Explain objectives of annealing? Discuss the various annealing processes? Is spheroidising different from annealing? Illustrate.

A  slow  cooling  rate  from  eutectoid  temperature  yields  course  pearlite  -  a  mixture  of comparatively coarse crystals of ferrite and  cementite. Such a slow cooling is known as annealing. Here,  sufficient  time  is  available  for  carbon  in  the  austenite  to  diffuse  and  redistribute itself to 0.02% in ferrite and 6.67% in cementite.  During annealing, effective transformation temperature  is  low,  where  rate  of  growth  is  rapid  compared  to  rate  of  nucleation. Hence, spheroidising is obviously different from annealing.