The US imported around $29 billion worth of steel in 2017.
What most people don't realize is that you can get different kinds of steel. For example, most people recognize the term "stainless steel." That's a type of steel with a high Chromium content, which limits rusting and staining.
The production process for varies for different kinds of steel based on the properties the manufacturer wants. This can mean adding other elements that make the steel non-magnetic or increase durability.
The production process can also vary in terms of heat treatments that also affect the properties of the finished steel. Two very common heat treatments are annealing and tempering.
So, what is the difference between tempering and annealing steel? Keep reading for an overview of the two processes and the results.
What Is the Tempering Process?
In tempering, the steel goes into an oven for heating. This happens at comparatively low temperatures. Typically, the temperature remains below the temperature where the steel will melt.
The steel remains at that temperature for a specific period of time. The goal is the reduction of the amount of martensite in the steel, which makes the metal brittle.
The kind of steel determines the exact temperature the steel must reach. Certain elements that create steel alloys can change the temperature at which the metal tempers properly.
After keeping the steel at the specified temperature for the specified amount of time, it comes out of the oven. It cools quickly in the open air.
Purpose of Tempering
Most steel undergoes a hardening process, but that also makes the metal much more brittle. It makes it so brittle, in fact, that it loses its usefulness for many applications. In any situations where the metal will experience serious stress, basic hardened steel won't work.
The temperating process reduces the brittleness of the steel. Depending on the type of steel and the temperature, tempering can improve toughness, strength, and impact resistance.
These qualities prove valuable for manufacturers who produce, for example, steel beams for construction, machine parts, or automotive parts.
In essence, tempering makes steel safe for use in products that experience high levels of stress or torque.
Take a vehicle's drive, for example. That drivetrain might see 100,000 miles of use or more over the vehicles lifetime. Ideally, the steel in that drivetrain must possess enough durability and strength to last the lifetime of the vehicle.
Steel made brittle by hardening couldn't take the daily abuse that most drive trains shrug off for years of daily use.
What Is the Annealing Process?
The annealing process is a straightforward one in principle. Steel manufacturers use large ovens or conveyor furnaces.
They place the steel in the oven or furnace and heat it. The exact temperature varies depending on the type of steel because of different alloy components. Once the metal reaches the desired temperature, it creates austenite.
Austenite has a different structure than the original steel at the microscopic level. This change doesn't cost the steel any alloy properties.
The steel must then cool very slowly for the metal to retain the structural change.
Cooling approaches vary. In some cases, the manufacturer simply turns off the furnace and lets it cool on its own. In other cases, the steel gets packed in a material that doesn't absorb heat well.
Purpose of Annealing
In the case of steel, annealing creates a comparatively softer alloy. That allows for easier machining of the steel. This softness benefits manufacturers in a few key ways.
It reduces wear and tear on the cutting and grinding tools used in machining. This lowers costs because the cutting and grinding don't get replaced as often.
This also lowers costs because production stops every time the cutting and grinding parts need replacement. Employees get paid whether the machine makes something or they wait while parts get replaced.
It also benefits manufacturers by allowing for faster production time on products. The softer metal doesn't take as long to machine, so you can make more parts in the same amount of time.
Annealing provides another benefit.
A lot of steel manufacturing happens at room or ambient temperatures, which is called cold working. Cold working steel can harden the metal until it's prone to cracking. Annealing prevents the metal from hardening and cracking this way.
That makes it easier for manufacturers to use the metal since they can shape or cut it repeatedly.
Annealed steel finds use in products where a certain level of flexibility matters. Manufacturers also use it in products that will experience little in the way of torque, such as kitchen sinks.
The Differences
There are actually several differences between tempering and annealing steel.
Tempering happens at a lower temperature than annealing. It aims at reducing the Annealed metals cool slowly in the oven or a material like sand. Tempered steel cools quickly, often in the air.
Annealing creates a softer steel that's easier to work within manufacturing certain kinds of products. Tempering creates a less brittle version of steel that finds use in building or industrial applications.
Parting Thoughts on the Difference between Tempering and Annealing Steel
Tempering and annealing steel follow two different processes that produce very different results.
The key thing you must bear in mind is that those results serve different purposes. The softer steel from annealing helps produce a wide variety of steel products that don't endure substantial stress.
You can find these products in homes across the world.
Tempered steel finds use in completely different areas. You see in situations where strength, toughness and even elasticity prove critical. A few applications include industrial machinery, large-scale construction, and automotive drive trains.
Without tempered steel, these applications would often prove unsustainable or far more dangerous.
Tempering and annealing both serve important, if very distinct, functions in our lives.
Miheu specializes in heat treating metals and machining services. For questions or pricing information about our services, contact us today.