Re-crystallization Annealing

Re-crystallization Annealing:
  • The process consists of heating steel above the recrystallization temperature, holding at this temperature and cooling thereafter. 
  • It is used to treat work hardened parts made out of low carbon steels (< 0.25%) carbon). This allows the parts to be soft enough to undergo further cold working without fracturing. 
  • Re-crystallization temp (Tr) is given by Tr = (0.3-0.5)Tmp 
  • As little scaling and de-carburization occurs in re-crystallization annealing, it is preferred over full annealing 
  • No phase change takes place and the final structure consists of strain free, equiaxed grains of fine ferrite produced at the expense of deformed elongated ferrite grains. 
  • However it would produce very coarse grains if the steel has undergone critical amount of deformation. In such cases, full annealing is preferred. 
Aims of re-crystallization Annealing: 
  • To restore ductility 
  • To refine coarse grains 
  • To improve electrical and mechanical properties in grain oriented Si steels
A typical re-crystallization curve at constant temperature: 

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