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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