What Does Recrystallization Mean?
Recrystallization is the process in which deformed grains of the crystal structure are replaced by a new set of stress-free grains that nucleate and grow until all the original grains have been consumed. The process is accomplished by heating the material to temperatures above that of crystallization. This process is utilized in the annealing of steel, to eliminate all the effects of strain hardening such as heavy plastic deformation produced during cold working.
Corrosionpedia Explains Recrystallization
When temperature is raised, the new, stress-free gains nucleate and grow inside the old deformed grains and also at the grain boundaries. This replaces the distorted grains produced by strain hardening. The metal’s mechanical properties revert back to their original, more ductile and weaker state.
The temperature above which the process occurs is not constant and is largely dependent on:
- Amount of time
- Steel composition
- Amount of cold work
The more strain hardening, the lower the recrystallization temperature and the smaller the new grain sizes. A minimum of between two and twenty percent cold work is required for recrystallization to occur.
Recrystallization temperature is typically one-third to one-half the melting point (in degrees Kelvin), and raises the atomic mobility, which results in recrystallization.
The recrystallization results in lower hardness and strength properties of the material, in addition to increased ductility. It might be an undesirable byproduct of another processing step.
Various applications include:
- Decreasing strength and hardness levels
- Increasing ductility
- Allowing recovery process by removal or reduction of cold-working effects
- Increasing equiaxed ferrite grains formed from elongated grains
This process is widely used in metal processing such as annealing of stamped parts in cold-rolled steel, and with forged parts to prepare them for subsequent operations like cold forming or machining.