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Heat it up really hot to make it better.

That's the basic idea behind annealing and other heat treatments for materials. The heat causes physical and even chemical changes in the properties of a material.

The way you cool it down also matters. There are different processes of annealing that you can use depending on the outcome you expect.

Let's learn about it here with these six frequently asked questions about annealing!

1. What Is Annealing?

First of all, the basic, burning question, what is annealing?

Annealing is a heat treatment for metals. The process is most commonly used with steel. But it also has applications for copper, aluminum, brass, silver, and other metals.

The process involves heating the metal up to a specific temperature above the metal's critical temperature. The temperature varies depending on the result that you want to achieve.

To heat up the metal involves putting it into a large oven. The oven must be big enough to allow for sufficient air circulation around the metal.

car-bottom furnace works well for smaller pieces of metal. If the metal is very large, however, a gas-fired conveyor furnace is a better choice.

2. How Do You Cool the Metal?

To give the metal time to complete the recrystallization process, it must be kept at its specific temperature for a period of time. Once the prescribed time has passed, it's time to cool down the metal.

You can't just cool it down any way you like, however. If the metal cools down too quickly, the microstructure won't have the refined effect you were looking for.

Thus, you can't just pull the metal out of the oven and call it good.

Sometimes, metalworkers leave it in a closed oven and allow the whole thing to slowly cool. Or they pull it out and immediately surround it with a material that has low conductivity. This could be sand, ashes, or anything of the like.

Just don't pick something flammable!

3. What Is the Result of Annealing?

Once the metal is cooled, how has it changed?

It depends a little on the process that you used. Different methods of annealing are used to produce different results.

Commonly, metalworkers are looking for these results:

  • They want to soften the metal for cold working
  • They want to improve machinability
  • They want to improve electrical conductivity
  • They want to improve plasticity
  • They want to eliminate internal stress to help avoid cracking and deformation

These results have practical applications in many fields.

4. How Does Annealing Help with Cold Working?

One of the most common reasons for annealing is to help with cold working. Metal is hard but brittle. That means that as metalworkers cold work a metal, it can become stressed to the point that it cracks.

The annealing process softens the metal and improves plasticity as we mentioned in the last section. This allows metalworkers the freedom to manipulate the metal without worrying that it will reach its breaking point and crack very easily.

If the metal has been properly annealed, they can machine and grind all they want without risk of cracking.

5. What Is the Difference between Annealing and Tempering?

But isn't tempering a common heat treatment as well? What's the difference between that and annealing?

The process is a little different, as well as the results.

Annealing heats the metal to a point above its critical temperature. Tempering, on the other hand, heats the metal to a point below the critical point.

6. Is There More than One Way to Anneal a Metal?

Yes, it is.

There are several different ways that you can anneal a metal. Metalworkers choose the method that produces the results they are looking for. Here are seven types of annealing methods.

Complete

Complete annealing is a total process. Metalworkers use it mainly for medium carbon steel and steel alloys.

The purpose is to get a fine grain and uniform structure. This process also takes care of internal stress, reduces the hardness, and makes it easier to machine the metal.

Isothermal

This type of annealing is similar to complete, but faster. It is used for high carbon steel, a metal that you can cool faster without adverse effects.

The result is the same as complete annealing.

Incomplete

The purpose of incomplete annealing is to get spherical pearlite tissues in the metal.

The process is similar to other types of annealing. It is used mainly for carbon tool steel, bearing steel, alloy tool steel, and other similar metals.

Diffusion

Diffusion annealing involves heating the metal to an extremely high temperature. The point is to eliminate segregation and create an even chemical composition.

Once the diffusion annealing process is complete, metalworkers further refine the material.

Stress Relief

Sometimes, the metalworker simply wants to reduce internal stress in a material. In this case, the metal can be heated to a slightly lower temperature to get that effect without the entire process of complete annealing.

Recrystallization

Metalworkers use recrystallization annealing to work out deformities in the metal. Through the process, the deformed grain becomes uniform. This helps take care of process hardening and residual stress.

Now You Know

We hope that after reading this article you have a better idea of what annealing is and how it differs from other heat treatments like tempering. As you can see, annealing is a very useful process.

Metalworkers wouldn't be able to do much of the machining and grinding necessary to cold work metal if it weren't for annealing.

To learn more about different heat treatments, feel free to visit our website and check out our services!

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