What You Should Know About Stress Relief Annealing

Annealing is a type of heat treatment in which an alloy gets heated up and held at a particular temperature, then gets cooled down in a controlled manner. The process allows for internal stresses in the alloy to be relieved, softens the material and creates a chemical homogenization and transformation of the grain structure of the metal into a much more stable state than it was initially. Annealing in Gastonia, NC also results in increased equilibrium of the metal structure, which allows for higher ductility.

The temperature and cooling rate used in the process will depend primarily on the composition of the alloy and the kind of annealing treatment you’ll be using. But what types of annealing treatments are available to you? Here’s a quick overview:

  • Full annealing: In this process, ferrous alloys are heated about 100 degrees Fahrenheit over the top range critical temperature. After this heating, they get soaked and slowly cooled in the furnace or in another medium to a certain temperature somewhere below the critical temperature. For non-ferrous alloys, full annealing involves softening of the metal after cold work, as opposed to the partial softening that comes with partial annealing.
  • Subcritical annealing: This type of annealing involves cold-worked steel that’s below the critical temperature on the iron-carbon phase diagram.
  • Recrystallization annealing: This process involves heating a cold-worked metal up to a temperature that lies somewhere over the recrystallization temperature. After this heating, the metal gets soaked for the necessary amount of time to allow for the grain structure to transform. This process is very commonly used as a means of intermediate softening between cold work processes like drawing and cold rolling. A combination of recrystallization annealing with cold work makes it easier for metal workers to control the grain size in the microstructure.
  • Spheroidizing annealing: This process features controlled healing and cooling of high carbon steels (the kinds of steels commonly used in developing tools) to create spherical forms of cementite inclusions. The result is improvements in the machining characteristics of the steel being worked.
  • Bright annealing: This is a type of annealing treatment that is performed in furnaces. The reducing atmosphere prevents the steel parts from sustaining surface oxidation.
  • Homogenizing annealing: This type of annealing is performed at a high temperature and is intended to cut down on the amount of chemical segregation that occurs as a result of diffusion. It is most commonly used for steel and aluminum ingots and casting.

Every type of annealing features three states. The first is recovery, in which the metal is softened and crystal defects are removed, along with the internal stresses they cause. The second is recrystallization, in which strain-free grains grow to replace those that were damaged by internal stresses. The final stage is grain growth, as the microstructure continues to coarsen.

For more information about what you should know about annealing and other forms of heat treatment in Gastonia, NC, we encourage you to contact J.F. Heat Treating Inc. today. We look forward to answering your questions!

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