Tempering and annealing are two of the most popular forms of heat treatment in the material processing industry at the moment. They’re especially used by manufacturers who see them as ideal ways to optimize manufacturing and processing.
However, while both steps usually aim to achieve the same thing, tempering and annealing aren’t necessarily the same. And, as you can expect, understanding the difference between both steps will go a long way in helping you to optimize your results.
So, is tempering the same as annealing? The answer is definitely a “No.” We’ll provide a thorough breakdown of both processes in this piece, so let’s get started.
The Importance Of Heat Treatments For Processing
Now, before we go into the annealing vs tempering debate, it is important to look into the umbrella they fall under – heat treatment.
Generally, heat treatment is a crucial part of material processing. Here, a material is heated and cooled at intervals and in different temperature formats in order to alter both its mechanical and physical properties.
From metallurgy and manufacturing to aerospace and automotive, heat treatments are used across the board. Some of the major reasons why this step is important include:
- Mechanical Property Alteration: Arguably the most significant reason why heat treatment is usually applied is for its ability to change the physical properties of materials. From strength and ductility to hardness and more, heat treatment helps workers to fashion materials to the specifications that they’d like.
- Strength Improvements: Manufacturers especially appreciate the ability of heat treatments to improve the strength of materials. This helps them to be more resistant to things like wear, tear, and strain. And, as you can expect, this means that the materials will be much stronger in the long run.
- Stress Relief and Dimensional Stability: In a manufacturing process – such as casting and forging, materials could easily develop residual stress and even go through several dimensional changes due to non-uniform cooling. The point of heat treatment here will be to ensure that this stress can be relieved, and the material can return to its original dimensions. In the long run, material uniformity can be ensured, and issues such as cracking can be avoided.
- Microstructure Refinement: Many heat treatment methods will also enable the proper refinement of a material’s microstructure by controlling its crystal structure, grain size, and phase distribution. All of this helps to ensure material uniformity and homogeneity, making for a more seamless manufacturing process.
Tempering vs Annealing: Differences In Processes
So, we understand the reason why heat treatment is critical in developing the right material. Now, let’s look into two of the most prominent heat treatment methods available – tempering and annealing.
Fundamental to understanding the tempered vs annealed debate will be to understand how each step works.
The Tempering Process
Tempering is a heat treatment method that generally involves reheating a material that’s been previously cooled to a specific temperature. From there, the material is once again cooled in a controlled manner.
Generally, tempering serves the purpose of relieving internal stress in a material and changing its mechanical property. This difference in purpose is one of the major points of distinction when considering annealed vs tempered glass.
Generally, tempering follows a detailed process. It might vary between manufacturers and metallurgists, but the general tempering process usually goes like this:
Before a material is even-tempered, it needs to be quenched. As the name suggests, the quenching process involves reducing the temperature from a high point to room temperature at the very least. The quenching process achieves two things primarily – it hardens the material, and it also introduces some internal stress to it.
As soon as the material is quenched, it is essentially ready for tempering. Next, it is heated in a furnace where its temperature is taken below its critical point. The precise temperature will depend on the material itself, as well as the manufacturer’s desired properties. This step is one of the defining points when comparing the differences between annealing and tempering.
Once the material is properly heated, it is held at the desired temperature for a while. This step makes it possible for several desired microstructural changes to take place, and it is one of the most critical in the entire tempering process.
After soaking, the material is then allowed to cool. The cooling step is done based on the manufacturer’s requirements, as well as the material itself. For instance, while air cooling is fine for some materials, others will need to be properly quenched in a medium – such as oil or water.
Multiple Temper Cycles:
It is worth noting that this is an optional part of the tempering process. In certain cases, multiple tempering cycles may be performed. This involves repeating the heating, soaking, and cooling steps multiple times. Each cycle helps refine the microstructure and further adjust the material’s properties.
Once the material is made to go through the tempering process, samples are taken out for quality control purposes. This step is critical to ensure that the material meets the right specifications and requirements and that it is up to code.
Testing steps include hardness testing, impact testing, and much more. And, the objective remains to ensure that the material looks and feels just right.
It is worth noting again that these steps aren’t necessarily uniform. Different manufacturers have their tempering processes, and they follow their specific methodologies.
For more information on how we handle tempering at Tuolian Metal, please feel free to reach out to us.
Tempering actually comes in different forms, all of which vary based on purpose and temperature range. The different variants include:
- Single Tempering: Single tempering is the easiest and most straightforward form of tempering. Here, the material is heated and cooled in a controlled manner, using a variety of methods. As long as the cooling and heating rates are properly adjusted, single tempering ensures that toughness and hardness can easily be achieved simultaneously.
- Double Tempering: The primary difference between single and double tempering is that in this scenario, the material is subjected to two separate tempering cycles. Once the initial tempering process has been done, the material is heated and cooled off once again. In most cases, this method is employed when the initial process didn’t quite nail the requirements for material specifications.
- High-Temperature Tempering: Also known as over tempering, this method involves heating the material to a significantly high temperature – somewhere close to its critical point. Once you engage this tempering method, you’re tipping the scales in favor of toughness against hardness. However, this imbalance also means that the material will be more capable of withstanding any significant damage or contact.
