Annealing and normalizing are heat treatment processes that are used in various industries for the pretreatment of metal stocks.
These techniques improve material properties, making them suitable for numerous industrial applications in the automotive, aerospace, and construction industries.
But how exactly do these two techniques differ? Which one should you choose for a specific application?
The difference between normalizing and annealing is the rate at which the workpiece is allowed to cool. While annealing involves controlled cooling of the workpiece inside the furnace, normalizing allows the workpiece to be cooled in ambient air. As a result, normalizing provides a faster cooling rate than annealing.
This article discusses the difference between the normalizing and annealing process by going through various parameters and helps you understand which heat-treated metal suits best for your application.
In the end, I've also discussed the difference between normalized and annealed steel workpieces.
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Difference between Normalizing and Annealing
| Parameter | Normalizing | Annealing |
|---|---|---|
| Process cooling | In ambient air outside the furnace | Controlled cooling inside the furnace |
| Cooling Rate | Comparatively faster | Slow |
| Ductility | Relatively lower | Higher |
| Other properties | Relatively higher hardness, strength, and toughness | Relatively lesser hardness, strength, and toughness |
| Grain Structure | Fine and more uniform | Coarse and less uniform |
| Internal Stresses | Slightly higher | Minimal |
| Costs | Lower | Higher |
| Applicable Materials | Mainly stainless steel, aluminum, brass, copper | Metals and metal alloys like steels, aluminum, brass, copper |
| Applications | Automotive industry, nuclear industry, and construction industry | Mechanical components, electrical components and household items |
Difference between normalizing and annealing
Both these metal processing techniques involve similar steps in the process: heating the workpiece above the recrystallization temperature, maintaining the heat, and then cooling it.
However, there are differences in process parameters, material properties, costs, applications, and application materials.
On the Basis of Process Parameters
Normalizing and annealing involve heating the workpiece to a specific temperature, maintaining that temperature for a particular period, and then cooling the workpiece under different conditions.
The heat-maintaining period in both processes depends upon the composition of the material being treated.
In the case of annealing, the heat-treated material is allowed to cool inside the furnace with controlled exposure to ambient air.
On the other hand, normalizing requires exposing the workpiece to ambient air outside the furnace for cooling purposes.
Therefore, annealing uses a controlled cooling mechanism to specifically alter the properties of the material, while normalizing provides faster cooling with no control over the cooling rate.
On the Basis of Material Properties
Heat treatment processes alter the microstructure of the material and realign the grains to reduce the irregularities in the structure.
Generally, normalizing results in fine grains with uniform structure, while annealing produces coarse grain structure with comparatively less uniform structure.
These alterations in the grain structure result in changes in the mechanical properties of the material.
Annealing is mainly used to relieve the internal stresses of the material and enhance its ductility.
Whereas normalizing is preferable for improving the strength, toughness, and hardness of the work material, similar to tempering.
On the Basis of Applicable Materials
For a material to be suitable for a particular heat treatment technique, it should produce favorable alterations in its grain size, without any side effects.
Both techniques apply to numerous materials, including non-metals like glass, plastics, and metals like copper, brass, and cast aluminum.
However, annealing is best suited for steels, while normalizing is ideal for stainless steels, nickel-based alloys, and iron-based alloys like cast iron.
Annealing can also be performed on soft metals like aluminum to release their internal stress after cold working.
Furthermore, the annealing of brass is used for recycling bullet cartridges made of 260 brass.
On the Basis of Their Applications
Normalizing produces metals with higher strength that provides them the ability to withstand extreme loads without failure.
As a result, normalized metals are generally used for making machine components that are subjected to fatigue or cyclic load.
Some of the popular examples include normalized stainless steel used for making automotive components and nickel-based alloys used for nuclear power plant components.
On the other hand, annealing improves ductility and enhances the machinability of the metal, making it ideal for applications like improving the ductility of copper stock to be drawn into wires, and manufacturing household items like kettles and other utensils.
On the Basis of The Equipment Required
The annealing process is more costly due to a highly controlled cooling process and specialized ovens for heating.
On the contrary, normalizing uses a simple furnace for heating and a basic cooling process in ambient air.
How to Choose between Normalizing and Annealing
A proper selection criterion is crucial before selecting a heat treatment process for your application.
