Working with metals can be a daunting task and it is important to properly handle your materials to ensure they retain the properties you desire. There are many different treatments with specific applications, but today we focus on annealing, a heat treatment used to reduce hardness and brittleness and reduce the risk of failure or fracture, allowing the metal to withstand further work or processing.
What is annealing?
In metal products, annealing is a common heat treatment process used to alter the physical and mechanical properties of certain metals to reduce hardness, increase ductility, and relieve internal stress. It is often used to reverse or reduce the effects of cold working to allow further processing. In some cases, annealing can also have an effect on the chemical and electrical properties of the metal.
Why use annealing?
The main purpose of annealing is to change the mechanical properties of the metal, making it softer and easier to work. Annealing reduces the risk of material fracture, cracking and deformation. Hard and brittle metals are also more likely to cause excessive wear or damage to tools and machinery, and annealing can reduce this effect. Annealing is often used after cold working processes such as wire drawing, grinding, roll forming or bending to reduce its effects and allow the metal to be worked further. It is also commonly used to relieve stress that occurs after welding. In some cases, annealing can be used to improve the electrical properties of the metal, making it more conductive.
How does annealing work?
Annealing works by heating the material above its recrystallization temperature, holding it at that temperature for the desired length of time, and then allowing it to cool at a specific predetermined rate.
This is divided into three stages:
In the first stage, called the recovery stage, a furnace or alternative heat source is used to raise the temperature of the metal to a level that relieves its internal stress.
The structure of metals is formed by crystal structures called grains. At this stage, the metal is further heated above its recrystallization temperature, allowing new grains to form without pre-existing stress. It is important to accurately calculate the required temperature to ensure it remains below the melting point of the metal.
Grain growing stage
In this final stage, new grains develop in a controlled environment by cooling the material at a pre-calculated rate. This rate determines the final composition of the metal. In some specific types of annealing, certain materials can be rapidly cooled by quenching in water. The metal is then ready for any further processing, such as shaping or forming.