Martensite and the Acicular Ferrite (AF) in the part between the center and the fusion line have higher hardness than Polygonal Ferrite (PF) in the weld seam center.
It regards especially a gradual degradation of integrity of internal cementite
skeleton binding ferrite and pearlite grains.
White Cast Iron: White cast iron occurs when all of the carbon in the casting is combined with iron to form cementite
If we make an equivalence between steel and polypropylene, Austenite is equivalent to molten polypropylene, Ferrite and Cementite
to [alpha]-monoclinic polypropylene, Martensite to the smectic form.
At different heats, the molecules in steel change their nature--actually becoming different minerals with such names as austenite and cementite
Moreover, according to the classical nucleation theory, there are the fluctuations of composition, microstructure and energy in the interfaces between cementite
and ferrite, which is beneficial to form an austenite nucleus.
However, since martensite is a non-equilibrium stage of the iron-iron carbide phase diagram, it has not been exposed that warming the part after the cryogenic treatment results in the re-transformation of the induced martensite back to austenite or to ferrite plus cementite
, negating the hardening result.
The initial microstructure consisted of pearlite with a small amount of cementite
precipitated along prior austenite boundaries (Fig.