Difference between Annealing and Spherodizing

Hi Pals,
Main difference between annealing and spheroidizing is application of Heat treatment.
Annealing is most conmanly used for stress reveling  and grain refinement where as spheroidizing is used to improve cold working ability of high carbon steel.  

Difference between annealing and spheroidizing HT Cycle:

Annealing 

Heating to a temperature (Austnizing) -> Holding at that temperature (Saoking in Austenizing zone) -> cooling to room temperature at appropriate rate.

Types -

Cycles falls in broad categories and can be classified according to the temperature to which steel is heated and cooling method. These can be classified as below –

1. Subcritical - Temperatures below lower critical temperature (A1).
2. Intercritical – Temperature above A1 and lower than the upper critical temperature (A3 / Acm)
3. Full  – Temperature above A3.

Spheroidizing 

Heating and cooling alternatively just above and below A1 (lower critical temperature) temperature for prolonged time followed by very slow cooling to room temperature.

Difference in Micro Structure:

Annealed plain carbon steel micro structure shows uniform and equiaxed grains of Ferrite and Pearlite. 
Spheroidized micro structure shows uniform distribution of spheroidized carbids in ferrite matrix.

Difference between annealing and spheroidizing HT application:

Steels are annealed to facilitate cold working. To relieve residual stresses induced in cold working.

Steels are spheroidized to improve cold formability and working ability in hypereutectoid steels (%C > 0.8%)