Annealing is a heat treatment process used to induce plasticity or the desired material properties into a metallic or alloy material. The annealing process involves heating the material to a specific temperature for a specific time and then cooling it at a specific rate. The rate of cooling and the cooling media used have an effect on the material properties. Cold working the material leaves the material’s internal structure in a stressedor disorganized condition; annealing relieves the stresses and allows the material to regain its ductility and internal structure resulting in improved machining and better material life.
Annealed metals are softer and easier to work with. Annealing makes metals easier to form and cut, because there are fewer internal stresses in the material as it is worked or shaped. Metals that are annealed also tend to be better and more consistent in terms of their machining and heat-treating properties.
Annealing is also used to increase the life of certain materials that are subject to high temperatures or mechanical stress. Processes such as drilling and tapping can cause internal stresses in a metal component; annealing can reduce or eliminate these stresses. By keeping metal parts more stable, components are less prone to cracking and other forms of degradation.
One form of annealing is called “Bright Annealing.” In this process, metal is heated to a process temperature, usually above normal atmospheric temperature but below welding temperature, until its surface brightness increases from the oxidation of the metal. Bright annealing is used to improve the workability and ductility of the metal. It is also used to reduce any heat degradation that may have occurred due to welding or bending during fabrication.
Bright annealing is particularly useful for components and parts that require precise measurements and exposure to high temperatures, such as pressure cooker parts, medical equipment, and aerospace components. The temperature at which bright annealing takes place depends on the type of metal being worked with, as each metal has a distinct process temperature. Above the process temperature, the metal begins to oxidize, and beneath the process temperature, work hardening occur. In the case of stainless steel and other refractory metals, the process temperature is higher, with air bright annealing temperatures often reaching 1400 -1600 degrees Fahrenheit (760 – 871) Celsius.
Although bright annealing is a heat treatment process, the result is usually a bright, clean part that requires no further surface treatment. This makes bright annealing a beneficial process for manufacture, as it significantly reduces the time and cost associated with a more complicated after-treatment.
Heat treatment processes, such as annealing, allow metal workers to create more reliable and higher quality metal products. Annealing can be a complicated science, and it is important to understand which metals and product specifications it is best suited for. Consulting a qualified metalworker or heat treatment provider can help ensure best results for products and components.
