Mechanical Engineering - Engineering Materials - Discussion

For stress relief the Metal is heated up to recrystallization temperature at that temp stress relief takes place then metal starts cooling simultaneously the crystallization takes place and henceforth the grain growth takes place.

When metals are subjected to cold working stress induced so to relieve the stress annealing is done (annealing means cooling in the furnace itself) so at that condition re crystallization occurs and grain growth starts. This process also improve the ductility of the worked metals.

Actually, the metal is heated above the crystallization temper then stress is rest.

The metal is heated to upper critical temperature and also stress will be reduced after atoms are re-generated.

So, the grains are formed.

The Recovery occurs at low temperatures and reduces or eliminates work-hardening effects. Interestingly, the grain structure is not affected, leaving existing grain boundaries (size) intact. As a result of recovery at low temperatures, small changes in hardness occur due to a decrease in the density of microstructural characteristics created by the initial cold work.

Recrystallization occurs when sufficient thermal energy is available to drive the creation and strain-free growth of new grains in the existing matrix. It is a diffusion process, driven by increased thermal energy. The growth of these new grains eliminates the distortions in the existing matrix, effectively erasing the increase in mechanical properties that had resulted from the cold work. This returns ductility to the material as well as reducing tensile and yield strength. For our shops, this means lower hardness and gummier, less brittle chips. In very high carbon grades, the diffusion into a spheroidal form of carbides results in an improvement in machinability and surface finish by increasing the mean free path of ferrite between the carbide spheroids.

Grain growth is the result of continued high temperatures past recrystallization as the grain boundaries are eliminated, increasing the present grain size regardless of its prior austenitic grain size. Large oversize grains observed in nominally fine-grained steel are evidence of time and temperature at or above the recrystallization temperature.

Please give an example for the answer.

For stress relief, the Metal is heated up to recrystallization temperature at that temp stress relief takes place then the metal starts cooling simultaneously the crystallization takes place and henceforth the grain growth takes place.