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What Is Annealing?

May 10th, 2023

Annealing is a heat treatment process where a metal is heated to a predetermined temperature and then cooled at a specific rate. During the annealing process, the metal undergoes physical and (sometimes) chemical changes that improve its ductility and reduce hardness.

The Stages of Annealing

As previously mentioned, annealing is a heat treatment method that increases the ductility of soft metals (steel, copper, brass, etc.). When these metals experience hardening, they lose their ductility and certain mechanical properties. The annealing process helps to enhance the metal’s original properties.

There are three primary stages within the annealing heat treatment process: recovery, recrystallization, and grain growth.

1. Recovery Stage

This initial stage is marked by heating the metal in an industrial furnace to a temperature that relieves the metal’s internal stress by removing dislocations (defects). During this initial stage, the metal is softened, and some of its original properties are recovered.

2. Recrystallization Stage

The second stage is called the recrystallization stage because the metal is heated below its melting temperature but above its recrystallization temperature. This initiates the formation of new stress-free grains that replace deformed grains of the metal’s crystal lattice structure.

3. Grain Growth Stage

During this final stage, the metal undergoes controlled cooling, which enables new grain growth. The metal is sometimes left inside the furnace and gradually cooled or placed in heat-conductive materials (sand). This final stage completely changes the metal’s microstructure, resulting in more ductility and lower hardness values.

Why Is Annealing Important?

The primary purpose of annealing is to undo some of the effects of work hardening, which can occur accidentally during some metal formation and fabrication processes. By undoing these effects, the metal’s overall hardness is reduced, which is important because the hardness of a metal will impact its workability. 

For example, if a complex part needs to be created from metal, that metal needs to be ductile to prevent cracking during the formation process.

Industrial Uses for Annealed Metal

Exceptionally ductile metals can withstand high-impact loads without breaking or fracturing, which is largely why the automotive industry is such a heavy user of annealed metals.

The construction industry is also heavily-dependant on annealed metals, as are manufacturers that need workable metal to create complex parts. 

The aerospace industry uses annealing to improve aluminum’s workability and eliminate the effects of strain hardening in aluminum. When aluminum has experienced repeated plastic deformation, its hardness increases and requires annealing to relieve its internal stresses.

Welding applications also benefit from annealed metals, as annealing helps reduce stresses that occur during the welding process.

Lastly, sheet metal fabricators may utilize annealing, as steel sheet fabrication processes can result in a material with too much hardness.

Learn More About Annealing Today

SST has been an innovator and leader in precision-controlled heat treatments since 1956. For over 60 years, we’ve adopted a customer-first mindset in multiple industries and markets, including aerospace, automotive, and heavy equipment. We’re also backed by multiple industry accreditations and certifications.

Please contact us today with general questions about annealing or to learn more about our heat treatment processes and capabilities.