- Induction Tempering: In this tempering variant, induction heating is employed, bringing in the precise heating that is required to especially temper a material’s small, intricate parts. Here, it is very important to be accurate enough with temperature and heating time to achieve the desired results.
- Flame Tempering: Unlike induction tempering, you get a flame or a torch in this tempering variant and use it to heat the material. When you need to focus on a specific part of the entire material, flame tempering is usually a great way to go.
How Annealing Works & Its Different Stages
Next, let’s take a look at an overview of the annealing process as well as the steps involved in getting it to work.
In annealing, a material is heated to a specific temperature for a prolonged period and then left to hang there. From there, the material is cooled and essentially changed.
It focuses on changing both the physical and chemical properties of a material, although most people tend to use the annealing process to make materials softer and more workable. So, when you see annealed metal, you should know that the process was most likely employed to ensure that the metal is more workable across the board.
While material softening is a major objective of the annealing process, you will also find that annealed metal tends to have higher ductility and a more refined microstructure. So, the process works pretty well.
In the annealing process, you have a bit of a more straightforward flowchart than tempering. The process usually goes thus:
The annealing process starts with heating. Here, the material is heated to a specific temperature that is set by the manufacturer and which will also depend on the material in question.
It is worth noting that the annealing temperature is usually less than the material’s boiling point. However, it is still high enough to cause changes to its microstructure and properties. Heating is usually done in a furnace, although there are other heating media that can be used.
Once the heating process is completed, the annealed material is held at that temperature for a prolonged period – what many manufacturers call the soaking period. This is another major point of distinction in the annealing vs tempering glass processes.
The point of this step is to help with atom diffusion in the material. Just as well, soaking helps to rearrange the material’s internal structure and remove any possible defects. Generally, the soaking period will depend on the material itself as well as its specifications – especially, its thickness.
Once the soaking period is over, the annealed material is allowed to cool – albeit in a slow, controlled manner. The cooling can be done by eliminating the heat source or letting the material cool gradually while still in the furnace.
It is worth noting that one major difference in the making of tempered glass vs annealed glass is that the cooling process in annealing is usually much slower. This lack of pace helps to prevent the formation of new material and stresses and to ensure that the annealed material can transform gradually into the desired structure.
Now, before we go ahead, it is worth noting that the annealing process can usually be grouped into four. These groupings will depend on the material in question, what you’re hoping to achieve, and the physical specifications you have in mind.
- Full Annealing: Here, the material is heated to the annealing temperature and then allowed to cool down in a gradual process. The goal here is to improve material ductility, optimize softness, and take out any possible impurities.
- Stress Relief Annealing: In stress relief annealing, the objective is to take out any internal stress that might have built up in a material due to other manufacturing processes – such as welding or machining. Here, the material is heated to a point below the critical range, then it is cooled slowly to reduce the risk of cracking or distortions.
- Recrystallization Annealing: This form of annealing is usually performed on stain-hardened or cold-worked materials. This goal here is to ensure that the materials are just as ductile and amenable to drawing as they were in their initial form. Metallurgists here will heat the material to a specific temperature where the material forms new grains, essentially displacing the old ones that were formed by cold working.
- Isothermal Annealing: For isothermal annealing, the material is held at a specific temperature for a long time. This process helps to optimize the materials’ transformation and improve their microstructure. In most cases, materials that tend to have uneven grain growth are those that are subjected to this process.
Tempering vs Annealing: Differences In Purpose
While there are many points of distinction in the annealing vs tempering debate, one of the most significant points is that of purpose.
For tempering, the major goal is to reduce the brittleness of a material that has previously been quenched. Just as well, it looks to ensure that the material’s hardness can remain and can be maintained. Other areas where tempering looks to improve include toughness, ductility, and general ability to perform under stress and withstand contact.
As for annealing, the main goals are to soften the material, relieve any form of internal stress, and optimize its microstructure at all levels. By rearranging the material’s structure and refining it, annealing also ensures to improve areas such as ductility and machinability.
So, if you’re a manufacturer, understanding the goals for tempered vs annealed materials will help you significantly. Annealed vs tempered steel aren’t the same thing, and the differences can easily boil down to the objectives of each method.
Tempering vs Annealing: Differences In Cost
Next, you want to consider the differences in price. So, how does the tempered glass vs annealed glass cost differ, for instance?
Determining the cost of tempering and annealing can be a bit of a hassle – primarily because both steps tend to be relatively complex and the cost you get will depend more on the manufacturer than anyone else.
However, the following factors tend to affect the cost of the processes in the long run:
- Equipment and Energy: As explained earlier, both tempering and annealing will require heating – a process that will impose energy costs on the facility that is handling it. Just as well, you’d find that quite a lot of equipment will be used during both processes to treat the material and ensure that it is in the best shape. These costs will add to the overall price of the processes.
- Materials: Just as well, you will also need to consider the cost of the material itself. For instance, the cost considerations for annealed glass vs tempered will not be the same when you’re comparing annealing vs tempering steel. Some materials will need more time to be processed, and this means that processing them will most likely cost more. Also, remember that things like material size, dimensions, and thickness tend to play roles.
