Annealing (materials science)

In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, leading to a change in ductility and hardness.

With knowledge of the composition and phase diagram, heat treatment can be used to adjust from harder and more brittle to softer and more ductile.

In the case of ferrous metals, such as steel, annealing is performed by heating the material (generally until glowing) for a while and then slowly letting it cool to room temperature in still air.

[6] The three stages of the annealing process that proceed as the temperature of the material is increased are: recovery, recrystallization, and grain growth.

The first stage is recovery, and it results in softening of the metal through removal of primarily linear defects called dislocations and the internal stresses they cause.

In grain growth, the microstructure starts to coarsen and may cause the metal to lose a substantial part of its original strength.

The inside of the oven is large enough to place the workpiece in a position to receive maximum exposure to the circulating heated air.

Typical methods of quench hardening materials involve media such as air, water, oil, or salt.

[citation needed] In the semiconductor industry, silicon wafers are annealed to repair atomic level disorder from steps like ion implantation.

Normalization is an annealing process applied to ferrous alloys to give the material a uniform fine-grained structure and to avoid excess softening in steel.

It involves heating the steel to 20–50 °C above its upper critical point, soaking it for a short period at that temperature and then allowing it to cool in air.

The process produces a tougher, more ductile material, and eliminates columnar grains and dendritic segregation that sometimes occurs during casting.

Normalizing improves machinability of a component and provides dimensional stability if subjected to further heat treatment processes.

Cold-worked steel normally tends to possess increased hardness and decreased ductility, making it difficult to work.

Its purpose is to originate a uniform and stable microstructure that most closely resembles the metal's phase diagram equilibrium microstructure, thus letting the metal attain relatively low levels of hardness, yield strength and ultimate strength with high plasticity and toughness.

Often the material to be machined is annealed, and then subject to further heat treatment to achieve the final desired properties.