The tempering furnace is an oven used for tempering. The heating process can increase the toughness of iron-based alloys such as cast iron or steel. Metal is usually put in a tempering furnace after hardening, and then heated to a 
certain temperature to remove excess hardness.

Tempering furnaces are mainly used to increase the toughness of metal or cast iron tools by reducing the hardness of these products.

These furnaces provide a range of temperatures because the hardness removed depends on the composition of the metal and the expected result of the product. The spring needs a higher temperature when placed in the oven, and harder tools 
need to be tempered at a lower temperature.