- Process Complexity: The complexity involved in each process will also be important in determining how much you end up paying. While the steps we outlined are how we process both steps at Tuolian Metal, other manufacturers might have different steps. And, you basically have to be careful with what you choose and how the material has been processed.
- Quality Control: Both tempering and annealing will need to go through tests and quality control procedures to ensure that the finished materials are up to code. The cost of running these tests will count against the overall margin at the end of the day.
- Labor Costs: Finally, manufacturers also have to deal with labor costs when it comes to tempering and annealing. From handling parts, operating equipment, and monitoring processes, technicians do a lot of work and deserve to be compensated properly.
Tempering vs. Annealing: Differences In Temperature Range
Considering that both tempering and annealing are heat treatment methods, you also want to look into the annealing process vs tempering process from a temperature standpoint.
Generally, tempering is done at temperatures that go below the material’s critical temperature range. For most materials, this is typically between 150°C and 650°C (or, 300°F to 1200°F). However, the specific temperature will depend on several factors – including the material itself and the desired mechanical properties that you have.
As for annealing, the temperature is usually kept below the melting point of the material. Rarely would you ever see an annealing process go above a few hundred degrees.
All in all, the temperature for annealing vs tempering glass is usually lower – and, that trend usually goes for other materials as well.
Tempering vs. Annealing: Differences In Cooling Methods
Considering the fact that both tempering and annealing require cooling to work, you might also be interested in understanding how these methods differ across the board.
In tempering, cooling is usually carried out in a controlled and subsided manner. This can be done by air cooling or quenching the material in a medium like water. And, the cooling rate for the tempering process is also much slower than the quenching rate when you complete the first hardening process.
Moving on to annealing, you have a much slower cooling method after the material has been left to harden. Air cooling is also allowed, although most manufacturers tend to just turn off the heat source in the furnace and let the material cool off by itself. This controlled cooling will essentially help manufacturers to bring out the desired physical properties and ensure that the material is up to code.
When considering the annealing vs tempering vs quenching tests, keep in mind that tempering is usually the slowest of the bunch.
Tempering vs. Annealing: Differences In Microstructural Effects
Microstructural adjustments are critical to the purpose of both tempering and annealing. And, as the two of them tend to differ, so do their effects on a material’s microstructure.
Generally, tempering causes the formation of carbide particles within a material. This eventually leads to instructions in material dislocation and basically ensures that the material is stronger on all fronts. In the tempered state, a material’s structure is stronger and more durable than in the quenched state.
On the flip side, annealing leads to the formation of new atoms and the elimination of any defects. This ensures that the microstructure is generally more refined across the board. Additional effects of this include greater ductility – albeit at the expense of hardness.
When To Temper & When To Anneal
You might be wondering where to install tempered vs annealed glass or when to use one method of heat treatment over the other.
Tempering is generally used in manufacturing processes where you want a proper mix of material hardness and ductility. This is what makes it so popular in steel manufacturing – as well as the fabrication of alloys and other machine parts.
As for annealing, you want to employ this method when the time comes to soften a material and optimize its workability. Stress relief is also a major reason why you might choose to anneal. Front resting metals and alloys to glass fabrication, annealing can be a major draw for many manufacturers.
You should also remember that you can make additional modifications to your tempered or annealed materials whenever you need them. So, for things like laminating annealed vs tempered glass, simply ensure that your method of annealing or tempering is compatible with lamination and you’re good to go
When working with tempered vs annealed steel – or, really, any other material – you’ll find that understanding the differences between both procedures will undoubtedly go a long way in helping you to make an overall decision.
Wherever you do choose, however, we at Tuolian Metal are here to ensure that you get the best service on tempered and annealed materials. Contact us today, and let’s help you out!
Frequently Asked Questions
Is annealed glass stronger than tempered glass?
No, it’s not. Tempered glass tends to be stronger than annealed glass, with both of them coming with different manufacturing processes and physical properties. Generally, though, the breaking strength of tempered vs annealed glass tends to be higher.
However, while annealed glass isn’t necessarily as strong as tempered glass, you should note that it is still being used in many situations where high mechanical strength might not necessarily be a top priority.
Does annealing provide advantages over tempering?
Both tempering and annealing have their pros and cons. However, the areas where annealing definitely takes the cake are simplicity and structural refinement.
You will find that the process of annealing is more straightforward and generally easier to achieve than tempering. And, with its ability to refine the microstructural properties of a material, it can lead to higher functionality and aesthetic appeal.
Still, we recommend that you focus more on what you are trying to achieve when making a choice here. If you’re a budget-conscious customer, you should also remember the cost of tempered glass vs annealed glass when making your decision.
Does tempering reduce hardness?
Indeed, tempering can reduce the hardness of a material. This is very true. When a material goes through tempering, its temperature is raised and then it is cooled later. This cooling does reduce strength, although it also leaves a way for heightened toughness in the material.
So, a tempered material is still very much able to withstand significant contact and hold its own over time.