Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating and maintaining at a suitable temperature, and then cooling. Annealing is used to induce softness, relieve internal stresses, refine the structure and improve cold working properties. Anneal may refer to: Annealing (metallurgy), a heat treatment wherein the microstructure of a material is altered, causing changes in its properties such as strength and hardness. ... Georg Agricola, author of De re metallica, an important early book on metal extraction Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. ... The Materials Science Tetrahedron, which often also includes Characterization at the center Materials science or Materials Engineering is an interdisciplinary field involving the properties of matter and its applications to various areas of science and engineering. ... Heat treatment is a method used to alter the physical, and sometimes chemical, properties of a material. ...

In the cases of copper, steel, and brass this process is performed by substantially heating the material (generally until glowing) for a period of time and allowing it to cool slowly. In this fashion the metal is softened and prepared for further work such as shaping, stamping, or forming. For other uses, see Copper (disambiguation). ... For other uses, see Steel (disambiguation). ... For other uses, see Brass (disambiguation). ...

Stages of annealing

There are three stages in the annealing process, with the first being the recovery phase, which results in softening of the metal through removal of crystal defects and the internal stresses which they cause. The second phase is recrystallization, where new grains nucleate and grow to replace those deformed by internal stresses. If annealing is allowed to continue once recrystallization has been completed, grain growth will occur, in which the microstructure starts to coarsen and may cause the metal to have less than satisfactory mechanical properties. Recovery is a process by which deformed grains can reduce their stored energy by the removal or rearrangement of defects in their crystal structure. ... This article does not cite any references or sources. ... For other uses, see Crystal (disambiguation). ... Recrystallization is a process by which deformed grains are replaced by a new set of undeformed grains that nucleate and grow until the original grains have been entirely consumed. ... Grain growth refers to the increase in size of grains (crystallites) in a material at high temperature. ...

Annealing in a controlled atmosphere

The high temperature of annealing ( about 50 deg.F above C3 line ) may result in oxidation of the metal’s surface, resulting in scale. If scale is to be avoided, annealing is carried out in an oxygen, carbon, and nitrogen free atmosphere (to avoid oxidation, carburization, and nitriding respectively) such as endothermic gas (a mixture of carbon monoxide, hydrogen gas, and nitrogen).

The magnetic properties of mu-metal (Espey cores) are introduced by annealing the alloy in a hydrogen atmosphere. For other uses, see Magnet (disambiguation). ... Mu-metal is a nickel-iron alloy (77% nickel, 15% iron, plus copper and molybdenum) that is very efficient for screening magnetic fields. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... For other uses, see Atmosphere (disambiguation). ...

Diffusion annealing of semiconductors

In the semiconductor industry, silicon wafers are annealed, so that dopant atoms, usually boron, phosphorus or arsenic, can be incorporated into substitutional positions in the crystal lattice, resulting in drastic changes in the electrical properties of the semiconducting material. A semiconductor is a solid whose electrical conductivity is in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark grey with bluish tinge Standard atomic weight 28. ... A dopant, also called doping agent and dope, is an impurity element added to a semiconductor lattice in low concentrations in order to alter the optical/electrical properties of the semiconductor. ... General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black/brown Standard atomic weight 10. ... General Name, Symbol, Number phosphorus, P, 15 Chemical series nonmetals Group, Period, Block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... The article on electrical energy is located elsewhere. ...

Thermodynamics of annealing

Annealing occurs by the diffusion of atoms within a solid material, so that the material progresses towards its equilibrium state. Heat is needed to increase the rate of diffusion by providing the energy needed to break and form new bonds. The movement of atoms has the effect of redistributing and destroying the dislocations in metals and (to a lesser extent) in ceramics. This alteration in dislocations allows metals to deform more easily, so increases their ductility. This article does not cite any references or sources. ... For the syntaxic operation, see Dislocation (syntax) For the medical term, see Dislocation (medicine) In materials science a dislocation is a linear crystallographic defect, or irregularity, in crystal structure. ... For the syntaxic operation, see Dislocation (syntax) For the medical term, see Dislocation (medicine) In materials science a dislocation is a linear crystallographic defect, or irregularity, in crystal structure. ... Ductility is the physical property of being capable of sustaining large plastic deformations without fracture (in metals, such as being drawn into a wire). ...

The amount of process-initiating Gibbs free energy in a deformed metal is also reduced by the annealing process. In practice and industry, this reduction of Gibbs free energy is termed "stress relief." In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ...

Thus, the relief of internal stresses is a thermodynamically spontaneous process, however, at room temperatures, it is a very slow process. Therefore, the high temperatures at which the annealing process occurs serve to accelerate this slow-albeit-spontaneous process.

The reaction facilitating the return of the cold-worked metal to its stress-free state has many reaction pathways, mostly involving the elimination of lattice vacancy gradients within the body of the metal. The creation of lattice vacancies are governed by the Arrhenius equation, and the migration/diffusion of lattice vacancies are governed by Fick’s laws of diffusion. The Arrhenius equation is a simple, but remarkably accurate, formula for the temperature dependence of a chemical reaction rate, more correctly, of a rate coefficient, as this coefficient includes all magnitudes that affect reaction rate except for concentration. ... Ficks laws of diffusion describe diffusion, and define the diffusion coefficient D. // Ficks laws of diffusion were derived by Adolf Fick in the year 1855. ...

Mechanical properties, such as hardness and ductility, change as dislocations are eliminated and the metal's crystal lattice is altered. On heating at specific temperature and cooling it is possible to bring the atom at the right lattice site and new grain growth can improve the mechanical properties.

Specialized annealing cycles

Normalization

Normalization is an annealing process in which a metal is cooled in air-cool to room temperature after heating.

This process is typically confined to hardenable steel. It is used to refine grains which have been deformed through cold work, and can improve ductility and toughness of the steel. It involves heating the steel to just above its upper critical point. It is soaked for a short period then allowed to cool in air. Small grains are formed which give a much harder and tougher metal with normal tensile strength and not the maximum softness achieved by annealing. Cold Work is a quality imparted on a material as a result of plastic deformation. ...

Full anneal

A full anneal typically results in the softest state a metal can assume. To perform a full anneal, a metal is heated to its annealing point, and the furnace is turned off. The metal is allowed to cool in the furnace, causing grain growth and resulting in a ductile metal with a lowered yield point.

See also

• Tempering, which is very similar to stress relieving and post-weld heat treat (PWHT) processes
• Annealing (glass)
• Heat treatment
• Hollomon-Jaffe parameter

Tempering is a heat treatment technique for metals and alloys. ... Annealing, in glassblowing and lampworking, is the process of heating, and then slowly cooling glass to increase softness (ductility) and durability. ... Heat treatment is a method used to alter the physical, and sometimes chemical, properties of a material. ... The Hollomon-Jaffe parameter, or HP, describes the effect of a heat treatment by isothermal holding at a temperature for a certain time. ...

External links

• Annealing with induction - Ameritherm offers annealing overview and Application Notes