What Is Metal Hardening?

There are a variety of processes used to heat up metal for various metalworking applications. Metal hardening is one of the more common ones.

Here’s some information about metal hardening and how it compares to other forms of heat treatment in Gastonia, NC.

What you can expect from metal hardening

Metal hardening is used to improve the various mechanical properties of metal, as well as its hardness, as the name suggests. The result is a tougher, more durable metal item.

During the process, alloys are heated to a level past the critical transformation temperature of the metal, and then cooled down quickly to cause the soft initial material to turn into a structure that is harder and stronger. These alloys can be cooled by air, or through quenching in oil, water or other liquids, depending on how many alloying elements are found in the material. The hardened materials will then typically be tempered or stress relieved as a means of improving their toughness even further.

When working with steel, it will usually be necessary to use heat treatments to obtain better mechanical properties, such as improved strength or hardness. The hardening process includes heating the components above the normalizing temperature, then holding that temperature for at least an hour per inch of thickness. This enables it to cool at a rate that’s fast enough to allow the material to transform into a harder, stronger structure.

Steel is an iron/carbon alloy, and some steel alloys have other metal elements in them as well. Heating up the material past its critical temperature causes the carbon (and some of these other elements) to go into a solid solution. The quenching process then “freezes” that microstructure in place. This then allows for easier tempering.

Quenching and tempering

Quenching and tempering are similar processes that differ slightly from your standard metal hardening procedure, so it’s important to know where those differences lie.

In quenching, the metal gets heated up to a specific temperature and then gets quenched in water or oil to allow it to harden to its optimal hardness level. Parts that are quenched must typically be aged, tempered or stress relieved as well to achieve the desired toughness, hardness and stability.

Tempering is performed to provide an additional level of toughness and to relieve the brittleness of the steel. Steels are never used in the condition they’re in immediately after quenching—they must be tempered as well to ensure the part will be tough enough to last through long-term use. The process involves reheating the steel at lower temperatures to allow for the precipitation and spheroidization of the carbines found in the steel’s microstructure. The result is harder, tougher metal.

For more information about the processes involved with metal hardening and how the various metal treatment processes differ from each other, we encourage you to contact the team at J. F. Heat Treating Inc. to learn more about heat treatment in Gastonia, NC. We look forward to answering any questions you have about the work we do!

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