Mumbai University > Mechanical Engineering > Sem 4 > Material Technology

Marks: 8M

Year: Dec 2014

Recrystallization is a process accomplished by heating whereby deformed grains are replaced by a new set of grains that nucleate and grow until the original grains have been entirely consumed. Recrystallization annealing is an annealing process applied to cold-worked metal to obtain nucleation and growth of new grains without phase change. This heat treatment removes the results of the heavy plastic deformation of highly shaped cold formed parts. The annealing is effective when applied to hardened or cold-worked steels, which recrystallize the structure to form new ferrite grains.

Benefits

• allows recovery process by reduction or removal of work-hardening effects (stresses)
• increases equiaxed ferrite grains formed from the elongated grains
• decreases the strength and hardness level
• increases ductility

Application and materials

• The annealing of stamped parts in cold-rolled steel is designed to produce a recrystallised ferrite microstructure from highly elongated, stressed grains resulting from cold work.
• The annealing of forged parts is performed to facilitate subsequent operations, like machining or cold forming.

Factors affecting recrystallization temperature

• Melting point: Higher the melting point of metal higher the recrystallization temperature
• Degree of cold work: Higher the degree of cold work lower the recrystallization temperature
• Grain size: Finer the grain size lower the recrystallization temperature
• Purity of metal: Presence of impurities increases recrystallization temperature
• Heating time: Longer the heating time, lower the recrystallization temperature