Troostite

The transformation structures of the pearlite stage (see Pearlite peak) correspond to .

Increasing cooling rates, however, change the structure ratio and the formation of pearlite with regard to flake distance. Structures of the lower pearlite stage with very fine flakes are referred to as sorbite and troostite. Their structure can no longer be seen under an optical microscope.

 

Generated pearlite with a ball-like or concentrated cementite phase is the exception. It is formed at very low cooling rates or by pendular annealing around the A1 point, i.e. under almost balanced conditions.

Transformation structures typical for hypo-eutectoid steel castings are characterized by the Widmannstätten structure. They feature needle-shaped and plate-shaped ferrite deposits which are formed at certain cooling rates in particular during the cooling of high austenitizing temperatures.

 

Additional references:
Metal matrix of cast iron

  • Fig. 1: Troostite formation innodular graphite cast ironwall thickness 5 mm, etched, 5000:1
  • Fig. 2:  Distance between the cementite lamella in the pearlite of figure 1
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