The study of physics first started in the 17th century. While physics has run the world we live in since before humans existed, the 17th century was when scientists first started trying to understand and name those processes.
In the centuries that followed, those studies led to the discovery of countless new and useful processes, including the isothermal process. Eventually, people were able to use isothermal quenching to heat-treat tool steels for guide rollers and much more. This process remains valuable for heat treatment to this day.
Want to learn why isothermal quenching is such a valuable way to treat tool steels? We'll answer your questions here -- keep reading to learn more!
What is an Isothermal Process?
Isothermal quenching is a type of isothermal process -- but what does that mean?
An isothermal process falls under the physics category of thermodynamics. Thermodynamics involves the study of heat, and how it can create physical or chemical changes. "Thermo" or "thermal" refers to heat, while "dynamics" refers to action or energy.
"Iso" means equal. So as you can probably see by now, "isothermal" means that the heat level stays the same.
To be defined as an isothermal process, the energy levels must change while the temperature stays the same. Most of the time, this can happen when the heat changes so slowly that thermal equilibrium can be maintained.
Isothermal Process Example
Isothermal processes are happening all around you, all the time. Anytime the cells in your body interact with other cells, they go through an isothermal process. And when water begins to steam or boil, that's another isothermal process.
Isothermal quenching is a specific isothermal process used to treat steel. Let's take a look at how it works.
The Isothermal Quenching Process
Isothermal quenching can actually be used on any ferrous metals, though it's most often used on ductile iron and steel. Ferrous metals are metals that have iron in them. They're different from other metals in two major ways: they're magnetic, and they don't usually resist corrosion well.
Let's dive into the steps involved in the isothermal quenching process.
1. Heat the Steel
First, the steel gets heated to super-high temperatures (think above 1,500 degrees Fahrenheit). This process should happen in a controlled environment -- otherwise, the metal could oxidize.
2. Quench in a Salt Bath
At the same time as the metal gets heated, a salt bath is prepared for quenching. The salt is so hot that it becomes liquid, so that it can effect the proper changes to the metal quenched in it.
3. Cool the Steel
Once quenched, the steel can cool down and is ready for use. It's now harder and more durable than it was before quenching.
History of Isothermal Quenching
How long have people been using this process to strengthen ferrous metals like steel?
It all started in the 1930s, at the U.S. Steel Corporation. Employees Edmund S. Davenport and Edgar C. Bain were the first to discover and use the isothermal quenching process.
They went through a series of experiments, using the knowledge they already had about heat treating methods, until they landed on isothermal quenching.
Soon, quenched steel was in use across the country. The harder steel was useful for everything from wartime weapons to automotive parts. Today, it remains a common process because it offers so many benefits.
Why Use Isothermal Quenching?
Just what makes this process so useful for treating steel? Here are some of the top benefits of isothermal quenching.
1. Creates Improved Microstructures
For an isothermal quenching process to be complete, the final product must have an ausferrite or bainite microstructure.
Microstructures refer to the structure of a metal that you need a microscope to see. While these changes aren't visible to the naked eye, they can have a huge impact on how tough a material is. The microstructure is responsible for many of the physical properties of a structure.
An ausferrite microstructure mixes ferrite with stabilized austenites. This mixture creates a much stronger structure that won't easily break.
Bainite microstructures mix ferrite with cementite. This microstructure also makes the material harder and more durable, so it's suitable for more uses. Bainite structure doesn't have any cracks and resists impact well.
2. No Oxidation
Because steel contains iron, it's prone to oxidation.
When steel oxidizes, it corrodes. You'll often see it in the form of rust. This makes the material weak and unusable for most purposes.
Fortunately, with the isothermal process of heat treating, steel won't oxidize. Instead, it becomes stronger.
3. Minimal Distortion
The salt quenching process avoids the distortion sometimes seen with other heat treatment process. This makes it easier to get a usable finished product every time.
Since thin steel parts are especially prone to distortion, you'll definitely want to use this process for any parts that are thin and delicate.
4. Better Shock Resistance
Treating steel in this way allows it to resist shock better, so it stays functional longer.
5. Reduced Costs
With isothermal quenching, parts become stronger, so you can reduce the amount of material used to get a durable finished product. Since you're paying less for raw material, this can translate into significant cost savings.
If you've been using other processes such as welding or forging, you'll find that making the transition to isothermal quenching saves in manufacturing costs, not just the cost of raw materials, too.
6. Improved Wear Resistance
Steel that's been through the isothermal process is also more wear resistant than lots of other materials. Since it's harder, it will stand up to wear better, so you'll need to replace parts less often -- offering yet another way to save money.
Your Resource for Heat Treatment
The isothermal process gives you a cost-effective, efficient way to treat steel for guide rollers and much more.
Looking for a retailer that offers a complete production process? Why not try Miheu, the largest Slovenian provider of heat treatment? Contact us to learn more.