Annealing vs Normalizing: What’s the Difference?


What are the types of Heat Treatment processes?

Steel is an alloy of iron and carbon, and is one of the most widely used materials in the world. It has a wide variety of applications, from construction to automotive manufacturing. Heat treatment is an important step in the manufacturing process of steel. It is used to improve the properties of the metal, such as strength and toughness. There are a variety of different heat treatments that can be used, depending on the desired results.

Usually, heat treatment processes can be divided into annealing, hardening, and quenching/tempering. In this context, the Figure below features the characteristic temperature ranges for important heat treatment processes in the Fe-Fe3C (Iron-Carbon System) system.

You will notice that the heat treatment temperature for various heat treatment processes is often dependent on the carbon content of the material. For example, a normalizing temperature for 0.8% Carbon will be around 723 Degree Celsius and for steel, with 0.2% Carbon content will be approximately 850 Degree Celsius. So, carbon will be the main contributing factor to decide the heat treatment temperature.

Heat treatment on Fe C diagram Annealing vs Normalizing: What's the Difference?
Different types of heat treatment shown on simple Fe-C Phase Diagram

Annealing vs. Normalizing

Annealing is a heat treatment process of heating the steels about 100°F above the upper critical temperature (A3 line) and lower critical temperature (A3,1 line) as shown in the above figure. Annealing is a Heat treatment, consisting of heating a material to a certain temperature, holding it at that temperature, and cooling in such a manner that the material is closer to equilibrium at room temperature.

Lamellar Tearing in Welding & carbon- Low alloy steels


Normalizing
is a heat treatment process by which steels are heated nearly 100°F above the upper critical temperature (A3 or Acm line). hypo-eutectoid steels (steel less than 0.8% carbon) are heated to a temperature of 30°C to 50°C above the AC3 line and hypo-eutectoid steels are heated to a temperature of 30°C to 50°C above the AC1 line (723°C).

The temperature at AC3 line depends as it varies based on the carbon percentage in the alloy while AC1 temperature is constant. A temperature equilibrium is brought to the part by holding it at certain temperature to have the uniform temperature throughout the part thickness, this is called dwell time. After that, it will be cooled in resting air. Because the steel is twice subjected to a y-α transformation, the material will be transformed into a uniform, fine-grained normal microstructure.

The purpose of the normalizing is also to obtain an uniform microstructure with fine lamellar pearlite in the material.

annealing microstructure Annealing vs Normalizing: What's the Difference?
normalzing microstructure Annealing vs Normalizing: What's the Difference?
Before & after normalizing microstructure

Cooling Medium

Cooling medium is one of the most important factors in heat treatment. The choice of cooling medium can affect the quality and properties of the product. There are many different cooling media available, each with its own advantages and disadvantages. Some of the most common cooling media are water, oil, and air.

The cooling method used in the Annealing is furnace cooling at a moderate cooling rate which means the parts are cooled inside the furnace in a controlled atmosphere and not in the natural air. Opposite of annealing is applicable for cooling in the Normalizing where parts are subjected to ambient air cooling & the cooling rates are not controlled .

The rate of air cooling in normalizing is much faster than the controlled furnace cooling that is applied in annealing heat treatment. The overall cost of Normalizing is lesser than the annealing process as the former does not require any controlled air cooling as mandatory in annealing.

normazling heat treatment Annealing vs Normalizing: What's the Difference?
Normalizing process and effect on grain size

Water is a very effective cooling medium. Oil is expensive than water but it is not as effective at transferring heat away from the product. Air is inexpensive and easy to use, but it does not transfer heat as effectively as water or oil. Solid materials are inexpensive and can be used in large quantities, but they are not very effective at transferring heat away from the product.

Material Properties post the heat treatment

The heat treatment process can change the material’s properties in a number of ways. The most common changes are: increasing or decreasing the hardness, ductility, and toughness. In general, the harder the material is, the less ductile it will be and the tougher it will be.

Conversely, softer materials are generally more ductile and tougher. The changes in material properties depend on the type of heat treatment process used, as well as on the composition and microstructure of the material.

Annealing specimenNormalized specimen
Lower hardness reduced tensile and improved toughness.Increased hardness, higher tensile than annealing, reduced toughness compare to annealing.
Uniform grain size after normalizingLess uniform grain size
Less internal stresseshigher internal stresses compare to normalizing
Coarse microstructureFine microstructure

 Purpose of annealing and normalizing

Annealing and normalizing are two different processes that are often confused. Annealing is the process of heating metal to a certain temperature and then slowly cooling it back down to room temperature. This process makes the metal more flexible and easier to work with.

Normalizing is the process of heating metal to a certain temperature and then cooling faster than annealing it back down to room temperature.

AnnealingNormalizing
1. To refine the crystalline structure and
2. To remove the residual stresses
3. To increase material ductility by minimizing the hardness and brittleness
1. To achieve a refined grain structure before hardening.
2. To minimize the segregation in the casting or forgings.
3. To harden the steel minimally.

Cost comparison between annealing and normalizing

The decision to anneal or normalize metal can be a difficult one. The cost of heat treatment should always be considered when making this decision. Annealing and normalizing are two types of heat treatments that are often used to improve the mechanical properties of metals. Both annealing and normalizing are performed at high temperatures, but they achieve different results.

The cost of annealing depends on the size and type of furnace required, as well as the fuel costs. Normalizing is a simpler process than annealing, so it typically costs less to perform.

Annealing:  Annealing heat treatment is more expensive compare to normalizing. The reason is high controlled heating & cooling involved in annealing process which increase the heat treatment time.

Normalizing: Normalizing is less expensive compare to annealing.

Difference between Annealing and Tempering

Annealing is a heat treatment process that softens the metal. It is a form of thermal treatment in which the metal is heated to a temperature below the recrystallization temperature and then cooled slowly. This procedure allows the dislocations in the metal to move and reorganize into a more stable arrangement. Annealing also increases the toughness and ductility of the metal.

Tempering is a heat treatment process that improves the mechanical properties of steel by decreasing its brittleness. The tempering process usually involves heating the steel to a temperature above the critical point and then cooling it in air, oil, or water. Tempering increases the toughness, strength, and hardness of steel while reducing its ductility and susceptibility to fractures.

Difference between Annealing and Hardening (Quenching)

There are many types of heat treatments that can be applied to metals, but two of the most common are annealing and hardening. Both processes serve to alter the metal’s microstructure and improve its mechanical properties, but they achieve this in different ways. Annealing involves heating the metal to a relatively low temperature and then allowing it to cool slowly, while hardening involves heating the metal to a much higher temperature and then quenching it in water or oil.

The main difference between annealing and hardening is that annealing results in a softer metal, while hardening produces a harder metal. This is because annealing relaxes the internal stresses in the metal caused by cold working or casting, whereas hardening causes these stresses to become locked into place.

Difference between Annealing and Aging

Annealing and aging are two processes that are often confused. Annealing is a process of heating and then cooling metal to make it softer. Aging is a process of leaving metal in a hot environment for an extended period of time. The difference between the two processes is that annealing makes metal softer, while aging makes metal harder.


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