What is Tempering?
Tempering is a heat-treating process used to increase the ‘toughness’ of iron-based alloys so they are able to resist fracture. Typically, this process is done after the hardening process so some of the hardness can be reduced. Less hardness in a material and more toughness equates to a lesser chance of breakage due to the metal being more ‘bendy’.
The tempering process involves repeated heating of a material at below its melting point often in a furnace capable of handling high temperatures. This is then followed by allowing the material to cool, and then repeating the heating step again. When metal is cooled quickly, the atoms are shocked and become very unstable. If you were to bend the metal at this point, it would more than likely snap or break. By reheating the metal again after cooling, the atoms have time to settle and rearrange in a far more stable position. When applying pressure to the material after this, it will more than likely bend instead of snap in half. While the hardness of the material does decrease, the toughness increases, allowing the material to be far more malleable. A great simple demonstration of this process can be found here.
The temperature used in this process determines how much hardness will be removed from the material. For example, tools like hammers that require both hardness, and toughness so it does not splinter or bend. Tools are often tempered at lower temperatures. Springs however require less hardness because they need to be able to bend, therefore springs are treated with much higher temperatures.
Tempering and it’s various forms helps to ensure the metal product is fit for its purpose, and reduce the likelihood of it breaking when in use. For more information on metal tempering, contact us!