The first and foremost aspect should be the purpose of the heat treatment process.
Annealing improves the ductility and machinability of the material by refining the crystalline structure (arrangement of atoms or molecules) to eliminate residual stresses.
On the other hand, normalizing primarily improves toughness and strength by refining the grain structure of the material.
Apart from the fundamental aspect, the criterion falls under five key factors.
Type of Workpiece Material
Material composition plays an important role in determining the optimal heat treatment process for the workpiece.
Generally, normalizing is preferred for steel workpieces with a carbon composition of less than 0.5 % as it improves their mechanical properties, whereas annealing is recommended for steel with higher carbon composition.
Apart from that, each heat treatment process suits a specific group of materials, which means that your workpiece material is crucial in selecting the best-suited technique.
For example, a steel stock required for manufacturing automobile axles should be normalized to enhance its toughness and durability, making it suitable to withstand fatigue and high loads.
On the contrary, copper stock required for electrical applications should be annealed to achieve enhanced ductility and conductivity.
Desirable Material Properties
The material properties resulting from each heat treatment process dictate its suitable applications.
For instance, normalizing will be the right option for treating steel rods required in building construction, as it can improve their ductility, toughness, and strength.
This process will then ensure the structural integrity of the building as the constituent rods will be more durable and resistant to loads.
On the other hand, annealing improves the machinability of the material, making it ideal for applications where the stock material is to be machined into the desired shape.
Cost of Operation
Cost is also a deciding factor in selecting the appropriate heat treatment technique.
Although the equipment required in both these techniques is similar, the process of normalizing is comparatively cheaper as it has a simple cooling process utilizing ambient air without a control system.
However, both processes involve significantly high initial and operational costs, making them unsuitable for DIY and small-scale production.
Time Taken to Complete the Process
Both techniques are time-consuming, but even a slight difference in process times can affect productivity, especially if a bulk manufacturing industry is in question.
The annealing process takes longer than normalizing as the cooling process is slower and more strictly controlled.
For instance, normalizing is best suited for bulk manufacturing applications where high strength and enhanced durability are to be achieved with quick cycle time.
Whereas annealing is recommended where enhanced ductility and machinability are of main importance, irrespective of the cycle time.
Normalized Steel vs Annealed Steel
| Normalized Steel | Annealed Steel |
|---|---|
| Relatively less ductile | More ductile |
| Slightly more internal stresses | Negligible internal stresses |
| Higher strength | Lower strength |
| Relatively higher hardness | Lower hardness |
| Smaller and more uniform grain size | Larger and less uniform grain size |
Properties of Normalized Steel vs Annealed Steel
Annealed and normalized steel differ in various aspects.
Annealed steel is more ductile and machinable due to its enhanced grain structure resulting from dislocations during the annealing process, rendering it suitable for applications requiring cold working or machining.
Normalized steel has higher strength and toughness, with relatively more hardness, which makes it suitable for applications requiring regular heavy or cyclic loading.
The faster cooling rate in normalizing induces internal stress in the steel, which enhances its hardness.
Conversely, annealed steel has negligible residual stresses, which leads to a comparatively lower hardness than normalized steel.
Due to a slower cooling rate in annealing, the grain dislocations are higher, leading to a larger and less uniform grain structure in annealed steel, while normalizing results in a smaller and more uniform grain structure.
Final Thoughts
Normalizing and annealing are heat treatment processes that result in improved mechanical properties and a refined grain structure of the material.
While annealing is recommended for applications that require enhanced ductility and machinability, normalizing provides greater strength and durability.
Apart from that, these techniques differ in various aspects, like process parameters, material applicability, applications, and cost.
Therefore, it is important to identify your requirement before selecting the heat treatment process that produces the most favorable results.
Frequently Asked Questions (FAQ)
Does normalized or annealed steel rust?
Yes, normalized and annealed steel can rust as these heat-treatment processes do not protect against rusting.
What are the different types of annealing?
Different types of annealing include complete annealing, isothermal annealing, incomplete annealing, diffusion annealing, spherification annealing, recrystallization annealing, and stress annealing.
Can plastics undergo normalizing?
Yes, plastics can undergo normalizing to increase their strength and durability.
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